Nonunitary triplet superconductivity tuned by field-controlled magnetization: URhGe, UCoGe, and UTe2

Abstract

We report on a theoretical study on ferromagnetic superconductors URhGe and UCoGe and identify the pairing state as a nonunitary spin-triplet one with time-reversal symmetry broken, analogous to the superfluid He3−A phase. A recently found superconductor UTe2 with almost ferromagnetism is analyzed by the same manner. Through investigating their peculiar upper critical field Hc2 shapes, it is shown that the pairing symmetry realized in all three compounds can be tuned by their magnetization curves under applied fields. This leads to the reentrant Hc2 in URhGe, an S-shaped in UCoGe and an L-shaped Hc2 in UTe2 observed for the magnetic hard b-axis direction. The identification with double chiral form d(k)=(b̂+iĉ)(kb+ikc) in UTe2 naturally enables us to understand (1) multiple phases with A1, A2, and A0 phases observed under pressure, (2) the enhanced reentrant Hc2 for the off-axis direction associated with first-order metamagnetic transition, and (3) Weyl point nodes oriented along the magnetic easy a axis. All three compounds are found to be topologically rich solid-state materials worth further investigation.

Source-reported materials — not catalogue approval

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