Biexciton crystal in a two-dimensional semiconductor heteropentalayer

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.