Multi-band superconductivity in LaFeAsO_{0.9}F_{0.1} single crystals probed by high-field vortex torque magnetometry

TL;DR

This study investigates multiband superconductivity in LaFeAsO_{0.9}F_{0.1} single crystals by analyzing angular-dependent torque measurements, revealing temperature and field-dependent anisotropy and gap suppression phenomena.

Contribution

It provides the first detailed analysis of the anisotropy parameter's dependence on temperature and magnetic field in this compound, indicating multiband effects and gap suppression.

Findings

Anisotropy parameter γ varies with T and H, reaching ~10 and decreasing towards 1.

Field dependence of penetration depth suggests suppression of a superconducting gap at H ≈ H_{c2}/3.

Effective mass anisotropy and gap behavior indicate multiband superconductivity.

Abstract

To probe manifestations of multiband superconductivity in oxypnictides, we measured the angular dependence of the magnetic torque $\tau(\theta)$ in the mixed state of LaO$_{0.9}$F$_{0.1}$FeAs single crystals as a function of temperature $T$ and magnetic fields $H$ up to 18 T. The paramagnetic contribution of the Fe ions is properly treated in order to extract the effective mass anisotropy parameter $\gamma=(m_c/m_{ab})^{1/2}$ from $\tau(\theta)$. We show that $\gamma$ depends strongly on both $T$ and $H$, reaching a maximum value of $\sim$ 10 followed by a decrease towards values close to 1 as $T$ is lowered. The observed field dependencies of the London penetration depth $\lambda_{ab}$ and $\gamma$ suggest the onset of suppression of a superconducing gap at $H \approx H_{c2}/3$.