Topological superconductivity, accompanying non-trivial topology in its superconducting wave function, has been one of the central topics in condensed-matter physics. During the recent extensive efforts to search for topological superconducting phenomena, nematic superconductivity, exhibiting spontaneous rotational symmetry breaking in bulk superconducting quantities, has been discovered in the bulk topological superconductors A_xBi₂Se₃ (A = Cu, Sr, Nb) [1]. In the in-plane field-angle dependence of various superconducting properties, such as the spin susceptibility [2], the specific heat [3], and the upper critical field [4], exhibit pronounced two-fold symmetric behavior although the underlying lattice has three-fold rotational symmetry.

More recently, we succeeded in controlling nematic superconductivity in Sr_xBi₂Se₃ via external uniaxial strain [5]. In the trigonal A_xBi₂Se₃ material, six kinds of nematic domains can be realized. By applying uniaxial strain in situ using a piezo-based uniaxial-strain device [6], we reversibly controlled the superconducting nematic domain structure. Namely, the multi-domain state under zero strain can be changed into a nearly single-domain state under 1% uniaxial compression along the a axis. This result indicates strong coupling between nematic superconductivity and lattice distortion. Moreover, this is the first demonstration of domain engineering using nematic superconductors.

In this talk, I overview experiments on nematic superconductivity, with a focus on our specific-heat study of Cu_xBi₂Se₃ [3]. I then explain our recent demonstration of uniaxial-strain control of nematic superconductivity in Sr_xBi₂Se₃ [5].

[1] For a recent review, see S. Yonezawa, Condens. Matter 4, 2 (2019).
[2] K. Matano et al., Nature Phys. 12, 852 (2016).
[3] S. Yonezawa et al., Nature Phys. 13, 123 (2017).
[4] Y. Pan et al., Sci. Rep. 6, 28632 (2016).
[5] I. Kostylev, S. Yonezawa et al., Nature Commun. 11, 4152 (2020).
[6] I. Kostylev, S. Yonezawa, Y. Maeno, J. Appl. Phys. 125, 082535 (2019).