759 research outputs found
Superconductivity in metal rich Li-Pd-B ternary Boride
8K superconductivity was observed in the metal rich Li-Pd-B ternary system.
Structural, microstructural, electrical and magnetic investigations for various
compositions proved that Li2Pd3B compound, which has a cubic structure composed
of distorted Pd6B octahedrons, is responsible for the superconductivity. This
is the first observation of superconductivity in metal rich ternary borides
containing alkaline metal and Pd as a late transition metal. The compound
prepared by arc melting has high density, is stable in the air and has an upper
critical field, Hc2(0), of 6T.Comment: 4 pages, 5 figur
Tuning in magnetic modes in Tb(Co_{x}Ni_{1-x})_{2}B_{2}C: from longitudinal spin-density waves to simple ferromagnetism
Neutron diffraction and thermodynamics techniques were used to probe the
evolution of the magnetic properties of Tb(Co_{x}Ni_{1-x})_{2}B_{2}C. A
succession of magnetic modes was observed as x is varied: the longitudinal
modulated k=(0.55,0,0) state at x=0 is transformed into a collinear
k=([nicefrac]\nicefrac{1}{2},0,[nicefrac]\nicefrac{1}{2})
antiferromagnetic state at x= 0.2, 0.4; then into a transverse c-axis modulated
k=(0,0,[nicefrac]\nicefrac{1}{3}) mode at x= 0.6, and finally
into a simple ferromagnetic structure at x= 0.8 and 1. Concomitantly, the
low-temperature orthorhombic distortion of the tetragonal unit cell at x=0 is
reduced smoothly such that for x >= 0.4 only a tetragonal unit cell is
manifested. Though predicted theoretically earlier, this is the first
observation of the k=(0,0,[nicefrac]\nicefrac{1}{3}) mode in
borocarbides; our findings of a succession of magnetic modes upon increasing x
also find support from a recently proposed theoretical model. The implication
of these findings and their interpretation on the magnetic structure of the
RM_{2}B_{2}C series are also discussed
Intersubband absorption linewidth in GaAs quantum wells due to scattering by interface roughness, phonons, alloy disorder, and impurities
We calculate the intersubband absorption linewidth in quantum wells (QWs) due
to scattering by interface roughness, LO phonons, LA phonons, alloy disorder,
and ionized impurities, and compare it with the transport energy broadening
that corresponds to the transport relaxation time related to electron mobility.
Numerical calculations for GaAs QWs clarify the different contributions of each
individual scattering mechanism to absorption linewidth and transport
broadening. Interface roughness scattering contributes about an order of
magnitude more to linewidth than to transport broadening, because the
contribution from the intrasubband scattering in the first excited subband is
much larger than that in the ground subband. On the other hand, LO phonon
scattering (at room temperature) and ionized impurity scattering contribute
much less to linewidth than to transport broadening. LA phonon scattering makes
comparable contributions to linewidth and transport broadening, and so does
alloy disorder scattering. The combination of these contributions with
significantly different characteristics makes the absolute values of linewidth
and transport broadening very different, and leads to the apparent lack of
correlation between them when a parameter, such as temperature or alloy
composition, is changed. Our numerical calculations can quantitatively explain
the previously reported experimental results.Comment: 17 pages, including 15 figure
Superconducting Properties of MgB2 Bulk Materials Prepared by High Pressure Sintering
High-density bulk materials of a newly discovered 40K intermetallic MgB2
superconductor were prepared by high pressure sintering. Superconducting
transition with the onset temperature of 39K was confirmed by both magnetic and
resistive measurements. Magnetization versus field (M-H) curve shows the
behavior of a typical Type II superconductor and the lower critical field
Hc1(0) estimated from M-H curve is 0.032T. The bulk sample shows good
connection between grains and critical current density Jc estimated from the
magnetization hysteresis using sample size was 2x104A/cm2 at 20K and 1T. Upper
critical field Hc2(0) determined by extrapolating the onset of resistive
transition and assuming a dirty limit is 18T.Comment: 3Pages PD
Universal behavior of spin-mediated energy transport in S=1/2 chain cuprates: BaCu2Si2O7 as an example
The thermal conductivity of the spin-1/2 chain cuprate BaCu2Si2O7 was
measured along different crystallographic directions in the temperature region
between 0.5 and 300 K. The thermal conductivity along the chain direction
considerably exceeds that along perpendicular directions. Near the
antiferromagnetic transition at T_N = 9.2 K the data indicates enhanced
scattering of phonons by critical fluctuations in the spin system. A comparison
of the data above T_N with available results on similar materials reveals
similarities in the main features of the temperature dependence of the mean
free path of itinerant spin excitations. This universal behavior is most likely
caused by the spin-lattice interaction.Comment: 7 pages, 3 figure
Microwave Surface-Impedance Measurements of the Magnetic Penetration Depth in Single Crystal Ba1-xKxFe2As2 Superconductors: Evidence for a Disorder-Dependent Superfluid Density
We report high-sensitivity microwave measurements of the in-plane penetration
depth and quasiparticle scattering rate in several
single crystals of hole-doped Fe-based superconductor
BaKFeAs (). While power-law temperature
dependence of with the power is found in crystals with
large , we observe exponential temperature dependence of superfluid
density consistent with the existence of fully opened two gaps in the cleanest
crystal we studied. The difference may be a consequence of different level of
disorder inherent in the crystals. We also find a linear relation between the
low-temperature scattering rate and the density of quasiparticles, which shows
a clear contrast to the case of d-wave cuprate superconductors with nodes in
the gap. These results demonstrate intrinsically nodeless order parameters in
the Fe-arsenides.Comment: 4 pages, 4 figures, 1 table. Accepted for publication in Phys. Rev.
Lett. Changed title as suggested by the PRL editor
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