Enhanced spin triplet superconductivity due to Kondo destabilization

Abstract

In a Kondo lattice system, suppression of effective Kondo coupling leads to the breakdown of the heavy-electron metal and a change in the electronic structure. Spin triplet superconductivity in the Kondo lattice UTe2 appears to be associated with spin fluctuations originating from incipient ferromagnetic order. Here we show clear evidence of twofold enhancement of spin-triplet superconductivity near the pressure-driven suppression of the Kondo coherence, implying that superconductivity is strengthened by the affiliated growth of both spin and charge fluctuations. The coherent Kondo state discontinuously transitions to ferromagnetic order at higher pressures. Application of magnetic field tunes the system back across a first-order phase boundary. Straddling this phase boundary, we find another example of reentrant superconductivity in UTe2. In addition to spin fluctuations associated with ferromagnetism, our results show that a Kondo-driven Fermi surface instability may be playing a role in stabilizing spin triplet superconductivity.