Anomalous Knudsen effect signaling long-lived modes in 2D electron gases

TL;DR

This paper reveals that in 2D electron gases, odd harmonics decay slower than even ones at finite temperatures, leading to an anomalous conductance peak known as the anomalous Knudsen effect, which signals long-lived modes in electron transport.

Contribution

It introduces the concept of the anomalous Knudsen effect caused by slow decay of odd harmonics, highlighting a new signature of long-lived modes in 2D electron transport.

Findings

Conductance exhibits a peak due to the anomalous Knudsen effect.

Long-lived odd harmonics dominate electron transport at low temperatures.

Observation of the Gurzhi effect following the Knudsen peak confirms the crossover to hydrodynamic behavior.

Abstract

Proper analysis of electron collisions in two spatial dimensions leads to the conclusion, that the odd harmonics of the electron distribution function decay much slower than the even ones at finite temperatures. The number of long-lived odd harmonics quickly shrinks with increasing temperature. Focusing on a channel geometry with boundary scattering, we show that such behavior of the odd decay rates leads to a characteristic behaviour of the conductance that we dub anomalous Knudsen effect: it initially grows with temperature but then starts to decrease, forming a peak. Further increase of the temperature forces the conductance to grow again due to the Gurzhi effect, associated with the crossover from ballistic to hydrodynamic transport. The simultaneous observation of the Gurzhi dip preceded by the anomalous Knudsen peak constitutes a particular signature of the long-lived modes in 2D electron transport at low temperatures.