The boson-fermion model: An exact diagonalization study

TL;DR

This paper investigates a boson-fermion model for electron pairing, demonstrating a crossover from metallic to superconducting behavior, pseudogap formation, and phase coherence using exact diagonalization on small rings, highlighting transport changes.

Contribution

It provides an exact diagonalization analysis of the boson-fermion model, confirming key features of electron pairing and transport in a correlated system, especially in the intermediate coupling regime.

Findings

Observation of a crossover from poor metal to insulator and superconductor

Detection of local electron pairing amplitude build-up below T*

Identification of a transition from single-electron to pair transport in mesoscopic rings

Abstract

The main features of a generic boson-fermion scenario for electron pairing in a many-body correlated fermionic system are: i) a cross-over from a poor metal to an insulator and finally a superconductor as the temperature decreases, ii) the build-up of a finite amplitude of local electron pairing below a certain temperature $T^*$, followed by the onset of long-range phase correlations among electron pairs below a second characteristic temperature $T_{\phi}$, iii) the opening of a pseudogap in the DOS of the electrons below $T^*$, rendering these electrons poorer and poorer quasi-particles as the temperature decreases, with the electron transport becoming ensured by electron pairs rather than by individual electrons. A number of these features have been so far obtained on the basis of different many-body techniques, all of which have their built-in shortcomings in the intermediate coupling regime, which is of interest here. In order to substantiate these features, we investigate them on the basis of an exact diagonalization study on rings up to eight sites. Particular emphasis has been put on the possibility of having persistent currents in mesoscopic rings tracking the change-over from single- to two-particle transport as the temperature decreases and the superconducting state is approached.