Topological quantum phase transition in in Ising-like antiferromagnet BaCo2V2O8

Orateur : Quentin FAURE (Institut Néel, UGA & CEA)

Since the seminal ideas of Berezinskii, Kosterlitz and Thouless [1,2], topological excitations are at the heart of our understanding of a novel class of phase transitions. In most of the cases, they are controlled by a single type of topological objects. There are however some situations, still poorly understood, where two dual topological excitations fight to control the transition. Finding experimental realization of such cases is thus of considerable interest. I will show in this presentation that this situation occurs in BaCo2V2O8, a spin-1/2 Ising-like quasi-one dimensional antiferromagnet [3], when subjected to a uniform magnetic field transverse to the Ising axis (the c-axis) [4]. Indeed, the application of a transverse magnetic field along the b direction, because of the non-diagonal anisotropic g-tensor of BaCo2V2O8, induces a staggered field along the a direction [5]. As a result, a quantum phase transition occurs at about 10 T. By using inelastic neutron scattering experiments combined with theoretical calculations, we have shown that this transition is well described by the so called dual-field double sine-Gordon model, reflecting the competition of two dual topological objects.

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