Magnetic field-induced non-trivial Lifshitz transition in TaCo2Te2

Abstract

Magnetic-field-driven Lifshitz transitions are typically considered zero-temperature phenomena involving Fermi-surface reconstruction without symmetry breaking. Here, we report an unconventional Lifshitz transition in TaCo2Te2 that emerges exclusively within a narrow finite-temperature window under cooperative tuning by both temperature and magnetic field. Bulk-sensitive transport and thermoelectric measurements demonstrate continuous Fermi-surface renormalization at low temperatures, where the transition is sharply triggered by a critical magnetic field. Crucially, neutron diffraction reveals the absence of structural or magnetic phase transitions, while angle-resolved photoemission spectroscopy shows no spectral anomalies in electronic structure without magnetic field. These observations constrain the mechanism to a Zeeman-driven process invisible to equilibrium probes, establishing a paradigm where Fermi-surface topology is jointly controlled by temperature and magnetic field.

Figures (4)

• Figure 1: Crystal structure and electronic properties of TaCo$_2$Te$_2$. (a) The solved crystallographic unit cell of TaCo$_2$Te$_2$, composed of two monolayers stacked along the $c$ axis through weak van der Waals interactions; the unit cell is indicated by the red rectangle. (b) Crystal structure viewed along the $c$ axis. (c) Room-temperature X-ray diffraction (XRD) pattern of a TaCo$_2$Te$_2$ single crystal. Inset: photographic image of a representative grown crystal. (d,e) First-principles electronic band structures calculated along the high-symmetry path, shown (d) without and (e) with inclusion of spin–orbit coupling (SOC). (f) Three-dimensional Fermi surface topology obtained from SOC-inclusive calculations.
• Figure 2: A distinct anomaly around 30 K in the transport measurements - points to a potential reconstruction of the Fermi surface : Magneto-resistance - (a) Temperature dependence of resistivity measured under $H$ = 0, 5, and 9 T magnetic fields. Lower inset: schematic of a Hall bar device. (b) The field-dependent magnetoresistance with the magnetic field perpendicular to the ${c}$ axis up to 14 T, at 1.8 and 10 K. (c) Details of the quantum oscillations at 1.8 K, after background subtraction, demonstrating the high quality of the crystal. Conventional Hall effect - (d) Field dependence of $\rho_{xy}(H)$ at various temperatures for the out-of-plane (OOP) configurations. (e) The temperature dependence of the Hall coefficient $R_\text{H}$ = $d\rho_\text{xx}(H)/dH$ at the zero field limit. (f) Temperature dependence of the concentration for electron-type ($n_e$) and hole-type ($n_h$) carriers, obtained from Two-band model fitting. The lines serve as a guide to the eye. (g) Angle ($\theta$)-dependent study of $\rho_\text{xy}$ at different temperatures under a magnetic field of 9 T. Planar Hall effect - (h) Angular variation of $\rho^\text{PHE}_\text{xy}$, measured under different temperatures. The continuous line indicates the fitted curve. (i) The temperature dependence of the PHE amplitude ($\rho^\text{PHE}_\text{xy}$), shown by hollow cubes, exhibits a pronounced maximum at 30 K. For these transport measurements, we used a flake with a thickness of about 51 nm.
• Figure 3: Thermelectric study : (a) Schematic diagram of the device for thermoelectric measurement. The sample is oriented with the magnetic field applied along the $c$ axis. The thickness of the flake is approximately 47 nm. (b) Temperature dependence of the resistivity under applied magnetic fields of $H = 0$, 3, 6, and 9 T. (c) Temperature dependence of the Seebeck coefficient under different magnetic fields. (d) Seebeck coefficient $S$ as a function of magnetic field at selected temperatures.
• Figure 4: Symmetry-conservation : (a) Temperature dependence of the field-cooled (FC) magnetization under an external magnetic field of 0.1 T. (b) Temperature-dependent neutron powder diffraction (NPD) patterns collected at 3.7 K and 100 K. (c) Rietveld refinement of the NPD data at 100 K, confirming the absence of structural or magnetic symmetry breaking. (d–f) Temperature-dependent ARPES spectra along the Z$_2$–S direction measured at (d) 10 K, (e) 25 K, and (f) 35 K. (g–i) ARPES spectra along the $\Gamma$–X direction at (g) 6 K, (h) 25 K, and (i) 45 K, showing no detectable band shifts across the measured temperature range.