1、70RANDOM WALK TO GRAPHENENobel Lecture, December 8, 2010byANDRE K. GEIMSchool of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom.If one wants to understand the beautiful physics of graphene, they will be spoiled for choice with so many reviews and
2、 popular science articles now available. I hope that the reader will excuse me if on this occasion I recommend my own writings 13. Instead of repeating myself here, I have chosen to describe my twisty scientific road that eventually led to the Nobel Prize. Most parts of this story are not described
3、anywhere else, and its time-line covers the period from my PhD in 1987 to the moment when our 2004 paper, recognised by the Nobel Committee, was accepted for publication. The story naturally gets denser in events and explanations towards the end. Also, it provides a detailed review of pre-2004 liter
4、ature and, with the benefit of hindsight, attempts to analyse why graphene has attracted so much inter-est. I have tried my best to make this article not only informative but also easy to read, even for non-physicists. ZOMBIE MANAGEMENTMy PhD thesis was called “Investigation of mechanisms of transpo
5、rt relaxa-tion in metals by a helicon resonance method”. All I can say is that the stuff was as interesting at that time as it sounds to the reader today. I published five journal papers and finished the thesis in five years, the official duration for a PhD at my institution, the Institute of Solid
6、State Physics. Web of Science so-berly reveals that the papers were cited twice, by co-authors only. The subject was dead a decade before I even started my PhD. However, every cloud has its silver lining, and what I uniquely learned from that experience was that I should never torture research stude
7、nts by offering them “zombie” projects. After my PhD, I worked as a staff scientist at the Institute of Micro-electronics Technology, Chernogolovka, which belongs to the Russian Academy of Sciences. The Soviet system allowed and even encouraged junior staff to choose their own line of research. Afte
8、r a year of poking in different directions, I separated research-wise from my former PhD supervisor, Victor Petrashov, and started developing my own niche. It was an experimental system that was both new and doable, which was nearly an oxymoron, taking into account the scarce resources available at
9、the time at Soviet research AndreGeim_lect_s70_95.indd 2 2011-08-29 08:48:4671institutes. I fabricated a sandwich consisting of a thin metal film and a super-conductor separated by a thin insulator. The superconductor served only to condense an external magnetic field into an array of vortices, and
10、this highly inhomogeneous magnetic field was projected onto the film under investiga-tion. Electron transport in such a microscopically inhomogeneous field (varying on a submicron scale) was new research territory, and I published the first experimental report on the subject 4, which was closely fol
11、lowed by an independent paper from Simon Bending 5. It was an interesting and reasonably important niche, and I continued studying the subject for the next few years, including a spell at the University of Bath in 1991 as a postdoctoral researcher working with Simon. This experience taught me an imp
12、ortant lesson: that introducing a new experimental system is generally more rewarding than trying to find new phenomena within crowded areas. The chances of success are much higher where the field is new. Of course, the fantastic results one originally hopes for are unlikely to materialise, but, in
13、the process of studying any new system, something original inevitably shows up. ONE MANS JUNK, ANOTHER MANS GOLDIn 1990, thanks to Vitaly Aristov, director of my Institute in Chernogolovka at the time, I received a six month visiting fellowship from the British Royal Society. Laurence Eaves and Pete
14、r Main from Nottingham University kindly agreed to accept me as a visitor. Six months is a very short period for experimental work, and circumstances dictated that I could only study de-vices readily available in the host laboratory. Available were submicron GaAs wires left over from previous experi
15、ments, all done and dusted a few years earlier. Under the circumstances, my experience of working in a poverty-stricken Soviet academy was helpful. The samples that my hosts considered practically exhausted looked like a gold vein to me, and I started working 100 hours per week to exploit it. This s
16、hort visit led to two Phys. Rev. Letters of decent quality 6,7, and I often use this experience to tease my younger colleagues. When things do not go as planned and people start complaining, I provoke them by proclaiming there is no such thing as bad samples; there are only bad postdocs/students. Se
17、arch carefully and you will always find something new. Of course, it is better to avoid such experiences and explore new territories, but even if one is fortunate enough to find an experimental system as new and exciting as graphene, meticulousness and perseverance allow one to progress much further
18、. The pace of research at Nottingham was so relentless and, at the same time so inspiring, that a return to Russia was not an option. Swimming through Soviet treacle seemed no less than wasting the rest of my life. So at the age of thirty-three and with an h-index of 1 (latest papers not yet publish
19、ed), I entered the Western job market for postdocs. During the next four years I moved between different universities, from Nottingham to Copenhagen to Bath and back to Nottingham. Each move allowed me to get acquainted with AndreGeim_lect_s70_95.indd 3 2011-08-29 08:48:4672yet another topic or two,
20、 significantly broadening my research horizons. The physics I studied in those years could be broadly described as mesoscopic and involved such systems and phenomena as two-dimensional electron gases (2DEGs), quantum point contacts, resonant tunnelling and the quantum Hall effect (QHE), to name but
21、a few. In addition, I became familiar with GaAlAs heterostructures grown by molecular beam epitaxy (MBE) and improved my expertise in microfabrication and electron-beam lithography, technologies I had started learning in Russia. All these elements came together to form the foundation for the success
22、ful work on graphene a decade later. DUTCH COMFORTBy 1994 I had published enough quality papers and attended enough con-ferences to hope for a permanent academic position. When I was offered an associate professorship at the University of Nijmegen, I instantly seized upon the chance of having some s
23、ecurity in my new post-Soviet life. The first task in Nijmegen was of course to establish myself. To this end, there was no start-up and no microfabrication to continue any of my previous lines of re-search. As resources, I was offered access to magnets, cryostats and electronic equipment available
24、at Nijmegens High Field Magnet Laboratory, led by Jan Kees Maan. He was also my formal boss and in charge of all the money. Even when I was awarded grants as the principal investigator (the Dutch funding agency FOM was generous during my stay in Nijmegen), I could not spend the money as I wished. Al
25、l funds were distributed through so-called working groups led by full professors. In addition, PhD students in the Netherlands could formally be supervised only by full professors. Although this probably sounds strange to many, this was the Dutch academic system of the 1990s. It was tough for me the
26、n. For a couple of years, I really struggled to adjust to the system, which was such a contrast to my joyful and productive years at Nottingham. In addition, the situation was a bit surreal because outside the university walls I received a warm-hearted welcome from everyone around, including Jan Kee
27、s and other academics. Still, the research opportunities in Nijmegen were much better than in Russia and, eventually, I managed to survive scientifically, thanks to help from abroad. Nottingham colleagues (in particular Mohamed Henini) provided me with 2DEGs that were sent to Chernogolovka, where Se
28、rgey Dubonos, a close colleague and friend from the 1980s, microfabricated requested devices. The research topic I eventually found and later focused on can be referred to as mesoscopic superconductivity. Sergey and I used micron-sized Hall bars made from a 2DEG as local probes of the magnetic field
29、 around small superconducting samples. This allowed measurements of their magnetisation with accuracy sufficient to detect not only the entry and exit of individual vortices but also much more subtle changes. This was a new experimental niche, made possible by the development of an original techniqu
30、e of ballistic Hall micromagnetometry 8. During the next few AndreGeim_lect_s70_95.indd 4 2011-08-29 08:48:4673years, we exploited this niche area and published several papers in Nature and Phys. Rev. Letters which reported a paramagnetic Meissner effect, vortices carrying fractional flux, vortex co
31、nfigurations in confined geometries and so on. My wife Irina Grigorieva, an expert in vortex physics 9, could not find a job in the Netherlands and therefore had plenty of time to help me with conquering the subject and writing papers. Also, Sergey not only made the devices but also visited Nijmegen
32、 to help with measurements. We established a very productive modus operandi where he collected data and I analysed them within an hour on my computer next door to decide what should be done next. A SPELL OF LEVITYThe first results on mesoscopic superconductivity started emerging in 1996, which made
33、me feel safer within the Dutch system and also more inquisi-tive. I started looking around for new areas to explore. The major facility at Nijmegens High Field Lab was powerful electromagnets. They were a major headache, too. These magnets could provide fields up to 20 T, which was somewhat higher t
34、han 16 to 18 T available with the superconducting magnets that many of our competitors had. On the other hand, the elec-tromagnets were so expensive to run that we could use them only for a few hours at night, when electricity was cheaper. My work on mesoscopic super-conductivity required only tiny
35、fields ( 0.01T), and I did not use the electro-magnets. This made me feel guilty as well as responsible for coming up with experiments that would justify the facilitys existence. The only competitive edge I could see in the electromagnets was their room temperature (T) bore. This was often considere
36、d as an extra disadvantage because research in condensed matter physics typically requires low, liquid-helium T. The con-tradiction prompted me, as well as other researchers working in the lab, to ponder on high-field phenomena at room T. Unfortunately, there were few to choose from. Eventually, I s
37、tumbled across the mystery of so-called magnetic water. It is claimed that putting a small magnet around a hot water pipe prevents formation of scale inside the pipe. Or install such a magnet on a water tap, and your kettle will never suffer from chalky deposits. These magnets are available in a gre
38、at variety in many shops and on the internet. There are also hundreds of articles written on this phenomenon, but the physics behind it remains unclear, and many researchers are sceptical about the very existence of the effect 10. Over the last fifteen years I have made several attempts to investiga
39、te “magnetic water” but they were inconclusive, and I still have nothing to add to the argument. However, the availability of ultra-high fields in a room T environment invited lateral thinking about water. Basically, if magnetic water existed, I thought, then the effect should be clearer in 20 T rat
40、her than in typical fields of 0.1 T created by standard magnets. With this idea in mind and, allegedly, on a Friday night, I poured water inside the labs electromagnet when it was at its maximum power. Pouring AndreGeim_lect_s70_95.indd 5 2011-08-29 08:48:4674water in ones equipment is certainly not
41、 a standard scientific approach, and I cannot recall why I behaved so unprofessionally. Apparently, no one had tried such a silly thing before, although similar facilities existed in several places around the world for decades. To my surprise, water did not end up on the floor but got stuck in the v
42、ertical bore of the magnet. Humberto Carmona, a visiting student from Nottingham, and I played for an hour with the water by breaking the blockage with a wooden stick and changing the field strength. As a result, we saw balls of levitating water (Figure 1). This was awesome. It took little time to r
43、ealise that the physics behind was good old diamagnetism. It took much longer to adjust my intuition to the fact that the feeble magnetic response of water (105), billions of times weaker than that of iron, was sufficient to compensate the earths gravity. Many colleagues, including those who worked
44、with high magnetic fields all their lives, were flabbergasted, and some of them even argued that this was a hoax. I spent the next few months demonstrating magnetic levitation to colleagues and visitors, as well as trying to make a non-boffin illustration for this beautiful phenomenon. Out of the ma
45、ny objects that we had floating inside the magnet, it was the image of a levitating frog (Figure 1) that started the media hype. More importantly, though, behind all the media noise, this image found its way into many textbooks. However quirky, it has become a beautiful symbol of ever-present diamag
46、netism, which is no longer perceived to be extremely feeble. Sometimes I am stopped at conferences by people exclaiming “I know you! Sorry, it is not about graphene. I start my lectures with showing your frog. Students always want to learn how it could fly.” The frog story, with some intricate physi
47、cs behind the stability of diamagnetic levitation, is described in my review in Physics Today 11. Figure 1. Levitating moments in Nijmegen. Left Ball of water (about 5 cm in diameter) freely floats inside the vertical bore of an electromagnet. Right The frog that learned to fly. This image continues
48、 to serve as a symbol showing that magnetism of nonmagnetic things, including humans, is not so negligible. This experiment earned Michael Berry and me the 2000 Ig Nobel Prize. We were asked first whether we dared to accept this prize, and I take pride in our sense of humour and self-deprecation tha
49、t we did.AndreGeim_lect_s70_95.indd 6 2011-08-29 08:48:4875FRIDAY NIGHT EXPERIMENTSThe levitation experience was both interesting and addictive. It taught me the important lesson that poking in directions far away from my immediate area of expertise could lead to interesting results, even if the initial ideas were extremely basic. This in turn influenced my research style, as I started making similar exploratory detours that somehow acquired the name Friday night experiments. The term is of course inaccurate. No serious work can be accomplis
