Semimetals show heat to electrical conversion efficiency
A team of researchers from RIKEN Centre for Emergent Matter Science (CEMS) and the University of Tokyo has found a layered semimetal compound that offers excellent efficiency of heat to electric current conversion at room temperature, outlining its potential to be used as a thermoelectric material. Semimetals are unclassifiable as either metal or non-metal, and like the early days of semiconductors, their use in electronics has so far been limited. With the recent findings of the research, the low-profile semimetals may soon see a change of roles.
Shintaro Ishiwata, previously from the CEMS and now with the University of Tokyo, had led a collaborative team in research on novel 'spintronic' devices—systems in which the magnetic properties of electrons are used rather than their electrical charge. Through those studies, the team discovered that a byproduct produced during their research, silver selenide (Ag2Se), displayed some interesting properties. The electrical resistance of the material was found to change remarkably depending on its interaction with magnetic fields. This effect, known as giant magnetoresistance (GMR), is used widely in modern electronic devices to read information from magnetic hard disc drives. Furthermore, the material also displayed high thermoelectric efficiency, generating a heat gradient when it passes an electrical current or generating an electrical current when cooled on one side and heated on the other. The combination of GMR and high thermoelectric efficiency is unusual, and the occurrence of GMR, in particular, shows that electrons can flow very easily through the material.
These behaviours had been reported before for Ag2Se, but Ishiwata and his colleagues were spurred to look deeper. "We started studying related materials and found that one of them, CuAgSe, shows stronger GMR effects and better thermoelectric efficiency," he stated. CuAgSe is a multi-layered semimetal consisting of alternating layers of silver (Ag) and copper selenide (CuSe).