6,288 research outputs found
Orbital Resonance Mode in Superconducting Iron Pnictides
We show that the fluctuations associated with ferro orbital order in the
and orbitals can develop a sharp resonance mode in the
superconducting state with a nodeless gap on the Fermi surface. This orbital
resonance mode appears below the particle-hole continuum and is analogous to
the magnetic resonance mode found in various unconventional superconductors. If
the pairing symmetry is , a dynamical coupling between the orbital
ordering and the d-wave subdominant pairing channels is present by symmetry.
Therefore the nature of the resonance mode depends on the relative strengths of
the fluctuations in these two channels, which could vary significantly for
different families of the iron based superconductors. The application of our
theory to a recent observation of a new -function-like peak in the
B Raman spectrum of BaKFeAs is discussed.Comment: 6 pages, 3 figure
Non-Fermi Liquid behavior at the Orbital Ordering Quantum Critical Point in the Two-Orbital Model
The critical behavior of a two-orbital model with degenerate and
orbitals is investigated by multidimensional bosonization. We find
that the corresponding bosonic theory has an overdamped collective mode with
dynamical exponent , which appears to be a general feature of a
two-orbital model and becomes the dominant fluctuation in the vicinity of the
orbital-ordering quantum critical point. Since the very existence of this
overdamped collective mode induces non-Fermi liquid behavior near the quantum
critical point, we conclude that a two-orbital model generally has a sizable
area in the phase diagram showing non-Fermi liquid behavior. Furthermore, we
show that the bosonic theory resembles the continuous model near the d-wave
Pomeranchuk instability, suggesting that orbital order in a two-orbital model
is identical to nematic order in a continuous model. Our results can be applied
to systems with degenerate and orbitals such as iron-based
superconductors and bilayer strontium ruthenates SrRuO.Comment: 5 pages, 2 figure
Descriptive Anatomy and Three-Dimensional Reconstruction of the Skull of the Early Tetrapod Acanthostega gunnari Jarvik, 1952
The early tetrapod Acanthostega gunnari is an iconic fossil taxon exhibiting skeletal morphology reflecting the transition of vertebrates from water onto land. Computed tomography data of two Acanthostega skulls was segmented using visualization software to digitally separate bone from matrix and individual bones of the skull from each other. A revised description of cranial and lower jaw anatomy in this taxon based on CT data includes new details of sutural morphology, the previously undescribed quadrate and articular bones, and the mandibular symphysis. Sutural morphology is used to infer loading regime in the skull during feeding, and suggests Acanthostega used its anterior jaws to initially seize prey while smaller posterior teeth were used to restrain struggling prey during ingestion. Novel methods were used to repair and retrodeform the skull, resulting in a three-dimensional digital reconstruction that features a longer postorbital region and more strongly hooked anterior lower jaw than previous attempts while supporting the presence of a midline gap between the nasals and median rostrals
- …