Evidence for a field-induced Lifshitz transition in the Weyl semimetal CeAlSi

TL;DR

This work demonstrates a field-induced Lifshitz transition in the Weyl semimetal CeAlSi, evidenced by an abrupt shift in Shubnikov–de Haas frequencies near $H_c \approx 14$ T when the system is in its ferromagnetic state. By combining high-field transport up to $68$ T with detailed quantum oscillation analysis, the authors identify a transition from a single low-field pocket ($\gamma \approx 20\,\mathrm{T}$) to two high-field pockets ($\alpha \approx 150\,\mathrm{T}$, $\beta \approx 50\,\mathrm{T}$), signaling a topological reconstruction of the Fermi surface. The results argue against Zeeman-driven renormalisation or heavy-fermion effects as the primary mechanism and instead highlight the role of magnetic exchange (RKKY) in tuning Weyl-node positions relative to the Fermi level. This work underscores how ferromagnetic order can drive topological electronic transitions in magnetic Weyl semimetals and informs strategies to control Weyl physics via external fields.

Abstract

The Weyl semimetal CeAlSi crystallises in the noncentrosymmetric tetragonal space group $I4_1md$ and exhibits ferromagnetic order below 8 K, thereby breaking both spatial inversion and time-reversal symmetries. This unique combination of properties establishes CeAlSi as a model system for studying the interplay between non-trivial topological states and strong electron correlations. In this work, we report observations of Shubnikov-de Haas oscillations in the electrical resistivity under magnetic fields up to 68 T applied parallel to the [001] crystallographic axis. Our measurements reveal an abrupt change in the oscillation frequencies near 14 T, which is indicative of a field-induced Lifshitz transition. Additionally, our results are consistent with the ferromagnetic order bringing the Weyl nodes closer to the Fermi level in CeAlSi. Furthermore, they suggest that the RKKY interaction plays an important role.

Figures (4)

• Figure 1: (a) Electrical resistivity ($\rho$) as a function of temperature for CeAlSi. Left inset: Magnified view of the low temperature region. Right inset: Longitudinal ($\rho$) and Hall resistivity ($\rho_{H}$) as a function of magnetic field applied parallel to $[001]$ at 2 K. The solid lines are two-band model fits used to estimate the charge carrier density. (b) Magnetoresistance, ${\rm MR}=[\rho(H)-\rho(H=0)]/\rho(H=0)$, as a function of magnetic field applied parallel to $[001]$ at different temperatures. Inset: Temperature evolution of the MR value at 68 T. The dashed line indicates $T_{C}$.
• Figure 2: Electrical resistivity ($\Delta \rho$) obtained by subtracting a smooth background (first order polynomial) as a function of inverse magnetic field at (a) magnified at 0.7 K and (b) at different temperatures to illustrate the temperature evolution. The dashed lines indicate the putative Lifshitz transition.
• Figure 3: (a) Electrical resistivity ($\Delta \rho$) obtained by subtracting a smooth background ($7^{\rm th}$ order polynomial) as a function of inverse magnetic field at several temperatures for the low field region ($4 {\rm~T} \leqslant \mu_{0}H \leqslant 14.5 {\rm~T}$). (b) Amplitude of the FFT performed on the curves shown in (a) as a function of frequency at different temperatures. Inset: Amplitudes as a function of temperature and the solid line is a Lifshitz-Kosevich fit.
• Figure 4: (a) Electrical resistivity ($\Delta \rho$) obtained by subtracting a smooth background ($5^{\rm th}$ order polynomial) as a function of inverse magnetic field at several temperatures for the high field region ($20 {\rm~T} \leqslant \mu_{0}H \leqslant 68 {\rm~T}$). (b) Amplitude of the FFT performed on the curves shown in (a) as a function of frequency at different temperatures. Inset: Amplitudes as a function of temperature and the solid lines are Lifshitz-Kosevich fits.