Strain engineering is widely used to manipulate the electronic and magnetic properties of complex materials 1, 2 . An attractive route to control magnetism with strain is provided by the piezomagnetic effect, whereby the staggered spin structure of an antiferromagnet is decompensated by breaking the crystal field symmetry, which induces a ferrimagnetic polarization. Piezomagnetism is especially attractive because unlike magnetostriction it couples strain and magnetization at linear order 3 , and allows for bi-directional control suitable for memory and spintronics applications 4, 5 . However, its use in functional devices has so far been hindered by the slow speed and large uniaxial strains required. Here, we show that the essential features of piezomagnetism can be reproduced with optical phonons alone, which can be driven by light to large amplitudes without changing the volume and hence beyond the elastic limits of the material. We exploit nonlinear, three-phonon mixing to induce the desired crystal field distortions in the antiferromagnet CoF2. Through this effect, we generate a ferrimagnetic moment of 0.2 μB per unit cell, nearly three orders of magnitude larger than achieved with mechanical strain 6 .
We report on the generation of high-energy (1.9 μJ) far-infrared pulses tunable between 4 and 18 THz frequency. Emphasis is placed on tunability and on minimizing the bandwidth of these pulses to less than 1 THz, as achieved by difference-frequency mixing of two linearly chirped near-infrared pulses in the organic nonlinear crystal DSTMS. As the two near-infrared pulses are derived from amplification of the same white light continuum, their carrier envelope phase fluctuations are mutually correlated, and hence the difference-frequency THz field exhibits absolute phase stability. This source opens up new possibilities for the control of condensed matter and chemical systems by selective excitation of low-energy modes in a frequency range that has, to date, been difficult to access.
Optical excitation in the cuprates has been shown to induce transient superconducting correlations above the thermodynamic transition temperature, TC, as evidenced by the terahertz frequency optical properties in the nonequilibrium state. In YBa2Cu3O6+x this phenomenon has so far been associated with the nonlinear excitation of certain lattice modes and the creation of new crystal structures. In other compounds, like La2-xBaxCuO4, similar effects were reported also for excitation at near infrared frequencies, and were interpreted as a signature of the melting of competing orders. However, to date it has not been possible to systematically tune the pump frequency widely in any one compound, to comprehensively compare the frequency dependent photo-susceptibility for this phenomenon. Here, we make use of a newly developed optical parametric amplifier, which generates widely tunable high intensity femtosecond pulses, to excite YBa2Cu3O6.5 throughout the entire optical spectrum (3 -750 THz). In the far-infrared region (3 -25 THz), signatures of non-equilibrium superconductivity are induced only for excitation of the 16.4 THz and 19.2 THz vibrational modes that drive c-axis apical oxygen atomic positions. For higher driving frequencies (25 -750 THz), a second weaker resonance is observed around the charge transfer band edge at ~350 THz. These observations highlight the importance of coupling to the electronic structure of the CuO2 planes, either mediated by a phonon or by charge transfer.
Aims: To isolate and characterize atrazine-degrading bacteria in order to identify suitable candidates for potential use in bioremediation of atrazine contamination. Methods and Results: A high efficiency atrazine-degrading bacterium, strain AD1, which was capable of utilizing atrazine as a sole nitrogen source for growth, was isolated from industrial wastewater. 16S rDNA sequencing identified AD1 as an Arthrobacter sp. The atrazine chlorohydrolase gene (atzA) isolated from strain AD1 differed from that found in the Pseudomonas sp. ADP by only one nucleotide. However, it was found located on the bacterial chromosome rather than on plasmids as previously reported for other bacteria. Conclusions: Atrazine chlorohydrolase gene, atzA, either encoded by chromosome or plasmid, is highly conserved. Significance and Impact of the Study: Comparison analysis of atrazine degradation gene structure and arrangement in this and other bacteria provides insight into our understanding of the ecology and evolution of atrazine-degrading bacteria.
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