965 research outputs found
Incommensurate heterostructures in momentum space
To make the investigation of electronic structure of incommensurate heterostructures computationally tractable, effective alternatives to Bloch theory must be developed. In [Multiscale Model. Simul., 15(2017), pp. 476--499] we developed and analyzed a real space scheme that exploits spatial ergodicity and near-sightedness. In the present work, we present an analogous scheme formulated in momentum space, which we prove has significant computational advantages in specific incommensurate systems of physical interest, e.g., bilayers of a specified class of materials with small rotation angles. We use our theoretical analysis to obtain estimates for improved rates of convergence with respect to total CPU time for our momentum space method that are confirmed in computational experiments
Long-range charge density wave proximity effect at cuprate-manganate interfaces
The interplay between charge density waves (CDWs) and high-temperature
superconductivity is currently under intense investigation. Experimental
research on this issue is difficult because CDW formation in bulk copper-oxides
is strongly influenced by random disorder, and a long-range-ordered CDW state
in high magnetic fields is difficult to access with spectroscopic and
diffraction probes. Here we use resonant x-ray scattering in zero magnetic
field to show that interfaces with the metallic ferromagnet
LaCaMnO greatly enhance CDW formation in the optimally
doped high-temperature superconductor YBaCuO (), and that this effect persists over several tens of nm. The wavevector
of the incommensurate CDW serves as an internal calibration standard of the
charge carrier concentration, which allows us to rule out any significant
influence of oxygen non-stoichiometry, and to attribute the observed phenomenon
to a genuine electronic proximity effect. Long-range proximity effects induced
by heterointerfaces thus offer a powerful method to stabilize the charge
density wave state in the cuprates, and more generally, to manipulate the
interplay between different collective phenomena in metal oxides.Comment: modified version published in Nature Material
2D materials and van der Waals heterostructures
The physics of two-dimensional (2D) materials and heterostructures based on
such crystals has been developing extremely fast. With new 2D materials, truly
2D physics has started to appear (e.g. absence of long-range order, 2D
excitons, commensurate-incommensurate transition, etc). Novel heterostructure
devices are also starting to appear - tunneling transistors, resonant tunneling
diodes, light emitting diodes, etc. Composed from individual 2D crystals, such
devices utilize the properties of those crystals to create functionalities that
are not accessible to us in other heterostructures. We review the properties of
novel 2D crystals and how their properties are used in new heterostructure
devices
Electron quantum metamaterials in van der Waals heterostructures
In recent decades, scientists have developed the means to engineer synthetic
periodic arrays with feature sizes below the wavelength of light. When such
features are appropriately structured, electromagnetic radiation can be
manipulated in unusual ways, resulting in optical metamaterials whose function
is directly controlled through nanoscale structure. Nature, too, has adopted
such techniques -- for example in the unique coloring of butterfly wings -- to
manipulate photons as they propagate through nanoscale periodic assemblies. In
this Perspective, we highlight the intriguing potential of designer
sub-electron wavelength (as well as wavelength-scale) structuring of electronic
matter, which affords a new range of synthetic quantum metamaterials with
unconventional responses. Driven by experimental developments in stacking
atomically layered heterostructures -- e.g., mechanical pick-up/transfer
assembly -- atomic scale registrations and structures can be readily tuned over
distances smaller than characteristic electronic length-scales (such as
electron wavelength, screening length, and electron mean free path). Yet
electronic metamaterials promise far richer categories of behavior than those
found in conventional optical metamaterial technologies. This is because unlike
photons that scarcely interact with each other, electrons in subwavelength
structured metamaterials are charged, and strongly interact. As a result, an
enormous variety of emergent phenomena can be expected, and radically new
classes of interacting quantum metamaterials designed
Two-dimensional topological superconductivity in Pb/Co/Si(111)
Just like insulators can host topological Dirac states at their edges,
superconductors can also exhibit topological phases characterized by Majorana
edge states. Remarkable zero-energy states have been recently observed at the
two ends of proximity induced superconducting wires, and were interpreted as
localized Majorana end states in one-dimensional (1D) topological
superconductor. By contrast, propagating Majorana states should exist at the 1D
edges of two-dimensional (2D) topological superconductors. Here we report the
direct observation of dispersive in-gap states surrounding topological
superconducting domains made of a single atomic layer of Pb covering magnetic
islands of Co/Si(111). We interpret the observed continuous dispersion across
the superconducting gap in terms of a spatial topological transition
accompanied by a chiral edge mode and residual gaped helical edge states. Our
experimental approach enables the engineering and control of a large variety of
novel quantum phases. This opens new horizons in the field of quantum materials
and quantum electronics where the magnetization of the domains could be used as
a control parameter for the manipulation of topological states.Comment: 12 pages, 3 figure
Phase separation and long wave-length charge instabilities in spin-orbit coupled systems
We investigate a two-dimensional electron model with Rashba spin-orbit
interaction where the coupling constant depends on the electronic
density. It is shown that this dependence may drive the system unstable towards
a long-wave length charge density wave (CDW) where the associated second order
instability occurs in close vicinity to global phase separation. For very low
electron densities the CDW instability is nesting-induced and the modulation
follows the Fermi momentum . At higher density the instability criterion
becomes independent of and the system may become unstable in a broad
momentum range. Finally, upon filling the upper spin-orbit split band, finite
momentum instabilities disappear in favor of phase separation alone. We discuss
our results with regard to the inhomogeneous phases observed at the
LaAlO/SrTiO or LaTiO/SrTiO interfaces.Comment: 6 pages, 6 figure
- …