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

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.

💡 Research Summary

This paper reports the groundbreaking discovery of a gate-tunable, giant negative magnetoresistance (GNMR) in two-dimensional tellurene (Te) films, reaching an unprecedented magnitude of -90% of the zero-field resistance (R0). This record-breaking effect, observed at cryogenic temperatures over a wide magnetic field range (up to 35 T), is attributed to a novel quantum geometric origin, distinct from conventional mechanisms like weak localization or the chiral anomaly.

The experimental platform utilizes dual-gated Hall-bar devices fabricated on Te flakes. The band structure of Te features spin-split conduction bands that cross at the H point to form a Weyl node, endowing it with nontrivial quantum geometry, while the valence band lacks such a crossing. By applying gate voltages, the carrier type and density can be continuously tuned. Strikingly, the n-type (electron) regime exhibits strong GNMR, whereas the p-type (hole) regime shows conventional positive magnetoresistance (PMR). The magnitude of the GNMR is most pronounced when the Fermi level is near the Weyl node in the conduction band and diminishes as the gate voltage shifts the Fermi level away from it, strongly suggesting a connection to the band’s topological feature.

Key experimental evidence includes detailed field-rotation studies. The GNMR persists for all magnetic field orientations but vanishes completely when the magnetic field (B) is aligned parallel to the intrinsic in-plane polarization electric field (E) arising from Te’s lone-pair electrons. This observation provides compelling evidence that the effect scales with the square of the cross product of E and B. Furthermore, the GNMR is strongly temperature-dependent, being prominent at low temperatures (e.g., 350 mK) and vanishing above approximately 54 K, consistent with a quantum mechanical origin.

To explain these observations, the authors propose two intertwined novel mechanisms. First, a quantum geometric enhancement of diffusion. In a multiband system like Te, the diffusion tensor, which determines conductivity via the Kubo-Greenwood formula, involves the time integral of velocity autocorrelations. The quantum metric between the spin-split conduction bands promotes these interband velocity correlations, effectively enhancing the diffusion constant and thus reducing resistance. Second, a new magnetoelectric spin interaction, termed “Drift-Zeeman coupling,” described by the Hamiltonian H_DZ = -γ (E×B)·σ. This interaction locks the spin of a Weyl fermion undergoing cyclotron motion in crossed E and B fields to its guiding-center drift direction. The energy splitting induced by this coupling, (Δε)^2 ~ (E×B)^2, acts as the driving parameter for the geometric diffusion enhancement.

Combining these mechanisms leads to a theoretical prediction for the parabolic negative magnetoresistance: ∆R_zz/R_0 = -β_g (E×B)^2, where the proportionality constant β_g is determined by the quantum metric. The excellent agreement between this derived formula and the experimental angular dependence (GNMR vanishing at B∥E) provides robust confirmation of the proposed theory.

In conclusion, this work establishes the first direct experimental manifestation of a non-Markovian memory effect in magnetotransport driven purely by quantum geometry. It unveils a previously unexplored pathway—leveraging the quantum metric and magnetoelectric couplings—to control electronic transport in complex and topological materials, opening new avenues for designing advanced electronic devices.