Excitation spectrum of Heisenberg spin ladders

Journal Article · Mon Feb 01 04:00:00 EST 1993 · Physical Review, B: Condensed Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.47.3196· OSTI ID:6941912

Barnes, T ^[1]; Dagotto, E; Riera, J ^[2]; Swanson, E S ^[3]

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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)

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.

• DOE Contract Number: FG05-91ER40627
• OSTI ID: 6941912
• Journal Information: Physical Review, B: Condensed Matter; (United States), Journal Name: Physical Review, B: Condensed Matter; (United States) Vol. 47:6; ISSN 0163-1829; ISSN PRBMDO
• Country of Publication: United States
• Language: English

Related Subjects

665000* -- Physics of Condensed Matter-- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANTIFERROMAGNETISM
CALCULATION METHODS
COUPLING
CRYSTAL MODELS
ENERGY GAP
ENERGY LEVELS
EXCITED STATES
HEISENBERG MODEL
MAGNETISM
MATHEMATICAL MODELS
MONTE CARLO METHOD
OXYGEN COMPOUNDS
PARTICLE MODELS
PERTURBATION THEORY
PHOSPHATES
PHOSPHORUS COMPOUNDS
SPIN WAVES
STRONG-COUPLING MODEL
TRANSITION ELEMENT COMPOUNDS
VANADIUM COMPOUNDS
VANADIUM PHOSPHATES