Determination of the phase diagram of the electron doped superconductor Ba(Fe1−x_{1-x}Cox_x)2_2As2_2

Systematic measurements of the resistivity, heat capacity, susceptibility and Hall coefficient are presented for single crystal samples of the electron-doped superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. These data delineate an $x-T$ phase diagram in which the single magnetic/structural phase transition that is observed for undoped BaFe$_2$As$_2$ at 134 K apparently splits into two distinct phase transitions, both of which are rapidly suppressed with increasing Co concentration. Superconductivity emerges for Co concentrations above $x \sim 0.025$, and appears to coexist with the broken symmetry state for an appreciable range of doping, up to $x \sim 0.06$. The optimal superconducting transition temperature appears to coincide with the Co concentration at which the magnetic/structural phase transitions are totally suppressed, at least within the resolution provided by the finite step size between crystals prepared with different doping levels. Superconductivity is observed for a further range of Co concentrations, before being completely suppressed for $x \sim 0.018$ and above. The form of this $x-T$ phase diagram is suggestive of an association between superconductivity and a quantum critical point arising from suppression of the magnetic and/or structural phase transitions

Military veterans with mental health problems: a protocol for a systematic review to identify whether they have an additional risk of contact with criminal justice systems compared with other veterans groups

BACKGROUND: There is concern that some veterans of armed forces, in particular those with mental health, drug or alcohol problems, experience difficulty returning to a civilian way of life and may subsequently come into contact with criminal justice services and imprisonment. The aim of this review is to examine whether military veterans with mental health problems, including substance use, have an additional risk of contact with criminal justice systems when compared with veterans who do not have such problems. The review will also seek to identify veterans' views and experiences on their contact with criminal justice services, what contributed to or influenced their contact and whether there are any differences, including international and temporal, in incidence, contact type, veteran type, their presenting health needs and reported experiences. METHODS/DESIGN: In this review we will adopt a methodological model similar to that previously used by other researchers when reviewing intervention studies. The model, which we will use as a framework for conducting a review of observational and qualitative studies, consists of two parallel synthesis stages within the review process; one for quantitative research and the other for qualitative research. The third stage involves a cross study synthesis, enabling a deeper understanding of the results of the quantitative synthesis. A range of electronic databases, including MEDLINE, PsychINFO, CINAHL, will be systematically searched, from 1939 to present day, using a broad range of search terms that cover four key concepts: mental health, military veterans, substance misuse, and criminal justice. Studies will be screened against topic specific inclusion/exclusion criteria and then against a smaller subset of design specific inclusion/exclusion criteria. Data will be extracted for those studies that meet the inclusion criteria, and all eligible studies will be critically appraised. Included studies, both quantitative and qualitative, will then undergo stage-specific analysis and synthesis. The final stage will combine the findings of both syntheses to enable new understandings of why, how, and by how much, military veterans with mental health problems, including problematic drug and alcohol use, come into contact with the criminal justice system

Boudica & field notes towards a dynamic film-poem form

The thesis comprises an original, book-length sequence of poems, Boudica, and a film-poem of the same name. Boudica engages in a topographical mediation on East Anglia, specifically the landscapes of Norfolk and north Suffolk. The subject of the sequence is Boudica, a young woman trapped within a stifling suburban upbringing and her dead-end job at the pub in her village. Structured in four parts, the poem explores her adolescent ennui, her ambivalence towards place and her small acts of existential rebellion against this condition. The verse itself is constructed of images from cinema and after cinema, images bound to the physicality of cinema. Poet and narrator are allowed access to the viewfinder: lines, images, and stanzas attempt to frame themselves within the logic of cinematography, a logic which asks that the poet’s eye becomes the camera lens, exploiting cinema and ekphrasis by projecting meaning without making it explicit. The film is composed of images which have been suggested by the lyrics, the cinematic sequencing of these images has then dictated the order in which the lyrics appear in the collection. The thematic and structural links between the film and the sequence of poems are the subject of the supporting reflective essay. This paper explores my practice-led methodology and approach to the making of Boudica, offering key definitions with regards to ekphrasis and the hybrid film-poem form. It explores dynamic points of intersection between film and poetry in Boudica as well as case studies in recent writing and practice on ekphrasis, poetry and cinema

Bulk Fermi surface coexistence with Dirac surface state in Bi2_2Se3_3: a comparison of photoemission and Shubnikov-de Haas measurements

Shubnikov de Haas (SdH) oscillations and Angle Resolved PhotoEmission Spectroscopy (ARPES) are used to probe the Fermi surface of single crystals of Bi2Se3. We find that SdH and ARPES probes quantitatively agree on measurements of the effective mass and bulk band dispersion. In high carrier density samples, the two probes also agree in the exact position of the Fermi level EF, but for lower carrier density samples discrepancies emerge in the position of EF. In particular, SdH reveals a bulk three-dimensional Fermi surface for samples with carrier densities as low as 10^17cm-3. We suggest a simple mechanism to explain these differences and discuss consequences for existing and future transport studies of topological insulators.Comment: 5 mages, 5 figure

Quantum oscillations in the parent pnictide BaFe2_2As2_2 : itinerant electrons in the reconstructed state

We report quantum oscillation measurements that enable the direct observation of the Fermi surface of the low temperature ground state of \ba122. From these measurements we characterize the low energy excitations, revealing that the Fermi surface is reconstructed in the antiferromagnetic state, but leaving itinerant electrons in its wake. The present measurements are consistent with a conventional band folding picture of the antiferromagnetic ground state, placing important limits on the topology and size of the Fermi surface.Comment: 5 pages, 3 figure

On the origin of non-monotonic doping dependence of the in-plane resistivity anisotropy in Ba(Fe1−xTx_{1-x}T_x)2_2As2_2, TT = Co, Ni and Cu

The in-plane resistivity anisotropy has been measured for detwinned single crystals of Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$. The data reveal a non-monotonic doping dependence, similar to previous observations for Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. Magnetotransport measurements of the parent compound reveal a non-linear Hall coefficient and a strong linear term in the transverse magnetoresistance. Both effects are rapidly suppressed with chemical substitution over a similar compositional range as the onset of the large in-plane resistivity anisotropy. It is suggested that the relatively small in-plane anisotropy of the parent compound in the spin density wave state is due to the presence of an isotropic, high mobility pocket of reconstructed Fermi surface. Progressive suppression of the contribution to the conductivity arising from this isotropic pocket with chemical substitution eventually reveals the underlying in-plane anisotropy associated with the remaining FS pockets.Comment: 12 pages, 9 figure

Destructive Adsorption of Carbon Tetrachloride on Alkaline Earth Metal Oxides

The destructive adsorption of CCl4 on MgO, CaO, SrO, and BaO has been studied as a function of the reaction temperature and the amount of CCl4 injected. The reaction was followed using in situ Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and 13 C magic angle spinning nuclear magnetic resonance spectroscopy. It was found that the activity toward CCl4 parallels the basicity of the alkaline earth metal oxide; i.e., the activity decreased in the order BaO > SrO > CaO > MgO. Barium oxide readily reacted with CCl4 at 200-300 °C, and, at these low temperatures, CO2 was the only gas-phase product that evolved from the surface. At higher reaction temperatures, other alkaline earth metal oxides, such as CaO and MgO, also became active, and COCl2 was found to be a reaction intermediate in the destruction of CCl4. Although the destruction process is initiated at the surface, the continuous O 2- /Cl - exchange results in the bulk transformation of the metal oxide to the metal chloride. Barium oxide could be regenerated by dissolving the chloride in water, followed by precipitation as barium carbonate and subsequent calcination. In addition, carbon tetrachloride destruction at around 600 °C resulted in the formation of an unusual alkaline earth metal oxide chloride, viz., M4OCl6 (M ) Ba, Sr, or Ca)