-
Kenji Ishida, Yusuke Nakai, Hideo Hosono
2009 Volume 78 Issue 6 Pages
062001
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
In this review, the authors present a summary of experimental reports on newly discovered iron-based superconductors as they were known at the end of 2008. At the same time, this paper is intended to be useful for experimenters to know the current status of these superconductors. The authors introduce experimental results that reveal basic physical properties in the normal and superconducting states. The similarities and differences between iron-pnictide superconductors and other unconventional superconductors are also discussed.
View full abstract
-
Yasumasa Takagi, Kota Tomatsu, Kan Nakatsuji, Fumio Komori
2009 Volume 78 Issue 6 Pages
063601
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
On the Ge(001) surface, it has previously been shown that a single-electron excitation process induces a local and reversible superstructure transformation between
c(4×2) and
p(2×2) by scanning tunneling microscopy. A structure transformation in the direction opposite to that of the previous result is demonstrated by increasing the tunneling current in the electron injection to the surface. In addition, the increased tunneling current shortens the range of hot electron propagation in the surface state. The observed results are attributed to the local increase in surface lattice temperature by a multiple electronic excitation process.
View full abstract
-
Yisheng Chai, Hongshun Yang, Jian Liu, Chenghai Sun, Huixian Gao, Xudo ...
2009 Volume 78 Issue 6 Pages
063602
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We report thermal transport measurements performed on the quasi-one-dimensional Bechgaard salts (TMTSF)
2ClO
4 and (TMTSF)
2PF
6 along the
a-direction. For both salts, magnon-drag effects are found to contribute considerably to thermopower above 80 K. These results imply spin–charge separation in the metallic state for both salts. Moreover, a linear temperature-dependent thermal conductivity is found to be unaffected by anion disorder below an anion ordering transition temperature
TAO∼25 K in (TMTSF)
2ClO
4.
View full abstract
-
Kenya Tanaka, Takahiro Namiki, Atsushi Imamura, Makoto Ueda, Takashi S ...
2009 Volume 78 Issue 6 Pages
063701
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We have succeeded in growing Pr
xOs
4Sb
12 single crystals under high pressure (∼4 GPa) for the first time, where the Pr site filling fraction is supposed to be enhanced. From the systematic measurement of the transport, magnetic, and thermal properties on the grown single crystals, we found a marked decrease in the onset superconducting transition temperature
Tc and a considerable increase in the 4
f-electron crystal field (CF) energy splitting between the ground state and the first excited state (Δ
CF), compared with those reported on the ambient-pressure grown single crystals. Furthermore, the mass enhancement is reduced in the high-pressure grown samples. The correlation between Δ
CF and both
Tc and mass enhancement indicates the crucial role of conduction electron scattering accompanied by the CF excitation in the superconductivity of this compound.
View full abstract
-
Taichi Terashima, Motoi Kimata, Hidetaka Satsukawa, Atsushi Harada, Ka ...
2009 Volume 78 Issue 6 Pages
063702
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We report resistivity measurements performed on KFe
2As
2 single crystals down to
T=0.3 K and in magnetic fields up to 17.5 T. The in-plane resistivity vs
T curve has a convex shape down to ∼50 K and shows a
T2 dependence below ∼45 K. The ratio of the
c-axis to in-plane resistivities is ∼10 at room temperature and ∼40 at 4.2 K. The superconducting upper critical field
Bc2(
T) has been determined from the resistivity data:
Bc2ab(0)=4.47 T and
Bc2c(0)=1.25 T. The anisotropy parameter Γ=
Bc2ab⁄
Bc2c increases with
T and is 6.8 at
T=
Tc. The strong curvature of the
Bc2ab(
T) curve indicates the existence of strong spin paramagnetic effects.
View full abstract
-
Atsushi Miyake, Dai Aoki, Jacques Flouquet
2009 Volume 78 Issue 6 Pages
063703
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
Fine pressure (
P) and magnetic field (
H) tuning on the ferromagnetic superconductor URhGe are reported in order to clarify the interplay between the mass enhancement, low field superconductivity (SC) and field reentrant superconductivity (RSC) by electrical resistivity measurements. With increasing
P, the transition temperature and the upper critical field of the low field SC decrease slightly, while the RSC dome drastically shifts to higher fields and shrinks. The spin reorientation field
HR also increases. At a pressure
P∼1.8 GPa, the RSC has collapsed while the low field SC persists and may disappear only above 4 GPa. Via careful (
P,
H) studies of the inelastic
T2 resistivity term, it is demonstrated that this drastic change is directly related with the
P dependence of the effective mass which determines the critical field of the low field SC and RSC on the basis of triplet SC without Pauli limiting field.
View full abstract
-
Satoru Masaki, Hisashi Kotegawa, Yudai Hara, Hideki Tou, Keizo Murata, ...
2009 Volume 78 Issue 6 Pages
063704
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We report the precise pressure dependence of FeSe from a resistivity measurement up to 4.15 GPa. Superconducting transition temperature (
Tc) increases sensitively under pressure, but shows a plateau between 0.5–1.5 GPa. The maximum
Tc, which is determined by zero resistance, is 21 K at approximately 3.5 GPa. The onset value reaches ∼37 K at 4.15 GPa. We also measure the nuclear spin–lattice relaxation rate 1⁄
T1 under pressure using
77Se-NMR measurement. 1⁄
T1 shows that bulk superconductivity is realized in the zero-resistance state. The pressure dependence of 1⁄
T1T just above
Tc shows a plateau as well as the pressure dependence of
Tc, which gives clear evidence of the close relationship between 1⁄
T1T and
Tc. Spin fluctuations are suggested to contribute to the mechanism of superconductivity.
View full abstract
-
Kazumasa Horigane, Nao Takeshita, Chul-Ho Lee, Haruhiro Hiraka, Kazuyo ...
2009 Volume 78 Issue 6 Pages
063705
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
High-pressure resistivity experiments were performed on FeSe
0.5Te
0.5. The onset temperature of
Tc (
Tconset) increases rapidly from 13.5 to 26.2 K upon applying pressure up to 2 GPa. Above 2 GPa,
Tc decreases linearly and the metallic phase was observed at
P=14 GPa. The same relationship between normalized
Tc and pressure in both FeSe
0.5Te
0.5 and FeSe suggests a universal pressure dependence in this system. This report presents the first observation of a phase transition from the superconducting to the metallic phase on the
P–
Tc phase diagram.
View full abstract
-
Kentaro Kitagawa, Naoyuki Katayama, Kenya Ohgushi, Masashi Takigawa
2009 Volume 78 Issue 6 Pages
063706
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We report results of
75As nuclear magnetic resonance (NMR) experiments on a self-flux grown high-quality single crystal of SrFe
2As
2. The NMR spectra clearly show sharp first-order antiferromagnetic (AF) and structural transitions occurring simultaneously. The behavior in the vicinity of the transition is compared with our previous study on BaFe
2As
2. No significant difference was observed in the temperature dependence of the static quantities such as the AF splitting and electric quadrupole splitting. However, the results of the NMR relaxation rate revealed difference in the dynamical spin fluctuations. The stripe-type AF fluctuations in the paramagnetic state appear to be more anisotropic in BaFe
2As
2 than in SrFe
2As
2.
View full abstract
-
Kazumichi Ikedo, Yuki Wakisaka, Sizuka Hirata, Kou Takubo, Takashi Miz ...
2009 Volume 78 Issue 6 Pages
063707
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We report on a new type of orbital symmetry breaking in the CoO
2 triangular lattice with hole doped
t2g bands. Unrestricted Hartree–Fock calculations on a multi-orbital
d–
p Hamiltonian show that, in the lightly hole doped
t2g bands, the
e′
g orbitals are fully occupied with a circular charge distribution, and the doped holes in the
a1g band form a hole pocket sandwiched by two concentric Fermi surfaces with sixfold (and almost continuous) rotational symmetry. This symmetric state has an instability to an anisotropic state with twofold rotational symmetry, where the hole pocket is split into two pieces. This transition is governed by the anisotropic interaction between the
a1g and
e′
g orbitals.
View full abstract
-
Tomoaki Nogawa, Koji Nemoto
2009 Volume 78 Issue 6 Pages
064001
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We study the thermal diffusion dynamics of a single vortex in a two-dimensional XY model. By numerical simulations, we find an abnormal diffusion such that the mobility decreases with time
t as 1⁄ln
t. In addition, we construct a one-dimensional diffusion-like equation to model the dynamics and confirm that it conserves the quantitative property of the abnormal diffusion. By analyzing the reduced model, we find that the radius of the collectively moving region together with the vortex core increases as
R(
t)∝
t1⁄2. This suggests that the mobility of the vortex is described by the dynamical correlation length as 1⁄ln
R(
t).
View full abstract
-
Ken Takiyama, Yasushi Naruse, Masato Okada
2009 Volume 78 Issue 6 Pages
064002
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We propose a multi-hypercolumn model consisting of
M hypercolumns. Adjacent hypercolumns interact with each other through horizontal connections. This model consists of inter-hypercolumn and intra-hypercolumn Mexican-hat-type interactions. We analyze our model using statistical–mechanical methods. In this model, we theoretically show that the free energy is equivalent to the posterior distribution in the Bayesian framework in extremely weak inter-hypercolumn interactions. A numerical experiment supports this equivalence. The results of this study reveal the relationship between a
microscopic neural structure and a
macroscopic computational theory.
View full abstract
-
Ken Takiyama, Kentaro Katahira, Masato Okada
2009 Volume 78 Issue 6 Pages
064003
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We apply image restoration methods to estimate the firing rate of neurons that include discontinuity according to the input stimulus. Image restoration methods are effective in estimating firing rate because images and firing rates can be respectively modeled by two-dimensional and one-dimensional Markov random field (MRF) models. Our method uses the line process, which was developed to detect edges in images, and to estimate discontinuous firing rates and entirely-unknown stimulus timings. We construct the firing rate estimation algorithm for our model using belief propagation (BP). BP gives the exact inference in the firing rate estimation because there is no loop in the first-order MRF. BP simultaneously estimates the discontinuous firing rate, unknown stimulus timings, and calculates a marginal likelihood value that enables us to estimate the hyperparameter based on an empirical Bayes method. By applying our method to synthetic spike trains, whose firing rates include discontinuity, we show that our method can be used to estimate firing rates and stimulus timings.
View full abstract
-
Takasi Endo, Shin’ichi Osano, Kouichi Toyoshima, Yutaka Hirayosh ...
2009 Volume 78 Issue 6 Pages
064004
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
A continuous-time quantum walk in a one-dimensional discrete system is considered. There are interactions h
v⁄Δ
x between adjacent sites, where Δ
x denotes the lattice spacing. If the initial state is spread over
N sites, the packet travels ballistically with velocity
v for
N>>1.
View full abstract
-
Jun-Xiao Zhao, Gegenhasi, Xing-Biao Hu
2009 Volume 78 Issue 6 Pages
064005
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We generalize the idea of the Commutativity of pfaffianization and Bäcklund transformations to two differential-difference systems: the two-dimensional Toda lattice equation and the differential-difference KP equations. By means of which, Bäcklund transformation formulae for their coupled systems are presented respectively.
View full abstract
-
Kosuke Morita, Kouji Morimoto, Daiya Kaji, Hiromitsu Haba, Kazutaka Oz ...
2009 Volume 78 Issue 6 Pages
064201
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
Decay properties of an isotope
266Bh and its daughter nucleus
262Db produced by the
248Cm(
23Na,5
n) reaction were studied by using a gas-filled recoil separator coupled with a position-sensitive semiconductor detector.
266Bh was clearly identified from the correlation of the known nuclide,
262Db. The obtained decay properties of
266Bh and
262Db are consistent with those observed in the
278113 chain, which provided further confirmation of the discovery of
278113.
View full abstract
-
Fei-lu Wang, David Salzmann, Hideaki Takabe, Gang Zhao, Steve J. Rose
2009 Volume 78 Issue 6 Pages
064301
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
A computer code has been developed to provide a straightforward, rapid tool for the calculation of the ionization and population distributions in plasmas. To provide rapid response we employ screened hydrogenic model to calculate the energy levels and the rates of radiative processes. The code is designed to interpret photoionization experiments in either steady-state or time-dependent situations. Comparisons with experiments show that the present code provides relatively accurate ionization distributions in photoionized plasmas and show reasonable agreement with other codes.
View full abstract
-
Jie Ma, Lirong Wang, Yanting Zhao, Liantuan Xiao, Suotang Jia
2009 Volume 78 Issue 6 Pages
064302
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We report on the photoassociation of cold Cs atoms giving spectroscopy data of the 0
u+ long-range molecular state in the asymptotic range of [−6.2, −2.5 cm
−1] close to the 6S
1⁄2+6P
3⁄2 dissociation limit using photon counting technique. 24 new high-lying vibrational levels of the 0
u+ long-range state are identified to lead to the formation of excited molecules in the photoassociation process. Fitting experimental data to improved LeRoy–Bernstein formula, we obtain long-range molecular coefficient with a high precision.
View full abstract
-
Akiko Masaki, Sota Tsukada, Hiroyuki Mori
2009 Volume 78 Issue 6 Pages
064303
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We numerically studied internal structure of Mott insulating state of Bose–Fermi mixture systems on a one-dimensional optical lattice by using quantum Monte Carlo simulations. We looked for Mott state carefully adjusting various parameters to prevent phase separation. From the calculation of density–density correlation functions we found a quasi long-range order in the particle distribution in the Mott state. The order was strongly dependent of the ratio of the number of the bosons to that of the fermions. For example, the bosons and the fermions showed a tendency of aligning alternately when equal number of the bosons and fermions are introduced in the system. The observation of the quasi long-range order in the one-dimensional system indicates the presence of true long-range order in Bose–Fermi mixtures on a three-dimensional optical lattice.
View full abstract
-
Yoshinari Fukazawa, Mitsuaki Funakoshi
2009 Volume 78 Issue 6 Pages
064401
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
The effect of inclination of sidewalls on two-dimensional thermal convection of a fluid in a parallelogram-shaped cavity is investigated under the assumption that all walls are rigid, with perfect thermal conductance and with a vertically linear temperature profile connecting the temperatures on the horizontal top and bottom walls. The critical Rayleigh number
Rc, at which a motionless state becomes unstable, is calculated numerically for several values of inclination angle φ of sidewalls from the vertical direction and aspect ratio
A. As φ increases from 0, the increase in
Rc and the exchange of most unstable eigenmode are observed for all
A satisfying 0.3≤
A≤3. Moreover, we find numerically that two steady convection states bifurcating from the motionless state at
Rc become unstable at different Rayleigh numbers for non-zero φ. Furthermore, the stability of the motionless state in an inclined fluid layer of infinite length is examined along with its relevance to stability in a parallelogram-shaped cavity.
View full abstract
-
Eiichi Yagi, Motoyasu Yoshii, Yoshinori Okada, Hiroshi Matsuba, Kazuya ...
2009 Volume 78 Issue 6 Pages
064601
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
In order to clarify a difference in hydrogen interaction with oversized solute atoms and with undersized solute atoms in bcc metals in the low solute concentration region, the site occupancy of hydrogen in Nb alloyed with 5 at. % of oversized Ta atoms has been studied at room temperature for hydrogen concentrations of 0.018 and 0.025 at the hydrogen-to-metal-atom ratio (
CH=[H]⁄[M]) by the channelling method utilizing a nuclear reaction
1H(
11B,α)αα with a
11B beam of an energy of 2.03 MeV. Clearly different from the result on hydrogen in Nb alloyed with undersized Mo atoms, in both specimens H atoms are distributed over tetrahedral (
T) sites and the displaced-
T sites (
d-
T sites) which are displaced from
T sites by about 0.25 Å towards their nearest neighbour octahedral (
O) sites. The
T site is more favourable for hydrogen occupancy, but the number of available
T sites is limited, and excess H atoms occupy the
d-
T sites. Therefore, in contrast to a strong attractive interaction between hydrogen and undersized Mo atoms (trapping), there exists no such a strong attractive interaction between hydrogen and oversized Ta atoms. It is considered that the trapping of hydrogen by undersized solute atoms is effective to the large enhancement of the terminal solubility of hydrogen (TSH) on alloying with undersized solute atoms, at least, in the low solute concentration region.
View full abstract
-
Ai Yamakage, Yoshio Kuramoto
2009 Volume 78 Issue 6 Pages
064602
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
Temperature dependent phonon spectra are derived for an anharmonic lattice model using the self-consistent harmonic approximation. The lattice consists of cage and guest ions with anharmonic guest–cage interaction. By using a quasi-isotropic harmonic interaction that leads to polarization-independent dynamical matrix, renormalized phonon spectra are derived explicitly for the whole Brillouin zone and for all branches. The largest softening with decreasing temperature occurs in an Einstein-like mode corresponding to oscillation of guest ions. Cage oscillations also show slight softening since the cage–cage force is partly mediated via guest ions. In the high-temperature region, frequency of the Einstein mode is proportional to
T1⁄4 in agreement with the behavior derived previously for an impurity model. As temperature decreases below the Einstein frequency, the renormalized phonon frequency decreases through an inflection point, and finally tends to
T2 variation. The behavior compares favorably with recent neutron scattering results in PrOs
4Sb
12. The temperature dependence of the sound velocity is also calculated, which agrees qualitatively with that observed in Sr
8Ga
16Ge
30.
View full abstract
-
Mary Clare Sison Escaño, Hiroshi Nakanishi, Hideaki Kasai
2009 Volume 78 Issue 6 Pages
064603
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We investigated the energetics of O
2 reaction on a model bimetallic system, Pt bilayer on Fe(001), using six-dimensional potential-energy surface derived from spin-polarized density functional theory calculations. The model system renders same surface geometry and binding energy with the reference system, unresconstructed Pt(001), thus a systematic investigation on the role of Fe substrate was appropriately conducted. Results show that O
2 dissociation may proceed from a “no barrier” molecular adsorption on bridge with O–O axis lying parallel to the surface and spanning towards top sites (
t–
b–
t) to translation towards four-fold hollow site (
b–
h–
b) yielding dissociated O atoms on the bridge. In this reaction pathway, O
2 should overcome an activation barrier of ∼0.15 eV with respect to the initial state, which is comparable to that of the reference system (∼0.14 eV). However, the binding energy of O
2 with respect to its gas phase in all three states (initial, transition and final) is less as compared to that of Pt(001). The close relationship between adsorption energies and activation barriers with the spin polarization of Pt d-states near the Fermi-level induced by the ferromagnetic Fe substrate is discussed.
View full abstract
-
Yoshiteru Takagi
2009 Volume 78 Issue 6 Pages
064701
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We propose a method for constructing an AB bipartite lattice network class, termed a “hypergraphene network”. Edge states are defined as evanescent wave solutions with a dumping factor for the hypergraphene network. Bulk electronic states of some hypergraphene networks based on the single tight binding model are similar to the π-electronic states of graphene, i.e., they display a linear dispersion relation, a massless Dirac spectrum, and zerogap semiconductor behavior. Our approach suggests a new method to design possible network structures having the character of graphene in not only two-dimensions, but also in systems with three- or more dimensions.
View full abstract
-
Yohei Nagao, Jun-ichi Yamaura, Hiroki Ogusu, Yoshihiko Okamoto, Zenji ...
2009 Volume 78 Issue 6 Pages
064702
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
The superconducting properties of two β-pyrochlore oxides, CsOs
2O
6 and RbOs
2O
6, are studied by thermodynamic and transport measurements using high-quality single crystals. It is shown that the character of superconductivity changes systematically from weak coupling for CsOs
2O
6 to moderately strong coupling for RbOs
2O
6, and finally to extremely strong coupling with BCS-type superconductivity for KOs
2O
6, with increasing
Tc. Strong-coupling correction analyses of the superconducting properties reveal that a low-energy rattling mode of the alkali metal ions is responsible for the mechanism of the superconductivity in each compound. The large enhancement of
Tc from Cs to K is attributed to the increase in the electron–rattler coupling with decreasing characteristic energy of the rattling and with increasing anharmonicity. The existence of weak anisotropy in the superconducting gap or in the electron–rattler interactions is found for the Cs and Rb compounds.
View full abstract
-
Shunichiro Kittaka, Taketomo Nakamura, Hiroshi Yaguchi, Shingo Yonezaw ...
2009 Volume 78 Issue 6 Pages
064703
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We have clarified how the enhanced superconductivity, often referred to as the 3-K phase superconductivity, develops in the Sr
2RuO
4–Ru eutectic system. From the detailed ac and dc susceptibility measurements on well-characterized crystals, we revealed strongly anisotropic shielding, governed by the direction of the screening current dominated within the RuO
2 plane rather than by the orientation of the Ru lamellae. The onset temperature of the 3-K phase superconductivity probed by diamagnetic screening is as high as 3.5 K. The temperature dependence of the diamagnetic shielding above around 2 K is well ascribed by the interfacial screening around each Ru lamella. Below around 2 K, the rapid development of the shielding fraction as well as its peculiar response to ac and dc magnetic fields are explained by the formation of the Josephson network consisting of inter-lamellar supercurrents.
View full abstract
-
Yositake Takane
2009 Volume 78 Issue 6 Pages
064704
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We study charge imbalance transport in a superconducting wire with focus on the influence of spatial variation of pair potential amplitude Δ. Assuming that a superconducting wire is coupled to two normal-metal electrodes via tunnel junctions, we consider the case in which charge imbalance is created at one junction and the resulting excess tunneling current
Iex is measured at the other junction. If Δ is locally suppressed in a short region between the two junctions, charge imbalance is relaxed by Andreev scattering induced by spatial variation of Δ, resulting in a reduction of
Iex. To observe this influence, we numerically calculate
Iex by employing a Boltzmann equation approach. It is shown that even a small suppression of Δ strongly reduces
Iex. This indicates that induced Andreev scattering significantly contributes to charge imbalance conversion.
View full abstract
-
Sunao Shimizu, Hidekazu Mukuda, Yoshio Kitaoka, Hijiri Kito, Yasuharu ...
2009 Volume 78 Issue 6 Pages
064705
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We report on the magnetic characteristics of four-layered high-
Tc superconductors Ba
2Ca
3Cu
4O
8(F
yO
1−y)
2 with apical fluorine through
63Cu- and
19F-NMR measurements. The substitution of oxygen for fluorine at the apical site increases carrier density (
Nh) and
Tc from 55 up to 102 K. The NMR measurements reveal that antiferromagnetic order, which can uniformly coexist with superconductivity, exists up to
Nh\\simeq0.15, which is somewhat smaller than
Nh\\simeq0.17, the quantum critical point (QCP) for five-layered compounds. The fact that the QCP for the four-layered compounds moves to a region of lower carrier density than for five-layered ones ensures that a decrease in the number of CuO
2 layers makes an interlayer magnetic coupling weaker.
View full abstract
-
Shun Fukushima, Tomonori Sato, Daisuke Akahoshi, Hideki Kuwahara
2009 Volume 78 Issue 6 Pages
064706
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We have synthesized
A-site ordered (
AO)- and
A-site disordered (
AD)-Y
1⁄4Sr
3⁄4CoO
3−δ (YSCO) with various oxygen deficiencies δ, and have made a comparative study of the structural and physical properties. We have found that
A-site (Y/Sr) ordering produces the unconventional oxygen-vacancy ordered (OO) structure, and that the magnetic and transport properties of YSCO strongly depend on the
A-site ordering and/or the oxygen-vacancy (or excess oxygen) ordering patterns.
AO-YSCO with a stoichiometric δ of 0.5 has an unconventional OO structure reflecting Y/Sr ordering pattern. With decreasing δ from 0.5, the overall averaged OO structure is essentially unchanged except for an increase of occupancy ratio for the oxygen-vacant sites. At δ=0.34, excess oxygen atoms are ordered to form a novel superstructure, which is significant for the room-temperature ferromagnetism of
AO-YSCO. In
AD-YSCO, on the other hand, the quite different OO structure, which is of a brownmillerite-type, is found only in the vicinity of δ=0.5.
View full abstract
-
Yoshiki Imai, Tetsuro Saso
2009 Volume 78 Issue 6 Pages
064707
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
Based on the recently proposed band model, the electronic specific heat of moderately heavy electron compound YbAl
3 are investigated. The band term of the Hamiltonian consists of three parts; conduction electrons described by the nearly free electron method, localized 4f electrons of Yb ions and the hybridization term between these electrons. Extracting several bands near the Fermi level, we reconstruct the low-energy effective Hamiltonian in order to consider the correlation effect, which is studied by using the self-consistent second order perturbation theory combined with local approximation. The temperature dependence of the specific heat
cv(
T) is calculated as a function of temperature
T from the numerical derivative of the internal energy. Sommerfeld coefficient γ is also calculated from the direct formula. The overall structure of
cv(
T)⁄
T is in quantitative agreement with the experimental results, which have the characteristic two-peak structures. They originate from the correlation effect and the structure of the non-interacting density of states, respectively. We show that our effective Hamiltonian yielding the realistic band structure may describe quantitatively heavy electron compounds with conduction bands composed of s- or p-electrons.
View full abstract
-
Yoshihiro Shimazu, Yuuki Saito, Zenpei Wada
2009 Volume 78 Issue 6 Pages
064708
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
A double-loop four-Josephson-junction (4-JJ) flux qubit has an advantage over a three-Josephson-junction flux qubit in that the energy gap Δ at the symmetry point can be controlled
in situ by varying the magnetic flux in one of the two loops. We report the results of a microwave spectroscopy measurement of a 4-JJ qubit. The magnetic fluxes in the two loops were controlled via a magnetic field and control flux. The excitation energy spectra at various values of control flux indicate the tunability of Δ via the control flux. Two branches of the excitation spectra were observed.
View full abstract
-
So Kitsunezaki
2009 Volume 78 Issue 6 Pages
064801
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
We investigated crack propagation in the drying process of a thin layer of calcium carbonate (CaCO
3) paste experimentally. Cracks are induced by uniform desiccation from the top surface of a layer at the approximately same water content for various drying conditions. We found that the crack speed is a nonlinear increasing function of the drying rate at the cracking time although the tensile stresses arising in the bulk of paste do not depend practically on the drying rate. The crack speed does not depend significantly on the layer thickness and decreases in the cases in which glycerol is mixed to increase the viscosity of paste. These results suggest that dynamical crack growth occurs with viscoplastic relaxation in the vicinity of crack tips.
View full abstract
-
Syuma Yasuzuka, Yasuhisa Yamamura, Wakako Kaneko, Masaaki Ohba, Susumu ...
2009 Volume 78 Issue 6 Pages
065001
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
-
Nao Takeshita, Kiichi Miyazawa, Akira Iyo, Hijiri Kito, Hiroshi Eisaki
2009 Volume 78 Issue 6 Pages
065002
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
-
Shuhei Nakakura, Yuki Nagai, Daijiro Yoshioka
2009 Volume 78 Issue 6 Pages
065003
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
-
Hiroo Totsuji
2009 Volume 78 Issue 6 Pages
065004
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS
-
Takaharu Mori, Hironori Kokubo, Hirofumi Shimizu, Masayuki Iwamoto, Sh ...
2009 Volume 78 Issue 6 Pages
068001
Published: June 15, 2009
Released on J-STAGE: December 28, 2011
JOURNAL
RESTRICTED ACCESS