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Title: Dynamical behaviour of intrinsic Josephson junctions
Author: Saleem, S.
ISNI:       0000 0004 2727 5899
Awarding Body: University College London (University of London)
Current Institution: University College London (University of London)
Date of Award: 2010
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Intrinsic Josephson Junctions (IJJs) are the subject of much of research due to their potential applications as high frequency oscillators and detectors in the THz range. A number of previous studies use a single junction model to explain their observations, as no fully agreed model for coupled IJJs exists. The influence of one or more IJJs in the voltage state on other junctions in the IJJ array is not yet fully understood. I have studied the dynamical behaviour of Tl_2Ba_2CaCu_2O_8 thin film IJJ arrays, focussing on how one junction in the voltage state influences the other junctions. This I have done by measuring (a) the switching current distributions, and (b) the influence of r.f. irradiation on the DC current-voltage characteristics. I have compared the switching current distributions when switching from the supercurrent branch with those when switching from the first quasiparticle branch. The supercurrent branch was found to be overdamped at the escape frequency whereas the first quasiparticle branch is underdamped, resulting in a larger switching current for the former than the latter. RF irradiation suppresses the mean switching current on the supercurrent branch accompanied by the appearance of a low-voltage flux flow branch. There is however no effect on the switching current of the quasiparticle branches. I explain these results in terms of the dissipative environment in which the junctions are embedded, and, furthermore, that switching of a single IJJ into the voltage state significantly changes the dissipation. IJJs were sub sequently isolated from their environment by FIB-deposited tungsten resistors of resistance between 100 and 500 Ω. The complete resistor-junction-resistor (RJR) structure is multibranched and shows a change in the DC current-voltage characteristics below and above the T^c of the tungsten. However, the presence of high resistance in the RJR structure at 4.2 K needs further investigation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available