Indirect excitons in van der Waals heterostructures
All known superfluid and superconducting states of condensed matter are enabled by composite bosons (atoms, molecules, 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 (TMD) and an atomically thin hexagonal boron nitride (hBN) spacer. Electrons and holes generated in the system would accumulate in the separate TMD layers and form bosonic bound states --- the indirect excitons. The resultant degenerate Bose gas of excitons would exhibit macroscopic occupation of a quantum state, vanishing viscosity, and superconductivity at high temperatures.