Light-wave-controlled Haldane model in monolayer hexagonal boron nitride

• Published in: Nature (London) Vol. 628; no. 8009; pp. 752 - 757
• Main Authors: Mitra, Sambit, Jiménez-Galán, Álvaro, Aulich, Mario, Neuhaus, Marcel, Silva, Rui E. F., Pervak, Volodymyr, Kling, Matthias F., Biswas, Shubhadeep
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 25-04-2024; Nature Publishing Group
• Subjects: 132/122; 639/301/119/999; 639/624/400/385; 639/766/119/2792; 639/766/400/584; Boron; Boron Compounds - chemistry; Boron nitride; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Electron Transport; Energy gap; Graphene; Hamiltonian functions; Humanities and Social Sciences; Lasers; Light; Monolayers; multidisciplinary; Optical control; Polarimetry; Quantum Theory; Science; Science (multidisciplinary); Spectrum analysis; Superlattices; Symmetry; Twisting; Ultrafast optics, Two-dimentional material, Topology, Lightwave engineering, Haldane model; Valleys; Waveforms
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-024-07244-z

In recent years, the stacking and twisting of atom-thin structures with matching crystal symmetry has provided a unique way to create new superlattice structures in which new properties emerge
1
,
2
. In parallel, control over the temporal characteristics of strong light fields has allowed researchers to manipulate coherent electron transport in such atom-thin structures on sublaser-cycle timescales
3
,
4
. Here we demonstrate a tailored light-wave-driven analogue to twisted layer stacking. Tailoring the spatial symmetry of the light waveform to that of the lattice of a hexagonal boron nitride monolayer and then twisting this waveform result in optical control of time-reversal symmetry breaking
5
and the realization of the topological Haldane model
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in a laser-dressed two-dimensional insulating crystal. Further, the parameters of the effective Haldane-type Hamiltonian can be controlled by rotating the light waveform, thus enabling ultrafast switching between band structure configurations and allowing unprecedented control over the magnitude, location and curvature of the bandgap. This results in an asymmetric population between complementary quantum valleys that leads to a measurable valley Hall current
7
, which can be detected by optical harmonic polarimetry. The universality and robustness of our scheme paves the way to valley-selective bandgap engineering on the fly and unlocks the possibility of creating few-femtosecond switches with quantum degrees of freedom.
We introduce strong tailored light-wave-driven time-reversal symmetry breaking in monolayer hexagonal boron nitride, realizing a sub-laser-cycle controllable analogue of the topological model of Haldane and inducing non-resonant valley polarization.