Possible topological protection and superconducting proximity effects in surface states of HfNiSn single crystals*

Surface states of HfNiSn single crystals were shown to exhibit unconventional properties like nonlocal transport, time-reversal symmetry breaking in the absence of external fields or magnetism, and nonlinear I(V) characteristics indicating electronic correlations [1], possible characteristics of a correlated topological state similar to a quantum Hall system. Oscillations in the magnetoresistance suggest quantum interference with coherence lengths up to 1 μm. The combination of quantum Hall edges or similar chiral one-dimensional states and superconductors is particularly attractive, as such junctions are expected to host the elusive Majorana fermions that could provide a possible platform for topological quantum computing, where the chiral nature of quantum Hall edge states could enable braiding operations. Our first tests of metal deposition on HfNiSn single crystals show promising results, where proximity to superconducting tin or niobium leads to conductance steps of approximately 0.5 e²/h. We further observe a clear disruption of quantum interference patterns at the superconducting transition, and magnetoresistance features associated with the critical field that can be traced up to 80 K.
[1] Steinke et al., arXiv:1805.06337