Impact of tiny Fermi pockets with extremely high mobility on the Hall anomaly in the kagome metal CsV$_3$Sb$_5$

TL;DR

The study addresses the Hall anomaly observed in the kagome metal CsV$_3$Sb$_5$ by combining comprehensive magnetotransport measurements with a mobility-spectrum ($\mu$-spectrum) analysis and Kramers-Kronig separation to identify tiny Fermi pockets with extremely high mobility that form below the CDW transition. The approach quantifies electron and hole contributions to $\sigma_{xx}$ and $\sigma_{xy}$, revealing high-mobility carriers responsible for the non-monotonic Hall effect. Electron irradiation tunes mobility without major changes to the Fermi surface, and the non-monotonic Hall component scales as $\sigma_{xx}^2$, consistent with Drude skew scattering rather than intrinsic anomalous Hall or TRS-breaking topology. Quantum oscillations corroborate the persistence of certain Fermi surfaces across CDW and support the identification of small pockets with high mobility as the origin of the Hall anomaly. Overall, the work clarifies that the Hall anomaly in CsV$_3$Sb$_5$ arises from high-mobility tiny pockets rather than topological or TRS-driven effects, with implications for understanding kagome CDW materials.

Abstract

The kagome metal CsV$_3$Sb$_5$ exhibits an unusual charge-density-wave (CDW) order, where the emergence of loop current order that breaks time-reversal symmetry (TRS) has been proposed. A key feature of this CDW phase is a non-monotonic Hall effect at low fields, often attributed to TRS breaking. However, its origin remains unclear. Here, we conduct comprehensive magnetotransport measurements on CsV$_3$Sb$_5$ and, through mobility spectrum analysis, identify the formation of tiny Fermi pockets with extremely high mobility below the CDW transition. Furthermore, electron irradiation experiments reveal that the non-monotonic Hall effect is significantly suppressed in samples with reduced mobility, despite no substantial change in the electronic structure. These results indicate that the non-monotonic Hall effect originates from these tiny Fermi pockets with high mobility carriers rather than anomalous Hall mechanisms, providing new insights into understanding the Hall anomaly in this kagome system.

Figures (6)

• Figure S1: (a)-(c) Normalized mangetoresistance $\rho_{xx}(H)/\rho_{xx}(0)$ of (a) pristine (0 C/cm$^2$), (b) 3 C/cm$^2$, and (c) 8.6 C/cm$^2$ irradiated CsV$_3$Sb$_5$ samples as a function of magnetic field measured at several temperatures. (d)-(f) Hall resistance $\rho_{yx}(H)$ of (d) pristine (0 C/cm$^2$), (e) 3 C/cm$^2$, and (f) 8.6 C/cm$^2$ irradiated CsV$_3$Sb$_5$ samples as a function of magnetic field measured at several temperatures.
• Figure S2: Overview of the analysis process using the $\mu$-spectrum method.
• Figure S3: (a), (b) $X(H)$ and $Y(H)$ at 5 K for pristine CsV$_3$Sb$_5$, respectively. The red lines represent Lorentzian fits to the experimental results (blue). (c), (d) Comparison between experimental and fitting results for $\sigma_{xx}(H)$ and $\sigma_{xy}(H)$, respectively.
• Figure S4: (a) Oscillatory components extracted from the magnetoresistivity for the 3 C/cm$^2$ irradiated sample at various temperatures. (b) FFT spectrum of the 3 C/cm$^2$ irradiated sample at various temperatures. Three peaks ($\alpha/\beta$, $\gamma$, and $\delta$ orbits) are observed, in addition to the first peak at the lowest frequency ($\sim$3 T), which is an artifact of the FFT. (c) Temperature dependence of FFT amplitude for each peak. The solid lines represent the Lifshitz-Kosevich formula. (d) Landau fan diagram plot of the pristine and 3 C/cm$^2$ irradiated CsV$_3$Sb$_5$ samples.
• Figure S5: (a)-(c) Non-monotonic components of the Hall conductivity for (a) pristine, (b) 3 C/cm$^2$, and (c) 8.6 C/cm$^2$ irradiated CsV$_3$Sb$_5$ samples.