Spin-gap mode in the charge-ordered phase ofNaV2O5studied by Raman scattering under high pressures

Abstract

By means of Raman-scattering measurement under pressures at low temperatures we study the "devil's staircase"-type phase of NaV 2 O 5 . The spin-gap mode shows a drastic softening with increasing pressure up to 0.9 GPa in C 1/4 phase and disappears between 0.9 and 1 GPa. It appears again between 1 and 2.3 GPa in C 0 phase, indicating that this phase is also a spin-gap state. Taking the charge ordering into consideration, we discuss the spin-gap states and clarify that the spin-gap mode is created by the exchange-interaction Ramanscattering mechanism and it comes from a gap between the spin-singlet ground state and the S x = 0 spin-triplet excited one. This model explains that the spin gap is almost independent of the applied magnetic field and it vanishes at about 10°lower than the critical temperature in C 1/4 phase.

Melting of ferromagnetic order on a trellis ladder

“…The trellis lattice is composed of a number of normal ladders coupled through zigzag bonds; alternatively, it can be considered as coupled zigzag ladders through rung interactions as shown in Fig. 1 [25,26] etc. The weak interladder exchange interactions in these materials form an effective 2D trellis like structure.…”

“…The effect of inter-ladder coupling on spin gap and magnon dispersion has been discussed in [22] exploiting a theoretical model which has also been compared with the experimental data of SrCu 2 O 3 and CaV 2 O 5 . The study of interladder coupling effect is important to explain the physical properties of some other materials like LaCuO 2.5 [23], Sr 14 Cu 24 O 41 [24], MgV 2 O 5 [17], NaV 2 O 5 [25,26] etc. The weak interladder exchange interactions in these materials form an effective 2D trellis like structure.…”