Observation of a superfluid-to-insulator transition of bilayer excitons

Yihang Zeng; Dihao Sun; Naiyuan J Zhang; Ron Q Nguyen; Qianhui Shi; A Okounkova; K Watanabe; T Taniguchi; J Hone; C R Dean; J I A Li

doi:10.1038/s41586-025-09986-w

Observation of a superfluid-to-insulator transition of bilayer excitons

Nature. 2026 Feb;650(8100):86-92. doi: 10.1038/s41586-025-09986-w. Epub 2026 Jan 28.

Authors

Yihang Zeng^#^{1

2}, Dihao Sun^#¹, Naiyuan J Zhang³, Ron Q Nguyen³, Qianhui Shi¹, A Okounkova¹, K Watanabe⁴, T Taniguchi⁵, J Hone⁶, C R Dean⁷, J I A Li⁸

Affiliations

¹ Department of Physics, Columbia University, New York, NY, USA.
² Department of Physics and Astronomy, Purdue University, West Lafayette, IN, USA.
³ Department of Physics, Brown University, Providence, RI, USA.
⁴ Research Center for Electronic and Optical Materials, National Institute for Materials Science, Tsukuba, Japan.
⁵ Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan.
⁶ Department of Mechanical Engineering, Columbia University, New York, NY, USA.
⁷ Department of Physics, Columbia University, New York, NY, USA. cdean@phys.columbia.edu.
⁸ Department of Physics, University of Texas at Austin, Austin, TX, USA. jia.li@austin.utexas.edu.

^# Contributed equally.

PMID: 41606325
DOI: 10.1038/s41586-025-09986-w

Abstract

One of the most remarkable properties associated with Bose-Einstein condensation (BEC) is superfluidity, in which the system exhibits zero viscosity and flows without dissipation. The superfluid phase has been observed in wide-ranging bosonic systems spanning naturally occurring quantum fluids, such as liquid helium, to engineered platforms such as bilayer excitons and cold atom systems^1-4. Theoretical works have proposed that interactions could drive the BEC ground state into another exotic phase that simultaneously exhibits properties of both a crystalline solid and a superfluid-termed a supersolid^5-8. Identifying a material system, however, that hosts the predicted BEC solid phase, driven purely by interactions and without imposing an external lattice potential, has remained unknown^9-11. Here we report observation of a superfluid-to-insulator transition in the layer-imbalanced regime of bilayer magnetoexcitons. Mapping the transport behaviour of the bilayer condensate as a function of density and temperature suggests that the insulating phase is an ordered state of dilute excitons, stabilized by dipole interactions. The insulator melts into a recovered superfluid on increasing the temperature, which could indicate that the low-temperature solid is also a quantum coherent phase.