Imaging the Anisotropic Non-linear Meissner Effect in the Millikelvin Range

The anisotropic non-linear Meissner effect of unconventional superconductors, which gives information about gap nodal structure, has been observed by measurements of anisotropic photoresponse for temperatures down to about 3 Kelvin.[1] Since the anisotropy of photoresponse originates from the non-linear Meissner effect coefficient, and theory predicts a strong temperature dependence for the photoresponse at temperatures below $0.1T_c$,[2] it will be interesting to measure photoresponse in that range. We are building a laser scanning microscope around a dilution refrigerator, and plan to measure photoresponse of unconventional superconductors in the millikelvin temperature range to test the predictions. Reference: $[1]$ A. P. Zhuravel, B. G. Ghamsari, C. Kurter, P. Jung, S. Remillard, J. Abrahams, A. V. Lukashenko, A. V. Ustinov, and S. M. Anlage, "Imaging the Anisotropic Nonlinear Meissner Effect in Nodal $\text{YBa}_2\text{Cu}_3\text{O}_{7-\delta}$ Thin-Film Superconductors" Phys. Rev. Lett. 110, 087002, 2013. $[2]$ T. Dahm and D.J. Scalapino, "Theory of Intermodulation in a Superconducting Microstrip Resonator", Journal of Applied Physics, vol. 81, pp. 2002-2009, 1997.