303 research outputs found
Localized Distributions of Quasi Two-Dimensional Electronic States near Defects Artificially Created at Graphite Surfaces in Magnetic Fields
We measured the local density of states of a quasi two-dimensional electron
system (2DES) near defects, artificially created by Ar-ion sputtering, on
surfaces of highly oriented pyrolytic graphite (HOPG) with scanning tunneling
spectroscopy (STS) in high magnetic fields. At valley energies of the Landau
level spectrum, we found two typical localized distributions of the 2DES
depending on the defects. These are new types of distributions which are not
observed in the previous STS work at the HOPG surface near a point defect [Y.
Niimi \textit{et al}., Phys. Rev. Lett. {\bf 97}, 236804 (2006).]. With
increasing energy, we observed gradual transformation from the localized
distributions to the extended ones as expected for the integer quantum Hall
state. We show that the defect potential depth is responsible for the two
localized distributions from comparison with theoretical calculations.Comment: 4 pages, 3 figure
Construction of a Versatile Ultra-Low Temperature Scanning Tunneling Microscope
We constructed a dilution-refrigerator (DR) based ultra-low temperature
scanning tunneling microscope (ULT-STM) which works at temperatures down to 30
mK, in magnetic fields up to 6 T and in ultrahigh vacuum (UHV). Besides these
extreme operation conditions, this STM has several unique features not
available in other DR based ULT-STMs. One can load STM tips as well as samples
with clean surfaces prepared in a UHV environment to an STM head keeping low
temperature and UHV conditions. After then, the system can be cooled back to
near the base temperature within 3 hours. Due to these capabilities, it has a
variety of applications not only for cleavable materials but also for almost
all conducting materials. The present ULT-STM has also an exceptionally high
stability in the presence of magnetic field and even during field sweep. We
describe details of its design, performance and applications for low
temperature physics.Comment: 6 pages, 9 figures. accepted for publication in Rev. Sci. Instru
- …