Unconventional Meissner screening induced by chiral molecules in a conventional superconductor

Abstract

The coupling of a superconductor (SC) to a different material often results in a system with unconventional superconducting properties. A conventional SC is a perfect diamagnet expelling magnetic fields out of its volume, a phenomenon known as the Meissner effect. Here, we show that the simple adsorption of a monolayer of chiral molecules (ChMs), which are nonmagnetic in solution, onto the surface of a conventional SC can markedly change its diamagnetic Meissner response. By measuring the internal magnetic field profile in superconducting Nb thin films under an applied transverse field by low-energy muon spin rotation spectroscopy, we demonstrate that the local field profile inside Nb is considerably modified upon molecular adsorption in a way that also depends on the applied field direction. The modification is not limited to the ChMs/Nb interface, but it is long ranged and occurs over a length scale comparable with the superconducting coherence length. Zero-field muon spin spectroscopy measurements in combination with our theoretical analysis show that odd-frequency spin-triplet states induced by the ChMs are responsible for the modification of the Meissner response observed inside Nb. These results indicate that a ChMs/SC system supports odd-frequency spin-triplet pairs due to the molecules acting as a spin-active layer, and therefore, they imply that such a system can be used as a simpler alternative to SC/ferromagnet or SC/topological insulator hybrids for the generation and manipulation of unconventional spin-triplet superconducting states.