A talk and discussion with Prof. Steven T. Bramwell
London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, U.K.
Abstract: Gauss' law for magnetism - one of Maxwell's equations - suggests the possible existence of magnetic charges and their currents, but this inference is normally seen as an error, as microscopic magnetic charges cannot be identified in normal materials. In recent years a new class of material has been developed which simultaneously obey Maxwell's equations and support discrete microscopic magnetic charges or "monopoles", that are free to move within the material. In their thermal and electromagnetic properties, these "spin ice materials" bear a remarkable analogy to water ice, a protonic semiconductor 1,2. In this talk I will explain the physics of spin ice, the emergence of magnetic monopoles 2-4 and the extent to which spin ice supports a magnetic equivalent of electricity, or "magnetricity".
I shall refer extensively to recent work from my group at UCL and my broader collaborations.
- Bramwell and Gingras, Science 294, 1495 (2001)
- Ryzhkin, J. Exp. and Theor. Phys. 101, 481 (2005)
- Castelnovo, Moessner and Sondhi, Nature 451, 42 (2008)
- Jaubert & Holdsworth, Nature Physics 5, 358 (2009).
Bio: Steve Bramwell graduated from Oxford with a degree in Chemistry in 1984, then held positions in Oxford and Grenoble, before joining UCL in 1997. Formerly a Professor of Physical Chemistry, he is now in the Department of Physics and Astronomy at UCL. Alongside his 1997 discovery and naming of of spin ice (with MJ Harris), he is known for his calculation of β = 0.23, a key critical exponent for magnetic films (with PCW Holdsworth, 1993) and a probability distribution named after him (the Bramwell-Holdsworth-Pinton Distribution, 1998). He was awarded the 2010 Holweck Prize of the Britsh Institue of Physics and the French Societe de Physique, to recognise his work on model magnets, and he was the co-recipient of the 2012 European Physical Society CMD Europhysics Prize for the discovery of magnetic monopoles in spin ice. His discovery of "magnetricity" in spin ice was recognised by the Times Higher Research project of the Year, 2010 and he appeared on The Times's 2010 list of the 100 most important UK scientists. He presented the 2012 Wohlfarth Lecture of the IOP.