"바카라 조작      * 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)바카라 조작4:00 ~ 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 the바카라 조작presence바카라 조작of a sufficiently
high density of defects. We present the results바카라 조작of systematic바카라 조작studies 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 were바카라 조작performed
with electrical transport and ac specific heat바카라 조작measurements. The geometry and strength
of the defects varied,바카라 조작including바카라 조작naturally occurring twin boundaries as well as detwinned
single crystals바카라 조작irradiated with successive doses of electrons,바카라 조작protons, or heavy바카라 조작ions.
Twin boundaries yield planar defects,바카라 조작electron irradiation yielded weak point바카라 조작defects,
proton irradiation yielded strong point-like defects and바카라 조작heavy바카라 조작ion바카라 조작irradiation yielded
strong columnar defects. Our results바카라 조작indicate that the바카라 조작origins바카라 조작of the upper and lower
critical points of the first order melting transition arise from different mechanisms. The
position of the lower critical바카라 조작point 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)바카라 조작바카라 조작"