The origin of the asymmetric shape for the exchange-scattering peak of 2Δg in the ladder antiferromagnet CaV2O5 with the singlet ground state Original Research Article

The exchange-scattering spectra are reproduced by the numerical calculation for the finite Heisenberg ladder, in which two-legs with antiferromagnetic bond Jc is connected by rungs with antiferromagnetic bond Jr. The numerical calculation is made in the system of 50×2 sites with spin=1/2 by the perturbation method for the extension of Jc/Jr. The singlet ground state in this system is considered to be expressed as the ordering of singlet dimers on rungs in the ladder for Jc/Jr→+0. The value of 0.1 is adopted to be the ratio of Jc/Jr in order to discuss the experimental work of the magnetic Raman spectra for the ladder of V4+ ions in the oxide compound CaV2O5 reported in Konstantinović et al. [Phys. Rev. B61 (2000) 15185]. As for the peak of twice the singlet–triplet spin gap, characteristic structures appear in the present calculation for the exchange-scattering: Quite an asymmetric shape is obtained in the Stokes line, though the corresponding density of state for singlet states at Γ point is almost symmetric. The agreement between the present calculation and the observed spectra at 795 cm−1 is quite well.