High-temperature superfluidity with indirect excitons in van der Waals heterostructures

Abstract

All known superfluid and superconducting states of condensed matter are enabled by composite bosons (atoms, molecules and Cooper pairs) made of an even number of fermions. Temperatures where such macroscopic quantum phenomena occur are limited by the lesser of the binding energy and the degeneracy temperature of the bosons. High-critical temperature cuprate superconductors set the present record of B100 K. Here we propose a design for artificially structured materials to rival this record. The main elements of the structure are two monolayers of a transition metal dichalcogenide separated by an atomically thin spacer. Electrons and holes generated in the system would accumulate in the opposite monolayers and form bosonic bound states-the indirect excitons. The resultant degenerate Bose gas of indirect excitons would exhibit macroscopic occupation of a quantum state and vanishing viscosity at high temperatures.

High-temperature superfluidity of the two-component Bose gas in a transition metal dichalcogenide bilayer

“…Let us mention that for our calculations we used an exciton concentration n = 3×10 11 cm −2 which is smaller than the maximal exciton concentration obtained in experiment [72]: n max = 5 × 10 11 cm −2 . The exciton concentration n = 3 × 10 11 cm −2 corresponds to the degenerate exciton Bose gas in the phase diagram [53]. While, in general, in a TMDC monolayer the electron-hole interaction is described by Keldysh's potential [68], we performed our calculations for a TMDC bilayer at the interlayer separation from D = 4 nm up to D = 5 nm, when the screening effects are negligible, and the electron-hole interaction is described by the Coulomb potential.…”

“…50, we conclude that for TMDC ρ 0 is estimated as 38Å for WS 2 , 41Å for MoS 2 , 45Å for WSe 2 , 52Å for MoSe 2 . The binding energy for the dipolar exciton was estimated for two MoS 2 layers separated by N hBN insulating layers from N = 1 up to N = 6 [53]. These dipolar excitons were observed experimentally for N = 2 [54].…”

“…It was recently proposed that a heterostructure design consisting of two TMDC monolayers separated by an hBN insulating barrier could be used to observe high temperature superfluidity in these materials [53]. The emission of neutral and charged excitons was controlled by the gate voltage, temperature, and the helicity and power of optical excitation.…”

Two-Dimensional MoS2-Graphene-Based Multilayer van der Waals Heterostructures: Enhanced Charge Transfer and Optical Absorption, and Electric-Field Tunable Dirac Point and Band Gap

“…Peculiar electronic [15][16][17] and optoelectronic properties 18,19 have been revealed in diverse 2D heterostructures based on layered materials such as GR, semiconducting transition metal dichalcogenides (TMDs) and insulating hexagonal boron nitride (h-BN). Interestingly, these heterostructures are also tunable hyperbolic metamaterial 20 and memory device with ultrahigh on/off ratio 21 , or have gate-induced superconductivity 22 and high-temperature superfluidity 23 .…”

Progress on Crystal Growth of Two-Dimensional Semiconductors for Optoelectronic Applications

“…Type II band alignment can be observed in the heterojunction of two different 2D semiconductors. Both simulation and experiments have revealed that the intrinsic 2D van der Waals hetero-structure can behave like p-n diodes, exhibiting remarkable spatial direct optical absorption and emission which suggests promising application in optoelectronics devices such as photodetectors and LED devices [6,75] [86] etc. On the other hand, the epitaxial growth of the heterojunction can provide more options and control in the growth direction both in the vertical and lateral.…”