106 research outputs found
Spin-orbit coupling in a Quantum Dot at high magnetic field
We describe the simultaneous effects of the spin-orbit (SO) perturbation and
a magnetic field on a disk shaped quantum dot (QD). {As it is known the}
combination of electrostatic forces among the electrons confined in the QD
and the Pauli principle can induce a spin polarization when (applied in the
direction orthogonal to the QD) is above a threshold value. In the presence of
an electric field parallel to , coupled to the spin by a Rashba term,
we demonstrate that a symmetry breaking takes place: we can observe it by
analyzing the splitting of the levels belonging to an unperturbed multiplet. We
also discuss the competitive effects of the magnetic field, the SO perturbation
and the electron electron interaction, in order to define the hierarchy of the
states belonging to a multiplet. We demonstrate how this hierarchy depends on
the QD's size. We show the spin texture due to the combined effects of the
Rashba effect and the interaction responsible for the polarization.Comment: 8 pages, 3 figures, PACS: 73.21.La,71.15.Mb,75.75.+
Spin Exciton in quantum dot with spin orbit coupling in high magnetic field
Coulomb interactions of few () electrons confined in a disk shaped
quantum dot, with a large magnetic field applied in the z-direction
(orthogonal to the dot), produce a fully spin polarized ground state. We
numerically study the splitting of the levels corresponding to the multiplet of
total spin (each labeled by a different total angular momentum )
in presence of an electric field parallel to , coupled to by a
Rashba term. We find that the first excited state is a spin exciton with a
reversed spin at the origin. This is reminiscent of the Quantum Hall
Ferromagnet at filling one which has the skyrmion-like state as its first
excited state. The spin exciton level can be tuned with the electric field and
infrared radiation can provide energy and angular momentum to excite it.Comment: 9 pages, 9 figures. submitted to Phys.Rev.
A Tunable Two-impurity Kondo system in an atomic point contact
Two magnetic atoms, one attached to the tip of a Scanning Tunneling
Microscope (STM) and one adsorbed on a metal surface, each constituting a Kondo
system, have been proposed as one of the simplest conceivable systems
potentially exhibiting quantum critical behaviour. We have succeeded in
implementing this concept experimentally for cobalt dimers clamped between an
STM tip and a gold surface. Control of the tip-sample distance with
sub-picometer resolution allows us to tune the interaction between the two
cobalt atoms with unprecedented precision. Electronic transport measurements on
this two-impurity Kondo system reveal a rich physical scenario which is
governed by a crossover from local Kondo screening to non-local singlet
formation due to antiferromagnetic coupling as a function of separation of the
cobalt atoms.Comment: 22 pages, 5 figure
Fully gapped topological surface states in BiSe films induced by a d-wave high-temperature superconductor
Topological insulators are a new class of materials, that exhibit robust
gapless surface states protected by time-reversal symmetry. The interplay
between such symmetry-protected topological surface states and symmetry-broken
states (e.g. superconductivity) provides a platform for exploring novel quantum
phenomena and new functionalities, such as 1D chiral or helical gapless
Majorana fermions, and Majorana zero modes which may find application in
fault-tolerant quantum computation. Inducing superconductivity on topological
surface states is a prerequisite for their experimental realization. Here by
growing high quality topological insulator BiSe films on a d-wave
superconductor BiSrCaCuO using molecular beam epitaxy,
we are able to induce high temperature superconductivity on the surface states
of BiSe films with a large pairing gap up to 15 meV. Interestingly,
distinct from the d-wave pairing of BiSrCaCuO, the
proximity-induced gap on the surface states is nearly isotropic and consistent
with predominant s-wave pairing as revealed by angle-resolved photoemission
spectroscopy. Our work could provide a critical step toward the realization of
the long sought-after Majorana zero modes.Comment: Nature Physics, DOI:10.1038/nphys274
Metallic, magnetic and molecular nanocontacts
Scanning tunnelling microscopy and break-junction experiments realize metallic and molecular nanocontacts that act as ideal one-dimensional channels between macroscopic electrodes. Emergent nanoscale phenomena typical of these systems encompass structural, mechanical, electronic, transport, and magnetic properties. This Review focuses on the theoretical explanation of some of these properties obtained with the help of first-principles methods. By tracing parallel theoretical and experimental developments from the discovery of nanowire formation and conductance quantization in gold nanowires to recent observations of emergent magnetism and Kondo correlations, we exemplify the main concepts and ingredients needed to bring together ab initio calculations and physical observations. It can be anticipated that diode, sensor, spin-valve and spin-filter functionalities relevant for spintronics and molecular electronics applications will benefit from the physical understanding thus obtained
Evaluation of fluorescence in situ hybridisation (FISH) for the detection of fungi directly from blood cultures and cerebrospinal fluid from patients with suspected invasive mycoses
The aim of this study was to evaluate the diagnostic performance of in-house FISH (fluorescence in situ hybridisation) procedures for the direct identification of invasive fungal infections in blood cultures and cerebrospinal fluid (CSF) samples and to compare these FISH results with those obtained using traditional microbiological techniques and PCR targeting of the ITS1 region of the rRNA gene. In total, 112 CSF samples and 30 positive blood cultures were investigated by microscopic examination, culture, PCR-RFLP and FISH. The sensitivity of FISH for fungal infections in CSF proved to be slightly better than that of conventional microscopy (India ink) under the experimental conditions, detecting 48 (instead of 46) infections in 112 samples. The discriminatory powers of traditional microbiology, PCR-RFLP and FISH for fungal bloodstream infections were equivalent, with the detection of 14 fungal infections in 30 samples. However, the mean times to diagnosis after the detection of microbial growth by automated blood culture systems were 5 hours, 20 hours and 6 days for FISH, PCR-RFLP and traditional microbiology, respectively. The results demonstrate that FISH is a valuable tool for the identification of invasive mycoses that can be implemented in the diagnostic routine of hospital laboratories. © 2015 Da Silva et al
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