Uniaxial strain dependence of superconductivity in 2H-NbSe_2

Uniaxial strain breaks crystal symmetries and couples to anisotropic electronic phenomena in solids. Such anisotropic electronic phenomena are commonly observed in unconventional superconductors such as the pnictides [1,2] and strontium ruthenate [3,4]. While spectacular effects on superconducting order have been observed in these compounds, the interaction between electronic anisotropies and superconductivity remains to be clarified. In this talk we will present data on the application of uniaxial strain to a conventional superconductor 2H-NbSe_2, which also hosts a charge density wave. We find a linear coupling of superconducting Tc to the anisotropic strain in line with previous work [5]. However, we also find a surprisingly large quadratic coupling of Tc to uniaxial strain, indicating the importance of uniaxial order or fluctuations in this material. We will discuss theoretical scenarios for how this electronic anisotropy and its coupling to superconductivity can be explained.
[1] Jiun-Haw Chu et al., Science 337, 710 (2012)
[2] Hsueh-Hui Kuo et al., Science 352, 958 (2017)
[3] Clifford W. Hicks et al., Science 344, 283 (2014)
[4] Alexander Steppke et al., Science 355, 148 (2017)
[5] C. Meingast et al., Phys. Rev. B, 41 11219 (1990)