Magnetic excitations in a quantum spin dimer system, Ba₃Cr₂O₈

Abstract

Neutron scattering measurements have been performed in a new non-Cu based quantum spin dimer system, Ba₃Cr₂O₈, where Cr⁵⁺ (s=1/2) ion with the unusual 5+ electronic valence forms quantum dimers along the c-axis and a frustrating triangular lattice in the ab-plane. We found that there exist three singlet-to-triplet excitation modes even without field. Our complete analysis shows that the three modes are due to spatially anisotropic interdimer interactions that are induced by local distortions of the tetrahedron of oxygen surrounding the Jahn-Teller active Cr⁵⁺(3d¹).