OLEDs: A Window to Ambient Macroscopic Spin Coherence

Datum

30.04.2015

Zeit

13:00 - 14:00

Sprecher

John M. Lupton

Zugehörigkeit

Universität Regensburg

Sprache

en

Hauptthema

Materialien

Andere Themen

Materialien

Host

G. Cuniberti

Beschreibung

The ability of a range of species such as birds, insects, and snails to navigate in Earth's magnetic field is truly perplexing. How can a tiny magnetic field of order one Gauss induce a physiologically relevant reaction when Zeeman shifts are over a million times smaller than the thermal energy? The secret appears to lie in modifications to hyperfine interactions which become relevant because of the exceptionally long (tens of microseconds) spin coherence times of radical pairs. OLEDs provide a unique molecular proving ground to explore the subtle interplay between spin coherence, spin correlations and external fields by measuring spin-dependent transport and luminescence. Spin-lattice relaxation in OLEDs is virtually independent of temperature and very slow. Spin dephasing on the microsecond timescale can be quantified by pulsed magnetic resonance and observed directly in transport (current) or luminescence. Slow spin dephasing gives rise to spin Rabi flopping of both electron and hole species, which, under suitable resonance conditions, couple to each other yielding spin beating. Such signals are, in principle, sensitive down to the individual carrier within the OLED, since the measurement reports on spin permutation symmetry rather than on thermal spin polarization. As the sole parameter determining the resonance condition is the g-factor, compact OLED-based low-frequency resonance circuits can be designed to serve as versatile magnetometers. With the emergence of metal-free triplet emitters, we can now even directly probe the singlet-triplet radical-pair mechanism under resonance simply by a color change in emission.

Letztmalig verändert: 30.04.2015, 09:40:33