Time-reversal symmetry breaking in superconductors through loop super-current order

Abstract

We propose a superconducting instability where microscopic supercurrent loops form spontaneously within a unit cell at the superconducting transition temperature with only uniform, onsite and intra-orbital singlet pairing. As a result of the circulating currents time-reversal symmetry is spontaneously broken in the superconducting state. Using Ginzburg-Landau theory, we describe in detail how these currents emerge in a toy model. We discuss the crystallographic symmetry requirements to realize such a state and show that they are met by the Re6X (X=Zr, Hf, Ti) family of time-reversal symmetry breaking, but otherwise seemingly conventional, superconductors. We estimate an upper bound for the resulting internal fields and find it to be consistent with recent muon-spin relaxation experiments.

10 pages, 3 figures (More references added)

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Cited by in corpus (6)

• Time-reversal symmetry breaking in the noncentrosymmetric Zr${}_3$Ir superconductor
• Spin-triplet superconductivity in Weyl nodal-line semimetals
• Nodeless superconductivity in Lu${}_{5-x}$Rh${}_6$Sn${}_{18+x}$ with broken time reversal symmetry
• Time reversal symmetry breaking and s-wave superconductivity in CaPd2Ge2: A $\mu$SR study
• Nodeless time-reversal symmetry breaking in the centrosymmetric superconductor Sc${}_5$Co${}_4$Si${}_{10}$ probed by muon-spin spectroscopy
• Spin-orbit-phonon interaction as an origin of helical-symmetry breaking spin-triplet superconducting state