Scott A. Crooker

Technical Staff Member
National High Magnetic Field Laboratory
Ph.D., Physics, University of California, Santa Barbara, 1997
B.A., Physics, Cornell University, 1992

Address:
National High Magnetic Field Laboratory
Los Alamos National Laboratory
Mail Stop E536
Los Alamos, New Mexico 87545    USA

Phone: (505) 665-7595
Lab: (505) 667-4323
Fax: (505) 665-4311
e-mail: crooker _at_ lanl.gov

Here's a link to my 'official' NHMFL page

 

Current Research Projects

Spin noise spectroscopy of electron and hole spins in semiconductors. Using methods for ultrasensitive magneto-optical Faraday rotation, we passively "listen" to the intrinsic, stochastic magnetization fluctuations that exist in an equilibrium spins system (in our case, electrons and holes trapped in InGaAs self-assembled quantum dots, and also in bulk n-type GaAs).  In accord with the fluctuation-dissipation theorem, we study how these fluctuations alone can be used to perform detailed magnetic resonance of the system under study, without ever perturbing the system away from thermal equilibrium [e.g., Phys. Rev. Lett (2012), Phys. Rev. Lett (2010), Phys. Rev. B (2009) & Nature (2004); Phys. Rev. A (2006) & Phys. Rev. A (2006)].  (in collaboration with theoreticians Darryl Smith and Nikolai Sinitsyn at Los Alamos).

Spin-polarized excitons in colloidal semiconductor nanocrystal quantum dots and magnetically-doped nanocrystals are investigated with static- and time-resolved polarized photoluminescence spectroscopy in high magnetic fields and low temperatures [e.g., Nature Nanotechnology (2012), Phys. Rev. Lett. (2011), Nature Materials (2009), Htoon et al Phys Rev. Lett. (2009) & PRB (2008); Furis et al J. Phys. Chem. B (2005)].  In other studies, we resonantly photoinject spin-up or spin-down excitons into CdSe nanocrystals at high magnetic fields, and detect the near-resonant  polarized emission from nearby exciton spin levels, with an aim of revealing the "fine structure" within the exciton states in nanocrystals [Furis et al  Phys. Rev. B Rapid Comm (2006)].  Polarization-resolved, low-temperature, high-B, single-nanocrystal PL microscopy studies are also currently underway [e.g., Htoon et al, PRB (2007)] (in collaboration with the group of  Dr. Victor Klimov at Los Alamos).

2-D imaging of optically- and electrically-injected spin currents in semiconductors for "spintronic" applications.  Using techniques for scanning magneto-optical Kerr-rotation microscopy, we spatially image the injection, lateral transport, and manipulation of spin-polarized electrons in GaAs.  The drift, diffusion, and precession of optically-injected spins are imaged in the presence of applied electric, magnetic, and strain fields, applied individually or in combination [Crooker et al, PRL (2005); Hruska et al, PRB (2006); Furis et al, New J. Physics (2007)].  Similar techniques are used to image and investigate electrically-injected spin currents in hybrid Fe/GaAs ferromagnet-semiconductor spin transport devices.  Measurements reveal efficient electrical spin injection, spin transport and manipulation, spin accumulation, and electrical spin detection in single devices  [Crooker et al PRB Rapid Comm (2009)Science (2005); X. Lou et al PRL (2006); X. Lou et al Nature Physics (2007)] (in collaboration with Prof. Paul Crowell at U. Minnesota and Prof. Chris Palmstrom at UCSB).

Ultrafast terahertz spectroscopy of correlated-electron systems in high magnetic fields.  We developed miniature, fiber-coupled THz emitters and gated photodetector antennas for use directly in the cryogenic bore of a high-field magnet [Gao & Crooker Appl. Phys. Lett (2006) & Crooker Rev. Sci Inst. (2002)].  These allow determination of high-frequency complex conductivities in the range 100-1500 GHz.  Topics of investigation include the THz dynamics of high Tc superconducting films in large magnetic fields to 18 T, and the frequency-dependent dynamics of electrons through the magnetic-field-driven metal-insulator transition in low-doped metals such as n:InSb.

Aharonov-Bohm phases in carbon nanotubes using ultrahigh magnetic fields (with the group of Prof. Junichiro Kono at Rice University).  Single-walled carbon nanotubes align in high magnetic fields, allowing magnetic flux to thread the nanotube bore. Using visible and NIR optical spectroscopy in ultrahigh pulsed magnetic fields to 75 Tesla, we investigate how this threaded flux leads to additional Aharonov-Bohm phases in the wavefunctions of nanotube excitons, which manifest as splitting of the spectral absorption peaks. [e.g., Zaric et al., Physica E 2005; PRL (2006).; Shaver et al, PRB Rapid Comm (2008)].

Charged excitons in II-VI (magnetic) 2D electron gases (with the groups of Prof. Dmitri Yakovlev (U. Dortmund) and Prof. Wolfgang Ossau (U. Wuerzburg) in Germany). We investigate singlet and triplet states of charged excitons (a correlated state of one hole + two electrons) in CdTe- and ZnSe-based quantum wells. We use low-temperature spin-polarized photoluminescence (PL), absorption, reflection, and PL excitation spectroscopy in pulsed magnetic fields to 50 Tesla (high fields drive the formation of spin-aligned triplet states).  Recent studies reveal the theoretically-predicted existence of an optically "dark" (forbidden) triplet ground state in the limit of large fields [e.g., Crooker & Samarth APL (2007); Astakhov et al., PRB Rapid Comm. (2005); Keller et al, PRB (2005)].

Experimental Techniques & Capabilities

Group Members

some  photos...


Bill Rice (Director's - funded Postdoctoral Fellow; Ph.D.: Rice University), Luyi Yang (Ph.D.: UC Berkeley) and honorary group member fellow staff scientist Dwight Rickel .

Bill measures optically induced & emergent magnetization in complex oxide materials and in colloidal nanocrystals.

Luyi listens very, very carefully for spontaneous spin noise of electrons and holes trapped in semiconductor quantum dots. Using lasers, of course.

Alumni: Yan Li (now Professor at U. Utah), Lili Cheng, Xuan Gao (now Professor at Case-Western University), Madalina Furis (now Professor at University of Vermont), Todd Barrick (now Staff Scientist, Sandia National Laboratory), Quinn McCulloch (LANL), Jin-Young Sohn (Korea), Nicolas Negre (France).

Journal Publications

Submitted/in press

Published

Selected Conference Publications

Tuning magnetic disorder in diluted magnetic semiconductors using high fields to 89 teslaS. A. Crooker, N. Samarth, Int'l J. Modern Physics B 23, 2575 (2009) . High Magnetic Fields in Semiconductor Physics (HMF-18;  Sao Pedro, Brazil, August 2008).

High field magneto-optical spectroscopy of highly aligned individual and ensemble single-walled carbon nanotubes, J. Shaver, A. Srivastava, J. Kono, S. A. Crooker, H. Htoon, V. I. Klimov, J. A. Fagan, E. K. Hobbie, N. Ubrig, O. Portugall, V. Perebeinos, P. H. Avouris, Int'l J. Modern Physics B 23, 2667 (2009) High Magnetic Fields in Semiconductor Physics (HMF-18;  Sao Pedro, Brazil, August 2008).

Trion states in a dense 2D electron gas, VP Kochereshko, AA Klochikhin, SA Crooker, G Karczewski, J Kossut,  Phys. Stat. Sol. (c) 6,  516  (2009) 9th Int'l Workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors, May 26-29, 2008 Klink, Germany

Many body effects in the optical behavior of quantum well excitons, VP Kochereshko, DA Andronikov, AA Klochikhin, SA Crooker, G Karczewski, J Kossut Phys. Stat. Sol. (c) 5, 2404 (2008); 10th Int'l Conf. on Optics of Excitons in Confined Systems, Sept 10-13, 2007 Messina, Italy

Multielectron processes in the optics of two-dimensional excitons, VP Kochereshko, DA Andronikov, AA Klochikhin, SA Crooker, G Karczewski, J Kossut, AIP Conference Proceedings 893, 405 (2007); ICPS-28, Vienna Austria, July 24-28 2006.

Combined exciton-electron processes in two-dimensional electron gas, Andronikov, AA Klochikhin, GV Mikhailov, SA Crooker, G Karczewski, J Kossut, International Journal of Modern Physics B 21, 1535 (2007);

Behavior of excitons and trions in CdTe/CdMgTe quantum-well structures with variations in temperature, DA Andronikov, M Fehr, VP Kochereshko, SA Crooker, G Karczewski, Physics of the Solid State 49, 1567 (2007);

Symmetry of trion states in modulation-doped CdTe/CdMgTe nanostructures under a high magnetic field, P. Tronc, D. Andronikov, V. Kochereshko, S. A. Crooker, and G. Karczewski Physica Stat. Sol. (b) 244, 669 (2007);

Exciton localization and Stokes' shift in ZnCdO thin films depending on chemical composition, HS Kang, SH Lim, JW Kim, HW Chang, GH Kim, JH Kim, SY Lee, Y. Li, JS Lee, JK Lee, MA Nastasi, SA Crooker, QX Jia, Journal of Crystal Growth 287, 70 (2006);

Optical property and Stokes' shift of ZnCdO thin films depending on Cd content. HS Kang, JW Kim, JH Kim, SY Lee, Y Li, JS Lee, JK Lee, MA Nastasi, SA Crooker, QX Jia, Journal of Applied Physics 99, 66113 (2006).

Magneto-optical spectroscopy of carbon nanotubes (invited), S Zaric, GN Ostojic, J Shaver, J Kono, X Wei, M Furis, SA Crooker, O Portugall, PH Frings, G Rikken, VC Moore, RH Hauge, and RE Smalley, Physica E 29, 469 (2005); 1st International Symposium on Nanometer-scale Quantum Physics, Jan. 26-28, Tokyo.

Multielectron processes in the optics of two-dimensional excitons, VP Kochereshko, DA Andronikov, SA Crooker, G Karczewski, J Kossut, Phys. Stat. Sol. (c) 3, 2485 (2006) 8th Int'l Workshop on Nonlinear Optics and Excitation Kinetics In Semiconductors (NOEKS 8), Feb 20-24, 2006 Munster Germany.

Measuring random spin fluctuations for perturbation-free probes of spin dynamics and magnetic resonance (invited), SA Crooker, DG Rickel, AV Balatsky, and DL Smith, Proc. Soc. Photo-Opt. Inst. Eng. (SPIE) 5843, 58 (2005);  SPIE Conf. on Fluctuations and Noise in Materials II; May 24-25, 2005; Austin, TX.

Exciton spin states in nanocrystal quantum dots revealed by spin-polarized resonant photoluminescence and Raman spectroscopy (invited), M Furis, T Barrick, P Robbins, SA Crooker, M Petruska, V Klimov, and AL Efros, International Journal of Modern Physics B 18, 3769-74 (2004); 16th Conf. on High Magnetic Fields in Semiconductor Physics (Semi-Mag 16), 2-6 Aug. 2004, Tallahassee.

Interband magneto-spectroscopy of a high-density two-dimensional electron gas in a strong in-plane magnetic field, YD Jho, X Wang, FV Kyrychenko, DH Reitze, CJ Stanton, J Kono, X Wei, SA Crooker, C Kadow, and AC Gossard, International Journal of Modern Physics B 18, 3831-4 (2004); 16th Conf. on High Magnetic Fields in Semiconductor Physics (Semi-Mag 16), 2-6 Aug. 2004, Tallahassee.

Time domain terahertz spectroscopy of the magnetic field induced metal-insulator transition in n:InSb, JY Sohn, XPA Gao, SA Crooker, AIP Conf. Proc. 772, 1216 (2005); 27th International Conference on the Physics of Semiconductors (ICPS-27); July 26-30, 2004; Flagstaff, AZ.

Excitons and trions in heavily doped QWs at high magnetic fields, V Kochereshko, D Andronikov, and G Karczewski, SA Crooker, AIP Conf. Proc. 772, 983-984 (2005); 27th International Conference on the Physics of Semiconductors (ICPS-27); July 26-30, 2004; Flagstaff, AZ.

Spin-polarized PL and Raman spectroscopy of nanocrystal quantum dots in high magnetic fields, M.Furis, PD Robbins, T Barrick, M. Petruska, VI Klimov, and SA Crooker, AIP Conf. Proc. 772, 709 (2005); 27th International Conference on the Physics of Semiconductors (ICPS-27); July 26-30, 2004; Flagstaff, AZ.

Excitons and trions in heavily doped QWs at high magnetic fields, Kochereshko, VP; Andronikov, DA; Karczewski, G; Crooker, SA, Physica Status Solidi C 2, 877 (2005); 4th International Conf. on Physics of Light-Matter Coupling in Nanostructures (PLMCN4); 2004; St. Petersburg, Russia.

Interband magnetoabsorption study of the shift of the Fermi energy of a 2DEG with an in-plane magnetic field, FV Kyrychenko, YD Jho, J Kono, SA Crooker, GD Sanders, DH Reitze, CJ Stanton, X Wei, C Kadow, AC Gossard, Physica E 22, 624 (2004); 15th International Conf. on Electronic Properties of 2D Systems (EP2DS-15), July 14-18 2003; Nara, Japan.

Identification of singlet and triplet states of negatively charged excitons in CdTe-based quantum wells, Astakhov, GV; Yakovlev, DR; Crooker, SA; Ossau, W.; Christianen, PCM; Rudenkov, VV; Karczewski, G.; Wojtowicz, T.; Kossut, J. Phys. Stat. Sol. C 1, 551-4 (2004); 8th Conference on Optics of Excitons in Confined Spaces, 15-17 Sept. 2003, Lecce, Italy.

Ultrafast Coherent Terahertz Spectroscopy in High Magnetic Fields and Directed Energy Flows in Quantum Dot Assemblies (invited), SA Crooker, T Barrick, JA Hollingsworth, and VI Klimov, Acta Physica Polonica A 104, 113 (2004); 32nd International School of Semicond. Compounds; June 2003; Jaszowiec, Poland.

Modulation of Energy Band Gap of ZnO Thin Films Grown by Pulsed Laser Deposition, SY Lee, Y Li, JS Lee, JK Lee, M Nastasi, SA Crooker, QX Jia, HS Kang, and JS Kang, MRS Proceedings 764, 413 (2003); New Applications for Wide-Bandgap Semiconductors; April 22-24, 2003, San Francisco, CA.

Singlet and triplet states of charged excitons in ZnSe-based QWs probed by high magnetic fields, DR Yakovlev, GV Astakhov, W Ossau, Q McCulloch, SA Crooker, and AB Dzyubenko, SPIE Proceedings 5023, 529 (2003); 10th International Symposium on Nanostructures; June 17-21 2002; St. Petersburg, Russia.

II-VI quantum wells with high carrier densities and in high magnetic fields, DR Yakovlev, GV Astakhov, W Ossau, SA Crooker, and A Waag, NATO Science Series II: 119, 137 (2003), NATO Adv. Res. Workshop on Optical Properties of 2D Systems with Interacting Electrons; June 2002; St. Petersburg, Russia.

Positively and negatively charged trions in ZnSe-based quantum wells, W Ossau, G Astakhov, DR Yakovlev, W Faschinger, VP Kochereshko, J Puls, F Henneberger, SA Crooker, Q McCulloch, and A Waag, NATO Science Series II 119, 41 (2003); NATO Adv. Res. Workshop on Optical Properties of 2D Systems with Interacting Electrons; June 2002; St. Petersburg, Russia.

Ultrafast coherent terahertz spectroscopy in high magnetic fields, SA Crooker and AJ Taylor, Int. J. of Modern Physics B 16, 3385 (2002); Physical Phenom. at High Mag. Fields IV, Oct. 19-25, 2001, Santa Fe, NM.

High magnetic field optical studies of charged exciton in CdTe 2D electron gases, N Negre, SA Crooker, A Wojs, and G Karczewski, International Journal of Modern Physics B 16, 2972 (2002),Physical Phenomena at High Magnetic Fields IV, Oct. 19-25, 2001, Santa Fe, NM.

Exciton diamagnetic shifts and magnetic field dependent linewidths in ordered and disordered InGaP alloys, Y Zhang, ED Jones, KK Bajaj, G Coli, SA Crooker, A Mascarenhas, and JM Olsen, MRS Proceedings 692, 313 (2001); Prog. in Semicond. Materials for Optoelectronic Applications; Nov 26-29, 2001; Boston, MA.

Trions in ZnSe-based quantum wells probed by 50 T magnetic fields, DR Yakovlev, GV Astakhov, W Ossau, SA Crooker, K Uchida, N Miura, A Waag, NA Gippius, AY Sivachenko, and AB Dzyubenko, Physica Status Solidi B 227, 353-63 (2001); Mini-Workshop on Trion Physics, 6-7 April 2001, Berlin, Germany.

High magnetic field optical studies of 2DEG in modulation-doped ZnSe quantum wells, W Ossau, DR Yakovlev, GV Astakhov, A Waag, CJ Meinig, HA Nickel, BD McCombe, and SA Crooker, Physica E 12, 512 (2002); 14th International Conf. on the Elec. Properties of 2-D Systems (EP2DS-14); Jul 30-Aug 3 2001, Prague, Czech Republic.

Optical spectroscopy of magnetic 2D electron gases at the Los Alamos pulsed magnetic field facility (invited), SA Crooker, DG Rickel, E Johnston-Halperin, DD Awschalom, R Knobel, N Samarth, SK Lyo, and A Efros, Physica B 298, 369 (2001); 14th International Conf. on High Magnetic Fields in Semiconductor Physics (Semi-Mag 14), Sept. 2000, Matsue, Japan.

Stability of charged excitons in strongly spin-polarized magnetic 2D electron gases, SA Crooker, E Johnston-Halperin, DD Awschalom, R Knobel, and N Samarth, Springer Proc. Phys. 87, 961-962 (2001), 25th International Conf. on the Physics of Semiconductors (ICPS-25); September 17-22, 2000; Osaka, Japan.

Spin-polarized quantum transport and magnetic field-dependent carrier density in magnetic two-dimensional electron gases, R Knobel, N Samarth, SA Crooker, and DD Awschalom, Physica E 6, 786-9 (2000), 13th International Conf. on the Electronic Properties of 2-D Systems (EP2DS-13); Aug 1-6, 1999; Ottawa, Canada.

Optical signatures from magnetic two-dimensional electron gases in magnetic fields to 60 T, SA Crooker, DG Rickel, IP Smorchkova, N Samarth, JM Kikkawa, and DD Awschalom, J. of Applied Physics 85, 5932 (1999), 43rd Annual Conference on Magnetism and Magnetic Materials, Nov 9-12, 1998, Miami, FL.

Spin transport and optically-probed coherence in magnetic semiconductor heterostructures, IP Smorchkova, FS Flack, N Samarth, JM Kikkawa, SA Crooker, and DD Awschalom, Physica B 249-251, 676 (1998), 12th International Conf. on the Elec. Properties of 2-D Systems (EP2DS-12), Sept. 22-26, 1997, Tokyo, Japan.

Growth dynamics and exciton localization in strained CdSe quantum structures, FS Flack, A Hunt, H Hennessey, N Samarth, J Levy, V Nikitin, SA Crooker, DD Awschalom, and M AlJassim, MRS Proceedings 417, 169-174 ; Optoelectronic Materials Symposium; Nov 28-30 1995; Boston, MA.

Ultrafast coherent transfer of spin angular momenta in magnetic semiconductor quantum wells, SA Crooker, JJ Baumberg, F Flack, N Samarth, and DD Awschalom, 23rd International Conference on the Physics of Semiconductors, p697, 21-26 July 1996, Berlin, Germany.

Spin beats and magnetic dynamics in II-VI quantum structures, J. J. Baumberg, S. A. Crooker, D. D. Awschalom, N. Samarth, Materials Science Forum 182-184, 429-434 (1995), Proceedings of the 4th International Workshop on Semimagnetic (Diluted Magnetic) Semiconductors; Sep 26-28 1994; Linz, Austria

Selected Invited Presentations

Optically-induced persistent magnetization in oxygen-deficient strontium titanate, SPIE Optics and Photonics Conference, San Diego, CA (August 25-29, 2013)

Listening to the spin noise of electrons and holes in semiconductor quantum dots, Int'l Conference on Spin-Optronics (ICSO-2013), Toulouse, France (June 10-14, 2013)

Magneto-optical spectroscopy of organic interfaces, Organic Solar Cells, Santa Fe, NM (May 6-8, 2013)

Listening to the spin noise of holes coupled to nuclear spin baths in semiconductor quantum dots, SPIE Photonics West, San Francisco, CA (February 4-7, 2013)

Long-lived photomagnetization in copper-doped ZnSe nanocrystals, SPIE Optics and Photonics Conference, San Diego, CA; (August 12-17, 2012)

Magnetic textures in quantum magnets in nondestructive 100+ Tesla fields, High Magnetic Fields in Semiconductor Physics (HMF-20), Chamonix, France (July 22-27, 2012)

"Listening" to the spin noise of electrons and holes in semiconductors, 4th Int'l Nano-MRI Conference, Ascona, Switzerland, (July 22-27, 2012)

"Listening" to the spin noise of electrons and holes in semiconductors, 41st "Jaszowiec" International School and Conference on the Physics of Semiconductors, Krynica, (Poland June 10, 2012)

"Listening" to the spin noise of electrons and holes in semiconductors, Department of Physics, Texas A&M University, College Station, TX (March 23, 2012)

"Listening" to the spin noise of electrons and holes in semiconductors, Department of Physics, Rice University, Houston, TX (March 22, 2012)

"Listening" to the spin noise of electrons and holes in semiconductor quantum structures, Department of Physics, Ohio State University, Columbus, OH (January 19, 2012)

"Listening" to the spin noise of electrons and holes in semiconductor quantum structures, Oregon Center for Optics, University of Oregon, Eugene, OR (November 7, 2011)

"Listening" to the spin noise of electrons and holes in semiconductor quantum structures, Argonne National Laboratory, Argonne, IL (October 26, 2011)

"Listening" to the spin noise of electrons and holes in semiconductor quantum structures, 2011 SPIE Optics and Photonics, San Diego, CA (August 20-23, 2011)

"Listening" to the spin noise of electrons and holes in InGaAs quantum dots, 2011 APS March Meeting, Dallas, TX (March 20-25, 2011)

Tunable coupling of electronic and magnetic degrees of freedom in colloidal nanocrystals, 2010 MRS Fall Meeting, Boston (November 28-December 3, 2010)

"Listening" to the spin noise of electrons and holes in semiconductors, Department of Physics Colloquium, University of Buffalo, Buffalo NY, October 7, 2010.

"Listening" to the spin noise of electrons and holes in semiconductors, Department of Electrical Engineering Colloquium, University of Rochester, Rochester NY, October 6, 2010.

"Listening" to the spin noise of electrons and holes in semiconductors, Laboratoire National des Champs Magnetiques Intenses, Toulouse, France, September 20 (2010)

"Listening" to the spin noise of electrons and holes in semiconductors, High Magnetic Field Laboratory, Grenoble, France, September 22 (2010)

Imaging spin injection and spin transport in semiconductors, DPG Physics School on Nano-Spintronics, Bad Honnef, Germany, September 15 (2010)

"Listening" to the spin noise of electrons and holes in semiconductors, DPG Physics School on Nano-Spintronics, Bad Honnef, Germany, September 17 (2010)

"Listening" to the spin noise of electrons and holes in semiconductors, 6th Int'l Conf. on Phys. and Appl. of Spin-Related Phenomena in Semiconductors (PASPS-6), Tokyo, Japan, (August 1-4, 2010)

Spin physics and exciton fine structure in semiconductor nanocrystals, Center for Advanced Solar Photophysics, Los Alamos, NM, March 8 (2010)

"Listening" to the spin noise of electrons and holes in semiconductors, Condensed Matter Seminar, UC San Diego (February 3, 2010)

Efficient electrical spin detection and optical spin noise spectroscopy, Seminar, Tohoku University, Sendai, Japan (December 9, 2009)

Optical spectroscopy of magnetic semiconductors in pulsed fields to 89 tesla, 6th IMR International Symposium on High Magnetic Field Spin Science in 100T, Sendai, Japan (Dec. 8, 2009)

Imaging the injection and flow of spin-polarized electrons in semiconductors, Seminar, Technical University of Dortmund, Dortmund, Germany (October 7, 2009)

Toward efficient electrical spin detection in lateral spin-transport devices, Symposium on Spin Manipulation in Solid-State Systems, Wurzburg, Germany (October 8-9, 2009)

Tunable magnetic exchange interactions in magnetically-doped core/shell nanocrystals, Excited State Processes in Electronic and Bio-nanomaterials (ESP-2009), Santa Fe, New Mexico  (June 29-July 2, 2009)

Toward efficient electrical spin detection in lateral spin-transport devices, Spins in Organic Semiconductors (SPINOS-2009), Salt Lake City, Utah (Feb. 4-7, 2009)

Imaging spin injection and transport in semiconductor spintronic devices, Optics Seminar, University of Oregon, Eugene OR  (Feb. 2, 2009)

Exciton fine structure in semiconductor nanocrystals using high-field and single-dot spectroscopy, DOE/BES program review, AMOS-2008, Warrington, VA (September 14-17, 2008)

Tuning magnetic disorder in diluted magnetic semiconductors using high fields to 89 T, High Mag. Fields in Semiconductor Physics (HMF-18), Sao Pedro, Brazil (August 3-8, 2008)

Imaging spin injection and spin transport in semiconductors, CLEO/QUELS 2008, San Jose, CA  (May, 2008)

Imaging the drift and diffusion of optically- and electrically-injected spins in semiconductors, APS March Meeting 2008, New Orleans, LA (March, 2008)

Imaging spin injection in ferromagnet/semiconductor spin transport devices, Experimental Condensed Matter Physics Seminar, Ohio State University (February 8, 2008)

Spin injection, transport, and imaging in epitaxial Fe/GaAs devices, 35th Conf. on the Physics and Chemistry of Semiconductor Interfaces (PCSI-35) (January 13-17, 2008, Santa Fe, NM)

Imaging spin flows in Fe/GaAs electrical spin injection and detection, 2007 Materials Research Society (MRS) Fall Meeting  (Boston, November 26-27,  2007)

Tuning the sign and sensitivity of Fe/GaAs electrical spin detectors [selected for contributed talk], SPINTECH-IV, (Maui, June 20-22, 2007)

Imaging spin injection and spin transport in lateral Fe/GaAs devices, Optical Properties of Low Dimensional Semiconductors (OPLDS-2007) (Ottawa, May 2007)

Imaging the injection and flow of spin polarized electrons in ferromagnet-semiconductor devices, Condensed Matter Seminar, Naval Research Laboratory (March 29, 2007)

Imaging spin injection in semiconductors, Condensed Matter Physics Seminar, Dept. of Physics, University of Pennsylvania  (March 28, 2007)

Imaging the injection and flow of spin polarized electrons in ferromagnet-semiconductor devices, Condensed Matter Seminar, Princeton University (March 26, 2007)

Imaging the injection and flow of spin polarized electrons in ferromagnet-semiconductor devices, Physics, Chemistry & Nanosciences Colloquium, Sandia National Laboratory, (March 21, 2007)

Imaging the injection and flow of spin polarized electrons in ferromagnet-semiconductor devices, Condensed Matter Seminar, Dept. of Physics, UC San Diego (Dec. 2006)

Imaging electrical spin injection in lateral ferromagnet-semiconductor devices, AVS 53rd International Symposium, (November 12-17, 2006, San Francisco, CA)

Imaging spin transport in lateral ferromagnet/semiconductor structures, 28th International Conference on the Physics of Semiconductors (ICPS-28) (July 2006, Vienna, Austria).

Imaging electrical spin injection and spin flow in ferromagnet-semiconductor devices (Plenary), 14th International Symp. on Nanostructures: Physics and Technology (St. Petersburg, Russia, June 2006).

Spectroscopy of spontaneous spin noise in atomic and solid state systems, Gordon Research Conference on Ultrafast Phenomena in Correlated Systems, February 2006 (Buellton, CA).

Imaging spin transport in lateral ferromagnet-semiconductor devices, Nanoscience Seminar, UC Riverside, January 2006.

Imaging the flow of spin-polarized electrons in semiconductors, Department of Physics Colloquium, UC Santa Cruz, January 2006.

Imaging electrical spin injection and spin flow in ferromagnet/semiconductor devices, Solid State and Optics Seminar, Yale University, October 5, 2005.

Imaging the flow of electron spins in semiconductors in the presence of electric, magnetic and strain fields, 16th International Conf. on Elec. Prop. of 2-D Systems (EP2DS-16), July 10-15, 2005, Albuquerque, NM.

Imaging spin flows in semiconductors in the presence of electric, magnetic, and strain fields, Exciton-Electron Interactions in Semiconductor Nanostructures, May 29-June 2, 2005, Bad Honnef, Germany.

Imaging spin flows in semiconductors in the presence of electric, magnetic, and strain fields, High Magnetic Field Laboratory, May 27, 2005, Radboud University, Nijmegen, The Netherlands.

 Measuring random spin fluctuations for perturbation-free probes of spin dynamics and magnetic resonance, 3rd SPIE International Symposium on Fluctuations and Noise, May 24-25, 2005, Austin, TX.

Spectroscopy of spontaneous spin noise for probes of spin dynamics and magnetic resonance, APS March Meeting 2005 (Los Angeles, CA).

Imaging spin flows in semiconductors, 35th Winter Colloquium on the Physics of Quantum Electronics (PQE-2005), Jan 2-6, 2005, Snowbird, UT.

Spin noise spectroscopy as a probe of magnetic resonance, Condensed, Atomic, and Molecular Physics Seminar, Pennsylvania State University, December 7, 2004.

Engineered energy flows in nanocrystals quantum dot assemblies, 34th Winter Colloquium on the Physics of Quantum Electronics (PQE-2004), Jan 4-8, 2004, Snowbird, UT.

High magnetic field terahertz spectroscopy of semiconductors and superconductors, 11th IEEE International Conf. on Terahertz Electronics (THz 2003), September 24-26, 2003, Sendai, Japan.

Terahertz spectroscopy in high magnetic fields and directed energy flows in quantum dot assemblies, 32nd International School of Semiconducting Compounds, May 30-June 6, 2003, Jaszowiec, Poland.

II-VI Heterostructures, Quantum Dots, and THz spectroscopy in high magnetic fields to 60 T, University of Wuerzburg , May 28, 2003.

Towards engineered energy flows in quantum dot assemblies, APS March Meeting 2003 (Austin, TX).

Dynamics of Exciton Transfer in Semiconductor Quantum-Dot Assemblies, Optical Society of America 18th Laser Science Conference (LS-XVIII), Sept 29-Oct 3, 2002, Orlando, FL.

Optical spectroscopy of magnetic 2-D electron gases at the Los Alamos pulsed magnetic field facility, 14th International Conf. on High Magnetic Fields in Semiconductor Physics, Sept 24-29, 2000, Matsue, Japan.

Static and time-resolved optical spectroscopies in pulsed fields: Magnetic 2-D electron gases to 60 Tesla, APS March Meeting 1999 (Atlanta, GA).

Collaborators