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Balance equation approach to the hot-electron transport in electric and magnetic fields is reformulated. The balance equations are re-derived from the Boltzmann equation. A new expression for the distribution function is reported in the present paper. It is homogeneous steady solution of the Boltzmann equation in constant relaxation time approximation. It holds when or . As an example, the mobility of 2D electron gas in the GaAs-AlGaAs heterojunction is computed as a function of electric field and magnetic field.

A theory of the c-axis infrared conductivity of a dx2-y2-wave superconductor due to the competition between the interlayer direct hopping and the hopping assisted by the spin fluctuations has been developed. The prediction of our theory captures the main feature of the experiment. Thus we argue that the anomalous behavior of the c-axis infrared conductivity of the underdoped cuprates in superconducting state may be properly understood within the theory.

The influence of pseudogap on the inelastic neutron scattering spectra of the underdoped lanthanum cuprate is studied on the basis of the model which incorporates both the superconducting state and pseudogap state. It is found that the striking effects of the influence of the pseudogap on the incommensurability of the spin excitation spectrum are that in the superconducting state the pseudogap makes the intensity of the incommensurate peak increase, in the normal state the pseudogap not only makes the intensity of the incommensurate peak increase, but also sharpens the incommensurate peak and increases incommensurability.

A mean field SDW analysis of pseudogap in the underdoped cuprates is proposed on the basis of the $t-t^{\prime}-U$ Hubbard model. The prediction of our theory is consistent with the experiment quite well within the uncertainty of the present experimental measurement. Therefore we argue that the pseudogap phenomenon in the underdoped cuprates can be well explained within the mean field approximation., RevTex 19 Pages, 8 Eps figures; The paper (cond-mat/9912481) is revised, Manuscript rewitten, figures revised

The magnetic contribution to the thermal expansion of Cu-O layer in YBa2Cu3O7-δ is studied with the nearly antiferromagnetic Fermi liquid model. Our analysis suggests that this additional thermal expansion due to antiferromagnetic spin fluctuation is the origin of the Cu-O plane buckling.

In this letter, we present an analysis to understand why the McMillan-like Tc formula: , proposed in a previous paper by the authors, applies to crystalline superconductors satisfactorily but less satisfactorily to non-crystalline ones.

The structure of the mixed state of a current-carrying thin film of ideal type II superconductors in longitudinal magnetic field He is analysed. We show that the lossless current flow through the films in the mixed state is possible only if He is larger than Hc1)(d). The curves of longitudinal critical current obtained have complex structure and show peak effect in general. The main feature of the theoretical Ic-He curve of the films with thickness d larger than 5λ is identical with that observed by Heaton and Rose-Innes in Nb55Ta45 alloys.

A model for the high-Tc Copper Oxides is studied. The localized nature of Cu 3d electrons is described as the RVB quantum spin liquid and the doped O 2p holes are described with an itinerant band. Our analysis shows that the virtual exchange of two spinons induces a pairing interaction between two holes.

In the present paper, the linear Eliashberg equation is converted into a new integral equation and from it, the following Tc formula is derived analytically in the weak coupling limit:, where ln γ=C=0.5772 is the Euler constant.