Browsing by Subject "Density of states"

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Open Access
Columnar antiferromagnetic order of a MBene monolayer
(American Physical Society, 2021-04-16) Ozdemir, I.; Kadioglu, Y.; Yüksel, Y.; Akıncı, Ü.; Üzengi Aktürk, O.; Aktürk, E.; Çıracı, Salim
First-principles density functional theory, combined with the Monte Carlo method, predicts that the Fe2B2 monolayer of the MBene family has a stable columnar antiferromagnetic (AFM) ground state. Below the critical temperature, Tc=115 K in equilibrium, the spins rotate by the same amount in every other column of Fe atoms, but they retain the same direction in the same column. Under applied tensile strains, Tc and the order parameter can increase nonmonotonically. The onset of the columnar order can result in a transition from two dimension (2D) to 1D in magnetic, electronic, and conduction properties. The ordered magnetic state itself can be tuned by external magnetic field, whereby the columnar magnetic order changes to ferromagnetic order with a double hysteresis behavior. When terminated by Fluorine atoms, the columnar order changes to the AFM order with Tc rising above room temperature. This situation is rather unusual and insofar is fundamental for a realistic, strictly 2D monolayer and can have critical consequences in spin conduction.
Open Access
Quantum transport regimes in quartic dispersion materials with Anderson disorder
(AIP Publishing LLC, 2024-04-28) Polat, Mustafa; Özkan, Hazan; Sevinçli, Hâldun
Mexican-hat-shaped quartic dispersion manifests itself in certain families of single-layer two-dimensional hexagonal crystals such as compounds of groups III-VI and groups IV-V as well as elemental crystals of group V. A quartic band forms the valence band edge in various of these structures, and some of the experimentally confirmed structures are GaS, GaSe, InSe, SnSb, and blue phosphorene. Here, we numerically investigate strictly one-dimensional and quasi-one dimensional (Q1D) systems with quartic dispersion and systematically study the effects of Anderson disorder on their transport properties with the help of a minimal tight-binding model and Landauer formalism. We compare the analytical expression for the scaling function with simulation data to distinguish the domains of diffusion and localization regimes. In one dimension, it is shown that conductance drops dramatically at the quartic band edge compared to the quadratic case. As for the Q1D nanoribbons, a set of singularities emerge close to the band edge, suppressing conductance and leading to short mean-free-paths and localization lengths. Interestingly, wider nanoribbons can have shorter mean-free-paths because of denser singularities. However, the localization lengths sometimes follow different trends. Our results display the peculiar effects of quartic dispersion on transport in disordered systems.