arXiv subjects

Jingtian Shi

Publications and source records attributed to Jingtian Shi.

12 recordsLinked to original sources

arXiv2026

Moiré-induced altermagnetism from nonmagnetic constituents

We propose a mechanism for nonmagnetic materials to develop altermagnetic order by moiré interference with nonmagnetic substrate, which is driven by structural relaxation and spontaneous twirls in moiré domain walls of lattice-mismatched moiré square lattices. When doped with one electron per moiré domain, a correlated insulating gap is opened by electron interaction. Depending on the location of the moiré potential minima, the moiré bands can show d-wave or g-wave altermagnetic splitting. The former can be enhanced by a finite twist angle; the latter is sensitive to strains that drive a transition to d-wave.

cond-mat.str-el↗

arXiv2026

Non-uniform quantum geometry stabilizes generalized Wigner crystals

Moiré materials host fractional Chern insulators and electron crystals in close proximity, but the mechanism selecting between them remains an open question. We address this competition in Chern bands with ideal but momentum-dependent quantum geometry -- Aharonov-Casher bands. We present an ansatz wave function for generalized Wigner crystals and, by comparing its energy to that of the competing Laughlin-like state, map out the phase diagram at filling fraction $ν=1/m$ as a function of the degree of geometric non-uniformity. Our work identifies quantum geometry-controlled zero point fluctuations of the charge density of the generalized Wigner crystal as the mechanism controlling its relative stability, implying a kind of quantum Lindemann criterion for the crystal-liquid phase boundary.

cond-mat.str-el↗

arXiv2026

Symmetry-protected cubic-touching topological surface bands with tunable singularities

We propose a class of topological surface bands in three-dimensional topological crystalline insulators that have symmetry-protected cubic-order band touching. Within the symmetry constraint, the band dispersion can continuously vary between cubic dispersion, moat band and multi-mini-valley structure with van Hove singularities by adjusting particle-hole asymmetry and anisotropy. Thus, there is a family of tunable density-of-state singularities ranging from power-law to logarithmic divergences. This offrs a versatile platform for engineering strongly correlated phases of matter in topological surface states. We provide an example realization in a prism-lattice tight-binding model of angular-momentum-3/2 electrons.

cond-mat.str-el↗

arXiv2026

Band mixing and particle-hole asymmetry in moiré fractional Chern insulators

We investigate the effect of remote band mixing on the stability of fractional Chern insulators in a family of models that approximate continuum descriptions of moiré materials. Our results suggest that the experimentally observed asymmetry between filling fractions $ν=1/3$ and $ν=2/3$ in twisted MoTe$_2$ originates from a competition between a fractional Chern insulator, an electron Wigner crystal, and a hole Wigner crystal. In the absence of band mixing, the leading instability at $ν= 1/3$ is the electron crystal, whereas at $ν= 2/3$ the main competing phase is the hole crystal. Remote band mixing substantially lowers the energy of the electron crystal but has only a weak effect on the hole crystal. Consequently, it destabilizes the fractional Chern insulator at $ν=1/3$ more strongly than at $ν=2/3$. This mechanism also provides an explanation for the emergence of re-entrant integer quantum anomalous Hall states in moiré MoTe$_2$ for fillings $ν>1/2$.

cond-mat.str-el↗

arXiv2025

Effects of Berry curvature on ideal fractional Chern insulator many-body gaps

We investigate the many-body ground states in a family of fractionally-filled bands where the Berry curvature fluctuations can be tuned while maintaining ideal quantum geometry. We numerically find that the neutral gap of the fractional Chern insulator (FCI) ground state decreases as the Berry curvature becomes less homogeneous, ultimately driving an instability to a charge density wave. We further extend our analysis to bands perturbed away from the ideal limit and give examples where a less ideal band geometry results in a more stable FCI phase. To explain our findings, we apply the single mode approximation to the ground state wave functions of the ideal band, from which we obtain analytic expressions for the magnetoroton minimum. Finally, we make a connection between our results and experimentally relevant systems where FCIs have been observed.

cond-mat.str-el↗

arXiv2025

Spontaneous Twirls and Structural Frustration in Moiré Materials

Structural twirls form spontaneously in the domain wall networks of some moiré materials. We show that in heterobilayers, neighboring twirl chiralities tend to anti-align, forming staggered patterns that are well described by antiferromagnetic lattice $ϕ^4$ theories. In moiré systems with triangular domains, this leads to frustration in the chirality configuration of the structural twirls and to hysteresis with respect to variation of the average twist angle and possibly other control parameters.

cond-mat.mtrl-sci↗

arXiv2024

Adiabatic Approximation and Aharonov-Casher Bands in Twisted Homobilayer TMDs

Topological flat moiré bands with nearly ideal quantum geometry have been identified in homobilayer transition metal dichalcogenide moiré superlattices, and are thought to be crucial for understanding the fractional Chern insulating states recently observed therein. Previous work proposed viewing the system using an adiabatic approximation that replaces the position-dependence of the layer spinor with a nonuniform periodic effective magnetic field. When the local zero-point kinetic energy of this magnetic field cancels identically against that of an effective Zeeman energy, a Bloch-band version of Aharonov-Casher zero-energy modes, which we refer to as Aharonov-Casher band, emerges leading to ideal quantum geometry. Here, we critically examine the validity of the adiabatic approximation and identify the parameter regimes under which Aharonov-Casher bands emerge. We show that the adiabatic approximation is accurate for a wide range of parameters including those realized in experiments. Furthermore, we show that while the cancellation leading to the emergence of Aharonov-Casher bands is generally not possible beyond the leading Fourier harmonic, the leading harmonic is the dominant term in the Fourier expansions of the zero-point kinetic energy and Zeeman energy. As a result, the leading harmonic expansion accurately captures the trend of the bandwidth and quantum geometry, though it may fail to quantitatively reproduce more detailed information about the bands such as the Berry curvature distribution.

cond-mat.mes-hall↗

arXiv2023

Magic Angles and Fractional Chern Insulators in Twisted Homobilayer TMDs

We explain the appearance of magic angles and fractional Chern insulators in twisted K-valley homobilayer transition metal dichalcogenides by mapping their continuum model to a Landau level problem. Our approach relies on an adiabatic approximation for the quantum mechanics of valence band holes in a layer-pseudospin field that is valid for sufficiently small twist angles and on a lowest Landau level approximation that is valid for sufficiently large twist angles. It simply explains why the quantum geometry of the lowest moiré miniband is nearly ideal at particular flat-band twist angles, predicts that topological flat bands occur only when the valley-dependent moiré potential is sufficiently strong compared to the interlayer tunneling amplitude, and provides a powerful starting point for the study of interactions

cond-mat.str-el↗

arXiv2023

Magnetic States of Graphene Proximitized Kitaev Materials

Single layer $α$-ruthenium trichloride ($\rmα-RuCl_3$) has been proposed as a potential quantum spin liquid. Graphene/$\rm RuCl_3$ heterobilayers have been extensively studied with a focus on the large interlayer electron transfer that dopes both materials. Here we examine the interplay between the competing magnetic state of $\rm RuCl_3$ layer and graphene electronic properties. We perform self-consistent Hartree-Fock calculations on a Hubbard-Kanamori model of the $4d^5$ $t_{2g}$ electrons of $\rmα-RuCl_3$ and confirm that out-of-plane ferromagnetic and zigzag antiferromagnetic states are energetically competitive. We show that the influence of hybridization between graphene and $\rmα-RuCl_3$ bands is strongly sensitive to the magnetic configuration of $\rm RuCl_3$ and the relative orientations of the two layers. We argue that strong hybridization leads to graphene magneto-resistance and that it may tilt the balance between closely competing magnetic states. Our analysis can be applied to any van der Waals heterobilayer system with weak interlayer hybridization and allows for arbitrary lattice constant mismatch and relative orientation.

cond-mat.str-el↗

arXiv2021

Theory of ARPES in Graphene-Based Moiré Superlattices

Graphene-based moiré superlattices are now established as an interesting platform for strongly-correlated many-electron physics, and have so far been characterized mainly by transport and scanning tunneling microscopy (STM) measurements. Motivated by recent experimental progress, we present a theoretical model study whose aim is to assess the potential of angle-resolved photoemission spectroscopy (ARPES) to resolve some of the many open issues in these systems. The theory is developed specifically for graphene on hexagonal boron nitride (G/hBN) and twisted bilayer graphene (TBG) moiré superlattices, but is readily generalized to any system with active degrees of freedom in graphene sheets.

cond-mat.str-el↗

arXiv2021

Moiré Commensurability and the Quantum Anomalous Hall Effect in Twisted Bilayer Graphene on Hexagonal Boron Nitride

The quantum anomalous Hall (QAH) effect is sometimes observed in twisted bilayer graphene (tBG) when it is nearly aligned with an encapsulating hexagonal boron nitride (hBN) layer. We propose that the appearance or absence of the QAH effect in individual devices could be related to commensurability between the graphene/graphene and graphene/hBN moiré patterns. We identify a series of points in the $(θ_{\rm GG},θ_{\rm GBN})$ twist-angle space at which the two moiré patterns are commensurate, allowing moiré band theory to be applied, and show that the band Chern numbers are in this case sensitive to a rigid in-plane hBN displacement. Given this property, we argue that the QAH effect is likely only when i) the $(θ_{\rm GG},θ_{\rm GBN})$ twist-angle-pair is close enough to a commensurate point that the two moiré patterns yield a supermoiré pattern with a sufficiently long length scale, and ii) the supermoiré has a percolating topologically non-trivial QAH phase. For twist angles far from commensurability, the hBN layer acts as a source of disorder that can destroy the QAH effect. Our proposal can explain a number of current experimental observations. Further experimental studies that can test this proposal more directly are suggested.

cond-mat.mes-hall↗

arXiv2017

One-way topological edge states in nonlinear gyroscopic phononic crystals

A unified form of time-reversal symmetry (TRS) breaking terms in phononic crystals, leading to nontrivial phononic topology, has been proposed recently, but is contradicted by some other works which introduce gyroscopic effect as TRS-breaking. We re-study gyroscopic phononic crystals using Newtonian mechanical method, and find the correct TRS-breaking term in consistent with the unified form. Applying this term we calculate the basic topological phononics in a honeycomb lattice. Furthermore, we study nonlinear phonon-phonon scattering effect on topological phononic edge states by molecular dynamics simulation. Generally edge states are not immune to such scattering effect, but under specific conditions some edge states run into bulk much more slowly, depending on the parameters of the model. This opens up the potential for effectively suppressing phonon dissipation by tuning the parameters, thereby realizing near-100% efficiency of one-way phonon transport in phonon devices.

cond-mat.mes-hall↗