Research Profile - Department of Materials Science and Metallurgy ...

John Durrell
EPSRC Advanced Research Fellow
MSci Imperial College
PhD University of Cambridge
+44 (0) 1223 331693
jhd25@cam.ac.uk
www.msm.cam.ac.uk/dmg/
Electrical Properties of Superconductors
I am interested in the pinning and behaviour of the flux-line lattice
in superconductors. This is of importance for the development of
commercially useful coated conductor materials, since the critical
current (in short the performance) of a superconductor is entirely
controlled by the nature and pinning of the vortex lattice. At present
I am particularly interested in looking at how the critical currents
vary at the micrometre scale in coated conductor materials.
Fundamental properties
The current-carrying capacity, which is the most common figure of
merit for a superconductor, is determined by the disposition and
pinning of the lines of magnetic flux ‘flux vortices’ that penetrate
into it. I seek to understand how the intrinsic properties of a
superconductor affect the flux vortices and by doing so to open
routes to improved critical current. This is achieved by studying
how the electrical properties of a superconducting material vary
with temperature, magnetic field and sample orientation.
Technical materials
Practical superconducting materials are of necessity complex. To
reduce the adverse effects of grain boundaries on current flow, a
practical material needs to approximate to an infinitely long single
crystal; they are thus materials with complex structures varying
over tens of micrometres. I study how the critical current in these
superconductors varies locally and how this is affected by microand
macro-structural features. I also study various techniques for
enhancing overall critical current.
A Palau, JH Durrell, JL MacManus-Driscoll, S Harrington, T Puig, F
Sandiumenge, X Obradors & MG Blamire, “Cross-over between channeling
and pinning at twin boundaries in YBa 2
Cu 3
O 7
thin films” Phys. Rev. Lett. 97,
257002 (2006).
NA Rutter, JH Durrell, MG Blamire, JL MacManus-Driscoll, H Wang &
SR Foltyn, “Benefits of current percolation in superconducting coated
conductors” Appl. Phys. Lett. 87, 162507 (2005).
JH Durrell, G Burnell, VN Tsaneva, ZH Barber, MG Blamire & JE Evetts,
“Critical currents in vicinal YBa 2
Cu 3
O 7–dδ
films” Phys. Rev. B 70, 214508
(2004).
JH Durrell, MJ Hogg, F Kahlmann, ZH Barber, MG Blamire & JE Evetts,
“The critical current of YBa 2
Cu 3
O 7–d
low angle grain boundaries” Phys. Rev.
Lett. 90, 247006 (2003).
Micrograph of an isolated grain boundary in a RABiTS
superconductor
18 Research Profile