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7 results on '"Kalmbach, C. -C."'

1. Towards a Graphene-Based Quantum Impedance Standard

Author

Kalmbach, C. -C., Schurr, J., Ahlers, F. J., Müller, A., Novikov, S., Lebedeva, N., and Satrapinski, A.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Other Condensed Matter
Abstract

Precision measurements of the quantum Hall resistance with alternating current (ac) in the kHz range were performed on epitaxial graphene in order to assess its suitability as a quantum standard of impedance. The quantum Hall plateaus measured with alternating current were found to be flat within one part in 10^7. This is much better than for plain GaAs quantum Hall devices and shows that the magnetic-flux-dependent capacitive ac losses of the graphene device are less critical. The observed frequency dependence of about -8x10^-8/kHz is comparable in absolute value to the positive frequency dependence of plain GaAs devices, but the negative sign is attributed to stray capacitances which we believe can be minimized by a careful design of the graphene device. Further improvements thus may lead to a simpler and more user-friendly quantum standard for both resistance and impedance.

Published
2014
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3. Nonequilibrium mesoscopic conductance fluctuations as the origin of 1/f noise in epitaxial graphene

Author

Kalmbach, C.-C., Ahlers, Franz-J., Schurr, J., Müller, A., Feilhauer, J., Kruskopf, M., Pierz, Klaus, Hohls, Frank, Haug, Rolf J., Kalmbach, C.-C., Ahlers, Franz-J., Schurr, J., Müller, A., Feilhauer, J., Kruskopf, M., Pierz, Klaus, Hohls, Frank, and Haug, Rolf J.

Abstract

We investigate the 1/f noise properties of epitaxial graphene devices at low temperatures as a function of temperature, current, and magnetic flux density. At low currents, an exponential decay of the 1/f noise power spectral density with increasing temperature is observed that indicates mesoscopic conductance fluctuations as the origin of 1/f noise at temperatures below 50 K. At higher currents, deviations from the typical quadratic current dependence and the exponential temperature dependence occur as a result of nonequilibrium conditions due to current heating. By applying the Kubakaddi theory [S. S. Kubakaddi, Phys. Rev. B 79, 075417 (2009)10.1103/PhysRevB.79.075417], a model describing the 1/f noise power spectral density of nonequilibrium mesoscopic conductance fluctuations in epitaxial graphene is developed and used to determine the energy loss rate per carrier. In the regime of Shubnikov-de Haas oscillations, a strong increase of 1/f noise is observed, which we attribute to an additional conductance fluctuation mechanism due to localized states in quantizing magnetic fields. When the device enters the regime of quantized Hall resistance, the 1/f noise vanishes. It reappears if the current is increased and quantum Hall breakdown sets in. © 2016 American Physical Society.

Published
2016

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