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

• Previously suggested model for Ba3Cr2O8 leads to contradictions with experiment.
• We propose a more realistic model for Ba3Cr2O8.
• We describe satisfactorily the majority of available experimental data for Ba3Cr2O8.
• We calculate observables in the second order in interdimer interaction.

Motivated by recent experiments on Ba3Cr2O8, we propose a theory describing low-temperature properties in magnetic field h   of dimer spin-1/2spin-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=hch=hc separating the paramagnetic phase (h