54,924 research outputs found
Plasmonics in topological insulators: Spin-charge separation, the influence of the inversion layer, and phonon-plasmon coupling
We demonstrate via three examples that topological insulators (TI) offer a
new platform for plasmonics. First, we show that the collective excitations of
a thin slab of a TI display spin-charge separation. This gives rise to purely
charge-like optical and purely spin-like acoustic plasmons, respectively.
Second, we argue that the depletion layer mixes Dirac and Schr\"odinger
electrons which can lead to novel features such as high modulation depths and
interband plasmons. The analysis is based on an extension of the usual formula
for optical plasmons that depends on the slab width and on the dielectric
constant of the TI. Third, we discuss the coupling of the TI surface phonons to
the plasmons and find strong hybridisation especially for samples with large
slab widths.Comment: 37 pages, 7 figure
Spin-charge separation of plasmonic excitations in thin topological insulators
We discuss plasmonic excitations in a thin slab of a topological insulators.
In the limit of no hybridization of the surface states and same electronic
density of the two layers, the electrostatic coupling between the top and
bottom layers leads to optical and acoustic plasmons which are purely charge
and spin collective oscillations. We then argue that a recent experiment on the
plasmonic excitations of Bi2Se3 [Di Pietro et al, Nat. Nanotechnol. 8, 556
(2013)] must be explained by including the charge response of the
two-dimensional electron gas of the depletion layer underneath the two
surfaces. We also present an analytic formula to fit their data.Comment: 7 pages, 5 figure
Density-Dependent Synthetic Gauge Fields Using Periodically Modulated Interactions
We show that density-dependent synthetic gauge fields may be engineered by
combining periodically modu- lated interactions and Raman-assisted hopping in
spin-dependent optical lattices. These fields lead to a density- dependent
shift of the momentum distribution, may induce superfluid-to-Mott insulator
transitions, and strongly modify correlations in the superfluid regime. We show
that the interplay between the created gauge field and the broken sublattice
symmetry results, as well, in an intriguing behavior at vanishing interactions,
characterized by the appearance of a fractional Mott insulator.Comment: 5 pages, 5 figure
Quantum Levy flights and multifractality of dipolar excitations in a random system
We consider dipolar excitations propagating via dipole-induced exchange among
immobile molecules randomly spaced in a lattice. The character of the
propagation is determined by long-range hops (Levy flights). We analyze the
eigen-energy spectra and the multifractal structure of the wavefunctions. In 1D
and 2D all states are localized, although in 2D the localization length can be
extremely large leading to an effective localization-delocalization crossover
in realistic systems. In 3D all eigenstates are extended but not always
ergodic, and we identify the energy intervals of ergodic and non-ergodic
states. The reduction of the lattice filling induces an ergodic to non-ergodic
transition, and the excitations are mostly non-ergodic at low filling.Comment: 5 pages, 6 figure
Ultracold dipolar gases - a challenge for experiments and theory
We present a review of recent results concerning the physics of ultracold
trapped dipolar gases. In particular, we discuss the Bose-Einstein condensation
for dipolar Bose gases and the BCS transition for dipolar Fermi gases. In both
cases we stress the dominant role of the trap geometry in determining the
properties of the system. We present also results concerning bosonic dipolar
gases in optical lattices and the possibility of obtaining variety of different
quantum phases in such case. Finally, we analyze various possible routes
towards achieving ultracold dipolar gases.Comment: This paper is based on the lecture given by M. Lewenstein at the
Nobel Symposium ''Coherence and Condensation in Quantum Systems'',
Gothesburg, 4-7.12.200
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