Fig. 1
From: Universal superconducting precursor in three classes of unconventional superconductors
Nonlinear response of four perovskite-based superconductors above Tc. a Strontium titanate SrTiO3 (STO) doped with 1 at.% of Nb, with a Tc of 350 mK. b Strontium ruthenate Sr2RuO4 (SRO), with a Tc of 1.51 K. c Slightly underdoped lanthanum strontium cuprate La2-xSrxCuO4 (LSCO), with a Tc of ~ 36 K (Sr doping level of 14%). d Slightly underdoped mercury barium cuprate HgBa2CuO4+δ (Hg1201), with a Tc of ~ 94 K. Measurements on four other Hg1201 samples are presented in Supplementary Note 3 and Supplementary Fig. 4, with essentially the same results. Arrows indicate the respective Tc values. For the three lamellar compounds b–d, the magnetic field is perpendicular to the transition-metal-oxygen planes, whereas for STO it is along one of the high-symmetry cubic directions. The four oxides show an exponential tail that stretches over at least two orders of magnitude, and with a slope that is approximately independent of excitation frequency. The low-frequency results are raw data, whereas the high-frequency results were multiplied by a constant to coincide with the low-frequency measurements. The constants depend on the setup and sample penetration depth, and are 0.7, 5, and 0.2 for STO, SRO, and LSCO, respectively (Hg1201 is measured at only one frequency)
