Molecule of the Month
May 2007
Spin Dynamics in the Quantum Magnet (C5D12N)2CuBr4

Piperidinium copper bromide is an unique model system for a spin ladder.
The small spin S=1/2 of Cu2+ and the tailored magnetic interactions make this compound a quantum magnet at temperatures in the 100 mK regime. Due to its coupling parameters of Jrung = 1.116(3) meV and Jleg = 0.274(4) meV and its critical fields of Hc1 = 6.6 T and Hc2 = 14.8 T all quantum phases of a spin ladder were experimentally accessible for the first time.
The spin liquid phase, the Luttinger liquid phase, and the polarized phase were fully characterized by inelastic neutron scattering and theoretically modelled. Investigations on the 3-D ordered phase are in progress. The neutron experiments were done at PSI (Villigen, CH), ILL (Grenoble, FR), and HMI (Berlin, D) on deuterated crystals grown in Bern.

This work was carried out in the groups of Prof. Hans Ulrich Güdel / Dr. Karl Krämer in collaboration with B. Thielemann (Laboratory for Neutron Scattering, ETH Zürich & PSI) and Ch. Rüegg (Centre for Nanotechnology, University College London).


  • B. Thielemann, Ch. Rüegg, H. M. Rønnow, A. M. Läuchli, J.-S. Caux, B. Normand, D. Biner, K. W. Krämer, H.-U. Güdel, J. Stahn, K. Habicht, K. Kiefer, M. Boehm, D. F. McMorrow, J. Mesot;
    "Direct Observation of Magnon Fractionalization in the Quantum Spin Ladder"
    Phys. Rev. Lett., 102, 107204/1-5, (2009); doi:10.1103/PhysRevLett.102.107204.