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Transport properties

Flash Physics: Graphene meets Silly Putty, new linear-collider bosses, Majorana pairs spotted

09 Dec 2016 Hamish Johnston

Flash Physics is our daily pick of the latest need-to-know developments from the global physics community selected by Physics World's team of editors and reporters

Not so silly: graphene and Silly Putty join forces

Graphene and Silly Putty make an excellent strain sensor

Extremely sensitive measurements of deformation and impact have been made using a sensor that is a combination of graphene and Silly Putty. Graphene is a layer of carbon just one-atom thick that has a number of very useful properties including high electrical conductivity. Silly Putty is a children’s toy that is essentially a lump of a viscoelastic polysilicone material. When mixed together by researchers at Trinity College Dublin and the University of Manchester, the resulting “G-putty” is a good conductor of electricity. However, when the material is subject to even a tiny strain or impact, its electrical resistance increases sharply – before relaxing to its original value as the material “self-heals”. This inspired Trinity’s Jonathan Coleman and colleagues to make a sensor from G-putty that when mounted on the neck and chest of a subject could measure breathing pulse and blood pressure. The sensor was even able to detect the footsteps of a small spider. “The behaviour we found with G-putty has not been found in any other composite material,” says Coleman, adding: “This unique discovery will open up major possibilities in sensor manufacturing worldwide”. The material is described in Science.

International Linear Collider Collaboration appoints new associate directors

The International Linear Collider Collaboration (LCC), which promotes the planning and construction of a new linear collider to complement CERN’s Large Hadron Collider (LHC), has appointed two new associate directors. Shinichiro Michizono of the Japanese particle-physics lab KEK will take over as associate director responsible for the International Linear Collider (ILC) design effort – taking over from Michael Harrison of Brookhaven National Laboratory in the US. James Brau of the University of Oregon will become associate director for physics and detectors for the LCC – replacing Hitoshi Yamamoto of Japan’s Tohoku University. Both appointments will take effect in January 2017. The ILC and the Compact Linear Collider (CLIC) are currently the two most popular proposals for a next generation of linear colliders. If built, such a facility will smash together electrons and positrons to make very precise measurements of the Higgs particle and other phenomena that occur at collision energies of a few teraelectronvolts.

Pairs of Majorana fermions seen by physicists

Majorana fermions have been spotted at the end of an atomically thin iron wire by Ernst Meyer and colleagues at the Swiss Nanoscience Institute and the University of Basel. First hypothesized in 1937 by the Italian physicist Ettore Majorana, the fermions are their own antiparticles. While fundamental Majorana fermions have never been detected, they do exist as quasiparticles – collective excitations of electrons in some solids. Meyer and colleagues created their Majorana fermions by growing tiny iron wires (just one-atom thick and up to 70 nm long) on the surface of a superconductor. According to calculations by team members Jelena Klinovaja and Daniel Loss, a pair of Majorana fermions should exist in the nanowire – one at each end. Using scanning-tunnelling and atomic-force microscopes, the team was able to see clear evidence of the quasiparticles (see figure). Despite being separated by tens of nanometres, the Majoranas form a quantum state that can either be occupied or unoccupied by an electron. As such, the nanowire could form the basis of a robust quantum bit (or qubit) of information. The research is described in Quantum Information.

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