UNIST and Max Planck Researchers Confirm Insulating Properties Theory
Advances in Quantum Mechanical Calculations Aid Development of Sensors, Evaluations, and Memory Devices
Research figure demonstrating the insulating properties of ditantalum disulfide through calculations.
[Asia Economy Yeongnam Reporting Headquarters Reporter Kim Yong-woo] Among sulfur compounds, there is one ‘peculiar’ substance that sometimes conducts electricity and sometimes does not.
It is TaS2 (tantalum disulfide), a compound formed by tantalum, an element with atomic number 73 belonging to group 5 of the periodic table, combined with two sulfur atoms.
Tantalum disulfide is generally considered a conductor that easily transmits heat and electricity, but at certain temperatures, it becomes an insulator, sparking decades-long debates over whether it is a conductor or an insulator.
So, is it a conductor or an insulator? The 40-year-old controversy in the physics community has finally been resolved. An international joint research team has revealed that TaS2 is an insulator.
The research team proved theoretically that this material is an insulator by correcting errors in the application of theories predicting electrical conductivity.
The prestigious physics journal Physical Review Letters published this research online on May 13.
Professor Park No-jeong’s team from the Department of Physics at Ulsan National Institute of Science and Technology (UNIST) and researchers from the Max Planck Institute in Germany discovered overlooked errors in the computational methods used to predict the electrical conductivity of TaS2.
By correcting these errors with a new computational method, they revealed that this material exists as an insulator at an absolute temperature of 200K (Kelvin).
TaS2 is uniquely a phase transition material that behaves as a good conductor at room temperature but becomes an insulator that does not conduct electricity below 200K absolute temperature.
However, theoretical physicists have argued that this material remains a conductor even below 200K based on quantum mechanics-based theoretical predictions.
Since electrical conductivity measurements below 200K absolute temperature (i.e., below -73.15°C) can always be subject to error, the theoretical physicists’ views were also considered valid.
The research team found that in the process of reducing calculation errors in density functional theory, the charge density wave state was not properly considered.
Density functional theory is a quantum mechanical computational method that allows the determination of the position and density of electrons.
Electrical conductivity, which is the flow of electrons, can also be predicted through this method. However, since this theory simplifies numerous electrons as a single particle system, it requires the integration of additional computational methods to reduce calculation errors.
The cause of the error was that the charge density wave (CDW) state, in which about 40 atoms move as one, was not properly accounted for during this process.
By correcting this, calculations show that TaS2 is in a special insulating state called a Mott insulator at 200K absolute temperature.
If a regular insulator is likened to a material with no path for electrons to move, a Mott insulator is a material where paths exist but are fully occupied by electrons like stepping stones, preventing electron movement.
Professor Park No-jeong explained, “This research represents an advancement in quantum mechanical computational methods that reveal material changes due to strong correlations among numerous electrons constituting solids.”
He added, “It will also help in understanding the characteristics of various phase transition materials and in developing sensors and electronic devices based on phase transition properties that sensitively respond to environmental factors such as temperature.”
This research was conducted jointly by Angelo Rubio, Director of the Max Planck Institute for the Structural Dynamics of Matter in Germany, Dr. Shin Dong-bin, Dr. Jin Zhang, researcher Nicolas Tancgone-Dejean, and UNIST Department of Physics researcher Mahmut Okyay.
The study was supported by the Ministry of Science and ICT and the National Research Foundation of Korea.
© The Asia Business Daily(www.asiae.co.kr). All rights reserved.
