Measurement of the superfluid fraction of a supersolid by Josephson effect

Year: 2024

Authors: Biagioni G., Antolini N., Donelli B., Pezzè L., Smerzi A., Fattori M., Fioretti A., Gabbanini C., Inguscio M., Tanzi L., Modugno G.

Autors Affiliation: Univ Firenze, Dipartimento Fis & Astron, Sesto Fiorentino, Italy; CNR, INO, Pisa, Italy; Univ Firenze, European Lab Nonlinear Spect, Sesto Fiorentino, Italy; CNR, INO, Florence, Italy; Quantum Sci & Technol Arcetri QSTAR, Florence, Italy; Univ Napoli Federico II, Naples, Italy; CNR, INO, Sesto Fiorentino, Italy; Univ Campus Biomed Roma, Dipartimento Ingn, Rome, Italy.

Abstract: A new class of superfluids and superconductors with spatially periodic modulation of the superfluid density is arising 1-12 . It might be related to the supersolid phase of matter, in which the spontaneous breaking of gauge and translational symmetries leads to a spatially modulated macroscopic wavefunction 13-16 . This relation was recognized only in some cases 1,2,5-9 and there is the need for a universal property quantifying the differences between supersolids and ordinary matter, such as the superfluid fraction, which measures the reduction in superfluid stiffness resulting from the spatial modulation 16-18 . The superfluid fraction was introduced long ago 16 , but it has not yet been assessed experimentally. Here we demonstrate an innovative method to measure the superfluid fraction based on the Josephson effect, a ubiquitous phenomenon associated with the presence of a physical barrier between two superfluids or superconductors 19 , which might also be expected for supersolids 20 , owing to the spatial modulation. We demonstrate that individual cells of a supersolid can sustain Josephson oscillations and we show that, from the current-phase dynamics, we can derive directly the superfluid fraction. Our study of a cold-atom dipolar supersolid 7 reveals a relatively large sub-unity superfluid fraction that makes realistic the study of previously unknown phenomena such as partially quantized vortices and supercurrents 16-18 . Our results open a new direction of research that may unify the description of all supersolid-like systems. A new method based on the Josephson effect is described, allowing to measure the superfluid fraction of a supersolid, which captures the effect of spatially periodic modulation leading to reduction in the stiffness of superfluids.

Journal/Review: NATURE

More Information: Financed by the European Union (ERC, SUPERSOLIDS, no. 101055319) and by the QuantERA Programme that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement nos. 731473 and 101017733, projects MENTA, SQUEIS and MAQS, with funding organization Consiglio Nazionale delle Ricerche. We acknowledge financial support from PNRR MUR project PE0000023-NQSTI financed by the European Union – Next Generation EU. We gratefully acknowledge technical assistance from A. Barbini, A. Hajeb, F. Pardini, M. Tagliaferri and M. Voliani.
KeyWords: Pair Density Wave; Einstein
DOI: 10.1038/s41586-024-07361-9

Citations: 2
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