Dirac Surface States and Nature of Superconductivity in Noncentrosymmetric BiPd

In non-magnetic bulk materials, inversion symmetry protects the spin degeneracy. If the bulk crystal structure lacks a centre of inversion, however, spin-orbit interactions lift the spin degeneracy, leading to a Rashba metal whose Fermi surfaces exhibit an intricate spin texture. In superconducting Rashba metals a pairing wavefunction constructed from these complex spin structures will generally contain both singlet and triplet character. Here we examine the possible triplet components of the order parameter in noncentrosymmetric BiPd, combining for the first time in a noncentrosymmetric superconductor macroscopic characterization, atomic-scale ultra-low-temperature scanning tunnelling spectroscopy, and relativistic first-principles calculations. While the superconducting state of BiPd appears topologically trivial, consistent with Bardeen-Cooper-Schrieffer theory with an order parameter governed by a single isotropic s-wave gap, we show that the material exhibits Dirac-cone surface states with a helical spin polarization.Comment: replaced by published versio

Dirac surface states and nature of superconductivity in Noncentrosymmetric BiPd

In non-magnetic bulk materials, inversion symmetry protects the spin degeneracy. If the bulk crystal structure lacks a centre of inversion, however, spin-orbit interactions lift the spin degeneracy, leading to a Rashba metal whose Fermi surfaces exhibit an intricate spin texture. In superconducting Rashba metals a pairing wavefunction constructed from these complex spin structures will generally contain both singlet and triplet character. Here we examine the possible triplet components of the order parameter in noncentrosymmetric BiPd, combining for the first time in a noncentrosymmetric superconductor macroscopic characterization, atomic-scale ultra-low-temperature scanning tunnelling spectroscopy, and relativistic first-principles calculations. While the superconducting state of BiPd appears topologically trivial, consistent with Bardeen-Cooper-Schrieffer theory with an order parameter governed by a single isotropic s-wave gap, we show that the material exhibits Dirac-cone surface states with a helical spin polarization. ©2015 Macmillan Publishers Limited. All rights reserved131261sciescopu

Dirac surface states and nature of superconductivity in noncentrosymmetric BiPd

In non-magnetic bulk materials, inversion symmetry protects the spin degeneracy. If the bulk crystal structure lacks a centre of inversion, however, spin-orbit interactions lift the spin degeneracy, leading to a Rashba metal whose Fermi surfaces exhibit an intricate spin texture. In superconducting Rashba metals a pairing wavefunction constructed from these complex spin structures will generally contain both singlet and triplet character. Here we examine possible triplet components of the order parameter in noncentrosymmetric BiPd, combining for the first time in a noncentrosymmetric superconductor macroscopic characterization, atomic-scale ultra-low temperature scanning tunnelling spectroscopy, and relativistic first-principles calculations. While the superconducting state of BiPd appears topologically trivial, consistent with Bardeen-Cooper-Schrieffer theory with an order parameter governed by a single isotropic s-wave gap, we show that the material exhibits Dirac-cone surface states with a helical spin polarization

Rankings and Accountability in Higher Education : Uses and Misuses

University Rankings: The Many Sides of the Debate / Marope, Mmantsetsa; Wells, Peter -- The Academic Ranking of World Universities and its future direction / Liu, Nian Cai An evolving methodology: the Times Higher Education World University Rankings / Baty, Phil -- Issues of transparency and applicability in global university rankings / Sowter, Ben -- World-class universities or world-class systems? Rankings and higher education policy choices / Hazelkorn, Ellen -- Rankings and online learning: a disruptive combination for higher education? / Daniel, John -- Ranking higher education institutions: a critical perspective / Scott, Peter -- Rankings, new accountability tools and quality assurance / Eaton, Judith -- An African perspective on rankings in higher education / Okebukola, Peter A. -- Rankings and information on Japanese universities / Yonezawa, Akiyoshi -- The national and institutional impact of university rankings : the case of Malaysia / Hapsah, Sharifah -- What’s the use of rankings? / Downing, Kevin -- A decade of international university rankings : a critical perspective from Latin America / Ordorika, Imanol; Lloyd, Marion -- If ranking is the disease, is benchmarking the cure? / Salmi, Jamil -- U-Multirank: a user-driven and multi-dimensional ranking tool in global higher education and research / Vught, Frans van; Ziegele, Frank -- Towards an international assessment of higher education learning outcomes : The OECD-led AHELO initiative / Yelland, Richard; Castañeda Valle, RodrigoIt brings together both promoters and opposers of rankings, to reflect the wide range of views that exist in the higher education community on this highly controversial topic. If learners, institutions and policy-makers are to be responsible users of ranking data and league table lists, it is vital that those compiling them make perfectly clear what criteria they are using to devise them, how they have weighted these criteria, and why they made these choices. It is hoped that this information will enable stakeholders to take informed decisions on higher education institutions

Does Effective Depression Treatment Alone Reduce Secondary HIV Transmission Risk? Equivocal Findings from a Randomized Controlled Trial

Depressed mood has been associated with HIV transmission risk behavior. To determine whether effective depression treatment could reduce the frequency of sexual risk behavior, we analyzed secondary outcome data from a 36-week, two-arm, parallel-design, randomized controlled trial, in which homeless and marginally housed, HIV-infected persons with comorbid depressive disorders were randomized to receive either: (a) directly observed treatment with the antidepressant medication fluoxetine, or (b) referral to a local public mental health clinic. Self-reported sexual risk outcomes, which were measured at 3, 6, and 9 months, included: total number of sexual partners, unprotected sexual intercourse, unprotected sexual intercourse with an HIV-uninfected partner or a partner of unknown serostatus, and transactional sex. Estimates from generalized estimating equations regression models did not suggest consistent reductions in sexual risk behaviors resulting from treatment. Mental health interventions may need to combine depression treatment with specific skills training in order to achieve durable impacts on HIV prevention outcomes