Northeastern University Physics professor Sergey V. Kravchenko along with colleagues Svetlana Anissimova (Northeastern University), A Punnoose (City College if the City University of New York), AM Finkelstein (Weizmann Institute of Science, Israel) and TM Klapwijk (Delft University of Technology, Netherlands), has published an important new paper in the August issue of Nature Physics which answers a long standing question in the field of condensed matter physics.
The discovery of the metal-insulator transition (MIT) in two-dimensional electron systems by Kravchenko and colleagues in 1994 challenged the veracity of one of the most influential conjectures in the physics of disordered electrons by Abrahams, Anderson, Licciardello and Ramakrishnan (1979) which stated that "in two dimensions, there is no true metallic behavior."
However, the 1979 theory did not account for interactions between electrons. In this new paper, Kravchenko and colleagues investigate the interplay between the electron-electron interactions and disorder near the MIT using simultaneous measurements of electrical resistivity and magnetoconductance.
The researchers show that both the resistance and interaction amplitude exhibit a fan-like spread as the MIT is crossed. From this data, the researchers have constructed a resistance-interaction flow diagram of the MIT that clearly reveals a quantum critical point, as predicted by the recent two-parameter scaling theory by two of the authors (A. Punnoose and A.M. Finkelstein). The metallic side of this diagram is accurately described by the renormalization-group theory without any fitting parameters. In particular, the metallic temperature dependence of the resistance sets in when the interaction amplitude reaches a value in remarkable agreement with the one predicted by theory.
"To the best of our knowledge, this is the first observation of the temperature dependence of the strength of the electron-electron interactions," said Kravchenko. "We found that the interaction grows in the metallic phase as the temperature is reduced and is suppressed in the insulating phase."
"Whether or not the electrons can conduct in two dimensions at very low temperatures is a question that has been hotly debated for more than a decade," said Kravchenko. "We now know that, because of the interactions between them, they can, and we have a theory that quantitatively and qualitatively explains things."
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Condensed matter physics is the field of physics that deals with the macroscopic physical properties of matter. In particular, it is concerned with the "condensed" phases that appear whenever the number of constituents in a system is extremely large and the interactions between the constituents are strong. The most familiar examples of condensed phases are solids and liquids, which arise from the bonding and electromagnetic force between atoms. More exotic condensed phases include the superfluid and the Bose-Einstein condensate found in certain atomic systems at very low temperatures, the superconducting phase exhibited by conduction electrons in certain materials, and the ferromagnetic and antiferromagnetic phases of spins on atomic lattices.
Condensed matter physics is by far the largest field of contemporary physics. Much progress has also been made in theoretical condensed matter physics. By one estimate, one third of all American physicists identify themselves as condensed matter physicists. Historically, condensed matter physics grew out of solid-state physics, which is now considered one of its main subfields. The term "condensed matter physics" was apparently coined by Philip Anderson when he renamed his research group - previously "solid-state theory" - in 1967. In 1978, the Division of Solid State Physics at the American Physical Society was renamed as the Division of Condensed Matter Physics. Condensed matter physics has a large overlap with chemistry, materials science, nanotechnology and engineering.
One of the reasons for calling the field "condensed matter physics" is that many of the concepts and techniques developed for studying solids actually apply to fluid systems. For instance, the conduction electrons in an electrical conductor form a type of quantum fluid with essentially the same properties as fluids made up of atoms. In fact, the phenomenon of superconductivity, in which the electrons condense into a new fluid phase in which they can flow without dissipation, is very closely analogous to the superfluid phase found in helium 3 at low temperatures.