arXiv subjects

Konstantin Davydov

Publications and source records attributed to Konstantin Davydov.

5 recordsLinked to original sources

arXiv2025

Unconventional domain tessellations in moiré-of-moiré lattices

Imposing incommensurable periodicity on the periodic atomic lattice can lead to complex structural phases consisting of locally periodic structure bounded by topological defects. Twisted trilayer graphene (TTG) is an ideal material platform to study the interplay between different atomic periodicities, which can be tuned by twist angles between the layers, leading to moiré-of-moiré lattices. Interlayer and intralayer interactions between two interfaces in TTG transform this moiré-of-moiré lattice into an intricate network of domain structures at small twist angles, which can harbor exotic electronic behaviors. Here we report a complete structural phase diagram of TTG with atomic scale lattice reconstruction. Using transmission electron microscopy combined with a new interatomic potential simulation, we show several large-scale moiré lattices, including triangular, kagome, and a corner-shared hexagram-shaped domain pattern. Each domain is bounded by a two-dimensional network of domain wall lattices. In the limit of small twist angles, two competing structural orders-rhombohedral and Bernal stackings-with a slight energy difference, cause unconventional lattice reconstruction with spontaneous symmetry breaking and nematic instability, highlighting the importance of long-range interlayer interactions across entire van der Waals layers. The diverse tessellation of distinct domains, whose topological network can be tuned by the adjustment of the twist angles, establishes TTG as a platform for exploring the interplay between emerging quantum properties and controllable nontrivial lattices.

cond-mat.mtrl-sci↗

arXiv2025

Tunable atomically enhanced moiré Berry curvatures in twisted triple bilayer graphene

We report a twisted triple bilayer graphene platform consisting of three units of Bernal bilayer graphene consecutively twisted at 1.49° and 1.68°. We demonstrate the atomic reconstruction between the two competing moiré superlattices strongly enhances the Berry curvature of each moiré band insulator state, characterized by measured strong nonlocal valley Hall effect that sensitively depends on the inter-moiré competition strength, tunable by manipulating the out-of-plane carrier distribution. Our study sheds light on the microscopic mechanism of atomic and electronic reconstruction in twisted multilayer systems, by systematically investigating transport signatures of moiré Berry curvature and its enhancement from moiré-of-moiré lattice reconstruction. We show that the reconstructed electronic band can be versatilely tuned by electrostatics, providing an approach toward engineering the band structure and its topology for a quantum material platform with designer electrical and optical properties.

cond-mat.mes-hall↗

arXiv2025

Stability diagram of layer-polarized quantum Hall states in twisted trilayer graphene

In the twisted trilayer graphene (tTLG) platform, the rich beating patterns between the three graphene layers give rise to a plethora of new length scales and reconstructed electronic bands arising from the emergent moiré and moiré-of-moiré superlattices. The co-existing lattices and superlattices interact and compete with each other to determine the overall transport properties of tTLG, the hierarchy of which can be electrostatically controlled by tuning the out-of-plane charge distribution or layer polarization. In this work, we measure the stability diagram of layer-polarized quantum Hall states in tTLG by systematically mapping out layer-specific Chern numbers in each layer, and intra- and interlayer Chern transitions as a function of displacement field D and total carrier density n. In contrast to twisted bilayer systems, the rich interplay between the three atomic layers gives rise to a complex layer-polarized stability diagram with unconventional transport features that evolve rapidly with electric and magnetic fields. The stability diagram quantitatively characterizes the interlayer screening and charge distribution in tTLG with implication of strong inter-atomic-layer Coulomb coupling. Our work provides comprehensive guidance and insights into predicting and controlling layer-polarization and interlayer transitions in tTLG, and for tuning the individual role and interactions of each participating constituent towards novel material properties.

cond-mat.mes-hall↗

arXiv2024

Easy-to-configure zero-dimensional valley-chiral modes in a graphene point junction

The valley degree of freedom in 2D materials can be manipulated for low-dissipation quantum electronics called valleytronics. At the boundary between two regions of bilayer graphene with different atomic or electrostatic configuration, valley-polarized current has been realized. However, the demanding fabrication and operation requirements limit device reproducibility and scalability toward more advanced valleytronics circuits. We demonstrate a new device architecture of a point junction where a valley-chiral 0D PN junction is easily configured, switchable, and capable of carrying valley current with an estimated polarization of ~80%. This work provides a new building block in manipulating valley quantum numbers and scalable valleytronics.

cond-mat.mes-hall↗

arXiv2023

Tunable Inter-Moiré Physics in Consecutively-Twisted Trilayer Graphene

We fabricate a twisted trilayer graphene device with consecutive twist angles of 1.33 and 1.64 degrees, in which we electrostatically tune the electronic states from each of the two co-existing moiré superlattices and the interactions between them. When both moiré superlattices contribute equally to electrical transport, we report a new type of inter-moiré Hofstadter butterfly. Its Brown-Zak oscillation corresponds to one of the intermediate quasicrystal length scales of the reconstructed moiré of moiré (MoM) superlattice, shedding new light on emergent physics from competing atomic orders.

cond-mat.mes-hall↗