39 research outputs found

    Electronic and Thermoelectric Properties of Few-Layer Transition Metal Dichalcogenides

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    The electronic and thermoelectric properties of one to four monolayers of MoS2_{2}, MoSe2_{2}, WS2_{2}, and WSe2_{2} are calculated. For few layer thicknesses,the near degeneracies of the conduction band KK and Ξ£\Sigma valleys and the valence band Ξ“\Gamma and KK valleys enhance the n-type and p-type thermoelectric performance. The interlayer hybridization and energy level splitting determine how the number of modes within kBTk_BT of a valley minimum changes with layer thickness. In all cases, the maximum ZT coincides with the greatest near-degeneracy within kBTk_BT of the band edge that results in the sharpest turn-on of the density of modes. The thickness at which this maximum occurs is, in general, not a monolayer. The transition from few layers to bulk is discussed. Effective masses, energy gaps, power-factors, and ZT values are tabulated for all materials and layer thicknesses

    Ising superconductivity: a first-principles perspective

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    The recent discovery of Ising superconductivity has garnered a lot of interest due in part to the resilience of these superconductors to large in-plane magnetic fields. In this Perspective we explain the basic concepts that define the behavior of Ising superconductors, provide an overview of the electronic structure and magnetic properties with a focus on NbSe2_2, summarize key experimental observations that have been made in this class of superconductors, highlight the role that defects and proximity-induced effects at interfaces have on Ising superconductivity and finally discuss the prospects for observing Ising superconductivity in bulk materials.Comment: 10 pages, 8 figure

    Ising superconductivity and magnetism in NbSe2_2

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    Recent studies on superconductivity in NbSe2_2 have demonstrated a large anisotropy in the superconducting critical field when the material is reduced to a single monolayer. Motivated by this recent discovery, we use density functional theory (DFT) calculations to quantitatively address the superconducting properties of bulk and monolayer NbSe2_2. We demonstrate that NbSe2_2 is close to a ferromagnetic instability, and analyze our results in the context of experimental measurements of the spin susceptibility in NbSe2_2. We show how this magnetic instability, which is pronounced in a single monolayer, can enable sizeable singlet-triplet mixing of the superconducting order parameter, contrary to contemporary considerations of the pairing symmetry in monolayer NbSe2_2, and discuss approaches as to how this degree of mixing can be addressed quantitatively within our DFT framework. Our calculations also enable a quantitative description of the large anisotropy of the superconducting critical field, using DFT calculations of monolayer NbSe2_2 in the normal stateComment: 13 pages, 6 figure