Gate-Tunable Giant Negative Magnetoresistance in Tellurene Driven by Quantum Geometry

TL;DR

This work reports gate-controllable giant negative magnetoresistance in n-type tellurene, persisting up to high magnetic fields and persuasively linked to Weyl-node quantum geometry. The authors develop a two-fold theoretical framework: a quantum-geometric diffusion mechanism, where interband diffusion is enhanced by the quantum metric, and a drift-Zeeman spin interaction that locks spin to the E×B-driven drift, producing a parabolic ΔR ∝ - (E × B)^2 dependence. The combination of geometric diffusion and spin-drift locking accounts for the angular, density, and temperature dependences, with a quantum-limit suppression of GNMR expected. These findings reveal a non-Markovian memory effect in magnetotransport and suggest new avenues for manipulating electronic transport in topological materials using gate and field control.

Abstract

Negative magnetoresistance in conventional two-dimensional electron gases is a well-known phenomenon, but its origin in complex and topological materials, especially those endowed with quantum geometry, remains largely elusive. Here, we report the discovery of a giant negative magnetoresistance, reaching a remarkable $- 90\%$ of the resistance at zero magnetic field, $R_0$, in $n$-type tellurene films. This record-breaking effect persists over a wide magnetic field range (measured up to $35$ T) at cryogenic temperatures and is suppressed when the chemical potential shifts away from the Weyl node in the conduction band, strongly suggesting a quantum geometric origin. We propose two novel mechanisms for this phenomenon: a quantum geometric enhancement of diffusion and a magnetoelectric spin interaction that locks the spin of a Weyl fermion, in cyclotron motion under crossed electric $\boldsymbol{\cal E}$ and magnetic ${\bf B}$ fields, to its guiding-center drift, $(\boldsymbol{\cal E}\times{\bf B})\cdotσ$. We show that the time integral of the velocity auto-correlations promoted by the quantum metric between the spin-split conduction bands enhance diffusion, thereby reducing the resistance. This mechanism is experimentally confirmed by its unique magnetoelectric dependence, $ΔR_{zz}(\boldsymbol{\cal E},{\bf B})/R_0=-β_{g}(\boldsymbol{\cal E}\times{\bf B})^2$, with $β_{g}$ determined by the quantum metric. Our findings establish a new, quantum geometric and non-Markovian memory effect in magnetotransport, paving the way for controlling electronic transport in complex and topological matter.

Figures (6)

• Figure 1: Device schematics and gate-tunable quantum transport in $p$- and $n$-type Te.a) Schematic illustration of a dual-gated Hall-bar device based on a Te flake for transport measurements. b) Band structure of Te. At zero gate bias, the Te is nearly intrinsic. Applying a positive gate voltage populates the conduction band, where the spin-split subbands cross at $\mathrm{H}$ point to form a Weyl node. In contrast, a negative gate voltage accesses the valence band without band crossing, enabling comparison between distinct quantum transport regimes governed by the quantum geometry. c) Color map of magnetoresistance ($R_{zz}$) as a function of back-gate voltage and magnetic field, showing negative MR for electron conduction and positive MR for hole conduction within the same device. d) Background-subtracted $\Delta R_{zz}$ revealing clear SdH oscillations in both $n$-type and $p$-type regimes. While for $n$-type the SdH oscillations are featured by a single characteristic frequency (single-layer 2DEG) for the $p$-type two characteristic frequencies are observed in the SdH oscillations (bilayer 2DHG). e) Overlay of normalized magnetoresistance curves for $p$-type (red) and $n$-type (blue) conduction, highlighting their contrasting field responses.
• Figure 2: Carrier-density dependence of negative magnetoresistance and the quantum Hall effect.a) Longitudinal magnetoresistance ($R_{zz}$) as a function of carrier density, showing a pronounced negative magnetoresistance (NMR) that persists until the system reaches the quantum limit at the lowest Landau level ($n = 0$). b) Transverse Hall resistance ($R_{zx}$) versus carrier density, revealing well-developed quantum Hall plateaus at filling factors $\nu = 3$, $4$, and $6$. c) Normalized magnetoresistance in the Te conduction band as a function of carrier density. The NMR gradually weakens with increasing gate voltage as the Fermi level shifts away from the Weyl node. $Inset$: Schematic illustration of the carrier-density-dependent Fermi level movement relative to the Weyl node, as the topgate voltage is swept from $-4V$ (black curves in all plots) to $4V$ (dark blue curves in all plots) in the conduction band.
• Figure 3: Angular, carrier density, and temperature dependence of the NMR.a) Magnetic field rotation within the $y$-$z$ plane, perpendicular to the device in-plane $x$-axis. The angle $\theta$ is measured from the film normal ($\hat{y}$). The giant NMR weakens but persists as the field approaches the in-plane $\hat{z}$ direction ($\theta=90^\circ$). b) Magnetic field rotation within the $y$-$x$ plane, perpendicular to the device in-plane $z$-axis. The angle $\phi$ is measured from the film normal ($\hat{y}$). The giant NMR vanishes completely when the field is aligned along the in-plane $\hat{x}$ direction $(\phi=90^\circ)$, which is parallel to the intrinsic polarization field $\boldsymbol{\mathcal{E}}$. c) Evolution of the SdH oscillation for tilted magnetic fields ($0\leq\theta \leq 75^\circ$). No significant change in the SdH sequences in low ($V_{\rm bg} = 10$ V) and high ($V_{\rm bg} = 30$ V) carrier densities indicating an ultra small $g$ factor in the Te conduction band. d) Temperature dependence of the NMR at different carrier densities. The effect is strongly suppressed with increasing temperature, vanishing entirely at approximately 54 K.
• Figure 4: Quantum geometry and spin-drift locking in Te.(a) Conduction bands $\epsilon_\pm(k_z)$ of Te at a given chemical potential, featuring a Weyl node located at $k_z=0$, which is the origin of its unique electronic properties, and its evolution with magnetic field, $\boldsymbol{B}\parallel\hat{\boldsymbol{y}}$. (b) Evolution of the radial configuration of the spin texture (blue and red arrows for the outer and inner Fermi surfaces) as the magnetic field is increased. (c) Quantum metric components, $g_{zz}(\boldsymbol{k})$ and $g_{zx}(\boldsymbol{k})$. (d) The locking of the spin to the guiding-center drift upon crossed electric $\boldsymbol{\@fontswitch\mathcal{E}}$ and magnetic $\boldsymbol{B}$ fields.
• Figure 5: Quantitative analysis of the GNMR in Te.(a) Fit of the PMR for $p$-type carriers in the valence band, from $V_{bg}=-10$V to $V_{bg}=-40$V and $V_{tg}=0$V, following the expected behavior for two hole accumulation layers. (b) Fit of the NMR for $n$-type carriers in the conduction band, from $V_{tg}=-4$V to $V_{tg}=+4$V and $V_{bg}=+16$V, following the parabolic enhanced diffusion from quantum geometry. (c) Angular evolution of the symmetric component $C(\theta)$ of the GNMR for scan rotations of the magnetic field, ${\bf B}$, confined to the $y$-$z$ plane. The ratio $C(0)/C(\pi/2)=\lambda_z^6/\lambda_\perp^6\approx 7.5$ is a direct measure of the anisotropy in the spin-orbit couplings $\lambda_z/\lambda_\perp\approx 1.4$. (d) Angular evolution of $C(\phi)$ of the GNMR for scan rotations of the magnetic field, ${\bf B}$, confined to the $y$-$x$ plane. (e) Evolution of $C(\theta=0)$ of the GNMR as a function of the top-gate voltage, $V_{tg}=-4$V to $V_{tg}=+1$V and $V_{bg}=+16$V, decreasing as the Fermi level is tuned away from the Weyl node (inset), consistent with a quantum geometric origin. For $-4$V$<V_{tg}<-3$V, at the bottom of the conduction band and very close to the Weyl node, hole accumulation occurs spoiling the agreement between theory and experiment. (f) Evolution of $C(\theta=0)$ of the GNMR as a function of temperature, $T=0.35$K to $T=54$K, at $V_{bg}=+18$V and $V_{tg}=0$V. The data (circles) are well described by $C(T) = C_0/(1 -\beta_{wl}\ln{(T/T_0)}+ \alpha_{ee}\sqrt{T})^2$ (solid line), describing quantum corrections to conductivity through the dimensional crossover 2D $\rightarrow$ 3D, for $L_\varphi\gg d$ and $L_\varphi\ll d$.