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MA: Fachverband Magnetismus

MA 5: Spin Structures and Magnetic Phase Transitions

MA 5.3: Vortrag

Montag, 26. März 2012, 10:00–10:15, H 0112

quantum phases in the S=1/2 heisenberg model on the cairo pentagonal lattice — •Ioannis Rousochatzakis^1,2, Andreas Laeuchli¹, and Roderich Moessner¹ — ¹Max Planck Institut für Physik Komplexer Systeme, Nöthnitzer Str. 38, 01187 Dresden, Germany — ²Institute for Theoretical Solid State Physics, IFW Dresden, 01171 Dresden, Germany

We present an extensive analytical and numerical exact diagonalization study of the spin S=1/2 antiferromagnetic Heisenberg model on the Cairo pentagonal lattice. This is the dual of the Shastry-Sutherland lattice and has been discussed as a possible new candidate for having a spin liquid ground state. More recently a close realization of this model has appeared in the S=5/2 compound Bi₂Fe₄O₉. Here we use a model with two different exchange couplings allowed by the symmetry of the lattice, and investigate the nature of the ground state as a function of their ratio x. After establishing the classical phase diagram we switch on quantum mechanics in a gradual way that highlights the different role of quantum fluctuations on the two inequivalent sites of the lattice. The most important findings include: (i) a surprising interplay between a collinear and a four-sublattice orthogonal phase due to an underlying order-by-disorder mechanism which is active at small x, and (ii) a non-magnetic and possibly spin-nematic phase with d-wave symmetry at intermediate x. The latter is driven by an effective 4-spin exchange term that first appears in fourth order perturbation theory in x.