Magnetic Vortex Crystals in Frustrated Mott Insulators

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Date/Time:Thursday, 06 Nov 2014 - Saturday, 08 Nov 2014
Location:PHYSICS Hall Room 3
Phone:515-294-5630
Channel:Condensed Matter Physics
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Cristian D. Batista
Theoretical Division of Los Alamos National Laboratory, 87545 Los Alamos, USA

Chiral spin textures with different length scales emerge in some itinerant magnets and are generating an increasing interest in the study of magneto-transport and possible applications to magnetic data storage and spin-electronic devices [1-5]. It is natural to ask if similar topological textures can emerge in Mott insulators and also lead to magneto-electric effects. In this talk I will show that this is indeed possible when the exchange interactions are geometrically frustrated. For this purpose, I will consider a frustrated S=1/2 XXZ Hamiltonian that is a low-energy effective model for Ba3Mn2O8, a layered spin-dimer compound, comprising magnetic dimers of Mn5+ ions arranged on triangular planes [6-8]. Successive layers are stacked following an 'ABC' sequence, such that the dimer units on adjacent planes are positioned in the center of the triangular plaquettes of the layers above and below. The effective exchange anisotropy of the low-energy model results from frustration between exchange interactions connecting the same pair of dimmers. The competition between intra and inter-layer exchange interactions leads to a triplon dispersion with six-fold degenerate minima at incommensurate wave vectors Qn (1 <= n <= 3). This degeneracy leads to a very rich quantum phase diagram near the magnetic field induced quantum critical point, that is constructed by adding ladder diagrams and minimizing the resulting energy functional [9]. The phase diagram includes different multi-Q magnetic orderings, which combine up to the six degenerate incommensurate lowest-energy modes Qn (1 <= n <= 3). In particular, it includes six-Q states that are crystals of magnetic vortices and other complex spin textures associated with different multi-Q ordered states.

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