Researchers
Dr. Jhinhwan Lee, Dr. Kazuhiro Fujita, Chung Koo Kim

Introduction

Since the discovery of High-Tc superconductivity (HTSC), materials based on Cu-O chain such as Bi₂Sr₂Ca_nCu_n+1O_6+2n (BSCCO), YBa₂Cu₃O₇ (YBCO), and La_2-xSr_xCuO₂ (LSCO) were in the center of research to understand the physics underlying HTSC.

Deep inside, the Cupper oxide planes have electron configuration of antiferromagnetic Mott-insulator. Upon hole-doping, however, with either partial substitution of elements or addition of oxygen, they exhibit metallic and even superconducting property, incorporating apparent extremes. This is one reason that makes understanding HTSC highly complicated requiring knowledges from almost all the subfields of condensed matter, but at the same time that attracts interest.

Instrument - Variable Temperature Spectroscopic Imaging STM
This system consists of a home-built UHV chamber with a variable temperature stage and compensated STM head. It is suspended in a very low boilrate Dewar from a massive low vibration cryostat. The cryostat is housed inside an acoustic shield room, itself supported on a 25 ton inertial black on vibration isolators. Again, this assembly is installed in an underground acoustic/vibration isolation vault. We use this system to study Bi₂Sr₂CaCu₂O_8+δ, Bi₂Sr₂Ca₂Cu₃O_10+δ, etc. Sample exchange to 4K takes ~4 hours.

Results
We have recently discovered that the Fermi Arc has finite length below the transition temperature (T_c) and that it evolves gradually as the temperature rises even passing through T_c. This result supports the picture of phase-incoherent d-wave superconductivity in the pseudogap regime. We also found spectroscopic differences between below and over T_c, which should be used to discriminate the two phases. Our results were reported to Science on 28 Aug (Vol. 325, page 1099), where the left figure is published.

Collaborators
S. Uchida - Tokyo University
H. Takagi - RIKEN
G. Gu - Brookhaven National Lab