arXiv subjects

Masatoshi Sato

Publications and source records attributed to Masatoshi Sato.

At least 199 records · Page 11Linked to original sources

arXiv2003

Spin-Glass-like Transition and Hall Resistivity of Y2-xBixIr2O7

Various physical properties of the pyrochlore oxide Y2-xBixIr2O7 have been studied. The magnetizations M measured under the conditions of the zero-field-cooling(ZFC) and the field-cooling(FC) have different values below the temperature T=TG. The anomalous T-dependence of the electrical resistivities r and the thermoelectric powers S observed at around TG indicates that the behavior of the magnetization is due to the transition to the state with the spin freezing. In this spin-frozen state, the Hall resistivities rH measured with the ZFC and FC conditions are found to have different values, too, in the low temperature phase (T<TG). Possible mechanisms which induce such the hysteretic behavior are discussed.

cond-mat.str-el↗

arXiv2003

Anomalous Hall Effect and Magnetoresistance of SrFe1-xCoxO3-d

Transport and magnetic studies on polycrystalline samples of SrFe1-xCoxO3-d have been carried out to investigate the relationship between the magnetic structure and the anomalous Hall resistivity rH. The hysteretic behavior of the magnetization observed in the measurements with varying temperature T up and then down after zero field cooling indicates that the system has the reentrant spin-glass phase, which is supported by the increasing width of the magnetic reflections observed by neutron diffraction with decreasing T below the Curie temperature TC. Detailed analyses of the observed Hall resistivity rH indicate that the anomalous Hall coefficient exhibits unusual behavior in the reentrant spin-glass phase. The magnetic field (H)- and T-dependence of the magnetoresistance of the present system can be understood by a spin dependent tunneling model.

cond-mat.str-el↗

arXiv2003

Transport and Magnetic Properties of R1-xAxCoO3 (R=La, Pr and Nd; A=Ba, Sr and Ca)

Transport and magnetic measurements have been carried out on perovskite Co-oxides R1-xAxCoO3 (R=La, Pr, and Nd; A=Ba, Sr and Ca; 0<x<0.5: All sets of the R and A species except Nd1-xBaxCoO3 have been studied.). With increasing the Sr- or Ba-concentration x, the system becomes metallic ferromagnet with rather large magnetic moments. For R=Pr and Nd and A=Ca, the system approaches the metal- insulator phase boundary but does not become metallic. The magnetic moments of the Ca-doped systems measured with the magnetic field H=0.1 T are much smaller than those of the Ba- and Sr-doped systems. The thermoelectric powers of the Ba- and Sr-doped systems decrease from large positive values of lightly doped samples to negative ones with increasing doping level, while those of Ca-doped systems remain positive. These results can be understood by considering the relationship between the average ionic radius of R1-xAx and the energy difference between the low spin and intermediate spin states. We have found the resistivity-anomaly in the measurements of Pr1-xCaxCoO3 under pressure in the wide region of x, which indicates the existence of a phase transition different from the one reported in the very restricted region of x~0.5 at ambient pressure [Tsubouchi et al. Phys. Rev. B 66 (2002) 052418.]. No indication of this kind of transition has been observed in other species of R.

cond-mat.str-el↗

arXiv2003

Effects of "Stripes" on the Magnetic Excitation Spectra of La1.48Nd0.4Sr0.12CuO4

The wave vector(q)- and energy(w)-dependent magnetic excitation spectra c"(q,w), have been studied in the temperature(T) range of 10 K<T<150 K on single crystals of La1.48Nd0.4Sr0.12CuO4, which has the static "stripe" order in the low temperature phase. The incommensurability d of the peak of c"(q,w) found by the q-scans and the peak width Dq exhibit characteristic T-dependences. Observed profiles show clear incommensurate structure even at rather high temperatures. The results indicate that effects of the slowly fluctuating "stripes" exist not only in the low temperature tetragonal (LTT) phase but also in the orthorhombic phase(LTO1) of the present system. The persistence of the local structural characteristics of the low-T phase seems to be important.

cond-mat.supr-con↗

arXiv2002

Anomalous Hall Effect of Reentrant Spin Glass System Fe1-xAlx (x ~ 0.3)

The anomalous Hall coefficient Rs has been studied for the reentrant spin glass system Fe0.7Al0.3 by measuring the magnetization M and the Hall resistivity r_H. We have found that R_s exhibits anomalous temperature dependence at the spin-glass transition temperature T_G, indicating that an additional term appears along with the beginning of the spin glass phase. The result is discussed in relation to the recent proposal of the chirality mechanism of the Hall effect in the spin glass phase.

cond-mat.str-el↗

arXiv2002

Neutron Scattering Studies of Pyrochlore Compound Nd2Mo2O7 in Magnetic Field

Neutron diffraction studies have been carried out in the applied magnetic field H(//[011]) on a single crystal of pyrochlore ferromagnet Nd2Mo2O7, whose Hall resistivity(r_H) has been reported to have quite unusual magnetic field (H)- and temperature (T)- dependences. The intensities of the observed magnetic reflections have been reproduced at 1.6 K as a function of H, by considering the change of the magnetic structure with H, where effects of the exchange fields at the Mo and Nd sites induced by the Mo-Mo and Mo-Nd exchange interactions and the single ion anisotropies of Mo- and Nd- moments are considered. From the H-dependent magnetic structure, the H-dependence of r_H has been calculated by using the chiral order mechanism. By comparing the result with the H-dependence of the observed r_H, it is found that the chiral order mechanism does not work well in the present system.

cond-mat.str-el↗

arXiv2002

Nonperturbative Aspects in N-fold Supersymmetry

Through a nonperturbative analysis on a sextic triple-well potential, we reveal novel aspects of the dynamical property of the system in connection with N-fold supersymmetry and quasi-solvability.

hep-th↗

arXiv2002

N-fold Supersymmetry in Quantum Mechanics - Analyses of Particular Models -

We investigate particular models which can be N-fold supersymmetric at specific values of a parameter in the Hamiltonians. The models to be investigated are a periodic potential and a parity-symmetric sextic triple-well potential. Through the quantitative analyses on the non-perturbative contributions to the spectra by the use of the valley method, we show how the characteristic features of N-fold supersymmetry which have been previously reported by the authors can be observed. We also clarify the difference between quasi-exactly solvable and quasi-perturbatively solvable case in view of the dynamical property, that is, dynamical N-fold supersymmetry breaking.

hep-th↗

arXiv2002

Detailed Structure of the Magnetic Excitation Spectra of YBa2Cu3Oy and Its Implication on the Physical Characteristics of the Electron System

Detailed structure of the magnetic excitation spectra x"(q,w) of the superconducting oxide YBa2Cu3O6.5(the transition temperature Tc ~ 52 K) in the wave vector (q)- and the energy(w)-space, and its temperature (T) dependence have been studied. By adopting an effective energy dispersion of the quasi particles which can reproduce the shape of the Fermi surface and by introducing the exchange interaction between the Cu spins, a rather satisfactory agreement between the calculation and the experimentally observed data can be obtained. In the study, it has been found that the effects of the quasi particle- energy broadening on the excitation spectra x"(q,w) is important. The sharp resonance peak observed at w ~ 40 meV for the optimally doped system of YBa2Cu3Oy can be naturally reproduced by the present model

cond-mat.str-el↗

arXiv2002

Neutron Scattering Study of the Spin Correlation in the Spin Ice System Ho2Ti2O7

Intensity distribution of the neutron magnetic scattering has been taken in the reciprocal space of a single crystal of the "spin ice" system Ho2Ti2O7 at the elastic energy position in the temperature (T) region between 0.4 K and 50 K. The short range magnetic correlation becomes appreciable with decreasing T at around 30 K. The freezing of the moment system takes place at around 1.5 K with decreasing T. Based on the mean field treatment of the moment system, the distribution of the observed intensity has been reproduced, where the dipolar interaction is confirmed to be primarily important for the determination of the magnetic correlation. Simple calculations of the scattering intensity carried out by using a cluster of 25 moments of Ho3+ ions indicate that there are many types of the moment arrangement within a cluster which have almost degenerated energies, indicating that the system cannot uniquely select the correlation pattern down to rather low temperature, and before going to the lowest energy state, the system undergoes the gradual slowing down to the glassy state.

cond-mat.str-el↗

arXiv2002

Transport and NQR Studies of Nd1.6-xCexSr0.4CuO4 with T* Structure

Transport and Cu-NQR studies have been carried out for the T*-type high temperature superconducting Cu oxide Nd1.6-xCexSr0.4CuO4 with single layered CuO2 planes formed by CuO5 pyramids. No anomaly related to the static or quasi static "stripe" order has been observed in the temperature T and x dependence of the thermoelectric powers S. We have not found such kind of anomaly in the x dependence of the superconducting transition temperature Tc, either. Although the decrease of the Cu NQR intensity with decreasing T (wipeout) has been observed in this system, it can be understood by considering the loss of the itinerant nature of the electrons, which takes place in the proximity region of the metal-insulator phase boundary, and cannot be connected with the static or quasi static "stripe" order.

cond-mat.supr-con↗

arXiv2002

Static Correlation and Dynamical Properties of Tb3+-moments in Tb2Ti2O7 -Neutron Scattering Study-

Static and dynamical properties of the magnetic moment system of pyrochlore compound Tb2Ti2O7 with strong magnetic frustration, have been investigated down to the temperature T=0.4 K by neutron scattering on a single crystal sample. The scattering vector (Q)-dependence of the magnetic scattering intensity becomes appreciable with decreasing T at around 30 K, indicating the development of the magnetic correlation. From the observed energy profiles, the elastic, quasi elastic and inelastic components have been separately obtained. The quasi elastic component corresponds to the diffusive motion of the magnetic moments within the lowest states, which are formed of the lowest energy levels of Tb3+ ions. Magnetic correlation pattern which can roughly reproduce the Q-dependence of the scattering intensities of the elastic and quasi elastic component is discussed based on the trial calculations for clusters of 7 moments belonging to two corner-sharing tetrahedra. A possible origin of the glassy state, which develops at around 1.5 K with decreasing T is discussed.

cond-mat.str-el↗

arXiv2001

Classification of Type A N-fold supersymmetry

Type A N-fold supersymmetry of one-dimensional quantum mechanics can be constructed by using sl(2) generators represented on a finite dimensional functional space. Using this sl(2) formalism we show a general method of constructing Type A N-fold supersymmetric models. We also present systematic generation of known models and several new models using this method.

hep-th↗

arXiv2001

N-fold Supersymmetry in Quantum Mechanics - General Formalism -

We report general properties of N-fold supersymmetry in one-dimensional quantum mechanics. N-fold supersymmetry is characterized by supercharges which are N-th polynomials of momentum. Relations between the anti-commutator of the supercharges and the Hamiltonian, the spectra, the Witten index, the non-renormalization theorems and the quasi-solvability are examined. We also present further investigation about a particular class of N-fold supersymmetric models which we dubbed type A. Algebraic equations which determine a part of spectra of type A models are presented, and the non-renormalization theorem are generalized. Finally, we present a possible generalization of N-fold supersymmetry in multi-dimensional quantum mechanics.

quant-ph↗

arXiv2001

sl(2) Construction of Type A N-fold supersymmetry

N-fold supersymmetry is an extension of the ordinary supersymmetry in one-dimensional quantum mechanics. One of its major property is quasi-solvability, which means that energy eigenvalues can be obtained for a portion of the spectra. We show that recently found Type A N-fold supersymmetry can be constructed by using sl(2) algebra, which provides a basis for the quasi-solvability. By this construction we find a condition for the Type A N-fold supersymmetry, which is less restrictive than the condition known previously. Several explicitly known models are also examined in the light of this construction.

hep-th↗

arXiv2001

General Forms of a N-fold Supersymmetric Family

We report general forms of one family of the N-fold supersymmetry in one-dimensional quantum mechanics. The N-fold supersymmetry is characterized by the supercharges which are N-th order in differential operators. The family reported here is defined as a particular form of the supercharges and is referred to as ``type A''. We show that a quartic and a periodic potentials, which were previously found to be N-fold supersymmetric by the authors, are realized as special cases of this type A family.

quant-ph↗

arXiv2000

N-fold Supersymmetry for a Periodic Potential

We report a new type of supersymmetry, "N-fold supersymmetry", in one-dimensional quantum mechanics. Its supercharges are N-th order polynomials of momentum: It reduces to ordinary supersymmetry for N=1, but for other values of N the anticommutator of the supercharges is not the ordinary Hamiltonian, but is a polynomial of the Hamiltonian. (For this reason, the original Hamiltonian is referred to as the "Mother Hamiltonian".) This supersymmetry shares some features with the ordinary variety, the most notable of which is the non-renormalization theorem. An N-fold supersymmetry was earlier found for a quartic potential whose supersymmetry is spontaneously broken. Here we report that it also holds for a periodic potential, albeit with somewhat different supercharges, whose supersymmetry is not broken.

quant-ph↗

arXiv2000

Unconventional odd-parity superconductivity in the ladder compounds

Superconductive properties of the two-leg ladder compounds are studied theoretically. The antiferromagnetic fluctuations are considered because of the good nesting of the Fermi surfaces. The attractive interaction which is most likely due to the electron-phonon coupling is also taken into account. Under this circumstance, it is shown that the superconductivity has two sets of spin-triplet pairings. The gaps for both pairings have no node.

cond-mat.supr-con↗