302 research outputs found
Evidence for a preformed Cooper pair model in the pseudogap spectra of a Ca10(Pt4As8)(Fe2As2)5 single crystal with a nodal superconducting gap
For high-Tc superconductors, clarifying the role and origin of the pseudogap
is essential for understanding the pairing mechanism. Among the various models
describing the pseudogap, the preformed Cooper pair model is a potential
candidate. Therefore, we present experimental evidence for the preformed Cooper
pair model by studying the pseudogap spectrum observed in the optical
conductivity of a Ca10(Pt4As8)(Fe2As2)5 (Tc = 34.6 K) single crystal. We
observed a clear pseudogap structure in the optical conductivity and observed
its temperature dependence. In the superconducting (SC) state, one SC gap with
a gap size of {\Delta} = 26 cm-1, a scattering rate of 1/{\tau} = 360 cm-1 and
a low-frequency extra Drude component were observed. Spectral weight analysis
revealed that the SC gap and pseudogap are formed from the same Drude band.
This means that the pseudogap is a gap structure observed as a result of a
continuous temperature evolution of the SC gap observed below Tc. This provides
clear experimental evidence for the preformed Cooper pair model.Comment: 15 pages, 4 figure
Optical Evidence of Itinerant-Localized Crossover of Electrons in Cerium Compounds
Cerium (Ce)-based heavy-fermion materials have a characteristic double-peak
structure (mid-IR peak) in the optical conductivity [] spectra
originating from the strong conduction ()-- electron hybridization. To
clarify the behavior of the mid-IR peak at a low - hybridization
strength, we compared the spectra of the isostructural
antiferromagnetic and heavy-fermion Ce compounds with the calculated unoccupied
density of states and the spectra obtained from the impurity Anderson model.
With decreasing - hybridization intensity, the mid-IR peak shifts to the
low-energy side owing to the renormalization of the unoccupied state, but
suddenly shifts to the high-energy side owing to the - on-site Coulomb
interaction at a slight localized side from the quantum critical point (QCP).
This finding gives us information on the change in the electronic structure
across QCP.Comment: 6 pages, 4 figures. To appear in JPSJ (Letters
Electronic-Structure-Driven Magnetic Ordering in a Kondo Semiconductor CeOs2Al10
We report the anisotropic changes in the electronic structure of a Kondo
semiconductor CeOsAl across an anomalous antiferromagnetic ordering
temperature () of 29 K, using optical conductivity spectra. The spectra
along the - and -axes indicate that a - hybridization gap emerges
from a higher temperature continuously across . Along the b-axis, on the
other hand, a different energy gap with a peak at 20 meV appears below 39 K,
which is higher temperature than , because of structural distortion. The
onset of the energy gap becomes visible below . Our observation reveals
that the electronic structure as well as the energy gap opening along the
b-axis due to the structural distortion induces antiferromagnetic ordering
below .Comment: 4 pages, 4 figure
Observation of Electronic Structure Modification in the Hidden Order Phase of CeCoSi
CeCoSi with no local inversion symmetric crystal structure ()
exhibits a phase transition of unknown origin (Hidden Order: HO) at about 12 K
() above the antiferromagnetic transition temperature ( K).
The electronic structure change across was investigated with
high-precision optical reflection spectroscopy. The optical spectrum changed
from a typical metallic behavior above to a gap-like structure at around
15 meV below . The gap-like structure was unchanged across
except for the narrowing of the Drude component of carriers due to the
suppression of magnetic fluctuations. This result suggests a slight change from
the typical metallic electronic structure above to that with an energy
gap near the Fermi level in the HO phase. The change in electronic structure in
the HO phase was concluded to be due to electron/valence instability.Comment: 5 pages, 4 figure
Optical signature of Weyl electronic structures in tantalum pnictides Ta ( P, As)
To investigate the electronic structure of Weyl semimetals Ta (P,
As), optical conductivity [] spectra are measured over a wide
range of photon energies and temperatures, and these measured values are
compared with band calculations. Two significant structures can be observed: a
bending structure at 85 meV in TaAs, and peaks at
50 meV (TaP) and 30 meV (TaAs). The bending structure
can be explained by the interband transition between saddle points connecting a
set of Weyl points. The temperature dependence of the peak intensity can
be fitted by assuming the interband transition between saddle points connecting
a set of Weyl points. Owing to the different temperature dependence of
the Drude weight in both materials, it is found that the Weyl points of TaAs
are located near the Fermi level, whereas those of TaP are further away.Comment: 8 pages, 6 figure
Spinal V2b neurons reveal a role for ipsilateral inhibition in speed control
The spinal cord contains a diverse array of interneurons that govern motor output. Traditionally, models of spinal circuits have emphasized the role of inhibition in enforcing reciprocal alternation between left and right sides or flexors and extensors. However, recent work has shown that inhibition also increases coincident with excitation during contraction. Here, using larval zebrafish, we investigate the V2b (Gata3+) class of neurons, which contribute to flexor-extensor alternation but are otherwise poorly understood. Using newly generated transgenic lines we define two stable subclasses with distinct neurotransmitter and morphological properties. These V2b subclasses synapse directly onto motor neurons with differential targeting to speed-specific circuits. In vivo, optogenetic manipulation of V2b activity modulates locomotor frequency: suppressing V2b neurons elicits faster locomotion, whereas activating V2b neurons slows locomotion. We conclude that V2b neurons serve as a brake on axial motor circuits. Together, these results indicate a role for ipsilateral inhibition in speed control
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