Tuesday, May 05, 2009

Explaining my neoteric research to school kids

I had to write a summery of my recent work for some promotional reason. As the evaluators of any event are always dumber and often unknowledgeable to that particular subject, I had to describe my stuff in the most simple fashion. Here is my attempt.

When an electron (the fundamental constituent of any physical matter) travels in a crystal, it only takes certain value of energy and velocity (related to its momentum) and the relation between the energy and momentum is called 'band'. In a word, 'band' is the well defined path in which the electron is allowed to travel within the crystal. During its motion, electron experiences disruptions due to various physical phenomenon and thus can not access certain bands which could have been permissible in free space. The band where electron can travel is called 'filled band' and the other is called 'empty bands' which are separated by an energy scale called 'band gap'. The structure of such bands and the amount of band gap determines how the matter will behave, for example iron is magnetic at room temperature whereas calcium is not. Further with variation of temperature and/or other factors such as insertion or exertion of extra electrons into the material may cause phase transitions in which the same material starts to behave differently (e.g. magnetic property may disappear).

Here we have developed a model to determine various characteristic of the band gap(s) experimentally seen in a class of material called superconductors. These materials with decreasing temperature enter into a new phase where they can carry the electrical current with out any loss of it (without resistance). (For experts information, we are not concern here with the superconducting gap, rather the so called 'pseudogap' which are present in its non-superconducting phase and may or may not survive in its superconducting state.) The problem in these material arises when various experimental probes find various energy scale of the gap; one class finds that the gap is considerably smaller in energy value where other family reports that the gap is very large (of the same energy scale as the total band width) with or without the presence of the other smaller gap. As the amount of gap determines the property of the material, therefore it remains a long standing puzzle to resolve in order to understand and make it usable.

In this research, we have been able to untangle this dilemma in which we find that both the gaps are present in the system, but appear accordingly depending on the capability of the experimental probe. We have also found that the smaller energy gap is associated with a magnetic phase called antiferromagnetism in which the electrons are arranged in a certain regular pattern so that the globally it is not a magnet, but locally it has small but finite value of magnetic properties. The other large gap which prohibits the electron to move from the 'filled band' to the 'empty band' is caused by the large repulsion of the electrons having finite negative charge (Coulomb repulsion). Thus we have been able to explain the two contrasting experimental observations in this context in a consistent way.

1 comment:

AD said...

TD....good attempt. It is simple to understand.