Formation of a protected sub-band for conduction in quantum point contacts under extreme biasing


Managing energy dissipation is critical to the scaling of current microelectronics1,2,3 and to the development of novel devices that use quantum coherence to achieve enhanced functionality4. To this end, strategies are needed to tailor the electron–phonon interaction, which is the dominant mechanism for cooling non-equilibrium (‘hot’) carriers5,6. In experiments aimed at controlling the quantum state7,8,9,10,11, this interaction causes decoherence that fundamentally disrupts device operation12,13. Here, we show a contrasting behaviour, in which strong electron–phonon scattering can instead be used to generate a robust mode for electrical conduction in GaAs quantum point contacts, driven into extreme non-equilibrium by nanosecond voltage pulses. When the amplitude of these pulses is much larger than all other relevant energy scales, strong electron–phonon scattering induces an attraction between electrons in the quantum-point-contact channel, which leads to the spontaneous formation of a narrow current filament and to a renormalization of the electronic states responsible for transport. The lowest of these states coalesce to form a sub-band separated from all others by an energy gap larger than the source voltage. Evidence for this renormalization is provided by a suppression of heating-related signatures in the transient conductance, which becomes pinned near 2e2/h (e, electron charge; h, Planck constant) for a broad range of source and gate voltages. This collective non-equilibrium mode is observed over a wide range of temperature (4.2–300 K) and may provide an effective means to manage electron–phonon scattering in nanoscale devices.

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Figure 1: Transient response of QPC-C.
Figure 2: Different regimes of nonlinear transport and their manifestation in the conductance.
Figure 3: Sub-band renormalization under high bias.


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This research was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering (award DE-FG02-04ER46180). The work was performed, in part, at the Center for Integrated Nanotechnologies, a US Department of Energy, Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration (contract DE-AC04-94AL85000). J.E.H. acknowledges support from the National Science Foundation (DMR-0907150).

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J.L. fabricated the devices and performed the measurements described in this paper. He also collaborated with J.P.B. on data analysis. J.E.H. performed the theoretical analysis and collaborated with J.P.B. on the writing of the manuscript. J.S. constructed the transient-measurement system and J.S. and J.P.B. designed the experiment. J.L.R. grew the high-quality semiconductor wafer, while S.X. performed magneto-characterization of its low-temperature electrical properties.

Correspondence to J. E. Han or J. P. Bird.

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Lee, J., Han, J., Xiao, S. et al. Formation of a protected sub-band for conduction in quantum point contacts under extreme biasing. Nature Nanotech 9, 101–105 (2014).

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