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TT: Fachverband Tiefe Temperaturen

TT 72: Correlated Electrons: Frustrated Magnets - General 2

TT 72.4: Vortrag

Donnerstag, 23. März 2017, 15:45–16:00, HSZ 204

J₁-J₂ Heisenberg model on a triangular-lattice bilayer — •Darshan G. Joshi¹ and Matthias Vojta² — ¹Max Planck Institute for Solid State Research, D-70569 Stuttgart, Germany — ²Institut für Theoretische Physik, Technische Universität Dresden, 01062 Dresden, Germany

We consider a triangular-lattice bilayer Heisenberg model for spins 1/2 with antiferromagnetic nearest-neighbor and next-nearest-neighbor interactions. We determine the phase diagram and the dispersion of elementary excitations using variants of bond-operator theory. Large inter-layer coupling yields a dimer quantum paramagnet, while magnetic order is possible for weak inter-layer coupling. Frustration can induce flat portions of triplon bands in the dimer phase, opening the window to find exotic states in the vicinity to the transition point to ordered phases. For weak inter-layer coupling we reproduce the possible spin-liquid state known from the single-layer J₁-J₂ model which occurs when 120^∘ order is destroyed by increasing J₂. Remarkably, this state is destabilized in favor of magnetic order with increasing inter-layer coupling before amplitude fluctuations destroy magnetic order at large inter-layer coupling.