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Register a new userTailoring spin defects in diamond
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Added by
Felipe Favaro De Oliveira
Publication date
2017
fields
Physics
and research's language is
English
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Atomic-size spin defects in solids are unique quantum systems. Most applications require nanometer positioning accuracy, which is typically achieved by low energy ion implantation. So far, a drawback of this technique is the significant residual implantation-induced damage to the lattice, which strongly degrades the performance of spins in quantum applications. In this letter we show that the charge state of implantation-induced defects drastically influences the formation of lattice defects during thermal annealing. We demonstrate that charging of vacancies localized at e.g. individual nitrogen implantation sites suppresses the formation of vacancy complexes, resulting in a tenfold-improved spin coherence time of single nitrogen-vacancy (NV) centers in diamond. This has been achieved by confining implantation defects into the space charge layer of free carriers generated by a nanometer-thin boron-doped diamond structure. Besides, a twofold-improved yield of formation of NV centers is observed. By combining these results with numerical calculations, we arrive at a quantitative understanding of the formation and dynamics of the implanted spin defects. The presented results pave the way for improved engineering of diamond spin defect quantum devices and other solid-state quantum systems.
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A promising approach for multi-qubit quantum registers is to use optically addressable spins to control multiple dark electron-spin defects in the environment. While recent experiments have observed signatures of coherent interactions with such dark spins, it is an open challenge to realize the individual control required for quantum information processing. Here we demonstrate the initialisation, control and entanglement of individual dark spins associated to multiple P1 centers, which are part of a spin bath surrounding a nitrogen-vacancy center in diamond. We realize projective measurements to prepare the multiple degrees of freedom of P1 centers - their Jahn-Teller axis, nuclear spin and charge state - and exploit these to selectively access multiple P1s in the bath. We develop control and single-shot readout of the nuclear and electron spin, and use this to demonstrate an entangled state of two P1 centers. These results provide a proof-of-principle towards using dark electron-nuclear spin defects as qubits for quantum sensing, computation and networks.
Non-invasive local probes are needed to characterize bulk defects in binary and ternary chalcogenides. These defects contribute to the non-ideal behavior of topological insulators. We have studied bulk electronic properties via $^{125}$Te NMR in Bi$_2$Te$_3$, Sb$_2$Te$_3$, Bi$_{0.5}$Sb$_{1.5}$Te$_3$, Bi$_2$Te$_2$Se and Bi$_2$Te$_2$S. A distribution of defects gives rise to asymmetry in the powder lineshapes. We show how the Knight shift, line shape and spin-lattice relaxation report on carrier density, spin-orbit coupling and phase separation in the bulk. The present study confirms that the ordered ternary compound Bi$_2$Te$_2$Se is the best TI candidate material at the present time. Our results, which are in good agreement with transport and ARPES studies, help establish the NMR probe as a valuable method to characterize the bulk properties of these materials.
There are a number of theoretical proposals based on strain engineering of graphene and other two-dimensional materials, however purely mechanical control of strain fields in these systems has remained a major challenge. The two approaches mostly used so far either couple the electrical and mechanical properties of the system simultaneously or introduce some unwanted disturbances due to the substrate. Here, we report on silicon micro-machined comb-drive actuators to controllably and reproducibly induce strain in a suspended graphene sheet, in an entirely mechanical way. We use spatially resolved confocal Raman spectroscopy to quantify the induced strain, and we show that different strain fields can be obtained by engineering the clamping geometry, including tunable strain gradients of up to 1.4 %/$mu$m. Our approach also allows for multiple axis straining and is equally applicable to other two-dimensional materials, opening the door to an investigating their mechanical and electromechanical properties. Our measurements also clearly identify defects at the edges of a graphene sheet as being weak spots responsible for its mechanical failure.
We report first-principles density-functional theory studies of native point defects and defect complexes in olivine-type LiFePO4, a promising candidate for rechargeable Li-ion battery electrodes. The defects are characterized by their formation energies which are calculated within the GGA+U framework. We find that native point defects are charged, and each defect is stable in one charge state only. Removing electrons from the stable defects always generates defect complexes containing small hole polarons. Defect formation energies, hence concentrations, and defect energy landscapes are all sensitive to the choice of atomic chemical potentials which represent experimental conditions. One can, therefore, suppress or enhance certain native defects in LiFePO4 via tuning the synthesis conditions. Based on our results, we provide insights on how to obtain samples in experiments with tailored defect concentrations for targeted applications. We also discuss the mechanisms for ionic and electronic conduction in LiFePO4 and suggest strategies for enhancing the electrical conductivity.
As device miniaturization approaches the atomic limit, it becomes highly desirable to exploit novel paradigms for tailoring electronic structures and carrier dynamics in materials. Elastic strain can in principle be applied to achieve reversible and fast control of such properties, but it remains a great challenge to create and utilize precisely controlled inhomogeneous deformation in semiconductors. Here, we take a combined experimental and theoretical approach to demonstrate that elastic strain-gradient can be created controllably and reversibly in ZnO micro/nanowires. In particular, we show that the inhomogeneous strain distribution creates an effective field that fundamentally alters the dynamics of the neutral excitons. As the basic principles behind these results are quite generic and applicable to most semiconductors, this work points to a novel route to a wide range of applications in electronics, optoelectronics, and photochemistry.
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