The semimetallic quasi-one-dimensional S = 1/2 Heisenberg antiferromagnet Yb4As3 was studied by low-temperature measurements of the specific heat C(T, B), thermal expansion α(T, B), and thermal conductivity κ(T, B). At finite magnetic fields (B ≤ 12 T) we observed the following distinct anomalies: (1) the magnon contribution to C(T, 0), γT, with large coefficient γ ≈ 200 mJ/(K2 mol), becomes strongly reduced with field, and (2) a broad hump in C(T, B = const) is induced at slightly higher temperatures. (3) The latter corresponds to a pronounced peak in α(T, B = const) as well as (4) to a broad minimum in κ(T, B = const)/κ(T, 0). These anomalies are well described by the classical sine-Gordon solution of a one-dimensional Heisenberg antiferromagnet with a weak easy-plane anisotropy. However, the soliton-rest energy deduced from the experimental results depends on the magnetic field like Es ∼ Bν, with an exponent ν ≈ 0.66, while the classical sine-Gordon model requires ν = 1. Thus, our results suggest an alternative description of soliton excitations in an antiferromagnetic S = 1/2 Heisenberg chain in terms of the quantum sine-Gordon model, for which an exponent ν = 2/3 is appropriate.
|Number of pages||10|
|Journal||Acta Physica Polonica A|
|Publication status||Published - 2000 Jan|
|Event||The European Conference: Physics of Magnetism '99 - Poznan, Poland|
Duration: 1999 Jun 21 → 1999 Jun 25
ASJC Scopus subject areas
- Physics and Astronomy(all)