Thermodynamic Properties and Elementary Excitations in Quantum Sine-Gordon Spin System KCuGaF₆

Abstract

Thermodynamic properties and elementary excitations in S ¼ 1=2 one-dimensional Heisenberg antiferromagnet KCuGaF 6 were investigated by magnetic susceptibility, specific heat and ESR measurements. Due to the Dzyaloshinsky-Moriya interaction with alternating D-vectors and/or the staggered g-tensor, the staggered magnetic field is induced when subjected to external magnetic field. Specific heat in magnetic field clearly shows the formation of excitation gap, which is attributed to the staggered magnetic field. The specific heat data was analyzed on the basis of the quantum sine-Gordon (SG) model. We observed many ESR modes including one soliton and three breather excitations characteristic of the quantum SG model. Studies of antiferromagnetic Heisenberg chain (AFHC) have long history. For S ¼ 1=2 uniform AFHC, the ground state, thermodynamic properties and magnetic excitations are well understood with the help of exact solutions [1][2][3][4] and accurate analytical and numerical calculations.5-8) These theoretical results demonstrate the importance of the quantum fluctuation characteristic of low-dimensional systems. In particular, exact result of the magnetic excitations in an external magnetic field H is qualitatively different from the results of the linear spin wave theory. The gapless excitations occur at incommensurate wave vectors q ¼ AE2mðHÞ and AE 2mðHÞ in addition to at q ¼ 0 and , where mðHÞ is the magnetization per site in the unit of g B . 4)Recently, the physics of S ¼ 1=2 AFHC in staggered magnetic field induced by the external magnetic field has been attracting considerable attention.9,10) The model Hamiltonian of such system is written aswhere h is the staggered field perpendicular to the external field H and is given by h ¼ c s H. This magnetic model is actualized in some S ¼ 1=2 AFHC systems such as (H 2 O) 2 (PM = pyrimidine). 15,16) The staggered field originates from the alternating g-tensor and the antisymmetric interaction of the Dzyaloshinsky-Moriya (DM) type with the alternating D vector. In these compounds, the fieldinduced gap ÁðHÞ almost proportional to H 2=3 was commonly observed. This field dependence of the gap cannot be explained by the linear spin wave theory, which derives ÁðHÞ / H 1=2 . Using the field theoretical approach, Oshikawa and Affleck 9,10) argued that the model (1) can be mapped onto the quantum sine-Gordon (SG) model with Lagrangian density L ¼ ð1=2Þð@ Þ þ hC cosð2R Þ, where is a canonical Bose field, is the dual field, R is the compactification radius and C is a coupling constant, and that the gap is expressed as ÁðhÞ ' 1:85Jðg B h=JÞ 2=3 lnðJ=g B hÞ 1=6 . Their result is in agreement with experimental results. [11][12][13][14][15][16] In the above-mentioned compounds, the exchange interaction is order of 10 K and the proportional coefficient is rather small, c s ¼ 0:08.13,16) For the comprehensive understanding of the systems described by the model (1), new compounds having different interaction constants are necessary. In this letter, we show that the static and d...

Orbital Arrangements and Magnetic Interactions in the Quasi-One-Dimensional Cuprates ACuMoO4(OH) (A = Na, K)

“…Similar behavior has been observed in Cu-benzoate, 27-29 Yb4As3, 30 and KCuGaF6 31 and well explained by the presence of staggered Dzyaloshinskii-Moriya (DM) interactions. 32,33 We think that a similar mechanism applies to the present compound.…”

Anisotropic field-induced gap in the quasi-one-dimensional antiferromagnet KCuMoO4(OH)

“…Staggered g-tensors and DM interactions in KCuMoO 4 (OH) give rise to enhanced magnetic susceptibility at low temperatures, large anisotropy in magnetization, and an exponential temperature-dependence in heat capacity, indicating the presence of the field-induced gapped excitations. In fact, these behaviors have been also observed in the other model compounds 14,15,31,33,35,37 .…”

“…The Curie contribution is introduced to represent a large increase of χ i due to the staggered susceptibility 33,35,36 , which is enough for the rough estimation of J. Totally, seven fitting parameters are included: J independent on the field direction, and g ii , C i varying with the field direction (i = a, b, or c).…”

Modulation of breathers in the three-dimensional nonlinear Gross-Pitaevskii equation

“…We briefly discuss the experimental feasibility of the results in Bose-Einstein condensates. [8,9], and semiconductor quantum wells [10], the breather excitations play an important role, directly affecting the electronic, magnetic, optical, vibrational and transport properties of the systems.In the above mentioned studies, one usually considers genuine breathers, i.e., solutions which oscillate in time when the nonlinear equation presents constant coefficients (i.e., without modulation). However, in a more realistic scenario the several parameters that characterize the physical systems may depend on both space and time, leading to breather solutions that can be modulated in space and time.…”

“…We briefly discuss the experimental feasibility of the results in Bose-Einstein condensates. [8,9], and semiconductor quantum wells [10], the breather excitations play an important role, directly affecting the electronic, magnetic, optical, vibrational and transport properties of the systems.…”