Abstract
A theoretical study is reported on the origin of an extremely high upper critical field T observed in with the transition temperature –2 K, which exceeds the conventional orbital depairing limit set by the Fermi velocity and 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 an external field. This produces the reduced internal field by canceling it via magnetization. We formulate a theory within the Ginzburg-Landau framework to describe this orbital limit violation and analyze experimental data on the upper critical fields for various field orientations in . We show that the orbital limit violation for a spin-triplet SC, as well as the Pauli-Clogston limit violation for a spin-singlet SC, constitutes a complete and useful framework for examining the high field physics of superconductors in the clean limit.
1 More- Received 12 January 2023
- Revised 24 April 2023
- Accepted 9 June 2023
DOI:https://doi.org/10.1103/PhysRevB.107.224512
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