125,243 research outputs found
Resurrecting the partially isotropic Haldane-Shastry model
No full textWe present an alternative, simpler expression for the Hamiltonian of the partially isotropic (XXZ-like) version of the Haldane-Shastry model, which was derived by D. Uglov over two decades ago in an apparently little-known preprint. While resembling the pairwise long-range form of the Haldane-Shastry model, our formula accounts for the multispin interactions obtained by Uglov. Our expression is physically meaningful, makes hermiticity manifest, and is computationally more efficient. We discuss the model\u27s properties, including its limits and (ordinary and quantum-affine) symmetries, and review the model\u27s exact spectrum found by Uglov for finite spin-chain length, which parallels the isotropic case up to level splitting due to the anisotropy. We also extend the partially isotropic model to higher rank, with SU(n) "spins," for which the spectrum is determined by sln motifs
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
The open Haldane-Shastry chain: thermodynamics and criticality
No full textWe study the thermodynamics and criticality of the su() Haldane-Shastry
chain of type with a general chemical potential term. We first derive a
complete description of the spectrum of this model in terms of -type
motifs, from which we deduce a representation for the partition function as the
trace of a product of site-dependent transfer matrices. In the thermodynamic
limit, this formula yields a simple expression for the free energy per spin in
terms of the Perron-Frobenius eigenvalue of the continuum limit of the transfer
matrix. Evaluating this eigenvalue we obtain closed-form expressions for the
thermodynamic functions of the chains with . Using the motif-based
description of the spectrum derived here, we study in detail the ground state
of these models and their low energy excitations. In this way we identify the
critical intervals in chemical potential space and compute their corresponding
Fermi velocities. By contrast with previously studied models of this type, we
find in some cases two types of low energy excitations with linear
energy-quasimomentum relation. Finally, we determine the central charge of all
the critical phases by analyzing the low-temperature behavior of the expression
for the free energy per spin.Comment: 46 pages, 6 figures, typeset in LaTe
Skyrmion-driven topological Hall effect in a Shastry-Sutherland magnet
No full textThe Shastry-Sutherland model and its generalizations have been shown to capture emergent complex magnetic properties from geometric frustration in several quasi-two-dimensional quantum magnets. Using an exchange model, we show here that metallic Shastry-Sutherland magnets can exhibit a topological Hall effect driven by magnetic skyrmions under realistic conditions. The magnetic properties are modeled with competing symmetric Heisenberg and
asymmetric Dzyaloshinskii-Moriya exchange interactions, while a coupling between the spins of the itinerant electrons and the localized moments describes the magnetotransport behavior. Our results, employing complementary Monte Carlo simulations and a novel machine learning analysis to investigate the magnetic phases, provide evidence for field-driven skyrmion crystal formation for an extended range of Hamiltonian parameters. By constructing an effective tight-binding model of conduction electrons coupled to the skyrmion lattice, we clearly demonstrate the appearance of the topological Hall effect.
We further elaborate on the effects of finite temperatures on both magnetic and magnetotransport properties.Ministry of Education (MOE)Published versionThe work of A.A.P. was supported by the Russian Science Foundation Project No. 20-72-00044. P.S. acknowledges support from the Ministry of Education (MOE), Singapore, in the form of AcRF Tier 2 Grant No. MOE2019-T2-2-119
Generalized plaquette state in the anisotropic Shastry-Sutherland model
No full textWe use a generalized Schwinger boson approach to investigate the nature of the intermediate phase (separating the antiferromagnetic and dimer phases) in the Shastry-Sutherland model with exchange anisotropy. Our results confirm the plaquette nature of the intermediate phase and demonstrate that exchange anisotropy (both Ising-like and XY-like) weakens the plaquette order and ultimately suppresses it altogether for sufficiently strong anisotropy. Interestingly, we find that the low-energy excitation spectrum of the plaquette state changes dramatically near the boundary with the dimer phase—the location of the minimum in the (gapped) lowest excitation mode changes from k=(0,0) to four degenerate points.Published versio
Recommended from our members
Quantum phases of the Shastry-Sutherland antiferromagnet: Application to SrCu 2 ( BO 3 ) 2
No full textWe study possible paramagnetic phases of antiferromagnets on the Shastry-Sutherland lattice by a gauge-theoretic analysis of fluctuations in a theory with Sp(2N) symmetry. In addition to the familiar dimer phase, we find a confining phase with plaquette order and a topologically ordered phase with deconfined S = 1/2 spinons and helical spin correlations. The deconfined phase is contiguous to the dimer phase and in a regime of couplings close to those found in the insulator SrCu2(BO3)(2). We suggest that a superconductor obtained by doping this insulator with mobile charge carriers will be an attractive candidate for observing the anomalous magnetic flux properties associated with topological order.Accepted Manuscrip
Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnet TmB4
No full textWe study TmB, a frustrated magnet on the Archimedean Shastry-Sutherland lattice, through magnetization and transport experiments. The lack of anisotropy in resistivity shows that TmB4 is an electronically three-dimensional system. The magnetoresistance (MR) is hysteretic at low temperature even though a corresponding hysteresis in magnetization is absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE) and is linear above saturation despite a large MR. We propose that complex structures at magnetic domain walls may be responsible for the hysteretic MR and may also lead to the AHE.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)Published versio
Exact spectral functions of a non-fermi liquid in one dimension
No full textWe study the exact one-electron propagator and spectral function of a solvable model of interacting electrons due to Schulz and Shastry. The solution previously found for the energies and wave functions is extended to give spectral functions that turn out to be computable, interesting, and nontrivial. They provide one of the few examples of cases where the spectral functions are known asymptotically as well as exactly
Exact spectral functions of a non-Fermi liquid in one dimension
No full textWe study the exact one-electron propagator and spectral function of a solvable model of interacting electrons due to Schulz and Shastry. The solution previously found for the energies and wave functions is extended to give spectral functions that turn out to be computable, interesting, and nontrivial. They provide one of the few examples of cases where the spectral functions are known asymptotically as well as exactly
- …
