Spin-Triplet Excitonic Insulator in the Ultra-Quantum Limit of HfTe5
arXiv:2501.12572 · doi:10.1103/bj2n-4k2w
Abstract
More than fifty years ago, excitonic insulators, formed by the pairing of electrons and holes due to Coulomb interactions, were first predicted. Since then, excitonic insulators have been observed in various classes of materials, including quantum Hall bilayers, graphite, transition metal chalcogenides, and more recently in moire superlattices. In these excitonic insulators, an electron and a hole with the same spin bind together and the resulting exciton is a spin singlet. Here, we report the experimental observation of a spin-triplet exciton insulator in the ultra-quantum limit of a three-dimensional topological material HfTe5. We observe that the spin-polarized zeroth Landau bands, dispersing along the field direction, cross each other beyond a characteristic magnetic field in HfTe5, forming the one-dimensional Weyl mode. Transport measurements reveal the emergence of a gap of about 250 μeV when the field surpasses a critical threshold. By performing the material-specific modeling, we identify this gap as a consequence of a spin-triplet exciton formation, where electrons and holes with opposite spin form bound states, and the translational symmetry is preserved. The system reaches charge neutrality following the gap opening, as evidenced by the zero Hall conductivity over a wide magnetic field range (10 - 72 T). Our finding of the spin-triplet excitonic insulator paves the way for studying novel spin transport including spin superfluidity, spin Josephson currents, and Coulomb drag of spin currents in analogy to the transport properties associated with the layer pseudospin in quantum Hall bilayers.
References in corpus (24)
- Strongly correlated excitonic insulator in atomic double layers
- Signatures of Electron Fractionalization in Ultraquantum Bismuth
- Evidence for equilibrium excitons and exciton condensation in monolayer WTe2
- Hartree-Fock study of the moiré Hubbard model for twisted bilayer transition metal dichalcogenides
- Crossover between Strongly-coupled and Weakly-coupled Exciton Superfluids
- Excitonic topological order in imbalanced electron-hole bilayers
- Evidences for the exciton gas phase and its condensation in monolayer 1T-ZrTe2
- Evidence of high-temperature exciton condensation in a two-dimensional semimetal
- Possible Excitonic Phase of Graphite in the Quantum Limit State
- Spin-triplet superconductivity from interband effect in doped insulators
- Topological Lifshitz transition and one-dimensional Weyl mode in HfTe5
- Signature of spin-triplet exciton condensations in LaCoO at ultrahigh magnetic fields up to 600 T
- Induced anomalous Hall effect of massive Dirac fermions in ZrTe5 and HfTe5 thin flakes
- Signatures of a magnetic-field-induced Lifshitz transition in the ultra-quantum limit of the topological semimetal ZrTe
- Spontaneous gap opening and potential excitonic states in an ideal Dirac semimetal TaPdTe
- Distinguishing the gapped and Weyl semimetal scenario in ZrTe: insights from an effective two-band model
- Critical point for Bose-Einstein condensation of excitons in graphite
- A gap-protected zero-Hall effect state in the quantum limit of the nonsymmorphic metal KHgSb
- Quantum-Hall physics and three dimensions
- Charge-Neutral Electronic Excitations in Quantum Insulators
- Electrical Breakdown of Excitonic Insulator
- Magnetic-field-induced nonlinear transport in HfTe5
- Magnetic field driven Lifshitz transition and one-dimensional Weyl nodes in three-dimensional pentatellurides
- Magnetism and Metallicity in Moiré Transition Metal Dichalcogenides