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SUMMARY:$\\mu$SR Study of Superconductivity Above $H_{c2}$: A Filamentary 
 State in Type-II Superconductors
DTSTART;VALUE=DATE-TIME:20220829T164000Z
DTEND;VALUE=DATE-TIME:20220829T170000Z
DTSTAMP;VALUE=DATE-TIME:20220826T105955Z
UID:indico-contribution-3767@indico.stfc.ac.uk
DESCRIPTION:Speakers: Vladimir Kozhevnikov (Tulsa Community College)\nThe 
 standard interpretation of the phase diagram of type-II superconductors wa
 s developed in the 1960s and has since been considered a well-established 
 part of classical superconductivity. In particular\, according to the stan
 dard picture\, in a sample of type-II materials of a planar geometry in a 
 parallel (in-plane) field\, superconductivity nucleates at Hc3 approximate
 ly twice as big as the upper critical field Hc2. Between these critical fi
 elds the superconducting phase exists in a form of a thin surface sheath. 
 Contrarily\, in the same sample but in the perpendicular (out-of-plane) fi
 eld superconductivity nucleates in the bulk at Hc2 and there is no superco
 nductivity above this field. However\, upon closer examination a number of
  fundamental issues arises that leads one to question this standard pictur
 e. To address these issues\, we studied equilibrium properties of niobium 
 samples near and above the critical field Hc2 in parallel and perpendicula
 r magnetic fields. The samples investigated were very high-quality films a
 nd single-crystal disks with the Ginzburg-Landau parameters in the range f
 rom 0.8 to 1.3. A set of complementary measurements has been performed\, w
 hich include bulk muSR\, dc magnetometry\, electrical transport and scanni
 ng Hall-probe microscopy. Contrary to the standard scenario\, we observed 
 that a superconducting phase is present in the sample bulk above Hc2 and t
 he field Hc3 is the same in both parallel and perpendicular fields. It wil
 l be shown that above Hc2 the superconducting phase forms filaments parall
 el to the field regardless of the field orientation. Near Hc2 the filament
 s preserve the hexagonal structure of the preceding vortex lattice of the 
 mixed state\, and the filament density continuously falls to zero at Hc3. 
 \n\nReferences:\nV. Kozhevnikov\, A.-M. Valente-Feliciano\, P. Curran\, et
  al.\, Phys. Rev. B 95\, 174509 (2017).\nV. Kozhevnikov\, Thermodynamics o
 f Magnetizing Materials and Superconductors\, CRC Press\, 2019.\n\nhttps:/
 /indico.stfc.ac.uk/event/53/contributions/3767/
LOCATION:Science and Technology Campus\, University of Parma
URL:https://indico.stfc.ac.uk/event/53/contributions/3767/
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