Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU
Dr Alex Eaton, Quantum Matter Group, University of Cambridge
Prof. Amalia Coldea
Abstract
Few known materials host two or more distinct superconducting phases. A spectacular example is the heavy fermion metamagnet UTe2, which for various conditions of applied pressure and magnetic field has been found to host up to five separate superconductive states. This talk will introduce the phenomenology of spin-triplet superconductivity, and outline the progress made into understanding the exotic superconductivity of UTe2 since its discovery in 2019. I will review our recent high magnetic field experiments on this material, which have focussed on (i) determining the normal-state electronic structure by quantum oscillation measurements, and (ii) mapping the rich multi-dimensional phase landscape by measuring a new generation of ultra-clean crystals. Remarkably, we have recently found that UTe2 has a higher superconducting critical temperature for B > 40 T than it does for B = 0 T. Furthermore, by performing pulsed field measurements up to 80 T we have discovered that magnetic field-induced superconductivity in UTe2 is anchored to a quantum critical phase boundary marked by the suppression of a first-order metamagnetic transition to zero temperature at a quantum critical end point (QCEP). Because this transition is sensitive to magnetic field components in each of the three orthogonal axes of Cartesian magnetic field space, this leads to the presence of an extended line of quantum criticality tracing out the locus of QCEPs in three-dimensional magnetic field space - a novel form of quantum critical phase boundary.