Schedule Jun 10, 2004
Magnetic Quantum Phase Transitions in Coupled Spin Dimer Systems
Hidekazu Tanaka (Tokyo Institute of Technology)

Research Center for Low Temperature Physics, Tokyo Institute of Technology

TlCuCl3 and KCuCl3 have the same monoclinic crystal structure composed of ch emical dimer Cu2Cl6 and are described magnetically as coupled spin dimer sys tems. Their magnetic ground states are spin singlets with excitation gaps D/ kB of 7.5 K and 31 K , respectively. In a magnetic field, created Sz=+1 comp onent of spin triplet which has recently been called triplon can hop to neig hboring dimers and interact with one another due to the transverse and longi tudinal components of the interdimer interaction. Hence, the system can be r epresented as a system of interacting triplon bosons. When the hopping term is dominant, triplons can undergo Bose-Einstein condensation in a magnetic f ield higher than the critical field Hc corresponding to the gap D. This lead s to field-induced transverse magnetic ordering. The gap can be also closed by hydrostatic pressure. Consequently, pressure-induced antiferromagnetic or dering can take place. In the conference, I will speak about

  1. field-induced magnetic ordering in TlCuCl3,
  2. field-induced magnetic ordering and localization of triplons in Tl1-xKxCuCl3,
  3. pressure-induced magnetic ordering in TlCuCl3, impurity- and field-induced magnetic ordering in TlCu1-xMgxCl3.

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