Magnetic excitations in the spin gap system KCuCl3

Single-crystal neutron inelastic scattering was performed in order to investigate the magnetic excitations of KCuCl3, which has a singlet ground state with an excitation gap. The constant-Q energy scan profiles are collected at T = 8 K for selected reciprocal points in the a*-c* plane which includes the double-chain direction (a-axis). Dispersion relations along the a*- and c*-axes are determined. It is suggested that the present system can be magnetically described as a coupled antiferromagnetic dimer system rather than a double spin chain. The lowest excitation energy is determined to be 2.70 meV at Q = (0, 0, -1) and (1, 0, +/-1), the value of which is consistent with our previous evaluation of the excitation gap from the high-field magnetization measurement.