Field-induced anomaly in the anisotropic non-Fermi-liquid normal state of UBe$_{13}$

TL;DR

This study demonstrates that UBe$_{13}$ exhibits a strongly anisotropic normal-state response under magnetic fields, with non-Fermi-liquid behavior at low fields that evolves into Fermi-liquid behavior as the field increases. High-resolution magnetization and specific-heat data reveal field-induced anomalies in the normal state, notably along [111], accompanied by a pronounced nonlinear fifth-order susceptibility, indicating field-driven multipolar correlations of $5f$ electrons and associated Fermi-surface reconstruction. The superconducting state shows an unusually large $H_{c2}(0)$ relative to the Pauli limit and potential odd-parity pairing, with the thermodynamic anomalies in the normal state linked to changes in the electronic density of states near the superconducting region. Overall, the work highlights a close relationship between field-induced multipolar correlations, NFL behavior, and Fermi-surface changes, offering key clues to the pairing mechanism and the nature of the anomalous normal state in this uranium-based heavy-fermion system.

Abstract

We report the results of high-resolution dc magnetization and specific-heat measurements at very low temperatures for a single crystal \color{black} of UBe$_{13}$ in magnetic fields applied along the [001] and [111] directions, in both the normal and superconducting states. In the normal state, magnetic susceptibility $χ(T) = M/H$ exhibits a logarithmic temperature dependence over a wide temperature range (1-20 K). However, with increasing field, this non-Fermi-liquid (NFL) behavior of $χ(T) $ at low temperatures is suppressed. Moreover, a susceptibility maximum occurs below 4 T, whereas Fermi-liquid coherence is recovered above 8 T. In addition, thermodynamic anomalies ($T_{\rm A}$ and $H_{\rm A}$) occur in both magnetic susceptibility and specific heat at intermediate fields (6--10 T) along the [111] direction. Furthermore, a nontrivial fifth-order nonlinear susceptibility is observed in the normal-state magnetization of UBe$_{13}$. These results suggest a close relationship between the field-induced multipolar correlations of $5f$-electron degrees of freedom and the Fermi-surface reconstruction accompanying the crossover from the NFL state to the Fermi-liquid state in UBe$_{13}$.

Figures (14)

• Figure 1: Temperature dependence of magnetic susceptibility of UBe$_{13}$ in $H ||$[001] at 0.1 T. Inset: temperature dependence of inverse susceptibility, with solid line representing Curie--Weiss fitting.
• Figure 2: Magnetization curve of UBe$_{13}$ at the lowest temperature of 80 mK along $H ||$ [111], where the arrows denote the increasing and decreasing processes.
• Figure 3: Temperature dependence of the magnetic susceptibility ($\chi = M/H$) of UBe$_{13}$ for $H ||$ [001] at 1, 8, and 13 T.
• Figure 4: Temperature dependence of magnetic susceptibility ($\chi = M/H$) of UBe$_{13}$ along $H ||$ [111] at 1, 8, and 13 T.
• Figure 5: (a) Temperature dependence of magnetic susceptibility ($\chi = M/H$) of UBe$_{13}$ along $H ||$ [111] at 2, 3.5, 5, and 6 T. (b) Temperature dependence of $\chi = M/H$ at 6 T ($H ||$ [111]) with its temperature derivative $d(M/H)/dT$. Here, the light-blue shaded region denotes the observed anomaly ($T_{\rm A}^{\chi }$) in the normal state, defined as the maximum in $d(M/H)/dT$.