Researchers from the University of Edinburgh, led by Dr. Jakkapat Seeyangnok and Dr. Udomsilp Pinsook, along with Professor Graeme J Ackland, have published a study in the journal Physical Review Letters that explores the intricate relationship between charge density waves (CDW) and superconductivity in a unique class of two-dimensional materials known as Janus hydrogenated transition metal chalcogenides.
The study focuses on Janus MoXH monolayers, where X can be either sulfur (S) or selenium (Se). These materials exhibit an unusual interplay between lattice instabilities, electron-phonon coupling, and superconductivity. Using advanced computational techniques, the researchers demonstrated that these monolayers naturally adopt a CDW ground state, which is a periodic modulation of the electron density that can coexist or compete with superconductivity.
The CDW state in these materials arises from soft phonon modes at specific points in the crystal’s Brillouin zone, rather than from the nesting of the Fermi surface, which is a common mechanism in other CDW materials. The researchers found that the CDW state lowers the total energy of the system and stabilizes the lattice, eliminating certain unstable phonon modes.
Interestingly, the interplay between CDW order and superconductivity varies depending on the specific material. In the case of 1T MoSH, the formation of the CDW state enhances low-energy phonon contributions and strengthens electron-phonon coupling, leading to an increased superconducting transition temperature. However, for 1T MoSeH and 2H MoSeH, the CDW phase suppresses electron-phonon coupling and reduces superconductivity.
The researchers also showed that external factors such as thermal fluctuations, compressive strain, and carrier doping can selectively suppress the CDW order and restore superconductivity. This tunability makes Janus MoXH monolayers a promising platform for exploring the competition between lattice-driven charge ordering and superconductivity.
The practical applications of these findings for the energy sector could be significant. Superconductors are materials that can conduct electricity without resistance, making them highly efficient for energy transmission. Understanding and controlling the factors that influence superconductivity in these two-dimensional materials could lead to the development of more efficient and practical superconductors for energy applications. Additionally, the tunability of these materials could enable the design of novel energy storage and conversion devices.
In conclusion, this research provides valuable insights into the complex interplay between CDW order and superconductivity in Janus MoXH monolayers. The findings could pave the way for the development of advanced materials for energy transmission, storage, and conversion, contributing to a more sustainable and efficient energy future.
Source: Physical Review Letters
This article is based on research available at arXiv.