Collective Excitations and Superconductivity in Reduced Dimensional SystemsPossible Mechanism for High T
Abstract
We study in full detail a possible mechanism of superconductivity in slender electronic systems of finite cross section. This mechanism is based on the pairing interaction mediated by the multiple modes of acoustic plasmons in these structures. First, we show that multiple nonLandaudamped acoustic plasmon modes exist for electrons in a quasione dimensional wire at finite temperatures. These plasmons are of two basic types. The first one is made up by the collective longitudinal oscillations of the electrons essentially of a given transverse energy level oscillating against the electrons in the neighboring transverse energy level. The modes are called Slender Acoustic Plasmons or SAP's. The other mode is the quasione dimensional acoustic plasmon mode in which all the electrons oscillate together in phase among themselves but out of phase against the positive ion background. We show numerically and argue physically that even for a temperature comparable to the mode separation Deltaomega the SAP's and the quasione dimensional plasmon persist. Then, based on a clear physical picture, we develop in terms of the dielectric function a theory of superconductivity capable of treating the simultaneous participation of multiple bosonic modes that mediate the pairing interaction. The effect of mode damping is then incorporated in a simple manner that is free of the encumbrance of the strongcoupling, Green's function formalism usually required for the retardation effect. Explicit formulae including such damping are derived for the critical temperature T_ c and the energy gap Delta_0. With those modes and armed with such a formalism, we proceed to investigate a possible superconducting mechanism for high T_ c in quasione dimensional singlewire and multiwire systems. Due to the small mass of the electrons and the effective plasmon frequency, the electronelectron coupling strength and therefore T _ c are enhanced in these systems. Numerical examples show T_ c in the 200 K range for both systems. However, the critical temperature of the multiwire is enhanced over the critical temperature of the singlewire system. This fact stems from the in phase wirewire Coulomb coupling. Finally we present general conclusions and point out the various ways in which this work could be further studied and expanded.
 Publication:

Ph.D. Thesis
 Pub Date:
 1989
 Bibcode:
 1989PhDT.......209S
 Keywords:

 C;
 Physics: Condensed Matter