Physicists have found a way to access information related to one of the fundamental physical phenomena, the Hall effect, that had eluded them for 140 years. As a reminder to our readers, physicist Edwin Hall discovered in 1879 that an electric current in a conductor placed in a magnetic field creates an electric field and a potential whose vector is directed perpendicular to the direction of the current. This phenomenon, called the Hall effect, is widely used in modern electronics and other fields, including the study of semiconductor materials. But unfortunately, it is the Hall effect itself that serves as an obstacle to some kinds of measurements.
Not long ago, researchers at IBM, Duke University and the Korea Advanced Institute of Science and Technology (KAIST) developed a method for obtaining information whose measurement was previously “blocked” by the Hall effect.
In order to understand what we are talking about, it is necessary to make a little excursion into physics. It is known that the movement of electric charges in semiconductors has a discrete character due to the fact that it is provided by the movement of negatively charged electrons and positively charged “electron holes”, which are the electron absent from the crystal structure of the material. Scientists use the Hall effect to study the movement of charge carriers in materials, calculating their density and speed of movement. Later, the Hall effect was used to study the effects of light on various materials, in which light knocked electrons out of atoms, forming free electrons and electron holes.
But all research methods based on the Hall effect can give significant results in relation to the charge carriers present in the material in larger quantities. That is, if there are more electrons in the material, it is possible to obtain information about electrons; in the opposite case, only information about carriers of the opposite charge, electron holes, becomes available.
Using theoretical calculations, the researchers found a way to simultaneously obtain information about carriers of electric charge of both types. And the key to this was the additional energy pumped into the material with the help of light. Under the influence of this additional energy, the charge carriers of different polarities begin to behave somewhat differently, and a certain imbalance occurs, the magnitude of which is determined by a mathematical equation developed by scientists.
In order for such a method to work in practice, technology is required to reduce thermal noise and other interference that distorts the effect of the Hall effect. To do this, IBM researchers developed a system called a parallel dipole line, which consists of a pair of cylindrical magnets whose combined field acts as a magnetic trap. Two samples are placed in this trap, one of the semiconductor material under study, the other of a light-sensitive material called perovskite. By taking measurements and using the equation mentioned above, scientists obtain data on electric charge carriers of both types simultaneously.
The method the scientists found could be a very useful tool in fields related to solar energy, photoelectronics, etc. In addition, it can be used to conduct scientific research of new types, which study the interactions between magnetic fields, electric current and light.
However, there are now a number of limitations that will hinder the practical use of the new method. It, this method, works reliably in the presence of a large number of electric charge carriers. Materials with few carriers need to be illuminated with light from a very powerful laser to get a meaningful result, and this high-energy light can melt the material or cause unwanted structural changes.
In any case, however, this achievement is something that can advance our understanding of what is actually going on inside fundamental physical phenomena. And this understanding, in turn, may in the future be the basis for the creation of a mass of new technologies, which seem to us now something out of the realm of science fiction.