Overhauser effect in individual InP/GaInP dots

Sizable nuclear spin polarization is pumped in individual InP/GaInP dots in a wide range of external magnetic fields B_ext=0-5T by circularly polarized optical excitation. We observe nuclear polarization of up to ~40% at Bext=1.5T and corresponding to an Overhauser field of ~1.2T. We find a strong feedback of the nuclear spin on the spin pumping efficiency. This feedback, produced by the Overhauser field, leads to nuclear spin bi-stability at low magnetic fields of Bext=0.5-1.5T. We find that the exciton Zeeman energy increases markedly, when the Overhauser field cancels the external field. This counter-intuitive result is shown to arise from the opposite contribution of the electron and hole Zeeman splittings to the total exciton Zeeman energy

Overhauser effect in individual InP/GaInP dots

Sizable nuclear spin polarization is pumped in individual InP/GaInP dots in a wide range of external magnetic fields B_ext=0-5T by circularly polarized optical excitation. We observe nuclear polarization of up to ~40% at Bext=1.5T and corresponding to an Overhauser field of ~1.2T. We find a strong feedback of the nuclear spin on the spin pumping efficiency. This feedback, produced by the Overhauser field, leads to nuclear spin bi-stability at low magnetic fields of Bext=0.5-1.5T. We find that the exciton Zeeman energy increases markedly, when the Overhauser field cancels the external field. This counter-intuitive result is shown to arise from the opposite contribution of the electron and hole Zeeman splittings to the total exciton Zeeman energy

Suppression of nuclear spin diffusion at a GaAs/AlGaAs interface measured with a single quantum dot nano-probe

Nuclear spin polarization dynamics are measured in optically pumped individual GaAs/AlGaAs interface quantum dots by detecting the time-dependence of the Overhauser shift in photoluminescence (PL) spectra. Long nuclear polarization decay times of ~ 1 minute have been found indicating inefficient nuclear spin diffusion from the GaAs dot into the surrounding AlGaAs matrix in externally applied magnetic field. A spin diffusion coefficient two orders lower than that previously found in bulk GaAs is deduced.Comment: 5 pages, 3 figures, submitted to Phys Rev

Long nuclear spin polarization decay times controlled by optical pumping in individual quantum dots

Nuclear polarization dynamics are measured in the nuclear spin bistability regime in a single optically pumped InGaAs/GaAs quantum dot. The controlling role of nuclear spin diffusion from the dot into the surrounding material is revealed in pump-probe measurements of the nonlinear nuclear spin dynamics. We measure nuclear spin polarization decay times in the range of 0.2-5 s, strongly dependent on the optical pumping time. The long nuclear spin decay arises from polarization of the material surrounding the dot by spin diffusion for long (>5s) pumping times. The time-resolved methods allow the detection of the unstable nuclear polarization state in the bistability regime otherwise undetectable in cw experiments

Metabarcoding reveals low fidelity and presence of toxic species in short chain-of-commercialization of herbal products

Herbal medicinal products gain increasing popularity. The growing demand for herbal medicine along with a lack of regulation render herbal products subject to intentional adulteration. The substitution of costly ingredients with unlabelled plant-based fillers of inferior quality has been widely reported. Such fraudulent practices erode consumer trust, but can also pose serious health risks. In this work, 71 herbal medicinal products were randomly purchased from Greek markets and analysed using ITS2 metabarcoding for species identification. The aim was to investigate possible adulterations and assess the efficacy of metabarcoding in plant-based product authentication. Of the 131 detected species in our analyses, 87 were not listed on the product labels. This indicates a high level of adulteration and/or contamination during processing and distribution. Two toxic species, Chelidonium majus and Nicotiana tabacum, were also detected as major ingredients of two herbal mixtures for medicinal purposes. Furthermore, the detection of wheat in eight samples raises concerns for people with gluten intolerance. This study stresses the need for stricter quality control of herbal products. In addition, to overcome the limitations of metabarcoding and augment the approach we used Bar-HRM for the first time as a verification tool. The combination of metabarcoding with species-specific Bar-HRM analysis can enhance the reliability of the results. © 2020 Elsevier Inc

Nuclear spin switch in semiconductor quantum dots.

We show that by illuminating an InGaAs/GaAs self-assembled quantum dot with circularly polarized light, the nuclei of atoms constituting the dot can be driven into a bistable regime, in which either a thresholdlike enhancement or reduction of the local nuclear field by up to 3 T can be generated by varying the pumping intensity. The excitation power threshold for such a nuclear spin “switch” is found to depend on both the external magnetic and electric fields. The switch is shown to arise from the strong feedback of the nuclear spin polarization on the dynamics of the spin transfer from electrons to the nuclei of the dot

The use of Abell-Tersoff potentials in atomistic simulations of InGaAsSb/GaAs

In this paper we show the use of an optimally parameterized empirical potential of the Abell–Tersoff type to study the strain energy of the quaternary alloy InGaAsSb. We use our results to compute modified segregation energies in an improved kinetic model of segregation for the combined effects of group III and V exchange processes during pitaxial growth and compare with experimental data from Scanning Tunnelling Microscopy

Control of Strain in GaSbAs/InAs/GaAs Quantum Dots

We discuss strain simulations of quantum dot structures covered with a GaSbAs strain reducing capping layer in the presence of Sb segregation. Cross Sectional Scanning Tunneling Microscopy shows strong Sb and In segregation in the material surrounding the quantum dot. Using the three layer model originally proposed for the SiGe system by D. J. Godbey, M. G. Ancona, J. Vac. Sci. Technol. A 15, 976 (1997) we accurately calculate the segregation profile and include a non uniform composition to our models. Using atomistic modeling, we present strain maps of the quantum dot structures that show the propagation of the strain into the GaAs region is strongly affected by the shape and composition of the strain reduction layer