453 research outputs found
Optical conductivity and penetration depth in MgB2
The complex conductivity of a MgB2 film has been investigated in the
frequency range 4 cm^{-1}< nu < 30 cm^{-1} and for temperatures 2.7 K < T <300
K. The overall temperature dependence of both components of the complex
conductivity is reminiscent of BCS-type behavior, although a detailed analysis
reveals a number of discrepancies. No characteristic feature of the isotropic
BCS gap temperature evolution is observed in the conductivity spectra in the
superconducting state. A peak in the temperature dependence of the real part of
the conductivity is detected for frequencies below 9 cm^{-1}. The
superconducting penetration depth follows a T^2 behavior at low temperatures.Comment: 4 pages, 4 figure
Observation of non-local dielectric relaxation in glycerol
Since its introduction, liquid viscosity and relaxation time have been
considered to be an intrinsic property of the system that is essentially local
in nature and therefore independent of system size. We perform dielectric
relaxation experiments in glycerol, and find that this is the case at high
temperature only. At low temperature, increases with system size and
becomes non-local. We discuss the origin of this effect in a picture based on
liquid elasticity length, the length over which local relaxation events in a
liquid interact via induced elastic waves, and find good agreement between
experiment and theory
Highly anisotropic energy gap in superconducting Ba(FeCo)As from optical conductivity measurements
We have measured the complex dynamical conductivity, , of superconducting Ba(FeCo)As ( K) at terahertz frequencies and temperatures 2 - 30 K. In the frequency
dependence of below , we observe clear signatures of the
superconducting energy gap opening. The temperature dependence of
demonstrates a pronounced coherence peak at frequencies below 15 cm (1.8
meV). The temperature dependence of the penetration depth, calculated from
, shows power-law behavior at the lowest temperatures. Analysis of
the conductivity data with a two-gap model, gives the smaller isotropic s-wave
gap of meV, while the larger gap is highly anisotropic with
possible nodes and its rms amplitude is meV. Overall, our
results are consistent with a two-band superconductor with an gap
symmetry.Comment: 6 pages, 4 figures, discussion on pair-barking scattering and
possible lifting of the nodes is adde
Polarization control of direct (non-sequential) two-photon double ionization of He
An ab initio parametrization of the doubly-differential cross section (DDCS) for two-photon double ionization (TPDI) from an s2 subshell of an atom in a 1S0-state is presented. Analysis of the elliptic dichroism (ED) effect in the DDCS for TPDI of He and its comparison with the same effect in the concurrent process of sequential double ionization shows their qualitative and quantitative differences, thus providing a means to control and to distinguish sequential and non-sequential processes by measuring the relative ED parameter
Geological-morphological description of the Ishtar Terra (photomap of the Venusian surface sheet B-5)
The main part of the Ishtar Terra east of the Maxwell Montes is covered with systems of areal dislocations of several directions, which are called Parquet. According to the structural patterns these may be divided into: (1) the central stable block; (2) the lesser peripheral blocks separated from the central one by gaps and grabens; (3) the zones of mobilized parquet, whose substance flowed downward at an incline in the directions away from the central block in the form of plastic flows; and (4) the partially parqueted lava sheets. The Maxwell Montes were formed as a result of the collision between the central parquet block and the Lakshmi Planum
Optical conductivity of multifold fermions: the case of RhSi
We measured the reflectivity of the multifold semimetal RhSi in a frequency
range from 80 to 20000 cm (10 meV - 2.5 eV) at temperatures down to 10
K. The optical conductivity, calculated from the reflectivity, is dominated by
the free-carrier (Drude) contribution below 1000 cm (120 meV) and by
interband transitions at higher frequencies. The temperature-induced changes in
the spectra are generally weak: only the Drude bands narrow upon cooling, with
an unscreened plasma frequency that is constant with temperature at
approximately 1.4 eV, in agreement with a weak temperature dependence of the
free-carrier concentration determined by Hall measurements. The interband
portion of conductivity exhibits two linear-in-frequency regions below 5000
cm ( 600 meV), a broad flat maximum at around 6000 cm (750
meV), and a further increase starting around 10000 cm ( 1.2 eV).
We assign the linear behavior of the interband conductivity to transitions
between the linear bands near the band crossing points. Our findings are in
accord with the predictions for the low-energy conductivity behavior in
multifold semimetals and with earlier computations based on band structure
calculations for RhSi.Comment: 7 pages, supplemental material added, figures improve
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