arXiv subjects

Keita Kishigi

Publications and source records attributed to Keita Kishigi.

25 records · Page 2Linked to original sources

arXiv2000

Two Kinds of the Coexistent States in One-Dimensional Quarter -Filled Systems under Magnetic Fields

The coexistent state of the spin density wave (SDW) and the charge density wave (CDW) in the one-dimensional quarter-filled system and with the Coulomb interaction up to the next-nearest sites under magnetic fields is studied. It is found that, in the coexistent state of $2k_{\rm F}$-SDW and $2k_{\rm F}$-CDW, the charge order is suppressed and $2k_{\rm F}$-SDW changes to $2k_{\rm F}$-SDW having the different alignment of spin under high magnetic fields, whereas, in the coexistent state of $2k_{\rm F}$-SDW and $4k_{\rm F}$-CDW, $4k_{\rm F}$-CDW still remains and $2k_{\rm F}$-SDW is suppressed. The critical temperature of the charge order is higher than that of the spin order when the inter-site Coulomb interaction is strong. These will be observed in experiments such as the X-ray scattering measurement and NMR.

cond-mat.mes-hall↗

arXiv2000

Coexistent State of Charge Density Wave and Spin Density Wave in One-Dimensional Quarter Filled Band Systems under Magnetic Fields

We theoretically study how the coexistent state of the charge density wave and the spin density wave in the one-dimensional quarter filled band is enhanced by magnetic fields. We found that when the correlation between electrons is strong the spin density wave state is suppressed under high magnetic fields, whereas the charge density wave state still remains. This will be observed in experiments such as the X-ray measurement.

cond-mat.mes-hall↗

arXiv1999

Spin Splitting in de Haas-van Alp-hen Oscillation in Two-Dimensional Two-Band Systems

We study the effects of the Zeeman term on the de Haas van Alphen (dHvA) oscillation in two-dimensional two-band systems. We found that the Fourier transform amplitudes of the oscillations are not described by the spin reduction factor in the Lifshitz-Kosevich formalism in two-dimensional systems. The anomalous dependence on the effective $g$-factor can be observed by tilting-angle dependence of the dHvA oscillation in quasi-two-dimensional organic conductors and Sr$_2$RuO$_4$.

cond-mat.mes-hall↗

arXiv1999

Possible Spin-Singlet Superconductivity in (TMTSF)2X: Superconducting Transition Temperature in a Magnetic Field

We study the transition temperature Tc(H) of a quasi-one-dimensional (Q1D) superconductivity which is derived from the quantum effect of an electron motion in a strong magnetic field. We calculate Tc(H) of both isotropic and anisotropic superconductivity by taking account of the optimal momentum of the Cooper pairs and the effect of higher harmonic terms along second conducting axis in the tight-binding model. We find that, although Tc(H) of the spin-singlet superconductivity is suppressed strongly by the Zeeman effect, the suppression of Tc(H) is not very severe if we take the optimal pair-momentum and the higher harmonic terms into account. The obtained Tc(H) for the spin-singlet superconductivity is consistent with the experimental results in TMTSF salts.

cond-mat.supr-con↗

arXiv1999

Enhancement of de Haas-van Alphen Oscillation due to Spin in the Magnetic Breakdown System

The effects of the Zeeman term on the de Haas-van Alphen oscillation is studied in the magnetic breakdown system. We find that the amplitude of the oscillation with the frequencies of $f_β + f_α$ and $f_β + 2f_α$ are enhanced by the Zeeman term, while they are expected to be reduced in the semiclassical theory. A possible interpretation of the experiments in organic conductors is discussed.

cond-mat↗

arXiv1999

Superconductivity of Quasi-Two-Dimensional Tight-Binding Electrons in a Strong Magnetic Field

We have investigated the transition temperature $T_{\rm c}(H)$ of superconductiv ity in quasi-two-dimensional (Q2D) tight-binding electrons in a strong magnetic field. When the magnetic field is parallel to 2D conducting plane, $T_{\rm c}(H) $ of the Q2D superconductor is shown to increase in an oscillatory manner as the magnetic field becomes large and to reach $T_{\rm c}(0)$ in a strong magnetic f ield limit for the spin-triplet superconductor. We consider the cases of on-site and nearest sites attractive interaction, and calculate the magnetic field depe ndences of the transition temperature for various types of symmetry. The first o rder transition from $p_y$-wave to $p_x$-wave is shown to occur at $H\sim 35$T w hen the magnetic field is parallel to the $y$ direction, which will be observed in a triplet superconductor, Sr$_2$RuO$_4$.

cond-mat.supr-con↗

arXiv1998

Superconductivity of Quasi-One and Quasi-Two Dimensional Tight-Binding Electrons in Magnetic Field

The upper critical field $H_{c2}(T)$ of the tight-binding electrons in the three-dimensional lattice is investigated. The electrons make Cooper pairs between the eigenstates with the same energy in the strong magnetic field. The transition lines in the quasi-one dimensional case are shown to deviate from the previously obtained results where the hopping matrix elements along the magnetic field are neglected. In the absence of the Pauli pair breaking the transition temperature $T_c(H)$ of the quasi-two dimensional electrons is obtained to oscillationally increase as the magnetic field becomes large and reaches to $T_c(0)$ in the strong field as in the quasi-one dimensional case.

cond-mat.supr-con↗