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