Electron spin quantum beats in positively charged quantum dots: nuclear field effects

We have studied the electron spin coherence in an ensemble of positively charged InAs/GaAs quantum dots. In a transverse magnetic field, we show that two main contributions must be taken into account to explain the damping of the circular polarization oscillations. The first one is due to the nuclear field fluctuations from dot to dot experienced by the electron spin. The second one is due to the dispersion of the transverse electron Lande g-factor, due to the inherent inhomogeneity of the system, and leads to a field dependent contribution to the damping. We have developed a model taking into account both contributions, which is in good agreement with the experimental data. This enables us to extract the pure contribution to dephasing due to the nuclei.Comment: 10 pages, 6 figure

Efficient dynamical nuclear polarization in quantum dots: Temperature dependence

We investigate in micro-photoluminescence experiments the dynamical nuclear polarization in individual InGaAs quantum dots. Experiments carried out in an applied magnetic field of 2T show that the nuclear polarization achieved through the optical pumping of electron spins is increasing with the sample temperature between 2K and 55K, reaching a maximum of about 50%. Analysing the dependence of the Overhauser shift on the spin polarization of the optically injected electron as a function of temperature enables us to identify the main reasons for this increase.Comment: 5 pages, 3 figure

Hafnium Silicate dielectrics fabricated by RF magnetron sputtering.

International audienceStructural and composition properties of hafnium silicate layers fabricated by RF magnetron sputtering were studied by means of spectroscopic ellipsometry, X-ray diffraction, transmission electron microscopy and attenuated total reflection infrared spectroscopy with respect to the deposition parameters and postdeposition annealing treatment. The variation of the deposition conditions allows the temperature of amorphous-crystalline phase transformation of pure hafnium oxide layers to be controlled. It is shown that the silicon incorporation in oxide matrix prevents the formation of interfacial silicon oxide layer and plays a major role in the stability of the structure of hafnium based layers remaining an amorphous state upon annealing at 900-950 °C

Beyond the Implicit/Explicit Dichotomy: The Pragmatics of Plausible Deniability

In everyday conversation, messages are often communicated indirectly, implicitly. Why do we seem to communicate so inefficiently? How speakers choose to express a message (modulating confidence, using less explicit formulations) has been proposed to impact how committed they will appear to be to its content. This commitment can be assessed in terms of accountability – is the speaker held accountable for what they communicated? – and deniability – can the speaker plausibly deny they intended to communicate it? We investigated two factors that may influence commitment to implicitly conveyed messages. In a preregistered online study, we tested the hypothesis that the degree of meaning strength (strongly or weakly communicated) and the level of meaning used by the speaker (an enrichment or a conversational implicature) modulate accountability and plausible deniability. Our results show that both meaning strength and level of meaning influence speaker accountability and plausible deniability. Participants perceived enrichments to be harder to deny than conversational implicatures, and strongly implied content as more difficult to deny than weakly implied content. Furthermore, participants held the speaker more accountable to content conveyed via an enrichment than to content conveyed via an implicature. These results corroborate previously found differences between levels of meaning (enrichment vs. implicature). They also highlight the largely understudied role of meaning strength as a cue to speaker commitment in communication

Bistability of the Nuclear Polarisation created through optical pumping in InGaAs Quantum Dots

We show that optical pumping of electron spins in individual InGaAs quantum dots leads to strong nuclear polarisation that we measure via the Overhauser shift (OHS) in magneto-photoluminescence experiments between 0 and 4T. We find a strongly non-monotonous dependence of the OHS on the applied magnetic field, with a maximum nuclear polarisation of 40% for intermediate magnetic fields. We observe that the OHS is larger for nuclear fields anti-parallel to the external field than in the parallel configuration. A bistability in the dependence of the OHS on the spin polarization of the optically injected electrons is found. All our findings are qualitatively understood with a model based on a simple perturbative approach.Comment: Phys Rev B (in press

Wernicke's region--where is it

In this subject, the first question both logically and chronologically was and is: Can a lesion (focal damage) of the cerebrum cause a loss of language without causing a loss of intelligence? That is the original question, still debated hotly by many people. Much of the heat is attributable to the way in which the question is phrased. Suppose we phrase it relatively, as follows: Can a lesion of the cerebrum produce a deficit in language that is far in excess of the concomitant deficit in intelligence? Asked in this way, almost everyone would answer yes. There are worthy persons who are still arguing that anyone who has a loss of language from a cerebral lesion must have some accompanying loss of intelligence. Similarly, there are equally worthy persons recurrently showing us that intelligence can be preserved in spite of severe aphasia. Both parties are undoubtedly correct. But the force of either argument is largely dissipated when the question is rephrased in the relative way. Of course, how much intelligence is lost (or retained) depends upon how one goes about measuring intelligence; but with almost any measures, except those strictly linguistic, the answer will be yes. Indeed, if the answer were not yes, there would not be such a thing a

A Critique of Automated Approaches to Code Facial Expressions: What Do Researchers Need to Know?

Facial expression recognition software is becoming more commonly used by affective scientists to measure facial expressions. Although the use of this software has exciting implications, there are persistent and concerning issues regarding the validity and reliability of these programs. In this paper, we highlight three of these issues: biases of the programs against certain skin colors and genders; the common inability of these programs to capture facial expressions made in non-idealized conditions (e.g., “in the wild”); and programs being forced to adopt the underlying assumptions of the specific theory of emotion on which each software is based. We then discuss three directions for the future of affective science in the area of automated facial coding. First, researchers need to be cognizant of exactly how and on which data sets the machine learning algorithms underlying these programs are being trained. In addition, there are several ethical considerations, such as privacy and data storage, surrounding the use of facial expression recognition programs. Finally, researchers should consider collecting additional emotion data, such as body language, and combine these data with facial expression data in order to achieve a more comprehensive picture of complex human emotions. Facial expression recognition programs are an excellent method of collecting facial expression data, but affective scientists should ensure that they recognize the limitations and ethical implications of these programs

Robust optical emission polarization in MoS2 monolayers through selective valley excitation

We report polarization resolved photoluminescence from monolayer MoS2, a two-dimensional, non-centrosymmetric crystal with direct energy gaps at two different valleys in momentum space. The inherent chiral optical selectivity allows exciting one of these valleys and close to 90% polarized emission at 4K is observed with 40% polarization remaining at 300K. The high polarization degree of the emission remains unchanged in transverse magnetic fields up to 9T indicating robust, selective valley excitation.Comment: 5 pages, 3 figure