Pu Superconductor

["Estabrooks, Bates (IHK) " <estabrookshb@Y12.doe.gov>]

		Radsafers,



		I found the following article on physicsweb.org and thought

it was interesting (as far as I understood it).  Can anyone explain to me

the 4th paragraph, especially the part about: "the transition where the 5f

electrons go from being delocalized to localized" ?



		Thanks.



		Bates Estabrooks





				Plutonium is also a superconductor

				20 November 2002 



				Superconductivity has been observed in a

plutonium-based material for the first time. John Sarrao and colleagues at

the Los Alamos National Laboratory, and co-workers at the University of

Florida and the Institute for Transuranium Elements in Germany, discovered

that an alloy of plutonium, cobalt and gallium exhibits superconductivity at

temperatures below 18.5 K. This is an unusually high transition temperature

and may mean that plutonium-based compounds are a new class of

superconductor, in addition to the so-called heavy-fermion systems,

high-temperature copper oxides and traditional superconducting materials (JL

Sarrao et al. 2002 Nature 420 297)



				Sarrao and co-workers found that the

transition temperature (Tc) in the plutonium compound - the temperature at

which the electrical resistance of a superconducting material drops to zero

- is an order of magnitude higher than the highest seen in the heavy fermion

systems (compounds based on uranium and cerium). The material also has a

large critical current, which would be of technological importance if it

were not for the hazardous radioactive properties of plutonium. This

critical current comes from pinning centres due to defects in the material,

created by radiation induced "self-damage". 



				The team observed the superconductivity in

measurements of magnetic susceptibility and specific heat. Further

measurements on temperature-dependent magnetic susceptibility and electrical

resistivity over a wide range of temperatures suggest that the degree of

localization of the 5f electrons lies between that of compounds based on

cerium and those based on uranium. 



				Plutonium is an actinide element located at

the transition where the 5f electrons go from being delocalized to

localized, which makes it one of the most complex materials known. The

researchers believe that the superconductivity in plutonium comes directly

from its anomalous electronic properties and that it is an intermediate

addition, in terms of Tc, to the two other new classes of "magnetically

mediated" superconductors - the heavy- fermion materials, which have Tcs of

about 1 K and the copper oxides, which have a Tcs of about 100 K. 



				The team hope that future research will

unearth superconductivity in other transuranic compounds with lower

toxicity. "Experience tells us that where one superconductor is found,

others are usually nearby, so there are many other related compounds to

explore," Sarrao told PhysicsWeb. 



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