1,014 research outputs found
Angular resolved specific heat in iron-based superconductors: the case for nodeless extended -wave gap
We consider the variation of the field-induced component of the specific heat
with the direction of the applied field in pnictides within
quasi-classical Doppler-shift approximation, with special emphasis to recent
experiments on FeSeTe [Zheng et al., arXiv:1004.2236]. We show
that for extended wave gap with no nodes, has
component, where is the angle between and the direction
between hole and electron Fermi surfaces. The maxima of are at
, , etc. if the applied field is smaller than , and
at , etc. if the applied field is larger than . The
angle-dependence of , the positions of the maxima, and the relative
magnitude of the oscillating component are consistent with the experiments
performed in the field of . We show that the observed
variation does not hold if the wave gap has accidental nodes along the two
electron Fermi surfaces.Comment: 5 pages, 4 figure
Sensor Simulation and position calibration for the CMS pixel detector
In this paper a detailed simulation of irradiated pixel sensors was used to
investigate the effects of radiation damage on charge sharing and position
determination. The simulation implements a model of radiation damage by
including two defect levels with opposite charge states and trapping of charge
carriers. We show that charge sharing functions extracted from the simulation
can be parameterized as a function of the inter-pixel position and used to
improve the position determination. For sensors irradiated to Phi=5.9x10^14
n/cm^2 a position resolution below 15 um can be achieved after calibration.Comment: Presented at the 14th Int. Workshop on Vertex Detectors (Vertex
2005), November 7-11 2005, Chuzenji Lake, Nikko, Japan. 4 pages, 1 figur
Polaron Effects on Superexchange Interaction: Isotope Shifts of , , and in Layered Copper Oxides
A compact expression has been obtained for the superexchange coupling of
magnetic ions via intermediate anions with regard to polaron effects at both
magnetic ions and intermediate anions. This expression is used to analyze the
main features of the behavior of isotope shifts for temperatures of three types
in layered cuprates: the Neel temperatures (), critical temperatures of
transitions to a superconducting state (), and characteristic temperatures
of the pseudogap in the normal state ().Comment: 4 pages, 1 figur
Simulation study of signal formation in position sensitive planar p-on-n silicon detectors after short range charge injection
Segmented silicon detectors (micropixel and microstrip) are the main type of detectors used in the inner trackers of Large Hadron Collider (LHC) experiments at CERN. Due to the high luminosity and eventual high fluence of energetic particles, detectors with fast response to fit the short shaping time of 20-25 ns and sufficient radiation hardness are required. Charge collection measurements carried out at the Ioffe Institute have shown a reversal of the pulse polarity in the detector response to short-range charge injection. Since the measured negative signal is about 30-60% of the peak positive signal, the effect strongly reduces the CCE even in non-irradiated detectors. For further investigation of the phenomenon the measurements have been reproduced by TCAD simulations. As for the measurements, the simulation study was applied for the p-on-n strip detectors similar in geometry to those developed for the ATLAS experiment and for the Ioffe Institute designed p-on-n strip detectors with each strip having a window in the metallization covering the p(+) implant, allowing the generation of electron-hole pairs under the strip implant. Red laser scans across the strips and the interstrip gap with varying laser diameters and Si-SiO2 interface charge densities (Q(f)) were carried out. The results verify the experimentally observed negative response along the scan in the interstrip gap. When the laser spot is positioned on the strip p(+) implant the negative response vanishes and the collected charge at the active strip increases respectively. The simulation results offer a further insight and understanding of the influence of the oxide charge density in the signal formation. The main result of the study is that a threshold value of Q(f), that enables negligible losses of collected charges, is defined. The observed effects and details of the detector response for different charge injection positions are discussed in the context of Ramo's theorem.Peer reviewe
Determination of glass transition temperature for polymers by methods of thermoactivation spectroscopy
For rapid determination of glass transition temperature for polymers, we propose a method of thermally stimulated luminescence. The experiments were carried for epoxy polymers dyed and undyed with organic dyes. It is shown that glass transition temperature depends on curing temperature and concentration of the dye. The comparison with the thermogravimetric analysis showed coincidence of the results obtained
Anisotropic Exchange in LiCuVO probed by ESR
We investigated the paramagnetic resonance in single crystals of LiCuVO
with special attention to the angular variation of the absorption spectrum. To
explain the large resonance linewidth of the order of 1 kOe, we analyzed the
anisotropic exchange interaction in the chains of edge-sharing CuO
octahedra, taking into account the ring-exchange geometry of the
nearest-neighbor coupling via two symmetric rectangular Cu-O bonds. The
exchange parameters, which can be estimated from theoretical considerations,
nicely agree with the parameters obtained from the angular dependence of the
linewidth. The anisotropy of this magnetic ring exchange is found to be much
larger than it is usually expected from conventional estimations which neglect
the bonding geometry. Hence, the data yield the evidence that in copper oxides
with edge-sharing structures the role of the orbital degrees of freedom is
strongly enhanced. These findings establish LiCuVO as one-dimensional
compound at high temperatures.
PACS: 76.30.-v, 76.30.Fc, 75.30.EtComment: 18 pages, 6 figure
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