Condensation of magnons and spinons in a frustrated ladder

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American Physical Society
Motivated by the ever-increasing experimental effort devoted to the properties of frustrated quantum magnets in a magnetic field, we present a careful and detailed theoretical analysis of a one-dimensional version of this problem, a frustrated ladder with a magnetization plateau at m=1/2. We show that even for purely isotropic Heisenberg interactions, the magnetization curve exhibits a rather complex behavior that can be fully accounted for in terms of simple elementary excitations. The introduction of anisotropic interactions (e.g., Dzyaloshinskii-Moriya interactions) modifies significantly the picture and reveals an essential difference between integer and fractional plateaus. In particular, anisotropic interactions generically open a gap in the region between the plateaus, but we show that this gap closes upon entering fractional plateaus. All of these conclusions, based on analytical arguments, are supported by extensive density matrix renormalization group calculations.
frustrated ladder, spinons, frustrated quantum magnets, magnetization plateau, magnons, isotropic Heisenberg interaction, elementary excitations, anisotropic interaction, density matrix renormalization group calculation, Dzyaloshinskii-Moriya interaction
Physical Review B (Condensed Matter and Materials Physics) 1 June 2006, vol.73, no.21, pp. 214405-1-13