Theory of field-induced quantum phase transition in spin dimer system Ba3Cr2O8

Abstract

Motivated by recent experiments on Ba3Cr2O8, we propose a theory describing low-temperature properties in magnetic field h of dimer spin-1 2 systems on a stacked triangular lattice with spatially anisotropic exchange interactions. Considering the interdimer interaction as a perturbation we derive in the second order the elementary excitations (triplon) spectrum and the effective interaction between triplons at the quantum critical point h = hc separating the paramagnetic phase (h < hc) and a magnetically ordered one (hc < h < hs, where hs is the saturation field). Expressions are derived for hc(T ) and the staggered magnetization M ⊥ (h) at h hc. We apply the theory to Ba3Cr2O8 and determine exchange constants of the model by fitting the triplon spectrum obtained experimentally. It is demonstrated that in accordance with experimental data the system follows the 3D BEC scenario at T < 1 K only due to a pronounced anisotropy of the spectrum near its minimum. Our expressions for hs, hc(T ) and M ⊥ (h) fit well available experimental data.

Localized and propagating excitations in gapped phases of spin systems with bond disorder

“…Defects impact on DOS is described by Eqs. (25) and (26) which are difficult to treat analytically in 2D systems. As in 1D systems, Eq.…”

“…It can be shown (see, e.g., Ref. 26 ) that triplons spectra are defined only by bilinear part of the Hamiltonian in the first order in J ij and one has to take into account quasiparticles interaction to find spectra in higher orders. Then, the bilinear part of the Hamiltonian…”

Prediction of Ultra-Narrow Higgs Resonance in Magnon Bose-Condensates

“…Although magnon BEC have attracted immense experimental [20][21][22][23][24][25][26][27] and theoretical [28][29][30][31][32][33] interest over the past two decades, see reviews [34,35], the issue of the Higgs magnon width in the BEC phase has not been addressed. Theoretically, the width in the usual AFM phase (i.e.…”