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Rainer Jany «  Ali Khairi Abdul-Qader Al-Hadeethi »  Thomas Mairoser
Ali Khairi Abdul-Qader Al-Hadeethi
Dc transport and optical measurements on the charge-density-wave compounds (K,Rb)0.3(Mo,W)O3
Supervisor: Prof. Dr. Christine Kuntscher [Experimental physics II]
Date of oral examination: 04/26/2013
145 pages, english
The temperature dependence of the linear and the non-linear transport properties in K0.3MoO3, (K0.5Rb0.5)0.3MoO3, and K0.3Mo0.99W0.01O3 are presented. The temperature dependence of the dc resistivity of the pure sample has shown the Peierls metal-insulator phase transition at 180 K, where the transition is very sharp. The rubidium doping shifts the transition temperature to a lower temperature (170 K) and smears out the metal-insulator phase transition, i.e., the rubidium doping broadens the transition peak. Compared with the rubidium doping, the tungsten doping broadens the transition peak more and shifts the transition temperature to a lower temperature (140 K). The temperature-dependent dc resistivity curves of pure, Rb-doped, and W-doped blue bronze K0.3MoO3 single crystals are analyzed in terms of the pseudogap just above TP and the Peierls energy gap below TP. The non-linear transport properties of pure, Rb-doped, and W-doped blue bronze K0.3MoO3 single crystals have shown a nonlinear conductivity due to an incoherent CDW sliding, when the applied electric field exceeds the first threshold field (ET). Furthermore, above a second threshold field (ET* > ET) a coherent CDW-sliding sets in. For all studied samples, we find a monotonic increase of ET and ET* with decreasing temperature. This finding is discussed mainly in terms of the incommensurate-commensurate transition of the CDW. The coherent and incoherent CDW movements are discussed within the frame of the Fukuyama-Lee-Rice model.