Observation and control of nematic superconductivity in doped Bi2Se3

Shingo Yonezawa
Kyoto University
Wednesday, January 15, 2020
4:00 pm
NS2 1201
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 topological-superconductor candidates AxBi2Se3 (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.
As an important next step toward clarification of fundamental issues such as the Cooper-pair glue or the mechanism determining the nematic director, we seek for strong coupling between the nematic superconductivity and an external symmetry breaking field. We recently succeeded in controlling nematic superconductivity in SrxBi2Se3, via external uniaxial strain [5]. By applying uniaxial strain in situ using a piezo-based uniaxial-strain device [6], we reversibly controlled the superconducting nematic domain structure. The suppression of subdomains indicates that the Δ4y state is most favored under compression. This fact determines the coupling parameter between nematic superconductivity and uniaxial distortion.
In this talk, I overview experiments on nematic superconductivity, with some focus on our specific-heat study of CuxBi2Se3[3]. I then explain our recent demonstration of uniaxial-strain control of nematic superconductivity in SrxBi2Se3 [5,6]. 

[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., arXiv: 1910.03252.
[6] I. Kostylev, S. Yonezawa, Y. Maeno, J. Appl. Phys. 125, 082535 (2019).
Jing Xia