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Direct Observation of the Spillover of High Magnetic Field-induced SC3 Superconductivity Outside the Spin-Polarized State in UTe2

Zheyu Wu, Hanyi Chen, Theodore I. Weinberger, Mengmeng Long, David Graf, Andrej Cabala, Vladimir Sechovsky, Michal Valiska, Gilbert G. Lonzarich, F. Malte Grosche, Alexander G. Eaton

Abstract

In our recent study of the high magnetic field phase landscape of UTe$_2$ [Phys. Rev. X 15, 021019 (2025)] we found indirect evidence that the SC3 superconducting phase spills out beyond the first-order phase boundary of the spin-polarized state. This prior study was limited to a maximal field strength of 41.5 T, and mapped the $b-ac$ rotation plane. Here we measure a high quality sample with residual resistivity ratio RRR = 605 under rotations in the $b-c$ plane up to 45 T. This extended field range helps to unambiguously demonstrate the spillover of SC3 outside the polarized paramagnetic state. This is identified by the observation of zero resistance at low temperatures, for magnetic field strengths lower than the metamagnetic transition field resolved at higher temperatures. This observation is consistent with the scenario that electronic pairing of the SC3 phase is mediated by quantum critical fluctuations.

Direct Observation of the Spillover of High Magnetic Field-induced SC3 Superconductivity Outside the Spin-Polarized State in UTe2

Abstract

In our recent study of the high magnetic field phase landscape of UTe [Phys. Rev. X 15, 021019 (2025)] we found indirect evidence that the SC3 superconducting phase spills out beyond the first-order phase boundary of the spin-polarized state. This prior study was limited to a maximal field strength of 41.5 T, and mapped the rotation plane. Here we measure a high quality sample with residual resistivity ratio RRR = 605 under rotations in the plane up to 45 T. This extended field range helps to unambiguously demonstrate the spillover of SC3 outside the polarized paramagnetic state. This is identified by the observation of zero resistance at low temperatures, for magnetic field strengths lower than the metamagnetic transition field resolved at higher temperatures. This observation is consistent with the scenario that electronic pairing of the SC3 phase is mediated by quantum critical fluctuations.
Paper Structure (4 sections, 3 figures)

This paper contains 4 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Experimental methods
  3. Results
  4. Discussion

Figures (3)

  • Figure 1: Resistivity $\rho$ versus magnetic field strength $H$ for rotations by angle $\theta$ in the $b-c$ plane. 0$\degree$ corresponds to field oriented along the $b$-axis, while 90$\degree$ represents the $c$-axis. The inset plots a zoom-in for a subset of curves in the range 25$\degree \leq \theta \leq 39\degree$, which exhibit an anomalous maximum in $\rho(H)$. We take this maximum to indicate the onset of the SC3 state.
  • Figure 2: Temperature evolution of $\rho(H)$ with H tilted to $\theta = 25\degree$ for 0.4 K $\leq T \leq$ 10 K. The 8 K and 10 K curves have been rescaled by a factor of $1/8$ for ease of comparison. The vertical dashed line marks the value of $H$ where zero resistivity at low $T$ identifies the low-$H$ boundary of the SC3 state. At 8 K the sharp peak in $\rho(H)$ -- identifying the metamagnetic transition into the spin-polarized state at $H^*$ -- clearly occurs at a higher value of $H$ than the dashed line.
  • Figure 3: UTe$_2$ low-$T$ high-$H$ phase diagram for the $b-c$ rotation plane. All triangular data points are from this study. Square points and the red fit line for $H^*(\theta)$ are reproduced from tony2024enhancedpnas24data, while circular points are from qclqcldata. PPM stands for polarized paramagnet. The onset of SC3 is determined by the maximum in $\rho(H)$ of the curves in Fig. \ref{['fig:angles']}, while the SC3 region itself is defined by the observation of zero resistance.