Yasin Yekta | Searcharxiv

arXiv2025

Two-dimensional M2X2 family with emerging semiconducting, semimetallic, and magnetic properties

The exploration for novel two-dimensional (2D) materials with diverse electronic characteristics has attracted growing interest in recent years. Using density functional theory (DFT) calculations, we have predicted a new family of 2D transition-metal (TM) based compounds under the nomenclature M_2X_2 (where M represents TMs, and X denotes chalcogen elements like S, Se, and Te). Our investigation delves into the examination of the formation energies, dynamical/thermal stabilities, mechanical properties, electronic structures, and magnetic properties of various systems within this family. Through our computational analyses, we have discovered a total of 35 thermodynamically and dynamically stable M_2X_2 monolayer materials that exhibit remarkable diversity in terms of their electronic and magnetic properties. Our findings will pave the way for the experimental realization of various M_2X_2 structures in the near future. In particular, among the predicted compounds, M_2X_2(M=Zn, Cd; X=S, Se, Te) are a direct band-gap semiconductor with band gaps between 0.9 to 2.6 eV (1.3 to 3.7 eV) by DFT+PBE (hybrid functional HSE) calculations. M_2X_2(M=Ti, Zr, Hf, Tc, Re) are zero-gap semiconductor (semimetals) in standard DFT+PBE calculation. Inclusion of spin-orbit coupling leads to a gap opening of 0.1 eV. Notably, our analysis has also unveiled the magnetic nature of certain materials, such as Mn_2X_2(X=S, Se), Fe_2X_2(X=Se, Te), and Ti_2Te_2. The prediction of semiconducting (magnetic) M_2X_2 materials not only offers valuable insights into the underlying electronic properties (magnetism) of 2D systems but also positions these materials as promising candidates for the development of advanced electronic (spintronic) devices.

cond-mat.mtrl-sci↗

arXiv2022

Tunning the tilt of a Dirac cone by atomic manipulations: application to 8Pmmn borophene

We decipher the microscopic mechanism of the formation of tilt in the two-dimensional Dirac cone of $8Pmmn$ borphene. In our ab-initio calculations, we identify relevant low-energy degrees of freedom on the $8Pmmn$ lattice and find that these atomic orbitals reside on an effective honeycomb lattice (inner sites), while the high-energy degrees of freedom reside on the rest of the $8Pmmn$ lattice (ridge sites). Integrating out the high-energy atomic orbitals, gives rise to remarkably large effective further neighbor hoppings on the coarse grained "honeycomb graph" of inner sites that determine the location and tilt of the Dirac cone. Molecular orbitals -- that can be modified by atomic manipulations -- are responsible for the creation of further neighbor edges on the honeycomb graph that controls the tilt of the resulting Dirac cone. This leads to an effective tight-binding model on a parent honeycomb graph that facilitates numerical modeling of various effects such as disorder/interactions/symmetry-breaking for tilted Dirac cone fermions. Since the tilt is a proxy to spacetime metric, our result offers a robust perspective on the fabrication of desired emergent spacetime structure and synthesis of geometric forces at ambient conditions that are likely to enhance our control on the movement of electrons in electric/optical devices.

cond-mat.mtrl-sci↗