Kazuo Hattori

Intermediate Coupling Theory of a Polaron in External Fields

A new extension of the Lee, Low and Pines (L-L-P) method to the problem of a polaron weakly bound in a Coulomb potential and/or in a weak magnetic field is developed. The effective Hamiltonian of a polaron bound in a Coulomb potential is derived exactly to order P 4 . The validity of replacing P 2 by [(P_{z}^{2}+eH{hbar}(2n+1)/c)] in the field-free polaron energy E ( P 2 ) within the framework of the L-L-P method is shown in the limit of a weak magnetic field H along the z axis in the intermediate coupling case. The energies of a polaron in a Coulomb potential and subject to a weak magnetic field are also discussed.

The Optical Absorption by Free Piezoelectric and Anisotropic Optical Polarons

The absorption coefficients of free piezoelectric and anisotropic optical polarons are calculated to the first order of the electron-phonon coupling constant, in the framework of the Lee, Low and Pines variational method. In the case of the anisotropic optical polaron, a bare electron is assumed to be on a spheroidal energy surface.

Effects of Intra-Site Vibrations on the Electrical Conductivity in a Disordered Hubbard Chain

Electrical conductivity is calculated in the Hubbard model for a disordered chain. The intra-site Coulomb repulsion is assumed to be sufficiently strong, and the electron-transfer term is treated as a perturbation. The interaction between electrons and intra-site vibrations is taken into account by two types of coupling terms. The effects of this interaction on the conductivity are discussed.

Curie Temperatures of Dilute Ferromagnets with the Site and Bond Disorders

Curie temperatures of dilute ferromagnets with the site and bond disorders are investigated in the Heisenberg and Ising models, using the effective Hamiltonian method. The systems are assumed to be quenched ones. Positive and negative exchange integrals as well as non-magnetic atoms are assumed to be randomly distributed. Numerical calculations of Curie temperatures are carried out for the Gaussian and rectangular distributions of exchange integrals. The critical conditions for ferromagnetism to occur at finite temperature are also discussed.

Polarons with an Anisotropic Band Mass at Finite Temperature

Intermediate coupling theory is applied to get the energy spectrum of an electron or a hole which is on a spheroidal energy surface and interacts with longitudinal optical phonons at finite tempera...

Theory of a Polaron with an Anisotropic Mass in External Fields

The intermediate coupling theory is applied to the problem of a polaron with an anisotropic mass. The energy levels of a polaron bound in a Coulomb potential are discussed. Hydrogenic wave functions are used as variational wave functions, and it is shown that each energy level depends not only on the principal quantum number but also on the azimuthal and magnetic quantum numbers owing to the anisotropy of the mass. The electric polarizability of a bound polaron is also calculated, and the effect of a weak magnetic field is discussed both in the absence and the presence of a Coulomb potential.

The Random Ising Model with a Term Corresponding to a Transverse Field

The random binary Ising system with a term corresponding to a transverse field has been investigated. Two kinds of spins (A and B spins) are assumed to be randomly distributed. The Curie and Neel temperatures are obtained in various cases. The susceptibility is also calculated in the paramagnetic phase.

Bound Polarons at Finite Temperature

Intermediate coupling theory at finite temperature is developed to the problem of a bound polaron. Ground state energy and energy levels of a few low lying excited states are calculated. Shallow donor levels in CdS are discussed. A good agreement of the theory with experiment is found, though piezoelectric and anisotropic effects are not taken into account.

Strongly-Coupled Polaron with Anisotropic Mass

The polaron strong-coupling theory is applied to the problem of an electron on a spheroidal energy surface strongly interacting with longitudinal optical phonons. The self-energy and the transverse and longitudinal polaron masses are calculated.

Theory of a Bound Piezoelectric Polaron

The energy levels of a piezoelectric polaron bound in a Coulomb potential are calculated in two different cases. One is the case in which a piezoelectric polaron is very weakly bound in a Coulomb potential. The other is the case in which a piezoelectric polaron is strongly bound and/or the electron-phonon interaction is strong. The former case is treated by the intermediate coupling theory at finite temperature. The latter is treated by the adiabatic approximation.