Strongly Correlated Electrons
Odd-parity magnon spin polarization from chiral four-spin exchange in a honeycomb antiferromagnet
Bektur Murzaliev and Mikhail Titov
Chiral four-
spin exchange generates a momentum-dependent
magnon spin in a compensated honeycomb antiferromagnet at zero
magnetic field. For a Néel vector tilted by an angle $\theta_0$ from the layer normal, the interaction contributes to intersublattice
magnon pairing already at harmonic order, with an amplitude proportional to $\cos\theta_0\sin^2\theta_0$. Biaxial anisotropy mixes the two longitudinal-
spin sectors, producing nonquantized mode
spins that are odd in momentum, while a sublattice-exchange relation keeps the
magnon energies reciprocal. A temperature gradient then induces a
spin density along the Néel axis through a redistribution of
magnon occupations. Reversing the four-
spin coupling reverses this
spin density and the mode
spins without changing the
magnon energies. MnPS$_3$ motivates the
magnetic geometry; realizing the interaction requires a structural modification compatible with the
symmetry assumptions of the model.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall
Composite Fermion Theory of Fractional Chern Insulators in Rhombohedral Graphene
Peize Ding, Andrew J. Millis and Yongxin Zeng
The experimental observation of the fractional
quantum anomalous Hall effect in rhombohedral
graphene multilayers has raised questions about the nature of the fractional Chern
insulator (FCI) states and the role of the moiré potential. In this Letter we develop a composite
fermion (CF) description and discuss how moiré modulation and Coulomb interactions stabilize the FCI ground states. Under a flux-attachment transformation and mean-field approximation, the CF spectrum forms Landau levels that are further split by the moiré potential. At moiré filling fractions in the Jain sequence, an integer number of CF bands are occupied, resulting in an incompressible ground state with fractionally quantized Hall response. Remarkably, when the attached flux opposes the Berry
curvature of the conduction band of rhombohedral
graphene, the CF Landau levels are widely spaced in energy and delocalized across layers, leading to a reduced density of states that helps protect the CF mean-field state and amplifying effects of the moiré potential acting on the layer away from the doped electrons. Interactions between CFs further enlarge the moiré-induced band gap and stabilize the FCI ground state. Our work sheds light on the nature of the FCI states in rhombohedral
graphene and provides a new theoretical framework for further studies.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Connectivity Controls Variational Accessibility in Symmetry-Preserving Quantum Circuits
Sahinur Reja
Designing expressive
quantum circuits for the variational
quantum eigensolver (VQE) is a central challenge in simulating interacting many-body systems. Even
symmetry-preserving (SP)
circuits need not access the full many-body
symmetry sector. We demonstrate this explicitly for the
spin-$1/2$ XXZ and Hubbard models, where
Hamiltonian-inspired nearest-neighbor (NN) SP
circuits generate restricted dynamical Lie
algebras (DLAs). While these restricted
manifolds can accurately represent the ground state near the free-
fermion limits, $J_z=0$ for XXZ and $U=0$ for Hubbard, interactions expose inaccessible many-body directions and severely limit VQE performance even at large
circuit depth. Remarkably, a minimal modification of the generator connectivity can reconstruct the full orthogonal DLA within all relevant
symmetry sectors studied in this work. For XXZ model, the addition of only one SP next-to-NN single-excitation connection triggers this dramatic reconstruction, whereas the Hubbard case requires a SP correlated double-excitation;–showing that the relevant connectivity can extend from the spatial
lattice to many-body configuration space. This reconstruction enlarges the tangent space and accessibility of the energy-lowering
Hamiltonian direction, leading to near-unit ground-state fidelity in VQE simulations. Our results establish a direct link between generator connectivity and variational accessibility and suggest a broader
circuit-design principle: identify minimal
symmetry-preserving generators that enlarge the accessible many-body space rather than increasing
circuit depth alone. This perspective may have broader relevance for
quantum many-body simulation at the interface of condensed-matter physics and
quantum computing.
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Strongly Correlated Electrons · Cross-listed from hep-th
Non-invertible SPT phases from fusion rings via Tannaka duality
Antonio Santaniello, Roberto Valandro and Massimo Zorzenon
In a (1+1)-dimensional QFT with non-invertible
symmetry, the fusion rules of topological lines are often the most accessible data, yet they do not fully determine whether the
symmetry is anomaly-free, i.e. whether it admits trivially gapped phases. Such phases are characterized by fiber functors of the corresponding fusion category. Building on Tannaka duality, we extract fiber functors from the fusion ring alone by solving simultaneously for monoidal structure maps and tensor automorphisms. This allows us to find categorifications admitting a fiber functor without solving the pentagon equations directly. We test this procedure on the known Tambara–Yamagami ring of $\mathbb{Z}_2\times\mathbb{Z}_2$. Our main result concerns the rank-11 fusion ring shared by the representation categories of the two extraspecial groups of order 27, which has a multiplicity 3 channel and is relevant to self-triality. In both cases we find more than one fiber functor, i.e. several non-invertible SPT phases. We use the explicit data of these fiber functors to derive the $F$-symbols of the two representation categories in a compact form depending on a non-degenerate alternating bicharacter and an invertible object $\epsilon$. Using the reconstructed data, we compute the anomalous
algebra on the interface between two different SPT phases.
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Strongly Correlated Electrons
Local-moment magnets on all close-packed lattices are equivalent
Sam Studdy, Alwyn Jose Raja and R. Ganesh
The Heisenberg antiferromagnet on the fcc
lattice is a canonical example of frustration. The fcc
lattice is but one of an infinite number of close-packed structures, all of which have the same frustration-inducing local geometry. In this letter, we demonstrate a hidden
symmetry that relates classical magnets on all close-packed
lattices. This
symmetry derives from a similar property in tight binding models that may explain the disordered low-temperature structures of lithium and sodium metals. In magnets, the
symmetry holds when couplings are restricted to nearest ($J_1$) and next-nearest neighbours ($J_2$). It guarantees that all close-packed
lattices are equivalent at the Luttinger-Tisza level. For any given values of $J_1$ and $J_2$, they have the same ground-state energy. Their ground state momenta are identical when projected onto the stacking plane. We construct a unified phase diagram as a function of $J_1$ and $J_2$ couplings for Heisenberg, XY and Ising magnets on any close-packed
lattice. In each phase, the ground-state degeneracy is the same on all close-packed
lattices, even after accounting for multi-Q spirals. This phase diagram can be easily adapted to any magnet composed of stacked triangular layers with similar couplings. Fluctuations above the classical ground state(s) are not related by any
symmetry. This suggests that close-packed structures can show interesting differences in order-by-disorder selection.
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Strongly Correlated Electrons
Chiral Parafermions in Floquet $\mathbb{Z}_N$ Topological Order
Melissa Will, Harald Schmid, Jan Egger et al. (+3 more)
Floquet topological order (FTO) extends
topology beyond
equilibrium, giving rise to phenomena, such as the dynamical transmutation of anyons. Here, we realize $\mathbb{Z}_N$ FTO in a generalized Kitaev honeycomb model with clock degrees of freedom using a three-step periodic drive. The driven system admits an emergent description in terms of constrained parafermions coupled to conserved $\mathbb{Z}_N$ gauge fields. At the boundary, the drive generates chiral parafermionic Floquet edge modes. We resolve their propagation through correlation functions, characterize their fractional
quantum-information transport through the radical chiral
unitary index, and use their dynamics to probe exchange statistics. In the bulk, we explore the dynamical anyon transmutation with a non-
equilibrium loop order parameter. At a Floquet sweet spot, where the drive becomes Clifford, these phenomena can be accessed using stabilizer simulations. Short-time
matrix-product-state simulations away from this point show that the chiral edge response persists at accessible times. Our results establish $\mathbb{Z}_N$ Kitaev models as a setting for exploring intrinsically non-
equilibrium topological phenomena on qudit-based
quantum processors.
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All authors Melissa Will, Harald Schmid, Jan Egger, Adam Gammon-Smith, Michael Knap, Frank Pollmann
Strongly Correlated Electrons
Heavy-fermion hybridization waves from Dirac spinons near a Kondo-breakdown quantum phase transition
Pedro M. Cônsoli, Matthias Vojta and Onur Erten
Motivated by the recent observation of spatially modulated screening in different paramagnetic heavy-
fermion materials, we propose a theoretical mechanism for the emergence of such hybridization waves in frustrated Kondo
lattices with no
magnetic order. By applying a parton mean-field theory and a perturbative calculation to a minimal Kondo-Heisenberg
lattice model, we demonstrate that a heavy Fermi
liquid can naturally develop hybridization waves when it approaches a
quantum phase transition where Kondo screening breaks down and the local
magnetic moments form a Dirac
spin liquid. We relate the strength of this mechanism to a kinematic condition on the electronic and spinon band structures and show that the spatial periodicity of the hybridization wave is set by a momentum $\vec{Q}$ connecting the nodes in the dispersion of the Dirac spinons to low-energy portions of the electronic band structure.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Rewire and reset are all you need: Minimal resources for manipulating non-Abelions
Chiu Fan Bowen Lo, Rohith Sajith, Anasuya Lyons et al. (+2 more)
Braiding and fusing anyons are fundamental to topological
quantum computation, yet existing
circuit protocols often employ ancillas and measurements. We determine the minimal
circuit resources for performing such anyon operations in
quantum double models of generic finite groups. Our approach braids anyons through a sequential
unitary circuit without ancillas. Intuitively, this is obtained by deforming the underlying graph on which the anyons live. More generally, we introduce graph rewiring, a diagrammatic calculus that assigns a
geometric interpretation to individual two-qudit gates and tracks their action on stabilizers. For fusion, we prove a general no-go
theorem excluding purely
unitary protocols for fusing unknown anyon types without introducing ancillas. Remarkably, we show such "input-agnostic" fusion is enabled by simply using a qudit reset. Hence, contrary to folklore, ancilla resources are not needed to braid or fuse non-Abelian anyons (non-Abelions). This work has implications in experimental efforts in error correction: our fusion protocol highlights reset as an underutilized primitive for error correction without the spacetime-overhead of ancillas and measurements.
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All authors Chiu Fan Bowen Lo, Rohith Sajith, Anasuya Lyons, Ashvin Vishwanath, Ruben Verresen
Strongly Correlated Electrons · Cross-listed from quant-ph
Engineering logical gates with irrep surface codes
Yabo Li, Zijian Song, Vieri Mattei et al. (+3 more)
Fault-tolerant
quantum computation typically relies on a fixed set of logical primitives, while realizing other desired operations can require substantial resources. We introduce irrep surface codes (ISCs), two-dimensional topological
quantum error-correcting codes engineered to transversally implement a prescribed set of logical gates. The engineered gates only need to satisfy two conditions: (i) they generate a finite group, which, up to global phases, is forced by the Eastin-Knill
theorem, and (ii) they are irreducible, meaning that any operator commuting with the set of gates must be proportional to the identity. This accommodates arbitrary finite groups of diagonal gates and arbitrary reversible classical gates, since each can be embedded into a larger irreducible finite group of gates. It also enables logical gates outside every finite level of the Clifford hierarchy. To incorporate these operations into surface-code computations, we further develop
lattice-surgery protocols to transfer the encoded information between surface codes and ISCs obeying either of two sufficient conditions. Together, these results establish a systematic method for tailoring topological codes to desired logical operations and integrating them into conventional computations.
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All authors Yabo Li, Zijian Song, Vieri Mattei, Naren Manjunath, Apoorv Tiwari, Tyler D. Ellison
Strongly Correlated Electrons
Unraveling Fermi liquid charge and heat transport in RuO$_{2}$
Harrison LaBollita, Fabian B. Kugler, Antoine Georges et al. (+1 more)
RuO$_2$ is a multi-orbital Fermi
liquid for which an array of complementary experimental measurements has recently become available, making it a stringent testbed for quantitative many-body electronic structure theory. Using realistic dynamical mean-field calculations, we compute the spectroscopic and transport properties of RuO$_2$ in the paramagnetic state. We identify RuO$_2$ as a moderately correlated Fermi
liquid and obtain (semi-)quantitative agreement with experiment for its optical conductivity, electrical resistivity, and thermopower. This broad agreement across complementary observables establishes a “precision” many-body description of RuO$_2$ and allows remaining discrepancies to be identified as meaningful tests of the theory. In particular, the calculated electronic thermal resistivity significantly undershoots the experimentally inferred low-temperature thermal resistivity, raising an important puzzle concerning the relative relaxation of charge and heat currents in the Fermi
liquid regime. We explore low-temperature electron-
phonon scattering as a possible mechanism for resolving this discrepancy, while a fully quantitative description remains an open problem. More broadly, our results demonstrate the power of combining precision DFT+DMFT calculations with complementary experimental probes to build and critically test quantitative descriptions of correlated
quantum materials.
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All authors Harrison LaBollita, Fabian B. Kugler, Antoine Georges, Cyrus E. Dreyer
Strongly Correlated Electrons
Strong metamagnetic switching and anisotropic magnetotransport in the distorted kagome magnet Tb6Ti4Al43
Lipika, Sneh, Shobha Singh et al. (+4 more)
We report a comprehensive investigation of the
magnetic, electrical, and thermodynamic properties of single crystalline Tb6Ti4Al43, in which Tb atoms form a distorted kagome
lattice embedded within a complex Ti-Al framework. Tb6Ti4Al43 exhibits pronounced
magnetic anisotropy and antiferromagnetic ordering at approximately 19 K. For
magnetic field applied along the c-axis, a strong metamagnetic switching is observed, accompanied by a clear asymmetric hysteresis at low temperatures, while for field applied along the ab plane, a
spin-flop transition is observed. The effect of field induced
magnetic states is strongly reflected in magnetotransport measurements, giving rise to pronounced anomalies in magnetoresistance and an anomalous Hall contribution. A significant intrinsic contribution to the anomalous Hall conductivity is observed, highlighting the Berry
curvature effects arising from the system's momentum-space
topology. Our results highlight the interplay of
spin, charge, and
lattice degrees of freedom in Tb6Ti4Al43 and establish this distorted kagome antiferromagnet as a promising platform for field-tunable multifunctional behaviour, including electrically readable
magnetic switching,
spin manipulation, and magneto-mechanical functionalities.
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All authors Lipika, Sneh, Shobha Singh, Ralf Koban, Walter Schnelle, Rie Umetsu, Kaustuv Manna
Strongly Correlated Electrons · Cross-listed from quant-ph
Climbing the Fusion Tree: Center Ordering and Decoding Hierarchy in Non-Abelian Mixed States
Pablo Sala, Vlad Temkin, Cenke Xu et al. (+2 more)
We develop an operational approach to strong-to-weak spontaneous
symmetry breaking (sw-SSB) of a non-Abelian
symmetry group G. We formulate it as the decoding task of distinguishing two strongly symmetric states that differ by a pair of inserted irreps, after both are corrupted by strongly symmetric decoherence. For finite G, this task is dual to distinguishing logical states of the
quantum double D(G) under pure-charge noise. We derive a hierarchy of statistical mechanics models describing optimal decoding from the fusion outcomes measured on successively larger nested regions. As for maximum-likelihood decoders of Abelian codes the measured irreps act as quenched disorder obeying a Nishimori-like condition. Strikingly, because local irreps do not determine how they fuse globally, the strong $G\times G$
symmetry is realized only nonlocally, and irreps trivially charged under Z(G) (the center of G) can hide inside noise-generated ones. As a result, the strong
symmetry spontaneously breaks down to Z(G), times the weak
symmetry. The only transition at nonzero error rate is then an ordering of the center, whose threshold cannot decrease as the hierarchy is ascended. This conclusion holds at any finite level of the hierarchy for non-nilpotent groups. We confirm these predictions with tensor-network calculations for $S_3$ and SU(2). At the first level, the $S_3$ model, whose center is trivial, shows no transition, and the fidelity correlations of all irreps provably decay to non-zero values. The SU(2) model exhibits a $Z_2$ transition consistent with the Nishimori-Ising universality class, where the fidelity correlations of
spin-$1/2$ irreps become long-range. The threshold rises from the first to the second level of the hierarchy by $16\%$. Our results provide a systematic framework for studying non-Abelian sw-SSB and for constructing decoders for non Abelian topological codes.
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All authors Pablo Sala, Vlad Temkin, Cenke Xu, Daniel Podolsky, Ehud Altman
Strongly Correlated Electrons
Interacting quantum criticality with U(1) symmetry breaking in 1+1 dimensions
Mutsumi Shimomura and Kohei Kawabata
The Hohenberg-Mermin-Wagner
theorem motivates the expectation that continuous
symmetries remain unbroken in one-dimensional
quantum ground states. Here, contrary to this expectation, we demonstrate the spontaneous breaking of U(1)
spin-rotation
symmetry and the emergence of an interacting
quantum critical point in
lattice spin-$1/2$ and
spin-$1$ chains. Using subsystem Binder scaling, we locate the critical point and determine the correlation-length critical exponent as $\nu = 0.60 \pm 0.02$, distinct from the Gaussian value $0.5$ but consistent with the perturbative renormalization-group prediction. We further analyze the finite-size scaling of the lowest neutral excitation gap and obtain the dynamical critical exponent $z=1.986 \pm 0.005$. The result $z < 2$ is incompatible with microscopic realizations of this critical theory by frustration-free models, implying a mechanism for continuous
symmetry breaking in one-dimensional
quantum ground states distinct from frustration freeness.
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Strongly Correlated Electrons
Dynamical Valence Fluctuations and Magnetic Anisotropy in Sm(Co,Cu)$_5$
Alexander B. Shick, Alexander V. Andreev, Evgenia A. Tereshina-Chitrova Institute of Physics et al. (+4 more)
The
magnetic properties of Sm-based intermetallics are governed by a delicate interplay between localized $4f$ states, exchange interactions, and valence fluctuations, yet the role of dynamical $4f$ correlations remains poorly understood. Here we investigate the electronic structure and
magnetic anisotropy of SmCo$_5$ and SmCu$_5$ using self-consistent DFT+$U$(ED), which explicitly treats dynamical fluctuations of the Sm $4f$ shell. We find that SmCo$_5$ exhibits pronounced Sm$^{2+}$–Sm$^{3+}$ valence fluctuations, with the $4f$ ground state dominated by $f^5$ and $f^6$ configurations. The resulting dynamical $4f$ correlations yield near compensation of the Sm
spin and orbital moments and provide a quantitative description of the electronic structure,
magnetic moments, and large uniaxial
magnetic anisotropy of SmCo$_5$. Upon replacing Co with Cu, the balance shifts toward the $f^6$ configuration, with substantial changes in the Sm
spin and orbital moments. In SmCu$_5$, this
evolution of the $4f$ configuration is accompanied by a pronounced reduction of both the total
magnetic moment and
magnetic anisotropy. These results demonstrate that dynamical $4f$ valence fluctuations are essential for understanding the contrasting
magnetic properties of SmCo$_5$ and SmCu$_5$ and provide a microscopic framework for describing
magnetic anisotropy upon Co to Cu substitution in Sm(Co,Cu)$_5$.
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All authors Alexander B. Shick, Alexander V. Andreev, Evgenia A. Tereshina-Chitrova Institute of Physics, the Czech Academy of Sciences, Na Slovance 2, CZ-18221 Prague, Czech Republic
Strongly Correlated Electrons · Cross-listed from quant-ph
A Practical Introduction to VQE: Methods, Challenges, and Applications in Physics and Chemistry
Jannis Ehrlich, Felix Rupprecht, Konstantin Lamp et al. (+6 more)
The Variational
Quantum Eigensolver (VQE) has become a central hybrid
quantum-classical method for addressing electronic structure and materials science problems on near-term
quantum hardware. As researchers across physics, chemistry, and
quantum information engage with VQE, they encounter a wide range of algorithmic choices, including problem encoding, ansatz construction, classical optimization, and measurement strategies to choose from. This article provides a structured overview of these components and discusses practical factors that influence VQE performance in real settings, such as noise characteristics, available error-mitigation techniques, and hardware-dependent
circuit considerations. Drawing partly on our early experiences, we highlight aspects that may be especially relevant for newcomers and outline common challenges observed in practical workflows. Our aim is to offer an accessible entry point for researchers approaching VQE-based
quantum simulation and to support informed decision-making as the method and underlying hardware continue to evolve, which we support by discussion of examples from physics and
quantum chemistry.
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All authors Jannis Ehrlich, Felix Rupprecht, Konstantin Lamp, Elias Walter, Alejandro D. Somoza, Manuel Enns, Christian Elsässer, Birger Horstmann, Daniel F. Urban
Strongly Correlated Electrons · Cross-listed from cond-mat.dis-nn
Disorder-driven loss of crystalline coherence in two-dimensional electron solids: Quantum Hartree-Fock and classical molecular dynamics
Sankar Das Sarma and Haining Pan
We investigate the effects of quenched disorder on two-dimensional electron solids using Hartree-Fock theory and classical molecular dynamics. Increasing disorder weakens crystalline correlations, broadens the structure factor, and reduces the measured coherence length toward the pristine
lattice spacing. This
evolution is consistent with the Imry-Ma and Larkin picture: random pinning disrupts translational order on sufficiently long scales, and stronger disorder reduces the distance over which crystalline organization survives. Classical simulations further show that stronger pinning raises the temperature for particle rearrangement even after crystalline order has disappeared. Disorder thus suppresses structural coherence while stabilizing an amorphous solid against thermal rearrangement.
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Strongly Correlated Electrons
Pairing order and condensate fraction across the BCS-BEC crossover in the two-dimensional attractive Hubbard model
Hao Du, Qian Sun, Zhuotao Xie et al. (+1 more)
We report a systematic study of the superconducting ground state in the two-dimensional attractive Hubbard model, employing the numerically exact auxiliary-field
quantum Monte Carlo method. We focus primarily on the pairing order and condensate fraction across the BCS-BEC crossover. Our numerical calculations cover a broad and physically relevant parameter regime, with the interaction strength $U/t=2\sim 12$ (where $t$ is the nearest-neighbor hopping amplitude) and
fermion density $n=0.25\sim 1.0$. We systematically characterize the dependence of the pairing order and condensate fraction on both the interaction strength and
fermion density, and perform finite-size extrapolations to obtain their thermodynamic-limit values. As complementary quantities, we also provide high-precision numerical results for the double occupancy and total energy. Furthermore, we investigate the effects of next-nearest-neighbor hopping on the superconducting properties of the model. Our results offer a comprehensive set of unbiased numerical data for the attractive Hubbard model, establishing quantitative
benchmarks for understanding superconductivity across the BCS-BEC crossover and for validating future theoretical and numerical approaches.
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All authors Hao Du, Qian Sun, Zhuotao Xie, Yuan-Yao He
Strongly Correlated Electrons · Cross-listed from quant-ph
Interferometric braiding of non-Abelian anyons
Francesco Debortoli and Fabian Grusdt
The manipulation of non-Abelian anyons is a foundational ingredient for topological
quantum computing and underlies topologically protected
quantum memories. Here we analyze a
quantum-impurity-based protocol for braiding non-Abelian anyons. Exploiting mobile impurities with addressable internal
spin states, we provide a concrete protocol to experimentally measure the
matrix elements of the $R$ and $F$
matrices that characterize the non-Abelian statistics of anyons. In particular, focusing on the case of Ising and Fibonacci anyons, we illustrate how the anyonic nature of the excitations emerges directly in the Ramsey interferometer we propose. Building on this framework, we further introduce a conventional-to-topological
qubit encoder to transfer
quantum information from conventional flying
qubits into a topologically protected
quantum memory.
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Strongly Correlated Electrons · Cross-listed from cond-mat.supr-con
Two superconducting pairing models with a Kitaev spin-liquid glue: microscopic kernel and parity alternation on odd-fold bond stars
Youping Dai
We construct two superconducting pairing models on doped Kitaev honeycomb, whose microscopic kernels are derived rather than assumed. Both are driven by a bond-local glue neutral between the even- and odd-parity pairing channels; the chirality–parity linkage is set by bond-
star geometry, not by the microscopic glue. (i) Model~1(odd-parity sector): the kernel follows from the flux-sector selection rule of the pure model, fixing its component-diagonal, nearest-neighbor separable, rank-one-per-bond form, with $w_\alpha=J_K^2\chi_\alpha\propto r_\alpha m_\alpha$, where $m_\alpha$ follows from the Hellmann–Feynman
theorem and $r_\alpha\simeq0.24$ is computed numerically. The
spin-vertex state is a
unitary triplet with a bond-locked anisotropic $\mathbf d$ vector; its gap is a Gram sum of bond sines, so nodal directions are fixed by geometry. (ii) Model~2(even): the kernel is fixed by the $C_3$ little-group selection rule of a zone-corner chiral
phonon, up to a Cooper-channel extension whose momentum constraint we state explicitly. The charge-vertex pairing is a $d+id$ singlet: the parity decomposition $f_\pm=g_\pm+p_\pm$ projects onto $g_\pm$, so chirality is slaved to the
phonon polarization, with $C=\pm4$ and $\kappa_{xy}/T=2\kappa_0$. Reversing the pump helicity reverses the Chern number, Kerr rotation, and thermal Hall sign. (iii) General
theorem: on odd-fold bond
stars, the angular-momentum ladder of a single-
star chiral form factor alternates in parity. Every chiral state selected by such a bond-local form factor is a geometrically enforced singlet–triplet composite with universal amplitude ratios ($n=3$: $d\oplus p$; $n=5$: $g\oplus p$ or $d\oplus f$); coherent doubled-
star combinations can restore parity purity. The Chern number of the mixed state follows the dominant on-shell component across a topological boundary. The
spin glue drives $C=\pm2$; the charge kernel $C=\pm4$.
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Strongly Correlated Electrons
Lifshitz transition and magnetic superconductivity in flat band systems
Sudeshna Pal, K.B. Yogendra, Madhuparna Karmakar et al. (+1 more)
A Lifshitz transition is a class of non-
symmetry-breaking transitions typically associated with metallic systems wherein the Fermi surface changes its connectivity as the chemical potential sweeps through a band extremum or a saddle point. The phenomenology naturally adapts itself to the superconducting state, where the object that reconstructs is the
manifold of minimum quasiparticle energy rather than the Fermi surface. This paper concerns Lifshitz-type transitions in multi-band
superconductors. Thus, we focus on the attractive Hubbard–Kondo model on the two-dimensional Lieb
lattice, with classical core
spins coupled to the itinerant electrons, by laying recourse to a real-space Bogoliubov–de Gennes mean-field theory and an analytic Green's function calculation. The competition between the Kondo and pairing channels yields a
magnetic superconductor throughout, with $(\pi,\pi)$ order near half filling giving way to $(0,\pi)$ and then, at stronger Kondo coupling, to an incommensurate spiral $(0,q)$. In such a multiband
superconductor hosting a flat band, we identify two inequivalent Lifshitz-type transitions. With the core
spins decoupled (the Kondo coupling set to zero), the minimum energy contour deforms with chemical potential, a hole pocket about $M$ opening into a perfectly nested square at $\mu=-2t$ and reconnecting into pockets about $\Gamma$; this nesting fixes where $(\pi,\pi)$ order sets in. At finite Kondo coupling, for certain chemical potential, the dimension of the
manifold itself drops. We obtain it analytically for each
magnetic order and show that only the spiral carries the minimum energy through zero, nucleating nodes and leaving a gapless
magnetic superconductor, with clear signatures in the density of states and the spectral function.
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All authors Sudeshna Pal, K.B. Yogendra, Madhuparna Karmakar, Rajesh Narayanan
Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall
Beyond the Flat-Band Paradigm: Open Orbits as a Route to Correlated States in Dispersive Moiré Minibands
Zihao Wang, Pablo M. Perez-Piskunow, Calvin Pei Yu Wong et al. (+16 more)
The realization of fractional Chern
insulators has largely relied on isolated flat bands in complex bilayer or multilayer moiré systems with ideal
quantum geometry. Whether such phases can emerge in genuinely dispersive bands, and by what mechanism, remains an open question. Here, we propose a mechanism for
magnetic-field-induced strong correlations in the highly dispersive bands of monolayer
graphene on hexagonal boron nitride. In the low-field classical-to-
quantum crossover regime of the second moiré miniband, we show that the interplay of the moiré potential and weak
magnetic fields (B < 1.5 T) profoundly alters electron dynamics. Saddle-point van Hove singularities produce extended open orbits that strongly suppress carrier propagation, potentially favoring a regime in which Coulomb interactions become comparatively more important, while weak
magnetic fields lift valley degeneracy and trigonal warping redistributes Berry
curvature. High-resolution magnetotransport and temperature-dependent measurements reveal fractional-slope transport features and signatures of interaction-driven incompressibility. Because the Hall conductivity is not fully quantized and the longitudinal resistance remains finite, we describe these observations as incipient FCI behavior: transport signatures consistent with a developing fractional Chern insulating state, without claiming a fully developed FCI phase established by complete Hall quantization and vanishing longitudinal resistance. Our results suggest a possible fermiology-driven route toward correlated topological states in dispersive bands in the classical-to-
quantum crossover, distinct from the conventional flat-band scenario.
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All authors Zihao Wang, Pablo M. Perez-Piskunow, Calvin Pei Yu Wong, Matthew Holwill, Hao Sun, Wei Fu, Junxiong Hu, Zheng Yuntian, Zhang Xuanrui, T. Taniguchi, K. Watanabe, A. Ariando, Geliang Yu, Li Lin, Kuan Eng Johnson Goh, Stephan Roche, Jeil Jung, Kostya S. Novoselov, Nicolas Leconte
Strongly Correlated Electrons
Nonthermal nonlinear many-body excitonic dynamics in high-purity silicon
Patrick Pilch, Siyu Duan, Yang Liu et al. (+3 more)
We report time-resolved optical pump-terahertz third-harmonic generation spectroscopy of picosecond nonthermal many-body charge dynamics in high-purity silicon at room temperature. Although in thermal
equilibrium excitons in silicon are unstable due to a lower binding energy than the thermal energy at room temperature, following pulsed non-resonant optical pumping we can identify the formation of transient excitonic states on the picosecond time scale in our high-resolution nonlinear spectroscopic measurements. In contrast to unbound electron-hole pairs, the nonthermal many-body excitonic dynamics feature a characteristic time-dependent
evolution, a distinct dependence on charge density, and a nonperturbative nonlinear terahertz response.
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All authors Patrick Pilch, Siyu Duan, Yang Liu, Manfred Bayer, Marc Assmann, Zhe Wang
Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall
Stability and current-driven dynamics of mixed-topology bimeron clusters
Philippe Heymes, Thomas L. Schmidt and Vladyslav M. Kuchkin
In this work, we study bimerons (in-plane skyrmions) and their clusters composed of states with mixed topological indices. These clusters provide flexibility in controlling the skyrmion Hall angle, which depends on the cluster's total topological charge. First, using the simplest such cluster, a bimeron-antibimeron pair, we examine its stability with the geodesic nudged elastic band method and identify three mechanisms – bimeron separation, interchange, and annihilation – with comparable energy barriers that determine the pair's overall stability. This provides an upper bound for the stability of more sophisticated clusters of bimerons and antibimerons. Then, we numerically study the clusters' dynamics for currents applied in-plane and perpendicular to the plane, corresponding to the Zhang-Li and Slonczewski mechanisms. Finally, we analyze the dynamics of a wide variety of bimeron clusters within the Thiele approach and show that their velocities always lie on a specific ellipse whose parameters are fully governed by the model
Hamiltonian.
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