Supersolidity combines superfluid flow with long-range spatial periodicity of solids1, two properties that are often mutually exclusive. The original discussion of quantum crystals2 and supersolidity focused on solid 4He and triggered extensive experimental efforts3,4 that, instead of supersolidity, revealed exotic phenomena including quantum plasticity and mass supertransport4. The concept of supersolidity was then generalized from quantum crystals to other superfluid systems that break continuous translational symmetry. Bose–Einstein condensates with spin–orbit coupling are predicted to possess a stripe phase5,6,7 with supersolid properties8,9. Despite several recent studies of the miscibility of the spin components of such a condensate10,11,12, the presence of stripes has not been detected. Here we observe the predicted density modulation of this stripe phase using Bragg reflection (which provides evidence for spontaneous long-range order in one direction) while maintaining a sharp momentum distribution (the hallmark of superfluid Bose–Einstein condensates). Our work thus establishes a system with continuous symmetry-breaking properties, associated collective excitations and superfluid behaviour.
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We thank S. Stringari for discussions and W. C. Burton for reading the manuscript. We acknowledge support from the NSF through the Center for Ultracold Atoms and from award 1506369, from ARO-MURI Non-equilibrium Many-body Dynamics (grant W911NF-14-1-0003) and from AFOSR-MURI Quantum Phases of Matter (grant FA9550-14-1- 0035).
The authors declare no competing financial interests.
Reviewer Information Nature thanks K. Hazzard and the other anonymous reviewer(s) for their contribution to the peer review of this work.
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Li, JR., Lee, J., Huang, W. et al. A stripe phase with supersolid properties in spin–orbit-coupled Bose–Einstein condensates. Nature 543, 91–94 (2017). https://doi.org/10.1038/nature21431
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