75 nanotimes News in Brief

A new class of unconventional superconductors: Researchers at the Rutherford Appleton Laboratory and at the universities of Kent, Bristol and Huddersfield, in UK, have discovered a new class of very exotic unconventional superconductors, namely LaNiGa2. The crystal structure of the new superconductor does have symmetry under inversion, but the chemical similarity of the two compounds suggests that they are two instances of a new family of superconductors that have non-unitary triplet pairing even though they are not ferromagnetic. The team shows, by a very general reasoning based on the fundamental symmetries of nature, that the natural tendencies in these materials to magnetise under the influence of an externally-applied magnetic field, what is called ‘paramagnetism’, can lead to the development of a magnetisation in response to the magnetic moments of the Cooper pairs themselves.  In other words, rather than relying on some pre-existing magnetisation, the magnetic moments of the Cooper pairs themselves create the magnetism that is required for their magnetisation to be energetically favourable – thus non-unitary triplet pairing can lift itself by its bootstraps. This would be a superconducting analogue of the way magnetism develops in ferromagnetic metals. A confirmation of this scenario would be quite spectacular, as it is a new form of magnetism that is generated by superconductivity.

A. D. Hillier, J. Quintanilla, B. Mazidian, J. F. Annett, and R. Cywinski: Nonunitary triplet pairing in the centrosymmetric superconductor LaNiGa2, In: Physical Review Letters [Accepted], June 22, 2012. http://prl.aps.org

During photosynthesis, plants capture solar energy and use it to drive chemical reactions. Their carbon source is the CO2 in air. In the journal Angewandte Chemie, American scientists have now proposed a new reaction mechanism that binds CO2 and strongly resembles photosynthesis. In this process, light energy is captured by silicon nanowires. It was successfully used to synthesize two precursors of the anti-inflammatory, pain reducing drugs ibuprofen and naproxen.

A team led by Kian L. Tan and Dunwei Wang at Boston College (Chestnut Hill, USA) has been inspired by the mechanisms of the dark reactions. To capture sunlight, the scientists used p-doped silicon nanowires as a photocathode. These very effectively convert solar energy to electrical energy, are easy to produce, and are amazingly stable under the reaction conditions needed. Captured photons release electrons from the atoms in the nanowires. These electrons can easily be transferred to organic molecules to trigger chemical reactions. The researchers chose aromatic ketones as their starting materials. Transfer of electrons from the photocathode "activates" these molecules so that they can attack and bind CO2. Over several steps, the reaction produces an α-hydroxy acid. This allowed the team to produce precursors of ibuprofen and naproxen with high selectivity and in high yield.

Rui Liu, Guangbi Yuan, Candice L. Joe, Dr. Thomas E. Lightburn, Prof. Dr. Kian L. Tan, Dunwei Wang: Silicon Nanowires as Photoelectrodes for Carbon Dioxide Fixation, In: Angewandte Chemie International Edition, Early View, May 22, 2012, DOI:10.1002/anie.201202569:

http://dx.doi.org/10.1002/anie.201202569