LIGHT SCATTERING OF MAGNETS IN THE PROXIMITY TO QUANTUM CRITICALITY

摘要

In the investigation of quantum critical spin systems light scattering experiments prove to be especially useful due to their high sensitivity and spectral resolution that perfectly match the relevant energy scales. The observed low energy collective excitations or bound states with singlet character play an important role characterizing fluctuations of the system. Furthermore, often spin or orbital related phonon anomalies are observed that include important symmetry information. The use of this experimental technique will be demonstrated on three model systems, the frustrated spin dimer system SrCu(BO_3)_2, the spin tetrahedra system Cu_2Te_2O_5Br_2 and the layered pseudo gap system TiOCl