scanning gate microscopy

Selective control of edge channel trajectories by SGM

Interference phenomena are a fundamental manifestation of the quantum mechanical nature of electrons and have promising applications in solid-state quantum information technology [1]. Two-dimensional electron systems (2DES) in the quantum Hall (QH) regime are especially suited for this purpose given the large electronic coherence length brought by edge channel chiral transport. In particular, the realization of electronic Mach-Zehnder (MZ) interferometers in QH systems appears at present a sound technology for the implementation of quantum information schemes. Despite this success, the edge topology of the single-channel MZs limits the complexity of these circuits to a maximum of two interferometers [2]. In order to overcome this constraint, new device architectures were recently proposed, where interference paths are built using two different parallel edge channels [1]. In this configuration, control over the interaction between the different edge channels is very challenging owing to the complex edge structure.

SGM-QHE

Figure 1: Conductance profile through the QPC as a function of filling factors g under the QPC gates. The left inset shows a two-dimensional SGM map of G vs. tip position for g1=g2=0. The vertical line indicates the profile position, the QPC border is outlined. The right inset is a sketch of the edge channels for g1=2, g2=1.

In order to address these issues we are exploring the use of scanning gate microscopy (SGM) to control the trajectory and interaction of edge channels based on our previous results on quantum point contact (QPC) devices in the QH regime [3]. Samples were fabricated starting from high-mobility AlGaAs heterostructures and Schottky split-gate QPCs. SGM experiments were performed at 400mK with magnetic field up to 9T. Figure 1 shows QPC conductance (G) as a function of the position of the biased SGM tip (Vtip= -3V). The (bulk) 2DES filling factor is set to v = 6 (3 spin-degenerate edge channels) while the QPC gates completely deplete the 2DES underneath (gate-region spin-degenerate filling factor g1 = g2 = 0). When the biased tip is brought close to the QPC, edge channels are backscattered one by one, and the conductance through the QPC decreases in a step-like manner to 0. The split-gate QPC however also allows to bias the individual gates asymmetrically and pre-select edges that can then be manipulated by the SGM tip. For instance in the case g1 = 2, g2 = 1 only the inner edge channel can be backscattered by the local action of the tip, while the others either flow (under the gate) far from the constriction or have no counterpart for the backscattering process to occur. In this latter case, the conductance value remains G = 4e2/h even when the tip completely pinches off the constriction region (Fig. 1, orange curve).

Our results are a crucial first step for the implementation of multi-edge beam mixers and interferometers.

References

  1. V. Giovannetti et al., Phys. Rev. B 77, 155320 (2008).
  2. I. Neder et al., Nature 448, 333 (2007).
  3. S. Roddaro et al., Phys. Rev. Lett. 95, 156804 (2005).

Publications

  1. N. Paradiso, S. Heun, S. Roddaro, L. N. Pfeiffer, K. W. West, L. Sorba, G. Biasiol, and F. Beltram: Selective control of edge-channel trajectories by scanning gate microscopy, Physica E 42 (2010) 1038 - 1041.

  2. Selected Application in the Attocube Product Catalog 2009 - 2010 (page 74).

  3. Selected Application in the Attocube Product Catalog 2010 - 2011 (page 54).

  4. NEST Activity Report 2007-2009: Selective control of quantum Hall edge-channel trajectories by scanning gate microscopy.

  5. NEST Activity Report 2007-2009: Interferometry and entanglement detection at the nanoscale.

Presented at

  1. N. Paradiso, S. Heun, S. Roddaro, L. Sorba, G. Biasiol, and F. Beltram: Scanning gate microscopy and individual control of edge-state transmission through a quantum point contact , Emergent Phenomena in Quantum Hall Systems 3 (EPQHS3), Villa Guinigi, Capannori, Lucca (Tuscany, Italy), 25 - 28 June 2009. [Abstract] [Poster]

  2. N. Paradiso, S. Heun, S. Roddaro, L. N. Pfeiffer, K. W. West, L. Sorba, G. Biasiol, and F. Beltram: Scanning gate microscopy and individual control of edge-channel transmission through a quantum point contact, NTT Basic Research Laboratories, Atsugi, Japan (Dr. H. Hibino), 16 July 2009. [Abstract] [Talk]

  3. N. Paradiso, S. Heun, S. Roddaro, L. N. Pfeiffer, K. W. West, L. Sorba, G. Biasiol, and F. Beltram: Scanning gate microscopy and individual control of edge-channel transmission through a quantum point contact, ISSP, Tokyo University (Prof. Y. Hasegawa), 17 July 2009. [Abstract] [Talk]

  4. N. Paradiso, S. Heun, S. Roddaro, L. N. Pfeiffer, K. W. West, and F. Beltram: Selective control of edge channel trajectories by SGM, 18th International Conference on Electronic Properties of Two-Dimensional Systems (EP2DS-18), Kobe, Japan, 19 - 24 July 2009. [Abstract] [Poster]

See also: The Scanning Gate Microscopy Laboratory at NEST

Contact

sample

Dr. Stefan Heun
Senior Scientist

NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore
Piazza San Silvestro 12
56127 Pisa, Italy

tel. office +39-050-509 472
SGM lab. +39-050-509 467
STM lab. +39-050-509 461
fax. +39-050-509 417

e-mail: stefan.heun@nano.cnr.it