5,338 research outputs found
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
Strongly Correlated Electrons and Neutron Scattering
Various aspects of close and interesting relationship between
antiferromagnetism and singlet ground states are introduced for which neutron
scattering have been playing vital roles. The special emphasis is on the
disorder-induced antiferromagnetism in spin-Peierls systems, which can be
viewed as a nucleation process of classical magnetic order in the background of
singlet state whose origin is purely quantum-mechanical. It is then pointed out
that similar features will be found in Ce_xCu_2Si_2 and high T_c cuprates.
Finally the possible charge ordering process in NaV_2O_5 is discussed which
leads to the quenching of localized spins.Comment: 8 pages, 3 figures, Proceedings of 7th ISSP International Symposium
"Frontiers in Neutron Scattering Research" (To appear in J. Phys. Chem.
Solids (1999)
Can The Majorana neutrino CP-violating phases be restricted ?
We reanalyze the constraints in neutrino masses and MNS lepton mixing
parameters using the new data from the terrestrial (KamLAND) and astrophysical
(WMAP) observations together with the HEIDELBERG-MOSCOW double beta decay
experiment. It leads us to the almost degenerate or inverse hierarchy neutrino
mass scenario. We discuss the possibility of getting the bound for the Majorana
CP violating phase.Comment: 6 pages, 2 figure
Study on successive superconducting transitions in TaSC from electrical resistivity and nonlinear AC magnetic susceptibility
TaSC compound undergoes superconducting transitions at K and K. The nature of successive
superconducting transitions has been studied from electrical resistivity,
linear and nonlinear AC magnetic susceptibilities. The resistivity at
= 0 shows a local maximum near , a kink-like behavior around
, and reduces to zero at below = 2.1 K. The dependence
of is observed at = 50 kOe at low temperatures, which is due to
two-dimensional weak-localization effect. Below a two-dimensional
superconducting phase occurs in each TaC layer. The linear and nonlinear
susceptibilities , ,
, and as well as the difference
() between the FC and ZFC
susceptibilities, start to appear below 6.0 K, the onset temperature of
irreversibility. A drastic growth of the in-plane superconducting coherence
length below 6.0 K gives rise to a three-dimensional superconducting phase
below , through interplanar Josephson couplings between adjacent TaC
layers. The oscillatory behavior of ,
, and below is
related to the nonlinear behavior arising from the thermally activated flux
flow.Comment: 11 pages, 10 figures, Physical Review B (accepted for publication
Determination of the mosaic angle distribution of Grafoil platelets using continuous-wave NMR spectra
We described details of a method to estimate with good accuracy the mosaic
angle distributions of microcrystallites (platelets) in exfoliated graphite
like Grafoil which is commonly used as an adsorption substrate for helium thin
films. The method is based on analysis of resonance field shifts in
continuous-wave (CW) NMR spectra of He ferromagnetic monolayers making
use of the large nuclear polarization of the adsorbate itself. The mosaic angle
distribution of a Grafoil substrate analyzed in this way can be well fitted to
a gaussian form with a deg spread. This distribution is quite
different from the previous estimation based on neutron scattering data which
showed an unrealistically large isotropic powder-like component.Comment: 6 pages, 5 figure
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