Nonreciprocal Meissner response in parity-mixed superconductors

The parity breaking gives rise to rich superconducting properties through the\nadmixture of even and odd-parity Cooper pairs. A new light has been shed on\nparity-breaking superconductors by recent observations of nonreciprocal\nresponses such as the nonlinear optical responses and the superconducting diode\neffect. In this Letter, we demonstrate that the nonreciprocal responses are\ncharacterized by a unidirectional correction to the superfluid density, which\nwe call nonreciprocal superfluid density. This correction leads to the\nnonreciprocal Meissner effect, namely, asymmetric screening of magnetic fields\ndue to the nonreciprocal magnetic penetration depth. Performing a microscopic\nanalysis of an exotic superconductor UTe$_2$ and examining the temperature\ndependence and renormalization effect, we show that the nonreciprocal Meissner\neffect is useful to probe parity-mixing properties and gap structures in\nsuperconductors.\n