A state of matter with a multi-component order parameter can give rise to vestigial order. In the vestigial phase, the primary order is only partially melted, leaving a remaining symmetry breaking behind, an effect driven by strong classical or quantum fluctuations. Vestigial states due to primary spin and charge-density-wave order have been discussed in iron-based and cuprate materials. Here we present the observation of a partially melted superconductivity in which pairing fluctuations condense at a separate phase transition and form a nematic state with broken Z3, i.e., three-state Potts-model symmetry. Thermal expansion, specific heat and magnetization measurements of the doped topological insulators NbxBi2Se3 and CuxBi2Se3 reveal that this symmetry breaking occurs at Tnem ≃ 3.8K above Tc ≃ 3.25K, along with an onset of superconducting fluctuations. Thus, before Cooper pairs establish long-range coherence at Tc, they fluctuate in a way that breaks the rotational invariance at Tnem and induces a crystalline distortion.
C. w. Cho et al., "Z₃-Vestigial Nematic Order Due to Superconducting Fluctuations in the Doped Topological Insulators NbₓBi₂Se₃ and CuₓBi₂Se₃," Nature Communications, vol. 11, no. 1, Nature Research, Jun 2020.
The definitive version is available at https://doi.org/10.1038/s41467-020-16871-9
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16 Jun 2020