Saturday, January 12, 2013

The Tao Effect (Superconducting Balls)

In 1999, R Tao, X. Zhang, X. Tang, PW Anderson, reported that fine paritcles of a Br-Sr-Ca-Cu-O superconductor would clump into a ball when suspended in liquid nitrogen and subjected to an electric field.  The discovery was covered in a physics news update article.  The last author PW Anderson is the Nobel prize winning PW Anderson.  The thoeretical explanation advanced by Tao et al. at the time was, (briefly),

This interesting phenomenon directly relates the surfacetension to the Josephson coupling energy.

I came across this research reading papers authored by JE Hirsch of UCSD.  Dr. Hirsch has advanced and interesting modification of the BCS theory of superconductors, 'the hole theory of superconductivity'.  If the 'Tao effect' was shown to be reproducible, it would help to confirm Hirsch's theory.  Recently however, Ghosh and Hirsch reported that they have observed the Tao effect in non-superconducting particles as well as in superconductor particles that are not in the superconducting state, (see picture below).  There work was reported in Physical Review B as well as on arxiv.  This interesting work will be reported at the APS March meeting this year in Baltimore Maryland.

Physical Review B article reporting the discovery

Physics News Update Article

PW Anderson on Wikipedia

JE Hirsch hole theory of superconductivity
and free on arxiv

Ghosh and Hirsch experiment:
Ghosh R.S.B. & Hirsch J.E. (2012). Spherical agglomeration of superconducting and normal microparticles with and without applied electric field, Physical Review B, 86 (5) DOI:

APS March Meeting presentation:

Picture of the Day

From 1/12/13

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