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Hidetoshi Fukuyama
2006 Volume 75 Issue 5 Pages
051001
Published: May 15, 2006
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Present status of research activities in conducting molecular solids is briefly reviewed. It is impressive to note that a systematic physical understanding of electronic properties is now possible in spite of apparently complicated crystal structures. This is due to the robustness of the molecular orbitals. The success of such an approach encourages widening the condensed matter research targets into molecular assemblies in general, which are not necessarily crystalline.
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Akiko Kobayashi, Yoshinori Okano, Hayao Kobayashi
2006 Volume 75 Issue 5 Pages
051002
Published: May 15, 2006
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The design of metallic crystals consisting of single-component molecules (
single-component molecular metal) is explained on the basis of the examinations of frontier molecular orbitals and the simple extended-Hückel tight-binding band pictures. To meet the conditions required to realize automatic carrier generation by self-assembly of the same kind of neutral molecules, a crystal of a transition metal complex molecule [Ni(tmdt)
2] with extended-TTF-type (TTF = tetrathiafulvalene) dithiolate ligands was synthesized, which was found to be the first single-component molecular metal. The X-ray structure analyses of the crystals of [(C
4H
9)
4N]
2[Ni(tmdt)
2] and neutral [Ni(tmdt)
2] provided information on the symmetry of the frontier molecular orbitals [the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)] from which the metallic bands are formed. The infrared and visible spectra of a crystalline powder sample of [Ni(tmdt)
2] showed a broad electronic absorption maximum at around 2200 cm
−1, suggesting an extremely small HOMO–LUMO gap. The physical properties of some of the hitherto-developed single-component molecular conductors are also briefly described.
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Hatsumi Mori
2006 Volume 75 Issue 5 Pages
051003
Published: May 15, 2006
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Since the first discovery of an organic superconductor, TMTSF
2PF
6 (TMTSF = tetramethyltetraselenafulvalene) with the superconducting transition temperature (
Tc)=0.9 K under 12 kbar, by the suppression of spin density wave (SDW) state, approximately 120 organic superconductors have been found. Among them, the highest
Tc is 14.2 K under 82 kbar for β′-(BEDT-TTF)
2ICl
2 [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene]. Organic superconductors are categorized into three groups. (1) A superconducting (SC) state neighbors the SDW state, and appears by the suppression of the SDW state to afford a
Tc below 1 K. (2) Another SC state is competitive with a nonmagnetic insulating state induced by anion ordering, charge density wave (CDW), or charge ordering, afford a
Tc below 2 K. (3) Yet another SC state is next to an antiferromagnetic (AF) order to afford a
Tc up to 14 K under an ambient condition or a pressurized condition. In this article, organic superconductors are reviewed on the basis of a variety of molecules, and finally, recent novel organic superconductors (MDT-TS)(AuI
2)
0.441 [MDT-TS = 5
H-2-(1,3-diselenol-2-ylidene)-1,3,4,6-tetrathiapentalene] obtained by suppression with an incommensurate AF state and β-(
meso-DMBEDT-TTF)
2I
3 [DMBEDT-TTF = dimethylbis(ethylenedithio)tetrathiafulvalene] in competition with a checkerboard-type charge-ordered (CO) state, are introduced.
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Leonardo Degiorgi, Denis Jérome
2006 Volume 75 Issue 5 Pages
051004
Published: May 15, 2006
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We review the transport and optical properties of an extended series of low dimensional organic Bechgaard conductors, which are hosting the first organic superconductor (TMTSF)
2PF
6. It is shown that all compounds of this family are one-dimensional Mott insulators with an activation energy for longitudinal transport depending on their chemical composition and decreasing under pressure. This activation energy in the transport results vanishes at a (chemical) pressure induced dimensionality cross-over, while a gap feature is still observable in the far-infrared spectrum. Particularly, according to the data of transverse transport, the signature of a gap in the quasi particle spectrum is observable even when the longitudinal transport becomes metal-like. In this survey, we address a variety of relevant problems and concepts associated with the physics of an interacting electron gas in low dimensions, such as non-Fermi liquid behavior, dimensionality crossover, and specifically the appearance of the Luttinger liquid state.
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Felix Nad, Pierre Monceau
2006 Volume 75 Issue 5 Pages
051005
Published: May 15, 2006
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We present a survey of the recent experimental results which provide the evidence for the formation in quasi-one-dimensional (Q1D) conductors of a charge ordered (CO) state corresponding to an electronic 4
kF charge density wave. The main attention is paid to the study of the dielectric response of Q1D organic compounds of the family of (TMTTF)
2X salts for which a divergence of the dielectric permittivity and of the relaxation time at the critical transition temperature into the CO state are found. Effects of pressure and deuteration on this transition and also the role of anions in the formation of the CO state are studied. On the basis of these results and existing theoretical approaches we suggest a phenomelogical explanation of the sequence of ground states developed in these compounds with decreasing temperature. The driven force for the formation of the CO state originates from strong electron correlation effects associated with long range Coulomb interactions. The stability of the CO state in (TMTTF)
2X compounds is expected to be provided by a shift of anion chains as a whole. A short comparison between peculiarities in the dielectric response of the CO state formation in Q1D and recently found in Q2D compounds will be given.
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T. Osada, E. Ohmichi
2006 Volume 75 Issue 5 Pages
051006
Published: May 15, 2006
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We discuss a quantum-mechanical picture for interlayer magnetotransport in quasi-one-dimensional layered conductors. We show that the lowest order contribution of interlayer coupling to interlayer conductivity, which originates from a single tunneling process between two neighboring layers, leads all of the fundamental angular effects; Lebed resonance, the Danner–Kang–Chaikin oscillations, and the third angular effect. We also discuss the mean field picture of charge density wave (CDW) and spin density wave (SDW) under magnetic fields. We see that the orbital quantization effect causes the successive transitions of field-induced SDW state. It is also discussed that the CDW state could show complicated phase transitions under magnetic fields as a result of competition between Zeeman effect and orbital effect.
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Kazushi Kanoda
2006 Volume 75 Issue 5 Pages
051007
Published: May 15, 2006
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One of the clear manifestations of electron correlation in condensed matter is metal–insulator (MI) transition. The organic conductors κ-(ET)
2X and (DCNQI)
2M are contrasting textbook materials exhibiting correlation-induced MI transition in a single-π band with half filling and a π–
d hybrid multiband with tunable band filling, respectively. By comparing these two systems, we learn prototypical manifestations of electron correlation in purely electronic and lattice-coupled manners.
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Toshihiro Takahashi, Yoshio Nogami, Kyuya Yakushi
2006 Volume 75 Issue 5 Pages
051008
Published: May 15, 2006
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Present status of experiments on charge ordering (CO) phenomena observed in organic molecular conductors is reviewed. Experimental techniques to detect and analyze the CO, i.e., NMR, X-ray and Infrared/Raman spectroscopy, are described and the experimental results in typical materials exhibiting CO are summarized. (DI-DCNQI)
2Ag, (TMTTF)
2X, α-(BEDT-TTF)
2I
3, θ-(BEDT-TTF)
2RbZn(SCN)
4 and related materials are discussed. Charge disproportionation without long-range order observed in numbers of materials are also included.
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Hitoshi Seo, Jaime Merino, Hideo Yoshioka, Masao Ogata
2006 Volume 75 Issue 5 Pages
051009
Published: May 15, 2006
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Theoretical studies on charge ordering phenomena in quarter-filled molecular (organic) conductors are reviewed. Extended Hubbard models including not only the on-site but also the inter-site Coulomb repulsion are constructed in a straightforward way from the crystal structures, which serve for individual study on each material as well as for their systematic understandings. In general the inter-site Coulomb interaction stabilizes Wigner crystal-type charge ordered states, where the charge localizes in an arranged manner avoiding each other, and can drive the system insulating. The variety in the lattice structures, represented by anisotropic networks in not only the electron hopping but also in the inter-site Coulomb repulsion, brings about diverse problems in low-dimensional strongly correlated systems. Competitions and/or co-existences between the charge ordered state and other states are discussed, such as metal, superconductor, and the dimer-type Mott insulating state which is another typical insulating state in molecular conductors. Interplay with magnetism, e.g., antiferromagnetic state and spin gapped state is considered as well. Distinct situations are pointed out: influences of the coupling to the lattice degree of freedom and effects of geometrical frustration which exists in many molecular crystals. Some related topics, such as charge order in transition metal oxides and its role in new molecular conductors, are briefly remarked.
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Naoya Tajima, Shigeharu Sugawara, Masafumi Tamura, Yutaka Nishio, Koji ...
2006 Volume 75 Issue 5 Pages
051010
Published: May 15, 2006
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We review the transport phenomena in an organic conductor α-(BEDT-TTF)
2I
3. It exhibits various types of transport depending on the circumstance in which it is placed. Under the ambient pressure, it is a charge-ordered insulator below 135 K. When high hydrostatic pressures are applied, it changes to a new type of narrow gap (or zero gap) semiconductor. The conductivity of this system is nearly constant between 300 and 1.5 K. In the same region, however, both the carrier (hole) density and the mobility change by about six orders of magnitude, in a manner so that the effects just cancel out giving rise to the temperature independent conductivity. The temperature (
T) dependence of the carrier density
n obey
n∝
T2 below 50 K. When it is compressed along the crystallographic
a-axis, it changes from the charge ordered insulator to a narrow gap semiconductor. At the boundary between these phases, there appears a superconducting phase. On the other hand, when compressed in the
b-axis, the system changes to a metal with a large Fermi surface. The effect of magnetic fields on samples in the narrow gap semiconductor phase was examined. Photo-induced transition from the charge ordered insulating state to a metallic state is also discussed.
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I. J. Lee, S. E. Brown, M. J. Naughton
2006 Volume 75 Issue 5 Pages
051011
Published: May 15, 2006
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The nature of superconductivity in a quasi-one-dimensional organic system has been controversial since its discovery in the early 80’s. Here, we discuss recent developments regarding the issue based mainly on studies of the upper critical field
Hc2(
T) and the nuclear magnetic resonance (NMR) Knight shift. A strong upward curvature found in the temperature dependent upper critical field and an absence of the shift in the resonant adsorption frequency upon cooling through the superconducting transition strongly support the notion that the nature of the low dimensional organic superconductor is spin triplet.
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Koichi Ichimura, Kazushige Nomura
2006 Volume 75 Issue 5 Pages
051012
Published: May 15, 2006
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The superconducting phase of organic superconductors κ-(BEDT-TTF)
2X was studied by the electron tunneling using scanning tunneling microscope (STM). Tunneling both at the conducting plane and lateral surfaces was performed on single crystals of κ-(BEDT-TTF)
2Cu(NCS)
2. Tunneling conductance curve obtained at the conducting plane is explained by the
d-wave gap symmetry. The temperature dependence of tunneling spectra is also consistent with the
d-wave symmetry. Tunneling spectra at lateral surfaces varies depending on the tunneling direction, suggesting the in-plane anisotropy of the gap. The directional dependence is also consistent with the
d-wave symmetry with line nodes π⁄4 from the
kb- and
kc-axes. It indicates that the superconducting pair wave function has the
dx2−y2-wave symmetry. (If we take the same conventions for the magnetic Brillouin zone as high-
Tc cuprates with the
dx2−y2-wave symmetry, the gap symmetry of κ-(BEDT-TTF)
2Cu(NCS)
2 is the
dxy-wave symmetry.) Protonated and partially deuterated κ-(BEDT-TTF)
2Cu[N(CN)
2]Br were also studied. Tunneling spectra are consistent with the
d-wave symmetry in all salts. Gap parameters obtained in each salt were discussed in the view point of the effective correlation. The large gap value suggests the strong coupling superconductivity. The pseudogap structure was found above
Tc. The zero bias conductance peak, which gives an evidence for nodes of the superconducting gap, was found.
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Kazuhiko Kuroki
2006 Volume 75 Issue 5 Pages
051013
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A review is given on theoretical studies concerning the pairing symmetry in organic superconductors. In particular, we focus on (TMTSF)
2X and κ-(BEDT-TTF)
2X, in which the pairing symmetry has been extensively studied both experimentally and theoretically. Possibilities of various pairing symmetry candidates and their possible microscopic origin are discussed. Also some tests for determining the actual pairing symmtery are surveyed.
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Shinya Uji, James S. Brooks
2006 Volume 75 Issue 5 Pages
051014
Published: May 15, 2006
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For conventional superconductors, superconductivity is destabilized by magnetic field. However, in BETS-based two dimensional organic conductors, where BETS is bis(ethylenedithio)tetraselenafulvalene, superconductivity is induced by high magnetic fields parallel to the conducting layers. The overall features of the field-induced superconductivity are well understood in terms of Jaccarino–Peter compensation mechanism, where the magnetic interaction between the conduction electrons on the BETS molecules and the localized magnetic moments in the insulating layers plays a crucial role. The experimental results of the field induced superconductivity observed in the BETS systems and the theoretical model are reviewed.
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Keizo Murata, Seiichi Kagoshima, Syuma Yasuzuka, Harukazu Yoshino, Ryu ...
2006 Volume 75 Issue 5 Pages
051015
Published: May 15, 2006
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High-pressure studies on organic conductors and superconductors are reviewed. It is stressed that almost all the organic conductors are studied by means of high pressures, but the role or meaning of pressure effect has been dependent on the salts and physics of interests. In organic molecular crystals, many intriguing physical phenomena such as the appearance of charge- and spin-density-waves, superconductivity, Mott insulator and charge ordering have been found. The application of hydrostatic and uniaxial pressures plays an essential role for understanding the nature of these electronic states, for guiding the material design, and for creating the unexpected quantum states as well as high-
Tc superconductivities. This review includes the history, pressure techniques, and works under conventional pressures of up to 1.5 GPa, ultra-high pressures up to 10 GPa as well as uniaxial pressure, but the topics which are dealt with in this same special issue are not covered.
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Sachio Horiuchi, Tatsuo Hasegawa, Yoshinori Tokura
2006 Volume 75 Issue 5 Pages
051016
Published: May 15, 2006
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The π-electronic functionalities of molecular donor (
D)–acceptor (
A) compounds have been attracting subjects for the solid state science as well as for the prospective technological exploitation in organic electronics. In this review, it is shown that the novel neutral–ionic valence instability in the charge-transfer (CT) complexes is closely related to valuable electric properties such as the current-induced resistance switching, quantum phase transition, gigantic dielectric response, and relaxor ferroelectricity. Furthermore, the displacive-type ferroelectricity has recently been developed on the
DA combinations in the hydrogen-bonded co-crystals. It is also discussed that the intermolecular CT mechanism in the molecular
DA compounds is promising to advance the potential of organic field-effect transistors (FETs) that are envisioned as key components in future organic electronics.
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Kouichi Hayashi, Tomohiro Matsushita, Eiichiro Matsubara
2006 Volume 75 Issue 5 Pages
053601
Published: May 15, 2006
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The incident electron beam angular distribution of Ti Kα characteristic X-rays from a strontium titanate single crystal was measured by scanning electron microscopy. The isotropy exhibits typical features observed in conventional photoelectron holography. Reconstructions by Fourier-transformation-based algorithm clearly show neighboring Sr and Ti atoms around Ti, the validity of which was verified by computer simulation. The demonstration paves the way to obtaining multiple energy holograms of nanostructured materials using the energy tunability of focused electron beams.
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Masaya Uchida, Roland Mathieu, Jinping He, Yoshio Kaneko, Atsushi Asam ...
2006 Volume 75 Issue 5 Pages
053602
Published: May 15, 2006
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Structural and magnetic properties have been investigated for half-doped single-layer manganites
RE0.5Sr
1.5MnO
4 [
RE = La, (La, Pr), Pr, Nd, Sm, and Eu]. Analyses of electron diffraction and ac susceptibility measurements have revealed that the long-range charge–orbital ordering (CO–OO) state as observed in La
0.5Sr
1.5MnO
4 is suppressed for the other materials: the CO–OO transition temperature, as well as the correlation length decreases with a decrease in the cation size of
RE. Such a short-range CO–OO state shows a spin-glass behavior at low temperatures. A new electronic phase diagram is established with quenched disorder as the control parameter.
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Yoshitsugu Okaue, Yasuhiro Saiga, Dai S. Hirashima
2006 Volume 75 Issue 5 Pages
053603
Published: May 15, 2006
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The ground state of
3He atoms confined in a narrow tube is studied by the variational Monte Carlo method. It is found that
3He atoms condense into a liquid state in the dilute limit in a certain range of the tube radius. The relevance of this finding in a recent experiment on
3He atoms in nanopores is discussed. The connection of the present results with those of recent studies of ultracold atoms in a quasi-one-dimensional trap is also pointed out.
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Syuma Yasuzuka, Keizo Murata, Tsutomu Fujimoto, Masahiro Shimotori, Ta ...
2006 Volume 75 Issue 5 Pages
053701
Published: May 15, 2006
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The title compound (TTM-TTP)I
3 with a highly one-dimensional (1D) half-filled energy band is almost metallized by the application of pressure beyond 7 GPa. It is theoretically predicted that the ground state of the 1D half-filled system is the Mott insulator at any positive on-site interaction
U. Nevertheless, (TTM-TTP)I
3 shows that the metal–insulator (M–I) transition temperature
TMI decreases linearly with increasing pressure and is directing towards 0 K near 10 GPa. Above 5.7 GPa, the metallic temperature variation appears in the high-temperature region for 70<
T<300 K, in which the metallic behavior is described by ρ(
T)∝
Tα with α∼0.3. The nature of the metallic state is discussed in terms of the Tomonaga-Luttinger liquid described by the Hubbard model.
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Hitoshi Sato, Arata Tanaka, Masahiro Sawada, Fumitoshi Iga, Kenichio T ...
2006 Volume 75 Issue 5 Pages
053702
Published: May 15, 2006
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The Ti 3
d electronic structure of Ti
2O
3 across metal–insulator transition (MIT) has been investigated by means of polarization-dependent soft X-ray absorption spectroscopy (XAS) at the Ti 2
p edge. The XAS spectra exhibit a remarkable linear dichroism (LD) between the polarization vectors of the incident light parallel and perpendicular to the Ti ion pair along the
c-axis. LD intensity is significantly reduced at 520 K in the metallic phase in comparison with that at 300 K in the insulating phase, indicating a large change in
a1g and
egπ orbital occupations. The results are qualitatively consistent with a recent theory, where the MIT is due to the change of the 3
d electronic configuration in the Ti pair along the
c-axis driven by a change in the
t2g level splitting relative to the on-site exchange interaction.
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J. D. Lee, J. Inoue, T. Kuroda
2006 Volume 75 Issue 5 Pages
053703
Published: May 15, 2006
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Optically induced spin dynamics are considered in a system of two localized spins (two-bit system) embedded in a semiconductor host. Through a nonperturbative treatment, an intense off-resonant laser radiation is found to induce an oscillation of the spin exchange synchronized by the Rabi oscillation of virtual excitons in the host. This is a direct consequence of oscillating quantum phases of virtual exciton states under Rabi oscillation and can be used as a new mechanism to control spin states with respect to externally controlled parameters-laser energy and laser intensity.
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Shigeharu Sugawara, Tetusya Ueno, Yoshitaka Kawasugi, Naoya Tajima, Yu ...
2006 Volume 75 Issue 5 Pages
053704
Published: May 15, 2006
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We succeeded in deriving an analytical expression that yields the electrical conductivity for quasi-one-dimensional electron systems, when the current is in the least conductive direction and the magnetic field is perpendicular to it. This formula is valid for the magnetic field along an arbitrary direction in the conducting layers and the field strength from zero to higher fields, where ωτ>>1. We verified the applicability of the formula using the experimental results for an organic quasi-one-dimensional layered metal (TMTSF)
2ClO
4. The formula was found to reproduce the experimental results fairly well.
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Yoshifumi Oshima, Keisuke Mouri, Hiroyuki Hirayama, Kunio Takayanagi
2006 Volume 75 Issue 5 Pages
053705
Published: May 15, 2006
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The conductance of helical multishell (HMS) gold nanowires was measured while simultaneously examining their structure using an ultrahigh-vacuum transmission electron microscope. It was found that thinning successively yielded 15-8-1, 14-7-1, 13-6, 12-5, and 11-4 HMS nanowires. The conductance of these nanowires was independent of their length. Conductance varied with the position of contact between the chiral nanowire and the crystalline electrode so that each nanowire had more than two conductance values. The channel transmissions were reduced at the nanowire-electrode contact. The observed conductance values for electrode-suspended chiral nanowires were compared with recent theoretical values.
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Masato Kubota, Kanta Ono, Yasuaki Oohara, Hiroshi Eisaki
2006 Volume 75 Issue 5 Pages
053706
Published: May 15, 2006
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We performed X-ray optical activity (XOA) measurements at Cu
K absorption edge for the underdoped Bi2212 (
Tc=80 K). X-ray natural circular dichroism (XNCD) appears below
T* (∼200 K) and becomes larger with decreasing temperature, whereas nonreciprocal X-ray linear dichroism (NRXLD) is not seen. It is revealed that time reversal symmetry is preserved in the pseudogap phase of the underdoped Bi2212. The results demonstrate that XOA is a powerful tool to clarify electronic structure in terms of time reversal and/or chiral symmetry.
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Hideki Kumazaki, Dai S. Hirashima
2006 Volume 75 Issue 5 Pages
053707
Published: May 15, 2006
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The impurity effects in a two-dimensional graphite sheet (graphene) are studied by self-consistent
T-matrix approximation. Conductivity is found to be modestly enhanced from a universal value 4
e2⁄(π
h2), where −
e is the electron charge and
h is the Planck constant, by strong long-range potential. The staggered susceptibility of π electrons is enhanced by strong impurity scattering irrespective of its range; it logarithmically diverges as
T→0 in the unitarity limit.
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Satoru Masaki, Takeshi Mito, Naomi Oki, Shinji Wada, Naoya Takeda
2006 Volume 75 Issue 5 Pages
053708
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To elucidate microscopically the metal–insulator transition (
TMI∼16.5 K) and an additional transition (
T*∼15 K) in Sm-based filled skutterudite compound SmRu
4P
12, we have carried out
31P-NMR (nuclear magnetic resonance) at various fields from 0.8 to 11 T. The peaks in the spin lattice relaxation rate 1⁄
T1 observed at
TMI and
T* under ∼7 T indicate that there are different magnetic fluctuation modes in SmRu
4P
12: one freezes below
TMI and the other does below
T*. The anomalous field and temperature dependences of the NMR spectrum are explained in terms of the occurrence of multipole ordering. We have examined the two possible scenarios to account for the experimental results, and both cases suggest that the M–I transition involves octapole ordering.
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Ryo Kawahara, Hiizu Nakanishi
2006 Volume 75 Issue 5 Pages
054001
Published: May 15, 2006
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We have performed numerical simulations on a pure electron plasma system under a strong magnetic field, in order to examine quasi-stationary states that the system eventually evolves into. We use ring states as the initial states, changing the width, and find that the system evolves into a vortex crystal state from a thinner-ring state while a state with a single-peaked density distribution is obtained from a thicker-ring initial state. For those quasi-stationary states, density distribution and macroscopic observables are defined on the basis of a coarse-grained density field. We compare our results with experiments and some statistical theories, which include the Gibbs–Boltzmann statistics, Tsallis statistics, the fluid entropy theory, and the minimum enstrophy state. From some of those initial states, we obtain the quasi-stationary states which are close to the minimum enstrophy state, but we also find that the quasi-stationary states depend upon initial states, even if the initial states have the same energy and angular momentum, which means the ergodicity does not hold.
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Ken-ichi Maruno, Yasuhiro Ohta
2006 Volume 75 Issue 5 Pages
054002
Published: May 15, 2006
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It is shown that the
N-dark soliton solutions of the integrable discrete nonlinear Schrödinger (IDNLS) equation are given in terms of the Casorati determinant. The conditions for reduction, complex conjugacy, and regularity for the Casorati determinant solution are also given explicitly. The relationship between the IDNLS and the relativistic Toda lattice is discussed.
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Xing-Biao Hu, Jun-Xiao Zhao, Chun-Xia Li
2006 Volume 75 Issue 5 Pages
054003
Published: May 15, 2006
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In this paper, the relations between three special forms of matrix integrals and their associated integrable differential-difference systems are considered. It turns out that these matrix integrals with special β=2 and 1,4 satisfy the differential-difference KP equation, the two-dimensional Toda lattice, the semi-discrete Toda equation and their Pfaffianized systems, respectively.
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Hidetsugu Sakaguchi
2006 Volume 75 Issue 5 Pages
054004
Published: May 15, 2006
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We study the Schlögl model in a vesicle with semi-permeable membrane. The diffusion constant takes a smaller value in the membrane region, which prevents the outflow of self-catalytic product. A nonequilibrium state is stably maintained inside of the vesicle. Nutrients are absorbed and waste materials are exhausted through the membrane by diffusion. It is interpreted as a model of primitive metabolism in a cell.
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Takashi Yoshidome, Akira Yoshimori, Takashi Odagaki
2006 Volume 75 Issue 5 Pages
054005
Published: May 15, 2006
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We propose a new method to construct the free energy landscape in the configurational space, where the density functional approach to the thermodynamic function is exploited. In order to demonstrate the validity of the method, we construct the free energy landscape for rearrangement of atoms in an FCC crystal of hard spheres. Analyzing the relaxation process, we deduce two concepts of rearranging region, one is the simultaneously rearranging region (SRR) which is defined by the difference between two adjacent regions. The other is the cooperatively rearranging region (CRR) which is the spheres involved in the saddle configuration between two adjacent regions. The latter region corresponds to the region introduced by Adam and Gibbs. We show that the SRR and the CRR can be determined explicitly from the free energy landscape.
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Hiroshi Tsujimoto
2006 Volume 75 Issue 5 Pages
054101
Published: May 15, 2006
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It is found that the seesaw mechanism not only explains the smallness of neutrino masses but also accounts for the large mixing angles simultaneously, even if the unification of the neutrino Dirac mass matrix with that of up-type quark sector is realized. In this mechanism, we show that the mixing matrix of the Dirac-type mass matrix gets extra rotations from the diagonalization of Majorana mass matrix. Assuming that the mixing angles to diagonalize the Majorana mass matrix are extremely small, we find that the large mixing angles of leptonic sector found in atmospheric and long baseline reactor neutrino oscillation experiments can be explained by these extra rotations. We also find that provided the mixing angle around y-axis to diagonalize the Majorana mass matrix vanishes, we can derive the information about the absolute values of neutrino masses and Majorana mass responsible for the neutrinoless double beta decay experiment through the data set of neutrino experiments. In the simplified case that there is no CP phase, we find that the neutrino masses are decided as
m1:
m2:
m3≈1:2:8 and that there are no solution which satisfy
m3<
m1<
m2 (inverted mass spectrum). Then, including all CP phases, we reanalyze the absolute values of neutrino masses and Majorana mass responsible for the neutrinoless double beta decay experiment.
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Naoyuki Yamashita, Nobuyuki Hasebe, Takashi Miyachi, Mitsuhiro Miyajim ...
2006 Volume 75 Issue 5 Pages
054201
Published: May 15, 2006
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Bombardment experiments with thick targets made of each of Al and Fe were performed using 230 MeV/nucleon helium and 210 MeV proton beams. The energies and intensities of prompt gamma rays emitted by inelastic nuclear scattering of energetic neutrons were measured by a high-purity Ge detector. This work presents the first experimental results concerning the emission of prompt gamma rays from thick targets anticipated by helium component in galactic cosmic rays, since no foregoing work related to this one has been done. It is concluded that helium has the capability of prompt gamma ray line emission through the inelastic nuclear reaction of neutrons with target material by a factor of 3.5 on average in comparison with proton. As regards the lunar and planetary nuclear spectroscopy, a consideration is given on the role of helium particles to the total production of gamma rays emitted from a planetary surface.
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Akira Narita, Masahiko Higuchi
2006 Volume 75 Issue 5 Pages
054301
Published: May 15, 2006
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The polynomial representations in
li·
lj are given for the relevant quantities to the unit tensor operators such as Coulomb interaction and Casimir’s operators in
f2. The eigenvalues for the quantities in
fn are considered by combining with those of Casimir’s operators on a basis of the representations. The expressions of
e1,
e2 and
e3 for the maximal spin multiplets are interestingly derived. The remarkable is that the procedures for finding the eigenvalues are performed without help of the group theoretical technique.
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Masaki Mukai, Makio Uwaha
2006 Volume 75 Issue 5 Pages
054601
Published: May 15, 2006
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Liquid-like motion of superfluid bubbles (negative crystals) in solid
4He has been observed (K. Yoneyama, R. Nomura and Y. Okuda: Phys. Rev. E
70 (2004) 021606). To understand this peculiar behavior, we study theoretically the motion of a superfluid bubble in bcc solid
4He. We adopt a simple model in which only the interface energy and the gravitational energy are taken into account and dissipation occurs only at the interface. We show that a spherical bubble rises at a constant velocity proportional to its radius, and that there is a critical size above which the bubble is detached from the flat bottom of the container. The radius of the critical bubble is proportional to the contact angle of the solid.
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Seiji Hiramatsu, Yasushi Ishii
2006 Volume 75 Issue 5 Pages
054602
Published: May 15, 2006
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Atomic structures of Al–Co–Ni decagonal quasicrystals are studied theoretically by Monte-Carlo type of calculation in a wide range of the atomic composition. It is found that two different tiling structures are obtained depending on the composition. A ternary phase diagram is obtained. It is discussed that the tiling structures are selected to avoid the non-ideal tile decoration introduced by a change of the Al concentration. A decagonal cluster with TM and Al pentagons at the center is found as a characteristic structural unit in the Co-rich samples and it is shown that the Al-transition metal interaction favors the atomic arrangement of the decagonal cluster.
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Kiyofumi Nitta, Takafumi Miyanaga, Takashi Fujikawa
2006 Volume 75 Issue 5 Pages
054603
Published: May 15, 2006
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We apply a finite temperature path integral method to study strongly anharmonic thermal factors in extended X-ray absorption fine structure (EXAFS), electron energy-loss spectroscopy (EELS) and angle resolved X-ray photoelectron spectroscopy (ARXPS). Two examples, symmetric and asymmetric double-well potentials are considered for the anharmonic potentials, which are used to describe structural phase transition and rattling mechanism. We discuss the quantum tunneling effects in the thermal factors. The validity of the classical approximation and the cumulant expansion are also studied for various asymmetric potentials. Complex plane expression is introduced to explain the specific features of the EXAFS thermal damping function. Degree of asymmetry of the potential can be estimated from the complex plane expression. In the temperature dependence of the higher order cumulant (third and fourth), minimum point (third order) and maximum point (fourth order) appear at the characteristic temperature, which depends on the potential asymmetry.
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Tsuneya Ando
2006 Volume 75 Issue 5 Pages
054701
Published: May 15, 2006
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Localization effects in a metallic carbon nanotube are studied as a function of Aharonov–Bohm magnetic flux. The conductance exhibits the behavior of strong localization except in the absence of a flux. When the Fermi level lies in higher bands, the localization effect becomes smaller at a half flux quantum due to the recovery of the time reversal symmetry. A clear symmetry crossover occurs due to perturbations such as trigonal band-warping and scatterers with potential range smaller than the lattice constant of the two-dimensional graphite.
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Bipul Pal, Michio Ikezawa, Yasuaki Masumoto, Ivan V. Ignatiev
2006 Volume 75 Issue 5 Pages
054702
Published: May 15, 2006
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We report millisecond-range spin memory of resident electrons in an ensemble of InP quantum dots (QDs) under a small magnetic field of 0.1 T applied along the optical excitation axis at temperatures up to about 5 K. A pump-probe photoluminescence (PL) technique is used for optical-orientation of electron spins by the pump pulses and for study of spin relaxation over the long time scale by measuring the degree of circular polarization of the probe PL as a function of pump-probe delay. Dependence of spin decay rate on temperature and magnetic field suggests two-phonon processes as the dominant spin relaxation mechanism in these QDs at low temperatures.
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S. Akbar Jafari, Takami Tohyama, Sadamichi Maekawa
2006 Volume 75 Issue 5 Pages
054703
Published: May 15, 2006
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We calculate the third order nonlinear optical response in the Hubbard model within the spin density wave (SDW) mean field ansatz in which the gap is due to onsite Coulomb repulsion. We obtain closed-form analytical results in one dimension (1D) and two dimension (2D), which show that nonlinear optical response in SDW insulators in 2D is stronger than both 3D and 1D. We also calculate the two photon absorption (TPA) arising from the stress tensor term. We show that in the SDW, the contribution from stress tensor term to the low-energy peak corresponding to two photon absorption becomes identically zero if we consider the gauge invariant current properly.
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Hiroki Wadati, Akira Chikamatsu, Ryuji Hashimoto, Masaru Takizawa, Hir ...
2006 Volume 75 Issue 5 Pages
054704
Published: May 15, 2006
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We have measured the temperature dependence of the photoemission and x-ray absorption spectra of La
1−xSr
xFeO
3 (LSFO) epitaxial thin films with
x=0.67, where charge disproportionation (3Fe
3.67+→2Fe
3++Fe
5+) resulting in long-range spin and charge ordering is known to occur below
TCD=190 K. With decreasing temperature we observed gradual changes of the spectra with spectral weight transfer over a wide energy range of ∼5 eV. Above
TCD the intensity at the Fermi level was relatively high compared to that below
TCD but still much lower than that in conventional metals. We also found a similar temperature dependence for
x=0.4, and to a lesser extent for
x=0.2. These observations suggest that a local charge disproportionation occurs not only in the
x=0.67 sample below
TCD but also over a wider temperature and composition range in LSFO. This implies that the tendency toward charge disproportionation may be the origin of the unusually wide insulating region of the LSFO phase diagram.
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Shinya Katayama, Akito Kobayashi, Yoshikazu Suzumura
2006 Volume 75 Issue 5 Pages
054705
Published: May 15, 2006
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We show a zero-gap semiconducting (ZGS) state in the quasi-two-dimensional organic conductor α-(BEDT-TTF)
2I
3 salt, which emerges under uniaxial pressure along the
a-axis (the stacking axis of the BEDT-TTF molecule). The ZGS state is the state in which a Dirac cone with the band spectrum of a linear dispersion exists around the Fermi point connecting an unoccupied (electron) band with an occupied (hole) band. The spectrum exhibits a large anisotropy in velocity, which depends on the direction from the Fermi point. By varying the magnitude of several transfer energies of a tight-binding model with four sites per unit cell, it is shown that the ZGS state exists in a wide pressure range, and is attributable to the large anisotropy of the transfer energies along the stacking axis.
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Tomohiko Nakajima, Hiroyuki Mitamura, Yutaka Ueda
2006 Volume 75 Issue 5 Pages
054706
Published: May 15, 2006
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We have successfully synthesized Ba
3Cr
2O
8 and investigated its crystal structure and magnetic properties. The crystal structure consists of Ba
2+ cations and isolated CrO
43− tetrahedra; magnetic chromium ions exist as rare Cr
5+ (3
d1,
S=1⁄2). An
S=1⁄2 compound Ba
3Cr
2O
8 was found to be a three-dimensional quantum spin system with a singlet ground state of dimer origin. From the analysis of magnetic susceptibility and high-field magnetization data, excitation gap is evaluated as Δ⁄
kB=16.1 K and intra- and interdimer exchange interactions are estimated as
J0⁄
kB=25.0 K and
J′⁄
kB=7.7 K, respectively. Comparing with a similar spin dimer compound Ba
3Mn
2O
8, Ba
3Cr
2O
8 has a more dominant intradimer interaction.
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Minoru Soda, Yukio Yasui, Taketo Moyoshi, Masatoshi Sato, Naoki Igawa, ...
2006 Volume 75 Issue 5 Pages
054707
Published: May 15, 2006
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Neutron diffraction studies have been carried out in the temperature (
T) range between 10 and 130 K on a single crystal of YBaCo
4O
7, which has the stacking of kagome and triangular lattices of CoO
4 tetrahedra along the
c-axis. Structural transitions have been found at two temperatures
Tc1∼70 K and
Tc2∼105 K. With decreasing
T, magnetic order appears along with the transition at
Tc2, but it does not grow to an ideal long-range order even at the lowest
T studied (∼10 K). Two groups of magnetic reflections, which originate from the Co moments of the kagome and triangular lattices, are observed. With further decreasing
T, the growth rates of the intensities of these two reflection groups are enhanced by another transition at
Tc1. These magnetic behaviors seem to be related to the release of the geometrical frustration. At 10 K, the patterns of the magnetic short-range order have been determined for both sites of the kagome and triangular lattices.
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Hideto Yanagihara, Manabu Hasegawa, Eiji Kita, Yusuke Wakabayashi, Hir ...
2006 Volume 75 Issue 5 Pages
054708
Published: May 15, 2006
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We report the structural characterization and transport properties of highly-ordered epitaxial γ-Fe
2O
3 thin films grown by a pure ozone-assisted molecular beam epitaxy method. X ray diffraction (XRD) measurements at a synchrotron facility indicated that the composition of films was close to that of γ-Fe
2O
3 with Fe vacancy only occurring at octahedral sites of a spinel. We revealed that the crystal symmetry was reduced from a cubic, giving rise to extra superlattice reflections along the
c* axis and this showed good agreement with a tetragonal structure with
c\\lesssim3
a. We succeeded in determining the position of vacancy sites as well as the unit cell by comparing the XRD results with calculated reflection patterns for plausible vacancy ordered models. The temperature dependent resistivity of the vacancy ordered γ-Fe
2O
3 was several orders higher than that of Fe
3O
4.
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Seongtae Park, Kiwan Jang, Ilgon Kim, Yong-Ill Lee, Hyo Jin Seo
2006 Volume 75 Issue 5 Pages
054709
Published: May 15, 2006
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Two kinds of Sm-doped Strontium Borates, SrB
4O
7 (STB) and SrB
6O
10 (SHB), were prepared for the spectral hole-burning experiment. Sm
3+-ions doped into the STB were well reduced to Sm
2+-ions in air environment. Though partial reduction was observed in SHB, the Sm
3+-ions successfully reduced in the subsequent X-ray irradiation (SHBX). Permanent spectral hole-burning experiments were conducted for
7F0–
5D1 transition band of Sm
2+-ions. The two samples STB and SHBX showed deep spectral holes at room temperature and 50 K, i.e., 40 and 72% of hole depths in STB and SHBX at 50 K, respectively. The STB showed type I hole-burning properties and SHBX type II. The spectral holes were sustained for over 24 h at room temperature. Multiple holes were burnt in an inhomogeneously broadened band to demonstrate the optical data storage in the frequency domain.
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B. W. Chung, A. J. Schwartz, B. B. Ebbinghaus, M. J. Fluss, J. J. Hasl ...
2006 Volume 75 Issue 5 Pages
054710
Published: May 15, 2006
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Resonant photoemission, a variant of photoelectron spectroscopy, has been demonstrated to have sensitivity to aging of Pu samples. The spectroscopic results are correlated with resistivity measurements and are shown to be the fingerprint of mesoscopic or nanoscale internal damage in the Pu physical structure. This means that a spectroscopic signature of internal damage due to aging in Pu has been established.
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Hiroshi Sakai, Yositake Takane
2006 Volume 75 Issue 5 Pages
054711
Published: May 15, 2006
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The conductance of disordered wires with symplectic symmetry is studied by a random-matrix approach. It has been believed that Anderson localization inevitably arises in ordinary disordered wires. A counterexample is recently found in the systems with symplectic symmetry, where one perfectly conducting channel is present even in the long-wire limit when the number of conducting channels is odd. This indicates that the odd-channel case is essentially different from the ordinary even-channel case. To study such differences, we derive the DMPK equation for transmission eigenvalues for both the even- and odd-channel cases. The behavior of dimensionless conductance is investigated on the basis of the resulting equation. In the short-wire regime, we find that the weak-antilocalization correction to the conductance in the odd-channel case is equivalent to that in the even-channel case. We also find that the variance does not depend on whether the number of channels is even or odd. In the long-wire regime, it is shown that the dimensionless conductance in the even-channel case decays exponentially as 〈
geven〉→0 with increasing system length, while 〈
godd〉→1 in the odd-channel case. We evaluate the decay length for the even- and odd-channel cases and find a clear even-odd difference. These results indicate that the perfectly conducting channel induces clear even-odd differences in the long-wire regime.
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Kiko Nakamura
2006 Volume 75 Issue 5 Pages
054712
Published: May 15, 2006
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Excitonic magnetic polarons in diluted magnetic semiconductor formed by the interaction between exciton carriers and magnetic ions within the range of exciton wave function are theoretically investigated. The Heitler–London model is applied to the polaron molecule. The binding energy of the exiton pair in triplet state is calculated and it is found that an attraction between triplet magnetic polaron pairs can occur.
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