141 research outputs found
Magnetic phase diagram of
Magnetometry, electrical transport, and neutron scattering measurements were
performed on single crystals of the Fe^{4+}-containing perovskite-related phase
Sr_3Fe_2O_7-x as a function of oxygen content. Although both the crystal
structure and electron configuration of this compound are closely similar to
those of well-studied ruthenates and manganates, it exhibits very different
physical properties. The fully-oxygenated compound (x=0) exhibits a
charge-disproportionation transition at T_D = 340 K, and an antiferromagnetic
transition at T_N = 115 K. For temperatures T \leq T_D, the material is a
small-gap insulator; the antiferromagnetic order is incommensurate, which
implies competing exchange interactions between the Fe^{4+} moments. The
fully-deoxygenated compound (x=1) is highly insulating, and its Fe^{3+} moments
exhibit commensurate antiferromagnetic order below T_N ~ 600 K. Compounds with
intermediate x exhibit different order with lower T_N, likely as a consequence
of frustrated exchange interactions between Fe^{3+} and Fe^{4+} sublattices. A
previous proposal that the magnetic transition temperature reaches zero is not
supported.Comment: 8 pages, 6 figure
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
Mechatronics teaching in preparing agricultural engineers for precision farming technology development
Smart Farming объединяет использование машин, компьютеров, спутниковых и сенсорных технологий для повышения эффективности сельскохозяйственных операций. В статье рассмотрены проблемы подготовки инженеров-механиков для агропромышленного комплекса и обоснована необходимость преподавания мехатроники, рассмотрен опыт Университета Харпер Адамс в преподавании мехатроники в соответствии с существующим учебным планом. В заключении определены возможности для будущего сотрудничества между Белорусской государственной сельскохозяйственной академией и Университетом Харпер Адамс через европейские программы
Two Gaps Make a High Temperature Superconductor?
One of the keys to the high-temperature superconductivity puzzle is the
identification of the energy scales associated with the emergence of a coherent
condensate of superconducting electron pairs. These might provide a measure of
the pairing strength and of the coherence of the superfluid, and ultimately
reveal the nature of the elusive pairing mechanism in the superconducting
cuprates. To this end, a great deal of effort has been devoted to investigating
the connection between the superconducting transition temperature Tc and the
normal-state pseudogap crossover temperature T*. Here we present a review of a
large body of experimental data that suggests a coexisting two-gap scenario,
i.e. superconducting gap and pseudogap, over the whole superconducting dome.Comment: Related material can be found at
http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/articles.htm
Neutron scattering search for static magnetism in oxygen ordered YBa2Cu3O6.5
We present elastic and inelastic neutron scattering results on highly oxygen
ordered YBa2Cu3O6.5 ortho-II. We find no evidence for the presence of ordered
magnetic moments to a sensitivity of 0.003 Bohr magnetons, an order of
magnitude smaller than has been suggested in theories of orbital or
d-density-wave (DDW) currents. The absence of sharp elastic peaks, shows that
the d-density-wave phase is not present, at least for the superconductor with
the doping of 6.5 and the ordered ortho-II structure. We cannot exclude the
possibility that a broad peak may exist with extremely short-range DDW
correlations. For less ordered or more doped crystals it is possible that
disorder may lead to static magnetism. We have also searched for the large
normal state spin gap that is predicted to exist in an ordered DDW phase.
Instead of a gap we find that the Q-correlated spin susceptibility persists to
the lowest energies studied, 6 meV. Our results are compatible with the
coexistence of superconductivity with orbital currents, but only if they are
dynamic, and exclude a sharp phase transition to an ordered d-density-wave
phase.Comment: 6 pages 4 figures RevTex Submitted to Phys Rev B January 23, 200
Observation of Dirac surface states in the noncentrosymmetric superconductor BiPd
Funding from the MPG-UBC center and the Engineering and Physical Sciences Research Council (EP/I031014/1 and EP/L505079/1) are acknowledged. This work was supported by the DFG within projects STA315/8-1 and BE5190/1-1.Materials with strong spin-orbit coupling (SOC) have in recent years become a subject of intense research due to their potential applications in spintronics and quantum information technology. In particular, in systems which break inversion symmetry, SOC facilitates the Rashba-Dresselhaus effect, leading to a lifting of spin degeneracy in the bulk and intricate spin textures of the Bloch wave functions. Here, by combining angular resolved photoemission (ARPES) and low temperature scanning tunneling microscopy (STM) measurements with relativistic first-principles band structure calculations, we examine the role of SOC in single crystals of noncentrosymmetric BiPd. We report the detection of several Dirac surface states, one of which exhibits an extremely large spin splitting. Unlike the surface states in inversion-symmetric systems, the Dirac surface states of BiPd have completely different properties at opposite faces of the crystal and are not trivially linked by symmetry. The spin-splitting of the surface states exhibits a strong anisotropy by itself, which can be linked to the low in-plane symmetry of the surface termination.PostprintPeer reviewe
Multidisciplinary investigation of two Egyptian child mummies curated at the University of Tartu Art Museum, Estonia (Late/Graeco-Roman Periods)
Two ancient Egyptian child mummies at the University of Tartu Art Museum (Estonia) were, according to museum records, brought to Estonia by the young Baltic-German scholar Otto Friedrich von Richter, who had travelled in Egypt during the early 19th century. Although some studies of the mummies were conducted, a thorough investigation has never been made. Thus, an interdisciplinary team of experts studied the remains using the most recent analytical methods in order to provide an exhaustive analysis of the remains. The bodies were submitted for osteological and archaeothanatological study, radiological investigation, AMS radiocarbon dating, chemical and textile analyses, 3D modelling, entomological as well as aDNA investigation. Here we synthesize the results of one of the most extensive multidisciplinary analyses of ancient Egyptian child mummies, adding significantly to our knowledge of such examples of ancient funerary practices.© 2020 Oras et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
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