Age differences in mental health literacy

BACKGROUND: The community's knowledge and beliefs about mental health problems, their risk factors, treatments and sources of help may vary as a function of age. METHODS: Data were taken from an epidemiological survey conducted during 2003–2004 with a national clustered sample of Australian adults aged 18 years and over. Following the presentation of a vignette describing depression (n = 1001) or schizophrenia (n = 997), respondents were asked a series of questions relating to their knowledge and recognition of the disorder, beliefs about the helpfulness of treating professionals and medical, psychological and lifestyle treatments, and likely causes. RESULTS: Participant age was coded into five categories and cross-tabulated with mental health literacy variables. Comparisons between age groups revealed that although older adults (70+ years) were poorer than younger age groups at correctly recognising depression and schizophrenia, young adults (18–24 years) were more likely to misidentify schizophrenia as depression. Differences were also observed between younger and older age groups in terms of beliefs about the helpfulness of certain treating professionals and medical and lifestyle treatments for depression and schizophrenia, and older respondents were more likely to believe that schizophrenia could be caused by character weakness. CONCLUSION: Differences in mental health literacy across the adult lifespan suggest that more specific, age appropriate messages about mental health are required for younger and older age groups. The tendency for young adults to 'over-identify' depression signals the need for awareness campaigns to focus on differentiation between mental disorders

Photonic integration of uniform GaAs nanowires in hexagonal and honeycomb lattice for broadband optical absorption

We present an experimental approach toward the realization of GaAs nanowires in the form of square, hexagonal, and honeycomb lattices for photonic integration toward enhanced optical properties. We have carried out a design and fabrication process on GaAs wafers using electron beam lithography patterning, reactive ion etching for hard mask removal, and inductively coupled plasma etching of the material. The resulting photonic crystals are analyzed by field emission scanning electron microscopy. Nanowire array designs in a square, hexagonal, and honeycomb lattice with a variable height of nanowires have been studied. Using finite-difference time-domain simulation, we can derive the comparative optical absorption properties of these nanowire arrays. A very high broadband absorbance of >94% over the 400 nm–1000 nm wavelength range is studied for hexagonal and honeycomb arrays, while a square lattice array shows only a maximum of 85% absorption. We report a minimum of 2% reflectance, or 98% optical absorbance, over 450 nm–700 nm and over a wide angle of 45° through hexagonal and honeycomb lattice integration in GaAs. These results will have potential applications toward broadband optical absorption or light trapping in solar energy harvesting

Interference effects in a tunable quantum point contact integrated with an electronic cavity

We show experimentally how quantum interference can be produced using an integrated quantum system comprising an arch-shaped short quantum wire (or quantum point contact, QPC) of 1D electrons and a reflector forming an electronic cavity. On tuning the coupling between the QPC and the electronic cavity, fine oscillations are observed when the arch QPC is operated in the quasi-1D regime. These oscillations correspond to interference between the 1D states and a state which is similar to the Fabry-Perot state and suppressed by a small transverse magnetic field of ±60  mT. Tuning the reflector, we find a peak in resistance which follows the behavior expected for a Fano resonance. We suggest that this is an interesting example of a Fano resonance in an open system which corresponds to interference at or near the Ohmic contacts due to a directly propagating, reflected discrete path and the continuum states of the cavity corresponding to multiple scattering. Remarkably, the Fano factor shows an oscillatory behavior taking peaks for each fine oscillation, thus, confirming coupling between the discrete and continuum states. The results indicate that such a simple quantum device can be used as building blocks to create more complex integrated quantum circuits for possible applications ranging from quantum-information processing to realizing the fundamentals of complex quantum systems

Resistance hysteresis in the integer and fractional quantum Hall regime

We present experimental results where hysteresis is observed depending on the magnetic field sweep direction in the integer quantum Hall regime of a high-mobility two-dimensional electron system formed in a GaAs/AlGaAs heterostructure. We analyze the results based on the screening theory and show that the anomalous effects observed stem from the nonequilibrium processes resulting from the formation of metal-like and insulator-like regions due to direct Coulomb interactions and the dissipative nature of the Hall bar together with the scattering-influenced contacts. Furthermore, the hysteretic behavior is shown for the integer filling factors ν=1, 2, and 4 and for certain fractional states at the longitudinal resistance. We argue that the nonequilibration is not only due to contacts, in contrast, but also due to the nature of the finite size dissipative Hall bar under interactions and Landau quantization

Engineering the spin polarization of one-dimensional electrons

We present results of magneto-focusing on the controlled monitoring of spin polarization within a one-dimensional (1D) channel, and its subsequent effect on modulating the spin-orbit interaction (SOI) in a 2D GaAs electron gas. We demonstrate that electrons within a 1D channel can be partially spin polarized as the effective length of the 1D channel is varied in agreement with the theoretical prediction. Such polarized 1D electrons when injected into a 2D region result in a split in the odd-focusing peaks, whereas the even peaks remain unaffected (single peak). On the other hand, the unpolarized electrons, achieved by reducing the effective length of the 1D channel, do not affect the focusing spectrum and the odd and even peaks remain as single peaks, respectively. The split in odd-focusing peaks is evidence of direct measurement of spin polarization within a 1D channel, where each sub-peak represents the population of a particular spin state. Confirmation of the spin splitting is determined by a selective modulation of the focusing peaks due to the Zeeman energy in the presence of an in-plane magnetic field. We suggest that the SOI in the 2D regime is enhanced by a stream of polarized 1D electrons. The spatial control of spin states of injected 1D electrons and the possibility of tuning the SOI may open up a new regime of spin-engineering with application in future quantum information schemes

Gate voltage dependent Rashba spin splitting in hole transverse magnetic focussing

Magnetic focussing of charge carriers in two-dimensional systems provides a solid state version of a mass spectrometer. In the presence of a spin-orbit interaction, the first focussing peak splits into two spin dependent peaks, allowing focussing to be used to measure spin polarisation and the strength of the spin-orbit interaction. In hole systems, the k^3 dependence of the Rashba spin-orbit term allows the spatial separation of spins to be changed in-situ using a voltage applied to an overall top gate. Here we demonstrate that this can be used to control the splitting of the magnetic focussing peaks. Additionally, we compare the focussing peak splitting to that predicted by Shubnikov-de Haas oscillations and k.p bandstructure calculations. We find that the focussing peak splitting is consistently larger than expected, suggesting further work is needed on understanding spin dependent magnetic focussing

Direct observation of exchange-driven spin interactions in one-dimensional system

We present experimental results of transverse electron focusing measurements performed on an ntype GaAs based mesoscopic device consisting of one-dimensional (1D) quantum wires as injector and detector. We show that non-adiabatic injection of 1D electrons at a conductance of e2/ h results in a single first focusing peak, which transforms into two asymmetric sub-peaks with a gradual increase in the injector conductance up to 2e2/ h , each sub-peak representing the population of spinstate arising from the spatially separated spins in the injector. Further increasing the conductance flips the spin-states in the 1D channel, thus reversing the asymmetry in the sub-peaks. On applying a source-drain bias, the spin-gap, so obtained, can be resolved, thus providing evidence of exchange interaction induced spin polarization in the 1D systems. V

Spin polarisation and spin dependent scattering of holes in transverse magnetic focussing

In 2D systems with a spin-orbit interaction, magnetic focussing can be used to create a spatial separation of particles with different spin. Here we measure hole magnetic focussing for two different magnitudes of the Rashba spin-orbit interaction. We find that when the Rashba spin-orbit magnitude is large there is significant attenuation of one of the focussing peaks, which is conventionally associated with a change in the spin polarisation. We instead show that in hole systems with a $k^3$ spin-orbit interaction, this peak suppression is due to a change in the scattering of one spin state, not a change in spin polarisation. We also show that the change in scattering length extracted from magnetic focussing is consistent with results obtained from measurements of Shubnikov-de Haas oscillations. This result suggests that scattering must be considered when relating focussing peak amplitude to spin polarisation in hole system

Probing Fermi surface shifts with spin resolved transverse magnetic focussing

Transverse magnetic focussing is the solid state equivalent of a mass spectrometer. It is unique among 2D measurement techniques as it is able to measure a well defined section of the Fermi surface, making it possible to detect changes that would be averaged out over the whole Fermi surface. Here, we utilise this unique property to probe non-adiabatic spin dynamics and spin dependent scattering of holes. We combine spin-resolved magnetic focussing with an additional independent in-plane magnetic field and observe a change in focussing peak amplitude that is not symmetric with respect to the field direction (i.e. $+B_{\parallel} \neq -B_{\parallel}$), and is extremely sensitive to the magnitude of the in-plane magnetic field. We show that the magnetic focussing signal is extremely sensitive to small changes in the Fermi velocity, which can be used to detect small shifts in the Fermi surface caused by an in-plane magnetic field. We also find that focussing can be used to detect the proximity between spin-split Fermi surfaces, which cause non-adiabatic spin dynamics