Letter to the Nobel Committee

posted Dec 23, 2010, 3:59 AM by Igor Lukyanchuk   [ updated Dec 23, 2010, 10:13 AM ]

(by Y. Kopelevich and I. Luk'yanchuk) Nobel Prize in Physics 2010 was given for “groundbreaking experiments regarding the two-dimensional material graphene.” In fact, before graphene has been extracted from graphite and measured, some of its fundamental physical properties have already been experimentally uncovered in bulk graphite. In this Letter to the Nobel Committee we propose to include those findings in the Scientific Background.

November 19, 2010                    


Yakov Kopelevich (1) and Igor A. Luk’yanchuk (2)

(1) Instituto de Física “Gleb Wataghin“, Universidade Estadual de Campinas, Unicamp 13083-859,
      Campinas, São Paulo, Brasil ;

(2) University of Picardie, Laboratory of Condensed Matter Physics, Amiens, 80039, France, and
      L. D. Landau Institute for Theoretical Physics, Moscow, Russia;

To: The Nobel Committee,
Class for Physics of the Royal Swedish Academy of Sciences

Dears Members of the Nobel Committee,

It appears that our present letter has been written practically at the same time as the Letter by Dr. Walt de Heer to the Nobel Committee commented online by Nature magazine by November 18th, 2010 (doi:10.1038/news.2010.620). With all our deep respect to the Nobel Committee and its valuable work, we feel that important issues are missed in the Scientific Background on the Nobel Prize in Physics 2010. According to the Official Announcement, the prize has been awarded for “groundbreaking experiments regarding the two-dimensional material graphene”. However, before graphene has been extracted from graphite and measured, fundamental properties of graphene layers have already been experimentally uncovered [1, 2]. The results obtained on graphite were the basis on which Manchester’s [3] and Columbia [4] groups built their research. We do believe that it would be only fair to mention the original results [1,2] and hence to establish the actual course of events.

We agree with the comment by Dr. de Heer that all electrical transport measurements given in Science 2004 by Novoselov et al. [5] have been performed on graphite but not single layer graphene samples, and some of those results are not original. Thus, presented by Novoselov et al. data on the Quantum Hall Effect (QHE) coincide with the results previously reported for graphite [1]; see Fig. 1 and Ref. [6]. Although the original work [1] has been cited by Novoselov et al. in their on-line preprint [7]: “This observation offers further support for recent speculations about a possible quantum Hall effect behaviour in graphite”, it has been omitted in the Science paper. Certainly, the original finding of QHE in graphite should be commented in the “Scientific Background”.

All the remarkable electrical properties of graphene described in “Scientific Background” are related to the unusual conic-like electronic spectrum of quasiparticles, known as Dirac Fermions, and the unambiguous evidence of Dirac fermions associated with decoupled graphene planes has been published one year before [2] of the articles by Novoselov [3] and Kim [4] in which we experimentally discovered the existence of the “majority holes with a 2D Dirac-like spectrum”. Unfortunately in the Nature publication [3] this work was cited as the theoretical one. We believe that this key result obtained on graphite should also be mentioned in the “Background”. More specifically, the quantum oscillation experiments [2] showed that Dirac fermions in graphite occupy an unexpectedly large phase volume, inconsistent with any previous 3D theoretical models. This is because the high-quality graphite contains nearly decoupled graphene planes whose electronic properties are governed by Dirac fermions. We stress that the occurrence of independent graphene layers with Dirac fermions in graphite has been confirmed in a large number of more recent experimental studies, see e. g. Refs. [8-11].

One consequence of the Dirac spectrum is that, the quantum effects are observable in graphite even at room temperature [6, 12] at low applied magnetic fields; B < 1 T. This is possible because of the exceptionally high mobility of electrons (holes) in graphite (10^6 - 10^7 cm2/Vs). In fact, the quality of graphene planes in graphite is much higher as compared to separated (extracted) graphene where the mobility is 10^5 cm2/Vs, at best. Hence, graphite and/or multilayer graphene is the most suitable material for quantum devices working under normal conditions, and can be considered as a natural solid state laboratory to test predictions of relativistic theories in the best way. In general, it has been demonstrated that few-layer graphite (e. g. grown on SiC substrate [13, 14]) is a more promising system for technological applications as compared to graphene.

Fig. 1. Normalized Hall conductance Gxy = 1/Rxy obtained for bulk highly oriented pyrolitic graphite (HOPG) [1] and few-layer-thick graphite samples [5]. The plot testifies a similar behavior of thick and thin graphite samples.

1. Y. Kopelevich, J. H. S. Torres, and R. R. da Silva, F. Mrowka, H. Kempa, and P. Esquinazi, Reentrant Metallic Behavior of Graphite in the Quantum Limit, Phys. Rev. Lett. 90, 156402 (2003).
2. I. A. Luk’yanchuk and Y. Kopelevich, Phase Analysis of Quantum Oscillations in Graphite, Phys. Rev. Lett. 93, 166402 (2004).
3. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, M. I. Katsnelson, I. V. Grigorieva, S. V. Dubonos and A. A. Firsov, Two-dimensional gas of massless Dirac fermions in graphene, Nature 438, 197 (2005).
4. Yuanbo Zhang, Yan-Wen Tan, Horst L. Stormer and Philip Kim, Experimental observation of the quantum Hall effect and Berry's phase in graphene, Nature 438, 201 (2005).
5. K. S. Novoselov. A. K. Geim, S. V. Morozov. D. Jiang,Y. Zhang, S. V. Dubonos. I. V. Grigorieva1 and. A. A. Firsov. Electric Field Effect in Atomically Thin Carbon Films, Science 306 666 (2004)
6. Yakov Kopelevich and Pablo Esquinazi, Graphene Physics in Graphite, Adv. Mater. 19, 4559 (2007).
7. K.S. Novoselov, A.K. Geim, S.V. Morozov, S.V. Dubonos, Y. Zhang, D. Jiang, Roomtemp erature electric field effect and carrier-type inversion in graphene films, arXiv:condmat/ 0410631 (2004).
8. I. A. Luk´yanchuk, Y. Kopelevich, and M. El Marssi, Dirac Fermions in Graphite: the State of Art, Physica B 404, 404 (2009).
9. G. Li, A. Luican, and E. Y. Andrei, Scanning Tunneling Spectroscopy of Graphene on Graphite, Phys. Rev. Lett. 102, 176804 (2009).
10. P. Neugebauer, M. Orlita, C. Faugeras, A. L. Barra and M. Potemski, How Perfect Can Graphene Be? Phys. Rev. Lett. 103, 136403 (2009).
11. J. Yan, S. Goler, T.D. Rhone, M. Han, R. He, P. Kim, V. Pellegrini, A.Pinczuk Observation of magneto-phonon resonance of Dirac fermions in graphite arXiv:1008.1206, Phys. Rev. Lett. , tbp (2010).
12. M. Orlita, C. Faugeras, P. Plochocka, P. Neugebauer, G. Martinez, D. K. Maude, A.-L. Barra, M. Sprinkle, C. Berger, W. A. de Heer, and M. Potemski, Approaching the Dirac Point in High-Mobility Multilayer Epitaxial Graphene Phys. Rev. Lett. 101, 267601 (2008).
13. Xiaosong Wu, Yike Hu, Ming Ruan, Nerasoa K Madiomanana, John Hankinson, Mike Sprinkle, Claire Berger, and Walt A. de Heer: Half integer quantum Hall effect in high mobility single layer epitaxial graphene, Appl. Phys. Lett. 95, 223108 (2009).
14. David L. Miller, Kevin D. Kubista, Gregory M. Rutter, Ming Ruan, Walt A. de Heer, Phillip N. First, Joseph A. Stroscio, Observing the Quantization of Zero Mass, Carriers in Graphene, Science, 324, 924 (2009).

Published in arXiv:1011.4680v1  on 21 Nov 2010

Scientists Crack Materials Mystery in Vanadium Dioxide

posted Dec 23, 2010, 3:54 AM by Igor Lukyanchuk

Theoretical research at Oak Ridge National Laboratory in collaboration with Igor Luk'yanchuk from the University of Picardy in France can help explain experimental results in vanadium dioxide, such as the formation of thin conductive channels (seen in white) that can appear under strain in a nanoscale vanadium dioxide sample.

Scientists have known that vanadium dioxide exhibits several competing phases when it acts as an insulator at lower temperatures. However, the exact nature of the phase behavior has not been understood since research began on vanadium dioxide in the early 1960s.Alexander Tselev, a research associate from the University of Tennessee-Knoxville working with ORNL's Center for Nanophase Materials Sciences, in collaboration with Igor Luk'yanchuk from the University of Picardy in France used a condensed matter physics theory to explain the observed phase behaviors of vanadium dioxide, a material of significant technological interest for optics and electronics.

"We discovered that the competition between several phases is purely driven by the lattice symmetry," Tselev said. "We figured out that the metallic phase lattice of vanadium oxide can 'fold' in different ways while cooling, so what people observed was different types of its folding."

Vanadium dioxide is best known in the materials world for its speedy and abrupt phase transition that essentially transforms the material from a metal to an insulator. The phase change takes place at about 68 degrees Celsius."These features of electrical conductivity make vanadium dioxide an excellent candidate for numerous applications in optical, electronic and optoelectronic devices," Tselev said.

Devices that might take advantage of the unusual properties of VO2 include lasers, motion detectors and pressure detectors, which could benefit from the increased sensitivity provided by the property changes of vanadium dioxide. The material is already used in technologies such as infrared sensors. Researchers said their theoretical work could help guide future experimental research in vanadium dioxide and ultimately aid the development of new technologies based on VO2.

"In physics, you always want to understand how the material ticks," said Sergei Kalinin, a senior scientist at the CNMS. "The thermodynamic theory will allow you to predict how the material will behave in different external conditions."

The results were published in the American Chemical Society's Nano Letters. The research team also included Ilia Ivanov, John Budai and Jonathan Tischler at ORNL and Evgheni Strelcov and Andrei Kolmakov at Southern Illinois University. The team's theoretical research expands upon previous experimental ORNL studies with microwave imaging that demonstrated how strain and changes of crystal lattice symmetry can produce thin conductive wires in nanoscale vanadium dioxide samples. Provided by Science Daily

See also: Ученые раскрыли загадку диоксида ванадия
       Раскрыта научная тайна последних десятилетий

Journal References:

Symmetry Relationship and Strain-Induced Transitions between Insulating M1 and M2 and Metallic R phases of Vanadium Dioxide, A. Tselev, I. A. Luk’yanchuk, I. N. Ivanov, et al. Nano Lett. 10, 4409 (2010);

Mesoscopic metal-insulator transition at ferroelastic domain walls in VO2
A. Tselev, V. Meunier, E. Strelcov, W.A. Shelton , I.A. Luk’yanchuk, et. al ACS NANO 44412 (2010)

Interplay between Ferroelastic and Metal−Insulator Phase Transitions in Strained Quasi-2D VO2 Nanoplatelets
A.Tselev, E. Strelcov, I. Luk’yanchuk et al. Nano Lett. 10 203 (2010)

Giant Nernst-Ettingshausen oscillations in classically strong magnetic fields

posted Dec 23, 2010, 3:42 AM by Igor Lukyanchuk   [ updated Dec 24, 2010, 1:42 AM ]

(Featured article) We consider the Nernst-Ettingshausen (NE) effect in the presence of classically strong magnetic fields for a quasi-two dimensional system with a parabolic or linear dispersion of carriers. We show that the occurring giant oscillations of the NE coefficient are coherent with the recent experimental observation in graphene, graphite and bismuth. In the 2D case we find the exact shape of these oscillations and show that their magnitude decreases/increases with enhancement of the Fermi energy for Dirac fermions/normal carriers. With a crossover to 3D spectrum the phase of oscillations shifts, their amplitude decreases and the peaks become asymmetric.
Authors: Igor A. Luk'yanchuk, Andrei A. Varlamov, Alexey V. Kavokin
Published in arXiv:1011.6067v1 on 28 Nov 2010

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