arXiv subjects

Kazuhiro Sano

Publications and source records attributed to Kazuhiro Sano.

24 records · Page 2Linked to original sources

arXiv1998

Magnetic Susceptibility for $CaV_4O_9$

We examine experimental magnetic susceptibility $χ^{tot}(T)$ for CaV$_4$O$_9$ by fitting with fitting function $αχ^{mag}(T) + c$. The function $χ^{mag}(T)$ is a power series of 1/T and the lowest order term is fixed as $C/T$, where $C$ is the Curie constant as determined by the experimental $g$-value (g=1.96). Fitting parameters are $α$, $c$ and expansion coefficients except for the first one in $χ^{mag}(T)$. We determine $α$ and $c$ as $α\simeq$ 0.73 and $c\simeq$ 0 for an experimental sample. We interpret $α$ as the volume fraction of CaV$_4$O$_9$ in the sample and $χ^{mag}(T)$ as the susceptibility for the pure CaV$_4$O$_9$. The result of $α\ne 1$ means that the sample includes nonmagnetic components. This interpretation consists with the result of a perturbation theory and a neutron scattering experiment.

cond-mat↗

arXiv1997

Superconductivity of the One-Dimensional d-p Model with p-p transfer

Using the numerical diagonalization method, we investigate the one-dimensional $d$-$p$ model, simulating a Cu-O linear chain with strong Coulomb repulsions. Paying attention to the effect of the transfer energy $t_{pp}$ between the nearest neighbor oxygen-sites, we calculate the critical exponent of correlation functions $K_ρ$ based on the Luttinger liquid relations and the ground state energy $E_0(ϕ)$ as a function of an external flux $ϕ$. We find that the transfer $t_{pp}$ increases the charge susceptibility and the exponent $K_ρ$ in cooperation with the repulsion $U_{d}$ at Cu-site. We also show that anomalous flux quantization occurs for $K_ρ>1$. The superconducting region is presented on a phase diagram of $U_{d}$ vs. $t_{pp}$ plane.

cond-mat.supr-con↗

arXiv1997

Determination of Exchange Parameters from Magnetic Susceptibility

We report a novel practical method to determine exchange parameters by using experimental susceptibility data in a relatively narrow temperature region and a low order high-temperature-expansion equation. This method is applied to a square lattice and a CaV_4O_9-type lattice, and its accuracy is discussed.

cond-mat.str-el↗

arXiv1996

A possible phase diagram of a t-J ladder model

We investigate a t-J ladder model by numerical diagonalization method. By calculating correlation functions and assuming the Luttinger liquid relation, we obtained a possible phase diagram of the ground state as a function of J/t and electron density $n$. We also found that behavior of correlation functions seems to consist with the prediction of Luttinger liquid relation. The result suggests that the superconducting phase appear in the region of $J/t \displaystyle{ \mathop{>}_{\sim}} 0.5$ for high electron density and $J/t \displaystyle{ \mathop{>}_{\sim}} 2.0$ for low electron density.

cond-mat↗

arXiv1995

Spin Gap of Two-Dimensional Antiferromagnet Representing CaV$_4$O$_9$

We examined a two-dimensional Heisenberg model with two kinds of exchange energies, $J_e$ and $J_c$. This model describes localized spins at vanadium ions in a layer of CaV$_4$O$_9$, for which a spin gap is found by a recent experiment. Comparing the high temperature expansion of the magnetic susceptibility to experimental data, we determined the exchange energies as $J_e \simeq$ 610 K and $J_c \simeq$ 150 K. By the numerical diagonalization we estimated the spin gap as $Δ\sim 0.2J_e \simeq$ 120 K, which consists with the experimental value 107 K. Frustration by finite $J_c$ enhances the spin gap.

cond-mat↗

arXiv1994

Phase diagrams of electronic state on One Dimensional d-p Model

We investigate the one-dimensional(1D) d-p model, simulating a Cu-O linear chain with strong Coulomb repulsion, by using the numerical diagonalization method. Using the Luttinger liquid theory, we obtained phase diagrams of the ground state on $U_d-U_{pd}$ plane, where $U_d$ and $U_{pd}$ represent on-site interaction at d-sites and the nearest-neighbor interaction between p- and d-sites respectively. In the weak coupling region, they agree with the g-ology; a superconducting phase (SC(I)) is restricted to attractive interaction $U_{pd}<0$. On the other hand, in the strong coupling region, we found a novel superconducting phase(SC(II)) for repulsive interaction $U_{pd}>|U_d|$ and a insulating state with a charge gap for $U_d>U_d^c$ and $U_{pd}>U_{pd}^c$ with critical values $U_d^c$ and $U_{pd}^c$ at half-filling. Away from half-filling, another superconducting phase (SC(III)) appears for $U_d>>U_{pd}>0$; which has been found for $U_d\to \infty$ in the previous paper [Physica {\bf C205} (1993) 170]. An analysis of the spin gap suggests that the SC(I) and SC(II) include the Luther-Emery region (with spin-gap) in part, while the SC(III) belongs to Tomonaga-Luttinger region (without spin-gap) in whole.

cond-mat↗