25,705 research outputs found
Observation of momentum-confined in-gap impurity state in BaKFeAs: evidence for anti-phase pairing
We report the observation by angle-resolved photoemission spectroscopy of an
impurity state located inside the superconducting gap of
BaKFeAs and vanishing above the superconducting
critical temperature, for which the spectral weight is confined in momentum
space near the Fermi wave vector positions. We demonstrate, supported by
theoretical simulations, that this in-gap state originates from weak
non-magnetic scattering between bands with opposite sign of the superconducting
gap phase. This weak scattering, likely due to off-plane Ba/K disorders, occurs
mostly among neighboring Fermi surfaces, suggesting that the superconducting
gap phase changes sign within holelike (and electronlike) bands. Our results
impose severe restrictions on the models promoted to explain high-temperature
superconductivity in these materials.Comment: 8 pages, 5 figures. Accepted for publication in Physical Review
Broadly defining lasing wavelengths in single bandgap-graded semiconductor nanowires.
Designing lasing wavelengths and modes is essential to the practical applications of nanowire (NW) lasers. Here, according to the localized photoluminescence spectra, we first demonstrate the ability to define lasing wavelengths over a wide range (up to 119 nm) based on an individual bandgap-graded CdSSe NW by forward cutting the NW from CdSe to CdS end. Furthermore, free spectral range (FSR) and modes of the obtained lasers could be controlled by backward cutting the NW from CdS to CdSe end step-by-step. Interestingly, single-mode NW laser with predefined lasing wavelength is realized in short NWs because of the strong mode competition and increase in FSR. Finally, the gain properties of the bandgap-graded NWs are investigated. The combination of wavelength and mode selectivity in NW lasers may provide a new platform for the next generation of integrated optoelectronic devices.This work is supported by National Key Basic Research Program of China (No.
2013CB328703), National Natural Science Foundation of China (No. 51372220,
61177062, 61125402 and 51172004), the Fundamental Research Funds for the
Central Universities, the Program for Zhejiang Leading Team of S&T Innovation and
the Fundamental Research Funds for the Central Universities.This is the author accepted manuscript. The final version can be found on the publisher's website at: http://pubs.acs.org/doi/abs/10.1021/nl500432m Copyright © 2014 American Chemical Societ
Longitudinal Schottky spectra of a bunched Ne10+ ion beam at the CSRe
The longitudinal Schottky spectra of a radio-frequency (RF) bunched and
electron cooled 22Ne10+ ion beam at 70 MeV/u have been studied by a newly
installed resonant Schottky pick-up at the experimental cooler storage ring
(CSRe), at IMP. For an RF-bunched ion beam, a longitudinal momentum spread of
has been reached with less than 107 stored ions. The reduction of momentum
spread compared with coasting ion beam was observed from Schottky noise signal
of the bunched ion beam. In order to prepare the future laser cooling
experiment at the CSRe, the RF-bunching power was modulated at 25th, 50th and
75th harmonic of the revolution frequency, effective bunching amplitudes were
extracted from the Schottky spectrum analysis. Applications of Schottky noise
for measuring beam lifetime with ultra-low intensity of ion beams are
presented, and it is relevant to upcoming experiments on laser cooling of
relativistic heavy ion beams and nuclear physics at the CSRe.Comment: to be published in Chinese Physics
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