The Particle - The wrong turn that led physics to a dead end

Engineer Xavier Borg - Blaze Labs

Fractional electron charges

Most of the matter we see around us is made from protons and neutrons, which are each composed of 3 quarks. There are six quarks, or quark flavours, but physicists usually talk about them in terms of three pairs: up/down, charm/strange, and top/bottom. Top and bottom types are the most elementary of them all, and are the ones that make up protons and neutrons. Quarks have the unusual characteristic of having a fractional electric charge, unlike the proton and electron, which have integer charges of +1 and -1 respectively. The up, charm and top quarks have a charge of +2/3, whilst the down, strange and bottom have a charge of -1/3. Although individual quarks have fractional electrical charges, they normally combine into 'hadrons' such that these hadrons have a net integer electric charge. Protons and neutrons are good examples of quark grouping or hadrons. Researchers at the Weizmann Institute of Science have provided the first unambiguous evidence that electrons can behave in an intriguing way that seems to defy the idea of the electron being an indivisible charged elementary unit.

An electron is by convention considered to be a tiny indivisible hard particle that carries the smallest negative charge in nature. Yet a daring theory of physics developed 15 years ago argues that under certain conditions, an electric current behaves as if it were made up of fractions of electronic charges. In an experiment described in September 11,1997 issue of Nature, Weizmann Institute physicists measured fractional charges one-third that of an electron.

"Mind-boggling as this may seem, this phenomenon is real," says study author Rafael de-Picciotto. "Of course, electrons don't split into fragments in an electric current, but under certain conditions it is indeed possible to measure a charge smaller than that of an electron." This means, that although the electron charge is always the same well known value, it can no longer be stated that this value is the smallest possible value for electrical charge.

Almost 100 years ago, ever since American physicist Robert Millikan first measured the charge of an electron as equal to 1.602E-19C, this value has been widely regarded as a basic unit of electric charge. Scientists have consequently come to view electrons that make up an electric current as a flow of negatively charged, indivisible elementary charged "balls." A current made up of fractions of an electronic charge, therefore, would seem not to fit in Millikan's findout.

However, if electrons are always regarded as a "whole" or fundamental, as understood by current science, it is extremely difficult to understand and describe their behavior under certain conditions. For example, some particular instances of this behavior, as in a phenomenon known as the fractional quantum Hall effect, observed in a strong magnetic field, remain unexplained.

In 1982, physicist Robert Laughlin of the United States proposed a theory that explained this effect and provided a very simple way of describing highly complex interactions between electrons. However, this explanation came at a cost for physics community: the theory made the bizarre assumption that an electric current can be made up of 1/3 fractions of an electron charge.

In a new experiment, Weizmann Institute scientists designed a sophisticated system to measure such fractional electric charges, should they exist. The system makes it possible to measure so-called "shot noise." In day-to-day environment, this noise results from random variations in the number and velocity of electrons and causes popping sounds in radio receivers and snow effects in television pictures. Under special laboratory conditions, "shot noise" can be analyzed to reveal the make-up of the electric current. This is possible because the noise has "ripples" left by the flow of electrons in a conductor. The size of each "ripple" is proportional to the unit of electric charge: the smaller the ripple, the smaller the charge, and vice versa.

The scientists passed an electric current through a semiconductor immersed in a high magnetic field, under conditions in which the fractional quantum Hall phenomenon is observed. They used sophisticated equipment to eliminate all extraneous sources of noise. The "shot noise" made by the current was then amplified and measured. It turned out to be made of charges one-third that of an electron.So this confirms that an electron is not a fundamental particle, since such element should be indivisible, simple and structureless.

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