Quantum phase transitions in a strongly entangled spin-orbital chains

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Date/Time:Thursday, 12 Jan 2012 - Thursday, 12 Jan 2012
Location:PHYSICS Room 5
Channel:Condensed Matter Physics
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Dr. Natalia Perkins, Assistant Professor, Department of Physics, University of Wisconsin-Madison

Motivated by recent experiments on quasi-1D vanadium oxides, we study quantum phase transitions in a one-dimensional spin-orbital model describing a Haldane chain and a classical Ising chain locally coupled by the relativistic spin-orbit interaction. We analyze the topology of the ground-state phase diagram and identify the nature of phase transitions, which strongly depend on the relative scales of the spin and orbital interactions. We find that when the orbital exchange is the dominating energy scale, a two-stage ordering takes place in which the magnetic transition is followed by melting of the orbital Ising order; both transitions belong to the two-dimensional Ising universality class. In the opposite limit, the low-energy orbital modes undergo a continuous reordering transition which represents a line of Gaussian critical points. On this line the orbital degrees of freedom form a Tomonaga-Luttinger liquid. We argue that the emergence of the Gaussian criticality results from merging of the two Ising transitions in the strong hybridization region where the characteristic spin and orbital energy scales become comparable. Finally, we show that, due to the spin-orbit coupling, an external magnetic field acting on the spins can induce an orbital Ising transition.