Singlet–Triplet Excitations and High-Field Magnetization in CuTe₂O₅

By measuring the THz electron spin resonance (ESR) transmission spectra and high-field magnetization on the spingapped system CuTe₂O₅, we identified the singlet–triplet excitations in the dimerized non-magnetic ground state. The determined spin-gap value of hnu₀ = 4.94 meV at the Gamma point (Q = 0) is significantly smaller than the strongest antiferromagnetic exchange interaction between the Cu ions predicted by theoretical investigations. We also observed the critical field H^a* _c1 = 37.6 T for H perp bc-plane and H^bc _c1 = 40.6 T for H parallel bc-plane at the onset of non-zero magnetization, consistent with the gap value and corresponding anisotropic g-factors determined previously. The observed singlet–triplet excitations in Faraday and Voigt configurations suggest a mixing of the singlet state with the S_z = 0 triplet state and the S_z = plus/minus 1 triplet states, respectively, due to the Dzyaloshinskii–Moriya (DM) interaction with a DM vector perpendicular to the crystalline bc-plane.