title: Magnetoconductance response in unipolar and bipolar organic diodes at ultrasmall fields.
abstract: We measured magnetoconductance (MC) response in a number of unipolar and bipolar organic diodes based on π-conjugated polymers and small molecules at fields |B|<100  mT and various bias voltages and temperatures. Similar to magneto-electroluminescence, the MC(B) response in bipolar diodes shows a sign reversal at ultrasmall |B|<1-2  mT due to interplay of hyperfine and Zeeman interactions in opposite-charge polaron pairs. Surprisingly, similar MC(B) response was also measured in unipolar devices, indicating the existence of like-charge polaron pairs, however, with a clear difference between the hyperfine interaction constants of electron polaron and hole polaron.
authors.affiliation: Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City, Utah 84112, USA.
authors.forename: T D
authors.initials: TD
authors.lastname: Nguyen
authors.forename: B R
authors.initials: BR
authors.lastname: Gautam
authors.forename: E
authors.initials: E
authors.lastname: Ehrenfreund
authors.forename: Z V
authors.initials: ZV
authors.lastname: Vardeny