Details

Autor(en) / Beteiligte

• Cheng, Ming

Titel

Electronic mechanism of high temperature superconductivity

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2006

Link zum Volltext

• ProQuest

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• A successful theory of conventional superconductivity, BCS (Bardeen, Cooper, Schrieffer) theory is constructed on the basis of phonon-mediated attraction between electrons. Little has proposed a model in which the pairing force is induced by electronic polarization of molecules embedded in the conductor. This model provides a non-phonon mechanism of superconductivity. Hirsch and Scalapino have studied a tight-binding model of this type in one-dimension and have found that superconductivity is dominated by charge-density-wave (CDW). We extended their calculations to two-dimensions. Our quantum Monte Carlo simulation results suggest that the CDW formation is limited to a region close to half-filling. Outside of that, superconductivity flourishes even in the presence of a finite onsite Coulomb repulsion, demonstrating the Little model as a viable model for electronic mechanism of high temperature superconductivity. A number of experiments have verified d-wave order parameter (OP) inhomogeneities in high temperature superconducting materials [1-4]. Motivated by this essential feature we developed a minimal inhomogeneity model. Using the Green's function formalism to compute the energy-dependent modulation of the local density of states (LDOS) both in real and k-space we modeled the broadening of the superconductivity coherence peak as observed in recent Scanning Tunneling Microscopy (STM) experiment. The results agree with experiments rather well and can be understood as interference of scattering between quasiparticles. The broadening of superconducting coherent peak observed in recent STM experiment can be explained by the strong OP inhomogeneities. To further refine our model, we considered more complicated inhomogeneity cases since nanoscale inhomogeneity seems to be a central feature of the d-wave superconductivity in the cuprates. Such a feature can strongly affect the LDOS and the spectral weight functions. Within the Bogoliubov-de Gennes formalism we examined various inhomogeneous configurations of the superconducting OP to see which ones better agree with the experimental data. Nanoscale large amplitude oscillations in the OP seem to fit the LDOS data for the underdoped cuprates. The one-particle spectral function for a general inhomogeneous configuration exhibits a coherent peak in the nodal direction. In contrast, the spectral function in the antinodal region is easily rendered incoherent by the inhomogeneity. This throws new light on the dichotomy between the nodal and antinodal quasiparticles in the underdoped cuprates. (Abstract shortened by UMI.)