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Nonequilibrium properties of graphene probed by superconducting tunnel spectroscopy

Accepted version
Peer-reviewed

Type

Article

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Authors

Zihlmann, S 
Makk, P 
Castilla, S 
Gramich, J 
Thodkar, K 

Abstract

© 2019 American Physical Society. We report on nonequilibrium properties of graphene probed by superconducting tunnel spectroscopy. A hexagonal boron nitride (hBN) tunnel barrier in combination with a superconducting Pb contact is used to extract the local energy distribution function of the quasiparticles in graphene samples in different transport regimes. In the cases where the energy distribution function resembles a Fermi-Dirac distribution, the local electron temperature can directly be accessed. This allows us to study the cooling mechanisms of hot electrons in graphene. In the case of long samples (device length L much larger than the electron-phonon scattering length le-ph), cooling through acoustic phonons is dominant. We find a crossover from the dirty limit with a power law T3 at low temperature to the clean limit at higher temperatures with a power law T4 and a deformation potential of 13.3 eV. For shorter samples, where L is smaller than le-ph but larger than the electron-electron scattering length le-e, the well-known cooling through electron out-diffusion is found. Interestingly, we find strong indications of an enhanced Lorenz number in graphene. We also find evidence of a non-Fermi-Dirac distribution function, which is a result of noninteracting quasiparticles in very short samples.

Description

Keywords

51 Physical Sciences, 5104 Condensed Matter Physics

Journal Title

Physical Review B

Conference Name

Journal ISSN

2469-9950
2469-9969

Volume Title

99

Publisher

American Physical Society
Sponsorship
Engineering and Physical Sciences Research Council (EP/K016636/1)
Engineering and Physical Sciences Research Council (EP/M506485/1)
European Commission Horizon 2020 (H2020) Future and Emerging Technologies (FET) (696656)
European Commission Horizon 2020 (H2020) Future and Emerging Technologies (FET) (785219)
This work has received funding from ERC project TopSupra (787414), the European Union Horizon 2020 research and innovation programme under Grant Agreement No. 696656 (Graphene Flagship), the Swiss National Science Foundation, the Swiss Nanoscience Institute, the Swiss NCCR QSIT, Topograph, ISpinText FlagERA networks and from the OTKA FK-123894 grants. P.M. acknowledges support from the Bolyai Fellowship and as a Marie Curie fellow. This research was supported by the National Research, Development and Innovation Fund of Hungary within the Quantum Technology National Excellence Program (Project No. 2017-1.2.1-NKP-2017-00001). S.H., Sa.C., and R.W. acknowledge support from the EPSRC (EP/K016636/1, EP/M506485/1).