Biexciton crystal in a two-dimensional semiconductor heteropentalayer

TL;DR

This study predicts a biexciton crystal formation in a 2D heteropentalayer semiconductor, revealing a new anti-ferroelectric lattice structure with specific concentration and voltage conditions, supported by electrostatic energy analysis.

Contribution

It introduces the concept of biexciton crystal formation in a 2D heteropentalayer, demonstrating the conditions for its stability and the associated electrostatic energy minimum.

Findings

Biexcitons form a staggered anti-ferroelectric square lattice.

Biexciton concentration at energy minimum is approximately 0.14 times the inverse square of layer thickness.

A critical voltage induces a biexciton crystal in a five-layer capacitor, with diverging differential capacitance.

Abstract

This paper is written for the Special Issue in Honor of Emmanuel Rashba. We study the gas of indirect dipolar excitons created by an interband illumination of a pentalayer WSe$_2$/MoSe$_2$/WSe$_2$/MoSe$_2$/WSe$_2$. We show that two colinear indirect excitons bind into a linear biexciton with twice larger dipole moment. Two biexcitons with opposite dipole directions attract each other at large distances and repel each other at short distances. Therefore, biexcitons form a staggered crystal with anti-ferroelectric square lattice. The electrostatic energy of this crystal per biexciton has a minimum at the biexciton concentration $n =n_c=0.14d^{-2}$, where $d \sim 0.7$ nm is a single layer thickness. At small illumination intensity, biexcitons condense into sparse crystallites with $n = n_c$, where photoluminescence frequency is red shifted and independent on the light intensity. We also study a capacitor made of five identical semiconductor monolayers separated by hBN spacers where a critical voltage applied between layers 1, 3, 5, and 2, 4 abruptly creates a similar biexciton crystal. At this voltage, the differential capacitance diverges.