Magnetically induced Bragg scattering of electrons in quantum-dot crystals

We demonstrate a novel manifestation of dynamic Bragg reflection in artificial quantum-dot crystals that is driven by the application of a magnetic field. This backscattering is coherently cascaded as the number of dots in the structure is increased, causing a superlinear damping of the electron wave function and the appearance of a series of gaps in the miniband spectrum. The evolution of the dynamic miniband structure as the magnetic field is varied gives rise to behavior analogous to a metal-insulator transition, which is manifest as a dramatic resonance in the magneto-resistance of the structures.

Figure 1

A micrograph of a seven-dot array realized by the split-gate technique. Lighter regions are the metal gates and the white lines show schematically the Hall-bar structure on top of which the gates are deposited.

Figure 2

Main panel: Magneto-resistance of the seven-dot array at several different gate voltages. Lower right inset: Simulated gate-voltage dependent magneto-resistance of the array. Upper right inset: A comparison of the experimental (dotted line) and computed (solid line) magneto-resistance. Also shown in the central inset is the probability density at 0.2 T in the first cell of the seven-dot array. Darker regions indicate higher probability density.

Figure 3

The top panel shows an example of a potential profile that is used in calculations. The middle two panels show the calculated electron probability density in the array at 0 T (upper plot) and 8 T (lower plot). The bottom figures show the computed bandstructure and density of states (DoS) of an infinite chain of quantum dots at 0 T (left) and 0.2 T.

Figure 4

Main panel: comparison of the magneto-resistance of the single dot and the three- and seven-dot arrays. Left inset: Magneto-resistance of the seven-dot array at 30 mK (solid line) and 8 K (dotted line). Right inset: Scaling of the conductance with dot number at 0 T (open symbols) and 0.2 T (filled symbols).