Vera Smolyaninova

Doped rare-earth manganese oxides (manganites) exhibit a wide variety of physical phenomena due to complex interplay of electronic, magnetic, orbital, and structural degrees of freedom and their sensitivity to external fields. A photoinduced insulator to conductor transition in charge-ordered (CO) manganites is especially interesting from the point of view of creating photonic devices. We have found that 50 nm Bi_1-xCa_xMnO₃thin film grown on NdCaAlO₄ (NCAO) substrate is very susceptible to increase of current and illumination with argon-ion laser light (wavelength ~ 500 nm). Application of these stimuli partially destroys CO and produces charge-disordered conductive phase (Fig.1). Combined application of illumination and current completely destroys the charge ordering in this material, while the application of one of these factors separately is not sufficient to produce such effect. This results in decrease of resistivity by more than two orders in magnitude at low temperatures. The I-V curves are nonlinear and hysteretic and depend on history with respect to application of current (Fig.2), which is related to appearance of a new conducting phase produced by increased current. Above the CO temperature there are no current-induced and photoinduced effects (Figs. 1 and 2). Such properties of these materials potentially could be used in opto-electronic switches. This work is supported by NSF Grant DMR-0348939. These results are published in Physical Review B (V. N. Smolyaninova et al., Phys. Rev. B 76, 104423)

Fig. 1. (a) Temperature dependence of the resistivity of the Bi0.4Ca0.6MnO3 thin film grown on (100) oriented NCAO substrate: red – I = 10-5 A; blue – I = 10-4 A; green – I = 10-3 A; dashed lines – the sample was illuminated. (b) Experimental current and voltage contact configuration with respect to illuminated region.	Fig. 2. Voltage-current dependencies for the Bi0.4Ca0.6MnO3 thin film grown on (001) oriented NCAO substrate with illumination (blue) and without illumination (red) for different temperatures: (a) T = 100 K; (b) T = 250 K. The sample was current biased.