Numerical Study of Two-fluid Flowing Equilibria of Helicity-driven Spherical Torus Plasmas

Two-fluid flowing equilibrium configurations of a helicity-driven spherical torus (HD-ST) are numerically determined by using the combination of the finite difference and the boundary element methods. It is found from the numerical results that electron fluids near the central conductor are tied to an external toroidal field and ion fluids are not. The magnetic configurations change from the high-$q$ HD-ST ($q$>1) with paramagnetic toroidal field and low-$\beta$ (volume average $\beta$ value, ($\approx$ 2 %) through the helicity-driven spheromak and RFP to the ultra low-$q$ HD-ST (0<q<1) with diagmagnetic toroidal field and high-$\beta$ ($\beta\approx 18\%) as the external toroidal field at the inner edge region decreases and reverses the sign. The two-fluid effecs are more significant in this equilibrium transition when the ion diagmagnetic drift is dominant in the flowing two-fluid.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Fermi Surface Study of Quasi-Two-Dimensional Organic Conductors by Magnetooptical Measurements

Magnetooptical measurements of several quasi-two-dimensional (q2D) organic conductors, which have simple Fermi surface structure, have been performed by using a cavity perturbation technique. Despite of the simple Fermi surface structure, magnetooptical resonance results show a dramatic difference for each sample. Cyclotron resonances (CR) were observed for q-(BEDT-TTF)2I3 and (BEDT-TTF)3Br(pBIB), while periodic orbit resonances (POR) were observed for (BEDT-TTF)2Br(DIA) and (BEDT-TTF)3Cl(DFBIB). The selection of the resonance seems to correspond with the skin depth for each sample. The effective mass of POR seems to have a mass enhancement due to the many-body effect, while effective mass of CR is independent of the strength of the electron-electron interaction. The scattering time deduced from each resonance's linewidth will be also presented.Comment: 10 pages, 8 figures, to be published to J. Phys. Soc. Jpn Vol.72 No.1 (accepted

Theory of Thermoelectric Power in High-Tc Superconductors

We present a microscopic theory for the thermoelectric power (TEP) in high-Tc cuprates. Based on the general expression for the TEP, we perform the calculation of the TEP for a square lattice Hubbard model including all the vertex corrections necessary to satisfy the conservation laws. In the present study, characteristic anomalous temperature and doping dependences of the TEP in high-Tc cuprates, which have been a long-standing problem of high-Tc cuprates, are well reproduced for both hole- and electron-doped systems, except for the heavily under-doped case. According to the present analysis, the strong momentum and energy dependences of the self-energy due to the strong antiferromagnetic fluctuations play an essential role in reproducing experimental anomalies of the TEP.Comment: 5 pages, 8 figures, to appear in J. Phys. Soc. Jpn. 70 (2001) No.10. Figure 2 has been revise

Evolution of Hall coefficient in two-dimensional heavy fermion CeCoIn5_5

We report on the pressure dependence of the Hall coefficient $R_H$ in quasi-2D heavy fermion CeCoIn$_5$. At ambient pressure, below a temperature associated with the emergence of non-Fermi liquid properties, $R_H$ is anomalously enhanced. We found that the restoration of the Fermi liquid state with applied pressure leads to a gradual suppression of this dramatic enhancement. Moreover, the enhancement in $R_H$ was found to be confined to an intermediate temperature window, where inelastic electron-electron scattering is dominant. Our results strongly support the presence of cold and hot spots on the Fermi surface probably due to anisotropic scattering by antiferromagnetic fluctuations, which may also prove relevant for the debate on the anomalous normal-state properties of high-$T_c$ cuprates.Comment: 9 pages, 5 fiqures, to be published in J. Phys. Soc. Jp

Electrical Conductivity of Fermi Liquids. I. Many-body Effect on the Drude Weight

On the basis of the Fermi liquid theory, we investigate the many-body effect on the Drude weight. In a lattice system, the Drude weight $D$ is modified by electron-electron interaction due to Umklapp processes, while it is not renormalized in a Galilean invariant system. This is explained by showing that the effective mass $m'$ for $D\propto n/m'$ is defined through the current, not velocity, of quasiparticle. It is shown that the inequality $D>0$ is required for the stability against the uniform shift of the Fermi surface. The result of perturbation theory applied for the Hubbard model indicates that $D$ as a function of the density $n$ is qualitatively modified around half filling $n\sim 1$ by Umklapp processes.Comment: 20 pages, 2 figures; J. Phys. Soc. Jpn. Vol.67, No.

Multi-indexed Wilson and Askey-Wilson Polynomials

As the third stage of the project multi-indexed orthogonal polynomials, we present, in the framework of 'discrete quantum mechanics' with pure imaginary shifts in one dimension, the multi-indexed Wilson and Askey-Wilson polynomials. They are obtained from the original Wilson and Askey-Wilson polynomials by multiple application of the discrete analogue of the Darboux transformations or the Crum-Krein-Adler deletion of 'virtual state solutions' of type I and II, in a similar way to the multi-indexed Laguerre, Jacobi and (q-)Racah polynomials reported earlier.Comment: 30 pages. Three references added. To appear in J.Phys.A. arXiv admin note: text overlap with arXiv:1203.586

Magnetoresistance in High-Tc Superconductors: The Role of Vertex Corrections

In high-Tc cuprates, the orbital magnetoresistance in plane (MR, $\Delta\rho/\rho$) is anomalously enhanced at lower tempemeratures compared with conventional Fermi liquids, and thus Kohler's rule is strongly violated. Moreover, it should be noted that an intimate relation between the MR and the Hall coefficient ($R_H$), $\Delta\rho/\rho \propto (R_H/\rho)^2$, holds well experimentally, and is called the "modified Kohler's rule". In this letter, we study this long-standing problem in terms of the nearly antiferromagnetic (AF) Fermi liquid. We analyze the exact expression for the MR by including the vertex corrections (VC's) to keep the conservation laws, and find the approximate "scaling relation" $\Delta\rho/\rho \propto \xi_{AF}^4 /\rho^2$ ($\xi_{AF}$ being the AF correlation length.) in the presence of AF fluctuations. The factor $\xi_{AF}^4$, which comes from the VC's for the current, gives the additional temperature dependence. By taking account of the relation $R_H \propto \xi_{AF}^2$ [Kontani et al., PRB 59 (1999) 14723.], we can naturally explain the modified Kohler's rule. In conclusion, based on the Fermi liquid theory, the famous {\it seemingly} non-Fermi liquid behaviors of the Hall coefficient and the MR in high-Tc cuprates are naturally understood on an equal footing.Comment: 5 pages, 5 figures, to appear in J. Phys. Soc. Jpn. 70 (2001) No.