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Title: Magneto-transport studies of some high temperature superconductors
Author: Guthrie, D.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2010
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In this thesis the magneto-transport properties of two classes of high temperature superconductors, the cuprates and the pnictides, are investigated and compared to some existing models. A range of theories exist for the magneto-resistivity (MR) of cuprates in the normal state. Anderson’s early theory uses two distinct scattering times for the in-plane resistivity and Hall angle to describe magneto-transport while several Fermi Liquid (FL)-like models use a single strongly k-dependent scattering time to account for the anomalous properties observed in the normal state. Here we present work measuring the normal state MR of BSCO single crystals, which show interesting results not well accounted for by theory. In pure BSCO the normal state MR appears to follow a T-4 power law at temperatures sufficiently high that the role of superconducting fluctuations will be minimised, as seen previously in Zn doped YBCO.  Upon replacing 2% of the Cu atoms with Fe or Co, the MR is substantially reduced and this T-4 dependence is no longer clearly observed. This is attributed to scattering caused by the magnetic moments of the dopants. These results are in conflict with Anderson’s theory and are better supported by a FL like model. There is still much uncertainty about magneto-transport in the pnictides largely due to their recent discovery. We present MR data for two of the undoped parent pnicitide compounds. SrFe2As2 and CaFe2As2 at a range of temperatures below Ts. We observe a large positive MR and compare this to previous work including an early model for pnicitide magneto-transport proposed by Zheng et al. We find a reasonable fit but question some of the basic assumptions of this model.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available