arXiv subjects

Michal Šindler

Publications and source records attributed to Michal Šindler.

3 recordsLinked to original sources

arXiv2025

Deeper insight into the terahertz response of conventional superconductors under magnetic field

We investigate the terahertz conductivity of conventional superconductors in Voigt and Faraday magneto-optical configurations. First, we review theoretical approaches describing the fundamental processes of suppression of superconductivity in magnetic field and how the in-gap states are filled. In the Voigt geometry, thin superconducting films are fully penetrated by the magnetic field which interacts with the spin, thus modifying the magnitudes of the optical gap and of the density of the condensate. In this configuration, we provide an alternative description of the recent experiments showing the gapless conductivity of a Nb film measured by Lee ${\it et\,al.}$ [Nat. Commun. 14,2737 (2023)], which better fits their data for magnetic fields above 1 T. In the Faraday geometry, we measured and analyzed the terahertz conductivity of three NbN films with varying thicknesses using the Maxwell-Garnett model, treating vortices as normal-state inclusions within a superconducting matrix. In both geometries, the optical conductivity can be comprehensively described by the model of Herman and Hlubina [Phys. Rev. B 96, 014509 (2017)] involving pair-conserving, and magnetic-field-dependent pair-breaking disorder scattering processes.

cond-mat.supr-con↗

arXiv2024

Two-fluid model analysis of the terahertz conductivity of YBaCuO samples: optimally doped, underdoped and overdoped cases

The complex conductivity of underdoped and optimally doped YBa$_2$Cu$_3$O$_{7-δ}$ samples and overdoped similar compound Y$_{0.7}$Ca$_{0.3}$Ba$_2$Cu$_3$O$_{7-δ}$ was measured using time-domain terahertz spectroscopy. In the normal state, the frequency dependence is described by the Drude model. Below the critical temperature $T_\mathrm{c}$, the two-fluid model was successfully employed to fit all the spectra, from 5 K up to $T_\mathrm{c}$. The temperature behaviour of fundamental parameters such as the scattering rate $1/τ$, the superfluid (normal) fraction $f_\mathrm{s}$ ($f_\mathrm{n}$) and the conductivity $σ$ was investigated at given frequencies. For the optimally doped and the overdoped samples, even at 5 K, a fifth of the electrons do not condense to the superfluid fraction. We observed that a substantial fraction of electrons do not condense to the superfluid fraction even at 5 K for optimally doped and overdoped samples. The real part of the conductivity $σ_1(T)$ exhibits a peak at low frequencies. It can be observed for all three stoichiometries and its exact shape depends on the quality of the sample. A further analysis shows that this peak is a consequence of the competition between the scattering time $τ(T)$ and the superfluid fraction $f_\mathrm{s}(T)$.

cond-mat.supr-con↗

arXiv2024

Perspective on the Vortex Mass Determination in Superconductors using Circular Dichroism

The effective mass of Abrikosov vortices in superconductors remains a challenging problem with limited experimental verification. In this paper, we present a method based on observation of the vortex mass in magnetic circular dichroism at terahertz frequencies. We demonstrate the emergence of dichroism with decreasing temperature in two YBa$_2$Cu$_3$O$_{7-δ}$ thin films of different doping. The experimental results can be explained within a theoretical model that takes into account the vortex mass and provides an expression for the optical complex conductivity. We discuss the model parameters and show how they are obtained from the supporting experiments.

cond-mat.supr-con↗