Z3-vestigial nematic order due to superconducting fluctuations in the doped topological insulators NbxBi2Se3 and CuxBi2Se3
Chang-Woo Cho, Junying Shen, Jian Lyu, Omargeldi Atanov, Qianxue Chen, Seng Huat Lee, Y. S. Hor, Dariusz Jakub Gawryluk, E. Pomjakushina, M. Bartkowiak, Matthias Hecker, Jörg Schmalian, Rolf Lortz
Abstract
Abstract 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 Z 3 , i.e., three-state Potts-model symmetry. Thermal expansion, specific heat and magnetization measurements of the doped topological insulators Nb x Bi 2 Se 3 and Cu x Bi 2 Se 3 reveal that this symmetry breaking occurs at $${{T}}_{\mathrm{nem}} \simeq 3.8\,K$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mi>nem</mml:mi></mml:mrow></mml:msub><mml:mo>≃</mml:mo><mml:mn>3.8</mml:mn><mml:mspace/><mml:mi>K</mml:mi></mml:math> above $${T}_{{\mathrm{c}}} \simeq 3.25\,K$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow></mml:msub><mml:mo>≃</mml:mo><mml:mn>3.25</mml:mn><mml:mspace/><mml:mi>K</mml:mi></mml:math> , along with an onset of superconducting fluctuations. Thus, before Cooper pairs establish long-range coherence at T c , they fluctuate in a way that breaks the rotational invariance at T nem and induces a crystalline distortion.