Low-Temperature Dynamical Structure Factor of the Two-Leg Spin-1/2 Heisenberg Ladder

We determine the dynamical structure factor of the two-leg spin-1/2 Heisenberg ladder at low temperatures in the regime of strong rung coupling. The dominant feature at zero temperature is the coherent triplon mode. We show that the lineshape of this mode broadens in a non-symmetric way at finite temperatures and that the degree of asymmetry increases with temperature. We also show that at low frequencies a temperature induced resonance akin to the Villain mode in the spin-1/2 Heisenberg Ising chain emerges.Comment: 13 pages, 7 figures, revte