Scientists at the Chair of Quantum Physics and Nanoelectronics develops the theoretical foundations of molecular electronics
The British journal “Physical Chemistry Chemical Physics” has published the results of joint research by MIET and the Lebedev Physical Institute of the Russian Academy of Sciences (LPI RAS) in which the scientists studied constructive and destructive quantum interference in the process of coherent charge transfer in molecular conductors.
The authors of the article (Nikolay Shubin, Alexei Emelyanov, Yuriy Uspenskyii and Alexander Gorbatsevich) developed an analytical model that describes the phenomenon of merging of antiresonances (ARs) - minima in the spectrum of tunnel transparency. When a certain parameter of the system changes, two minima with a zero transparency value in each, approaching each other, can merge into one minimum with a non-zero transparency. In this case, the position of the ARs energies mathematically corresponds to the behavior of the eigenvalues of some non-Hermitian PT-symmetric operator, which can merge at a singular point and turn from a pair of real ones (corresponding to two different minima with zero transparency) into a pair of complex conjugate ones (corresponding to the absence of minima with zero transparency). The results of the model were confirmed by ab initio for the cyclobutadiene molecule in the Synopsys Quantum ATK program.
The scientists also managed to research the mutual influence of ARs and resonances (tunnel transparency maxima) - the coincidence of their energies leads to the appearance of a bound state in the continuum (BIC). BIC is a state in which a particle remains localized in space, but at the same time has an energy that lies in the continuous spectrum. This phenomenon in other systems was known before, but the formation of BIC in molecular structures was demonstrated in this research for the first time. BIC in a molecule is a highly localized molecular orbital that is not connected to electrodes and does not participate in the transport of charge carriers.
“Using the benzene molecule as an example, we have shown that in the symmetric configuration, para-connection results in the formation of BIC and there are no ARs. The addition of radical groups slightly changes the geometry of the molecule, its symmetry is broken, and BIC is destroyed. In this case, a narrow AR is formed, which interferes with the electrons transport at a certain energy,” - commented one of the co-authors, Associate Professor of the Chair of Quantum Physics and Nanoelectronics Nikolay Shubin.
The research can help to solve one of the central problems of modern nanoelectronics - reducing energy consumption. The key approach to solving this problem is the development of current control mechanisms based on qualitatively new physical principles. One option is molecular electronics, which proposes the use of single molecules instead of transistors. The tunnel transport of charge carriers through single molecules is described by the laws of quantum mechanics and, accordingly, quantum interference is manifested in it. The results of the research of the scientific group represent a theoretical basis for understanding the features of such processes and can naturally be applied to develop design rules for promising basic elements of molecular electronics.
