Evidence for an excitonic insulator phase in a zero-gap InAs/GaSb bilayer

TL;DR

This study provides electrical transport evidence suggesting the formation of an excitonic insulator phase in a zero-gap InAs/GaSb bilayer, characterized by a high-resistance state and strong temperature dependence.

Contribution

It presents experimental evidence supporting the existence of an excitonic insulator phase in a zero-gap semiconductor heterostructure, aligning with early theoretical predictions.

Findings

High resistivity (~500 kΩ) in the charge neutrality region

Strong temperature activation above 7 K

Resistance stability under magnetic fields

Abstract

Many-body interactions can produce novel ground states in a condensed-matter system. For example, interacting electrons and holes can spontaneously form excitons, a neutral bound state, provided that the exciton binding energy exceeds the energy separation between the single particle states. Here we report on electrical transport measurements on spatially separated two-dimensional electron and hole gases with nominally degenerate energy subbands, realized in an InAs(10 nm)/GaSb(5 nm) coupled quantum well. We observe a narrow and intense maximum (~500 k\Omega) in the four-terminal resistivity in the charge neutrality region, separating the electron-like and hole-like regimes, with a strong activated temperature-dependence above T = 7 K and perfect stability against quantizing magnetic fields. By quantitatively comparing our data with early theoretical predictions, we show that such unexpectedly large resistance in our nominally zero-gap semi-metal system is probably due to the formation of an excitonic insulator state.