토토 세븐PHYSICS/BK21 Colloquium(09/3/13)

"토토 세븐* PHYSICS/BK21 Colloquium *

“Investigations of the Effects of Defects
on the First Order Vortex Melting Transition
in YBa2Cu3O7-δ Single Crystals”

  
ØSpeaker : Prof. Lisa Paulius [Western Michigan University]
ØPlace : Physics Seminar Room (Science Bldg, 3-201)
ØDate & Time : Mar. 13(Fri)토토 세븐4:00 ~ 5:00 pm

Abstract
  
The first order vortex melting transition is very sensitive to the presence of disorder and
can be supplanted by a second order phase transition in the토토 세븐presence토토 세븐of a sufficiently
high density of defects. We present the results토토 세븐of systematic토토 세븐studies on the effects of
defects on the first order vortex melting transition in YBa2Cu3O7-δ single crystals, with a
special focus on the upper and lower critical points. The experiments were토토 세븐performed
with electrical transport and ac specific heat토토 세븐measurements. The geometry and strength
of the defects varied,토토 세븐including토토 세븐naturally occurring twin boundaries as well as detwinned
single crystals토토 세븐irradiated with successive doses of electrons,토토 세븐protons, or heavy토토 세븐ions.
Twin boundaries yield planar defects,토토 세븐electron irradiation yielded weak point토토 세븐defects,
proton irradiation yielded strong point-like defects and토토 세븐heavy토토 세븐ion토토 세븐irradiation yielded
strong columnar defects. Our results토토 세븐indicate that the토토 세븐origins토토 세븐of the upper and lower
critical points of the first order melting transition arise from different mechanisms. The
position of the lower critical토토 세븐point is determined by the pinning strength of the defect,
whereas the upper critical point shifts in response to the geometrical correlation of the
defects.

Contact Person : Prof. Ki Bong Lee (054-279-2068, kibong@postech.ac.kr)토토 세븐 "