Temperature dependence of density of states near the Fermi level in a strain-free epitaxial film of the hole-doped manganiteLa0.7Ca0.3MnO3

Abstract

Scanning tunneling spectroscopy measurements were performed on an epitaxial thin film of La 0.7 Ca 0.3 MnO 3 grown on a NdGaO 3 substrate. The temperature variation of the density of states ͑DOS͒ close to the ferromagnetic transition temperature ͑T c ͒ was investigated. The strain-free film exhibiting a sharp metal-insulator transition at T p Ϸ T c Ϸ 268 K shows no phase separation as seen by the conductivity map, allowing unambiguous determination of the tunneling spectra as a function of T. The temperature dependence of the conductance ͑dI / dV͒ curves and the normalized DOS clearly indicate a depletion in DOS near T c , which fills up as the sample is cooled below T c. The metal-insulator transition at T c also shows up in the bias dependence of the tunneling curve as the temperature is changed across the transition. In the metallic phase we find that the DOS is similar to what is expected in a correlated metal.

A persistent metal–insulator transition at the surface of an oxygen-deficient, epitaxial manganite film

“…From Figure 3(a) it is clear that the tunneling current at higher bias voltage has a minimum value between 100 K and 120 K. The three I(V) spectra presented in Figure 3(b) confirm this observation, with the dashed curve recorded at 106 K showing a significantly lower current at high tunneling biases. A similar temperature dependence of the I(V) curves near the metal-insulator transition temperature (T MIT ) was also observed by others on related La 0.7 Ca 0.3 MnO 3 films 36 . Following the reasoning in this work we conclude this high-bias minimum is a signature of a metal-insulator phase transition in the surface DOS of our oxygen deficient LPCMO films.…”

“…The increase in ZBC above the T MIT is consistent with that observed in La 0.7 Ca 0.3 MnO 3 36 , where it was attributed to thermal broadening of the spectroscopic data in the presence of a small polaronic gap, see Refs. 36,38 and the discussion below. Clearly a zero-field temperature dependent MIT is present at the surface of oxygen-deficient, insulating, 3D perovskite LPCMO films with a Mn-O termination.…”

“…The ZBC displays a strong temperature dependence, decreasing below 190 K, reaching a minimum value around 120 K 36 , in close agreement with T MIT in Figure 3(a), and increasing rapidly with decreasing temperature below 120 K. The increase in ZBC below T MIT can be attributed to changes in the DOS due to an increase in delocalized carrier density or a decrease in polaron density in the metallic phase as proposed in Refs. [36][37][38] . The increase in ZBC above the T MIT is consistent with that observed in La 0.7 Ca 0.3 MnO 3 36 , where it was attributed to thermal broadening of the spectroscopic data in the presence of a small polaronic gap, see Refs.…”

Comparison on Morphological and Optical Properties of TiO<SUB>2</SUB> Thin Films Grown by Single-Pulse and Multi-Pulse Laser Ablation

“…The presence of these micrometric particles in the initial stages of growth of the nanolayers may bring about an accumulative effect of defects on the final surface of the film, thus causing an accelerated increase in the roughness. In addition, it was suggested that the film roughness is influenced by strain induced in the film by a lattice mismatch with the substrate [19], this affect the roughness both ablation regimens. Figure 6 shows images obtained by scanning electron microscopy (SEM) of the films grown with 6000 and 12,000 shots, with a single-pulse and multi-pulse regime, respectively.…”

Spin-polarized tunneling spectroscopic studies of the intrinsic heterogeneity and pseudogap phenomena in colossal magnetoresistive manganiteLa0.7Ca0.3MnO3Hughes1, Beyer2, Yeh3 2010Phys. Rev. B6020View full textAdd to dashboardCite

“…The substrates were chosen because of their small lattice mismatch ͑about 0.3%͒ with the bulk LCMO, which ensures minimized strain in the resulting films to prevent excess strain-induced effects on the electronic properties. 21,22,34 The films were deposited in a 100 mTorr oxygen background pressure to a thickness of ͑110Ϯ 10͒ nm with the substrate temperature kept at 650°C, and were subsequently annealed at the same temperature for 2 h in 100 Torr O 2 and then cooled slowly to room temperature. The epitaxy of these films was confirmed by x-ray diffraction, and the film quality was further verified by atomic force microscopy and STM measurements, showing terraced growth with step heights corresponding to one c-axis lattice constant of the bulk LCMO, as exemplified in Fig.…”