Anisotropic fluctuations and quasiparticle excitations in FeSe_0.5Te_0.5

TL;DR

This study investigates the anisotropic fluctuations and quasiparticle excitations in FeSe0.5Te0.5, revealing a power-law behavior of the penetration depth and strong fluctuation effects similar to high-Tc cuprates, using multiple measurement techniques.

Contribution

The paper provides comprehensive measurements of magnetic penetration depth, heat capacity, resistivity, and magnetic torque on the same single crystal, revealing anisotropic fluctuation effects in FeSe0.5Te0.5.

Findings

Penetration depth follows a T^2.2 power law, indicating sign-changing pairing with strong scattering.

Fluctuation effects are strongly anisotropic, affecting the phase transition at Hc2.

Heat capacity resembles high-Tc cuprates with fluctuation effects wiping out the phase transition.

Abstract

We present data for the temperature dependence of the magnetic penetration depth lambda(T), heat capacity C(T), resistivity R(T) and magnetic torque ?tau for highly homogeneous single crystal samples of Fe1:0Se0:44(4)Te0:56(4). lambda(T) was measured down to 200mK in zero field. We find lambda(T) follows a power law lambda~T^n with n = 2.2 +/- 0.1. This is similar to some 122 iron-arsenides and likely results from a sign-changing pairing state combined with strong scattering. Magnetic fields of up to B =55T or 14T were used for the ? tau(B) and C(T)/R(T) measurements respectively. The specific heat, resistivity and torque measurements were used to map out the (H,T) phase diagram in this material. All three measurements were conducted on exactly the same single crystal sample so that the different information revealed by these probes is clearly distinguished. Heat capacity data strongly resemble those found for the high Tc cuprates, where strong fluctuation effects wipe-out the phase transition at Hc2. Unusually, here we find the fluctuation effects appear to be strongly anisotropic.