1,698 research outputs found
Ageing in granular aluminium insulating thin films
We present a new set of electrical field effect measurements on granular
aluminium insulating thin films. We have explored how the conductance
relaxations induced by gate voltage changes depend on the age of the system,
namely the time elapsed since its quench at low temperature. A clear age
dependence of the relaxations is seen, qualitatively similar to ageing effects
seen in other well studied glassy systems such as spin glasses or polymers. We
explain how our results differ from the previous ones obtained with different
protocols in indium oxide and granular aluminium thin films. Our experimental
findings bring new information on the dynamics of the system and put new
constraints on the theoretical models that may explain slow conductance
relaxations in disordered insulators.Comment: 4 pages, 13th Transport in interacting disordered systems (TIDS13)
conference, 31.08.2009 - 05.09.2009, Rackeve, Hungar
Hopping models and ac universality
Some general relations for hopping models are established. We proceed to
discuss the universality of the ac conductivity which arises in the extreme
disorder limit of the random barrier model. It is shown that the relevant
dimension entering into the diffusion cluster approximation (DCA) is the
harmonic (fracton) dimension of the diffusion cluster. The temperature scaling
of the dimensionless frequency entering into the DCA is discussed. Finally,
some open questions about ac universality are mentioned.Comment: 6 page
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