Our research focuses on understanding the interactions of electron spins and light in materials. This understanding could enable applications in novel spintronic and optoelectronic devices.

Research Projects

Electron-nuclear spin interactions

Optical pumping of electron spins has been shown to generate dynamic nuclear polarization in bulk semiconductors, quantum wells, and quantum dots. Our group has shown that current-induced electron spin polarization can align nuclear spin polarization both along and against an external magnetic field and that periodic optical spin pumping reveals a dynamic nuclear spin polarization whose sign depends on whether the field is being increased or decreased.

For more information about this work, please see:

• C. J. Trowbridge et al., "Dynamic nuclear polarization from current-induced electron spin polarization," Physical Review B 90, 085122 (2014)
• M. Macmahon et al., "Observation of magnetic field sweep direction dependent dynamic nuclear polarization under periodic optical electron spin pumping," Physical Review B 99, 075201 (2019)
• M. J. Dominguez et al., "Dynamic nuclear polarization by optical Stark effect in periodically pumped gallium arsenide," Physical Review B 101, 205203 (2020)

Spin/valley polarization in 2D materials

Monolayer transition metal dichalcogenides (TMDs) can be direct bandgap semiconductors. Time-resolved Kerr rotation measurements on MOCVD-grown monolayer tungsten diselenide showed a long-lived signal (~80 ns) at 10 K, which we attributed to spin/valley polarization of the resident holes.

For more information about this work, please see:

• X. Song et al., "Long-Lived Hole Spin/Valley Polarization Probed by Kerr Rotation in Monolayer WSe₂," Nano Letters 16, 5010-5014 (2016)

Spin-orbit coupling and electrical generation of spin polarization in semiconductors

Electron spin polarization in semiconductors can be electrically generated through current-induced spin polarization. Our group has investigated how the magnitude of current-induced spin polarization depends on the spin-orbit splitting and other material parameters. We have also showed that modified voltage waveforms can recover the linear dependence of spin generation with electric field even at larger applied voltages by reducing the effects of heating.

For more information about this work, please see:

• B. M. Norman et al., "Mapping spin-orbit splitting in strained (In,Ga)As epilayers," Physical Review B 82, 081304(R) (2010)
• C. J. Trowbridge et al., "Electron spin polarization-based integrated photonic devices," Optics Express 19, 14845-14851 (2011)
• B. M. Norman et al., "Current-Induced Spin Polarization in Anisotropic Spin-Orbit Fields," Physical Review Letters 112, 056601 (2014)
• M. Luengo-Kovac et al., "Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities," Physical Review B 96, 195206 (2017)
• J. R. Iafrate et al., "Effect of modified periodic waveforms on current-induced spin polarization measurements," AIP Advances 8, 065133 (2018)

Templated quantum dots and photonic crystal cavities

Semiconductor quantum dots are a promising system for implementing quantum information processing. However, self-assembled dots are typically randomly distributed, while some applications would benefit from precise dot placement. We have shown that focused-ion-beam templating can be used to produce optically-active quantum dots at desired locations.

For more information about this work, please see:

• T. W. Saucer et al., "Photoluminescence of patterned arrays of vertically stacked InAs/GaAs quantum dots," Solid State Communications 151, 269-271 (2011)
• J.-E. Lee et al., "Photoluminescence Imaging of Focused Ion Beam Induced Individual Quantum Dots," Nano Letters 11, 1040-1043 (2011)
• J.-E. Lee et al., "Time-Resolved Two-Pulse Excitation of Quantum Dots Coupled to a Photonic Crystal Cavity in the Purcell Regime," Physical Review Letters 110, 013602 (2013)
• M. Luengo-Kovac et al., "Analyzing pattern retention for multilayer focused ion beam induced quantum dot structures," Journal of Vacuum Science & Technology B 31, 031208 (2013)
• T. W. Saucer et al., "Optimizing nanophotonic cavity designs with the gravitational search algorithm," Optics Express 21, 20831-20836 (2013)