Anisotropic colossal electro-resistance effect in epitaxial layered Pr0.5Ca1.5MnO4 films

Colossal electro-resistance (CER), i.e., the change in the electric resistivity up to orders of magnitude with an increasing electric field or current, is a central empirical feature of many manganite perovskites. Here, we study the anisotropy of polaronic transport in a layered Ruddlesden–Popper charge-ordered compound. The epitaxial growth of c-axis in-plane Pr0.5Ca1.5MnO4 (RP-PCMO) thin films on (110)-oriented SrTiO3 (STO) substrates enabled the measurement of the electric resistivity along the a,b,-axis and c-axis with a CER effect of up to two orders of magnitude in both directions. For transport along the a,b-direction, this effect occurs only at low temperatures, whereas along the c-axis, a large CER is present at higher temperatures above 300 K. The CER in the a,b-direction can be qualitatively understood as arising from nonlinear resistivity due to the electric field dependence of the polaronic activation barrier in the adiabatic Holstein two-site model. This is accompanied by the melting of the charge order. For the c-direction, we propose that the two orders of magnitude higher resistivity, than in the a,b-direction, is due to a crystallographic barrier of the rock salt layer that adds to the polaronic barrier. Since both barriers depend only weakly on the average electric field, the strong CER indicates defect-induced percolative transport in the c-direction.