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.  One of the most intriguing properties of manganites is coexistence of two (or several) distinct electronic phases. 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 created a sub-micron phase coexistence of CO insulating phase (Fig. 1, darker regions) and conducting (lighter regions) by illuminating a Bi_0.4Ca_0.6MnO₃ thin film with visible light (~500 nm) through the tip of a NSOM. Such phase coexistence is possible because of the presence of two local energy minima corresponding to CO insulating and charge-disordered conducting phases in the energy landscape.  To better understand the physics of phase coexistence in manganites we studied the process of relaxation from the photoinduced conducting phase (shallower energy minimum) to CO insulating state (deeper energy minimum). Time dependencies of resistivity were measured after sample illumination was switched off.  An exponential increase of resistivity was observed at different temperatures (Fig. 2). If approximated with an activation model, the temperature dependence of the relaxation time constant gives a value of E = 235 K (20.3 meV) for the energy barrier separating the CO insulating and conducting states.  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)