A superconducting material has no electrical resistance, so a current can pass through it without losing any energy. This is due to the coherent behaviour of electrons, analogous to photons in a laser. A classic property of superconductors is that they expel magnetic fields.
One class of superconductors, however, can form spontaneous magnetic fields in the superconducting state. This leads to breaking of time-reversal symmetry, which occurs when a physical system in a symmetric state ends up in an asymmetric state. These 'unconventional superconductors' are of particular interest due to their potential application in quantum computing and spintronics. One subset of these is noncentrosymmetric superconductors, which lack inversion symmetry.
The concept of a noncentrosymmetric superconductor that breaks TRS presents a promising platform for realising the intrinsic superconducting diode effect. This phenomenon enables ohmic current flow in one direction and dissipationless supercurrent in the other, and could revolutionise the field of quantum electronics.
In this paper, published in Advanced Materials, the researchers established that the Weyl semimetal HfRhGe fits these criteria, and is a noncentrosymmetric superconductor with strong spin orbit coupling that spontaneously breaks TRS in the superconducting state.
The team from Indian Institute of Science Education and Research Bhopal, Indian Institute of Technology Kanpur, Université de Sherbrooke, Technion-Israel Institute of Technology and ISIS used magnetisation and thermodynamic measurements alongside muon spectroscopy on MuSR.
Muon spectroscopy is a very sensitive probe for local magnetic field inside a sample, making it a key technique for investigating TRS breaking superconductors. Their zero-field µSR showed spontaneous TRS breaking in the superconducting state and transverse-field µSR and specific heat data showed evidence of an isotropic, fully gapped superconducting state.
“These observations collectively suggest HfRhGe as a potential candidate for a loop supercurrent superconducting ground state involving multiple bands, opening new avenues for exploring unconventional superconductivity," the authors say.
“Our comprehensive investigation of HfRhGe, employing a synergistic combination of advanced experimental techniques and rigorous theoretical analyses, unveils a fascinating interplay between the topological band structure and unconventional superconductivity."
“This unique synergy paves the way for the development of highly efficient intrinsic superconducting diodes, with exciting applications in topological quantum computing and dissipationless quantum electronics - offering fundamental insights and technological advancements."
Further information
The full paper can be found at DOI: 10.1002/adma.202415721
