Elementary excitation spectrums for correlated electron systems at finite temperatures

Sergio Conti

Sei-ichiro Suga, A. Okiji, N. Kawakami

Spectral density for the elementary excitation of the multichannel Kondo model is investigated at finite temperatures with the use of the Bethe-ansatz method. Our formulation is based on the method of Yang and Yang developed in one-dimensional interacting boson systems. In the orbital singlet case, the narrow peak structure develops in the low-energy region as the temperature is decreased, whereas in the underscreened case, the excitation spectrum exhibits a divergence property at zero excitation energy, irrespective of the temperature. In the overscreened case, in which the non-Fermi-liquid fixed point is stable in the ground state, the peak structure develops in the low-energy region and the weight at zero excitation energy increases as the temperature is decreased. We discuss characteristic properties of the excitation spectrum in connection with bulk properties.

Asako Tomiyama, Sei-ichiro Suga, A. Okiji

The elementary excitations for the one-dimensional Hubbard model at finite temperatures are studied with the use of the Bethe ansatz solution. The formulation is based on the method of Yang and Yang, which was developed for the one-dimensional boson systems with the -function type interaction. The dispersion relations and the excitation spectrums are obtained numerically for the charge and the spin degrees of freedom.

Shiwei Zhang

Sadamichi Maekawa, Takami Tohyama, Seiji Yunoki

Daryl W. Hess

Several topics in quantum liquids are discussed including the elementary excitation spectrum of 3 He under pressure, spin polarized 3 He, and an early attempt to formulate a Fermi liquid theory to describe the low temperature thermodynamic and transport properties of the heavy electron system UPt3. The elementary excitation spectrum of ordinary liquid 3 He is calculated at several pressures using the polarization potential theory of Aldrich and Pines together with a simple model to describe the effect of multipair excitations. The calculated elementary excitation spectra, with no adjustable parameters, agree well with the recent experiment of Scherm et al. The effective interactions between quasi particles in fully spin polarized 3 He are obtained from physical arguments and sum rules. The interactions between two down spin impurities and that between an up and down spin are also deduced. The volume occupied by a down spin impurity is found to be 17% to 7% less than that occupied by an up· spin. Nonlocal scalar pseudopotentials of the Aldrich-Pines form are developed along with two extreme models for the momentum dependent backflow potential. The transport properties are calculated and found to be two to three orders of magnitude larger than those of the unpolarized liquid at the same density. The elementary excitation spectrum is found to be quite sensitive to the momentum dependence of the backflow potential. The regime of small polarization is considered next. Using the phenomenological model of Bedell and Sanchez-Castro together with an ansatz form for the spin flip interaction, a large increase in the singlet scattering rate as a function of polarization is obtained. The transport properties are calculated as a function of polarization and the viscosity obtained is found to be in good agreement with the recent experiment of P. Kopietz et al. Finally, an early attempt at describing the low temperature thermodynamic and transport properties of the heavy electron system UPt3 by an extension of Landau Fermi liquid theory is described. Although the Fermi surface geometry is treated naively, the transport calculations underscore the importance of electron-electron scattering in these systems.