28 research outputs found
Why does a metal-superconductor junction have a resistance?
This is a tutorial article based on a lecture delivered in June 1999 at the
NATO Advanced Study Institute in Ankara. The phenomenon of Andreev reflection
is introduced as the electronic analogue of optical phase-conjugation. In the
optical problem, a disordered medium backed by a phase-conjugating mirror can
become completely transparent. Yet, a disordered metal connected to a
superconductor has the same resistance as in the normal state. The resolution
of this paradox teaches us a fundamental difference between phase conjugation
of light and electrons.Comment: 12 pages, 5 postscript figures [v2: all figures inline
Primordial magnetic fields at preheating
Using lattice techniques we investigate the generation of long range
cosmological magnetic fields during a cold electroweak transition. We will show
how magnetic fields arise, during bubble collisions, in the form of magnetic
strings. We conjecture that these magnetic strings originate from the alignment
of magnetic dipoles associated with EW sphaleron-like configurations. We also
discuss the early thermalisation of photons and the turbulent behaviour of the
scalar fields after tachyonic preheating.Comment: 7 pages. Talk presented at Lattice200