arXiv subjects

Owen Benton

Publications and source records attributed to Owen Benton.

At least 19 recordsLinked to original sources

arXiv2025

Engineering Topological Bands in Strained Covalent Organic Frameworks

The tunability of covalent organic frameworks (COFs) opens opportunities to engineer topological electronic phases, including topological insulators (TIs) and higher-order topological insulators (HOTIs)--materials that host in-gap states localized at their edges, hinges, or corners. Here we explore how chemically feasible perturbations can drive triazine-based COFs (CTFs) into topological regimes. Using a tight-binding model on the Honeycomb lattice inspired by the frontier electronic states of CTFs, we show that introducing an effective uniaxial strain--implemented as a modulation of electron hopping on a subset of bonds--can generate a series of distinct topological band structures. This effect can be realized in practice through chemical substitution of linkers along the strained bonds. First-principles calculations demonstrate that replacing biphenyl with pyrene linkers drives a CTF to the brink of a HOTI phase, suggesting a viable route toward topological band-structure engineering in COFs.

cond-mat.mtrl-sci↗

arXiv2025

Imprinting electrically switchable scalar spin chirality by anisotropic strain in a Kagome antiferromagnet

Topological chiral antiferromagnets, such as Mn$_{3}$Sn, are emerging as promising materials for next-generation spintronic devices due to their intrinsic transport properties linked to exotic magnetic configurations. Here, we demonstrate that anisotropic strain in Mn$_{3}$Sn thin films offers a novel approach to manipulate the magnetic ground state, unlocking new functionalities in this material. Anisotropic strain reduces the point group symmetry of the manganese (Mn) Kagome triangles from $C_{3v}$ to $C_{1}$, significantly altering the energy landscape of the magnetic states in Mn$_{3}$Sn. This symmetry reduction enables even a tiny in-plane Dzyaloshinskii-Moriya (DM) interaction to induce canting of the Mn spins out of the Kagome plane. The modified magnetic ground state introduces a finite scalar spin chirality and results in a significant Berry phase in momentum space. Consequently, a large anomalous Hall effect emerges in the Kagome plane at room temperature - an effect that is absent in the bulk material. Moreover, this two-fold degenerate magnetic state enables the creation of multiple-stable, non-volatile anomalous Hall resistance (AHR) memory states. These states are field-stable and can be controlled by thermal assisted current-induced magnetization switching requiring modest current densities and small bias fields, thereby offering a compelling new functionality in Mn$_{3}$Sn for spintronic applications.

cond-mat.mtrl-sci↗

arXiv2025

Numerical Block Diagonalization and Linked-Cluster Expansion for Deriving Effective Hamiltonians: Applications to Spin Excitations

We present a numerical, non-perturbative framework for constructing effective Hamiltonians that describe the dynamics of low-energy degrees of freedom within a restricted Hilbert space in quantum many-body systems. The approach is based on block diagonalization guided by a minimal-deformation principle imposed within a selected target sector. The formulation is designed to remain compatible with the numerical linked-cluster expansion. For gapped systems, the relation between minimal deformation and cluster additivity requires careful treatment when excited eigenstates contain finite admixtures of the ground state. After establishing a cluster-additive basis that reproduces the H\"ormann-Schmidt construction, the minimal-deformation criterion uniquely determines the effective Hamiltonian within each excitation sector. The same criterion also provides a practical numerical procedure for selecting relevant low-energy eigenstates, including regimes characterized by strong level mixing and avoided crossings. The framework is illustrated using two spin models: the one-dimensional transverse-field Ising model as a benchmark and the two-dimensional Shastry-Sutherland model with Dzyaloshinskii-Moriya interactions, relevant to SrCu$_2$(BO$_3$)$_2$. In both cases, the resulting effective Hamiltonians accurately capture the excitation dynamics and the associated band structures.

cond-mat.str-el↗

arXiv2025

An Atlas of Classical Pyrochlore Spin Liquids

Frustrated magnetism in the pyrochlore lattice magnet has proven to be a most fruitful setting for the experimental and theoretical search for spin liquids. Besides the canonical case of spin ice, recent works have identified a variety of new classical and quantum spin liquids engendered by the generic nearest-neighbor anisotropic spin Hamiltonian for that lattice. However, a general framework for the thorough and systematic classification and characterization of these exotic states of matter has been lacking, as has an exhaustive list of all possible spin liquids that this model can support and, perhaps most interesting, what is the corresponding structure of their emergent field theory description. In this work, we develop such a theoretical framework to identify the interaction parameters stabilizing different classical spin liquids and derive their corresponding effective generalized Gauss's laws at low temperatures. Combining this with Monte Carlo simulations, we systematically identify all classical spin liquids for the general nearest-neighbor anisotropic spin Hamiltonian on the pyrochlore lattice. In doing so, we uncover new spin liquid models with exotic forms of generalized Gauss's law and multipole conservation laws. Our approach allows us to compile an atlas of all spin liquids realized in the phase diagram, providing a global picture of their mutual connections in parameter space and transitions between them. Our work will inform future theoretical and experimental studies of classical and quantum spin liquids on the pyrochlore lattice and help rationalize the exotic properties of pyrochlore magnets.

cond-mat.str-el↗

arXiv2025

Tunable topological protection in Rydberg lattices via a novel quantum Monte Carlo approach

Rydberg atom arrays have recently been conjectured to host $Z_2$ quantum spin liquids (QSLs) in certain parameter regimes. Due to the strong interactions between these atoms, it is not possible to analytically study these systems, and one must resort to Monte Carlo sampling of the path integral to reach definite conclusions. We use a tailored update, specifically designed to target the low energy excitations of the QSL. This allows us to reliably simulate Rydberg atoms on a triangular lattice in the proposed QSL regime. We identify a correlated paramagnetic phase at low temperatures which hosts topological protection similar to a $Z_2$ spin liquid up to a length scale tuned by Hamiltonian parameters. However, this correlated paramagnet seems to be continuously connected to the trivial paramagnetic regime and thus does not seem to be a true QSL. This result indicates the feasibility of Rydberg atom arrays to act as topological qubits.

cond-mat.str-el↗

arXiv2025

Signatures of spinon dynamics and phase structure of dipolar-octupolar quantum spin ices in two-dimensional coherent spectroscopy

We study how sharp signatures of fractionalization emerge in nonlinear spectroscopy experiments on spin liquids with separated energy scales. Our model is that of dipolar-octupolar rare earth pyrochlore materials, prime candidates for realising quantum spin ice. This family of three dimensional quantum spin liquids exhibits fractionalization of spin degrees of freedom into spinons charged under an emergent $U(1)$ gauge field. We show that the technique of two dimensional coherent spectroscopy (2DCS) can identify clear signatures of fractionalised spinon dynamics in dipolar-octupolar quantum spin ices. However, at intermediate temperatures, spinon dynamics are heavily constrained in the presence of an incoherent spin background, leading to a broad 2DCS response. At lower temperatures, a sharp signal emerges as the system enters a coherent spin liquid state. This lower temperature signal can in turn distinguish between zero-flux and $π$-flux forms of quantum spin ice.

cond-mat.str-el↗

arXiv2024

Fragile spin liquid in three dimensions

Motivated by the recent appearance of the trillium lattice in the search for materials hosting spin liquids, we study the ground state of the classical Heisenberg model on its linegraph, the trilline lattice. We find that this network realises the recently proposed notion of a fragile spin liquid in three dimensions. Additionally, we analyze the Ising case and argue for a possible $\mathbb{Z}_2$ quantum spin liquid phase in the corresponding quantum dimer model. Like the well-known $U(1)$ spin liquids, the classical phase hosts moment fractionalisation evidenced in the diluted lattice, but unlike these, it exhibits exponential decay both in spin correlations and interactions between fractionalised moments. This provides the first instance of a purely short-range correlated classical Heisenberg spin liquid in three dimensions.

cond-mat.str-el↗

arXiv2024

Exploiting polarization dependence in two dimensional coherent spectroscopy: examples of Ce$_2$Zr$_2$O$_7$ and Nd$_2$Zr$_2$O$_7$

Two dimensional coherent spectroscopy (2DCS) probes the nonlinear optical response of correlated systems. An interesting application is the study of fractionalized excitations, which are challenging to distinguish unambiguously in linear response. Here we demonstrate how the sensitivity of optical matrix elements to variations in the photon polarization allows one to probe different aspects of low lying excitations in models of the candidate fractionalized materials Ce$_2$Zr$_2$O$_7$ and Nd$_2$Zr$_2$O$_7$, which host effective one-dimensional spin chains when subjected to a [110] magnetic field. We show how both fractionalized spinon excitations or conventional magnons can be picked out in the 2DCS response, and how the response from polarized spin chains can be used to probe the dipolar-octupolar mixing angle $θ$ through the relative intensity of one- and two-magnon signals. Further, we find that a $[001]$ polarization of the probe field is particularly sensitive to lower band edge of the spinon continuum and can be used as a measure of the proximity of a quantum critical point in Ce$_2$Zr$_2$O$_7$. 2DCS can thus be employed to provide invaluable and detailed information both on the constituent degrees of freedom of a quantum material and on their collective behaviour.

cond-mat.str-el↗

arXiv2024

Irrational moments and signatures of higher-rank gauge theories in diluted classical spin liquids

Classical spin liquids (CSLs) have proved to be a fruitful setting for the emergence of exotic gauge theories. Vacancy clusters in CSLs can introduce gauge charges into the system, and the resulting behavior in turn reveals the nature of the underlying theory. We study these effects for a series of CSLs on the honeycomb lattice. We find that dilution leads to the emergence of effective free spins with tuneable, and generally irrational, size. For a specific higher-rank CSL, described by a symmetric tensor gauge fields, dilution produces non-decaying spin textures with a characteristic quadrupolar angular structure, and infinite-ranged interactions between dilution clusters.

cond-mat.str-el↗

arXiv2023

Abundance of hard-hexagon crystals in the quantum pyrochlore antiferromagnet

We propose a simple family of valence-bond crystals as potential ground states of the $S=1/2$ and $S=1$ Heisenberg antiferromagnet on the pyrochlore lattice. Exponentially numerous in the linear size of the system, these can be visualized as hard-hexagon coverings, with each hexagon representing a resonating valence-bond ring. This ensemble spontaneously breaks rotation, inversion and translation symmetries. A simple, yet accurate, variational wavefunction allows a precise determination of the energy, confirmed by DMRG and numerical linked cluster expansion, and extended by an analysis of excited states. The identification of the origin of the stability indicates applicability to a broad class of frustrated lattices, which we demonstrate for the checkerboard and ruby lattices. Our work suggests a perspective on such quantum magnets, in which unfrustrated motifs are effectively uncoupled by the frustration of their interactions.

cond-mat.str-el↗

arXiv2023

Ising Fracton Spin Liquid on the Honeycomb Lattice

We study a classical Ising model on the honeycomb lattice with local two-body interactions and present strong evidence that at low temperature it realizes a higher-rank Coulomb liquid with fracton excitations. We show that the excitations are (type-I) fractons, appearing at the corners of membranes of spin flips. Because of the three-fold rotational symmetry of the honeycomb lattice, these membranes can be locally combined such that no excitations are created, giving rise to a set of ground states described as a liquid of membranes. We devise a cluster Monte-Carlo algorithm purposefully designed for this problem that moves pairs of defects, and use it to study the finite-temperature behavior of the model. We show evidence for a first order transition from a high-temperature paramagnet to a low-temperature phase whose correlations precisely match those predicted for a higher-rank Coulomb phase.

cond-mat.str-el↗

arXiv2023

Classification of Classical Spin Liquids: Typology and Resulting Landscape

Classical spin liquids (CSL) lack long-range magnetic order and are characterized by an extensive ground state degeneracy. We propose a classification scheme of CSLs based on the structure of the flat bands of their Hamiltonians. Depending on absence or presence of the gap from the flat band, the CSL are classified as algebraic or fragile topological, respectively. Each category is further classified: the algebraic case by the nature of the emergent Gauss's law at the gap-closing point(s), and the fragile topological case by the homotopy of the eigenvector winding around the Brillouin zone. Previously identified instances of CSLs fit snugly into our scheme, which finds a landscape where algebraic CSLs are located at transitions between \fragile topological ones. It also allows us to present a new, simple family of models illustrating that landscape, which hosts both fragile topological and algebraic CSLs, as well as transitions between them.

cond-mat.str-el↗

arXiv2023

Classification of Classical Spin Liquids: Detailed Formalism and Suite of Examples

The hallmark of highly frustrated systems is the presence of many states close in energy to the ground state. Fluctuations between these states can preclude the emergence of any form of order and lead to the appearance of spin liquids. Even on the classical level, spin liquids are not all alike: they may have algebraic or exponential correlation decay, and various forms of long wavelength description, including vector or tensor gauge theories. Here, we introduce a classification scheme, allowing us to fit the diversity of classical spin liquids (CSLs) into a general framework as well as predict and construct new kinds. CSLs with either algebraic or exponential correlation-decay can be classified via the properties of the bottom flat band(s) in their soft-spin Hamiltonians. The classification of the former is based on the algebraic structures of gapless points in the spectra, which relate directly to the emergent generalized Gauss's laws that control the low temperature physics. The second category of CSLs, meanwhile, are classified by the fragile topology of the gapped bottom band(s). Utilizing the classification scheme we construct new models realizing exotic CSLs, including one with anisotropic generalized Gauss's laws and charges with subdimensional mobility, one with a network of pinch-line singularities in its correlation functions, and a series of fragile topological CSLs connected by zero-temperature transitions.

cond-mat.str-el↗

arXiv2022

Spin ice in a general applied magnetic field: Kasteleyn transition, magnetic torque and rotational magnetocaloric effect

Spin ice is a paradigmatic frustrated system famous for the emergence of magnetic monopoles and a large magnetic entropy at low temperatures. It exhibits unusual behavior in the presence of an external magnetic field as a result of the competition between the spin ice entropy and the Zeeman energy. Studies of this have generally focused on fields applied along high symmetry directions: [111], [001], and [110]. Here we consider a model of spin ice with external field in an arbitrary direction. We find that the Kasteleyn transition known for $[001]$ fields, appears also for general field directions and calculate the associated Kasteleyn temperature $T_K$ as a function of field direction. $T_K$ is found to vanish, with a logarithmic dependence on field angle, approaching certain lines of special field directions. We further investigate the thermodynamic properties of spin ice for $T>T_K$, using a Husimi cactus approximation. As the system is cooled towards $T_K$ a large magnetic torque appears, tending to align the $[001]$ crystal axis with the external field. The model also exhibits a rotational magnetocaloric effect: significant temperature changes can be obtained by adabiatically rotating the crystal relative to a fixed field.

cond-mat.str-el↗

arXiv2022

Dynamical scaling as a signature of multiple phase competition in Yb$_2$Ti$_2$O$_7$

$\rm Yb_2Ti_2O_7$ is a celebrated example of a pyrochlore magnet with highly-frustrated, anisotropic exchange interactions. To date, attention has largely focused on its unusual, static properties, many of which can be understood as coming from the competition between different types of magnetic order. Here we use inelastic neutron scattering with exceptionally high energy resolution to explore the dynamical properties of $\rm Yb_2Ti_2O_7$. We find that spin correlations exhibit dynamical scaling, analogous to behavior found near to a quantum critical point. We show that the observed scaling collapse can be explained within a phenomenological theory of multiple--phase competition, and confirm that a scaling collapse is also seen in semi--classical simulations of a microscopic model of $\rm Yb_2Ti_2O_7$. These results suggest a general picture for dynamics in systems with competing ground states.

cond-mat.str-el↗

arXiv2021

Topological Route to New and Unusual Coulomb Spin Liquids

Coulomb spin liquids are topological magnetic states obeying an emergent Gauss' law. Little distinction has been made between different kinds of Coulomb liquids. Here we show how a series of distinct Coulomb liquids can be generated straightforwardly by varying the constraints on a classical spin system. This leads to pair creation, and coalescence, of topological defects of an underlying vector field. The latter makes higher-rank spin liquids, of recent interest in the context of fracton theories, with attendant multi-fold pinch points in the structure factor, appear naturally. New Coulomb liquids with an abundance of pinch points also arise. We thus establish a new and general route to uncovering exotic Coulomb liquids, via the manipulation of topological defects in momentum space.

cond-mat.str-el↗

arXiv2021

Exactly solvable spin-1/2 XYZ models with highly-degenerate, partially ordered, ground states

Exactly solvable models play a special role in Condensed Matter physics, serving as secure theoretical starting points for investigation of new phenomena. Changlani et al. [Phys. Rev. Lett. 120, 117202 (2018)] have discovered a limit of the XXZ model for $S=1/2$ spins on the kagome lattice, which is not only exactly solvable, but features a huge degeneracy of exact ground states corresponding to solutions of a three-coloring problem. This special point of the model was proposed as a parent for multiple phases in the wider phase diagram, including quantum spin liquids. Here, we show that the construction of Changlani et al. can be extended to more general forms of anisotropic exchange interaction, finding a line of parameter space in an XYZ model which maintains both the macroscopic degeneracy and the three-coloring structure of solutions. We show that the ground states along this line are partially ordered, in the sense that infinite-range correlations of some spin components coexist with a macroscopic number of undetermined degrees of freedom. We therefore propose the exactly solvable limit of the XYZ model on corner-sharing triangle-based lattices as a tractable starting point for discovery of quantum spin systems which mix ordered and spin liquid-like properties.

cond-mat.str-el↗

arXiv2021

Ordered ground states of kagome magnets with generic exchange anisotropy

There is a growing family of rare-earth kagome materials with dominant nearest-neighbor interactions and strong spin orbit coupling. The low symmetry of these materials makes theoretical description complicated, with six distinct nearest-neighbor coupling parameters allowed. In this Article, we ask what kinds of classical, ordered, ground states can be expected to occur in these materials, assuming generic (i.e. non-fine-tuned) sets of exchange parameters. We use symmetry analysis to show that there are only five distinct classical ground state phases occurring for generic parameters. The five phases are: (i) a coplanar, 2-fold degenerate, state with vanishing magnetization (${\sf A_1}$), (ii) a noncoplanar, 2-fold degenerate, state with magnetization perpendicular to the kagome plane (${\sf A_2}$), (iii) a coplanar, 6-fold degenerate, state with magnetization lying within the kagome plane (${\sf E}$-coplanar), (iv) a noncoplanar, 6-fold degenerate, state with magnetization lying within a mirror plane of the lattice (${\sf E}$-noncoplanar$_{6}$), (v) a noncoplanar, 12-fold degenerate, state with magnetization in an arbitrary direction (${\sf E}$-noncoplanar$_{12}$). All five are translation invariant (${\bf q}=0$) states. Having found the set of possible ground states, the ground state phase diagram is obtained by comparing numerically optimized energies for each possibility as a function of the coupling parameters. The state ${\sf E}$ noncoplanar$_{12}$ is extremely rare, occupying $<1\%$ of the full phase diagram, so for practical purposes there are four main ordered states likely to occur in anisotropic kagome magnets with dominant nearest neighbor interactions. These results can aid in interpreting recent experiments on ``tripod kagome'' systems R$_3$A$_2$Sb$_3$O$_{14}$, as well as materials closer to the isotropic limit such as Cr- and Fe- jarosites.

cond-mat.str-el↗