9,559 research outputs found
Suppressed Superconductivity of the Surface Conduction Layer in BiSrCaCuO Single Crystals Probed by {\it c}-Axis Tunneling Measurements
We fabricated small-size stacks on the surface of
BiSrCaCuO (BSCCO-2212) single crystals with the bulk
transition temperature 90 K, each containing a few intrinsic
Josephson junctions. Below a critical temperature ( ), we have
observed a weakened Josephson coupling between the CuO superconducting
double layer at the crystal surface and the adjacent one located deeper inside
a stack. The quasiparticle branch in the data of the weakened Josephson
junction (WJJ) fits well to the tunneling characteristics of a d-wave
superconductor()/insulator/d-wave superconductor (DID) junction. Also,
the tunneling resistance in the range agrees well with the
tunneling in a normal metal/insulator/d-wave superconductor (NID) junction. In
spite of the suppressed superconductivity at the surface layer the symmetry of
the order parameter appears to remain unaffected.Comment: 13 pages, 6 figure
Ultraviolet photodepletion spectroscopy of dibenzo-18-crown-6-ether complexes with alkali metal cations
Ultraviolet photodepletion spectra of dibenzo-18-crown-6-ether complexes with alkali metal cations (M+-DB18C6, M = Cs, Rb, K, Na, and Li) were obtained in the gas phase using electrospray ionization quadrupole ion-trap reflectron time-of-flight mass spectrometry. The spectra exhibited a few distinct absorption bands in the wavenumber region of 35450−37800 cm^(−1). The lowest-energy band was tentatively assigned to be the origin of the S_0-S_1 transition, and the second band to a vibronic transition arising from the “benzene breathing” mode in conjunction with symmetric or asymmetric stretching vibration of the bonds between the metal cation and the oxygen atoms in DB18C6. The red shifts of the origin bands were observed in the spectra as the size of the metal cation in M^+-DB18C6 increased from Li^+ to Cs^+. We suggested that these red shifts arose mainly from the decrease in the binding energies of larger-sized metal cations to DB18C6 at the electronic ground state. These size effects of the metal cations on the geometric and electronic structures, and the binding properties of the complexes at the S_0 and S_1 states were further elucidated by theoretical calculations using density functional and time-dependent density functional theories
Sub-100-as timing jitter optical pulse trains from mode-locked Er-fiber lasers
We demonstrate sub-100-attosecond timing jitter optical pulse trains
generated from free-running, 77.6-MHz repetition-rate, mode-locked Er-fiber
lasers. At -0.002(\pm0.001) ps2 net cavity dispersion, the rms timing jitter is
70 as (224 as) integrated from 10 kHz (1 kHz) to 38.8 MHz offset frequency,
when measured by a 24-as-resolution balanced optical cross-correlator. To our
knowledge, this result corresponds to the lowest rms timing jitter measured
from any mode-locked fiber lasers so far. The measured result also agrees
fairly well with the Namiki-Haus analytic model of quantum-limited timing
jitter in stretched-pulse fiber lasers.Comment: 4 pages, 2 figures, to appear in Optics Letter
Instantaneous ionization rate as a functional derivative
We describe an approach defining instantaneous ionization rate (IIR) as a
functional derivative of the total ionization probability. The definition is
based on physical quantities which are directly measurable, such as the total
ionization probability and the waveform of the pulse. The definition is,
therefore, unambiguous and does not suffer from gauge non-invariance. We
compute IIR by solving numerically the time-dependent Schrodinger equation for
the hydrogen atom in a strong laser field. We find that the IIR lags behind the
electric field, but this lag is entirely due to the long tail effect of the
Coulomb field. In agreement with the previous results using attoclock
methodology, therefore, the IIR we define does not show measurable delay in
strong field tunnel ionization
Focused Ion Beam Platinum Nanopatterning for GaN Nanowires: Ohmic Contacts and Patterned Growth
Nanopatterned Pt by Ga+ focused ion beam (FIB) decomposition of an organometallic precursor forms low resistance ohmic contacts on 40–70 nm diameter GaN nanowires (NWs) grown by thermal reaction of Ga2O3 and NH3. With no intentional doping, the wires are presumed to be n-type. Thus, the linear I-V behavior is surprising since evaporated Pt usually forms Schottky barriers on n-GaN. Ohmic behavior was not obtained for 130–140 diameter wires, even with thicker Pt contacts. A second application of FIB Pt nanopatterning was demonstrated by position-selective growth of GaN NWs on Pt catalyst dots. NW locations and density are defined by the position, size, and thickness of the Pt deposit. Combining these techniques provides a versatile platform for nanostructure research and development
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