46 research outputs found
Magnetic moment of an electron gas on the surface of constant negative curvature
The magnetic moment of an electron gas on the surface of constant negative
curvature is investigated. It is shown that the surface curvature leads to the
appearance of the region of the monotonic dependence at low magnetic
fields. At high magnetic fields, the dependence of the magnetic moment on a
magnetic field is the oscillating one. The effect of the surface curvature is
to increase the region of the monotonic dependence of the magnetic moment and
to break the periodicity of oscillations of the magnetic moment as a function
of an inverse magnetic field.Comment: 4 pages, 1 figur
Observation of extremely slow hole spin relaxation in self-assembled quantum dots
We report the measurement of extremely slow hole spin relaxation dynamics in
small ensembles of self-assembled InGaAs quantum dots. Individual spin
orientated holes are optically created in the lowest orbital state of each dot
and read out after a defined storage time using spin memory devices. The
resulting luminescence signal exhibits a pronounced polarization memory effect
that vanishes for long storage times. The hole spin relaxation dynamics are
measured as a function of external magnetic field and lattice temperature. We
show that hole spin relaxation can occur over remarkably long timescales in
strongly confined quantum dots (up to ~270 us), as predicted by recent theory.
Our findings are supported by calculations that reproduce both the observed
magnetic field and temperature dependencies. The results suggest that hole spin
relaxation in strongly confined quantum dots is due to spin orbit mediated
phonon scattering between Zeeman levels, in marked contrast to higher
dimensional nanostructures where it is limited by valence band mixing.Comment: Published by Physical Review
Gallstone ileus in a middle-aged male with an atypical history: a case report
Currently, gallstone ileus is an unusual complication of cholelithiasis (0.3–3.0 %) and a rare cause of mechanical bowel obstruction (0.1–4.0 %). The rarity of the condition makes it impossible to plan the large prospective randomized clinical trials, so the analysis of case reports is significant for decision making in the management of gallstone ileus. We report a case of gallstone ileus in a middle-aged male who had a history of surgery for duodenal ulcer perforation in past. A combination of peptic ulcer disease and cholelithiasis is based on a reduced gastrointestinal hormones secretion. Clinical specialists need to consider information about the greater frequency and asymptomatic clinical course of gallstone disease against a background of duodenal ulcer. Duodenal ulcer scar and bulbar deformity may promote to the cholecystoduodenal fistula formation. In the presence of an acute bowel obstruction symptoms and the absence of gallbladder instrumental examination results, it is possible to recommend the prior gastroduodenoscopy for the pre-operative pneumobilia detection. The optimal surgical approaches for acute gallstone ileus are still controversial
Spin decoherence of a heavy hole coupled to nuclear spins in a quantum dot
We theoretically study the interaction of a heavy hole with nuclear spins in
a quasi-two-dimensional III-V semiconductor quantum dot and the resulting
dephasing of heavy-hole spin states. It has frequently been stated in the
literature that heavy holes have a negligible interaction with nuclear spins.
We show that this is not the case. In contrast, the interaction can be rather
strong and will be the dominant source of decoherence in some cases. We also
show that for unstrained quantum dots the form of the interaction is
Ising-like, resulting in unique and interesting decoherence properties, which
might provide a crucial advantage to using dot-confined hole spins for quantum
information processing, as compared to electron spins
Electrical control over single hole spins in nanowire quantum dots
Single electron spins in semiconductor quantum dots (QDs) are a versatile
platform for quantum information processing, however controlling decoherence
remains a considerable challenge. Recently, hole spins have emerged as a
promising alternative. Holes in III-V semiconductors have unique properties,
such as strong spin-orbit interaction and weak coupling to nuclear spins, and
therefore have potential for enhanced spin control and longer coherence times.
Weaker hyperfine interaction has already been reported in self-assembled
quantum dots using quantum optics techniques. However, challenging fabrication
has so far kept the promise of hole-spin-based electronic devices out of reach
in conventional III-V heterostructures. Here, we report gate-tuneable hole
quantum dots formed in InSb nanowires. Using these devices we demonstrate Pauli
spin blockade and electrical control of single hole spins. The devices are
fully tuneable between hole and electron QDs, enabling direct comparison
between the hyperfine interaction strengths, g-factors and spin blockade
anisotropies in the two regimes
Semiconductor Spintronics
Spintronics refers commonly to phenomena in which the spin of electrons in a
solid state environment plays the determining role. In a more narrow sense
spintronics is an emerging research field of electronics: spintronics devices
are based on a spin control of electronics, or on an electrical and optical
control of spin or magnetism. This review presents selected themes of
semiconductor spintronics, introducing important concepts in spin transport,
spin injection, Silsbee-Johnson spin-charge coupling, and spindependent
tunneling, as well as spin relaxation and spin dynamics. The most fundamental
spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling.
Depending on the crystal symmetries of the material, as well as on the
structural properties of semiconductor based heterostructures, the spin-orbit
coupling takes on different functional forms, giving a nice playground of
effective spin-orbit Hamiltonians. The effective Hamiltonians for the most
relevant classes of materials and heterostructures are derived here from
realistic electronic band structure descriptions. Most semiconductor device
systems are still theoretical concepts, waiting for experimental
demonstrations. A review of selected proposed, and a few demonstrated devices
is presented, with detailed description of two important classes: magnetic
resonant tunnel structures and bipolar magnetic diodes and transistors. In most
cases the presentation is of tutorial style, introducing the essential
theoretical formalism at an accessible level, with case-study-like
illustrations of actual experimental results, as well as with brief reviews of
relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure