A peak in the critical current for quantum critical superconductors

Generally, studies of the critical current I(c) are necessary if superconductors are to be of practical use, because I(c) sets the current limit below which there is a zero-resistance state. Here, we report a peak in the pressure dependence of the zero-field I(c), I(c)(0), at a hidden quantum critical point (QCP), where a continuous antiferromagnetic transition temperature is suppressed by pressure toward 0 K in CeRhIn(5) and 4.4% Sn-doped CeRhIn(5). The I(c)(0)s of these Ce-based compounds under pressure exhibit a universal temperature dependence, underlining that the peak in zero-field I(c)(P) is determined predominantly by critical fluctuations associated with the hidden QCP. The dc conductivity σ(dc) is a minimum at the QCP, showing anti-correlation with I(c)(0). These discoveries demonstrate that a quantum critical point hidden inside the superconducting phase in strongly correlated materials can be exposed by the zero-field I(c), therefore providing a direct link between a QCP and unconventional superconductivity.