Excitation Spectrum of a Trapped Dipolar Supersolid and Its Experimental Evidence

We study the spectrum of elementary excitations of a dipolar Bose gas in a three-dimensional anisotropic trap across the superfluid-supersolid phase transition. Theoretically, we show that, when entering the supersolid phase, two distinct excitation branches appear, respectively associated with domi...

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Bibliographic Details
Published in:Physical review letters 2019-08, Vol.123 (5), p.050402-050402, Article 050402
Main Authors: Natale, G, van Bijnen, R M W, Patscheider, A, Petter, D, Mark, M J, Chomaz, L, Ferlaino, F
Format: Article
Language:English
Subjects:
Bose-Einstein condensates
Elementary excitations
Excitation spectra
Fluids
Frequency response
Helium
Phase diagrams
Phase transitions
Quadrupoles
Size effects
Superfluidity
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Summary:We study the spectrum of elementary excitations of a dipolar Bose gas in a three-dimensional anisotropic trap across the superfluid-supersolid phase transition. Theoretically, we show that, when entering the supersolid phase, two distinct excitation branches appear, respectively associated with dominantly crystal and superfluid excitations. These results confirm infinite-system predictions, showing that finite-size effects play only a small qualitative role, and connect the two branches to the simultaneous occurrence of crystal and superfluid orders. Experimentally, we probe compressional excitations in an Er quantum gas across the phase diagram. While in the Bose-Einstein condensate regime the system exhibits an ordinary quadrupole oscillation, in the supersolid regime we observe a striking two-frequency response of the system, related to the two spontaneously broken symmetries.
ISSN:0031-9007
1079-7114
DOI:10.1103/physrevlett.123.050402