Chester Supersolid of Spatially Indirect Excitons in Double-Layer Semiconductor Heterostructures

A supersolid, a counter-intuitive quantum state in which a rigid lattice of particles flows without resistance, has to date not been unambiguously realized. Here we reveal a supersolid ground state of excitons, formed from electrons and holes that are spatially separated in a double-layer semiconductor heterostructure. The supersolid spans a wide range of layer separations lying outside the focus of recent transport experiments on exciton superfluidity in these systems [1]. Our supersolid conforms to the original Chester concept of a supersolid [2] with one exciton per supersolid site. It is distinct from alternative versions observed in cold-atom systems which are characterized by a periodic modulation of the superfluid density [3]. We provide the phase diagram, augmented by the supersolid. This new phase appears at layer separations much smaller than the predicted exciton normal solid [4], and it persists up to a solid-solid transition where the quantum phase coherence collapses while leaving the translational symmetry preserved. The ranges of layer separations and exciton densities in our phase diagram are well within reach of current experimental capabilities.

[1] G. W. Burg, et al., Phys. Rev. Lett. 120, 177702 (2018); L. Ma, et al., Nature 598, 585 (2021)

[2] G. V. Chester Phys. Rev. A 2 256 (1970)

[3] G. Natale, et al., Phys. Rev. Lett. 123, 050402 (2019); F. Böttcher, et al., Phys. Rev. X 9, 011051 (2019)

[4] G. E. Astrakharchik, et al., Phys. Rev. Lett. 98, 060405 (2007)