Pairing Fluctuations and Anomalous Transport Above the BCS-BEC Crossover in the Two Dimensional Attractive Hubbard Model

TL;DR

This paper investigates the evolution of transport properties and the BCS-BEC crossover in a two-dimensional attractive Hubbard model, revealing how increasing interaction strength leads from metallic to insulating behavior before the system becomes a BEC superconductor.

Contribution

It introduces a new Monte Carlo method to map the BCS-BEC crossover and explicitly computes resistivity, providing detailed insights into the metal-insulator-superconductor transition.

Findings

Resistivity shows insulating behavior above T_c at intermediate coupling.

The crossover from metallic to insulating behavior occurs before the BEC regime.

Transport properties are thoroughly characterized across the BCS-BEC crossover.

Abstract

A Fermi liquid with weak attractive interaction undergoes a BCS transition to a superconductor with reducing temperature. With increasing interaction strength, the thermal transition is progressively modified as the high temperature `metallic' phase develops a pseudogap due to pairing fluctuations and the resistivity above T_c shows insulating behaviour. The crossover to insulating character occurs much before the system can be considered to be in the BEC regime of preformed fermion pairs. We use a new Monte Carlo tool to map out the BCS-BEC crossover in the attractive Hubbard model on large two dimensional lattices and explicitly compute the resistivity to demonstrate how the metal to superconductor (MS) thermal transition at weak coupling crosses over to an insulator to superconductor (IS) transition at intermediate coupling. Our high resolution access to the single particle and optical spectrum at finite temperature allows us to completely describe the transport crossover in this longstanding problem.