Spins in solids are cornerstone elements of quantum spintronics. Leading contenders such as defects in diamond or individual phosphorus dopants in silicon have shown spectacular progress, but either lack established nanotechnology or an efficient spin/photon interface. Silicon carbide (SiC) combines the strength of both systems: it has a large bandgap with deep defects and benefits from mature fabrication techniques. Here, we report the characterization of photoluminescence and optical spin polarization from single silicon vacancies in SiC, and demonstrate that single spins can be addressed at room temperature. We show coherent control of a single defect spin and find long spin coherence times under ambient conditions. Our study provides evidence that SiC is a promising system for atomic-scale spintronics and quantum technology.

Electron spin is fundamental in electrical and optical properties of organic electronic devices. Despite recent interest in spin mixing and spin transport in organic semiconductors, the actual spin coherence times in these materials have remained elusive. Measurements of spin coherence provide impartial insight into spin relaxation mechanisms, which is significant in view of recent models of spin-dependent transport and recombination involving high levels of spin mixing. We demonstrate coherent manipulation of spins in an organic light-emitting diode (OLED), using nanosecond pulsed electrically detected electron spin resonance to drive singlet-triplet spin Rabi oscillations. By measuring the change in photovoltaic response due to spin-dependent recombination, we demonstrate spin control of electronic transport and thus directly observe spin coherence over 0.5 s. This surprisingly slow spin dephasing underlines that spin mixing is not responsible for magnetoresistance in OLEDs. The long coherence times and the spin manipulation demonstrated are crucially important for expanding the impact of organic spintronics.

Organic semiconductors offer a unique environment to probe the hyperfine coupling of electronic spins to a nuclear spin bath. We explore the interaction of spins in electron-hole pairs in the presence of inhomogeneous hyperfine fields by monitoring the modulation of the current through an organic light emitting diode under coherent spin-resonant excitation. At weak driving fields, only one of the two spins in the pair precesses. As the driving field exceeds the difference in local hyperfine field experienced by electron and hole, both spins precess, leading to pronounced spin beating in the transient Rabi flopping of the current. We use this effect to measure the magnitude and spatial variation in hyperfine field on the scale of single carrier pairs, as required for evaluating models of organic magnetoresistance, improving organic spintronics devices, and illuminating spin decoherence mechanisms.

A study of donor electron spins and spin-dependent electronic transitions involving phosphorous ( 31 P) atoms in proximity of the (111) oriented crystalline silicon (c-Si) to silicon dioxide (SiO 2 ) interface is presented for [ 31 P] = 10 15 cm −3 and [ 31 P] = 10 16 cm −3 at about liquid 4 He temperatures (T = 5 K − 15 K). Using pulsed electrically detected magnetic resonance (pEDMR), spin-dependent transitions between the 31 P donor state and two distinguishable interface states are observed, namely (i) P b centers which can be identified by their characteristic anisotropy and (ii) a more isotropic center which is attributed to E ′ defects of the SiO 2 bulk close to the interface. Correlation measurements of the dynamics of spin-dependent recombination confirm that previously proposed transitions between 31 P and the interface defects take place. The influence of these electronic near-interface transitions on the 31 P donor spin coherence time T 2 as well as the donor spin-lattice relaxation time T 1 is then investigated by comparison of spin Hahn-echo decay measurements obtained from conventional bulk sensitive pulsed electron paramagnetic resonance and surface sensitive pEDMR, as well as surface sensitive electrically detected inversion recovery experiments. The measurements reveal that both T 2 and T 1 of 31 P donor electrons spins in proximity of energetically lower interface states at T ≤ 13 K are reduced by several orders of magnitude.

An appealing avenue for organic spintronics lies in direct coherent control of the spin population by means of pulsed electron spin resonance techniques. Whereas previous work has focused on the electrical detection of coherent spin dynamics, we demonstrate here the equivalence of an all-optical approach, allowing us to explore the influence of materials chemistry on the spin dynamics. We show that deuteration of the conjugated polymer side groups weakens the local hyperfine fields experienced by electron-hole pairs, thereby lowering the threshold for the resonant radiation intensity at which coherent coupling and spin beating occur. The technique is exquisitively sensitive to previously obscured material properties and offers a route to quantifying and tuning hyperfine fields in organic semiconductors.

Continuous wave optically and electrically detected magnetic resonance spectroscopy (cwODMR/cwEDMR) allow the investigation of paramagnetic states involved in spin-dependent transitions, like recombination and transport. Although experimentally similar to conventional electron spin resonance (ESR), there exist limitations when applying models originally developed for ESR to observables (luminescence and electric current) of cwODMR and cwEDMR. Here we present closed-form solutions for the modulation frequency dependence of cwODMR and cwEDMR based on an intermediate pair recombination model and discuss ambiguities which arise when attempting to distinguish the dominant spin-dependent processes underlying experimental data. These include: 1) a large number of quantitatively different models cannot be differentiated, 2) signs of signals are determined not only by recombination, but also by other processes like dissociation, intersystem-crossing, pair generation, and even experimental parameter such as, modulation frequency, microwave power, and temperature, 3) radiative and non-radiative recombination cannot be distinguished due to the observed signs of cwODMR and cwEDMR experiments.

We present a theoretical investigation of the effect of spin manipulation of polaron pairs ͑PPs͒ on the conductivity of organic semiconductors. Control of the PP spin state is achieved using pulsed electron-spin resonance. We demonstrate that manipulation of PPs will result in changes in the free-polaron density in the material, with corresponding changes in the conductivity due to the contribution of PP dissociation to the free-carrier density. The time-dependent form of this conductivity change following spin resonant perturbation is determined, and the effect of a number of experimental variables investigated. We find that, under certain conditions, these time-dependent current measurements reveal the dynamics of PP intersystem crossing. We compare these predictions with previous experiments on organic light-emitting diodes made of poly͓2-methoxy-5-͑2Ј-ethyl-hexyloxy͒-1,4-phenylene vinylene͔ and conclude that PP intersystem crossing times isc in this material may exceed 10 s at low temperatures.

Carbon‐based materials have an intrinsically weak spin–orbit coupling which imposes spin selection rules on many electronic transitions. The spin degree of freedom of electrons and nuclei can therefore play a crucial role in the electronic and optical properties of these materials. Spin‐selection rules can be studied via magnetic resonance techniques such as electron–spin resonance and optically detected magnetic resonance as well as electrically detected magnetic resonance (EDMR). The latter has progressed in recent years to a degree where the observation of coherent spin motion via current detection has become possible, providing experimental access to many new insights into the role that paramagnetic centers play for conductivity and photoconductivity. While mostly applied to inorganic semiconductor materials such as silicon, this new, often called pulsed‐(p) EDMR spectroscopy, has much potential for organic (carbon‐based) semiconductors. In this study, progress on the development of pEDMR spectroscopy on carbon‐based materials is reviewed. Insights into materials properties that can be gained from pEDMR experiments are explained and limitations are discussed. Experimental data on radiative polaron‐pair recombination in poly[2‐methoxy‐5‐(20‐ethyl‐hexyloxy)‐1,4‐phenylene vinylene] (MEH‐PPV) organic light emitting diodes (OLEDs) are shown, revealing that under operating conditions the driving current of the device can be modulated by spin‐Rabi nutation of the polaron spin within the charge carrier pairs. From this experimental data it becomes clear that for polaron pairs, the precursor states during exciton formation, exchange interaction is not the predominant influence on the observed pEDMR spectra.