arXiv subjects

Naoto Nakatsuji

Publications and source records attributed to Naoto Nakatsuji.

12 recordsLinked to original sources

arXiv2026

One-Dimensional Electronic States in a Moiré Superlattice of Twisted Bilayer WTe2

One-dimensional (1D) moiré superlattices provide a new route to engineering reduced-dimensional electronic states in van der Waals materials, yet their electronic structure and microscopic origin remain largely unexplored. Here, we investigate the structural relaxation and electronic properties of a 1D moiré superlattice formed in twisted bilayer 1T$'$-WTe$_2$ using density functional theory calculations, complemented by high-angle annular dark-field scanning transmission electron microscopy. We show that lattice relaxation strongly reconstructs the moiré stripes, leading to stacking-dependent stripe widths that are in excellent agreement with experimental observations. The relaxed structure hosts quasi-one-dimensional electronic bands near the Fermi level, characterized by strong dispersion along the stripe direction and nearly flat dispersion in the perpendicular direction. By comparing the full bilayer with isolated relaxed layers, we establish that these 1D electronic states are governed predominantly by an intralayer moiré potential induced by in-plane lattice relaxation, rather than by interlayer hybridization. We extract this position-dependent moiré potential directly from DFT calculations and construct an effective tight-binding model that reproduces both the band dispersion and the real-space localization of the electronic wave functions. Our results identify lattice relaxation as the key mechanism underlying 1D electronic states in 1D moiré superlattices. %and establish twisted bilayer WTe$_2$ as a promising platform for exploring emergent one-dimensional moiré physics. The framework developed here provides a unified theoretical basis for realizing and exploring one-dimensional moiré physics in a broad class of anisotropic two-dimensional materials.

cond-mat.mes-hall↗

arXiv2026

Twist-configured moire-moire reconstruction governs diverse commensurate double-moire phases in twisted bilayer graphene on h-BN

The coexistence of multiple moire lattices in van der Waals heterostructures raises a fundamental question: how do distinct moire patterns interact and reconstruct? Here, we investigate twisted bilayer graphene (tBG) on hexagonal boron nitride (h-BN), where tBG and graphene/h-BN moire structures coexist, using conductive atomic force microscopy combined with continuum-model simulations. We show that reconstruction between these moire lattices-moire-moire reconstruction-manifests across multiple length scales, giving rise to diverse commensurate double-moire phases. Locally, the stacking registry between the two moire lattices is uniquely selected by the global twist configuration (helical or alternate), mediated by rotational relaxation of the shared graphene layer. This registry, together with twist angle and strain, governs commensurate domains from C3z-symmetric to strained symmetry-modified structures. These results establish moire-moire reconstruction as a general framework for engineering structural and electronic order -- including theoretically predicted topological flat bands below the magic angle -- in multilayer moire materials.

cond-mat.mtrl-sci↗

arXiv2025

High-throughput discovery of moiré homobilayers guided by topology and energetics

Van der Waals heterostructures promise on-demand designer quantum phases through control of monolayer composition, stacking, twist angle, and external fields. Yet, experimental efforts have been narrowly focused, leaving much of this vast moiré landscape unexplored and potential promises unrealized. Here, we present a scalable workflow for high-throughput characterization of twisted homobilayers and apply it to $K$-valley semiconductors. Combining small-scale density functional theory with perturbation theory, we efficiently extract moiré band gaps, valley Chern numbers, magic angles, and the threshold for lattice relaxation. Beyond this rapid high-throughput characterization, we parameterize a continuum model for each material, which provides a starting point for more detailed study. Our survey delivers an actionable map for systematic exploration of correlated and topological phases in moiré homobilayers, and identifies promising new platforms: chromium-based transition metal dichalcogenides for high-temperature quantum anomalous Hall effects, transition metal nitride halides for intertwined superconducting and moiré physics, and atomically thin $\rm{III-V}$ semiconductors for room-temperature-scale moiré effects.

cond-mat.mtrl-sci↗

arXiv2025

Emergent electronic insulating states in a one-dimensional moiré superlattice

Two-dimensional (2D) van der Waals (vdW) moiré superlattices have provided a powerful knob to engineer a plethora of new quantum states. However, extending such moiré engineering to one-dimensional (1D) vdW systems has remained challenging. Here we report the moiré-engineered electronic insulating states in a new 1D moiré superlattice, by crystallographically aligning an armchair single-walled carbon nanotube (SWNT) to 2D hexagonal boron nitride (hBN) substrate. Remarkably, we observe the emergence of pronounced insulating states at charge neutrality point (CNP), full and half moiré fillings in lattice-aligned armchair SWNT/hBN heterostructures by low-temperature electrical transport measurements. In strong contrast, armchair SWNT devices without hBN alignment do not show any of these insulating behaviors, providing compelling evidence for the significant 1D moiré effect. Our density functional theory (DFT) and tight-binding calculations reveal that synergetic nanotube partial flattening and in-plane lattice reconstruction at 1D moiré interface expand the most stable AB' stacking regions (carbon on top of boron) and open sizable band gaps at both CNP and full moiré fillings at the single-particle level. Our one-body theory predicts no band gaps at half moiré fillings, suggesting that electron correlation and/or electron-phonon interaction may give rise to these emergent insulating behaviors in our 1D moiré systems. Our work establishes a new and definite moiré engineering route for 1D vdW materials and opens an exciting avenue for exploring interaction-induced quantum phases in 1D.

cond-mat.mes-hall↗

arXiv2025

One-dimensional moiré engineering in zigzag graphene nanoribbons on hBN

We study the structural relaxation and electronic properties of a one-dimensional (1D) moiré system composed of a zigzag graphene nanoribbon (GNR) placed on a hexagonal boron nitride (hBN) substrate. Using an effective grid model derived from continuum elasticity theory, we calculate the relaxed atomic structure of the GNR/hBN system for various twist angles and ribbon widths. The relaxation gives rise to a characteristic 1D domain structure consisting of alternating commensurate AB$'$ regions and two distinct types of domain boundaries. At finite twist angles, the ribbon adopts a wavy shape, locally tracing the hBN zigzag direction but occasionally sliding to adjacent atomic rows. The resulting moiré potential strongly modulates the electronic structure: the zero-energy zigzag edge states are modulated by the local stacking, leading to densely packed subbands in the AB$'$ domains and sharply localized domain-wall states in the energy gaps between domain plateaus, which together realize gate-tunable one-dimensional arrays of quantum-confined electronic states. Our results demonstrate that moiré modulation in GNR/hBN heterostructures provides a versatile platform for electronic structure engineering and the design of 1D moiré nanodevices.

cond-mat.mes-hall↗

arXiv2025

Four Moiré materials at One Magic Angle in Helical Quadrilayer Graphene

We introduce helical twisted quadrilayer graphene (HTQG), four graphene sheets rotated by the same small angle, as a versatile and experimentally accessible platform for correlated topological matter. HTQG consists of three moiré lattices, formed by interference between adjacent graphene layers, that are twisted relative to each other. Lattice relaxation produces four types of large-scale commensurate domains. The domains are characterized by the stacking of the three moiré lattices and come in two types: Type-I "Bernal" stacking and Type-II "rhombohedral" stacking. Domain walls between adjacent stackings often host topologically protected edge states, forming networks at the supermoiré and super-supermoiré scales. Remarkably, all four moiré substructures have narrow bands at the same magic angle $θ\approx 2.3^\circ$, allowing their correlated phases to be simultaneously targeted in device manufacturing. We argue that the Type-I domains are especially suitable for realizing robust superconductivity which emerges from doping topological insulators, and Chern insulators in $C = \pm 2$ bands.

cond-mat.str-el↗

arXiv2025

Moiré Band Engineering in Twisted Trilayer WSe2

We present a systematic theoretical study on the structural and electronic properties of twisted trilayer transition metal dichalcogenide (TMD) WSe$_2$, where two independent moiré patterns form between adjacent layers. Using a continuum approach, we investigate the optimized lattice structure and the resulting energy band structure, revealing fundamentally different electronic behaviors between helical and alternating twist configurations. In helical trilayers, lattice relaxation induces $αβ$ and $βα$ domains, where the two moiré patterns shift to minimize overlap, while in alternating trilayers, $αα'$ domains emerge with aligned moiré patterns. A key feature of trilayer TMDs is the summation of moiré potentials from the top and bottom layers onto the middle layer, effectively doubling the potential depth. In helical trilayers, this mechanism generates a Kagome lattice potential in the $αβ$ domains, giving rise to flat bands characteristic of Kagome physics. In alternating trilayers, the enhanced potential confinement forms deep triangular quantum wells, distinct from those found in bilayer systems. Furthermore, we demonstrate that a moderate perpendicular electric field can switch the layer polarization near the valence band edge, providing an additional degree of tunability. In particular, it enables tuning of the hybridization between orbitals on different layers, allowing for the engineering of diverse and controllable electronic band structures. Our findings highlight the unique role of moiré potential summation in trilayer systems, offering a broader platform for designing moiré-based electronic and excitonic phenomena beyond those achievable in bilayer TMDs.

cond-mat.mes-hall↗

arXiv2024

Manipulating moires by controlling heterostrain in van der Waals devices

Van der Waals (vdW) moires offer tunable superlattices that can strongly manipulate electronic properties. We demonstrate the in-situ manipulation of moire superlattices via heterostrain control in a vdW device. By straining a graphene layer relative to its hexagonal boron nitride substrate, we modify the shape and size of the moire. Our sliding-based technique achieves uniaxial heterostrain values exceeding 1%, resulting in distorted moires that are larger than those achievable without strain. The stretched moire is evident in transport measurements, resulting in shifted superlattice resistance peaks and Landau fans consistent with an enlarged superlattice unit cell. Electronic structure calculations reveal how heterostrain shrinks and distorts the moire Brillouin zone, resulting in a reduced electronic bandwidth as well as the appearance of highly anisotropic and quasi-1-dimensional Fermi surfaces. Our heterostrain control approach opens a wide parameter space of moire lattices to explore beyond what is possible by twist angle control alone.

cond-mat.mes-hall↗

arXiv2023

Multi-scale lattice relaxation in general twisted trilayer graphenes

We present comprehensive theoretical studies on the lattice relaxation and the electronic structures in general non-symemtric twisted trilayer graphenes. By using an effective continuum model, we show that the relaxed lattice structure forms a patchwork of moiré-of-moiré domains, where a moiré pattern given by layer 1 and 2 and another pattern given by layer 2 and 3 become locally commensurate. The atomic configuration inside the domain exhibits a distinct contrast between chiral and alternating stacks, which are determined by the relative signs of the two twist angles. In the chiral case, the electronic band calculation reveals a wide energy window ($>$ 50 meV) with low density of states, featuring sparsely distributed highly one-dimensional electron bands. These one-dimensional states exhibit a sharp localization at the boundaries between super-moiré domains, and they are identified as a topological boundary state between distinct Chern insulators. The alternating trilayer exhibits a coexistence of the flat bands and a monolayer-like Dirac cone, and it is attributed to the formation of moiré-of-moiré domains equivalent to the mirror-symmetric twisted trilayer graphene.

cond-mat.mes-hall↗

arXiv2022

Moiré disorder effect in twisted bilayer graphene

We theoretically study the electronic structure of magic-angle twisted bilayer graphene with disordered moiré patterns. By using an extended continuum model incorporating non-uniform lattice distortion, we find that the local density of states of the flat band is hardly broadened, but splits into upper and lower subbands in most places. The spatial dependence of the splitting energy is almost exclusively determined by the local value of the effective vector potential induced by heterostrain, whereas the variation of local twist angle and local moiré period give relatively minor effects on the electronic structure. We explain the exclusive dependence on the local vector potential by a pseudo Landau level picture for the magic-angle flat band, and we obtain an analytic expression of the splitting energy as a function of the strain amplitude.

cond-mat.mes-hall↗

arXiv2020

Exact Plaquette-Ordered Ground States with Exact Edge States of the Generalized Hubbard Model in Corner Sharing Lattices

We discuss exact plaquette-ordered ground states of the generalized Hubbard model based on the projection operator method for several corner sharing lattices: Kagome, checkerboard, and pyrochlore lattices. The obtained exact ground states are interpreted as Néel ordered states on the plaquette-located electrons. We demonstrate that these models also have exact edge states. We also calculate the entanglement entropy exactly in these systems.

cond-mat.str-el↗

arXiv2020

Hofstadter butterfly and the quantum Hall effect in twisted double bilayer graphenes

We study the energy spectrum and quantum Hall effects of the twisted double bilayer graphene in uniform magnetic field. We investigate two different arrangements, AB-AB and AB-BA, which differ in the relative orientation but have very similar band structures in the absence of a magnetic field. For each system, we calculate the energy spectrum and quantized Hall conductivities at each spectral gap by using a continuum Hamiltonian that satisfies the magneto-translation condition. We show that the Hofstadter butterfly spectra of AB-AB and AB-BA stackings differ significantly, even though their zero magnetic field band structures closely resemble; the spectrum of AB-AB has valley degeneracy, which can be lifted by applying interlayer potential asymmetry, while the spectrum of AB-BA has no such degeneracy in any case. We explain the origin of the difference from the perspectives of lattice symmetry and band topology.

cond-mat.mes-hall↗