Electron orbital valves made of multiply connected armchair carbon   nanotubes with mirror-reflection symmetry: tight-binding study
  Using the tight-binding method and the Landauer-B\"{u}ttiker conductance formalism, we demonstrate that a multiply connected armchair carbon nanotube with a mirror-reflection symmetry can sustain an electron current of the $\pi$-bonding orbital while suppress that of the $\pi$-antibonding orbital over a certain energy range. Accordingly, the system behaves like an electron orbital valve and may be used as a scanning tunneling microscope to probe pairing symmetry in d-wave superconductors or even orbital ordering in solids which is believed to occur in some transition-metal oxides. 
Gunn Kim, Sang Bong Lee, Hoonkyung Lee, and Jisoon Ihm