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Title: Excitation spectrum of Heisenberg spin ladders

Abstract

Heisenberg antiferromagnetic spin ladders'' (two coupled spin chains) are low-dimensional magnetic systems which for [ital S]=1/2 interpolate between half-integer-spin chains, when the chains are decoupled, and effective integer-spin one-dimensional chains in the strong-coupling limit. The spin-1/2 ladder may be realized in nature by vanadyl pyrophosphate, (VO)[sub 2]P[sub 2]O[sub 7]. In this paper we apply strong-coupling perturbation theory, spin-wave theory, Lanczos techniques, and a Monte Carlo method to determine the ground-state energy and the low-lying excitation spectrum of the ladder. We find evidence of a nonzero spin gap for [ital all] interchain couplings [ital J][sub [perpendicular]][gt]0. A band of spin-triplet excitations above the gap is also analyzed. These excitations are unusual for an antiferromagnet, since their long-wavelength dispersion relation behaves as ([ital k][minus][ital k][sub 0])[sup 2] (in the strong-coupling limit [ital J][sub [perpendicular]][much gt][ital J], where [ital J] is the in-chain antiferromagnetic coupling). Their band is folded, with a minimum energy at [ital k][sub 0]=[pi], and a maximum between [ital k][sub 1]=[pi]/2 (for [ital J][sub [perpendicular]]=0) and 0 (for [ital J][sub [perpendicular]]=[infinity]). We also give numerical results for the dynamical structure factor [ital S]([ital q],[omega]), which can be determined in neutron scattering experiments. Finally, possible experimental techniques for studying the excitationmore » spectrum are discussed.« less

Authors:
 [1]; ;  [2];  [3]
  1. Physics Division and Center for Computationally Intensive Physics, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6373 (United States) Department of Physics, University of Tennessee, Knoxville, Tennessee 37996-1200 (United States)
  2. Department of Physics, Center for Materials Research and Technology and Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida 32306 (United States)
  3. Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
Publication Date:
OSTI Identifier:
6941912
DOE Contract Number:  
FG05-91ER40627
Resource Type:
Journal Article
Journal Name:
Physical Review, B: Condensed Matter; (United States)
Additional Journal Information:
Journal Volume: 47:6; Journal ID: ISSN 0163-1829
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; HEISENBERG MODEL; EXCITED STATES; ANTIFERROMAGNETISM; COUPLING; ENERGY GAP; MONTE CARLO METHOD; PERTURBATION THEORY; SPIN WAVES; STRONG-COUPLING MODEL; VANADIUM PHOSPHATES; CALCULATION METHODS; CRYSTAL MODELS; ENERGY LEVELS; MAGNETISM; MATHEMATICAL MODELS; OXYGEN COMPOUNDS; PARTICLE MODELS; PHOSPHATES; PHOSPHORUS COMPOUNDS; TRANSITION ELEMENT COMPOUNDS; VANADIUM COMPOUNDS; 665000* - Physics of Condensed Matter- (1992-)

Citation Formats

Barnes, T, Dagotto, E, Riera, J, and Swanson, E S. Excitation spectrum of Heisenberg spin ladders. United States: N. p., 1993. Web. doi:10.1103/PhysRevB.47.3196.
Barnes, T, Dagotto, E, Riera, J, & Swanson, E S. Excitation spectrum of Heisenberg spin ladders. United States. https://doi.org/10.1103/PhysRevB.47.3196
Barnes, T, Dagotto, E, Riera, J, and Swanson, E S. Mon . "Excitation spectrum of Heisenberg spin ladders". United States. https://doi.org/10.1103/PhysRevB.47.3196.
@article{osti_6941912,
title = {Excitation spectrum of Heisenberg spin ladders},
author = {Barnes, T and Dagotto, E and Riera, J and Swanson, E S},
abstractNote = {Heisenberg antiferromagnetic spin ladders'' (two coupled spin chains) are low-dimensional magnetic systems which for [ital S]=1/2 interpolate between half-integer-spin chains, when the chains are decoupled, and effective integer-spin one-dimensional chains in the strong-coupling limit. The spin-1/2 ladder may be realized in nature by vanadyl pyrophosphate, (VO)[sub 2]P[sub 2]O[sub 7]. In this paper we apply strong-coupling perturbation theory, spin-wave theory, Lanczos techniques, and a Monte Carlo method to determine the ground-state energy and the low-lying excitation spectrum of the ladder. We find evidence of a nonzero spin gap for [ital all] interchain couplings [ital J][sub [perpendicular]][gt]0. A band of spin-triplet excitations above the gap is also analyzed. These excitations are unusual for an antiferromagnet, since their long-wavelength dispersion relation behaves as ([ital k][minus][ital k][sub 0])[sup 2] (in the strong-coupling limit [ital J][sub [perpendicular]][much gt][ital J], where [ital J] is the in-chain antiferromagnetic coupling). Their band is folded, with a minimum energy at [ital k][sub 0]=[pi], and a maximum between [ital k][sub 1]=[pi]/2 (for [ital J][sub [perpendicular]]=0) and 0 (for [ital J][sub [perpendicular]]=[infinity]). We also give numerical results for the dynamical structure factor [ital S]([ital q],[omega]), which can be determined in neutron scattering experiments. Finally, possible experimental techniques for studying the excitation spectrum are discussed.},
doi = {10.1103/PhysRevB.47.3196},
url = {https://www.osti.gov/biblio/6941912}, journal = {Physical Review, B: Condensed Matter; (United States)},
issn = {0163-1829},
number = ,
volume = 47:6,
place = {United States},
year = {1993},
month = {2}
}