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Properties of the low-temperature order in the 1D semiconductor (NbSe4)3I
Two groups from Institut za fiziku have recently published an article in Physical Review B studying the phase transitions in (NbSe4)3I semiconductor by ultrafast time resolved spectroscopy, which is the first time the technique has been established and utilized at our institute. This also marks the fruitful beginning of collaboration for our two groups which cover two distinct areas of physics: atomic physics and condensed matter physics.
Static and dynamic properties of low-temperature order in the one-dimensional semiconductor (NbSe4)3I
D. Dominko, S. Vdović, H. Skenderović, D. Starešinić, K. Biljaković, D. Ristić, M. Ivanda, J. E. Lorenzo, J. Demsar
Physical Review B 94, 104113 (2016). doi: 10.1103/PhysRevB.94.104113
(NbSe4)3I is an insulator with a chain-like structure. Previous Raman and XRD results point towards two structural phase transitions into antiferroelectric (AFE) states by Nb5+ ion displacements (Figure 1). However, details of these phase transitions, including precise temperature of one of them, have so far been unresolved. Together with colleagues from Institute Ruđer Bošković and within an international cooperation this latest paper reports on static and dynamic properties of these phase transitions in more detail using Raman spectroscopy and XRD.
Detailed characteristics of this material have been studied covering all the relevant temperatures using ultrafast time-resolved spectroscopy (Institut za fiziku and University of Mainz), Raman spectroscopy (Institute Ruđer Bošković, group of dr. Ivanda), and XRD (Grenoble Synchrotron) as shown by Figures 1 and 2. Along with the pseudo-Jahn-Teller transition to the antiferroelectric state at TC = 274 K, the results consistently point to a second structural transition at T* = 160 K which is shown to be a strongly modulated AFE state. Our observations suggest that between T* and TC the system is in the state of strong thermal fluctuations of Nb5+ ion position, with only a weak AFE order parameter. Below T* these fluctuations get frozen and the system undergoes a transition into a state of a stronger antiferroelectric order (Figure 1d) and 3).