1,287 research outputs found
Effect of Point Defects on the Optical and Transport Properties of MoS2 and WS2
Imperfections in the crystal structure, such as point defects, can strongly
modify the optical and transport properties of materials. Here, we study the
effect of point defects on the optical and DC conductivities of single layers
of semiconducting transition metal dichalcogenides with the form S,
where =Mo or W. The electronic structure is considered within a six bands
tight-binding model, which accounts for the relevant combination of
orbitals of the metal and orbitals of the chalcogen . We use the
Kubo formula for the calculation of the conductivity in samples with different
distributions of disorder. We find that and/or S defects create mid-gap
states that localize charge carriers around the defects and which modify the
optical and transport properties of the material, in agreement with recent
experiments. Furthermore, our results indicate a much higher mobility for
-doped WS in comparison to MoS
Fixed Points of the Dissipative Hofstadter Model
The phase diagram of a dissipative particle in a periodic potential and a
magnetic field is studied in the weak barrier limit and in the tight-biding
regime. For the case of half flux per plaquette, and for a wide range of values
of the dissipation, the physics of the model is determined by a non trivial
fixed point. A combination of exact and variational results is used to
characterize this fixed point. Finally, it is also argued that there is an
intermediate energy scale that separates the weak coupling physics from the
tight-binding solution.Comment: 4 pages 3 figure
Pseudomagnetic fields and ballistic transport in a suspended graphene sheet
We study a suspended graphene sheet subject to the electric field of a gate
underneath. We compute the elastic deformation of the sheet and the
corresponding effective gauge field, which modifies the electronic transport.
In a clean system the two-terminal conductance of the sample is reduced below
the ballistic limit and is almost totally suppressed at low carrier
concentrations in samples under tension. Residual disorder restores a small
finite conductivity.Comment: 4 page
Topological superconductivity in lead nanowires
Superconductors with an odd number of bands crossing the Fermi energy have
topologically protected Andreev states at interfaces, including Majorana states
in one dimensional geometries. Superconductivity, a low number of 1D channels,
large spin orbit coupling, and a sizeable Zeeman energy, are present in lead
nanowires produced by nanoindentation of a Pb tip on a Pb substrate, in
magnetic fields higher than the Pb bulk critical field. A number of such
devices have been analyzed. In some of them, the dependence of the critical
current on magnetic field, and the Multiple Andreev Reflections observed at
finite voltages, are compatible with the existence of topological
superconductivity
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