Tunneling signatures of interband coherence in dilute exciton condensates

TL;DR

This paper explores how scanning tunneling microscopy can detect interband coherence and exciton condensation in dilute monolayer and bilayer systems, revealing signatures like oscillating conductance and characteristic peaks.

Contribution

It provides a theoretical framework linking tunneling signatures to interband coherence and exciton density in dilute exciton condensates, including analytical and numerical analysis.

Findings

Interband coherence causes spatial oscillations in tunneling conductance.

A peak in conductance indicates the formation of an exciton insulator.

The exciton wavefunction can be extracted from STM measurements.

Abstract

We theoretically investigate signatures of exciton condensation and the underlying interband coherence in scanning tunneling microscopy. We consider both monolayer and bilayer condensates in the regime of a dilute condensate of tightly bound excitons. For monolayer condensates, interband coherence is directly encoded in spatially oscillating contributions to the tunneling conductance, which break the underlying lattice symmetry. We show how scanning tunneling microscopy allows one to extract the exciton wavefunction. For bilayer condensates, we show that the formation of the exciton insulator is signaled by the emergence of a characteristic peak in the tunneling conductance, which can be used to extract the (local) exciton density. Our results are based on analytical considerations using a systematic solution of the mean-field equations in powers of the exciton density as well as numerical calculations.