Browsing by Author "Danneau, R."
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- Controlling supercurrents using single-walled carbon nanotube weak links
School of Science | A4 Artikkeli konferenssijulkaisussa(2009) Wu, F.; Danneau, R.; Queipo, P.; Kauppinen, Esko I.; Tsuneta, T.; Hakonen, Pertti J.We have investigated proximity-induced supercurrents in single-walled carbon nanotubes. Phase diffusion is found to be present in the maximum measured supercurrent of 4.8 nA, which results in a minimum of 100Ω zero bias resistance in superconducting state. We also observe that the supercurrent is very sensitive to the measurement bandwidth and large phase fluctuations can even destroy the supercurrents. Our results shed light on the methods of how to improve the performance of high frequency superconducting single-walled nanotube devices. - Energy distribution controlled ballistic Josephson junction
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-12-07) Pandey, P.; Beckmann, D.; Danneau, R.We report an experimental study on the tuning of supercurrent in a ballistic graphene-based Josephson junction by applying a control voltage to a transverse normal channel. In this four-terminal geometry, the control voltage changes the occupation of Andreev states in the Josephson junction, thereby tuning the magnitude of the supercurrent. As a function of gate voltage, we find two different regimes characterized by a double-step distribution and a hot-electron distribution, respectively. Our work opens opportunities to design highly controllable Josephson junctions for tunable superconducting quantum circuits. - Highly sensitive and broadband carbon nanotube radio-frequency single-electron transistor
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2008) Andresen, S. E. S.; Wu, F.; Danneau, R.; Gunnarsson, D.; Hakonen, Pertti J.We have investigated radio-frequency single-electron transistor operation of single-walled carbon nanotube quantum dots in the strong tunneling regime. At a temperature of 4.2 K and with a carrier frequency of 754.2 MHz, we reach a charge sensitivity of 2.3×10 exp −6e/√Hz over a bandwidth of 85 MHz. Our results indicate a gain-bandwidth product of 3.7×10 exp 13 Hz exp (3/2)/e, which is by one order of magnitude better than those for typical radio-frequency single-electron transistors. - Shot noise and conductivity at high bias in bilayer graphene
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2011-12-14) Fay, A.; Danneau, R.; Viljas, J. K.; Wu, F.; Tomi, M. Y.; Wengler, J.; Wiesner, M.; Hakonen, P. J.We have studied electronic conductivity and shot noise of bilayer graphene (BLG) sheets at high bias voltages and low bath temperature T 0=4.2 K. As a function of bias, we find initially an increase of the differential conductivity, which we attribute to self-heating. At higher bias, the conductivity saturates and even decreases due to backscattering from optical phonons. The electron-phonon interactions are also responsible for the decay of the Fano factor at bias voltages V>0.1 V. The high bias electronic temperature has been calculated from shot-noise measurements, and it goes up to ∼1200 K at V=0.75 V. Using the theoretical temperature dependence of BLG conductivity, we extract an effective electron-optical phonon scattering time τ e-op. In a 230-nm-long BLG sample of mobility μ=3600 cm2V -1s -1, we find that τ e-op decreases with increasing voltage and is close to the charged impurity scattering time τ imp=60 fs at V=0.6 V. - Shot noise and conductivity at high bias in bilayer graphene: Signatures of electron-optical phonon coupling
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2011) Fay, A.; Danneau, R.; Viljas, J. K.; Wu, F.; Tomi, M. Y.; Wengler, J.; Wiesner, M.; Hakonen, Pertti J.We have studied electronic conductivity and shot noise of bilayer graphene (BLG) sheets at high bias voltages and low bath temperature T0=4.2 K. As a function of bias, we find initially an increase of the differential conductivity, which we attribute to self-heating. At higher bias, the conductivity saturates and even decreases due to backscattering from optical phonons. The electron-phonon interactions are also responsible for the decay of the Fano factor at bias voltages V>0.1 V. The high bias electronic temperature has been calculated from shot-noise measurements, and it goes up to ∼1200 K at V=0.75 V. Using the theoretical temperature dependence of BLG conductivity, we extract an effective electron-optical phonon scattering time τe–op. In a 230-nm-long BLG sample of mobility μ=3600 cm exp 2 exp V−1 s exp −1, we find that τe–op decreases with increasing voltage and is close to the charged impurity scattering time τimp=60 fs at V=0.6 V. - Shot Noise in Ballistic Graphene
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2008) Danneau, R.; Wu, F.; Craciun, M. F.; Russo, S.; Tomi, M. Y.; Salmilehto, J.; Morpurgo, A. F.; Hakonen, Pertti J.We have investigated shot noise in graphene field effect devices in the temperature range of 4.2–30 K at low frequency (f=600–850 MHz). We find that for our graphene samples with a large width over length ratio W/L, the Fano factor F reaches a maximum F∼1/3 at the Dirac point and that it decreases strongly with increasing charge density. For smaller W/L, the Fano factor at Dirac point is significantly lower. Our results are in good agreement with the theory describing that transport at the Dirac point in clean graphene arises from evanescent electronic states. - Shot noise suppression and hopping conduction in graphene nanoribbons
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2010) Danneau, R.; Wu, F.; Tomi, M. Y.; Oostinga, J. B.; Morpurgo, A. F.; Hakonen, Pertti J.We have investigated shot noise and conduction of graphene field-effect nanoribbon devices at low temperature. By analyzing the exponential I−V characteristics of our devices in the transport gap region, we found out that transport follows variable range hopping laws at intermediate bias voltages 1 - Single-walled carbon nanotube weak links in Kondo regime with zero-field splitting
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2009) Wu, F.; Danneau, R.; Queipo, P.; Kauppinen, Esko I.; Tsuneta, T.; Hakonen, Pertti J.We have investigated proximity-induced supercurrents in single-walled carbon nanotubes in the Kondo regime and compared them with supercurrents obtained on the same tube with Fabry-Pérot resonances. Our data display a wide distribution of Kondo temperatures TK=1–14 K, and the measured critical current ICM vs TK displays two distinct branches; these branches, distinguished by zero-field splitting of the normal-state Kondo conductance peak, differ by an order of magnitude at large values of TK. Evidence for renormalization of Andreev levels in Kondo regime is also found.