663 research outputs found
Angular dependent magnetothermopower of α-(ET)₂KHg(SCN)₄
The magnetic field and angular dependences of the thermopower and Nernst effect of the quasi-twodimensional (q2D) organic conductor α-(ET)₂KHg(SCN)₄ are experimentally measured at temperatures below (4 K) and above (9 K) the transition temperature to fields of 31 T. In addition, a theoretical model which involves a magnetic breakdown effect between the q1D and q2D bands is proposed in order to simulate the data. Analysis of the background components of the thermopower and Nernst effect imply that at low temperatures, in the CDW state, the properties of α-(ET)₂KHg(SCN)₄ are determined mostly by the orbits on the new open Fermi sheets. Quantum oscillations observed in the both thermoelectric effects, at fields above 8 T, originate only from the α orbit
Inter- and Intra-granular flux Pinning in Ba(Fe0.91Co0.09)2As2 Superconductors
AbstractThermally assisted flux flow (TAFF) and flux pinning energiesare studied in a Ba(Fe0.91Co0.09)2As2 (Tc = 25.3K) sample via resistivity and AC susceptibility measurements in magnetic fields up to 18T. The flux pinning energy U(T,H) is determined from the Arrhenius law. The pinning maxima well determined by resistivity measurements ranged from 1724K at 0 T to 585K at 18 T with a sharp drop off so that U(T=Tc) varied with the applied field H as . The pinning activation energies determined from the AC susceptibility data but were by a factor of three higher, which is explained here. Both inter- and intra-granular pinning energies are determined in low fields. The onset of TAFF temperature and the crossover temperature Tx from TAFF to flux flow are determined, showing the limitations of the Anderson-Kim model
Frequency Dependent Flux Dynamics and Activation Energies in Pnictide Bulk (Ba0.56K0.44)Fe2As2 Superconductor
AbstractThermally activated flux de-pinning and flux activation de-pinning energies are studied in a (Ba0.56K0.44)Fe2As2 (Tc=38.5K) bulk superconductor in DC magnetic fields up to 18 T. Ac susceptibility was measured as a function of temperature, DC and AC magnetic fields, and frequency. Ac susceptibility curves shift to higher temperatures as the frequency is increased from 75 to 1997Hz in all fields. We model this data by Arrhenius law to determine flux activation energies as a function of AC and DC magnetic fields. The activation energy ranges from 8822K at μ0 Hdc = 0 T to 1100K at 18 T for Hac =80 A/m. The energies drop quickly in a non-linear manner as DC field rises above 0 T and around 1 T, which we describe as pinning transition field, the drop levels and continues more slowly in a linear like manner as DC field approaches to 18 T. Furthermore, the activation energy drops quickly as AC field increases from 80 A/m to 800 A/m at 0 DC field. As the DC field rises above 0, the activation energy has significantly weaker dependence on the AC field amplitude. Extensive map of the de-pinning, or irreversibility, lines shows broad dependence on the magnitude of the small AC field, frequency, in addition to the DC field
The molecular systems composed of the charmed mesons in the doublet
We study the possible heavy molecular states composed of a pair of charm
mesons in the H and S doublets. Since the P-wave charm-strange mesons
and are extremely narrow, the future experimental
observation of the possible heavy molecular states composed of
and may be feasible if they really exist.
Especially the possible states may be searched for via the
initial state radiation technique.Comment: 42 pages, 4 tables, 31 figures. Improved numerical results and
Corrected typos
Possible Molecular States of System and Y(4140)
The interpretation of Y(4140) as a molecule is studied
dynamically in the one boson exchange approach, where , and
exchange are included. Ten allowed states with
low spin parity are considered, we find that the , ,
, and configurations are most
tightly bound. We suggest the most favorable quantum numbers are
for Y(4140) as a molecule, however,
and can not be excluded. We propose to search for the
and partners in the and final
states, which is an important test of the molecular hypothesis of Y(4140) and
the reasonability of our model. The molecule is
deeply bound, experimental search in the channel at Tevatron
and LHC is suggested.Comment: 13 pages,2 figure
Magnetic Field Dependent Behavior of the CDW ground state in Per2M(mnt)2 (M = Au, Pt)
The Per2M(mnt)2 class of organic conductors exhibit a charge density wave
(CDW) ground state below about 12 K, which may be suppressed in magnetic fields
of order 20 to 30 T. However, for both cases of counter ion M(mnt)2 species
studied (M = Au (zero spin) and M = Pt (spin 1/2)), new high field ground
states evolve for further increases in magnetic field. We report recent
investigations where thermopower, Hall effect, high pressure and additional
transport measurements have been carried out to explore these new high field
phases.Comment: 6 pages, 10 figures, 27 reference
Pressure dependence of the thermoelectric power of single-walled carbon nanotubes
We have measured the thermoelectric power (S) of high purity single-walled
carbon nanotube mats as a function of temperature at various hydrostatic
pressures up to 2.0 GPa. The thermoelectric power is positive, and it increases
in a monotonic way with increasing temperature for all pressures. The low
temperature (T < 40 K) linear thermoelectric power is pressure independent and
is characteristic for metallic nanotubes. At higher temperatures it is enhanced
and though S(T) is linear again above about 100 K it has a nonzero intercept.
This enhancement is strongly pressure dependent and is related to the change of
the phonon population with hydrostatic pressure.Comment: 4 pages, 3 figure
Neutron beam test of CsI crystal for dark matter search
We have studied the response of Tl-doped and Na-doped CsI crystals to nuclear
recoils and 's below 10 keV. The response of CsI crystals to nuclear
recoil was studied with mono-energetic neutrons produced by the
H(p,n)He reaction. This was compared to the response to Compton
electrons scattered by 662 keV -ray. Pulse shape discrimination between
the response to these 's and nuclear recoils was studied, and quality
factors were estimated. The quenching factors for nuclear recoils were derived
for both CsI(Na) and CsI(Tl) crystals.Comment: 21pages, 14figures, submitted to NIM
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