Tuning the magnetic ground state of Ce1−xYbxRhIn5 by Yb valence fluctuations

We characterize the properties of Ce1−xYbxRhIn5 single crystals with 0 ⩽ x ⩽ 1 using measurements of powder x-ray diffraction, energy dispersive x-ray spectroscopy, electrical resistivity, magnetic susceptibility, specific heat, x-ray absorption near edge structure (XANES), and neutron diffraction. The Yb valence vYb, calculated from the magnetic susceptibility and measured using XANES, decreases from 3+ at x = 0 to ∼2.1+ at xact = 0.2, where xact is the measured Yb concentration. A transition from incommensurate to commensurate antiferromagnetism is observed in neutron diffraction measurements along Q = (0.5, 0.5, l) between 0.2 ⩽ xact ⩽ 0.27; this narrative is supported by specific-heat measurements in which a second robust feature appears at a temperature TI (TI \u3c TN) for the same concentration range. Magnetic susceptibility measurements also reveal features which provide additional evidence of magnetic ordering. The results of this study suggest that the evolution of the Yb valence plays a critical role in tuning the magnetic ground state of Ce1−xYbxRhIn5

Attosecond optoelectronic field measurement in solids

The sub-cycle interaction of light and matter is one of the key frontiers of inquiry made accessible by attosecond science. Here, we show that when light excites a pair of charge carriers inside of a solid, the transition probability is strongly localized to instants slightly after the extrema of the electric field. The extreme temporal localization is utilized in a simple electronic circuit to record the waveforms of infrared to ultraviolet light fields. This form of petahertz-bandwidth field metrology gives access to both the modulated transition probability and its temporal offset from the laser field, providing sub-fs temporal precision in reconstructing the sub-cycle electronic response of a solid state structure. Characterization of light pulses is important in order to understand their interaction with matter. Here the authors demonstrate a nonlinear photoconductive sampling method to measure electric field wave-forms in the infrared, visible and ultraviolet spectral ranges

Diversity of a cytokinin dehydrogenase gene in wild and cultivated barley

The cytokinin dehydrogenase gene HvCKX2.1 is the regulatory target for the most abundant heterochromatic small RNAs in drought-stressed barley caryopses. We investigated the diversity of HvCKX2.1 in 228 barley landraces and 216 wild accessions and identified 14 haplotypes, five of these with ten or more members, coding for four different protein variants. The third largest haplotype was abundant in wild accessions (51 members), but absent from the landrace collection. Protein structure predictions indicated that the amino acid substitution specific to haplotype 3 could result in a change in the functional properties of the HvCKX2.1 protein. Haplotypes 1–3 have overlapping geographical distributions in the wild population, but the average rainfall amounts at the collection sites for haplotype 3 plants are significantly higher during November to February compared to the equivalent data for plants of haplotypes 1 and 2. We argue that the likelihood that haplotype 3 plants were excluded from landraces by sampling bias that occurred when the first wild barley plants were taken into cultivation is low, and that it is reasonable to suggest that plants with haplotype 3 are absent from the crop because these plants were less suited to the artificial conditions associated with cultivation. Although the cytokinin signalling pathway influences many aspects of plant development, the identified role of HvCKX2.1 in the drought response raises the possibility that the particular aspect of cultivation that mitigated against haplotype 3 relates in some way to water utilization. Our results therefore highlight the possibility that water utilization properties should be looked on as a possible component of the suite of physiological adaptations accompanying the domestication and subsequent evolution of cultivated barley

Efficient, octave-spanning difference-frequency generation using few-cycle pulses in simple collinear geometry

We present experimental observations and corresponding numerical simulations illustrating the difference-frequency generation of mid-infrared radiation using few-cycle near-infrared-to-visible pulses, which yields conversion efficiencies above 12% in beta-barium borate crystal. Type I and type II phase-matching are shown to yield qualitatively different intensity-scaling behavior, with the former showing higher overall efficiency, especially with the addition of a zero-order wave plate for modifying the polarization state of the pulse, and the latter having a better stability of the spectrum versus input intensity

Decoupling chaotic amplification and nonlinear phase in high-energy thin-disk amplifiers for stable OPCPA pumping

The dynamics of chirped pulse amplification in thin-disk regenerative amplifiers relevant to the pumping of optical parametric chirp pulse amplification systems are described. It is shown that the suitability for reproducible pumping of subsequent nonlinear processes requires a balance between the demands of avoiding chaotic pulse train dynamics and providing a reproducible spectral phase. We describe measures that may be taken to ensure that a laser system operates in the desired stable regime

Decoupling chaotic amplification and nonlinear phase in high-energy thin-disk amplifiers for stable OPCPA pumping

The dynamics of chirped pulse amplification in thin-disk regenerative amplifiers relevant to the pumping of optical parametric chirp pulse amplification systems are described. It is shown that the suitability for reproducible pumping of subsequent nonlinear processes requires a balance between the demands of avoiding chaotic pulse train dynamics and providing a reproducible spectral phase. We describe measures that may be taken to ensure that a laser system operates in the desired stable regime. (C) 2014 Optical Society of AmericaX116sciescopu