Nature of carrier injection in metal/2D semiconductor interface and its implications to the limits of contact resistance

Monolayers of transition metal dichalcogenides (TMDCs) exhibit excellent electronic and optical properties. However, the performance of these two-dimensional (2D) devices are often limited by the large resistance offered by the metal contact interface. Till date, the carrier injection mechanism from metal to 2D TMDC layers remains unclear, with widely varying reports of Schottky barrier height (SBH) and contact resistance (Rc), particularly in the monolayer limit. In this work, we use a combination of theory and experiments in Au and Ni contacted monolayer MoS2 device to conclude the following points: (i) the carriers are injected at the source contact through a cascade of two potential barriers - the barrier heights being determined by the degree of interaction between the metal and the TMDC layer; (ii) the conventional Richardson equation becomes invalid due to the multi-dimensional nature of the injection barriers, and using Bardeen-Tersoff theory, we derive the appropriate form of the Richardson equation that describes such composite barrier; (iii) we propose a novel transfer length method (TLM) based SBH extraction methodology, to reliably extract SBH by eliminating any confounding effect of temperature dependent channel resistance variation; (iv) we derive the Landauer limit of the contact resistance achievable in such devices. A comparison of the limits with the experimentally achieved contact resistance reveals plenty of room for technological improvements.Comment: Accepted in Physical Review

Magnetism in AV3Sb5 (A = Cs, Rb, K): Complex Landscape of the Dynamical Magnetic Textures

We have investigated the dynamical magnetic properties of the V-based kagome stibnite compounds by combining the ab-initio calculated magnetic parameters of a spin Hamiltonian like inter-site exchange parameters, magnetocrystalline anisotropy and site projected magnetic moments, with full-fledged simulations of atomistic spin-dynamics. Our calculations reveal that in addition to a ferromagnetic order along the [001] direction, the system hosts a complex landscape of magnetic configurations comprised of commensurate and incommensurate spin-spirals along the [010] direction. The presence of such chiral magnetic textures may be the key to solve the mystery about the origin of the experimentally observed inherent breaking of the C6 rotational symmetry- and the time-reversal symmetry.Comment: Accepted In Physical Review

Magnetism in AV3Sb5 (Cs, Rb, K): Origin and Consequences for the Strongly Correlated Phases

The V-based kagome systems AV3Sb5 (A = Cs, Rb and K) are unique by virtue of the intricate interplay of non-trivial electronic structure, topology and intriguing fermiology, rendering them to be a playground of many mutually dependent exotic phases like charge-order and superconductivity. Despite numerous recent studies, the interconnection of magnetism and other complex collective phenomena in these systems has yet not arrived at any conclusion. Using first-principles tools, we demonstrate that their electronic structures, complex fermiologies and phonon dispersions are strongly influenced by the interplay of dynamic electron correlations, non-trivial spin-polarization and spin-orbit coupling. An investigation of the first-principles-derived inter-site magnetic exchanges with the complementary analysis of q-dependence of the electronic response functions and the electron-phonon coupling indicate that the system conforms as a frustrated spin-cluster, where the occurrence of the charge-order phase is intimately related to the mechanism of electron-phonon coupling, rather than the Fermi-surface nesting.Comment: Accepted in Physical Review Letter