Magnetic signatures of pressure-induced multicomponent superconductivity in UTe$_2$

Abstract: The phase diagram of the heavy fermion compound UTe$_2$ contains multiple superconducting phases, several of which show characteristics of odd-parity pairing. We have investigated the pressure dependence of the superconducting transition in high-quality crystals of UTe$_2$ by tracking its signature in the magnetic susceptibility $\chi(T)$. A single, sharp superconducting transition is observed at low pressures 0.3 GPa. At higher pressure, a second feature emerges in $\chi(T)$, which is located at the lower-temperature thermodynamic phase boundary previously identified in specific heat measurements. This second transition anomaly in $\chi(T)$ can be attributed to a step change in the London penetration depth, providing direct evidence for a change in the superconducting order parameter of UTe$_2$. Thermodynamic constraints suggest that the low temperature, high pressure superconducting state is distinct from zero pressure superconductivity as well as from the high pressure, high temperature superconducting state, raising the possibility of multicomponent superconductivity in high pressure UTe$_2$.