45 research outputs found
Electronic and Thermoelectric Properties of Few-Layer Transition Metal Dichalcogenides
The electronic and thermoelectric properties of one to four monolayers of
MoS, MoSe, WS, and WSe are calculated. For few layer
thicknesses,the near degeneracies of the conduction band and
valleys and the valence band and valleys enhance the n-type and
p-type thermoelectric performance. The interlayer hybridization and energy
level splitting determine how the number of modes within of a valley
minimum changes with layer thickness. In all cases, the maximum ZT coincides
with the greatest near-degeneracy within 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
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 NbSe,
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 NbSe
Recent studies on superconductivity in NbSe 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 NbSe. We demonstrate that
NbSe is close to a ferromagnetic instability, and analyze our results in
the context of experimental measurements of the spin susceptibility in
NbSe. 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 NbSe, 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
NbSe in the normal stateComment: 13 pages, 6 figure