Strongly correlated two-dimensional plasma explored from entropy measurements

TL;DR

This paper introduces a highly sensitive thermodynamic method to measure entropy per electron in two-dimensional electron systems, enabling exploration of the correlated plasma regime previously inaccessible experimentally.

Contribution

A novel entropy measurement technique with greatly improved sensitivity, allowing investigation of the correlated plasma regime in 2D electron systems.

Findings

Mapped the entropy evolution from plasma to Fermi-liquid regime

Revealed the correlated plasma behaves like a non-degenerate Fermi gas with enhanced effective mass

Enabled experimental access to the correlated plasma regime in 2D systems

Abstract

Charged plasma and Fermi liquid are two distinct states of electronic matter intrinsic to dilute two-dimensional electron systems at elevated and low temperatures, respectively. Probing their thermodynamics represents challenge because of lacking an adequate technique. Here we report thermodynamic method to measure the entropy per electron in gated structures. Our technique appears to be three orders of magnitude superior in sensitivity to the ac calorimetry, allowing entropy measurements with only $10^8$ electrons. This enables us to investigate the correlated plasma regime, previously inaccessible experimentally in two-dimensional electron systems in semiconductors. In experiments with clean two-dimensional electron system in Si-based structures we traced entropy evolution from the plasma to Fermi-liquid regime by varying electron density. We reveal that the correlated plasma regime can be mapped onto the ordinary non-degenerate Fermi gas with an interaction-enhanced temperature dependent effective mass. Our method opens up new horizons in studies of low-dimensional electron systems.