arXiv subjects

Daniele Guerci

Publications and source records attributed to Daniele Guerci.

At least 19 recordsLinked to original sources

arXiv2026

Higher-Winding Fractionalization

Higher-winding skyrmion textures can generate emergent magnetic fields with multiple flux quanta per unit cell. This opens an intriguing route toward fractionalization, allowing fractionalized quantum anomalous Hall states to arise even at integer filling of the microscopic unit cell. We show that, in this setting, increasing lattice-scale inhomogeneity of the emergent magnetic field drives a Berezinskii--Kosterlitz--Thouless (BKT) transition between a fractionalized liquid and a crystalline dielectric state. This transition carries a topological signature: under flux insertion, the many-body polarization defines a quantized winding number that is nonzero in the fractionalized phase and vanishes in the dielectric crystal.

cond-mat.str-el↗

arXiv2026

Rhombohedral Graphene: A Tale of Many Crystals

Experiments on rhombohedral graphene have uncovered an extraordinary wealth of correlated quantum phases - from chiral superconductors to electronic crystals - all within a single family of atomically thin materials. Here, we introduce a simple indicator, derived from the noninteracting band dispersion, that identifies strongly correlated regions in the phase diagram of rhombohedral graphene as a function of carrier density and displacement field. We develop a neural-network variational Monte Carlo method, combined with Hartree-Fock theory, to solve the interacting ground states. Our calculation reveals a variety of electron crystals with no classical analog. These include, at increasing density: Wigner crystal, self-doped Wiger crystal, as well as ''anticrystal'', a lattice of holes in an electron liquid. We discuss their experimental manifestations and possible connection to superconductivity.

cond-mat.str-el↗

arXiv2026

Attention-Based Foundation Model for Quantum States

We present an attention-based foundation model architecture for learning and predicting quantum states across Hamiltonian parameters, system sizes, and physical systems. Using only basis configurations and physical parameters as inputs, our trained neural network is able to produce highly accurate ground state wavefunctions. For example, we build the phase diagram for the 2D square-lattice $t-V$ model with $N$ particles, from only 18 parameters $(V/t,N)$. Thus, our architecture provides a basis for building a universal foundation model for quantum matter.

cond-mat.str-el↗

arXiv2026

Anomalous Hall effect in rhombohedral graphene

Motivated by recent experiments on rhombohedral stacked multilayer graphene and the observation of the anomalous Hall effect in a spontaneous spin-valley polarized quarter metal state, we calculate the anomalous Hall conductivity for this system in the presence of two types of impurities: weak and dense as well as sparse and strong. Our calculation of $σ_{xy}$ is based on the Kubo-Streda diagrammatic approach. In a model with Gaussian disorder applicable to weak dense impurities, this involves all non-crossing diagrams (intrinsic, side-jump and Gaussian skew-scattering contributions) and additionally diagrams with two intersecting impurities, X and $Ψ$, representing diffractive skew-scattering processes. A "Mercedes star" diagram (non-Gaussian skew scattering) is furthermore included to treat in the case of strong, sparse impurities. We supplement our asymptotically exact analytical solutions for an isotropic model without warping effects by semi-numerical calculations accounting perturbatively for warping, which plays a crucial role in the low-energy band structure.

cond-mat.mes-hall↗

arXiv2026

Topological Kondo Insulator from Spin Loop Currents

We demonstrate that interacting electrons in AB-stacked $\mathrm{MoTe}_2/\mathrm{WSe}_2$ realize a topological Kondo insulator at hole filling $ν=2$ per moiré unit cell. In the presence of only local correlations, a symmetry of the moiré-scale bandstructure enforces a compensated topological semimetal by tying band inversion to band overlap. We show that non-local interactions change the physics qualitatively, since they allow intrinsic, quantum-geometry-induced spin loop currents to feed back on the effective bandstructure, which lift the remaining accidental degeneracies and open a full gap in the spectrum, leading to a fully gapped topological Kondo insulator. We establish this using real-frequency dynamical mean-field theory to capture Kondo physics alongside Hartree-Fock for non-local interactions. The topological Kondo insulator emerges at intermediate displacement fields, where strong correlations manifest through an enhanced spin susceptibility, a suppressed charge susceptibility, and a stronger thermal dependence of the resistivity. Our results are in good agreement with recent experiments on $\mathrm{MoTe}_2/\mathrm{WSe}_2$ bilayers demonstrating topological to trivial phase transitions controlled by the displacement field.

cond-mat.str-el↗

arXiv2026

Topological superconductivity with emergent vortex lattice in twisted semiconductors

The coexistence of superconductivity and fractional quantum anomalous Hall (FQAH) effect has recently been observed in twisted MoTe$_2$ and theoretically demonstrated in a model of repulsively interacting electrons under an emergent magnetic field arising from the layer pseudospin texture in moiré superlattice. Here, we show that this superconducting state is a chiral $f$-wave superconductor hosting an array of $double$ vortices, which are induced by the emergent magnetic field with $h/e$ flux quanta per moiré unit cell. This superconducting vortex lattice state is topological and features Chern number $-1/2$, giving rise to a half-integer thermal Hall conductance. Our theory provides a common mechanism and unified understanding of FQAH and topological superconductivity, with a rich phase diagram controlled by the spatial modulation of the emergent magnetic field.

cond-mat.supr-con↗

arXiv2025

Higher Chern bands in helical homotrilayer transition metal dichalcogenides

We propose helically twisted homotrilayer transition metal dichalcogenides as a platform for realizing correlated topological phases of matter with higher and tunable Chern numbers. We show that a clear separation of scales emerges for small twist angles, allowing us to derive a low-energy continuum model that captures the physics within moiré-scale domains. We identify regimes of twist angle and displacement field for which the highest-lying hole band is isolated from other bands and is topological with $K$-valley Chern number $C=-2$. We demonstrate that varying the displacement field can induce a transition from $C=-2$ to $C=-1$, as well as from a topologically trivial band to a $C=-1$ band. We derive an effective tight-binding description for a high-symmetry stacking domain which is valid for a wide range of twist angles, and we show that the $C=-2$ band can remain stable at filling fraction $ν=-1$ in the presence of interactions in Hartree-Fock calculations.

cond-mat.mes-hall↗

arXiv2025

From Fractionalization to Chiral Topological Superconductivity in a Flat Chern Band

We show that interacting electrons in a flat Chern band can form, in addition to fractional Chern insulators, a chiral $f$-wave topological superconductor that hosts neutral Majorana fermion edge modes. Superconductivity emerges from an interaction-induced metallic state that exhibits anomalous Hall effect, as observed in rhombohedral graphene and near the $ν=\frac{2}{3}$ fractional Chern insulator in twisted transition metal dichalcogenides.

cond-mat.supr-con↗

arXiv2025

Spontaneous vortex-antivortex lattice and Majorana fermions in rhombohedral graphene

The discovery of superconducting states in multilayer rhombohedral graphene with spin and valley polarization has raised an interesting question: how does superconductivity cope with time-reversal symmetry breaking? In this work, using Ginzburg-Landau theory and microscopic calculation, we predict the existence of a new superconducting state at low electron density, which exhibits a spontaneously formed lattice of vortices and antivortices hosting Majorana zero-modes in their cores. We further identify this vortex-antivortex lattice (VAL) state in the experimental phase diagram and describe its experimental manifestations.

cond-mat.supr-con↗

arXiv2025

Ferromagnetic superconductivity with excitonic Cooper pairs: Application to $Γ$-valley twisted semiconductors

We present a theory of ferromagnetic superconductivity that emerges upon doping a correlated ferromagnetic insulator through the condensation of excitonic Cooper pairs, which are charge-$2e$ bosonic quasiparticles made of Cooper pairs strongly hybridized with excitons. By solving a model of spin-polarized electrons using the strong-coupling expansion to the second order, we demonstrate the emergence of excitonic Cooper pairs from electron-hole fluctuations upon doping a strongly correlated insulator. We characterize their binding energy, effective mass, and the resulting superconducting transition temperature. We propose possible realization of spin-polarized superconductivity in twisted semiconductors with honeycomb moiré superlattice.

cond-mat.supr-con↗

arXiv2025

Topologically enabled superconductivity: possible implications for rhombohedral graphene

We present a topological mechanism for superconductivity emerging from Chern-2 insulators. While, naively, time-reversal symmetry breaking is expected to prevent superconductivity, it turns out that the opposite is the case: An explicit model calculation for a generalized attractive-U Haldane-Hubbard model demonstrates that superconductivity is only stabilized near the quantum anomalous Hall state, but not near a trivial, time-reversal symmetric band insulator. As standard Bardeen-Cooper-Schrieffer-like mean-field theory fails to capture any superconducting state, we explain this using an effective fractionalized field theory involving fermionic chargeons, bosonic colorons and an emergent U(1) gauge field. When the chargeons form a gapped topological band structure, the proliferation of single monopoles of this gauge field is forbidden. However, long-ranged monopole-antimonopole correlations emerge, and we argue that those correspond to superconducting order. Using random phase approximation on top of extensive slave-rotor mean-field calculations we characterize coherence length and stiffness of the superconductor. Thereby, we deduce the phase diagram in parameter space and furthermore discuss the effect of doping, temperature and an external magnetic field. We complement the fractionalized theory with calculations using an effective spin model and Gutzwiller projected wavefunctions. While mostly based on a simple toy model, we argue that our findings contribute to a better understanding of superconductivity emerging out of spin- and valley polarized rhombohedral graphene multilayers in a parameter regime with nearby quantum anomalous Hall insulators.

cond-mat.str-el↗

arXiv2024

Charge transfer spin-polarons and ferromagnetism in weakly doped AB-stacked TMD heterobilayers

We study the formation of ferromagnetic and magnetic polaron states in weakly doped heterobilayer transition metal dichalcogenides in the ``heavy fermion'' limit in which one layer hosts a dense set of local moments and the other hosts a low density of itinerant holes. We show that interactions among the carriers in the itinerant layer induces a ferromagnetic exchange. We characterize the ground state finding a competition, controlled by the carrier concentration and interlayer exchange, between a layer decoupled phase of itinerant carriers in a background of local moments, a fully polarized ferromagnet and a canted antiferromagnet. In the canted antiferromagnet phase the combination of the in-plane 120$^{\circ}$ Néel order and Ising spin orbit couplings induces winding in the electronic wavefunction giving rise to a topologically non-trivial spin texture and an observable anomalous Hall effect. At larger carrier density the ferromagnetically ordered phase transitions into a paramagnetic heavy Fermi liquid state. This theory enables a comprehensive understanding of the existing experimental observations while also making predictions including experimental signatures enabling direct imaging of spin polaron bound states with scanning tunneling microscopy. Our work shows that the prevailing paradigm of the (Doniach) phase diagram of heavy fermion metals is fundamentally modified in the low doping regime of heterobilayer transition metal dichalcogenides.

cond-mat.str-el↗

arXiv2024

Topological superconductivity from repulsive interactions in twisted WSe$_2$

The recent observation of superconductivity in twisted bilayer WSe$_2$ raises intriguing questions concerning the origin and the properties of superconducting states realized in bands with non-trivial topological properties and repulsive electron-electron interactions. Using a continuum band structure model, we analyze a mechanism for Coulomb interaction-driven superconductivity in twisted bilayers of WSe$_2$. We discuss the symmetries and the phenomenological properties of the resulting superconducting phases and their evolution with interlayer potential difference, tunable via an out of plane electric field. The pairing strength is a non-monotonic function of interlayer potential, being larger at intermediate values due to mixing of singlet and triplet pairing. In contrast, at larger interlayer potential, the pairing tendency is suppressed due to enhanced Coulomb repulsion. The superconducting state is chiral in a large regime of parameters and undergoes a transition to a nodal nematic superconductor at a critical potential difference. The chiral state, characterized by an intervalley-symmetric superposition of triplet and singlet pairs, is classified as a topological superconductor within the Altland-Zirnbauer class C. At zero interlayer potential difference, the superconducting state is instead of class D, which hosts Majorana zero modes, making it a promising candidate for applications in quantum computation.

cond-mat.supr-con↗

arXiv2024

Layer skyrmions for ideal Chern bands and twisted bilayer graphene

Ideal $C=1$ Chern bands exhibit a Landau level correspondence: they factorize as a lowest Landau levels and a spinor wavefunction that spans the layer index. We demonstrate that, in single Dirac moiré models, the spinor develops generally a Skyrme texture in real space with an associated Berry phase which compensates exactly the magnetic phase of the Landau level. For ideal bands with higher Chern numbers $C>1$, we find that $C$ color Landau levels are carried by $C$ spinors with Skyrme textures. We identify a SU(C) gauge symmetry in the color space of spinors and an emergent non-Abelian connection in real space intimately linked to the Pontryagin winding index of the layer skyrmions. They result in a total real-space Chern number of $-1$, screening the magnetic phase, irrespective of $C$ and of the number of layers. The topologically robust Skyrme texture remains remarkably intact in twisted bilayer graphene, even far from the chiral limit, and for realistic values of corrugation, making it an experimentally testable feature. We verify our predictions at the first magic angle of twisted bilayer, trilayer, and monolayer-bilayer graphene.

cond-mat.mes-hall↗

arXiv2024

Helical trilayer graphene in magnetic field: Chern mosaic and higher Chern number ideal flat bands

Helical trilayer graphene (hTG) exhibits a supermoiré pattern with large domains centered around stacking points ABA and BAB, where two well-separated low-energy bands appear with different total Chern numbers at each valley, forming a Chern mosaic pattern. In the chiral limit, the low-energy bands become exactly flat at zero energy for magic-angle twists. Here we investigate these zero-energy flat bands and their topological properties in the presence of a perpendicular magnetic field. We show that hTG retains the precise flatness of the zero-energy bands, even at finite magnetic fields. We find topological phase transitions at fields corresponding to unit and half magnetic flux leading to an emergence of higher Chern number flat bands. Consequently the Chern mosaic gets modified for finite magnetic fields. We further find the analytical forms of zero-energy wave functions and identify a set of hidden wave functions, which gives crucial insights into both the topological transitions and enhancement of Chern numbers across them. We also find topological transitions away from the chiral limit with finite corrugations and at different magic angles.

cond-mat.mes-hall↗

arXiv2024

Topological Kondo semimetal and insulator in AB-stacked heterobilayer transition metal dichalcogenides

Recent experiments reported the realization of a heavy Fermi liquid in AB-stacked MoTe$_2$/WSe$_2$ heterobilayers. In this paper we show that the AB-stacked heterobilayer configuration is particularly suited to realize topological Kondo semimetal and topological Kondo insulator ground states at a doping of two holes per moiré unit cell. The small lattice mismatch between the MoTe$_2$ and WSe$_2$ monolayers and the different bandwidths of their highest lying moiré valence bands means that, in the experimentally relevant range of hole dopings, the MoTe$_2$ layer is effectively a Mott insulator with only low-lying magnetic excitations Kondo-coupled to more itinerant electrons in the WSe$_2$. The crucial consequence of the AB-stacking configuration is that the interlayer tunnelling connects orbitals of opposite parity in the two layers, leading to a chiral Kondo coupling. We show that the chiral Kondo coupling favors a topological Kondo semimetal at filling $ν=1+1$, with a non-quantized spin Hall conductance arising from edge modes, whose spectrum and overlap with bulk states we determine. We further show that a spatially random strain field that locally breaks the rotation symmetry can convert the Kondo semimetal to a narrow gap topological Kondo insulator featuring a quantized spin Hall conductance.

cond-mat.str-el↗

arXiv2024

Absence of quantization in the circular photogalvanic effect in disordered chiral Weyl semimetals

The circularly polarized photogalvanic effect (CPGE) is studied in chiral Weyl semimetals with short-ranged quenched disorder. Without disorder, the topological properties of chiral Weyl semimetals lead to the quantization of the CPGE, which is a second-order optical response. Using a combination of diagrammatic perturbation theory in the continuum and exact numerical calculations via the kernel polynomial method on a lattice model we show that disorder perturbatively destabilizes the quantization of the CPGE.

cond-mat.mes-hall↗

arXiv2024

Electrical Transport in the Hatsugai-Kohmoto Model

We show that in models with the Hatsugai-Kohmoto type of interaction that is local in momentum space thus infinite-range in real space, Kubo formulas neither reproduce the correct thermodynamic susceptibilities, nor yield sensible transport coefficients. Using Kohn's trick to differentiate between metals and insulators by threading a flux in a torus geometry, we uncover the striking property that Hatsugai-Kohmoto models with an interaction-induced gap in the spectrum sustain a current that grows as the linear size at any non-zero flux and which can be either diamagnetic or paramagnetic.

cond-mat.str-el↗