Unconventional Hall effect in oriented Ca$_3$Co$_4$O$_9$ thin films

TL;DR

This study investigates the transport properties of Ca$_3$Co$_4$O$_9$ thin films, revealing unconventional Hall effect behavior linked to strong electronic correlations and substrate-induced strain effects.

Contribution

It provides new insights into the temperature-dependent Hall effect and transport phenomena in epitaxial Ca$_3$Co$_4$O$_9$ thin films, highlighting unconventional behaviors not observed in bulk materials.

Findings

High temperature maxima in resistivity and Hall resistance indicating strong correlations

Non-monotonic Hall resistance at low temperatures suggesting anomalous Hall contributions

Substrate-induced strain mimics high-pressure effects in single crystals

Abstract

Transport properties of the good thermoelectric misfit oxide Ca$_3$Co$_4$O$_9$ are examined. In-plane resistivity and Hall resistance measurements were made on epitaxial thin films which were grown on {\it c}-cut sapphire substrates using the pulsed laser deposition technique. Interpretation of the in-plane transport experiments relates the substrate-induced strain in the resulting film to single crystals under very high pressure ($\sim$ 5.5 GPa) consistent with a key role of strong electronic correlation. They are confirmed by the measured high temperature maxima in both resistivity and Hall resistance. While hole-like charge carriers are inferred from the Hall effect measurements over the whole investigated temperature range, the Hall resistance reveals a non monotonic behavior at low temperatures that could be interpreted with an anomalous contribution. The resulting unconventional temperature dependence of the Hall resistance seems thus to combine high temperature strongly correlated features above 340 K and anomalous Hall effect at low temperature, below 100 K.