Finite-temperature dynamics of the spin-12bond alternating Heisenberg antiferromagnetic chain

Abstract

We present results for the dynamic structure factor of the S = 1/2 bond alternating Heisenberg chain over a large range of frequencies and temperatures. Data are obtained from a numerical evaluation of thermal averages based on the calculation of all eigenvalues and eigenfunctions for chains of up to 20 spins. Interpretation is guided by the exact temperature dependence in the noninteracting dimer limit which remains qualitatively valid up to an interdimer exchange λ ≈ 0.5. The temperature induced central peak around zero frequency is clearly identified and aspects of the crossover to spin diffusion in its variation from low to high temperatures are discussed. The onemagnon peak acquires an asymmetric shape with increasing temperature. The two-magnon peak is dominated by the S = 1 bound state which remains well defined up to temperatures of the order of J. The variation with temperature and wavevector of the integrated intensity for one-magnon and two-magnon scattering and of the central peak are discussed.

Anomalous dynamical line shapes in a quantum magnet at finite temperature

“…10 Other results for the dynamical correlations in the AHC at finite temperature have relied on exact diagonalization. 21 Here we calculate the spin response using the method described in Ref. 9, which is summarized below for convenience.…”

“…21 The scattering, including all possible transitions, weighted by thermal population and scattering cross sections and corrected for both the magnetic form factor for Cu 2+ and the instrumental resolution, has been computed. These computations also predict the asymmetric line shape in agreement with the measurements, demonstrating an accurate handling of background effects in the neutronscattering data.…”

Finite-temperature dynamical structure factor of alternating Heisenberg chains

“…As such the regime in which these materials are understood is dominated by quantum fluctuations. In contrast, far less is known about their finite temperature behaviour where there is an interplay of quantum and thermal fluctuations 6,7,8,9,10,11 . Though the chemistry of these materials can be exceedingly complicated, a wide range of their properties, up to energy scales set by their exchange constants, are well described by simple lattice models of the form…”

Time-dependent correlations in quantum magnets at finite temperature

“…The concomitant asymmetry cannot be described by a pure Lorentzian at finite temperatures. Hence, the details of the scattering processes have a considerable impact on the correlations, and more sophisticated theories have been employed to explain this phenomenon [10,[12][13][14][15][16][17][18][19][20][21][22].…”