Multi-frequency electrically detected magnetic resonance spectroscopy from the very-low to very-high magnetic field regime
| Date/Time: | Thursday, 27 Apr 2017 from 4:10 pm to 5:00 pm |
|---|---|
| Location: | Physics 3 |
| Phone: | 515-294-7377 |
| Channel: | College of Liberal Arts and Sciences |
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Magneto-optoelectronic properties of organic semiconductors, such as organic magnetoresistance or magneto-electroluminescence, are strongly influenced by the interplay of proton induced hyperfine fields to which charge carrier spins are coupled1-3. In addition, the weak but non-negligible spin-orbit effects caused by the material's structural disorder can affect spin-dependent processes4,5.
In order to quantitatively access and discriminate between both coupling mechanisms influence on spin-dependent electronic transitions, we have investigated the inhomogeneous broadening of charge-carrier pair spin-resonances using electrically detected magnetic resonance (EDMR) spectroscopy at various magnetic fields between approximately 3mT and 12T using different technological approaches for the generation of AC magnetic fields in the radio frequency (RF), microwave, and millimeter-wave domain4-6.
While random local hyperfine fields cause an EDMR line broadening of charge carriers that is independent from the strengths of externally applied magnetic fields, spin-orbit contributions give rise to distributions of the charge carrier g-factors, the so-called ?g-effect, and thus, a linear magnetic field dependence of EDMR lines. For the several polymer materials that we have studied, we have observed EDMR lines that are largely field-independent in the low-magnetic field regime, but show substantial broadening and line shape changes at higher fields.
By analysis of this experimental data by a numerical model that takes the field-dependence of the line shape into account, we can determine the magnitude of hyperfine and spin-orbit effects. Under low-field conditions, in the regime where the RF excitation field exceeds the static field, a strong coupling regime emerges, which is marked by collective spin effects analogous to the optical Dicke effect4,7.
[1] Nguyen et al., Nat. Mater. 9, 345-352 (2010).
[2] McCamey et al. Phys. Rev. Lett. 104, 017601 (2010).
[3] H. Malissa et al., Science 345, 1487-1490 (2014).
[4] W. J. Baker et al., Nat. Commun. 3, 898 (2012).
[5] G. Joshi et al., Appl. Phys. Lett. 109, 103303 (2016).
[6] J. van Tol et al., Rev. Sci Instrum. 76, 074101 (2005).
[7] D. P. Waters et al., Nat. Phys. 11, 910-194 (2015).