arXiv subjects

A. A. Kalenyuk

Publications and source records attributed to A. A. Kalenyuk.

3 recordsLinked to original sources

arXiv2021

Superconducting THz sources with 12% power efficiency

Low power efficiency is one of the main problems of THz sources, colloquially known as the THz gap. In this work we present prototypes of THz devices based on whisker-crystals of a hightemperature superconductor Bi2Sr2CaCu2O8+d with a record high radiation power efficiency of 12% at a frequency of 4 THz. We employ various on- and off-chip detection techniques and, in particular, use the radiative cooling phenomenon for accurate evaluation of the emission power. We argue that such devices can be used for creation of tunable, monochromatic, continuous-wave, compact and power-efficient THz sources.

cond-mat.supr-con↗

arXiv2021

Influence of the Fermi surface geometry on a Josephson effect between an iron-pnictide and conventional superconductors

We study Josephson junctions between a multi-band iron-pnictide Ba1-xNaxFe2As2 and conventional s-wave superconductors Nb and Cu/Nb bilayer. We observe that junctions with a Cu interlayer exhibit much larger IcRn, despite a weaker proximity-induced superconductivity. This counterintuitive result is attributed to the difference in Fermi surface geometries of Nb and Cu, which leads to a selective one-band tunneling from Cu and a non-selective multi-band tunnelng from Nb. The latter leads to a mutual cancellation of supercurrents due to the sign-reversal s+- symmetry of the order parameter in the pnictide. Our results indicate that Fermi surface geometries play a crucial role for pnictide-based junctions. This provides a new tool for phase sensitive studies and paves a way to a conscious engineering of such junctions.

cond-mat.supr-con↗

arXiv2018

Phase-sensitive evidence for the sign-reversal s+- symmetry of the order parameter in an iron-pnictide superconductor using Nb/Ba1-xNaxFe2As2 Josephson junctions

Josephson current between two superconductors provides a phase sensitive tool for probing their pairing symmetries. Here we fabricate and study experimentally high-quality Josephson junctions between a conventional s-wave superconductor Nb and a multi-band iron-pnictide Ba$_{1-x}$Na$_x$Fe$_2$As$_2$. Junctions exhibit a large enough critical current density to preclude the d-wave symmetry of the order parameter in the pnictide. However, the $I_cR_n$ product is very small $\simeq 3~μ$V, which is not consistent with the sign-preserving $s_{++}$ symmetry either. We argue that the small $I_cR_n$ value along with its unusual temperature dependence provide evidence for the $s_{\pm}$ symmetry of the order parameter in Ba$_{1-x}$Na$_x$Fe$_2$As$_2$. We conclude that it is the phase sensitivity of our junctions that leads to an almost complete (bellow a sub-percent) cancellation of opposite supercurrents from the sign-reversal $s_{\pm}$ bands in the pnictide.

cond-mat.supr-con↗