Krill Prize 2014
Dr. Shahal Ilani (ד”ר שחל אילני)
Quantum design in carbon nanotubes – Carbon nanotube, a long molecule made entirely of carbon atoms, is one of the most remarkable condensed matter systems given to us by nature. Contrary to conventional metals and semiconductors, nanotubes grow virtually free of structural defects, making them a perfect solid for studying fundamental concepts in quantum mechanics. A nanotube suspended over a “piano” of electrical gates could be the cleanest solid-state approach to localize and control individual electrons, thus forming a powerful lab for studying the physics of electrons, spins, and nano-mechanics in one-dimension. However, so far it was impossible to make such an electronic device without damaging the pristine nature of the nanotube, leaving their huge potential for performing fundamental physics experiments largely unrealized.
In the last few years my group has developed a conceptually new approach for device fabrication that overcomes this barrier. Our approach relies on accurate nano-assembly of pristine nanotubes on electrical circuits of unlimited complexity. With this technique we routinely create devices that are far more complex and clean than was possible so far, enabling us to realize condensed matter experiments that were unimaginable few years ago.
Electronic Phases in One-Dimension – A major thrust of our studies focuses on quantum phases of electrons in one-dimension. We demonstrated that with an array of gates we can virtually shape the wavefunctions of electrons along the axis of a suspended nanotube. We further realized the simplest system in which Coulomb interactions make a dramatic appearance, that of two electrons on a “string”. We showed that the two electrons form a strongly-correlated Wigner-molecule, the simplest manifestation of the quantum crystal of electrons predicted by Eugene Wigner eighty years ago. Currently we study a variety of other canonical phases: Mott insulators in artificially-engineered potential lattices that should exhibit quasiparticles with a fractional charge, Luttinger liquids in which electrons decompose into spin and charge bosonic excitations, and coupled nanotube systems that are predicted to exhibit exciton superfluidity.
Nano-Electro-Mechanics –Suspended nanotubes are also an interesting nano-mechanical system, particularly because their small size means that their mechanical motion is on the verge of being quantum mechanical. Using our devices we can engineer unique nano-mechanical systems in which we fully tailor the coupling between electrons and phonons, by controlling how the electronic system looks in real-space. This coupling is the main ingredient of fundamental physical phenomena such as superconductivity and ferroelectricity, and its arbitrary control on the nanoscale allow us to realize bottom-up these phenomena in very interesting regimes that are unattainable in bulk materials found in nature.
Novel scan probes – A large research activity in our lab is devoted to real-space imaging of correlated one- and two- dimensional systems on the nanoscale. Here we also use nanotubes, but this time playing the role of an ultra-sensitive potential detector. We developed a nanotube based scanning single-electron-transistor capable of measuring a tiny fraction of the electronic charge with nanometric resolution, and we utilize this unique tool to unravel the microscopic physics governing quantum system that were otherwise probed only by macroscopic means.
Complex oxide interfaces – A rich playground for studying correlated electron phenomena has emerged recently with the discovery of a conducting two-dimensional electron system at the interface between two oxide insulators. The experiments that we performed on this system has shown that the large set of emergent phenomena, observed previously in these system, are related to a universal band transition, they further unraveled that this system exhibits a gate-tunable magnetic ground state, and finally, using our nanotube-based scanning single-electron-transistor, discovered the existence of striped domain order with important consequences on the physics of the two-dimensional electrons.