The Physics of Bargaining

 

We don't expect nature to negotiate. Yet Weizmann Institute scientists have shown recently that nature sometimes has a surprisingly opportunistic streak.

This phenomenon was revealed in an experiment examining the behavior of particles whose electric charge is one-third that of an electron. These particles were first observed several years ago by Prof. Moty Heiblum and members of his team at the Condensed Matter Physics Department.

Until recently, the accepted wisdom was that the charge of an electron, first measured some 80 years ago by American physicist Robert Millikan, was the smallest basic unit of electric charge. However, in 1982, American physicist Robert Laughlin explained certain electronic phenomena by proposing a theory based on the assumption that, under certain conditions, the electric current gives rise to "quasi"particles, each of which carries an electric charge smaller than the basic charge of a single electron (one-third, one-fifth, one-seventh, or even smaller, depending on the circumstances).

The first evidence that Laughlin's theory was correct was supplied some four years ago by the Weizmannscientists, who managed, for the first time, to measure an electric charge one-third that of a single electron. This evidence played an important role in the decision to grant Robert Laughlin, Horst Stoermer, and Daniel Tsui the 1998 Nobel Prize in Physics. However, the properties of quasi particles remained a mystery, and Heiblum's team continued to pursue them.

In one series of experiments, the scientists examined how quasi particles act when they run into an obstacle. They discovered that when particles with one-third the charge of an electron arrive en masse at a tall barrier, they "join forces,"creating partnerships of three (that is, together forming a whole electron). Only then are they able to penetrate the obstacle and reach the other side. This cooperative effort has since become known as one of their basic properties.

However, in a more recent series of experiments, the scientists created a beam in which each quasi particle was separated from the others and thus arrived at the barrier alone. The scientists had predicted that the individual particles would be unable to penetrate the tall barrier, but much to their surprise it turned out that when a single particle ran into the obstacle, it was able to cross to the other side!

This event can be compared to bargaining at a toll booth. Imagine that a highway inspector charges all drivers who arrive en masse a toll of three dollars, but when a particular driver arrives alone with only one dollar, the inspector makes sure nobody is watching and agrees to let him pass through at one-third the price. "One would expect to encounter such a phenomenon, say, in the market, where people bargain over price,"says Heiblum, "but laws of nature are supposed to have more 'integrity.'They are expected to be 'unbiased'and consistent."Heiblum's team included graduatestudent Eyal Comforti, visiting scientist Dr. Yungchul Chung, Dr. Vladimir Umansky, and Dr. Diana Mahalu. The scientists are now searching for a theory to explain the hidden logic allowing nature to bend its own rules.

Prof. Heiblum's research is supported by the Joseph H. and Belle R. Braun Center for Submicron Research; Dan and Hermann Mayer, France; the Wolfson Family Foundation Charitable Trust; Mr. Hugo Ramniceanu, France; Mr. Uzi Zucker, New York, NY; Mr. and Mrs. Harold Simpson, Delray Beach, FL; and Mr. Joe Gurwin, Kings Point, NY. He holds the Alex and Ida Sussman Chair in Submicron Electronics.