arXiv subjects

D. Gammon

Publications and source records attributed to D. Gammon.

25 records · Page 2Linked to original sources

arXiv2005

Electrical Spin Pumping of Quantum Dots at Room Temperature

We report electrical control of the spin polarization of InAs/GaAs self-assembled quantum dots (QDs) at room temperature. This is achieved by electrical injection of spin-polarized electrons from an Fe Schottky contact. The circular polarization of the QD electroluminescence shows that a 5% electron spin polarization is obtained in the InAs QDs at 300 K, which is remarkably insensitive to temperature. This is attributed to suppression of the spin relaxation mechanisms in the QDs due to reduced dimensionality. These results demonstrate that practical regimes of spin-based operation are clearly attainable in solid state semiconductor devices.

cond-mat.mtrl-sci↗

arXiv2004

Optical pumping of electronic and nuclear spin in single charge-tunable quantum dots

We present a comprehensive examination of optical pumping of spins in individual GaAs quantum dots as we change the charge from positive to neutral to negative using a Schottky diode. We observe that photoluminescence polarization memory has the same sign as the net charge of the dot. Optical pumping of ground state electron spins enhances this effect, as demonstrated through the first measurements of the Hanle effect on an individual quantum dot. With the Overhauser effect in a high longitudinal magnetic field, we demonstrate efficient optical pumping of the quantum dot's nuclear spins for all three charge states.

cond-mat.mtrl-sci↗

arXiv2004

Suppression of Dyakonov-Perel Spin Relaxation in high mobility n-GaAs

We report a large and unexpected suppression of the free electron spin relaxation in lightly-doped n-GaAs bulk crystals. The spin relaxation rate shows weak mobility dependence and saturates at a level 30 times less then that predicted by the Dyakonov-Perel theory. The dynamics of the spin-orbit field differs substantially from the usual scheme: although all the experimental data can be self-consistently interpreted as a precessional spin relaxation induced by a random spin-orbit field, the correlation time of this random field, surprisingly, is much shorter than, and is independent of, the momentum relaxation time determined from transport measurements. Understanding of this phenomenon could lead to high temperature engineering of the electron spin memory.

cond-mat.other↗

arXiv2003

Theory of Quantum Optical Control of Single Spin in a Quantum Dot

We present a theory of quantum optical control of an electron spin in a single semiconductor quantum dot via spin-flip Raman transitions. We show how an arbitrary spin rotation may be achieved by virtual excitation of discrete or continuum trion states. The basic physics issues of the appropriate adiabatic optical pulses in a static magnetic field to perform the single qubit operation are addressed.

cond-mat↗

arXiv2003

Optical Read-Out and Initialization of an Electron Spin in a Single Quantum Dot

We describe theoretically the resonant optical excitation of a trion with circularly polarized light and discuss how this trion permits the read-out of a single electron spin through a recycling transition. Optical pumping through combination of circularly polarized optical $π$--pulses with permanent or $π$-- pulsed transverse magnetic fields suggests feasible protocols for spin initialization.

cond-mat.mtrl-sci↗

arXiv2002

Low-temperature spin relaxation in n-type GaAs

Low-temperature electron spin relaxation is studied by the optical orientation method in bulk n-GaAs with donor concentrations from 10^14 cm^{-3} to 5x10^17 cm^{-3}. A peculiarity related to the metal-to-insulator transition (MIT) is observed in the dependence of the spin lifetime on doping near n_D = 2x10^16 cm^{-3}. In the metallic phase, spin relaxation is governed by the Dyakonov-Perel mechanism, while in the insulator phase it is due to anisotropic exchange interaction and hyperfine interaction

cond-mat↗

arXiv2002

Manipulation of the Spin Memory of Electrons in n-GaAs

We report on the optical manipulation of the electron spin relaxation time in a GaAs based heterostructure. Experimental and theoretical study shows that the average electron spin relaxes through hyperfine interaction with the lattice nuclei, and that the rate can be controlled by the electron-electron interactions. This time has been changed from 300 ns down to 5 ns by variation of the laser frequency. This modification originates in the optically induced depletion of n-GaAs layer.

cond-mat↗