Todd Karin

Alignment of the Diamond Nitrogen Vacancy Center by Strain Engineering

The nitrogen vacancy (NV) center in diamond is a sensitive probe of magnetic field and a promising qubit candidate for quantum information processing. The performance of many NV-based devices improves by aligning the NV(s) parallel to a single crystallographic direction. Using ab initio theoretical techniques, we show that NV orientation can be controlled by high-temperature annealing in the presence of strain under currently accessible experimental conditions. We find that (89 ± 7)% of NVs align along the [111] crystallographic direction under 2% compressive biaxial strain (perpendicular to [111]) and an annealing temperature of 970 °C.

Giant permanent dipole moment of two-dimensional excitons bound to a single stacking fault

Two-dimensional potentials are excellent test beds for the physics of interacting excitonic gases, but engineering highly homogeneous potentials can be challenging. In this work, the authors investigate excitons bound to a single 10-\ensuremath{\mu}m scale stacking fault, finding excitonic luminescence with unprecedented homogeneity. The authors further show that stacking-fault-bound excitons are mobile and have a giant permanent dipole moment by means of the magneto-Stark effect. These results indicate that stacking faults may be a promising platform to probe the many-body physics of interacting dipoles in an atomically smooth potential.

Optical visualization of radiative recombination at partial dislocations in GaAs

Individual dislocations in an ultra-pure GaAs epi-layer are investigated with spatially and spectrally resolved photoluminescence imaging at 5 K. We find that some dislocations act as strong non-radiative recombination centers, while others are efficient radiative recombination centers. We characterize luminescence bands in GaAs due to dislocations, stacking faults, and pairs of stacking faults. These results indicate that low-temperature, spatially-resolved photoluminescence imaging can be a powerful tool for identifying luminescence bands of extended defects. This mapping could then be used to identify extended defects in other GaAs samples solely based on low-temperature photoluminescence spectra.

Radiative properties of multicarrier bound excitons in GaAs

Excitons in semiconductors can have multiple lifetimes due to spin dependent oscillator strengths and interference between different recombination pathways. In addition, strain and symmetry effects can further modify lifetimes via the removal of degeneracies. We present a convenient formalism for predicting the optical properties of

Observation of optically stimulated depletion of carbon acceptor bound excitons in GaAs

{k=0}

Population Pulsation Resonances of Excitons in Monolayer MoSe2 with Sub-1 μeV Linewidths

excitons with an arbitrary number of charge carriers in different symmetry environments. Using this formalism, we predict three distinct lifetimes for the neutral acceptor bound exciton in GaAs, and confirm this prediction through polarization dependent and time-resolved photoluminescence experiments. We find the acceptor bound-exciton lifetimes to be

Longitudinal spin relaxation of donor-bound electrons in direct band-gap semiconductors

{T_o (1,3,3/4)}

Fundamental properties of 2D excitons bound to single stacking faults in GaAs

where

Stacking faults as a novel 2D potential for excitons

{T_o = (0.61 \pm 0.12) \text{ns}}

Nonlinear spectroscopy of Valley excitons in 2D semiconductors and heterostructures

. Furthermore, we provide an estimate of the intra-level and inter-level exciton spin-relaxation rates.