32 research outputs found
Insulating Phases Induced by Crossing of Partially Filled Landau Levels in a Si Quantum Well
We study magnetotransport in a high mobility Si two-dimensional electron
system by in situ tilting of the sample relative to the magnetic field. A
pronounced dip in the longitudinal resistivity is observed during the Landau
level crossing process for noninteger filling factors. Together with a Hall
resistivity change which exhibits the particle-hole symmetry, this indicates
that electrons or holes in the relevant Landau levels become localized at the
coincidence where the pseudospin-unpolarized state is expected to be stable.Comment: 4 pages, 4 figure
Well-width dependence of valley splitting in Si/SiGe quantum wells
The valley splitting in Si two-dimensional electron systems is studied using
Si/SiGe single quantum wells (QWs) with different well widths. The energy gaps
for 4 and 5.3 nm QWs, obtained from the temperature dependence of the
longitudinal resistivity at the Landau level filling factor , are much
larger than those for 10 and 20 nm QWs. This is consistent with the well-width
dependence of the bare valley splitting estimated from the comparison with the
Zeeman splitting in the Shubnikov-de Haas oscillations.Comment: 3 pages, 2 figure
Metallic Behavior of Cyclotron Relaxation Time in Two-Dimensional Systems
Cyclotron resonance of two-dimensional electrons is studied at low
temperatures down to 0.4 K for a high-mobility Si/SiGe quantum well which
exhibits a metallic temperature dependence of dc resistivity . The
relaxation time shows a negative temperature dependence, which
is similar to that of the transport scattering time obtained from
. The ratio at 0.4 K increases as the electron
density decreases, and exceeds unity when approaches the critical
density for the metal-insulator transition.Comment: 4 pages, 3 figure
Electronic Transport Properties of the Ising Quantum Hall Ferromagnet in a Si Quantum Well
Magnetotransport properties are investigated for a high mobility Si two
dimensional electron systems in the vicinity of a Landau level crossing point.
At low temperatures, the resistance peak having a strong anisotropy shows large
hysteresis which is attributed to Ising quantum Hall ferromagnetism. The peak
is split into two peaks in the paramagnetic regime. A mean field calculation
for the peak positions indicates that electron scattering is strong when the
pseudospin is partially polarized. We also study the current-voltage
characteristics which exhibit a wide voltage plateau.Comment: 4 pages, 4 figure
Excitonic Aharonov-Bohm Effect in Isotopically Pure 70Ge/Si Type-II Quantum Dots
We report on a magneto-photoluminescence study of isotopically pure 70Ge/Si
self-assembled type-II quantum dots. Oscillatory behaviors attributed to the
Aharonov-Bohm effect are simultaneously observed for the emission energy and
intensity of excitons subject to an increasing magnetic field. When the
magnetic flux penetrates through the ring-like trajectory of an electron moving
around each quantum dot, the ground state of an exciton experiences a change in
its angular momentum. Our results provide the experimental evidence for the
phase coherence of a localized electron wave function in group-IV Ge/Si
self-assembled quantum structures.Comment: 4 pages, 4 figure
Room-temperature local magnetoresistance effect in n-Ge devices with low-resistive Schottky-tunnel contacts
Two-terminal local magnetoresistance (MR) effect in n-type germanium (Ge) based lateral spin-valve (LSV) devices can be observed at room temperature. By using phosphorus δ-doped Heusler-alloy/Ge Schottky-tunnel contacts, the resistance-area product of the contacts is able to be less than 0.20 kΩ μm 2 , which is the lowest value in semiconductor based LSV devices. From the one-dimensional spin drift-diffusion model, the interface spin polarization of the Heusler-alloy/Ge contacts in the present LSV devices can be estimated to be ∼0.018 at room temperature. We experimentally propose that it is important for enhancing the local MR ratio in n-Ge based LSV devices to improve the interface spin polarization of the Heusler-alloy/Ge contacts
Cubic Rashba spin-orbit interaction of two-dimensional hole gas in strained-Ge/SiGe quantum well
The spin-orbit interaction (SOI) of the two-dimensional hole gas in the
inversion symmetric semiconductor Ge is studied in a strained-Ge/SiGe quantum
well structure. We observed weak anti-localization (WAL) in the
magnetoconductivity measurement, revealing that the WAL feature can be fully
described by the k-cubic Rashba SOI theory. Furthermore, we demonstrated
electric field control of the Rashba SOI. Our findings reveal that the heavy
hole (HH) in strained-Ge is a purely cubic-Rashba-system, which is consistent
with the spin angular momentum mj = +-3/2 nature of the HH wave function.Comment: To be published in Phys. Rev. Let