"
  
    “Spectroscopic Fingerprint of Phase Incoherent
       Superconductivity in the Pseudogap State of
                Underdoped Bi2Sr2CaCu2O8+δ”
  
♦Speaker : Dr. Jhinhwan Lee (Cornell University)
♦Place : Physics Seminar Room (Science Bldg, 3-201)
♦Date & Time : June, 10(Wed)보증 토토2:00보증 토토~보증 토토3:00 pm

Abstract
  
One possible explanation for the mysterious ‘pseudogap’ state of the hole-doped cuprate superconductors
is that it is a d-wave superconductor보증 토토but보증 토토without보증 토토quantum보증 토토phase보증 토토rigidity.보증 토토While보증 토토several보증 토토transport보증 토토and
thermodynamic studies indicate this to be true for some regions of the phase보증 토토diagram,보증 토토unanimity보증 토토on보증 토토the
extent of these regions is lacking. Thus the spectroscopic ‘fingerprint’ of phase incoherent superconductivity
would be invaluable to determine precisely where this state occurs. One spectroscopic signature of d-wave
superconductivity is the particle-hole symmetric ‘octet’ of dispersive Bogoliubov quasiparticle interference
(QPI) modulations. In this presentation I will report the temperature dependence of the complete QPI octet
from low temperatures to well into the pseudogap regime. Remarkably, we find no dramatic changes in the
QPI octet phenomenology at the superconductor’s critical temperature Tc and, indeed, show that it exists at
all temperatures up to at least T ~ 1.5Tc.보증 토토Thus,보증 토토our보증 토토data provide direct spectroscopic evidence for phase
incoherent superconductivity in the underdoped보증 토토pseudogap보증 토토regime보증 토토and보증 토토also보증 토토a보증 토토new보증 토토perspective on the
temperature evolution of보증 토토the보증 토토superconducting보증 토토energy보증 토토gap.보증 토토Moreover,보증 토토they보증 토토reveal보증 토토that보증 토토the보증 토토pseudogap
electronic structure consists보증 토토of보증 토토three보증 토토distinct보증 토토elements:보증 토토the보증 토토Fermi arc,보증 토토the보증 토토gap보증 토토to보증 토토coherent보증 토토k-space
excitations of a phase disordered d-wave superconductor, and the gap to non-dispersive locally symmetry
breaking excitations at the pseudogap energy scale.보증 토토I will also address in detail the technical challenges in
the high-precision variable-temperature QPI measurement and present a new cross-sectional QPI analysis
scheme that can be used to more accurately determine보증 토토the보증 토토Green’s보증 토토function보증 토토and보증 토토the보증 토토scattering보증 토토matrix
elements. Together they will form the technological basis of mapping the Green’s function and the scattering
matrix elements over the entire phase diagram of an unknown material.

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


"