Temperature dependence of the gap in the density of states near the Fermi level in a hole doped manganite

In this paper, we report a model-based quantitative analysis of temperature dependent scanning tunneling spectroscopy (STS) data taken on epitaxial thin films of the hole doped manganite La0.7Ca0.3MnO3. The film, grown on lattice matched NdGaO3 substrate, has a ferromagnetic transition temperature Tc=268 K. The analysis allows us to evaluate how the tunneling curve evolves across the transition temperature. We find that there is a gap Δ in the density of states (DOS), which peaks at T≈Tc. The gap closes in the ferromagnetic state following the evolution of the magnetization. The gap closing is gradual and not sudden at T=Tc. Above Tc the gap reduces from the peak value and reaches a limiting value of ≈75 meV for T/Tc≥1.1 which is close to the value of 60 meV seen from transport experiments.