Polar discontinuities to engineer 1D electron wires in 2D honeycomb lattices.

by Giovanni Pizzi (EPFL, CH)

Tuesday 19 May 2015, 11:00 → 12:00 Europe/Stockholm

Nordita West (122:026)

Unprecedented and fascinating phenomena have been recently observed at oxide interfaces between centrosymmetric cubic materials, such as LaAlO3/SrTiO3. At these interfaces, the polar discontinuity between the two insulating materials can give rise to polarization charges and electric fields that drive a metal-insulator transition and the appearance of a high-density two-dimensional electron gas at the interface, without the need to dope the system. Lower dimensional analogues are possible, where for instance 1D conducting electron "wires" can be engineered within a two-dimensional system. In particular, honeycomb lattices offer a fertile playground thanks to their versatility and the extensive on-going experimental efforts in graphene and related materials, transition-metal dichalcogenides, and other novel 2D materials. After discussing the origin of the electron gas in the framework of the so-called "Modern Theory of Polarization", I will discuss several realistic pathways to engineer polar discontinuities in honeycomb lattices: nanoribbons (where a polar discontinuity occurs between the material and vacuum), selective or total functionalizations (where covalent ligands can change the polarization of the parent material and thus induce a polar discontinuity), and grain and phase boundaries. All these suggestions are supported by extensive first-principles calculations using density-functional theory (DFT). All the cases considered have the potential to deliver innovative applications in ultra-thin and flexible solar-energy devices and in micro- and nano- electronics. ​JOURNAL REFERENCE: M. Gibertini, G. Pizzi, and N. Marzari, Engineering polar discontinuities in honeycomb lattices, Nat Commun. 5, 5157 (2014).