124 research outputs found
The critical field and specific heat in the electron- and hole-doped graphene superconductors
Doping is one of the most prominent techniques to alter properties of a given
material. Herein, the influence of the electron- and hole-doping on the
selected superconducting properties of graphene are considered. In details, the
Migdal-Eliashberg formalism is employed to analyze the specific heat and the
critical magnetic field in the representative case of graphene doped with
nitrogen or boron, respectively. It is found that the electron doping is much
more favorable in terms of enhancing the aforementioned properties than its
hole counterpart. These findings are appropriately summarized by the means of
the dimensionless thermodynamic ratios, familiar in the
Bardeen-Cooper-Schrieffer theory. To this end, the perspectives for future
research on superconductivity in graphene are drawn.Comment: 5 pages, 2 figures, 1 tabl
The superconducting energy gap in the hole-doped graphene beyond the Migdal's theory
In this work we analyze impact of non-adiabatic effects on the
superconducting energy gap in the hole-doped graphene. By using the Eliashberg
formalism beyond the Migdal's theorem, we present that the non-adiabatic
effects strongly influence the superconducting energy gap in the exemplary
boron-doped graphene. In particular, the non-adiabatic effects, as represented
by the first order vertex corrections to the electron-phonon interaction,
supplement Coulomb depairing correlations and suppress the superconducting
state. In summary, the obtained results confirm previous studies on
superconductivity in two-dimensional materials and show that the corresponding
superconducting phase may be notably affected by the non-adiabatic effects.Comment: conference material, 4 pages, 2 figure
Vacuum and Residual Gas Composition MEMS Sensor
AbstractThe paper presents a MEMS-type vacuum and residual gas composition sensor, which in contrast to the other miniature sensors, works in medium and high vacuum (10−5−10Pa). It operates on the principle of ionization of gases inside a silicon-glass microchamber. Pressure is estimated on the basis of the discharge current value, and gas composition − on the basis of spectra of the glowing gases, recorded by a miniature fiber spectrometer
Entropy of financial time series due to the shock of war
The concept of entropy is not uniquely relevant to the statistical mechanics
but among others it can play pivotal role in the analysis of a time series,
particularly the stock market data. In this area sudden events are especially
interesting as they describe abrupt data changes which may have long-lasting
effects. Here, we investigate the impact of such events on the entropy of
financial time series. As a case study we assume data of polish stock market in
the context of its main cumulative index. This index is discussed for the
finite time periods before and after outbreak of the 2022 Russian invasion of
Ukraine, acting as the sudden event. The analysis allows us to validate the
entropy-based methodology in assessing market changes as driven by the extreme
external factors. We show that qualitative features of market changes can be
captured quantitatively in terms of the entropy. In addition to that, the
magnitude of the impact is analysed over various time periods in terms of the
introduced entropic index. To this end, the present work also attempts to
answer whether or not the recent war can be considered as a reason or at least
catalyst to the current economic crisis.Comment: 8 pages, 5 figure
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