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Yoshio Kitaoka, Hidekazu Mukuda, Mitsuharu Yashima, Atsushi Harada
2007 Volume 76 Issue 5 Pages
051001
Published: May 15, 2007
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We review the studies on the unconventional superconducting pairing states and their relevance with magnetism in the
f-electron derived heavy-fermion (HF) systems by means of nuclear-magnetic-resonance (NMR) and nuclear-quadrupole-resonance (NQR). These studies have unraveled a rich variety of the phenomena in the ground state of HF systems. In this article, we address an intimate relationship between the onset of strong-coupling superconductivity (SC) and critical magnetic fluctuations emerging in the vicinity of quantum critical point (QCP). Furthermore, we focus on the novel phase diagram of the HF antiferromagnet CeRhIn
5 under pressure which is characterized by the tetracritical point separating the pure antiferromagnetism (AFM) phase, the AFM+SC uniformly coexisting phase, and the paramagnetic SC phase. A comparison is also presented on the AFM+SC uniformly coexisting phase in high-temperature superconductors as the function of carrier doping. As a consequence, we raise a question; Do we need a bosonic glue to pair electrons in these superconductors? Finally, we address a possible origin of the novel SC in the itinerant ferromagnet UGe
2, which is mediated by ferromagnetic spin-density fluctuations relevant with the first-order transition inside the ferromagnetic states.
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Alexander T. Holmes, Didier Jaccard, Kazumasa Miyake
2007 Volume 76 Issue 5 Pages
051002
Published: May 15, 2007
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Many cerium-based heavy fermion (HF) compounds have pressure–temperature phase diagrams in which a superconducting region extends far from a magnetic quantum critical point. In at least two compounds, CeCu
2Si
2 and CeCu
2Ge
2, an enhancement of the superconducting transition temperature was found to coincide with an abrupt valence change, with strong circumstantial evidence for pairing mediated by critical valence, or charge transfer, fluctuations. This pairing mechanism, and the valence instability, is a consequence of a
f–
c Coulomb repulsion term
Ufc in the Hamiltonian. While some non-superconducting Ce compounds show a clear first order valence instability, analogous to the Ce α–γ transition, we argue that a weakly first order valence transition may be a general feature of Ce-based HF systems, and both magnetic and critical valence fluctuations may be responsible for the superconductivity in these systems.
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Rikio Settai, Tetsuya Takeuchi, Yoshichika Onuki
2007 Volume 76 Issue 5 Pages
051003
Published: May 15, 2007
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We present the recent advances in Ce-based heavy fermion superconductivity. Heavy fermions are formed by the competition between the Ruderman–Kittel–Kasuya–Yosida interaction and the Kondo effect. The application of pressure is useful for controlling the electronic states in antiferromagnets such as CeRh
2Si
2, Ce
2Ni
3Ge
5, CeIn
3, CeRhIn
5, and CeIrSi
3. For these compounds, the Néel temperature
TN decreases with increasing pressure and reaches zero at the quantum critical pressure
Pc. Superconductivity appears around
Pc. In CeRu
2, CeCoIn
5, and CePt
3Si, superconductivity is realized at ambient pressure. For these pressure-induced and ambient-pressure superconductors, we clarified their unconventional characteristics of superconductivity, the close relationship between superconductivity and the dimensionality of the electronic states, and a new aspect of superconductivity in the non-centrosymmetric crystal structure, together with its Fermi surface instability at
Pc.
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Toshiro Sakakibara, Atsushi Yamada, Jeroen Custers, Kazuhiro Yano, Tak ...
2007 Volume 76 Issue 5 Pages
051004
Published: May 15, 2007
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Heavy electron superconductors mostly have anisotropic gap function which vanishes (has nodes) for certain directions in the momentum space. Since the nodal structure is closely related to the pairing mechanism, its experimental determination is very important. In anisotropic superconductors, low energy spectrum of the quasiparticles in the vortex state much depends on the nodal structure. In particular, the electronic specific heat has been demonstrated to exhibit the characteristic dependence on the angle between the field and the nodal direction, thereby the nodal structure can be probed experimentally. In this contribution, we present our recent experimental results on the field-orientation dependence of the specific heat on
f electron superconductors CeRu
2, CeCoIn
5, PrOs
4Sb
12, and URu
2Si
2, and discuss their gap structures.
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Yuji Matsuda, Hiroshi Shimahara
2007 Volume 76 Issue 5 Pages
051005
Published: May 15, 2007
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The Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state is a novel superconducting state in a strong magnetic field characterized by the formation of Cooper pairs with nonzero total momentum (
k↑,−
k+
q↓), instead of the ordinary BCS pairs (
k↑,−
k↓). A fascinating aspect of the FFLO state is that it exhibits inhomogeneous superconducting phases with a spatially oscillating order parameter and spin polarization. The FFLO state has been of interest in various research fields, not only in superconductors in solid state physics, but also in neutral Fermion superfluid of ultracold atomic gases and in color superconductivity in high energy physics. In spite of extensive studies of various superconductors, there has been no undisputed experimental verification of the FFLO state, mainly because of the very stringent conditions required of the superconducting materials. Among several classes of materials, certain heavy fermion and organic superconductors are believed to provide conditions that are favorable to the formation of the FFLO state. This review presents recent experimental and theoretical developments of the FFLO state mainly in heavy fermion superconductors. In particular we address the recently discovered quasi-two-dimensional superconductor CeCoIn
5, which is a strong candidate for the formation of the FFLO state.
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Yuji Aoki, Takashi Tayama, Toshiro Sakakibara, Keitaro Kuwahara, Kazua ...
2007 Volume 76 Issue 5 Pages
051006
Published: May 15, 2007
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This review presents a summary and evaluation of the experimental properties of unconventional superconductivity in PrOs
4Sb
12. After a brief introduction of filled skutterudites, we argue that the normal-state properties of PrOs
4Sb
12 are quite different from ordinary heavy-fermion superconductors, in the sense that the 4
f-electrons seem to be well localized even at low temperatures where the superconductivity appears. This is reflected in the existence of a field-induced antiferro-quadrupole ordering of Pr 4
f-electrons. It is shown that the 4
f collective excitations can be described as
quadrupolar excitons. Their strong temperature dependence in close correlation with the superconductivity suggests a conjecture that the superconducting mechanism may involve quadrupolar-exciton-mediated pairing of some kind. Although the structure of the superconducting order parameter is far from conclusive, outstanding experimental observations reported to date reveal the uniqueness of the unconventional superconducting state. Special focus is given to time-reversal symmetry breaking in the superconducting state. The article concludes with a discussion of some key issues and desirable future work.
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Tatsuo C. Kobayashi, Akihiro Hori, Satoshi Fukushima, Hiroyuki Hidaka, ...
2007 Volume 76 Issue 5 Pages
051007
Published: May 15, 2007
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Pressure-induced superconductivity is found in UIr without inversion symmetry. The pressure–temperature phase diagram has been investigated by means of the electrical resistivity, ac-susceptibility and magnetization measurements under high pressure. The phase diagram consists of three magnetic phases FM1–3 and a superconducting phase. The huge enhancement of residual resistivity and the negative magnetoresistance are found in the intermediate pressure region. These behavior may be induced by the pressure-induced structural phase transition and the accompanied phase separation in this pressure range. The superconducting phase with narrow pressure range is embedded in the FM3 phase, adjacent to zero-temperature FM3-to-nonmagnetic transition. The temperature dependence of resistivity above
TSC follows non-Fermi liquid form of
T1.6. From these experimental facts, superconductivity is considered to be associated with the ferromagnetic fluctuation.
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Satoshi Fujimoto
2007 Volume 76 Issue 5 Pages
051008
Published: May 15, 2007
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This article is a pedagogical review of theoretical studies of noncentrosymmetric superconductors with particular emphasis on the role played by electron correlation, which is important for heavy fermion systems. We survey unique properties of parity-violated superconductivity such as the admixture of spin singlet and triplet states, unusual paramagnetism, large Pauli limiting fields, magnetoelectric effects, the helical vortex phase, and the anomalous Hall effect. It is pointed out that these remarkable features are strengthened by a strong electron correlation effect, and thus are prominent in heavy fermion superconductors without inversion symmetry. We also discuss possible pairing states realized in the heavy fermion system CePt
3Si.
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Ernst Bauer, Heinich Kaldarar, Andry Prokofiev, Esmael Royanian, Alex ...
2007 Volume 76 Issue 5 Pages
051009
Published: May 15, 2007
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Heavy fermion superconductivity in absence of inversion symmetry of the crystal structure is basically controlled by a Rashba-like antisymmetric spin orbit coupling which splits the Fermi surface and removes the spin degeneracy of electrons. The Fermi surface splitting originates a mixing of spin-singlet and spin-triplet states in the superconducting condensate. Such constraints are responsible for various uncommon features of the superconducting ground state and are discussed here in view of CePt
3Si, the first heavy fermion superconductor missing a centre of symmetry. We recall and discuss normal and superconducting properties of CePt
3Si and relate them to recently developed phenomenological theories.
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Noriaki Kimura, Yuji Muro, Haruyoshi Aoki
2007 Volume 76 Issue 5 Pages
051010
Published: May 15, 2007
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We review the normal and superconducting properties in the noncentrosymmetric heavy-fermion CeRhSi
3. In the normal state, CeRhSi
3 exhibits the antiferromagnetic order at low temperatures (1.6 K at ambient pressure) although its Kondo temperature is much higher than the ordering temperature
TN. With applying pressure
P,
TN initially increases and subsequently decreases. The superconductivity arises at the pressures where the antiferromagnetic transition occurs.
TN does not seem to fall to zero but becomes nearly constant with further application of pressure, and then
TN vs
P merges with the superconducting transition temperature
Tc vs
P at 26 kbar where
Tc reaches the maximum. Nearly perfect magnetic-shielding associated with the superconductivity is observed below 26 kbar, suggesting that the bulk superconductivity is realized below
TN. We observe an anomaly below
Tc in the resistivity as well as in the ac-susceptibility. The origin of the both anomalies seem to be the same but have not been clarified. The magnetic field–temperature (
H–
T) phase diagram of the superconducting state for fields along the tetragonal
a-axis is unusual. It has a concave structure and the upper-critical-field
Hc2 at zero temperature exceeds the paramagnetic limiting field expected from the BCS model. The pressure dependence of
H–
T phase diagram implies that the paramagnetic effect exists and the effect is much reduced in CeRhSi
3. This result is consistent with the theoretical prediction for the noncentrosymmetric superconductor.
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A. D. Huxley, S. J. C. Yates, F. Lévy, I. Sheikin
2007 Volume 76 Issue 5 Pages
051011
Published: May 15, 2007
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The study of the emergence of superconductivity close to quantum critical points affords a powerful means to identify the mechanism that drives the formation of unconventional superconductivity in heavy fermion materials. The recent discovery of superconducting states close to quantum critical points in ferromagnets UGe
2 and URhGe is reviewed in this light. For URhGe we examine whether the predominant type of magnetic excitations involved are longitudinal excitations, hitherto considered theoretically to be the most promising candidate to mediate equal-spin-paired superconductivity.
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Yoshinori Haga, Hironori Sakai, Shinsaku Kambe
2007 Volume 76 Issue 5 Pages
051012
Published: May 15, 2007
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Recent advances in the understanding of the 5
f-relevant electronic states and unconventional superconducting properties are reviewed in actinide compounds of UPd
2Al
3, UPt
3, URu
2Si
2, UGe
2, and PuRhGa
5. These are based on the experimental results carried out on high-quality single crystal samples, including transuranium compounds, which were grown by using combined techniques. The paring state and the gap structure of these superconductors are discussed, especially for the corresponding Fermi surfaces which were clarified by the de Haas–van Alphen experiment and the energy band calculations. A detailed systematic study using the NQR/NMR spectroscopy reveals the
d-wave superconductivity in PhRhGa
5 and the difference of magnetic excitations due to the difference of ground states in U-, Np-, and Pu-based AnTGa
5 (T: transition metal) compounds.
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John L. Sarrao, Joe D. Thompson
2007 Volume 76 Issue 5 Pages
051013
Published: May 15, 2007
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Over the past five or so years, a family of cerium- and plutonium-based superconductors that crystallize in the HoCoGa
5 structure has attracted considerable attention. These materials display heavy fermion behavior consistent with proximity to magnetic order and low-temperature superconducting properties suggestive of d-wave pairing. The availability of high-quality single crystals and the ability to tune physical properties through a variety of chemical substitutions and other means have enabled advances in our understanding of these fascinating materials. In particular, the evolution of electronic structure and characteristic spin fluctuations reveals rich phase diagrams and places in context fundamental questions for the broader field of strongly correlated superconductors.
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Masaki Tezuka
2007 Volume 76 Issue 5 Pages
053001
Published: May 15, 2007
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We propose an initialization procedure for the density-matrix renormalization group (DMRG):
the recursive sweep method. In a conventional DMRG calculation, the infinite-system algorithm, where two new sites are added to the system at each step, has been used to achieve the target system size. We then need to obtain the ground state for a different system size for every site addition. Thus, 1) it is difficult to supply a good initial vector for the numerical diagonalization for the ground state, and 2) when the system reduced to a 1D one that consists of an array of nonequivalent sites as in the case of ladders or in the Hubbard–Holstein model, special care has to be taken. Our procedure, which we call the
recursive sweep method, provides a solution to these problems and in fact provides a faster algorithm for the Hubbard model and the complicated ones such as the Hubbard–Holstein model.
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Hiroshi Ajiki, Hajime Ishihara
2007 Volume 76 Issue 5 Pages
053401
Published: May 15, 2007
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We present a new concept of entangled photon generation via biexciton from a quantum-well embedded in a microcavity. The coupled states of the biexciton and cavity photons play an important role in the entangled photon generation. In fact, a suitable design of the level scheme of the coupled states can considerably enhance the generation process. We present the optimal condition for entangled photon generation in terms of the biexcitonic cavity quantum electrodynamics (QED).
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Masanori Inui, Shinya Hosokawa, Kazuhiro Matsuda, Satoshi Tsutsui, Alf ...
2007 Volume 76 Issue 5 Pages
053601
Published: May 15, 2007
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The dynamic structure factor of liquid Se was measured at 523 K using high-resolution inelastic X-ray scattering. Anomalous narrowing of the spectrum was observed at 15 nm
−1, where the static structure factor
S(
Q) exhibits a weak shoulder, but the elastic part of the dynamic structure factor
S(
Q,
E=0) exhibited a strong maximum. The second frequency moment, which is estimated from only the quasi-elastic peak, is consistent with the motion of rigid six-atom clusters, while a formal agreement with the first-moment sum rule is preserved by the appearance of a weak intramolecular mode at 30 meV.
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Yositake Takane, Katsunori Wakabayashi
2007 Volume 76 Issue 5 Pages
053701
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We study the conductance of disordered quantum wires with unitary symmetry focusing on the case where
m excess one-way conducting channels are present. The excess channels make the channel number in one direction by
m greater than that in the opposite direction, resulting in the stabilization of
m perfectly conducting channels. The case of
m=1 can be realized in zigzag nanographene ribbons. Due to the presence of perfectly conducting channels, the dimensionless conductance
g behaves as
g→
m with increasing system length, indicating the absence of the Anderson localization. To describe the anomalous behavior, we generalize the unitary class to allow
m excess one-way channels and derive the corresponding Fokker–Planck equation for transmission eigenvalues. It is shown that the conductance decay length is reduced with increasing
m. We present an extended classification table for the standard three classes.
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Takahiro Fukui, Yasuhiro Hatsugai
2007 Volume 76 Issue 5 Pages
053702
Published: May 15, 2007
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We derive an efficient formula for Z
2 topological invariants characterizing the quantum spin Hall effect. It is defined in a lattice Brillouin zone, which enables us to implement numerical calculations for realistic models even in three dimensions. Based on this, we study the quantum spin Hall effect in Bi and Sb in quasi-two and three dimensions using a tight-binding model.
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Miho Itoi, Mika Kano, Nobuyuki Kurita, Masato Hedo, Yoshiya Uwatoko, T ...
2007 Volume 76 Issue 5 Pages
053703
Published: May 15, 2007
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We have investigated the transport properties of the quasi-one-dimensional (1-D) organic conductor (TMTTF)
2AsF
6 at high pressures. A superconducting transition was observed, for the first time, at 2.38 K from a resistance measurement at 4.5 GPa. The presence of zero resistance was also confirmed at ∼2.3 K in the pressure range of 4.65≤
P≤5 GPa. We discuss the electron correlation in (TMTTF)
2AsF
6 based on its pressure–temperature phase diagram.
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Kenji Goto, Toyotaka Osakabe, Kazuhisa Kakurai, Yoshiya Uwatoko, Akira ...
2007 Volume 76 Issue 5 Pages
053704
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KCuCl
3 is a three dimensionally coupled spin dimer system, which undergoes a pressure-induced quantum phase transition from a gapped ground state to an antiferromagnetic state at a critical pressure of
Pc\\simeq8.2 kbar. Magnetic excitations in KCuCl
3 at a hydrostatic pressure of 4.7 kbar have been investigated by conducting neutron inelastic scattering experiments using a newly designed cylindrical high-pressure clamp cell. A well-defined single excitation mode is observed. The softening of the excitation mode due to the applied pressure is clearly observed. From the analysis of the dispersion relations, it is found that an intradimer interaction decreases under hydrostatic pressure, while most interdimer interactions increase.
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Yuta Hayashi, Masao Ogata
2007 Volume 76 Issue 5 Pages
053705
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Motivated by the observation of a gapless spin liquid state in κ-(BEDT-TTF)
2Cu
2(CN)
3, we analyze the anisotropic triangular lattice
S=1⁄2 Heisenberg model with the resonating valence bond mean-field approximation. Paying attention to the small quasi-one-dimensional anisotropy of the material, we take an approach from one-dimensional (1D) chains coupled with frustrating zigzag bonds. By calculating one-particle excitation spectra changing anisotropy parameter
J′⁄
J from the decoupled 1D chains to the isotropic triangular lattice, we find almost gapless excitations in the wide range from the 1D limit. This one-dimensionalization by frustration is considered to be a candidate for the mechanism of the gapless spin liquid state.
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Masaichiro Mizumaki, Satoshi Tsutsui, Hajime Tanida, Tomoya Uruga, Dai ...
2007 Volume 76 Issue 5 Pages
053706
Published: May 15, 2007
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The X-ray absorption spectra of the heavy fermion compounds SmFe
4P
12 and SmOs
4Sb
12 have been measured near the Sm
L3-edge at selected temperatures below 300 K. The spectra show the valence of Sm ions in SmFe
4P
12 to be trivalent between 14 and 300 K with no significant temperature dependence. In contrast, that in SmOs
4Sb
12 is 2.83 at 300 K and shows a significant decrease below 150 K, indicating an important role of the nonmagnetic Sm
2+ ions in the heavy fermion state that are insensitive to an applied magnetic field.
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Takashi U. Ito, Wataru Higemoto, Kazuki Ohishi, Tatsuya Fujimoto, Robe ...
2007 Volume 76 Issue 5 Pages
053707
Published: May 15, 2007
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We performed muon spin relaxation measurements on randomly aligned single-crystalline samples of SmRu
4P
12 down to 0.02 K to investigate static and dynamical magnetic properties in low fields. The local field at the muon site develops gradually with decreasing temperature below a metal–insulator transition temperature of
TMI=16.5 K, growing steeply below
T′=3 K with an accompanying suppression of magnetic fluctuations. We discuss the contribution of a possible octupole moment to the local magnetic states and the magnetic anomaly at
T′.
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Yasuhiro Tanaka, Kenji Yonemitsu
2007 Volume 76 Issue 5 Pages
053708
Published: May 15, 2007
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Charge ordering accompanied by lattice distortion in quasi-two dimensional organic conductors θ-(ET)
2X (ET = BEDT-TTF) is studied by using an extended Hubbard model with Peierls-type electron–lattice couplings within the Hartree–Fock approximation. It is found that the horizontal-stripe charge-ordered state, which is experimentally observed in θ-(ET)
2RbZn(SCN)
4, is stabilized by the self-consistently determined lattice distortion. Furthermore, in the presence of the anisotropy in nearest-neighbor Coulomb interactions
Vij, the horizontal charge order becomes more stable than any other charge patterns such as diagonal, vertical and 3-fold-type states. At finite temperatures, we compare the free energies of various charge-ordered states and find a first-order transition from a metallic state with 3-fold charge order to the insulating state with the horizontal charge order. The role of lattice degrees of freedom in the realization of the horizontal charge order and the relevance to experiments on θ-(ET)
2X are discussed.
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Mikio Shimizu
2007 Volume 76 Issue 5 Pages
053801
Published: May 15, 2007
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Some hydrophilic amino acids such as glutamic acid, lysine, cysteine, and tyrosine having the side chains whose p
KR are in or near the physiological pH range were shown to act as rate-enhancers or catalysts in various metabolic reactions weakly but specifically, as well as histidine discussed earlier. Anticodonic tri-ribonucleotides corresponding to the above amino acid catalysts (for example, UpUpU to lysine) also acted as catalysts similarly in each metabolic reaction. The primitive cell containing these molecules and metabolites could be the first minimal biomolecular system with metabolism and inheritance, possibly called as genetic code world.
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K. Andriopoulos, P. G. L. Leach
2007 Volume 76 Issue 5 Pages
054001
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We provide the explicit solution of the
n-dimensional generalised ladder system, that is the homogeneous quadratic system of first-order differential equations of the form \\dot
xi=
xi∑
j=1naijxj,
i=1,
n, where (
aij)=(1+
ai−
aj),
i,
j=1,
n introduced by Imai and Hirata [J. Phys. Soc. Jpn.
72 (2003) 973]. These systems are characterised by the
n2−1 symmetries
Yml=
xmual−am−1(∑
j=1nxj∂
xj−
u∂
xl), but are not the most general systems invariant under these symmetries. The more general systems are called hyperladder systems and we discuss their integrability.
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Tomoyuki Obuchi, Hidetoshi Nishimori, David Sherrington
2007 Volume 76 Issue 5 Pages
054002
Published: May 15, 2007
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The phase diagram of the
p-spin-interacting spin glass model in a transverse field is investigated in the limit
p→∞ under the presence of ferromagnetic bias. Using the replica method and the static approximation, we show that the phase diagram consists of four phases: Quantum paramagnetic, classical paramagnetic, ferromagnetic, and spin-glass phases. We also show that the static approximation is valid in the ferromagnetic phase in the limit
p→∞ by using the large-
p expansion. Since the same approximation is already known to be valid in other phases, we conclude that the obtained phase diagram is exact.
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Mika Yoshida, Tatsuya Uezu, Toshiyuki Tanaka, Masato Okada
2007 Volume 76 Issue 5 Pages
054003
Published: May 15, 2007
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We study the problem of performance evaluation of code-division multiple-access (CDMA) multiuser detectors by means of statistical mechanics using the replica method. The replica symmetric solutions were analyzed previously. As is well known, the replica symmetric solution becomes unstable when the temperature (magnitude of noise) is lowered. In this paper, we investigate both the behavior and the stability of the replica symmetric solutions in the low temperature region. We find that the solutions have complicated bifurcation structures in the low temperature region where the solutions coexist. We also find that there are two types of replica symmetry breaking, Almeida–Thouless (AT)-instability and freezing. We obtain the one-step replica symmetry breaking solution in each case. Further, we compare the theoretical results with the results from the Monte-Carlo simulations. Consequently, we find that the theoretical results agree with the numerical simulations.
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Shigetoshi Sota, Masaki Itoh
2007 Volume 76 Issue 5 Pages
054004
Published: May 15, 2007
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An oscillation-free Fourier expansion is proposed and applied to the polynomial expansion of resolvent operator, as an alternative treatment for Gibbs phenomenon to the kernel polynomial method (KPM) by Voter
et al. [Phys. Rev. B
53 (1996) 12733]. Adopting regulated Legendre polynomial as basis functions, the recurrence algorithm underlying the KPM is practically preserved, while it eliminates unphysical oscillations entirely. The resolution is uniform in the frequency domain, and improved without limitation by extending the truncation range of the expansion. The method can also be used to calculate the eigenvector with remarkably high precision. It is further extended to the time domain, being able to deal with the quantum evolution in the same algorithm. A numerical test was performed against a lattice dynamics of 19
3 atoms, as well as of a computer generated Lennard–Jones glass of 1000 atoms. Not only it serves as a most efficient simulation scheme for a bulk, confirmed was also that the calculation converges to exact results within realistic computation time.
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Franklin Lambert, Johan Springael, Samuel Colin, Ralph Willox
2007 Volume 76 Issue 5 Pages
054005
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In this paper we present a systematic and elementary construction of the Hirota equations (in an equivalent formulation) that make up the bilinear KP and modified KP hierarchies. Our construction leads to a natural gradation of the Hirota equations of a given weight in each bilinear hierarchy, providing useful insight into their mutual relationship.
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Akinori Igarashi
2007 Volume 76 Issue 5 Pages
054301
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Eigenvalue problems for radial Dirac equation are treated by expanding wavefunction over kinetically balanced B-splines. Spurious states which may appear in the eigenvalue problem hardly occur, and the present calculation is effective to calculate energy for bound-state and to prepare a set of eigenstates.
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Mitsuru Kodera, Katsuhiko Higuchi, Akira Narita, Masahiko Higuchi
2007 Volume 76 Issue 5 Pages
054302
Published: May 15, 2007
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We provide a density functional scheme for calculating the orbital-dependent exchange-correlation potential using the virial theorem as a sum rule. This is different from the optimized effective potential (OEP) method. To confirm the validity, atomic-structure calculations are performed for closed-shell atoms. The exchange energies are in good agreement with the previous values obtained by the OEP method, whereas the numerical speed has been considerably improved.
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Kunihiro Kamataki, Yoshihiko Nagashima, Shunjiro Shinohara, Yoshinobu ...
2007 Volume 76 Issue 5 Pages
054501
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This paper reports the experimental and theoretical investigation on the coexistence of the collisional drift and flute wave instabilities in the bounded linear electron cyclotron resonance (ECR) plasma. The drift wave instability is excited by the steep density gradient and imposed axial boundary conditions in the device. The flute instability is excited by the bad curvature of the magnetic field. Emphasis is made on the effect of the ion–neutral (i–n) particle collisions. It is observed that the drift wave instability is excited when the i–n particle collision frequency ν
in is low, but it is stabilized when ν
in is high. Furthermore, the drift and flute modes are coexistent for the intermediate values of ν
in. The Hasegawa–Wakatani model which describes the dispersion relation of the collisional drift-interchange mode is used for understanding the experimental observations. It is found that the experimentally observed drift frequency is consistent with the numerical calculation. The present result has shown that the i–n particle collisions play an important role in the stabilization of the collisional drift wave instability in the ECR plasma.
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Masaru Nakada, Osamu Yamamuro, Kenji Maruyama, Masakatsu Misawa
2007 Volume 76 Issue 5 Pages
054601
Published: May 15, 2007
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Quasielastic neutron scattering has been used to investigate the hydration of alcohol clusters in
tert-butyl alcohol–water mixture. The measurements were made in a range of alcohol concentration,
xTBA, from 0.0 to 0.17 in mole fraction at 25 °C. Fraction, α, of water molecules hydrated to fractal-surface of alcohol clusters in
tert-butyl alcohol–water mixture was obtained as a function of alcohol concentration. Average hydration number
Nws of
tert-butyl alcohol molecule was derived from the value of α as a function of alcohol concentration. The value of
Nws for an isolated alcohol molecule in water was 19–21. The anomalous excess partial molar volume of
tert-butyl alcohol–water mixture was interpreted successfully by applying the same model with the same values of volume parameter as used for 1-propanol–water mixture, δ
1 (=−0.36 cm
3·mol
−1) and δ
2 (=0.60 cm
3·mol
−1).
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Hideki Seto, Mafumi Hishida, Hidekazu Nobutou, Norifumi L. Yamada, Mic ...
2007 Volume 76 Issue 5 Pages
054602
Published: May 15, 2007
Released on J-STAGE: August 12, 2010
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Temperature, pressure, and ethanol concentration dependences of the structure and dynamics of dipalmitoyl phosphatidylcholine (DPPC) aqueous solution were investigated by small-angle neutron scattering and neutron spin echo experiments. The effect of ethanol is almost the same as that of applying pressure to induce the interdigitated gel phase. A swollen phase, in which the mean repeat distance of lipid bilayers is larger than these of the other phases, is found between the liquid-crystalline phase and the interdigitated gel phase. The nature of the swollen phase is similar to the anomalous swelling observed above the transition point between the liquid-crystalline phase and the ripple gel phase. However, the temperature dependence of the mean repeat distance and the bending rigidity of lipid bilayers in the swollen phase are different from those of the anomalous swelling.
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Manabu Hirai, Yasuharu Kodama, Hijiri Kito, Yasumoto Tanaka, Kazuyasu ...
2007 Volume 76 Issue 5 Pages
054701
Published: May 15, 2007
Released on J-STAGE: August 12, 2010
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We report the anomalous
Tc behavior in a five-layered compound of the cuprate superconductor (Cu,C)Ba
2Ca
4Cu
5O
y. The
Tc decreases once from 94.7 K (as-synthesized) to 93.3 K (annealed at 460 °C under N
2 flow), and then increases to 99.0 K (annealed at 530 °C under N
2 flow). We argue that this
Tc change reflects the CuO
2 planes governing the bulk
Tc, shifting from the three inner CuO
2 planes to the two outer CuO
2 planes. A model to explain this behavior is proposed, drawing two bell-shaped curves against the oxygen content (doping state), and the
Tc values change along the curves from that of the inner CuO
2 plane to that of outer one.
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Ming-Fang Li, Toshihiro Ariizumi, Shugo Suzuki
2007 Volume 76 Issue 5 Pages
054702
Published: May 15, 2007
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We study the magneto-optical Kerr effect using fully relativistic calculations. Spin–orbit coupling is dealt with exactly solving the Dirac equation directly and the matrix elements of the Dirac matrices
α are used in a fully relativistic expression of the Kubo formula for the optical conductivity derived with a relativistic sum rule. We also perform approximate calculations of the optical conductivity to examine the accuracy of a partly relativistic expression in which the matrix elements of the momentum operator
p are used instead. As an example, we carry out calculations for bcc Fe and fcc Ni using the fully relativistic full-potential linear-combination-of-atomic-orbitals method. It is found that the partly relativistic treatment is good for the diagonal optical conductivity while it is not very good for the off-diagonal optical conductivity, the Kerr rotation angle, and the Kerr ellipticity. The results of the present study are compared to those of experimental and other theoretical studies.
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Naoya Sasaki, Yasuhiro Takayama, Satoshi Nakamura, Hiroyoshi Ishii, Ts ...
2007 Volume 76 Issue 5 Pages
054703
Published: May 15, 2007
Released on J-STAGE: August 12, 2010
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We have measured the resonant-inverse photoemission spectra for PrSn
3, PrCo
2, and PrAg in the Pr 4
d–4
f excitation region. Similar to the case of Ce compounds, the spectra strongly depend on the energy of the incident electron. We determined the “on-resonance” and “off-resonance” energies as 124 and 115 eV, respectively, and these energies are common to all the Pr compounds. The dependence of the spectra on the energy of the incident electron is well explained by the calculation based on the single-impurity Anderson model considering the bulk and surface components. A clear shoulder near the Fermi energy was observed in the on-resonance spectra for PrSn
3 and PrCo
2, and this shoulder is assigned to the
f2 final-state peak. The result of the analysis shows that the Pr 4
f electron in PrSn
3 and PrCo
2 has more itinerant charactaristics compared with that in PrAg, which is consistent with the result of the photoemission spectroscopy experiments.
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Toshiyuki Arakane, Takafumi Sato, Takashi Takahashi, Hong Ding, Takeno ...
2007 Volume 76 Issue 5 Pages
054704
Published: May 15, 2007
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We have performed angle-resolved photoemission spectroscopy (ARPES) on M
xCoO
2 (M: Na, K, and Rb) with both soft X-ray and ultraviolet light to clarify the electronic structure intrinsic to the bulk CoO
2 plane. We observed a large holelike
a1g Fermi surface centered at the Γ(A) point with no signatures for a theoretically predicted small
e′g hole pocket around the K(H) point, irrespective of the species of alkali metal and its content (
x). We also found that the band dispersion near the Fermi level shows a kink structure indicative of the band hybridization and/or the strong mass renormalization due to electron-phonon coupling.
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M. Mori, S. Hikino, S. Takahashi, S. Maekawa
2007 Volume 76 Issue 5 Pages
054705
Published: May 15, 2007
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We study the influence of magnetic scattering on the Josephson critical current,
Ic, in a superconductor/ferromagnetic metal/superconductor (SFS) junction by a tunneling Hamiltonian approach. An analytical formula of
Ic is given in the fourth order perturbation theory as regards the tunneling matrix element. The
Ic exhibits the damped oscillatory dependence on the thickness of the ferromagnetic metal,
d, and shows the transition between 0- and π-states with
d. When the superconducting transition temperature is comparable to the ferromagnetic Curie temperature, the period of oscillation is obviously changed by increasing temperature,
T, due to the magnetic scattering, which induces the 0–π transition with
T. The magnetic scattering provides rich variety of Josephson effect in the SFS junction. Our results present an appropriate condition of a superconductor and a ferromagnetic metal to control the 0- and the π-states.
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Abdul Hannan, Yasushi Okayama, Toyotaka Osakabe, Keitaro Kuwahara, Mas ...
2007 Volume 76 Issue 5 Pages
054706
Published: May 15, 2007
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We have studied the origin of the anomalous peak structure of resistivity of the low-carrier system CeSb appeared around the antiferromagnetic transition temperature
TN under high pressures by means of simultaneous measurement of lattice parameter by X-ray diffraction and resistivity together with neutron diffraction technique. It was found that there is a strong relationship between the unusual decrease of lattice parameter and the unusual increase of resistance below
TN under high pressure. Both of these phenomena can be explained by the appearance of Γ
8-like magnetic state of Ce
3+ ion below
TN.
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Gen Tatara, Hiroshi Kohno, Junya Shibata, Yann Lemaho, Kyung-Jin Lee
2007 Volume 76 Issue 5 Pages
054707
Published: May 15, 2007
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The nonadiabatic correction to spin transfer torque arising from fast-varying spin texture is calculated treating the conductions electron fully quantum mechanically. The torque is nonlocal in space, and is shown to be equivalent to a force (due to momentum transfer) acting on the center of mass of the texture. Another kind of force exists in the adiabatic regime, and it is identified to be of topological origin. These forces are shown to be the counter-reactions of electric transport properties, resistivity and the Hall effect.
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Takahiro Namiki, Hideyuki Sato, Hitoshi Sugawara, Yuji Aoki, Rikio Set ...
2007 Volume 76 Issue 5 Pages
054708
Published: May 15, 2007
Released on J-STAGE: August 12, 2010
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We have investigated the thermoelectric power (TEP) and Hall coefficient (
RH), along with the field dependence of Hall resistivity (ρ
H) and magnetoresistance (MR) in single crystals of CeCu
5.9Au
0.1 and CeCu
6. In both compounds,
RH is highly anisotropic with respect to the field direction below ∼10 K. For
H||[001], a negative minimum in ρ
H and a positive MR peak grow at low temperatures near 1.7 T, where a metamagnetic-like anomaly was reported for CeCu
6. The Au substitution induces drastic changes in
RH depending on the magnetic field direction, which is discussed in correlation with the predicted change in the Fermi surface across the quantum critical point. In CeCu
5.9Au
0.1, an unexpectedly large positive MR has been found at low temperatures and in low fields; its origin is discussed in comparison with the Hall resistivity. For all the principal axes, the Au-substitution effect on TEP is minor in both magnitude and anisotropy down to ∼1.5 K, suggesting no essential change in the electronic structure in the energy region above a few K.
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Hwayong Noh
2007 Volume 76 Issue 5 Pages
054709
Published: May 15, 2007
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The in-plane magnetoresistance of dilute two-dimensional holes in a (100) GaAs heterostructure has been measured for various directions of a parallel magnetic field. The magnetoresistance exhibits a strong anisotropy, and changes its field dependence at a field corresponding to the full spin depopulation. The spin susceptibility deduced from the depopulation field also shows a strong anisotropy at higher densities while the anisotropy is absent at a lower density.
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Hosho Katsura
2007 Volume 76 Issue 5 Pages
054710
Published: May 15, 2007
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We give a brief review of the Kondo effect and exactly solve the nonequilibrium Kondo problem at the special point in the parameter space of the model with spin-dependent chemical potentials. Using the obtained solution, we compute several experimentally observable quantities: charge current, spin current and magnetic properties. Applications to the physically important cases such as the case where the impurity spin is placed in between two ferromagnetically polarized leads are discussed.
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Ayaka Sakata, Masato Hisakado, Shintaro Mori
2007 Volume 76 Issue 5 Pages
054801
Published: May 15, 2007
Released on J-STAGE: August 12, 2010
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We introduce an infectious default and recovery model for
N obligors. The obligors are assumed to be exchangeable and their states are described by
N Bernoulli-type random variables
Si (
i=1,…,
N). They are expressed by multiplying independent Bernoulli variables
Xi,
Yij, and
Y′
ij, and the default and recovery infections are described by
Yij and
Y′
ij. We obtain the default probability function
P(
k) for
k defaults. By considering a continuous limit, we find two nontrivial probability distributions with a reflection symmetry of
Si↔1−
Si. Their profiles are singular and oscillating and we theoretically investigate it. We also compare
P(
k) with an implied default distribution function inferred from the quotes of iTraxx-CJ, which is a portfolio credit derivative of Japanese 50 companies. In order to explain the behavior of the implied distribution, the recovery effect may be necessary.
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Shigemasa Matsuo, Sahel Ashhab, Toshiyuki Fujii, Franco Nori, Katsuhik ...
2007 Volume 76 Issue 5 Pages
054802
Published: May 15, 2007
Released on J-STAGE: August 12, 2010
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We consider the possibility of generating macroscopic entangled states in capacitively coupled phase qubits. First we discuss the operation of phase qubits and the implementation of the basic gate operations in them. We then analyze two possible procedures that can be used to generate
n-qubit entangled states, such as the Greenberger–Horne–Zeilinger state for the case
n=3. The procedures we propose are constructed under the experimentally motivated constraint of trying to minimize the number of control lines used to manipulate the qubits.
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Hideki Tou, Norihiko Tsugawa, Masafumi Sera, Hisatomo Harima, Yoshinor ...
2007 Volume 76 Issue 5 Pages
058001
Published: May 15, 2007
Released on J-STAGE: August 12, 2010
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