《自然》[Nature]12年3月15日出版pdf全文 , }5 G3 ` [) m) K4 g! Z ) v* X5 r* b VThe electronic structure of certain solids causes them to exhibit ‘Dirac points', which lie at the heart of many fascinating phenomena in condensed-matter physics. In graphene, for example, they cause electrons to act as massless Dirac fermions, able to travel at the speed of light. Two very different methods for controlling the properties of Dirac fermions are presented in this issue of Nature. In conventional solids, the electronic structure of the material cannot be varied, so it is difficult to see how the properties of Dirac fermions could be controlled. To avoid this constraint, Tarruell et al. create a tunable system of ultracold quantum gases within an adjustable honeycomb optical lattice. This model simulates condensed-matter physics, with atoms in the role of electrons. The Dirac points can be moved and merged to explore the physics of exotic materials such as topological insulators and graphene. On the cover, the band structure of artificial graphene with intersections at two Dirac points. Gomes et al. describe a more direct approach, creating an artificial form of molecular graphene by arranging carbon monoxide molecules, with atomic precision, in a honeycomb pattern on top of a two-dimensional electron system. Lattice parameters are adjustable, allowing the study of the properties of Dirac electrons and even the production of 'pseudo' electric and magnetic fields. This work highlights an innovative technique for constructing artificial materials with molecular assembly, including designer Dirac materials harbouring new ground states.Cover: Thomas Uehlinger / Inset: Shutterstock5 i3 x: |. b. p1 t/ O
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9 o4 ~+ w4 }( g+ o 作者: tpwang 时间: 2012-3-15 10:16
