July 09, 2008

High magnetism reveals the inner electronic structure of high temperature superconductors

University of Cambridge researchers have discovered where the charge 'hole' carriers that play a significant role in the superconductivity originate within the electronic structure of copper-oxide superconductors. A correct and detailed understanding what is going on in high temperature superconductors will help to get to a correct theory for superconductors and can lead to the development of room temperature superconductors. This work has revealed how magnetism and superconductance interact. This is part of a series of major discoveries in the field of superconductors this year.

These findings are particularly important for the next step of deciphering the glue that binds the holes together and determining what enables them to superconduct.

Dr Suchitra E. Sebastian, lead author of the study, commented, "An experimental difficulty in the past has been accessing the underlying microscopics of the system once it begins to superconduct. Superconductivity throws a manner of 'veil' over the system, hiding its inner workings from experimental probes. A major advance has been our use of high magnetic fields, which punch holes through the superconducting shroud, known as vortices - regions where superconductivity is destroyed, through which the underlying electronic structure can be probed.

"We have successfully unearthed for the first time in a high temperature superconductor the location in the electronic structure where 'pockets' of doped hole carriers aggregate. Our experiments have thus made an important advance toward understanding how superconducting pairs form out of these hole pockets."


The paper 'A multi-component Fermi surface in the vortex state of an underdoped high-Tc superconductor' will be published in the 09 July edition of Nature.


By determining exactly where the doped holes aggregate in the electronic structure of these superconductors, the researchers have been able to advance understanding in two vital areas:

(1) A direct probe revealing the location and size of pockets of holes is an essential step to determining how these particles stick together to superconduct.

(2) Their experiments have successfully accessed the region betwixt magnetism and superconductivity: when the superconducting veil is partially lifted, their experiments suggest the existence of underlying magnetism which shapes the hole pockets. Interplay between magnetism and superconductivity is therefore indicated - leading to the next question to be addressed.

Do these forms of order compete, with magnetism appearing in the vortex regions where superconductivity is killed, as they suggest? Or do they complement each other by some more intricate mechanism? One possibility they suggest for the coexistence of two very different physical phenomena is that the non-superconducting vortex cores may behave in concert, exhibiting collective magnetism while the rest of the material superconducts.

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