Dephasing time of composite fermions

TL;DR

This paper investigates the dephasing mechanisms of composite fermions interacting with fluctuating gauge fields, revealing a breakdown of Fermi's golden rule and its impact on quantum oscillation experiments.

Contribution

It demonstrates the role of strong dephasing in composite fermions and emphasizes the importance of considering both dephasing effects and mass renormalization in interpreting experimental data.

Findings

Dephasing causes a faster than exponential decay in fermion coherence.

The suppression of SdH oscillations is significantly influenced by dephasing and mass renormalization.

Effective mass extracted from experiments differs from the quasiparticle mass in Fermi liquid theory.

Abstract

We study the dephasing of fermions interacting with a fluctuating transverse gauge field. The divergence of the imaginary part of the fermion self energy at finite temperatures is shown to result from a breakdown of Fermi's golden rule due to a faster than exponential decay in time. The strong dephasing affects experiments where phase coherence is probed. This result is used to describe the suppression of Shubnikov-de Haas (SdH) oscillations of composite fermions (oscillations in the conductivity near the half-filled Landau level). We find that it is important to take into account both the effect of dephasing and the mass renormalization. We conclude that while it is possible to use the conventional theory to extract an effective mass from the temperature dependence of the SdH oscillations, the resulting effective mass differs from the $m^\ast$ of the quasiparticle in Fermi liquid theory.