"사이트 토토      * 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)사이트 토토4:00 ~ 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 the사이트 토토presence사이트 토토of a sufficiently
high density of defects. We present the results사이트 토토of systematic사이트 토토studies 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 were사이트 토토performed
with electrical transport and ac specific heat사이트 토토measurements. The geometry and strength
of the defects varied,사이트 토토including사이트 토토naturally occurring twin boundaries as well as detwinned
single crystals사이트 토토irradiated with successive doses of electrons,사이트 토토protons, or heavy사이트 토토ions.
Twin boundaries yield planar defects,사이트 토토electron irradiation yielded weak point사이트 토토defects,
proton irradiation yielded strong point-like defects and사이트 토토heavy사이트 토토ion사이트 토토irradiation yielded
strong columnar defects. Our results사이트 토토indicate that the사이트 토토origins사이트 토토of the upper and lower
critical points of the first order melting transition arise from different mechanisms. The
position of the lower critical사이트 토토point 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)사이트 토토사이트 토토"