Abstract
A dramatic drop of ≈5 orders of magnitude in the resistance (R) ofLa0.175Pr0.45Ca0.375MnO3 epitaxial films upon exposure to optical photons derived from bothcontinuous and pulsed lasers, as well as broad-band sources at temperatures(T) < 30 K is reported. The strength of change is a sensitive function of both the incident photon flux andtemperature. Under isothermal conditions the photo-generated low resistance state persistseternally after removal of light. This non-equilibrium state is metallic, as revealed by the positivedR/dT forT ≤ Tp (≈120 K). This electrically conducting state is presumably ferromagnetic asTp coincides with the temperature where a weak ferromagnetism sets in on cooling the insulatingfilm from room temperature. To rule out the possibility of photon-induced local heating ofthe sample as a mechanism of the observed effects, photo-illumination experiments wereperformed under identical conditions on thin films of two non-charge-ordered manganitesdeposited on substrates of similar thermal conductivity. Our model for the observed transitionencompasses a global charge-ordered state in which ferromagnetic metallic clusters of fractionp much less than thecritical fraction pc for percolation exists at low temperatures. Photo-inducedmelting of the charge-ordered state increases this fraction beyondpc in a cumulative manner as successive pulses of light fall on the sample.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call