Quantum matter in high magnetic fields

Abstract:

Recently, Borisenko et al have posted a Comment (arXiv:1108.1159) where they suggest an alternative interpretation of our de Haas-van Alphen (dHvA) measurements on the superconductor LiFeAs. In our original paper (arXiv:1107.4375) we concluded that our measurements of the bulk Fermi surface were not consistent with the surface bands observed thus far by ARPES. Borisenko et al dispute this and suggest the two measurements are consistent if some of the orbits we observe are due to magnetic breakdown. We argue here that this scenario is inconsistent with the experimental data and therefore that our original conclusion stands.

Abstract:

We present data for the temperature dependence of the magnetic penetration depth λ (T), heat capacity C (T), resistivity ρ (T), and magnetic torque τ for highly homogeneous single-crystal samples of Fe1.0 Se0.44 (4) Te0.56 (4). λ (T) was measured down to 200 mK in zero field. We find λ (T) follows a power law Δλ∼ Tn 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=55 or 14 T were used for the τ (B) and C (T) /ρ (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. © 2010 The American Physical Society.