arXiv subjects

Trithep Devakul

Publications and source records attributed to Trithep Devakul.

At least 19 recordsLinked to original sources

arXiv2026

Quantized Transport through a Supermoir\'e Chern Mosaic

Magic-angle helical trilayer graphene---three graphene layers sequentially twisted in the same direction by $\sim1.8^\circ$---relaxes into a mosaic of domains that, at zero field, carry opposite valley-resolved Chern numbers, with boundaries hosting a network of gapless conducting modes. Charge transport through this network depends sensitively on how the modes connect and scatter, making well-quantized transport unlikely. Contrary to this expectation, we observe a field-induced Chern gap with Chern number $C=-6$ emanating from charge neutrality; in this gap, the Hall resistance is quantized to within $2\%$ of the expected value, $-h/6e^2$, at 4.6 K. We explain this behavior using both Hofstadter and orbital Zeeman calculations, which show that a moderate magnetic field drives a valley-selective topological transition. Above the transition, the total Chern number of the occupied states in each spin-valley flavor becomes identical across neighboring domains, and the domain-wall modes can become gapped. Though the central valence-band Chern numbers still differ between the two domain types, the observed quantized transport attests to a global gap.

cond-mat.mes-hall↗

arXiv2026

Skyrmion Fractional Chern Insulator: An Intrinsically Multiband Route to Fractionalization in Rhombohedral Graphene

We propose an unconventional microscopic origin for the fractional quantum anomalous Hall (FQAH) effect in rhombohedral graphene moir\'e superlattices: skyrmion fractionalization. We view the state at filling $\nu<1$ as a metal of skyrmion vacancies, charge $+e$ objects formed by removing layer-pseudospin skyrmions from the interaction-generated skyrmion lattice Chern insulator at $\nu=1$. These vacancies are intrinsically multiband degrees of freedom, absent in single Chern band-projected studies. Building on a recently proposed ideal limit, we first develop an effective field theory showing that skyrmion vacancies can themselves fractionalize, thereby inducing charge fractionalization. Focusing on $\nu=\frac{2}{3}$, we then construct explicit variational trial wavefunctions for the resulting skyrmion fractional Chern insulator and provide numerical evidence, together with general arguments, showing that this process is energetically favored. Our results establish a realistic route to the FQAH that does not rely on a partially filled Chern band, but instead arises from fractionalization of collective pseudospin textures.

cond-mat.mes-hall↗

arXiv2026

Fermiology and the Candidate Chiral Superconductor in Rhombohedral Tetralayer Graphene

Chiral superconductivity, in which the phase of the superconducting order parameter winds in momentum space, has long been sought for its close link to topological superconductivity. Recent work reported a superconductor in rhombohedral multilayer graphene emerging from a time-reversal symmetry broken normal state, suggesting that it could be a chiral superconductor. However, the possibility of chirality depends on the symmetry and structure of the normal-state Fermi surface, which have not been directly measured. Here we measure quantum oscillations in rhombohedral tetralayer graphene over a broad range of the phase diagram, including the superconducting region. At densities well above the onset of superconductivity, we reproduce previously-reported oscillations consistent with a spin- and valley-polarized quarter metal with a single simply-connected Fermi pocket. As the carrier density is reduced, we find a transition to a complex "multitone" state that persists through the superconducting region. This state's spectrum of quantum oscillations is incompatible with a simply-connected quarter metal. The next-simplest candidate normal states suggested by our microscopic modeling (fully-polarized annular, nematic, and three-pocket states) are inconsistent with our measurements, albeit difficult to rule out entirely. The normal state is thus seen to be richer than previously envisaged, reshaping the search for the superconducting mechanism and the possible chirality of the pairing channel.

cond-mat.supr-con↗

arXiv2026

Visualizing orbital magnetism in electron doped rhombohedral multilayer graphene

Electron doped rhombohedral multilayer graphene at high displacement field features an exceptionally flat band minimum with near-ideal quantum geometry. Experiments in this regime observe the formation of a 'quarter metal,' in which the electron liquid condenses into a single spin- and valley flavor. Remarkably, recent experiments have found a zero resistance state in the same region of the density- and displacement-field-tuned parameter space, attributed to the formation of a chiral superconductor from an orbitally ferromagnetic normal state. Here, we use nanoSQUID-on-tip magnetometry to map the orbital magnetization of electron-doped rhombohedral graphene devices ranging in thickness between 3 and 15 layers. Magnetization within the quarter metal phases peaks at finite density, consistent with concentration of the Berry curvature in a finite-momentum 'ring of fire'. Correlating transport and local magnetometry data in a superconducting tetralayer sample reveals a finite orbital ferromagnetic moment, providing direct evidence of valley polarization in the superconducting ground state. We further show that widely observed stochastic switching of the resistivity in both metallic and superconducting regimes arises from a density-tuned sign change in the valley-resolved total magnetic moment. This leads to the formation of metastable magnetic domains under typical gate control sequences and can also be harnessed for electric-field controlled switching of the magnetization across the entire device. Finally, high resolution measurements of the magnetization across a superconducting transition allow us to put an upper bound on the 'condensation magnetization' of 0.1 Bohr magneton per carrier, placing a strong quantitative restriction on theoretical models for ferromagnetic superconductivity.

cond-mat.mes-hall↗

arXiv2026

Mesoscopic transport in a Chern mosaic

We analyze mesoscopic electronic transport in a Chern mosaic: a regular pattern of domains whose electronic bands carry differing local Chern numbers. An example platform where a Chern mosaic can arise is a moir\'e heterostructure, where variations in the local moir\'e parameters can produce such domains. We compute resistances at linear response for a variety of domain wall network geometries at zero temperature and magnetic field. Simple domain configurations can exhibit zero, integer, or fractional multiples of the quantum of resistance in both the longitudinal and transverse (Hall) responses. Our simple semi-classical analysis provides a useful computational method and comparative catalog for ongoing experiments in two-dimensional topological materials.

cond-mat.mes-hall↗

arXiv2026

Electrically controllable valence-conduction band reversals in helical trilayer graphene

In moir\'e graphene systems, electronic interactions lift spin and valley degeneracies, leading to symmetry-broken ground states. In helical trilayer graphene (HTG), we uncover a distinct interaction-driven mechanism in which the roles of sublattice-polarized valence and conduction bands are cyclically reversed. Using scanning nano-SQUID magnetometry, we detect a series of sharp magnetic signatures consistent with seesaw-like transitions, where occupied and unoccupied valence and conduction bands interchange repeatedly with doping, accompanied by a novel form of magnetic hysteresis. These transitions occur entirely within metallic regimes and leave only weak fingerprints in transport measurements. Self-consistent Hartree-Fock calculations reveal that interactions reorganize all eight low-energy flat bands, driving abrupt changes in orbital magnetization. Our results establish HTG as the first system where electronic interactions provide doping-controlled access to all three internal degrees of freedom - spin, valley, and sublattice - introducing a new class of correlated phase transitions.

cond-mat.mes-hall↗

arXiv2025

The ideal limit of rhombohedral graphene: Interaction-induced layer-skyrmion lattices and their collective excitations

We introduce an ideal limit of rhombohedral graphene multilayers. In this limit, we show analytically how short-range repulsion stabilizes a layer-pseudospin skyrmion lattice, which generates an effective magnetic field and gives rise to a Chern band. This establishes the real-space origin of interaction-driven topology in moir\'e rhombohedral graphene. The resulting interaction-induced skyrmion lattice is physically analogous to magnetic skyrmion crystals and hosts a hierarchy of collective excitations naturally described within the framework of skyrmion-lattice dynamics.

cond-mat.mes-hall↗

arXiv2025

Nonvolatile Switching of Magnetism via Gate-Induced Sliding in Tetralayer Graphene

Interlayer sliding degrees of freedom often determine the physical properties of two-dimensional (2D) materials. In graphene, for instance, the metastable rhombohedral stacking arrangement hosts correlated and topological electronic phases, which are absent in conventional Bernal stacking. Here, we demonstrate a sliding-induced first-order structural phase transition between Bernal and rhombohedral tetralayer graphene driven by gate voltages. Through transport measurement, we observe bistable switching between a Bernal-dominant state and a rhombohedral-Bernal mixed state across a wide space of the gate-voltage phase diagram. The structural phase transition results in nonvolatile switching between a paramagnet and a ferromagnet accompanied by the anomalous Hall effect. The sign reversal of the anomalous Hall effect under opposite displacement fields suggests that it may originate from domain boundaries between the Bernal and rhombohedral regions. Our discovery paves the way for on-demand toggling of quantum phases based on the sliding phase transition of 2D materials and offers a playground to explore unconventional physics at the stacking domain boundaries.

cond-mat.mes-hall↗

arXiv2025

Link between thermodynamic correlation signatures and superconductivity in twisted trilayer graphene

Twisted graphene multilayers exhibit strong electronic correlations, which manifest in a range of experimental signatures. Yet how these signatures relate to each other and the microscopic ground states-and how twist angle and band structure reshape them-remains poorly understood. Here we study this interplay by correlating local thermodynamic and transport measurements in a twisted trilayer graphene (TTG) sample with unequal angles and flat electronic bands. We use a scanning single-electron transistor to map the impact of electron-electron interactions in a region of the sample where the local twist angle evolves smoothly. We observe gapped correlated insulators and a sawtooth in electronic compressibility, both exhibiting pronounced electron-hole (e-h) asymmetry with distinct magic angles for conduction and valence bands. Subsequent transport measurements in the same region reveal robust superconductivity with a similar e-h asymmetry. Our measurements indicate that superconductivity is not directly tied to the correlated insulators. Instead, its critical temperature correlates closely with the strength of the sawtooth in compressibility, suggesting a common origin or link between the two. By combining a local probe with transport measurements, we uncover connections between superconductivity and thermodynamic correlation signatures that are not apparent from either technique in isolation, highlighting the power of our dual approach and establishing their dependence on interlayer twist angles in TTG.

cond-mat.mes-hall↗

arXiv2025

Magic continuum in multi-moir\'e twisted trilayer graphene

Moir\'e lattices provide a highly tunable platform for exploring the interplay between electronic correlations and band topology. Introducing a second moir\'e pattern extends this paradigm: interference between the two moir\'e patterns produces a supermoir\'e modulation, opening a route to further tailor electronic properties. Twisted trilayer graphene generally exemplifies such a system: two distinct moir\'e patterns arise from the relative twists between adjacent graphene layers. Here, we report the observation of correlated phenomena across a wide range of twisted trilayer graphene devices whose twist angles lie along two continuous lines in the twist-angle parameter space. Depending on the degree of lattice relaxation, twisted trilayer graphene falls into two classes: moir\'e polycrystals, composed of periodic domains with locally commensurate moir\'e order, and moir\'e quasicrystals, characterized by smoothly varying local moir\'e configurations. In helically twisted moir\'e polycrystals, we observe an anomalous Hall effect, consistent with topological bands arising from domains with broken $xy$-inversion symmetry. In contrast, superconductivity appears generically in our moir\'e quasicrystals. A subset of these systems exhibits signatures of spatially modulated superconductivity, which we attribute to the supermoir\'e structure. Our findings uncover the organizing principles of the observed correlated phases in twisted trilayer graphene, highlight the critical roles of the supermoir\'e modulation and lattice relaxation, and suggest a broader framework in which magic conditions arise not as isolated points but as extended manifolds within the multi-dimensional twist-angle space of complex moir\'e materials.

cond-mat.mes-hall↗

arXiv2025

Shot noise in strongly correlated double quantum spin Hall edges

We consider the effects of interactions on the edges of ``double" quantum spin Hall insulators (DQSHIs), motivated by recent experiments on moir\'e twisted metal dichalcogenides. Without interactions, a DQSHI can be understood as two copies of a conventional quantum spin Hall insulator. If interactions are present and $s^z$-spin is conserved, we show that there are two possible phases for the DQSHI edge. First is a weakly correlated edge which has two pairs of helical modes and is adiabatically equivalent to two conventional quantum spin Hall edges. Second is a strongly correlated edge with only one pair of helical modes. The strongly correlated edge also has a gap to single electrons, but is gapless to pairs of electrons. In a quantum point contact geometry, this single-electron gap leads to a Fano factor of $2$ in shot noise measurements, compared to a Fano factor of $1$ for a weakly correlated edge.

cond-mat.mes-hall↗

arXiv2025

How pairing mechanism dictates topology in valley-polarized superconductors with Berry curvature

We investigate how the pairing mechanism influences topological superconductivity in valley-polarized systems with Berry curvature. We demonstrate that short-range attractive interactions, such as those mediated by phonons, favor superconducting states where the Bogoliubov-de Gennes (BdG) Chern number has the same sign as the Berry curvature. In contrast, overscreened repulsive interactions, as in the Kohn-Luttinger mechanism, favor superconducting states where the BdG Chern number has the opposite sign as the Berry curvature. We establish these trends in a fully controlled limit and apply them to a recently reported chiral superconductor in rhombohedral multilayer graphene. Our theory provides a concrete experimental criterion for distinguishing between different pairing mechanisms in valley-polarized topological superconductors.

cond-mat.supr-con↗

arXiv2024

Magnetic Hofstadter cascade in a twisted semiconductor homobilayer

Transition metal dichalcogenide moir\'e homobilayers have emerged as a platform in which magnetism, strong correlations, and topology are intertwined. In a large magnetic field, the energetic alignment of states with different spin in these systems is dictated by both strong Zeeman splitting and the structure of the Hofstadter's butterfly spectrum, yet the latter has been difficult to probe experimentally. Here we conduct local thermodynamic measurements of twisted WSe$_2$ homobilayers that reveal a cascade of magnetic phase transitions. We understand these transitions as the filling of individual Hofstadter subbands, allowing us to extract the structure and connectivity of the Hofstadter spectrum of a single spin. The onset of magnetic transitions is independent of twist angle, indicating that the exchange interactions of the component layers are only weakly modified by the moir\'e potential. In contrast, the magnetic transitions are associated with stark changes in the insulating states at commensurate filling. Our work achieves a spin-resolved measurement of Hofstadter's butterfly despite overlapping states, and it disentangles the role of material and moir\'e effects on the nature of the correlated ground states.

cond-mat.mes-hall↗

arXiv2024

Fractional Chern mosaic in supermoir\'e graphene

We propose the realization of a fractional Chern mosaic: a state characterized by a spatially varying topological order. This state is enabled by a separation of length scales that emerges when three graphene sheets are sequentially rotated by a small twist angle. The resulting structure features not only conventional moir\'e lattices, but also a much larger supermoir\'e lattice. We demonstrate that a fractional Chern mosaic arises when electron correlations induce fractionalization locally on the moir\'e scale, while the pattern of fractionalization varies at the supermoir\'e scale.

cond-mat.str-el↗

arXiv2024

Imaging supermoir\'e relaxation in helical trilayer graphene

In twisted van der Waals materials, local atomic relaxation can alter the underlying electronic structure. Characterizing lattice reconstruction and its susceptibility to strain is essential for understanding emergent electronic states, especially in multilayers in which interference between moir\'e lattices yields larger supermoir\'e patterns whose energy is highly sensitive to local stacking. Here we image spatial modulations in the electronic character of helical trilayer graphene, which indicate relaxation into a superstructure of large domains with uniform moir\'e periodicity. We show that the supermoir\'e domain size is increased by strain and can be altered in the same device while preserving the local properties within each domain. Finally, we observe a higher conductance at the domain boundaries, consistent with predictions that they host counter-propagating edge modes. Our work provides a real-space visualization of moir\'e-periodic domains, reveals two independently tunable length scales and demonstrates strain engineering as a route towards designing correlated topological networks at the supermoir\'e scale.

cond-mat.mes-hall↗

arXiv2024

Wavefunction approach to the fractional anomalous Hall crystal

We propose fractional anomalous Hall crystals (FAHCs) as possible ground states of strongly interacting electrons in parent bands with Berry curvature. FAHCs are exotic states of matter that spontaneously break continuous translation symmetry to form a fractional Chern insulator. We construct a unified family of variational wavefunctions that describe FAHCs and their competing states in the presence of uniform parent Berry curvature. We calculate their variational energy with Coulomb interactions semi-analytically in the thermodynamic limit. Our analysis reveals that FAHCs can be energetically favorable over both Wigner crystals and integer anomalous Hall crystals for sufficiently strong interactions or flat dispersion.

cond-mat.mes-hall↗

arXiv2024

Parent Berry curvature and the ideal anomalous Hall crystal

We study a model of electrons moving in a parent band of uniform Berry curvature. At sufficiently high parent Berry curvature, we show that strong repulsive interactions generically lead to the formation of an anomalous Hall crystal: a topological state with spontaneously broken continuous translation symmetry. Our results are established via a mapping to a problem of Wigner crystallization in a regular 2D electron gas. Interestingly, we find that a periodic electrostatic potential induces a competing state with opposite Chern number. Our theory offers a unified perspective for understanding several aspects of the recently observed integer and fractional quantum anomalous Hall effects in rhombohedral multilayer graphene and provides a recipe for engineering new topological states.

cond-mat.mes-hall↗

arXiv2024

Theory of Half-Integer Fractional Quantum Spin Hall Insulator Edges

We study the edges of fractional quantum spin Hall insulators (FQSH) with half-integer spin Hall conductance. These states can be viewed as symmetric combinations of a spin-up and spin-down half-integer fractional quantum Hall state (FQH) that are time-reversal invariant, and conserve the z-component of spin. We consider the non-Abelian states based on the Pfaffian, anti-Pfaffian, PH-Pfaffian, and 221 FQH, and generic Abelian FQH. For strong enough spin-conserving interactions, we find that all the non-Abelian and Abelian edges flow to the same fixed point that consists of a single pair of charged counter-propagating bosonic modes. If spin-conservation is broken, the Abelian edge can be fully gapped in a time-reversal symmetric fashion. The non-Abelian edge with broken spin-conservation remains gapless due to time-reversal symmetry, and can flow to a new fixed point with a helical gapless pair of Majorana fermions. We discuss the possible relevance of our results to the recent observation of a half-integer edge conductance in twisted MoTe2.

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