Field-induced compensation of magnetic exchange as the possible origin of reentrant superconductivity in UTe${}_2$

Abstract

The potential spin-triplet heavy-fermion superconductor UTe${}_2$ exhibits signatures of multiple distinct superconducting phases. For field aligned along the $b$ axis, a metamagnetic transition occurs at $\hat{I}{¼}_0{H}_{\mathrm{m}}\approx 35$T. It is associated with magnetic fluctuations that may be beneficial for the field-reinforced superconductivity surviving up to $H_{\mathrm{m}}$. Once the field is tilted away from the $b$ towards the $c$ axis, a reentrant superconducting phase emerges just above $H_{\mathrm{m}}$. In order to better understand this remarkably field-resistant superconducting phase, we conducted magnetic-torque and magnetotransport measurements in pulsed magnetic fields. We determine the record-breaking upper critical field of $\hat{I}{¼}_0{H}_{c2}\approx 73$T and its evolution with angle. Furthermore, the normal-state Hall effect experiences a drastic suppression indicative of a reduced band polarization above $H_{\mathrm{m}}$ in the angular range around $30^{\circ }$ caused by a partial compensation between the applied field and an exchange field. This promotes the Jaccarino-Peter effect as a likely mechanism for the reentrant superconductivity above $H_{\mathrm{m}}$.

Main text: 29 pages, 4 figure; Supplement: 12 pages, 6 figures