Spin dynamics in the $S=1/2$ weakly-coupled chains antiferromagnet BaCu${}_2$Si${}_2$O${}_7$

Abstract

Inelastic neutron scattering is used to identify single-particle and continuum spin excitations in the quasi-one-dimensional $S=1/2$ antiferromagnet \ba. In the data analysis, close attention is given to resolution effects. A gap in the continuum spectrum at ${\Delta }_c=\mathrm{4.74.8}$ meV is directly observed. The gap energy is in excellent agreement with existing theoretical predictions. Below the gap, the spectrum is dominated by sharp accoustic spin wave excitations.

9 pages 8 figures