Unitary limit and quantum interference effect in disordered two-dimensional crystals with nearly half-filled bands

TL;DR

This paper investigates quantum interference effects in disordered two-dimensional crystals near half-filling, revealing unconventional anti-localization phenomena due to $ ext{ extpi}$-modes and their impact on conductivity behavior.

Contribution

It introduces the role of $ ext{ extpi}$-modes in quantum interference in the unitary limit, showing their influence on conductivity and anti-localization effects in nearly nested Fermi surfaces.

Findings

$ ext{ extpi}$-modes cause anti-localization near nesting.

Thermal fluctuations significantly dephase $ ext{ extpi}$-mode interference.

Conductivity exhibits non-monotonic temperature dependence.

Abstract

Based on the self-consistent $T$-matrix approximation, the quantum interference (QI) effect is studied with the diagrammatic technique in weakly-disordered two-dimensional crystals with nearly half-filled bands. In addition to the usual 0-mode cooperon and diffuson, there exist $\pi$-mode cooperon and diffuson in the unitary limit due to the particle-hole symmetry. The diffusive $\pi$-modes are gapped by the deviation from the exactly-nested Fermi surface. The conductivity diagrams with the gapped $\pi$-mode cooperon or diffuson are found to give rise to unconventional features of the QI effect. Besides the inelastic scattering, the thermal fluctuation is shown to be also an important dephasing mechanism in the QI processes related with the diffusive $\pi$-modes. In the proximity of the nesting case, a power-law anti-localization effect appears due to the $\pi$-mode diffuson. For large deviation from the nested Fermi surface, this anti-localization effect is suppressed, and the conductivity remains to have the usual logarithmic weak-localization correction contributed by the 0-mode cooperon. As a result, the dc conductivity in the unitary limit becomes a non-monotonic function of the temperature or the sample size, which is quite different from the prediction of the usual weak-localization theory.