Speaker
Description
Superconductors that spontaneously break rotational symmetry in their electronic ground state are called nematic superconductors. Cu$_x$Bi$_2$Se$_3$ and CaSn$_3$ are two notable examples that have been studied extensively. Yet, proving the existence of the nematic superconducting state is challenging. Recent theoretical work predicts that odd-parity nematic SC should exhibit a unique magnetic response to external fields, consisting of skyrmion-stripe chains of spatially separated half-quantum vortices. The interplay of their two length scales, the distance between chains and the separation of skyrmions within a chain, leads to a double-peaked structure in the local magnetic field probability density distribution, very different from the conventional single-peak structure associated with standard vortex lattices.
To date, muon-spin rotation (µSR) is the most effective method to detect this skyrmion-stripe pattern, allowing us to identify the double peak structure by the Fourier transform of the time-dependent µSR polarization. We illustrate this by reporting our recent transverse-field µSR results on high-purity LiFeAs single crystals. Our results reveal a splitting of the SC peak in a 30-mT magnetic field parallel to the c-axis, which persists up to about 6 K. Our discovery supports the occurrence of nematic superconductivity in LiFeAs and provides a new pathways to systematically study this new type of SC.
