Speaker: Ziyang Meng Universität Stuttgart, Germany
Time: 2011-08-04 15:00-2011-08-04 16:00
Venue: FIT 1-222
At sufficiently low temperatures, condensed-matter systems tend to develop order. An notable exception to this behavior is quantum spin-liquids, where fluctuations prevent transition to an ordered state down to the lowest temperatures. Using large-scale quantum Monte Carlo simulations, we found a quantum spin-liquid phase of correlated electrons on the honeycomb lattice, this spin-liquid emerges between the state described by massless Dirac fermions and an antiferromagnetically ordered Mott insulator, and is found to be a short-range resonating valence bond liquid, akin to the one proposed for high temperature superconductors .
We have also extended our quantum Monte Carlo study to correlated electrons on graphene nanoribbons to investigate the edge-state magnetism. Static magnetic correlations are found to be short-ranged, but the correlation length increases rapidly with the width of the ribbon that already for moderately wide ribbons we observe a strong trend towards the mean-field type ferromagnetic correlations along the zigzag edge. These ferromagnetic correlations are furthermore shown to be accompanied by a dominant low-energy peak in the local spectral function which can be used as dynamic singature to detect the edge-state magnetism in STM experiments. Meanwhile, the magnetic excitations along the edge demonstrate the effect of an interaction-mediated antiferromagnetic coupling between the opposite edges .
 Z. Y. Meng, T. C. Lang, S. Wessel, F. F. Assaad and A. Muramatsu, "Quantum spin liquid emerging in two-dimensional correlated Dirac fermions", Nature 464, 847 (2010)
 H. Feldner, Z. Y. Meng, T. C. Lang, F. F. Assaad, S. Wessel and A. Honecker, "Dynamical signatures of edge-state magnetism on Graphene nanoribbons", Phys. Rev. Lett. 106, 226401 (2011)