Physics Nobel Prize 2007 for 'Giant Magnetoresistance'

Albert Fert (left) and Peter Grünberg (right) [Photo Courtesy: Unité mixte de physique CNRS/Thales, Orsay and Institut für Festkörperforschung, Forschungszentrum Jülich ]

Laptops, iPods and so many other small-sized devices that have defined a new generation of our civilization owe a large part of their existence to the discovery of a fundamental effect in Physics about 19 years back and this year's Nobel Prize celebrates this path-breaking advancement that influenced so much the growth of the computer industry and days of our lives.

The Royal Swedish Academy of Sciences has awarded the Nobel Prize in physics for 2007 jointly to Albert Fert (France) and Peter Grünberg (Germany) for the discovery of 'Giant Magnetoresistance’ or GMR.

Albert Fert is currently professor at Université Paris-Sud, Orsay, since 1976 and scientific director of the Unité mixte de physique CNRS/Thales, Orsay, since 1995. He earned his PhD in 1970 at the Université Paris-Sud. He was born on 7 March 1938 at Carcassonne. Peter Grünberg is a Professor at Institut für Festkörperforschung, Forschungszentrum Jülich, Germany, since 1972. He was born on May 18, 1939. Grünberg received his Ph.D in 1969 at Darmstadt University of Technology in Germany.

About 'Giant Magnetoresistance’ (GMR): In 1988 the Frenchman Albert Fert and the German Peter Grünberg each independently discovered this totally new physical effect. They observed that very weak magnetic changes give rise to major differences in electrical resistance in a GMR system. A system of this kind is the perfect tool for reading data from hard disks when information registered magnetically has to be converted to electric current.

A hard disk stores information, such as music, in the form of microscopically small areas magnetized in different directions. The information is retrieved by a read-out head that scans the disk and registers the magnetic changes. The smaller and more compact the hard disk, the smaller and weaker the individual magnetic areas. More sensitive read-out heads are therefore required if information has to be packed more densely on a hard disk. A read-out head based on the GMR effect can convert very small magnetic changes into differences in electrical resistance and therefore into changes in the current emitted by the read-out head. The current is the signal from the read-out head and its different strengths represent ones and zeros.

Soon after the discovery of Fert and Grünberg, researchers and engineers began work to enable use of the effect in read-out heads. In 1997 the first read-out head based on the GMR effect was launched and this soon became the standard technology. Thanks to this technology that it has been possible to miniaturize hard disks so radically in recent years. Sensitive read-out heads are needed to be able to read data from the compact hard disks used in laptops and some music players, for instance. Even the most recent read-out techniques of today are further developments of GMR.

"The GMR effect was discovered thanks to new techniques developed during the 1970s to produce very thin layers of different materials. If GMR is to work, structures consisting of layers that are only a few atoms thick have to be produced. For this reason GMR can also be considered one of the first real applications of the promising field of nanotechnology", The Royal Swedish Academy of Sciences said.

Homepage of Albert Fert: http://www2.cnrs.fr/en/338.htm
Homepage of Peter Grünberg: http://www.fz-juelich.de/portal/gruenberg/

Those Historic Papers:
"Giant Magnetoresistance of (001)Fe/(001)Cr Magnetic Superlattices",
M. N. Baibich, J. M. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff, P. Eitenne, G. Creuzet, A. Friederich, J. Chazelas,
Phys. Rev. Lett. 61, 2472, (1988), Abstract.
&
"Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange",
G. Binasch, P. Grünberg, F. Saurenbach, and W. Zinn,
Phys. Rev. B 39 (7), 4828-4830 (1989). Abstract.

A Single-Photon Transistor using Nanoscale Surface Plasmons

Author: Darrick Edward Chang

Affiliation: Physics Department, Harvard University

[This is an invited article based on a recent work done by the author and his collaborators and published in 'Nature']

Finding ways to make pulses of light interact with each other has been an active area of research for several decades. In fact, the study of “nonlinear optics” has led to countless breakthroughs and technological advances in fields as diverse as imaging, spectroscopy, laser physics, communications, and signal processing [1]. Interactions between pulses of light are achieved by their common interaction with some material medium. However, because such processes are generally very weak, optical nonlinearities typically become significant only when very large light intensities are used.

The ability to achieve nonlinear interactions at low optical powers would enable a new generation of devices that consume much less power than their predecessors and enable new applications as well. The ultimate limit would be to achieve nonlinear interactions between individual photons, the constituent particles that comprise light. Recently, there has been great interest in this area in part because of potential applications in quantum computing and quantum information science [2,3].

The interaction strength between matter and light can be increased by confining the light in space to very small dimensions, which causes the associated optical fields to become very intense. In normal dielectric media, light cannot be confined to regions smaller than an optical wavelength. However, the situation changes dramatically when light is coupled to the free electrons in a conductor. The unique properties of these coupled excitations of light and charge (known as surface plasmons) [4] allow them to be confined to arbitrarily small dimensions.

Image: An illustration of how a single atom near a nanowire can prevent light from propagating past it

Recently, we proposed [5] and experimentally investigated [6] the strong interaction between single atoms (or other optical emitters) and individual surface plasmons tightly confined to a conducting nanowire. The strong coupling causes the nanowire to act as a “super-lens” that directs the majority of emission into the surface plasmon modes. More recently, we have theoretically shown that such a system also leads to remarkable nonlinear optical effects [7]. In particular, the confinement of the surface plasmons is so strong that when a single surface plasmon (i.e., a single photon) is incident on a single emitter, the two must interact, and this interaction prevents the photon from being transmitted past the emitter. However, because the emitter cannot interact with more than a single photon at a time, its response to a second incident photon becomes fundamentally different and transmission is now much more likely. In this sense, the single emitter behaves as an efficient, single-photon switch.

One can gain even further control over the nonlinear optical interactions in this system by using techniques from quantum optics to coherently manipulate the emitter. In fact, we have shown that the system can behave as a single-photon transistor, where the presence or absence of a single photon in a “gate” field can prevent or allow the propagation of a whole stream of “signal” photons. In analogy to the role that electronic transistors play in electronic computing devices, a single-photon transistor would open the door to optical computing devices and many other possibilities.

Our experimental efforts to explore the nonlinear properties of this system are just beginning, and considerable work remains to be done before large-scale, integrated quantum plasmonic devices can be practically realized. More broadly, however, work such as this suggests the great promise of merging the tools of quantum optics with plasmonics and the many other novel optical materials that have recently arisen. Ultimately this merger may help us to achieve unprecedented control over the interactions of light quanta.

This work was done in collaboration with Mikhail Lukin and Eugene Demler, both in the Physics Dept. at Harvard University, and Anders Sorensen in the Physics Dept. at the Niels Bohr Institute, Copenhagen, Denmark.

References:
[1] R.W. Boyd, Nonlinear Optics (Academic, New York, 1992).
[2] L.-M. Duan and H.J. Kimble, Phys. Rev. Lett. 92, 127902 (2004) Abstract.
[3] M.D. Lukin and A. Imamoglu, Phys. Rev. Lett. 84, 1419 (2000) Abstract.
[4] H.A. Atwater, Sci. Am. 296, 53 (2007).
[5] D.E. Chang, A.S. Sorensen, P.R. Hemmer, M.D. Lukin, Phys. Rev. Lett. 97, 053002 (2006) Abstract.
[6] A.V. Akimov et al., accepted by Nature (2007).
[7] D.E. Chang, A.S. Sorensen, E.A. Demler, and M.D. Lukin, Nature Physics advance online publication, doi:10.1038/nphys708 (2007) Abstract

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