6 research outputs found
Interface engineering of quantum Hall effects in digital transition metal oxide heterostructures
Topological insulators are characterized by a nontrivial band topology driven
by the spin-orbit coupling. To fully explore the fundamental science and
application of topological insulators, material realization is indispensable.
Here we predict, based on tight-binding modeling and first-principles
calculations, that bilayers of perovskite-type transition-metal oxides grown
along the [111] crystallographic axis are potential candidates for
two-dimensional topological insulators. The topological band structure of these
materials can be fine-tuned by changing dopant ions, substrates, and external
gate voltages. We predict that LaAuO bilayers have a
topologically-nontrivial energy gap of about 0.15 eV, which is sufficiently
large to realize the quantum spin-Hall effect at room temperature. Intriguing
phenomena, such as fractional quantum Hall effect, associated with the
nearly-flat topologically-nontrivial bands found in systems are also
discussed.Comment: Main text 11 pages with 4 figures and 1 table. Supplementary
materials 4 pages with 2 figure
Interpretation of the spin glass behaviour of diluted magnetic semiconductors below the nearest-neighbour percolation threshold via realistic Monte Carlo simulations
Solid-state harmonics beyond the atomic limit
Strong-field laser excitation of solids can produce extremely nonlinear electronic and optical behaviour. As recently demonstrated, this includes the generation of high harmonics extending into the vacuum-ultraviolet and extreme-ultraviolet regions of the electromagnetic spectrum. High harmonic generation is shown to occur fundamentally differently in solids and in dilute atomic gases. How the microscopic mechanisms in the solid and the gas differ remains a topic of intense debate. Here we report a direct comparison of high harmonic generation in the solid and gas phases of argon and krypton. Owing to the weak van der Waals interaction, rare (noble)-gas solids are a near-ideal medium in which to study the role of high density and periodicity in the generation process. We find that the high harmonic generation spectra from the rare-gas solids exhibit multiple plateaus extending well beyond the atomic limit of the corresponding gas-phase harmonics measured under similar conditions. The appearance of multiple plateaus indicates strong interband couplings involving multiple single-particle bands. We also compare the dependence of the solid and gas harmonic yield on laser ellipticity and find that they are similar, suggesting the importance of electron-hole recollision in these solids. This implies that gas-phase methods such as polarization gating for attosecond pulse generation and orbital tomography could be realized in solids