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Alexander Seidel

Publications and source records attributed to Alexander Seidel.

At least 19 recordsLinked to original sources

Exactly solvable non-planar $\mathbb{Z}_{2}$ dimer liquids on checkerboard and ruby lattices

We generalize an influential framework for exactly solvable quantum dimer models with dual Ising gauge theory descriptions realizing the $\mathbb{Z}_{2}$ topological phase from trivalent to tetravalent parent lattices. The resulting quantum dimer models live on crossed-medial lattices and possess the remarkable feature of having crossed plaquettes, leading to transition graphs with generically intersecting loops. This non-planar structure runs counter to established templates for analytically tractable dimer liquids. As the simplest realization of the construction, we introduce an exactly solvable quantum dimer model on the checkerboard lattice that allows an exact mapping to the toric code, thus providing a particularly direct connection between the latter and Anderson's short range resonating valence bond paradigm. We further show that a corresponding crossed ruby lattice construction, dual to an Ising gauge theory on the kagome lattice, naturally falls within the same framework. More generally, the construction gives rise to a broad class of exactly solvable crossed-medial quantum dimer models and admits natural iteration, generating cascades of solvable $\mathbb{Z}_{2}$ topological dimer liquids beyond the standard planar setting. We furthermore extend Kasteleyn methods to the relevant non-planar graphs, enabling controlled wave-function deformations away from the commuting-projector points while retaining efficient evaluation of correlation functions.

cond-mat.str-el

Giant nonlinear conductivity in 2D electron gas from substrate-induced dipolar scattering

Despite a surge of interest in the nonlinear transport in 2D materials, a fundamental puzzle remains: existing theoretical frameworks are unable to quantitatively account for the giant nonlinear conductivities ($\gtrsim 1 \frac{\mu \text{m}}{\Omega \text{V}}$) recently reported in 2D van der Waals heterostructures. Here, we introduce a mechanism based on electron scattering from a substrate-induced dipole array linked to short-range impurities. We show that the strict kinematic constraints, inherent to 2D scattering, lead to a singular enhancement of the nonlinear response, fundamentally dictating a natural scale of $1 \frac{\mu \text{m}}{\Omega \text{V}}$.

cond-mat.str-el

Non-Abelian fractional Chern insulators from an exactly solvable two-body model

We construct a class of lattice Hamiltonians whose single-particle spectrum consists of an arbitrary number of exactly degenerate flat bands that reproduce the analytic structure of the first $p$ Landau levels restricted to the lattice. When combined with local bosonic contact interactions, these models become exactly solvable frustration-free parent Hamiltonians for FCIs that realize both Abelian and non-Abelian parton quantum Hall states. Using exact diagonalization, we confirm the expected zero-mode counting for variants of the model stabilizing the bosonic Jain-21 state as well as the non-Abelian 22- and 33-states, which are expected to support Ising- and Fibonacci-type anyons, respectively. Our construction provides an exactly solvable lattice realization of multi Landau-level physics and offers a new framework for studying FCIs with Chern number $C > 1$. More broadly, it supplies a family of idealized lattice models that capture the analytic structure of continuum Landau levels while remaining compatible with exponentially local hopping.

cond-mat.str-el

Emergent Fracton Hydrodynamics of Ultracold Atoms in Partially Filled Landau Levels

The realization of synthetic gauge fields for charge neutral ultracold atoms and the simulation of quantum Hall physics has witnessed remarkable experimental progress. Here, we establish key signatures of fractional quantum Hall systems in their non-equilibrium quantum dynamics. We show that in the lowest Landau level the system generically relaxes subdiffusively.The slow relaxation is understood from emergent conservation laws of the total charge and the associated dipole moment that arise from the effective Hamiltonian projected onto the lowest Landau level, leading to subdiffusive fracton hydrodynamics. We discuss the prospect of rotating quantum gases as well as ultracold atoms in optical lattices for observing this unconventional relaxation dynamics.

cond-mat.quant-gas

Observability of cyclotron resonance in the hydrodynamic regime of bilayer graphene

We offer theoretical predictions for the frequency of the resonant frequency of transport for the hydrodynamic description of bilayer graphene, as well as provide quantification for the relative strength of this signal throughout phase space. Our calculations are based on classical fluid dynamics equations derived from the Boltzmann equation for bilayer graphene in arXiv:1901.07039, and suggest that while this resonance is accessible to current experimental techniques, the same mechanism which causes the hydrodynamic resonance to differ from the Fermi liquid value is responsible for a significant broadening of the peak.

cond-mat.mes-hall

Infrared spectroscopy of phase transitions in the lowest Landau levels of bilayer graphene

We perform infrared magneto-spectroscopy of Landau level (LL) transitions in dual-gated bilayer graphene. At $\nu=4$ when the zeroth LL (octet) is filled, two resonances are observed indicating the opening of a gap. At $\nu=0$ when the octet is half-filled, multiple resonances disperse non-monotonically with increasing displacement field, $D$, perpendicular to the sheet, showing a phase transition at modest displacement fields from a canted anti-ferromagnet (CAFM) to the layer-polarized state, with a gap that opens linearly in $D$. When $D=0$ and $\nu$ is varied, resonances at $\pm\nu$ show an electron-hole asymmetry with multiple line splittings as the octet is progressively filled. The $\nu=4$ data show good agreement with predictions from a mean-field Hartree-Fock calculation when accounting for multiple tight-binding terms in a four-band model of bilayer graphene. However even by incorporating a valley interaction anisotropy tuned to the CAFM ground state, only partial agreement is found at $\nu=0$. Our results suggest additional physics is required to understand bilayer graphene at half-filling.

cond-mat.mes-hall

Linking infinite bond-dimension matrix product states with frustration-free Hamiltonians

The study of frustration-free Hamiltonians and their relation to finite bond-dimension matrix product states (MPS) has a long tradition. However, fractional quantum Hall (FQH) states do not quite fit into this theme since the known MPS representations of their ground states have infinite bond dimensions, which considerably obscures the relations between such MPS representations and the existence of frustration-free parent Hamiltonians. This is related to the fact that the latter necessarily are of infinite range in the orbital basis. Here, we present a theorem tailored to establishing the existence of frustration-free parent Hamiltonians in such a context. We explicitly demonstrate the utility of this theorem in the context of non-Abelian Moore-Read FQH states but argue the applicability of this theorem to transcend considerably beyond the realm of conformal-field-theory-derived MPSs or quasi-one-dimensional Hilbert spaces.

cond-mat.str-el

Competing phases and intertwined orders in coupled wires near the self-dual point

The interplay between different quantum phases plays an important role in strongly correlated systems, such as high-$T_c$ cuprates, quantum spin systems, and ultracold atoms. In particular, the application of effective field theory model and renormalization group analysis suggested that the coexistence of density wave (DW) and superfluid (SF) orders can lead to a supersolid phase of ultracold bosons. Here we revisit the problem by considering weakly coupled wires, where we treat the intra-wire interactions exactly via bosonization and inter-wire couplings using a mean-field theory which becomes asymptotically exact in the limit of high dimensionality. We obtain and solve the mean-field equations for the system near the self-dual point, where each wire has the Luttinger parameter $K=1$ and the inter-wire DW and SF coupling strengths are identical. This allows us to find explicit solutions for the possible supersolid order. An energy comparison between different possible solutions shows that the supersolid order is energetically unfavorable at zero temperature. This suggests that the density wave and superfluid phases are connected by a first order transition near the self-dual point. We also discuss the relation between our work and the intertwining of charge density wave and superconducting orders in cuprates.

cond-mat.str-el

From frustration-free parent Hamiltonians to off-diagonal long-range order: Moore-Read and related states in second quantization

We construct a recursive second-quantized formula for Moore-Read Pfaffian states. We demonstrate the utility of such second-quantized presentations by directly proving the existence of frustration-free parent Hamiltonians, without appealing to polynomial clustering properties. Furthermore, we show how this formalism is connected to the existence of a non-local order parameter for Moore-Read states and give a proof that the latter exhibit off-diagonal long-range order (ODLRO) in these quantities. We also develop a similar second-quantized presentation for the fermionic antiand PH-Pfaffian states, as well as f- and higher wave paired composite fermion states, and discuss ODLRO in most cases.

cond-mat.str-el

Sequencing the Entangled DNA of Fractional Quantum Hall Fluids

We introduce and prove the "root theorem", which establishes a condition for families of operators to annihilate all root states associated with zero modes of a given positive semi-definite $k$-body Hamiltonian chosen from a large class. This class is motivated by fractional quantum Hall and related problems, and features generally long-ranged, one-dimensional, dipole-conserving terms. Our theorem streamlines analysis of zero-modes in contexts where "generalized" or "entangled" Pauli principles apply. One major application of the theorem is to parent Hamiltonians for mixed Landau-level wave functions, such as unprojected composite fermion or parton-like states that were recently discussed in the literature, where it is difficult to rigorously establish a complete set of zero modes with traditional polynomial techniques. As a simple application we show that a modified $V_1$ pseudo-potential, obtained via retention of only half the terms, stabilizes the $\nu=1/2$ Tao-Thouless state as the unique densest ground state.

cond-mat.str-el

Inner workings of fractional quantum Hall parent Hamiltonians: A matrix product state point of view

We study frustration-free Hamiltonians of fractional quantum Hall (FQH) states from the point of view of the matrix product state (MPS) representation of their ground and excited states. There is a wealth of solvable models relating to FQH physics, which, however, is mostly derived and analyzed from the vantage point of first-quantized "analytic clustering properties". In contrast, one obtains long-ranged frustration-free lattice models when these Hamiltonians are studied in an orbital basis, which is the natural basis for the MPS representation of FQH states. The connection between MPS-like states and frustration-free parent Hamiltonians is the central guiding principle in the construction of solvable lattice models, but thus far, only for short-range Hamiltonians and MPSs of finite bond dimension. The situation in the FQH context is fundamentally different. Here we expose the direct link between the infinite-bond-dimension MPS structure of Laughlin-conformal field theory (CFT) states and their parent Hamiltonians. While focusing on the Laughlin state, generalizations to other CFT-MPSs will become transparent.

cond-mat.str-el

Mechanism for particle fractionalization and universal edge physics in quantum Hall fluids

Advancing a microscopic framework that rigorously unveils the underlying topological hallmarks of fractional quantum Hall (FQH) fluids is a prerequisite for making progress in the classification of strongly-coupled topological matter. Here we advance a second-quantization framework that helps reveal an exact fusion mechanism for particle fractionalization in FQH fluids, and uncover the fundamental structure behind the condensation of non-local operators characterizing topological order in the lowest-Landau-level (LLL). We show the first exact analytic computation of the quasielectron Berry connections leading to its fractional charge and exchange statistics, and perform Monte Carlo simulations that numerically confirm the fusion mechanism for quasiparticles. Thus, for instance, two quasiholes plus one electron of charge $e$ lead to an exact quasielectron of fractional charge $e/3$, and exchange statistics $1/3$, in a $\nu=1/3$ Laughlin fluid. We express, in a compact manner, the sequence of (both bosonic and fermionic) Laughlin second-quantized states highlighting the lack of local condensation. Furthermore, we present a rigorous constructive subspace bosonization dictionary for the bulk fluid and establish universal long-distance behavior of edge excitations by formulating a conjecture based on the DNA, or root state, of the FQH fluid.

cond-mat.str-el

Quantum many-body scars with chiral topological order in 2D and critical properties in 1D

We construct few-body, interacting, nonlocal Hamiltonians with a quantum scar state in an otherwise thermalizing many-body spectrum. In one dimension, the embedded state is a critical state, and in two dimensions, the embedded state is a chiral topologically ordered state. The models are defined on slightly disordered lattices, and the scar state appears independent of the precise realization of the disorder. A parameter allows the scar state to be placed at any position in the spectrum. We show that the level spacing distributions are Wigner-Dyson and that the entanglement entropies of the states in the middle of the spectrum are close to the Page value. Finally, we confirm the topological order in the scar state by showing that one can insert anyons into the state.

cond-mat.str-el

Topological Quantum Many-Body Scars in Quantum Dimer Models on the Kagome Lattice

We present a class of quantum dimer models on the kagome lattice with full translational invariance that feature a quantum many-body scar state of analytically known entanglement properties within their spectra. Using exact diagonalization on lattices of up to 60 sites, we show that non-scar states conform to the eigenstate thermalization hypothesis. Specifically, we show that energies are distributed according to the Gaussian ensemble expected of their respective symmetry sector, illustrate the existence of the scar from bipartite entanglement properties, and demonstrate revival phenomena in studies of fidelity dynamics.

cond-mat.str-el

Exact Solution and Correlations of a Quantum Dimer Model on the Checkerboard Lattice

We present analytic results for a special dimer model on the {\em non-bipartite} and {\em non-planar} checkerboard lattice that does not allow for parallel dimers surrounding diagonal links. We {\em exactly} calculate the number of closed packed dimer coverings on finite checkerboard lattices under periodic boundary conditions, and determine all dimer-dimer correlations. The latter are found to vanish beyond a certain distance. We find that this solvable model, despite being non-planar, is in close kinship with well-known paradigm-setting planar counterparts that allow exact mappings to $\mathbb{Z}_2$ lattice gauge theory.

cond-mat.str-el

Local two-body parent Hamiltonians for the entire Jain sequence

Using an algebra of second quantized operators, we develop local two-body parent Hamiltonians for all unprojected Jain states at filling factor $n/(2n{\sf p}+1)$, with integer $n$, and (half-)integer ${\sf p}$. We rigorously establish that these states are uniquely stabilized and that zero mode counting reproduces mode counting in the associated edge conformal field theory. We further establish an associated "entangled Pauli principle" describing these states and associated zero mode spaces, as well as an emergent SU($n$) symmetry.

cond-mat.str-el

Interlayer correlated fractional quantum Hall state in the {\nu} = 4/5 bilayer system

We perform exact diagonalization studies for fractional quantum Hall states at filing factor 4/5 in a bilayer system, on a torus with various aspect ratios and angles. We find that in the absence of tunneling, two weakly coupled 2/5-layers undergo a phase transition into an interlayer-correlated regime, which is also Abelian with the five-fold degeneracy on the torus. In the limit of zero layer separation, this phase becomes a singlet in the pseudospin variable describing the layer degree-of-freedom. By studying the Chern-number matrix, we show that the K-matrix describing the interlayer-correlated regime requires matrix dimension larger than two and this regime is in particular not described by a Halperin state. A detailed analysis of possible 4 X 4 K-matrices having the requisite symmetries and quantum numbers shows that there is only one equivalence class of such matrices. A model wave function representing this universality class is constructed. The role of separate particle number conservation in both layers is discussed, and it is argued that this additional symmetry allows for the further distinction of two different symmetry protected Abelian phases in the interlayer correlated regime. Interlayer tunneling breaks this symmetry, and can drive the system into a single-layer regime when strong enough. A qualitative phase diagram in the tunneling-layer separation parameter space is proposed based on our numerical results.

cond-mat.str-el

Composite fermions in Fock space: Operator algebra, recursion relations, and order parameters

We develop recursion relations, in particle number, for all (unprojected) Jain composite fermion (CF) wave functions. These recursions generalize a similar recursion originally written down by Read for Laughlin states, in mixed first-second quantized notation. In contrast, our approach is purely second-quantized, giving rise to an algebraic, `pure guiding center' definition of CF states that de-emphasizes first quantized many-body wave functions. Key to the construction is a second-quantized representation of the flux attachment operator that maps any given fermion state to its CF counterpart. An algebra of generators of edge excitations is identified. In particular, in those cases where a well-studied parent Hamiltonian exists, its properties can be entirely understood in the present framework, and the identification of edge state generators can be understood as an instance of `microscopic bosonization'. The intimate connection of Read's original recursion with `non-local order parameters' generalizes to the present situation, and we are able to give explicit second quantized formulas for non-local order parameters associated with CF states.

cond-mat.str-el