The authors have carried out a study of the electrical conduction in semiconductors, by developing a method which makes use of an evolution operator, connected intimately with one evolution operator they reported earlier in regard to the behaviour of Bloch electrons in an electric field. The method formulated in this paper has a very general basis and is capable of providing the transport theory of semiconductors for all situations under which Stark ladders (SL) would occur, and also for the conditions under which Stark ladders are not expected. Their broad investigations are concerned with (i) the derivation of the most general form of the steady-state current density, and (ii) the derivation of the form of current density for all situations under which SL would occur. In the context of these broad results, they have given (a) a detailed treatment of the SL-dependent current for a special model, with the inclusion of the electron-phonon interaction only up to second order, and (b) a formula for the low-field (ohmic) current. The principal findings in regard to the aspect (a) are the following: (i) in the presence of Stark ladders, the differential conductivity becomes negative; and (ii) in presence of the Stark ladders the current field characteristic shows, as well as (i), resonance-type anomalies; such anomalies occur for fields which make the longitudinal optical phonon energy equal to an integral multiple of SL spacing and are prominent specially at low temperatures. The observations relevant to the detailed treatment of the special model are valuable in analysing the experimental results about the effects of SL on the electrical conduction in semiconductors.

https://iopscience.iop.org/article/10.1088/0022-3719/16/4/019/pdf

A study of electrical conduction in semiconductors using an evolution operator

An effective potential is proposed as a means to study the mechanism of pairing of high-T c superconductivity in cuprates. The relation between size and energy of bound states evaluated in a first approximation is comparable to recent calculations obtained through quantum electrodynamics in (2 + 1) dimensions. In a second approximation, we consider that pairing occurs at the minimum of this effective potential, the problem being related to the quantum mechanical behavior of a particle described by polar coordinates in a plane. So, according to the present model, the topological constraint determined by the CuO 2 planes seems to be most relevant in the understanding of the pairing mechanism.

An Effective Potential for High-Temperature Superconductivity in Cuprates

Relevance of the μ(T) Dependence for 2D Superconductivity

A method of computing electric current caused by phonon induced hopping between Wannier-Stark states

It is suggested, that interlayer interaction enhances the value of T C in high-Tc-superconductors. An estimation of the value of T C is given for various parameters. Besides on the parameters of the suggested interaction this enhancement depends also on the critical temperature determined merely by the in-layer interactions.

Interlayer interaction in high-TC superconductors

Explanation of Temperature Independent Energy Gap in High‐Tc Superconductors

On considere que ces «molecules» facilement polarisables sont formees par des ions situees dans deux couches adjacentes, puis dans trois couches. Pour un plus grand nombre de couches, la situation est plus compliquee a cause des plusieurs modes d'onde de polarisation

Dependence of Tc on the Number of CuO2 Layers in High‐Tc Superconductors

A method for calculating the current due to the phonon induced hopping between Wannier-Stark states, taking into account the space charge field resulting from the localization of these states, is suggested.



Es wird eine Methode vorgeschlagen, um den Strom zu berechnen, der durch Phonon-induzierte Ubergange zwischen Wannier-Stark-Zustanden entsteht. Dabei wird der Einflus des Raumladungs-feldes berueksichtigt, das durch die Lokalisierung dieser Zustande bedingt ist.

J. Foltin

Papers

Explanation of Temperature Independent Energy Gap in High‐Tc Superconductors

Dependence of Tc on the Number of CuO2 Layers in High‐Tc Superconductors

On the Phonon Induced Hopping between Stark Levels

Possible Explanation of the Generic Phase Diagram of the Cuprate Oxides

On the Tc Enhancement of Y–Ba–Cu–O Samples Processed and Enclosed in an Oxygen Atmosphere