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 ~100 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. Superfluidity typically occurs at cryogenic temperatures. But Fogler et al. predict that an excitonic superfluid could emerge at much higher temperatures, perhaps even approaching room temperature, in a heterostructure of atomically thin layers of molybdenum disulphide and hexagonal boron nitride.