Growth and characterization of the La_3Ni_2O_7-δ thin films: dominant contribution of the d_x^2-y^2 orbital at ambient pressure
arxiv(2024)
Abstract
By using the pulsed-laser-ablation technique, we have successfully grown the
La_3Ni_2O_7-δ thin films with c-axis orientation
perpendicular to the film surface. X-ray diffraction shows that the (00l) peaks
can be well indexed to the La_3Ni_2O_7-δ phase. Resistive
measurements show that the samples can be tuned from weak insulating to
metallic behavior through adjusting the growth conditions. Surprisingly, all
curves of ρ-T in the temperature region of 2∼300 K do not show the
anomalies corresponding to either the spin density wave or the charge density
wave orders as seen in bulk samples. Hall effect measurements show a linear
field dependence with the dominant hole charge carriers, but the Hall
coefficient R_H=ρ_xy/H exhibits strong temperature dependence. The
magnetoresistance above about 50 K is positive but very weak, indicating the
absence of multiband effect. However, a negative magnetoresistance is observed
at low temperatures, which shows the delocalization effect. Detailed analysis
on the magnetoresistance suggests that the delocalization effect at low
temperatures is due to the Kondo-like effect, rather than the Anderson weak
localization. Our transport results suggest that, the electronic conduction is
fulfilled by the d_x^2-y^2 orbital with holes as the dominant charge
carriers, while the interaction through Hund's coupling with the localized
d_z^2 orbital plays an important role in the charge dynamics.
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