Semiconductor Physics Group
Semiconductor Physics Group, Cavendish Laboratory
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Dr Mark BuitelaarE-mail: mrb51@cam.ac.ukOffice phone number: +44 (0)1223 337332 Fax: +44 (0)1223 337271 Secretary: +44 (0)1223 337482 Office: Room 330A, Mott Building Address:
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I am a Royal Society Dorothy Hodgkin Fellow at the Cavendish Laboratory, University of Cambridge.
Research interests:
Spin physics in carbon nanotube quantum dots and graphene
In our group we investigate spin transport and spin coherent phenomena in carbon nanotubes and graphene. We focus in particular on the exciting possibilities offered by carbon nanotubes and the emerging field of graphene electronics for quantum computation with electron spins. Due to the combination of their unique transport properties and the absence of hyperfine interaction in the dominant 12C isotope, these materials have very specific advantages over other, more developed, semiconductor systems. We have recently demonstrated that the spin degree of freedom in carbon nanotubes can be converted to a much easier measurable charge state or current using the Pauli exclusion principle [3]. We are now using this phenomenon in a controlled way in gate-defined carbon nanotube and graphene quantum dots to measure their spin relaxation and coherence times. In collaboration with the Department of Materials at Oxford University we have also been investigating electron transport in Sc@C82@SWNT peapods [1]. This work is of fundamental interest because of the exceptionally long spin coherence times of the unpaired electrons on the Sc@C82 molecules and the possibility this offers for studying one-dimensional spin chains in carbon nanotubes.
Charge pumping in carbon nanotubes
In our group we have developed an innovative approach to manipulate and measure electrons in carbon nanotubes by coupling them to surface acoustic waves - tiny ripples of mechanical deformation - on piezoelectric substrates. In these devices, the mechanical wave on the surface of the substrate is accompanied by a travelling potential wave which sets the electrons in motion and generates a current, even in the absence of an applied bias voltage. We have already demonstrated that this technique allows us to pump charge in semiconducting carbon nanotubes [6] or modulate the potential on nanotube quantum dots [3]. We now intend to use this technique to probe the correlated nature of the electron system in ultra clean carbon nanotubes. While in non-interacting systems the pumping mechanism by a surface acoustic wave is not unlike the pumping of water by an Archimedean screw, the effects are predicted to be dramatically different in interacting quantum systems such as nanotubes in which electronic correlations are strong. For example, the electrons can flow against the direction of the pump or the pump can deliver a spin current with a vanishing charge current, a phenomenon known as spin-charge separation. Yet, a further exciting possibility is the observation of currents which are precisely quantized in integers, or even rational fractions, of the electron charge.
As the pumping current directly reflects the nature of the interactions and the response of the system to time-dependent parameters, this research will provide new insight in the dynamic behaviour of correlated electron systems. At the same time, the studied phenomena are of practical interest in a variety of scientific disciplines. For example, quantized currents have an important application as a current standard in electrical metrology and we collaborate with the National Physical Laboratory , the UK’s standards institute, towards this aim. Likewise, a device that generates pure spin currents would be an important tool in the field of spintronics which is expected to add considerable functionality to the next generation of electronic applications.
Previous research:
Carbon nanotubes coupled to superconductors
Whereas the fields of mesoscopic superconductivity and quantum dots have both been studied intensively, they have remained largely unrelated. To connect the two, I have made novel devices consisting of a carbon nanotube quantum dot coupled to superconducting leads. The physics that describes the electrical properties of these structures proved to be very rich. In particular, I showed that Kondo correlations and superconductivity can coexist on the quantum dots provided that the Kondo temperature exceeds the superconducting gap energy [10]. In a collaborative effort with theoretical physicists I analyzed in detail how the observed multiple Andreev reflection processes in these devices uniquely depend on the energy of the single-electron states in the quantum dots [7,8].
This work has been part of my PhD in the group of Christian Schönenberger in Basel (CH). The work also included the study of electron transport in multiwall carbon nanotube quantum dots (including the first observation of the predicted 4-fold degeneracy in the electron spectra [11]), quantum inteference phenomena, Luttinger liquid behaviour and the sensitivity of the transport to environmental conditions. My thesis can be downloaded here (for requests of a hardcopy, please send me an email).Research students:
- Zoë Penfold-Fitch
- Reuben Puddy
Refereed journal papers:
[1] "Electronic transport properties of Sc@C82 single-wall carbon nanotube
peapods",
A.L. Cantone, M.R. Buitelaar, C.G. Smith, D. Anderson, G.A.C. Jones, S.J. Chorley, C.
Casiraghi, A. Lombardo, A.C. Ferrari, H. Shinohara, A. Ardavan, J. Warner, A.A.R. Watt, K. Porfyrakis, and
G.A.D. Briggs
J. Appl. Phys. 104, 083717 (2008).
[2] "Adiabatic charge pumping in carbon nanotube quantum dots",
M.R. Buitelaar, V. Kashcheyevs, P.J. Leek, V.I. Talyanskii, C.G. Smith, D. Anderson, G.A.C. Jones, J. Wei, and D.H. Cobden
Phys. Rev. Lett. 101, 126803 (2008).
[3] "Pauli spin blockade in carbon nanotube double quantum dots",
M.R. Buitelaar, J. Fransson, A.L. Cantone, C.G. Smith, D. Anderson, G.A.C. Jones, A. Ardavan, A.N. Khlobystov, A.A.R. Watt, K. Porfyrakis, and G.A.D. Briggs
Phys. Rev. B 77, 245439 (2008).
[4] "Simultanuous fabrication of nanogap gold electrodes by electroless gold plating using a
common medical liquid",
Y. Yasutake, K. Kono, M. Kanehara, T. Teranishi, M.R. Buitelaar, C.G. Smith, and Y. Majima
Appl. Phys. Lett. 91, 203107 (2007).
[5] "Charge pumping and current quantization in surface acoustic-wave-driven carbon nanotube devices",
M.R. Buitelaar, P.J. Leek, V.I. Talyanskii, C.G. Smith, D. Anderson, G.A.C. Jones, J. Wei and D.H. Cobden
Semicon. Sci. Technol. 21, S69 (2006).
[6] "Charge Pumping in Carbon Nanotubes",
P.J. Leek, M.R. Buitelaar, V.I. Talyanskii, C.G. Smith, D. Anderson, G.A.C. Jones, J. Wei and D.H. Cobden
Phys. Rev. Lett. 95, 256802 (2005).
[7] "Conductance properties of nanotubes coupled to superconducting leads: signatures of Andreev states dynamics",
E. Vecino, M.R. Buitelaar, A. Martín-Rodero, C. Schönenberger and A. Levy Yeyati
Solid State Comm. 131, 625 (2004).
[8] "Multiple Andreev Reflections in a Carbon Nanotube Quantum Dot",
M.R. Buitelaar, W. Belzig, T. Nussbaumer, B. Babic, C. Bruder and C. Schönenberger
Phys. Rev. Lett. 91, 057005 (2003).
[9] "Sensitivity of single multiwalled carbon nanotubes to the environment",
M. Krüger, I. Widmar, T. Nussbaumer, M.R. Buitelaar and C. Schönenberger
New Journal of Physics 5, 138 (2003).
[10] "Quantum Dot in the Kondo Regime Coupled to Superconductors",
M.R. Buitelaar, T. Nussbaumer and C. Schönenberger
Phys. Rev. Lett. 89, 256801 (2002).
[11] "Multiwall Carbon Nanotubes as Quantum Dots",
M.R. Buitelaar, A. Bachtold, T. Nussbaumer, M. Iqbal and C. Schönenberger
Phys. Rev. Lett. 88, 156801 (2002).
[12] "Suppression of Tunneling into Multiwall Carbon Nanotubes",
A. Bachtold, M. de Jonge, K. Grove-Rasmussen, P.L. McEuen, M.R. Buitelaar and C. Schönenberger
Phys. Rev. Lett. 87, 166801 (2002).
[13] "Electrochemical carbon nanotube field-effect transistor",
M. Krüger, M.R. Buitelaar, T. Nussbaumer, L. Forró and C. Schönenberger
Appl. Phys. Lett. 78, 1291 (2001).
[14] "Spatially resolved scanning tunneling spectroscopy on single-walled carbon nanotubes",
L.C. Venema, J.W. Janssen, M.R. Buitelaar, J.W.G. Wildöer, S.G. Lemay, L.P. Kouwenhoven and C. Dekker
Phys. Rev. B 62, 5238 (2000).
Refereed conference papers:
[C1] "Charge Pumping in Carbon Nanotubes",
V.I. Talyanskii, P.J. Leek, M.R. Buitelaar, C.G. Smith, D. Anderson, G.A.C. Jones, J. Wei and D.H. Cobden
Physica E 34, 662 (2006).
[C2] "Doping state of multi-wall carbon nanotube wires and quantum dots",
C. Schönenberger, M.R. Buitelaar, M. Krüger, I. Widmar, T. Nussbaumer and M. Iqbal
Proceedings of the 36th Rencontres de Moriond, Les Arcs, France (2001).
