Nuclear magnetic resonance inverse spectra of InGaAs quantum dots: Atomistic level structural information

A wealth of atomistic information is contained within a self-assembled quantum dot (QD), associated with its chemical composition and the growth history. In the presence of quadrupolar nuclei, as in InGaAs QDs, much of this is inherited to nuclear spins via the coupling between the strain within the polar lattice and the electric quadrupole moments of the nuclei. Here, we present a computational study of the recently introduced inverse spectra nuclear magnetic resonance technique to assess its suitability for extracting such structural information. We observe marked spectral differences between the compound InAs and alloy InGaAs QDs. These are linked to the local biaxial and shear strains, and the local bonding configurations. The cation-alloying plays a crucial role especially for the arsenic nuclei. The isotopic line profiles also largely differ among nuclear species: While the central transition of the gallium isotopes have a narrow linewidth, those of arsenic and indium are much broader and oppositely skewed with respect to each other. The statistical distributions of electric field gradient (EFG) parameters of the nuclei within the QD are analyzed. The consequences of various EFG axial orientation characteristics are discussed. Finally, the possibility of suppressing the first-order quadrupolar shifts is demonstrated by simply tilting the sample with respect to the static magnetic field.Comment: Published version, 17 pages, 18 figure

Direct measurement of the hole-nuclear spin interaction in single quantum dots

We use photoluminescence spectroscopy of ''bright'' and ''dark'' exciton states in single InP/GaInP quantum dots to measure hyperfine interaction of the valence band hole with nuclear spins polarized along the sample growth axis. The ratio of the hyperfine constants for the hole (C) and electron (A) is found to be C/A~-0.11. In InP dots the contribution of spin 1/2 phosphorus nuclei to the hole-nuclear interaction is weak, which enables us to determine experimentally the value of C for spin 9/2 indium nuclei as C_In~-5 micro-eV. This high value of C is in good agreement with recent theoretical predictions and suggests that the hole-nuclear spin interaction has to be taken into account when considering spin qubits based on holes.Comment: to be submitted to Phys Rev Let

Optically tunable nuclear magnetic resonance in a single quantum dot

We report optically detected nuclear magnetic resonance (ODNMR) measurements on small ensembles of nuclear spins in single GaAs quantum dots. Using ODNMR we make direct measurements of the inhomogeneous Knight field from a photoexcited electron which acts on the nuclei in the dot. The resulting shifts of the NMR peak can be optically controlled by varying the electron occupancy and its spin orientation, and lead to strongly asymmetric line shapes at high optical excitation. The all-optical control of the NMR line shape will enable position-selective control of small groups of nuclear spins inside a dot

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

Spin-order-dependent magneto-elastic coupling in two dimensional antiferromagnetic MnPSe3_3 observed through Raman spectroscopy

Layered antiferromagnetic materials have emerged as a novel subset of the two-dimensional family providing a highly accessible regime with prospects for layer-number-dependent magnetism. Furthermore, transition metal phosphorous trichalcogenides, MPX3 (M = transition metal; X = chalcogen) provide a platform for investigating fundamental interactions between magnetic and lattice degrees of freedom providing new insights for developing fields of spintronics and magnonics. Here, we use a combination of temperature dependent Raman spectroscopy and density functional theory to explore magnetic-ordering-dependent interactions between the manganese spin degree of freedom and lattice vibrations of the non-magnetic sub-lattice via a Kramers-Anderson super-exchange pathway in both bulk, and few-layer, manganese phosphorous triselenide (MnPSe$_3$). We observe a nonlinear temperature dependent shift of phonon modes predominantly associated with the non-magnetic sub-lattice, revealing their non-trivial spin-phonon coupling below the N{\'e}el temperature at 74 K, allowing us to extract mode-specific spin-phonon coupling constants.Comment: 20 pages, 4 figures, Submitted to ACS Nano Letter

Nonlinear dynamics of polariton scattering in semiconductor microcavity: bistability vs stimulated scattering

We demonstrate experimentally an unusual behavior of the parametric polariton scattering in semiconductor microcavity under a strong cw resonant excitation. The maximum of the scattered signal above the threshold of stimulated parametric scattering does not shift along the microcavity lower polariton branch with the change of pump detuning or angle of incidence but is stuck around the normal direction. We show theoretically that such a behavior can be modelled numerically by a system of Maxwell and nonlinear Schroedinger equations for cavity polaritons and explained via the competition between the bistability of a driven nonlinear MC polariton and the instabilities of parametric polariton-polariton scattering.Comment: 5 pages, 4 Postscript figures; corrected typo

Spin diffusion in the Mn2+ ion system of II-VI diluted magnetic semiconductor heterostructures

The magnetization dynamics in diluted magnetic semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te has been studied experimentally by optical methods and simulated numerically. In the samples with nonhomogeneous magnetic ion distribution this dynamics is contributed by spin-lattice relaxation and spin diffusion in the Mn spin system. The spin diffusion coefficient of 7x10^(-8) cm^2/s has been evaluated for Zn(0.99)Mn(0.01)Se from comparison of experimental and numerical results. Calculations of the giant Zeeman splitting of the exciton states and the magnetization dynamics in the ordered alloys and parabolic quantum wells fabricated by the digital growth technique show perfect agreement with the experimental data. In both structure types the spin diffusion has an essential contribution to the magnetization dynamics.Comment: 12 pages, 11 figure