Spintronics and Quantum Information Processing are currently two central issues in the physics and applications of semiconductors. They can have tremendous impact on future information technology by revolutionizing the way we process and store information.

“Spintronic” devices are those in which the spin degree of freedom of the electron is actively used in addition to, or in place of, the charge (orbital) degrees of freedom. Expected improvements to conventional charge-based devices include nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities. Electron spins in semiconductors have been recognized as the ideal medium on which to encode quantum bits (or “qubits”) due to their very long spin lifetimes as demonstrated by recent experiments. It is also expected that electronic, magnetic, and photonic functions can be incorporated into single devices to create spin-based multifunctional devices.

Magnetic III-V semiconductors (e.g., InMnAs and GaMnAs), first grown by Hiroo Munekata in 1989, have emerged as a prime candidate for these innovative device applications, demonstrating carrier-inducedferromagnetism, sensitive to applied electric fields and light. We are investigating various aspects of magneto-optical properties of InMnAs, InGaMnAs, and GaMnAs, particularly ultrafast optical manipulation of ferromagnetism.

Successful exploitation and manipulation of spins is desired for these revolutionary device ideas as well as for the solid-state realization of quantum information processing, computation and communications. Because of the carrier-induced nature of ferromagnetism in (III,Mn)V ferromagnets, carrier-density-tuning is the key to the successful manipulation of ferromagnetic order. Here, we create a large density of spin-polarized transient carriers within the InMnAs magnetic layer using intense 140 fs mid-infrared pulses, and then time-resolved magneto-optical Kerr effect spectroscopy is used to monitor the transient magnetic properties induced by the photogenerated carriers.

Review Article:

J. Wang et al., “Ultrafast Magneto-Optics in Ferromagnetic III-V Semiconductors” (topical review), J. Phys.: Cond. Matt. 18, R501 (2006). (abstract, full text)

Regular Journal Articles:

C. Sun et al., “Anomalous Magneto-optical Kerr Hysteresis Loops in Fe0.25TaS2,” Phys. Rev. B 84, 224402 (2011). (abstract, full text)

C. Sun et al., “Above-Bandgap Magneto-optical Kerr Effect in Ferromagnetic GaMnAs,” Phys. Rev. B 83, 125206 (2011). (abstract, full text)

J. Wang et al., “Femtosecond Demagnetization and Hot-Hole Relaxation in Ferromagnetic Ga_1-xMn_xAs,” Phys. Rev. B 77, 235308 (2008). (abstract, full text)

H. Zhan et al., “Temperature Dependence of Terahertz Emission from InMnAs,” Appl. Phys. Lett. 90, 012103 (2007). (abstract, full text)

J. Wang et al., “Ultrafast Quenching of Ferromagnetism in InMnAs Induced by Intense Laser Irradiation,”Phys. Rev. Lett. 95, 167401 (2005). (abstract, full text)

G. D. Sanders et al., “Theory of Carrier Dynamics and Time-Resolved Reflectivity in InMnAs/GaSb Heterostructures,” Phys. Rev. B 72, 245302 (2005). (abstract, full text)

J. Wang et al., “Propagating Coherent Acoustic Phonon Wave Packets in InMnAs/GaSb,” Phys. Rev. B 72, 153311 (2005). (abstract, full text)

J. Wang et al., “Ultrafast Optical and Magneto-Optical Studies of III-V Ferromagnetic Semiconductors,” J. Mod. Opt. 51, 2771 (2004). (full text)

J. Wang et al., “Ultrafast Softening in InMnAs” (invited paper), Physica E 20, 412 (2004). (full text, erratum)

J. Wang et al., “Ultrafast Carrier Dynamics in Ferromagnetic InGaMnAs,” Superlattices and Microstructures34, 563 (2004). (full text)

G. A. Khodaparast et al., “Terahertz Dynamics of Photo-generated Carriers in Ferromagnetic InGaMnAs,” J. Appl. Phys. 93, 8286 (2003). (abstract, full text)

J. Wang et al., “Ultrafast Optical Manipulation of Ferromagnetic Order in InMnAs/GaSb,” J. Superconductivity16, 373 (2003). (full text)