arXiv subjects

Benjamin T. Zhou

Publications and source records attributed to Benjamin T. Zhou.

At least 19 recordsLinked to original sources

arXiv2026

Floquet Topological Spin-Valley-Layertronics on a Layered Dice Lattice

The recent discovery of long-sought dice flat band in layered YCl electride has opened up rich possibilities of correlation and topological physics in dice lattice systems [Nature Communications 17, 2213 (2026), arXiv:2509.05958]. Here, we reveal a plethora of distinctive correlated topological phases in a generic layered dice lattice system at band filling of $\nu =4$ under on-site Hubbard interactions: (i) the system is an intrinsic sublattice anti-ferromagnetic (AFM) quantum spin-valley Hall insulator; (ii) a circularly polarized light (CPL) drives the AFM spin-valley insulator into a Floquet odd-parity $f$-wave altermagnet(AM) insulator; (iii) a vertical displacement field turns the Floquet $f$-wave AM insulator into a spin-valley-layer-polarized Chern insulator, with the sign of spin, valley and Chern number all controlled by the direction of the displacement field. Our results not only establish the layered dice lattice as a versatile platform for electrically switchable magnetic and topological phases, but also provide an all-electrical scheme for integrated spin-valley-layertronics for non-volatile information storage and processing.

cond-mat.mtrl-sci↗

arXiv2026

Entwined lattice of atoms and anionic electrons in layered electride LaCl

Controlling the lattice geometry that governs electronic structure is a central theme in condensed-matter physics, yet in crystalline solids this geometry is usually fixed by the atomic framework. Electrides offer an alternative route to electronic structure design in which their excess electrons can organize into anionic electron lattice (AEL) and provide a lattice-like degree of freedom. Recent work has highlighted the standalone limit, where the AEL in YCl yields bands well described by the dice-lattice model. Here, using angle-resolved photoemission spectroscopy (ARPES), we show that LaCl, although isostructural to YCl, realizes a qualitatively different regime where the AEL is entwined with the La cation framework, producing a fully reconstructed electronic structure. Combining the ARPES result with tight-binding model analysis, we demonstrate that this radical divergence stems from the activation of direct hopping channels between the AEL and the La atomic lattice. This coupling reshapes the effective lattice geometry, reconstructs the electronic states, and modifies the associated Chern band topology, transforming the bipartite dice-lattice network in YCl into a tripartite structure in LaCl. Our findings demonstrate that the coupling between the AEL and the atomic lattice can actively shape the effective lattice geometry that governs the electronic structure. This coupling can act as a powerful tuning knob for electronic structure design that is inaccessible in conventional materials.

cond-mat.str-el↗

arXiv2026

Hidden Quantum Geometry in Bilayer Exciton Condensates

When an electron-doped layer is stacked with a hole-doped layer with approximately equal carrier density, inter-layer Coulomb interaction turns the bilayer system into an exciton condensate (EC). In this Letter, we reveal a fundamental property of bilayer ECs: the excitonic order gives rise to nontrivial hidden quantum geometric effects in the correlated electron-hole bands, even when the non-interacting bands are trivial. Such peculiar EC-driven quantum geometry manifests itself in a characteristic out-of-plane polarization response upon applying an in-plane AC electric field to the bilayer EC system. In particular, the second-order response exhibits a characteristic inverse square scaling with the bilayer EC order parameter. Our finding reveals a fundamental hidden Berry phase effect driven by electron-hole correlations, and establishes bilayer EC as a promising platform for rich nonlinear physics.

cond-mat.mes-hall↗

arXiv2026

YCl Electride as a Multi-Orbital Correlated Topological Dice Lattice System

The long-sought dice lattice flat band has recently been discovered for the first time in two-dimensional layered electride yttrium monochloride (YCl) [Nature Communications 17, 2213 (2026)]. While essential flat band features of YCl were captured by an idealized simple dice lattice model, we reveal in this Letter that a unique layer-orbital-valley coupling in YCl puts up a fundamental obstruction against a simple three-band dice lattice description of the flat band, and necessitates a multi-orbital description that faithfully represents the symmetry, topology, and correlation physics in the first-ever dice metal. Using an ab initio based multi-orbital Hubbard model with local interactions, we predict that the multi-orbital flat band supports a robust ferromagnetic ground state and electrically tunable correlated quantum anomalous Hall phases that are absent in an interacting single-orbital dice lattice. Our findings open a new avenue for exploring correlation and topology in electride systems.

cond-mat.mtrl-sci↗

arXiv2026

Magnons in multiorbital Hubbard models, from Lieb to kagome

We investigate the magnetic orders and excitations in a half-filled Hubbard model that continuously interpolates between the Lieb and kagome lattices. Using self-consistent Hartree-Fock approximation combined with real-time two-particle response functions from the Bethe-Salpeter equation in the random phase approximation, we map the $U-t'$ phase diagram of the Lieb-kagome lattices, identifying the typical magnetic states and the corresponding magnetic excitation spectra. In addition to gapless Goldstone magnons, the ferrimagnetic and antiferromagnetic symmetry-broken phases also exhibit gapped Higgs magnon bands, which originate from amplitude fluctuations in the order parameter characterizing spontaneous symmetry breaking.

cond-mat.str-el↗

arXiv2025

Experimental realization of dice-lattice flat band at the Fermi level in layered electride YCl

Flat electronic bands, where interactions among electrons overwhelm their kinetic energies, hold the promise for exotic correlation physics. The dice lattice has long been theorized as a host of flat bands with intriguing band topology. However, to date, no material has ever been found to host the characteristic flat bands of a dice lattice. Here, using angle-resolved photoemission spectroscopy (ARPES), we discover a dice-lattice flat band at $E_F$ in the van der Waals (vdW) electride [YCl]$^{2+}$: 2e-. In this system, excess valence electrons from Y deconfine from the cation framework to form an interstitial anionic electron lattice that constitutes the dice lattice. Our ARPES measurements unambiguously identify two sets of dice-lattice bands in YCl, including a nearly dispersionless band at the Fermi level. The flat bands and other dispersive bands observed in ARPES find excellent agreement with first-principles calculations, and theoretical analysis reveals that the near-$E_F$ electronic structure is well captured by a simple dice-lattice model. Our findings thus end the long quest of a real dice flat band material and establish vdW electride YCl as a prototype of dice metals. Our results further demonstrate the anionic electron lattice as a novel scheme for realizing lattice geometries and electronic structures rare to find in conventional crystalline systems.

cond-mat.str-el↗

arXiv2025

Pseudo-Ising superconductivity induced by $p$-wave magnetism

Unconventional magnetic orders usually interplay with superconductivity in intriguing ways. Here we propose that a conventional superconductor in proximity to a compensated $p$-wave magnet exhibits behaviors analogous to those of Ising superconductivity found in transition-metal dichalcogenides, which we refer to as pseudo-Ising superconductivity. The pseudo-Ising superconductivity is characterized by several distinctive features: (i) it stays much more robust under strong $p$-wave magnetism than usual ferromagnetism or $d$-wave altermagnetism, thanks to the apparent time-reversal symmetry in $p$-wave spin splitting; (ii) in the low-temperature regime, a second-order superconducting phase transition occurs at a significantly enhanced in-plane upper critical magnetic field $B_{c2}$; (iii) the supercurrent-carrying state establishes non-vanishing out-of-plane spin magnetization, which is forbidden by symmetry in Rahsba and Ising superconductors. We further propose a spin-orbit-free scheme to realize Majorana zero modes by placing superconducting quantum wires on a $p$-wave magnet. Our work establishes a new form of unconventional superconductivity generated by $p$-wave magnetism.

cond-mat.supr-con↗

arXiv2024

Quantum-Geometric Origin of Out-of-plane Stacking Ferroelectricity

Stacking ferroelectricity (SFE) has been discovered in a wide range of van der Waals materials and holds promise for applications, including photovoltaics and high-density memory devices. We show that the microscopic origin of out-of-plane stacking ferroelectric polarization can be generally understood as a consequence of nontrivial Berry phase borne out of an effective Su-Schrieffer-Heeger model description with broken sublattice symmetry, thus elucidating the quantum-geometric origin of polarization in the extremely non-periodic bilayer limit. Our theory applies to known stacking ferroelectrics such as bilayer transition-metal dichalcogenides in 3R and T$_{\rm d}$ phases, as well as general AB-stacked honeycomb bilayers with staggered sublattice potential. Our explanatory and self-consistent framework based on the quantum-geometric perspective establishes quantitative understanding of out-of-plane SFE materials beyond symmetry principles.

cond-mat.mtrl-sci↗

arXiv2023

Cu-substituted lead phosphate apatite as an inversion-asymmetric Weyl semimetal

Based on symmetry arguments and the latest density functional results for the copper-substituted lead phosphate apatite (`LK-99'), we show that, at the non-interacting level, the material is an inversion-asymmetric Weyl semimetal. A pair of Weyl nodes with opposite chiralities emerge at different energies in the vicinity of the time-reversal-invariant $Γ$ and ${\rm A}$ points of the 3D Brillouin zone. These are characterized by unusual Weyl charges of $C_{\rm W} = \pm 2$ and are connected by two branches of topologically protected Fermi arc states on surfaces parallel to the principal $c$-axis. We further study important effects of the atomic spin-orbit coupling on the band structure and the electronic properties of the material in general. Possible implications of the proposed band topology on the strong correlation physics are also discussed.

cond-mat.mtrl-sci↗

arXiv2022

Non-Abelian topological superconductivity in maximally twisted double-layer spin-triplet valley-singlet superconductors

Recent theoretical and experimental studies point to a novel spin-triplet valley-singlet (STVS) superconducting phase in certain two-valley electron liquids, including rhombohedral trilayer graphene, Bernal bilayer graphene and ZrNCl. This fully gapped phase is exotic in that it combines into Cooper pairs same-spin electrons from valleys centered around the opposing corners of a hexagonal Brillouin zone, but is, nevertheless, topologically trivial. Here, we predict that upon stacking two layers of an STVS material with an angular twist, a novel chiral topological phase -- an $f \pm if'$-wave superconductor -- emerges in the vicinity of the `maximal' twist angle of 30$^{\circ}$ where the system becomes an extrinsic quasi-crystal with 12-fold tiling. The resulting composite is a non-Abelian topological superconductor (TSC) with an odd number of chiral Majorana modes at its edges and a single Majorana zero mode (MZM) localized in the vortex core. Through symmetry analysis and detailed microscopic modelling based on a novel quasi-crystal band structure technique, we demonstrate that the non-Abelian TSC forms when the isolated Fermi pockets coalesce into a single connected Fermi surface around the center of the moiré Brillouin zone and is stable over a wide range of electron density. We further discuss how the energetics leading to the $f \pm if'$-wave phase results in anomalous $π$-periodic inter-layer Josephson effect, which can serve as a distinctive signature of the chiral phase. Distinct from the valley-preserving moiré physics in small-angle twisted graphene, our results establish the large-angle moiré physics arising near maximal twist as a new avenue toward intrinsic TSC with non-Abelian excitations.

cond-mat.supr-con↗

arXiv2022

Moiré flat Chern bands and correlated quantum anomalous Hall states generated by spin-orbit couplings in twisted homobilayer MoS$_2$

We predict that in a twisted homobilayer of transition-metal dichalcogenide MoS$_2$, spin-orbit coupling in the conduction band states from $\pm K$ valleys can give rise to moiré flat bands with nonzero Chern numbers in each valley. The nontrivial band topology originates from a unique combination of angular twist and local mirror symmetry breaking in each individual layer, which results in unusual skyrmionic spin textures in momentum space with skyrmion number $\mathcal{S} = \pm 2$. Our Hartree-Fock analysis further suggests that density-density interactions generically drive the system at $1/2$-filling into a valley-polarized state, which realizes a correlated quantum anomalous Hall state with Chern number $\mathcal{C} = \pm 2$. Effects of displacement fields are discussed with comparison to nontrivial topology from layer-pseudospin magnetic fields.

cond-mat.mes-hall↗

arXiv2022

Spontaneous Polarization Induced Photovoltaic Effect In Rhombohedrally Stacked MoS$_2$

Stacking order in van der Waals materials determines the coupling between atomic layers and is therefore key to the materials' properties. By exploring different stacking orders, many novel physical phenomena have been realized in artificial vdW stacks. Recently, 2D ferroelectricity has been observed in zero-degree aligned hBN and graphene-hBN heterostructures, holding promise in a range of electronic applications. In those artificial stacks, however, the single domain size is limited by the stacking-angle misalignment to about 0.1 to 1 $μ$m, which is incompatible with most optical or optoelectronic applications. Here we show MoS$_2$ in the rhombohedral phase can host a homogeneous spontaneous polarization throughout few-$μ$m-sized exfoliated flakes, as it is a natural crystal requiring no stacking and is, therefore free of misalignment. Utilizing this homogeneous polarization and its induced depolarization field (DEP), we build a graphene-MoS$_2$ based photovoltaic device with high efficiency. The few-layer MoS$_2$ is thinner than most oxide-based ferroelectric films, which allows us to maximize the DEP and study its impact at the atomically thin limit, while the highly uniform polarization achievable in the commensurate crystal enables a tangible path for up-scaling. The external quantum efficiency of our device is up to 16% at room temperature, over one order larger than the highest efficiency observed in bulk photovoltaic devices, owing to the reduced screening in graphene, the exciton-enhanced light-matter interaction, and the ultrafast interlayer relaxation in MoS$_2$. In view of the wide range of bandgap energy in other TMDs, our findings make rhombohedral TMDs a promising and versatile candidate for applications such as energy-efficient photo-detection with high speed and programmable polarity.

cond-mat.mes-hall↗

arXiv2020

Giant nonlinear Hall effect in strained twisted bilayer graphene

Recent studies have shown that moiré flat bands in a twisted bilayer graphene(TBG) can acquire nontrivial Berry curvatures when aligned with hexagonal boron nitride substrate [1, 2], which can be manifested as a correlated Chern insulator near the 3/4 filling [3, 4]. In this work, we show that the large Berry curvatures in the moiré bands lead to strong nonlinear Hall(NLH) effect in a strained TBG with general filling factors. Under a weak uniaxial strain $\sim 0.1\%$, the Berry curvature dipole which characterizes the nonlinear Hall response can be as large as $\sim$ 200Å, exceeding the values of all previously known nonlinear Hall materials [5-14] by two orders of magnitude. The dependence of the giant NLH effect as a function of electric gating, strain and twist angle is further investigated systematically. Importantly, we point out that the giant NLH effect appears generically for twist angle near the magic angle due to the strong susceptibility of nearly flat moiré bands to symmetry breaking induced by strains. Our results establish TBG as a practical platform for tunable NLH effect and novel transport phenomena driven by nontrivial Berry phases.

cond-mat.mes-hall↗

arXiv2020

Spin-orbit-parity coupled superconductivity in topological monolayer WTe$_2$

Recent experiments reported gate-induced superconductivity in the monolayer 1T$'$-WTe$_2$ which is a two-dimensional topological insulator in its normal state [1, 2]. The in-plane upper critical field $B_{c2}$ is found to exceed the conventional Pauli paramagnetic limit $B_p$ by 1-3 times. The enhancement cannot be explained by conventional spin-orbit coupling which vanishes due to inversion symmetry. In this work, we unveil some distinctive superconducting properties of centrosymmetric 1T$'$-WTe$_2$ which arise from the coupling of spin, momentum and band parity degrees of freedom. As a result of this spin-orbit-parity coupling: (i) there is a first-order superconductor-metal transition at $B_{c2}$ much higher than the Pauli paramagnetic limit $B_p$, (ii) spin-susceptibility is anisotropic with respect to in-plane directions and results in anisotropic $B_{c2}$ and (iii) the $B_{c2}$ exhibits a strong gate dependence as the spin-orbit-parity coupling is significant only near the topological band crossing points. The importance of SOPC on the topologically nontrivial inter-orbital pairing phase is also discussed. Our theory generally applies to centrosymmetric materials with topological band inversions.

cond-mat.supr-con↗

arXiv2020

Highly tunable nonlinear Hall effects induced by spin-orbit couplings in strained polar transition-metal dichalcogenides

Recently, signatures of nonlinear Hall effects induced by Berry-curvature dipoles have been found in atomically thin 1T'/Td-WTe$_2$. In this work, we show that in strained polar transition-metal dichalcogenides(TMDs) with 2H-structures, Berry-curvature dipoles created by spin degrees of freedom lead to strong nonlinear Hall effects. Under an easily accessible uniaxial strain of order 0.2%, strong nonlinear Hall signals, characterized by a Berry-curvature dipole on the order of 1Å, arise in electron-doped polar TMDs such as MoSSe, and this is easily detectable experimentally. Moreover, the magnitude and sign of the nonlinear Hall current can be easily tuned by electric gating and strain. These properties can be used to distinguish nonlinear Hall effects from classical mechanisms such as ratchet effects. Importantly, our system provides a potential scheme for building electrically switchable energy-harvesting rectifiers.

cond-mat.mes-hall↗

arXiv2019

Strongly enlarged topological regime and enhanced superconducting gap in nanowires coupled to Ising superconductors

An external magnetic field is needed to drive a nanowire in proximity to an s-wave superconductor into a topological regime which supports Majorana end states. However, a magnetic field generally suppresses the proximity superconducting gap induced on the nanowire. In recent experiments using InSb nanowires coupled to Al, the induced proximity gap vanishes at magnetic fields B~1T. This results in a small superconducting gap on the wire and a narrow topological regime which is proportional to the strength of the magnetic field. In this work, we show that by placing nanowires in proximity to recently discovered Ising superconductors such as the atomically thin transition-metal dichalcogenide(TMD) NbSe2, the topological superconducting gap on the wire can maintain at a large magnetic field as strong as B~10T. This robust topological superconducting gap is induced by the unique equal-spin triplet Cooper pairs of the parent Ising superconductor. The strong magnetic field allows a topological regime ten times larger than those in InSb wires coupled to Al. Our work establishes a realistic platform for building robust Majorana-based qubits.

cond-mat.supr-con↗

arXiv2019

Spin-orbit coupling induced valley Hall effects in transition-metal dichalcogenides

In transition-metal dichalcogenides, electrons in the K-valleys can experience both Ising and Rashba spin-orbit couplings. In this work, we show that the coexistence of Ising and Rashba spin-orbit couplings leads to a special type of valley Hall effect, which we call spin-orbit coupling induced valley Hall effect. Importantly, near the conduction band edge, the valley-dependent Berry curvatures generated by spin-orbit couplings are highly tunable by external gates and dominate over the intrinsic Berry curvatures originating from orbital degrees of freedom under accessible experimental conditions. We show that the spin-orbit coupling induced valley Hall effect is manifested in the gate dependence of the valley Hall conductivity, which can be detected by Kerr effect experiments.

cond-mat.mes-hall↗

arXiv2018

Intrinsic valley Hall transport in atomically thin MoS2

Electrons hopping in two-dimensional honeycomb lattices possess a valley degree of freedom in addition to charge and spin. In the absence of inversion symmetry, these systems were predicted to exhibit opposite Hall effects for electrons from different valleys. Such valley Hall effects have been achieved only by extrinsic means, such as substrate coupling, dual gating, and light illuminating. Here, we report the first observation of intrinsic valley Hall transport without any extrinsic symmetry breaking in the non-centrosymmetric monolayer and trilayer MoS2, evidenced by considerable nonlocal resistance that scales cubically with local resistance. Such a hallmark survives even at room temperature with a valley diffusion length at micron scale. By contrast, no valley Hall signal is observed in the centrosymmetric bilayer MoS2. Our work elucidates the topological quantum origin of valley Hall effects and marks a significant step towards the purely electrical control of valley degree of freedom in topological valleytronics.

cond-mat.mes-hall↗