"토토 바카라      * 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 바카라4:00 ~ 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 바카라presence토토 바카라of a sufficiently
high density of defects. We present the results토토 바카라of systematic토토 바카라studies 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 바카라performed
with electrical transport and ac specific heat토토 바카라measurements. The geometry and strength
of the defects varied,토토 바카라including토토 바카라naturally occurring twin boundaries as well as detwinned
single crystals토토 바카라irradiated with successive doses of electrons,토토 바카라protons, or heavy토토 바카라ions.
Twin boundaries yield planar defects,토토 바카라electron irradiation yielded weak point토토 바카라defects,
proton irradiation yielded strong point-like defects and토토 바카라heavy토토 바카라ion토토 바카라irradiation yielded
strong columnar defects. Our results토토 바카라indicate that the토토 바카라origins토토 바카라of the upper and lower
critical points of the first order melting transition arise from different mechanisms. The
position of the lower critical토토 바카라point 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 바카라토토 바카라"