Relativistic Ginzburg-Landau equation: An investigation for overdoped cuprate films
By introducing the imaginary time, Gor'kov's Ginzburg-Landau equation at zero temperature can be extended to an exact relativistic form without any phenomenological parameter, which is intended to describe the zero-temperature overdoped cuprate. By using such a relativistic equation, we have shown that the two-class scaling observed in the overdoped side of single-crystal $La_{2-x}Sr_xCuO_4$ (LSCO) films [Nature 536, 309-311 (2016)] can be derived exactly. In this paper, we further test the validity of the relativistic Ginzburg-Landau equation. By applying the perturbation method into this equation, we theoretically predict that near the superconductor-metal transition point in the overdoped side of LSCO films, the zero-temperature correlation length $\xi(0)$ and the transition temperature $T_c$ should yield a novel scaling $\xi(0)\propto T_c^{-\sigma}$ with a critical exponent $\sigma \approx 1.31 $ (up to the two-loop approximation). Here, we propose a diffraction experiment between $X$-rays and zero-temperature LSCO films to measure the critical exponent $\sigma$.