Nanoscale Quantum Physics Group

Research - Project One

Making Fizeau fringes with a quantum wedge and internal electron waves.

We have introduced a new and fascinating quantum object which we named “quantum wedge”. A quantum wedge is a nano-scale wedge with its thickness varying monotonically by discrete atomic planes. In a quantum wedge, electron waves are strongly quantized normal to its surface, and electrons occupy a set of two- dimensional energy bands. An increase of the thickness by each atomic plane introduces new sub-bands in that particular slab, causing the electron energy spectrum to shift, and the energy separation to narrow. Thus, a quantum wedge can be viewed as an assembly of artificial atoms across a “periodic table”. It offers us a rather unique new structure for studying quantum confinement at atomic precision.

To realize such a geometry experimentally, we use epitaxial growth of Pb on a stepped Si substrate. The need for this hetero-epitaxial system to reduce its internal strain and its surface energy drives the Pb to form a flat-topped island; thus the desired wedge geometry is obtained.

One of the most striking results on these Pb wedges is the observation of the electron interference fringes spontaneously formed on the surface of the wedge. This experiment demonstrates a quantum mechanical analog of the classical optical Fizeau fringe experiment.

For a detailed description see: Altfeder, I.B., Matveev, K.A., Chen, D.M. “Electron fringes on a quantum wedge”, Phys. Rev. Lett., 78, 2815-2818 (1997).