Excitonic versus electron-hole liquid phases in Tm[Se,Te] compounds

TL;DR

This paper theoretically investigates excitonic phases in TmSe0.45Te0.55 during pressure-induced semiconductor-semimetal transition, comparing electron-hole pair density and exciton binding energy, and discusses factors stabilizing excitons.

Contribution

It provides a theoretical analysis of excitonic phase stability in TmSe0.45Te0.55, highlighting the role of scattering processes in stabilizing excitons contrary to initial predictions.

Findings

Excitons are predicted to be suppressed based on pair density and binding energy comparison.

Experimental evidence suggests excitonic phases are present despite theoretical suppression.

Inter-valley and exciton-phonon scattering may stabilize excitons in the material.

Abstract

We discuss, from a theoretical point of view, excitonic phases at the pressure induced semiconductor-semimetal transition in $\rm TmSe_{0.45}Te_{0.55}$,focusing, in particular, on the stability against an electron-hole liquid. The electron-hole pair density parameter $r_s(E_g,T)$ is calculated within the quasi-static plasmon pole approximation as a function of temperature $T$ and energy gap $E_g$ and converted into $-E_g(r_s,T)$. A comparison of this quantity, which is the electron-hole pair chemical potential, with the exciton binding energy reveals that excitons should be suppressed in contrast to experimental evidence for excitonic phases. We suspect therefore inter-valley exciton scattering and exciton-phonon scattering to substantially stabilise excitons in $\rm TmSe_{0.45}Te_{0.55}$.