Critical phenomena and femtosecond ordering dynamics associated with electronic and spin-ordered phases in YVO 3 and GdVO 3
Résumé
We present a systematic study of the electronic- and spin-excitation dynamics associated with the sequence of spin- and orbital-ordering phase transformations in the complex vanadates YVO 3 and GdVO 3 with ultrafast optical pump-probe reflectance spectroscopy. Relaxation dynamics occurs on a different time scale for each of the ordering transitions, which enables us to unambiguously associate the critical behavior in the dynamics with the observed ordering phenomena. Spin-ordering dynamics is observed on two time scales: r 2ps rise time and s 300-3000 ps decay time , observed below T N in both compounds. In contrast, the relaxation dynamics associated with orbital ordering occurs in YVO 3 on a time scale of o 20-50 ps. From the temperature dependence of the dynamics, we observe that in both the G-type and C-type orbitally ordered OO phases of YVO 3 spin order develops in a second-order mean-field fashion with the Nèel temperature of the C-OO phase found from our data T N C =83 7 K.InGdVO 3 we identify the emergence of a new ordered phase within the phase-separated state below 60 K. A new response component with a lifetime of 60 ps is observed below 60 K together with other anomalies in the R / R t data. This new phase is not resolved in x-ray diffraction and is not present in YVO 3
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