Exciton-polaron complexes in pulsed electrically-detected magnetic resonance

Several microscopic pathways have been proposed to explain the large magnetic effects observed in organic semiconductors, but identifying and characterising which microscopic process actually influences the overall magnetic field response is challenging. Pulsed electrically-detected magnetic resonance provides an ideal platform for this task as it intrinsically monitors the charge carriers of interest and provides dynamical information which is inaccessible through conventional magnetoconductance measurements. Here we develop a general time domain theory to describe the spin-dependent reaction of exciton-charge complexes following the coherent manipulation of paramagnetic centers through electron spin resonance. A general Hamiltonian is treated, and it is shown that the transition frequencies and resonance positions of the exciton-polaron complex can be used to estimate inter-species coupling. This work also provides a general formalism for analysing multi-pulse experiments which can be used to extract relaxation and transport rates

The Relationship Between Selected Factors of Leadership Behavior and Selected Factors of Teacher and Principal Self-concepts

Purpose. The purpose of the study was to determine if relationships existed between (1) the observed leader behavior of the school principal as seen by representative teachers and the self concepts of those same teachers, (2) principal self concept and teacher self concept, (3) principal self concept and principal leader behavior, and (4) the way teachers with high self esteem perceived the leadership behavior of the principal and the way teachers with low self esteem perceived the leadership behavior of the same principal. (Abstract shortened.

Design of Some Active Compensators of Feedback Controls

Certain networks capable of producing transfer functions with complex zeros (or complex poles) are presented. The equations for the s-plane loci of the complex singularities are developed and are equations of circles. Working equations are tabulated as an aid to design. Using these in conjunction with Carpenter's graphical construction, the network can be designed so that the roots of the compensated system lie at a specified location for a specified gain

Contemporary Perspectives: The Impact of Social Media on the Field of Human Resources Management

The Winter 2019 edition of the journal is our first special issue. The objective of this special issue is to explore current research in both social media (SM) and human resource management (HRM) by examining the intersection of these two fields of study. Articles are presented that investigate ways social media is used to provide greater or more meaningful outcomes for organizations, by use or integration of SM in organizational HRM programs and practices, or for individuals as they use SM to explore facets of the employment life cycle including recruiting, onboarding, development, retention, and retirement

Using coherent dynamics to quantify spin-coupling within triplet-exciton/polaron complexes in organic diodes

Quantifying the spin-spin interactions which influence electronic transitions in organic semiconductors is crucial for understanding their magneto-optoelectronic properties. By combining a theoretical model for three spin interactions in the coherent regime with pulsed electrically detected magnetic resonance experiments on MEH-PPV diodes, we quantify the spin-coupling within complexes comprising three spin-half particles. We determine that these particles form triplet-exciton:polaron pairs, where the polaron:exciton exchange is over 5 orders of magnitude weaker (less than 170 MHz) than that within the exciton. This approach providing a direct spectroscopic approach for distinguishing between coupling regimens, such as strongly bound trions, which have been proposed to occur in organic devices.Comment: 5 pages, 4 figure

Spin-dependent processes at the crystalline Si-SiO2 interface at high magnetic fields

Journal ArticleAn experimental study on the nature of spin-dependent excess charge-carrier transitions at the interface between (111)-oriented phosphorous-doped ([P]) ~ 1015 cm−3) crystalline silicon and silicon dioxide at high magnetic field (B0~8.5 T) is presented. Electrically detected magnetic-resonance (EDMR) spectra of the hyperfine split 31P donor-electron transitions and paramagnetic interface defects were conducted at temperatures in the range of 3 K≤ T ≤ 12 K. The results at these previously unattained (for EDMR) magnetic-field strengths reveal the dominance of spin-dependent processes that differ from the previously well investigated recombination between the 31P donor and the Pb state, which dominates at low magnetic fields. While magnetic resonant current responses due to 31P and Pb states are still present, they do not correlate and only the Pb contribution can be associated with an interface process due to spin-dependent tunneling between energetically and physically adjacent Pb states. This work provides an experimental demonstration of spin-dependent tunneling between physically adjacent and identical electronic states as proposed by Kane [Nature (London) 393, 133 (1998)] for readout of donor qubits

Differentiation between polaron-pair and triplet-exciton polaron spin-dependent mechanisms in organic light-emitting diodes by coherent spin beating

Pulsed electrically detected magnetic resonance offers a unique avenue to distinguish between polaron-pair (PP) and triplet-exciton polaron (TEP) spin-dependent recombination, which control the conductivity and magnetoresistivity of organic semiconductors. Which of these two fundamental processes dominates depends on carrier balance: by injecting surplus electrons we show that both processes simultaneously impact the device conductivity. The two mechanisms are distinguished by the presence of a half-field resonance, indicative of TEP interactions, and transient spin beating, the signature of PPs. Coherent spin Rabi flopping in the half-field (triplet) channel is observed, demonstrating that the triplet exciton has an ensemble phase coherence time of at least 60 ns, offering insight into the effect of carrier correlations on spin dephasing

Fast nuclear spin hyperpolarization of phosphorus in silicon

Journal ArticleWe experimentally demonstrate a method for obtaining nuclear spin hyperpolarization, that is, polarization significantly in excess of that expected at thermal equilibrium. By exploiting a nonequilibrium Overhauser process, driven by white light irradiation, we obtain more than 68% negative nuclear polarization of phosphorus donors in silicon. This polarization is reached with a time constant of ~150 sec, at a temperature of 1.37 K and a magnetic field of 8.5 T. The ability to obtain such large polarizations is discussed with regards to its significance for quantum information processing and magnetic resonance imaging