arXiv subjects

Muhammad Rizwan Khan

Publications and source records attributed to Muhammad Rizwan Khan.

4 recordsLinked to original sources

arXiv2023

Noble gas functional defect with unusual relaxation pattern in solids

The conventional understanding has always been that noble gases are chemically inert and do not affect materials properties. This belief has led to their use as a standard reference in various experimental applications through noble gas implantation. However, in our research, using first-principles calculations, we delve into the effects of noble gas defects on the properties of several functional oxides, thereby questioning this long-held assumption. We provide evidence that noble gases can indeed serve as functional defects. They have the potential to decentralize the localized defect states and prompt a shift of electrons from a localized state to the main conduction band. Our investigation unveils that noble gas defects can indeed significantly alter material properties. Thus, we underscore the importance of factoring in such defects when assessing material properties.

cond-mat.mtrl-sci↗

arXiv2023

Optical Properties and Electronic Structures of Intrinsic Gapped Metals: Inverse Materials Design Principles for Transparent Conductors

Traditional solid-state physics has long correlated the optical properties of materials with their electronic structures. However, recent discoveries of intrinsic gapped metals have challenged this classical view. Gapped metals possess electronic properties distinct from both metals and insulators, with a large concentration of free carriers without any intentional doping and an internal band gap. This unique electronic structure makes gapped metals potentially superior to materials designed by intentional doping of the wide band gap insulators. Despite their promising applications, such as transparent conductors, designing gapped metals for specific purposes remains challenging due to the lack of understanding of the correlation between their electronic band structures and optical properties. This study focuses on representative examples of gapped metals and demonstrates the cases of (i) gapped metals (e.g., CaN2) with strong intraband absorption in the visible range, (ii) gapped metals (e.g., SrNbO3) with strong interband absorption in the visible range, (iii) gapped metals (e.g., Sr5Nb5O17) that are potential transparent conductors. We explore the complexity of identifying potential gapped metals for transparent conductors and propose inverse materials design principles for discovering new-generation transparent conductors.

cond-mat.mtrl-sci↗

arXiv2023

Spontaneous off-stoichiometry as the knob to control dielectric properties of gapped metals

Using the first-principles calculations and La3Te4 as an example of an n-type gapped metal, we demonstrate that gapped metals can develop spontaneous defect formation resulting in off-stoichiometric compounds. Importantly, these compounds have different free carrier concentrations and can be realized by optimizing synthesis conditions. The ability to manipulate the free carrier concentration allows to tailor intraband and interband transitions, thus controlling the optoelectronic properties of materials in general. Specifically, by realizing different off-stochiometric La3-xTe4 compounds, it is possible to reach specific crossings of the real part of the dielectric function with the zero line, reduce plasma frequency contribution to absorption spectra, or, more generally, induce metal-to-insulator transition. This is particularly important in the context of optoelectronic, plasmonic, and epsilon-near-zero materials, as it enables materials design with a target functionality. While this work is limited to the specific gapped metal, we demonstrate that the fundamental physics is transferable to other gapped metals and can be generally used to design a wide class of new optoelectronic/plasmonic materials.

cond-mat.mtrl-sci↗

arXiv2022

Fermi Level Instability as a Way to Tailor Properties of La3Te4

Traditionally, the formation of off-stoichiometric compounds is believed to be the growth effect rather than the intrinsic tendency of the system. However, here, using the example of La3Te4, we demonstrate that in n-type gapped metals having a large internal gap between principal band edges and the Fermi level inside of the principal conduction band, Fermi-level instability can develop, resulting in a reduction of formation energy for acceptor defects. Specifically, La vacancies in La3Te4 form spontaneously to produce the acceptor states and remove a fraction of free carriers from the principal conduction band via electron-hole recombination. Such a unique self-doping mechanism allows to stabilize a range of off-stoichiometric La3-xTe4 compounds, which have different electronic properties. Moreover, we thus show how controlling synthesis conditions can be used as a knob to reach the target functionality, including controllable metal-to-insulator transition.

cond-mat.mtrl-sci↗