1,056 research outputs found
Single-photon exchange interaction in a semiconductor microcavity
We consider the effective coupling of localized spins in a semiconductor
quantum dot embedded in a microcavity. The lowest cavity mode and the quantum
dot exciton are coupled and close in energy, forming a polariton. The fermions
forming the exciton interact with localized spins via exchange. Exact
diagonalization of a Hamiltonian in which photons, spins and excitons are
treated quantum mechanically shows that {\it a single polariton} induces a
sizable indirect exchange interaction between otherwise independent spins. The
origin, symmetry properties and the intensity of that interaction depend both
on the dot-cavity coupling and detuning. In the case of a (Cd,Mn)Te quantum
dot, Mn-Mn ferromagnetic coupling mediated by a single photon survives above 1
K whereas the exciton mediated coupling survives at 15 K.Comment: 4 pages, 3 figure
Long-range spin-qubit interaction mediated by microcavity polaritons
We study the optically-induced coupling between spins mediated by polaritons
in a planar micro-cavity. In the strong coupling regime, the vacuum Rabi
splitting introduces anisotropies in the spin coupling. Moreover, due to their
photon-like mass, polaritons provide an extremely long spin coupling range.
This suggests the realization of two-qubit all-optical quantum operations
within tens of picoseconds with spins localized as far as hundreds of
nanometers apart.Comment: 5 pages, 3 figure
Spin splitting in a polarized quasi-two-dimensional exciton gas
We have observed a large spin splitting between "spin" and
heavy-hole excitons, having unbalanced populations, in undoped GaAs/AlAs
quantum wells in the absence of any external magnetic field. Time-resolved
photoluminescence spectroscopy, under excitation with circularly polarized
light, reveals that, for high excitonic density and short times after the
pulsed excitation, the emission from majority excitons lies above that of
minority ones. The amount of the splitting, which can be as large as 50% of the
binding energy, increases with excitonic density and presents a time evolution
closely connected with the degree of polarization of the luminescence. Our
results are interpreted on the light of a recently developed model, which shows
that, while intra-excitonic exchange interaction is responsible for the spin
relaxation processes, exciton-exciton interaction produces a breaking of the
spin degeneracy in two-dimensional semiconductors.Comment: Revtex, four pages; four figures, postscript file Accepted for
publication in Physical Review B (Rapid Commun.
Construction of two Neurospora crassa Lambda ZapII-cDNA libraries
In the presence of the anti-microtubule agent benomyl, N. crassa synthesizes and secretes a major 60 kDa protein in the culture medium. This protein is absent in untreated cells (Rossier et al. 1989. Eur. J. Cell Biol. 50:333-339). To clone the gene coding for the 60 kDa protein and to unravel its function, we have constructed a cDNA library from benomyl-treated cells ( benomyl cDNA library). A second cDNA library was constructed from untreated cells in order to clone genes coding for cytoskeletal proteins ( standard cDNA library)
Mitotic instability in benomyl-resistant transformants of a fluffy strain of Neurospora crassa
The isolation of the beta-tubulin gene from a benomyl-resistant Neurospora crassa strain (Orbach et al. 1986 Mol. Cell. Biol. 6:2452-2461) has provided a dominant selectable marker usable in transformation experiments with N. crassa
Differential associations of personal and general just-world beliefs with the Five-Factor and HEXACO models of personality.
Recent literature evidences differential associations of personal and general just-world beliefs with constructs in the interpersonal domain. In line with this research, we examine the respective relationships of each just-world belief with the Five-Factor and the HEXACO models of personality in one representative sample of the working population of Switzerland and one sample of the general US population, respectively. One suppressor effect was observed in both samples: Neuroticism and emotionality was positively associated with general just-world belief, but only after controlling for personal just-world belief. In addition, agreeableness was positively and honesty-humility negatively associated with general just-world belief but unrelated to personal just-world belief. Conscientiousness was consistently unrelated to any of the just-world belief and extraversion and openness to experience revealed unstable coefficients across studies. We discuss these points in light of just-world theory and their implications for future research taking both dimensions into account
Anisotropic magnetoresistance in nanocontacts
We present ab initio calculations of the evolution of anisotropic
magnetoresistance (AMR) in Ni nanocontacts from the ballistic to the tunnel
regime. We find an extraordinary enhancement of AMR, compared to bulk, in two
scenarios. In systems without localized states, like chemically pure break
junctions, large AMR only occurs if the orbital polarization of the current is
large, regardless of the anisotropy of the density of states. In systems that
display localized states close to the Fermi energy, like a single electron
transistor with ferromagnetic electrodes, large AMR is related to the variation
of the Fermi energy as a function of the magnetization direction.Comment: 7 pages, 4 figures; revised for publication, new figures in greyscal
Magneto-optical Kerr effect in spin split two-dimensional massive Dirac materials
Two-dimensional (2D) massive Dirac electrons possess a finite Berry curvature, with Chern number 1/2, that entails both a quantized dc Hall response and a subgap full-quarter Kerr rotation. The observation of these effects in 2D massive Dirac materials such as gapped graphene, hexagonal boron nitride or transition metal dichalcogenides (TMDs) is obscured by the fact that Dirac cones come in pairs with opposite sign Berry curvatures, leading to a vanishing Chern number. Here, we show that the presence of spin-orbit interactions, combined with an exchange spin splitting induced either by diluted magnetic impurities or by proximity to a ferromagnetic insulator, gives origin to a net magneto-optical Kerr effect in such systems. We focus on the case of TMD monolayers and study the dependence of Kerr rotation on frequency and exchange spin splitting. The role of the substrate is included in the theory and found to critically affect the results. Our calculations indicate that state-of-the-art magneto-optical Kerr spectroscopy can detect a single magnetic impurity in diluted magnetic TMDs.We thank Allan H MacDonald, Elaine Li, Alejandro Molina-Sanchez and Joao C G Henriques for fruitful discussions. GC acknowledges Fundacao para a Ciencia e a Tecnologia (FCT) for Grant No. SFRH/BD/138806/2018. GC and JF-R acknowledge financial support from FCT through Grant No. P2020-PTDC/FIS-NAN/4662/2014. NMRP acknowledges financial support from European Commission through project 'Graphene-Driven Revolutions in ICT and Beyond' (Ref. No. 785219), FCT in the framework of Strategic Financing (Ref. No. UID/FIS/04650/2019), and COMPETE2020, PORTUGAL2020, FEDER and FCT for Grants No. PTDC/FIS-NAN/3668/2013, No. POCI-01-0145-FEDER-028114, No. POCI-01-0145-FEDER-029265 and No. PTDC/NANOPT/29265/2017. JF-R acknowledges FCT for Grant No. UTAP-EXPL/NTec/0046/2017, as well as Generalitat Valenciana funding Prometeo2017/139 and MINECO-Spain (Grant No. MAT201678625-C2)
New mutants of Neurospora crassa highly resistant to the microtubule inhibitor benomyl
Mutants of N. crassa highly resistant to benomyl with respect to hyphal growth were obtained by mutagenizing wild type strain St. Lawrence 74A or mutant Bml 511(r) which is moderately resistant to the fungicide. One of these, strain E1-91 that has a mutation mapping at the Bml (beta-tubulin) locus, showed temporary sensitivity to the benzimidazole
Electric-Field Tuning of Spin-Dependent Exciton-Exciton Interactions in Coupled Quantum Wells
We have shown experimentally that an electric field decreases the energy
separation between the two components of a dense spin-polarized exciton gas in
a coupled double quantum well, from a maximum splitting of meV to
zero, at a field of 35 kV/cm. This decrease, due to the field-induced
deformation of the exciton wavefunction, is explained by an existing
calculation of the change in the spin-dependent exciton-exciton interaction
with the electron-hole separation. However, a new theory that considers the
modification of screening with that separation is needed to account for the
observed dependence on excitation power of the individual energies of the two
exciton components.Comment: 5 pages, 4 eps figures, RevTeX, Physical Review Letters (in press
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