期刊
JOURNAL OF PHYSICS-CONDENSED MATTER
卷 22, 期 27, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0953-8984/22/27/275502
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资金
- Indo-French Center for Promotion of Advanced Research
- IIT Kanpur
- Department of Information Technology
A dramatic drop of approximate to 5 orders of magnitude in the resistance (R) of La0.175Pr0.45Ca0.375MnO3 epitaxial films upon exposure to optical photons derived from both continuous 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 and temperature. Under isothermal conditions the photo-generated low resistance state persists eternally after removal of light. This non-equilibrium state is metallic, as revealed by the positive dR/dT for T <= T-p (approximate to 120 K). This electrically conducting state is presumably ferromagnetic as T-p coincides with the temperature where a weak ferromagnetism sets in on cooling the insulating film from room temperature. To rule out the possibility of photon-induced local heating of the sample as a mechanism of the observed effects, photo-illumination experiments were performed under identical conditions on thin films of two non-charge-ordered manganites deposited on substrates of similar thermal conductivity. Our model for the observed transition encompasses a global charge-ordered state in which ferromagnetic metallic clusters of fraction p much less than the critical fraction p(c) for percolation exists at low temperatures. Photo-induced melting of the charge-ordered state increases this fraction beyond p(c) in a cumulative manner as successive pulses of light fall on the sample.
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