Anisotropic collapse of electronic correlations in the ferromagnet UGe$_2$ under high magnetic field

TL;DR

This work demonstrates a strong anisotropic response of electronic correlations in the ferromagnet UGe$_2$ under pulsed magnetic fields up to 60 T. Electrical resistivity reveals rapid suppression of FM-related signatures along the easy axis $\mathbf{a}$, while hard-axis directions $\mathbf{b},\mathbf{c}$ show much weaker field effects, indicating Ising-like fluctuations that shape the low-temperature transport and Fermi-surface topology. Quantum oscillations at $H>50$ T for $\mathbf{H}\parallel\mathbf{b}$ unveil a cylindrical Fermi surface with a large cross-sectional area ($F=7600$ T) and heavy cyclotron mass ($m_c=(14\pm3)m_0$), reinforcing a quasi-two-dimensional electronic structure. The results connect magnetic anisotropy, electronic correlations, and Fermi-surface features, and suggest that field and pressure tune different aspects of the fluctuations relevant to ferromagnetism and potentially superconductivity in this U-based system.

Abstract

We present electrical-resistivity measurements on the prototypical heavy-fermion ferromagnet UGe$_2$ under pulsed magnetic field up to 60~T. An anisotropic field-induced suppression of the electronic correlations is revealed. The electrical resistivity strongly decreases when a magnetic field $\mathbf{H}$ is applied along the easy magnetic axis $\mathbf{a}$, while it remains almost unchanged when $\mathbf{H}$ is applied along the hard magnetic axes $\mathbf{b}$ and $\mathbf{c}$. The field-induced destabilization of the ferromagnetic state is also anisotropic: the anomaly at the Curie temperature $T_C$ disappears in fields higher than $\gtrsim1$~T for $\mathbf{H}\parallel\mathbf{a}$ and in fields higher than $\gtrsim20$~T for $\mathbf{H}\parallel\mathbf{b},\mathbf{c}$. At temperatures below 2~K, we observe quantum oscillations in fields larger than 50~T applied along $\mathbf{b}$, which support the presence of a two-dimensional Fermi surface similar to that previously observed at low fields.

Figures (12)

• Figure 1: Magnetic-field dependence of the electrical resistivity $\rho_{zz}$ of UGe$_2$ at temperatures from 500 mK to 80 K under magnetic fields (a) $\mathbf{H}\parallel\mathbf{a}$, (b) $\mathbf{H}\parallel\mathbf{b}$, and (c) $\mathbf{H}\parallel\mathbf{c}$.
• Figure 2: Temperature dependence of $\rho_{zz}$ of UGe$_2$ at constant magnetic fields (a) $\mu_0\mathbf{H}\parallel\mathbf{a}$, (b) $\mu_0\mathbf{H}\parallel\mathbf{b}$, and (c) $\mu_0\mathbf{H}\parallel\mathbf{c}$ up to 50 T. Temperature dependence of $\Delta\rho_{zz}$, estimated after subtraction of a background resistivity $\rho_{zz}^{BG} = \rho_{zz}(\mathbf{H}\parallel\mathbf{a}, \rm{50~T})$, at constant magnetic fields (d) $\mu_0\mathbf{H}\parallel\mathbf{a}$, (e) $\mu_0\mathbf{H}\parallel\mathbf{b}$, and (f) $\mu_0\mathbf{H}\parallel\mathbf{c}$ up to 50 T.
• Figure 3: Temperature dependance of $\partial\rho_{zz}/\partial T$ of UGe$_2$ at constant magnetic fields (a) $\mu_0\mathbf{H}\parallel\mathbf{a}$, (b) $\mu_0\mathbf{H}\parallel\mathbf{b}$, and (c) $\mu_0\mathbf{H}\parallel\mathbf{c}$ up to 50 T. $\partial\rho_{zz}/\partial T$ versus $T$ in reduced temperature and magnetic field windows, with $T$ from 45 to 60 K and (d) $\mu_0\mathbf{H}\parallel\mathbf{a}$ up to 1 T, (e) $\mu_0\mathbf{H}\parallel\mathbf{b}$ and (f) $\mu_0\mathbf{H}\parallel\mathbf{c}$ up to 10 T.
• Figure 4: Magnetic-field-temperature phase diagram of UGe$_2$ under a magnetic field (a) $\mathbf{H}\parallel\mathbf{a}$, (b) $\mathbf{H}\parallel\mathbf{b}$, and (c) $\mathbf{H}\parallel\mathbf{c}$. FM and PPM label the ferromagnetic phase and the polarized paramagnetic regime, respectively.
• Figure 5: Shubnikov-de-Haas quantum oscillations (a) in $\rho_{zz}$ versus $H$ and (b) in $\partial\rho_{zz}/\partial H$ vs $1/H$ of UGe$_2$ at temperatures from 500 mK to 1.55 K under a magnetic field $\mu_0\mathbf{H}\parallel\mathbf{b}$ from 51 to 57.5 T, (c) FFT spectra of $\partial\rho_{zz}/\partial H$ vs $1/H$ at temperatures from 500 mK to 1.55 K and (d) temperature dependence of the amplitude of the peak observed in FFT spectra at the frequency $F=7600$ T and its fit by the Lifshitz-Kosevich formula (dashed grey line).