[show abstract][hide abstract] ABSTRACT: We employ ultrafast pump-probe spectroscopy with photocurrent readout to
directly probe the dynamics of a single hole spin in a single, electrically
tunable self-assembled quantum dot molecule formed by vertically stacking
InGaAs quantum dots. Excitons with defined spin configurations are initialized
in one of the two dots using circularly polarized picosecond pulses. The
time-dependent spin configuration is probed by the spin selective optical
absorption of the resulting few Fermion complex. Taking advantage of sub-5 ps
electron tunneling to an orbitally excited state of the other dot, we
initialize a single hole spin with a purity of >96%, i.e., much higher than
demonstrated in previous single dot experiments. Measurements in a lateral
magnetic field monitor the coherent Larmor precession of the single hole spin
with no observable loss of spin coherence within the ~300 ps hole lifetime.
Thereby, the purity of the hole spin initialization remains unchanged for all
investigated magnetic fields.
[show abstract][hide abstract] ABSTRACT: Circularly polarized light is demonstrated to inject partially spin-polarized electrons and holes in bulk germanium via both direct and indirect optical transitions. While the degree of spin polarization is markedly reduced when compared to prototypical III-V semiconductors, coherent spin precessions in an external magnetic field are well resolved in ultrafast magneto-optics. At cryogenic temperatures, hole (electron) spins exhibit remarkably long coherence times of ~100 ps (~1 ns).
[show abstract][hide abstract] ABSTRACT: Electron spin relaxation times in n-doped as well as in nominally undoped bulk GaSb are measured with time-resolved circular dichroism and Faraday rotation induced by 1.55 µm, 150 fs pulses. Degenerately n-doped samples are characterized by ultrashort relaxation times of ~2 ps. In contrast, we find much larger time constants and a strong temperature dependence of the spin relaxation time in moderately n-doped and undoped GaSb. The longest spin relaxation time is found to be ~30 ps for an undoped sample at temperatures below T = 50 K. Many aspects of the results can be attributed to the large spin–orbit coupling in GaSb, consistent with the D'yakonov–Perel' theory of spin relaxation. In addition, magneto-optical measurements reveal an effective electronic Landé factor of |g*| = 9 ± 1.
Semiconductor Science and Technology 01/2009; 24(2):025018. · 1.92 Impact Factor