Anisotropic $H_{c2}$ determined up to 92 T and the signature of multi-band superconductivity in Ca$_{10}$(Pt$_{4}$As$_{8}$)((Fe$_{1-x}$Pt$_{x}$)$_{2}$As$_{2}$)$_{5}$ superconductor

TL;DR

This study measures the anisotropic upper critical fields of a Ca-based superconductor up to 92 T, revealing signatures of multi-band superconductivity through temperature-dependent behavior and anisotropy reduction.

Contribution

It provides the first high-field measurements of $H_{c2}$ in this superconductor, demonstrating multi-band effects and temperature-dependent anisotropy.

Findings

Upward curvature in $H_{c2}^{ ext{parallel c}}(T)$ indicates multi-band superconductivity.

Anisotropy parameter decreases from ~7 near $T_c$ to ~1 at low temperatures.

Superconductivity is dominated by two bands, affecting $H_{c2}$ behavior.

Abstract

The upper critical fields, $H_{c2}$($T$), of single crystals of the superconductor Ca$_{10}$(Pt$_{4-\delta}$As$_{8}$)((Fe$_{0.97}$Pt$_{0.03}$)$_{2}$As$_{2}$)$_{5}$ ($\delta$ $\approx$ 0.246) are determined over a wide range of temperatures down to $T$ = 1.42 K and magnetic fields of up to $\mu_{0}H$ $\simeq$ 92 T. The measurements of anisotropic $H_{c2}$($T$) curves are performed in pulsed magnetic fields using radio-frequency contactless penetration depth measurements for magnetic field applied both parallel and perpendicular to the \textbf{ab}-plane. Whereas a clear upward curvature in $H_{c2}^{\parallel\textbf{c}}$($T$) along \textbf{H}$\parallel$\textbf{c} is observed with decreasing temperature, the $H_{c2}^{\parallel\textbf{ab}}$($T$) along \textbf{H}$\parallel$\textbf{ab} shows a flattening at low temperatures. The rapid increase of the $H_{c2}^{\parallel\textbf{c}}$($T$) at low temperatures suggests that the superconductivity can be described by two dominating bands. The anisotropy parameter, $\gamma_{H}$ $\equiv$ $H_{c2}^{\parallel\textbf{ab}}/H_{c2}^{\parallel\textbf{c}}$, is $\sim$7 close to $T_{c}$ and decreases considerably to $\sim$1 with decreasing temperature, showing rather weak anisotropy at low temperatures.