Violation of the orbital depairing limit in a non-unitary state --on the high field phase in the heavy Fermion superconductor UTe${}_2$--

Abstract

A theoretical study is reported on the origin of extremely high upper critical field $\sim$70T observed in UTe${}_2$ with the transition temperature T${}_{\mathrm{c}}$=1.6K-2K, far exceeding the conventional orbital depairing limit set by the Fermi velocity and T${}_{\mathrm{c}}$ for a superconductor (SC) in the clean limit. We investigate possible violation of the orbital limit in terms of a spin-triplet nonunitary state, which is effectively coupled to the underlying magnetization induced by external field. This in turn produces the reduced internal field by cancelling it via magnetization. We formulate a theory within Ginzburg-Landau framework to describe this orbital limit violation and analyze experimental data on the upper critical fields for various field orientations in UTe${}_2$. It is pointed out that the orbital limit violation for a spin-triplet SC together with the Pauli-Clogston limit violation for a spin-singlet SC constitutes a complete and useful framework to examine the high field physics in superconductors in the clean limit.

11 pages, 7 figures

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Cited by in corpus (4)

• Superconducting Diode Effect in Multiphase Superconductors
• Clear Reduction in Spin Susceptibility and Superconducting Spin Rotation for $H\parallel a$ in the Early-Stage Sample of Spin-Triplet Superconductor UTe${}_2$
• Superconducting Order Parameters in Spin Space Groups: Methodology and Application
• Theoretical studies on off-axis phase diagrams and Knight shifts in UTe${}_2$ -- Tetra-critical point, d-vector rotation, and multiple phases