Violation of Kirchoff’s laws for a coherent RC nanocircuit

[nanoorg]

Violation of Kirchoff’s laws for a coherent RC nanocircuit

French researchers pointed up for the first time remarkable properties of a circuit at a nanometric scale. They confirm Büttiker’s theories: fundamentals laws of electricity cannot describe nanoelectronics circuit properties

French researchers from ENS, CNRS and CEA tested properties of a quantum circuit made with a quantum capacitor realized using a 2DEG (2 dimensional electron gas) and a quantum resistor (a QPC).

In a classic series association, Kirchoff’s laws predict addition of impedances for the measurement of global impedance and more generally define additivity of series resistances. But nonadditivity was also observed in a series of transport experiments at low temperature where phase coherence extends over the mesoscopic scale. That’s why it is generally accepted that the conductance of a phase-coherent quantum conductor is given by the Landauer formula, which relates the conductance to the transmission of electronic waves by the conductance quantum e²/h.

Here researchers tried to know if this formula remains valid when conductance combines with non dissipative elements such as capacitor or inductor.
Their conclusions were:
•Series association of a quantum capacitor and a model quantum resistor doesn’t respect the law of impedance addition.
•The charge-relaxation resistance is no more given by the Landauer formula resistance but instead is constant and equals h/2e².

This discovery is fundamental for nanocircuits properties knowledge which is the stake of electronics next generation. It can be fundamental also for molecular electronics because it will allow a better understanding of electronics equivalent of a molecular circuit via its quantum equivalent.


Source and further information:
http://www2.cnrs.fr/presse/communique/910.htm

http://www.sciencemag.org/


This story was first posted on 2nd August 2006.