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Current
research highlights
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Fe-based superconductors
The new Fe-based pnictide and chalcogenide
superconductors have Tc's of up to 55K. What makes the electrons form pairs?
Left top: schematic superconducting gap function on various Fermi
surface sheets, both conventional (left) and sign-changing (right).
Left bottom: phase diagram of generic Fe-pnictide material with calculated gap
structure from spin
fluctuation theory.
Gap
strength and sign indicated by false color. Taken from our
recent review: Hirschfeld, Korshunov and Mazin, Rep. Prog. Phys.
74, 124508 (2011)
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| Defects in correlated systems Impurities induce magnetic droplets in strongly correlated systems (see Rev. Mod. Phys. 81, 45 (2009)),
cover photo shown at right). The overlap of these droplets
leads to long-range antiferromagnetic order, an "order by disorder"
phenomenon enhanced by d-wave superconductivity. Recently we showed how
fluctuating spin order is "frozen" by impurities, strongly resembling
puzzling behavior observed in cuprate superconductors. See Phys. Rev.
Lett.
105, 147002 (2010).
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Grain boundary transport
For many years an exponential decrease of the critical current at
grain boundaries of cuprate high-Tc superconductors as a function of
misorientation angle has been observed. It is believed that this
effect limits the performance of high-Tc power transmission
applications. In Nat. Phys. 6, 609 (2010)
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we present a solution for the origin of this effect via modelling of
the charge inhomogeneity at the boundary. Left: YBCO grain boundary reconstructed
by molecular dynamics. See also
News and Views .
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