M. L. W. Thewalt, A. Yang, M. Steger, T. Sekiguchi, K. Saeedi, Dept. of Physics, Simon Fraser University, Burnaby BC, Canada V5A 1S6 T. D. Ladd, E. L. Ginzton Laboratory, Stanford University, Stanford CA, USA (now HRL) K. M. Itoh, Keio University, Yokohama, Japan H. Riemann, N. V. Abrosimov, IKZ, Berlin, Germany A. V. Gusev, A. D. Bulanov, ICHPS, Nizhny Novgorod, Russia A. K. Kaliteevskii, O. N. Godisov, “Centrotech-ECP”, St Petersburg, Russia P. Becker, PTB, Braunschweig, Germany H.­J. Pohl, VITCON Projectconsult GmbH, Jena, Germany J. J. L. Morton, Oxford, UK S. A. Lyon, Princeton, USA Avogadro Project Highly Enriched 28 Si – new frontiers in semiconductor spectroscopy SILICON – 2010 Nizhny Novgorod

E T 0 R.T. bare E G actual E G E G depends on M due to zero point motion ΔE The renormalization goes as M -1/2 recent review: Cardona and Thewalt Reviews of Modern Physics 77, 1173 (2005) Natural Si: 92.2% 28 Si + 4.7% 29 Si + 3.1% 30 Si I = 0 I = ½ I = 0 Why does the isotopic composition affect electronic and optical properties? the electron-phonon interaction E g (0) increases by ~2 meV from 28 Si to 30 Si ~62 meV for nat Si

D. Karaiskaj et al., Phys. Rev. Lett. 86, 6010 (2001) [ FWHM < cm -1 ] P BE Boron BE The spectroscopic challenge of highly enriched 28 Si ( 8 cm -1 ~ 1 meV )

Boron BE 200 neV !

a Improved shallow bound exciton linewidths – observation of the 31 P ground state hyperfine splitting in the donor bound exciton transition. Phys. Rev. Lett. 97, (2006). Nuclear and electron spin readout… 31 P prime Si qubit candidate can we use this to polarize the spins? Initialization problem

Almost zero equilibrium polarization Hyperpolarization using optical pumping Phys. Rev. Lett. 102, (2009)

Resolved bound exciton hyperfine spectroscopy gives the populations of all four donor hyperfine levels in a single measurement Nuclear polarization of 76% and electronic polarization of 90% are achieved simultaneously – in less than 1 second! Higher polarization should be possible with reduced linewidths New experiments: NMR on dilute 31 P in 28 Si using optical polarization and optical nuclear spin readout

CW NMR

Why 845 Gauss? Schematic energy diagram Magnetic field (nonlinear) Max MHz Min MHz 844.9G34,043G A = MHz Energy (nonlinear) A g e = g 31 P = e, 31 P            

Magnetic Field Dependence

transient NMR - Rabi Oscillations

First pulsed NMR - Ramsey Fringe Experiment  /2  Lasers on (polarizing) measurement off RF pulses on off RF freq. = Resonance freq. +/– 1 kHz  fringes of 1 kHz signal

Ramsey Fringes Temperature (Pressure) dependence Pump 8(  ), Probe 10(  ), ; RF  = 55,847,712 Hz; probe pump RF     

31 P Donor Hyperfine Constant meme RF freq. (Hz) Fringe freq. (Hz) NMR freq. (Hz)  55,845,712.01, ,846,736.8(1) 55,847, Σ = 2,000.3  61,676,172.01, ,677,199.1(1) 61,678, Σ = 2,000.1  Hyperfine constant A = (2) MHz at T=1.3K [existing value (2) MHz]  At 4.2 K and 1 atm, A is kHz (26.5 ppm) lower! Why?  At T=1.3K (P=1.0Torr)

Pulsed NMR —Hahn echo method—  /2  Lasers (Pump&Probe) on measurement off RF pulses on off f RF = f NMR Signal decay with 2   measurement of T 2 PL signal rotation for optical readout refocusing (initialization)  

T 2 from Hahn Echo Method probe pump RF       T 2 = 250 ms 2  (ms) PL intensity Pump 6(  ), Probe 4(  ); RF  = 61,677,199 Hz; B = G, T = 1.3 K (P = 1.0 Torr)

Highly Enriched 28 Si – new frontiers in semiconductor spectroscopy Resolved donor bound exciton hyperfine structure: - optical readout of 31 P electron and nuclear spin - fast optical hyperpolarization of electron and nuclear spin - possibility of single donor readout - promising new approaches to silicon quantum computing - have begun NMR of 31 P in 28 Si combining optical readout and optical hyperpolarization Studies which were thought to be limited to isolated single atoms and ions in vacuum are now becoming possible in semiconductors.