Landau Quantization and Highly Mobile Fermions in an Insulator

Abstract

In strongly correlated materials, quasiparticle excitations can carry fractional quantum numbers. An intriguing possibility is the formation of fractionalized, charge-neutral fermions, e.g., spinons and fermionic excitons, that result in neutral Fermi surfaces and Landau quantization in an insulator. While previous experiments in quantum spin liquids, topological Kondo insulators, and quantum Hall systems have hinted at charge-neutral Fermi surfaces, evidence for their existence remains far from conclusive. Here we report experimental observation of Landau quantization in a two dimensional (2D) insulator, i.e., monolayer tungsten ditelluride (WTe${}_2$), a large gap topological insulator. Using a detection scheme that avoids edge contributions, we uncover strikingly large quantum oscillations in the monolayer insulator's magnetoresistance, with an onset field as small as ~ 0.5 tesla. Despite the huge resistance, the oscillation profile, which exhibits many periods, mimics the Shubnikov-de Haas oscillations in metals. Remarkably, at ultralow temperatures the observed oscillations evolve into discrete peaks near 1.6 tesla, above which the Landau quantized regime is fully developed. Such a low onset field of quantization is comparable to high-mobility conventional two-dimensional electron gases. Our experiments call for further investigation of the highly unusual ground state of the WTe${}_2$ monolayer. This includes the influence of device components and the possible existence of mobile fermions and charge-neutral Fermi surfaces inside its insulating gap.

arXiv comment33 pages, 4 Main Figures + 10 Extended Data Figures + 1 SI Figure

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• Direct observation of vortices in an electron fluid
• One-Dimensional Luttinger Liquids in a Two-Dimensional Moiré Lattice
• Orbit-transfer torque driven field-free switching of perpendicular magnetization
• Bulk Photovoltaic Effect Driven by Collective Excitations in a Correlated Insulator
• Unconventional Superconducting Quantum Criticality in Monolayer WTe2
• A New Era of Excitonic Insulators
• Quantum oscillations in interaction-driven insulators
• Theory of competing excitonic orders in insulating WTe${}_2$ monolayers
• Quantum oscillations in 2D insulators induced by graphite gates
• Surface-Confined Two-Dimensional Crystal Growth on a Monolayer
• Quantum Oscillation of Thermally Activated Conductivity in a Monolayer WTe${}_2$-like Excitonic Insulator
• Evidence for Two Dimensional Anisotropic Luttinger Liquids at Millikelvin Temperatures
• Probing the Quantum Noise of the Spinon Fermi Surface with NV Centers
• The universal shear conductivity of Fermi liquids and spinon Fermi surface states and its detection via spin qubit noise magnetometry
• $f$-electron hybridised metallic Fermi surface in magnetic field-induced metallic YbB${}_{12}$
• Multi-Band Superconductivity in Strongly Hybridized 1T'-WTe${}_2$/NbSe${}_2$ Heterostructures
• Critical role of magnetic moments in heavy-fermion materials: revisiting mysteries of SmB${}_6$
• Theory of Difference Frequency Quantum Oscillations
• Quantum Oscillations in the Magnetisation and Density of States of Insulators
• Electronic Density of States of a $U\left(1\right)$ Quantum Spin Liquid with Spinon Fermi Surface. I. Orbital Magnetic Field Effects
• Charge-Neutral Electronic Excitations in Quantum Insulators
• Reshaped Weyl fermionic dispersions driven by Coulomb interactions in MoTe2
• Third-harmonic generation in excitonic insulators
• Tuning multiple Landau Quantization in Transition-Metal Dichalcogenide with Strain
• Coherent heavy charge carriers in an organic conductor near the bandwidth-controlled Mott transition
• Magnetoresistance oscillations in vertical junctions of 2D antiferromagnetic semiconductor CrPS${}_4$
• Effect of many-body interaction on de Haas-van Alphen oscillations in insulators
• Quantum oscillations in field-induced correlated insulators of a moiré superlattice
• Quantum Oscillations in an Impurity-Band Anderson Insulator
• Quantum oscillation study of the large magnetoresistance in Mo substituted WTe${}_2$ single crystals
• Notes on Quantum oscillation for Hatsugai-Kohmoto model
• A Platform for Far-Infrared Spectroscopy of Quantum Materials at Millikelvin Temperatures
• The Detection of Unconventional Quantum Oscillations in Insulating 2D Materials
• Inverse-current quantum electro-oscillations in a charge-density wave insulator
• Magnetic-field effect on excitonic condensation emergent in extended Falicov-Kimball model
• The out-of-plane magnetoresistance in a Van der Waals thin film of WTe2
• Residual quantum coherent electron transport in doped graphene leads