61 research outputs found
Energy Partitioning of Tunneling Currents into Luttinger Liquids
Tunneling of electrons of definite chirality into a quantum wire creates
counterpropagating excitations, carrying both charge and energy. We find that
the partitioning of energy is qualitatively different from that of charge. The
partition ratio of energy depends on the excess energy of the tunneling
electrons (controlled by the applied bias) and on the interaction strength
within the wire (characterized by the Luttinger liquid parameter ),
while the partitioning of charge is fully determined by . Moreover,
unlike for charge currents, the partitioning of energy current should manifest
itself in experiments on wires contacted by conventional (Fermi-liquid)
leads.Comment: 5 pages, 2 figure
Photon Assisted Tunneling of Zero Modes in a Majorana Wire
Hybrid nanowires with proximity-induced superconductivity in the topological
regime host Majorana zero modes (MZMs) at their ends, and networks of such
structures can produce topologically protected qubits. In a double-island
geometry where each segment hosts a pair of MZMs, inter-pair coupling mixes the
charge parity of the islands and opens an energy gap between the even and odd
charge states at the inter-island charge degeneracy. Here, we report on the
spectroscopic measurement of such an energy gap in an InAs/Al double-island
device by tracking the position of the microwave-induced quasiparticle (qp)
transitions using a radio-frequency (rf) charge sensor. In zero magnetic field,
photon assisted tunneling (PAT) of Cooper pairs gives rise to resonant lines in
the 2e-2e periodic charge stability diagram. In the presence of a magnetic
field aligned along the nanowire, resonance lines are observed parallel to the
inter-island charge degeneracy of the 1e-1e periodic charge stability diagram,
where the 1e periodicity results from a zero-energy sub-gap state that emerges
in magnetic field. Resonant lines in the charge stability diagram indicate
coherent photon assisted tunneling of single-electron states, changing the
parity of the two islands. The dependence of resonant frequency on detuning
indicates a sizable (GHz-scale) hybridization of zero modes across the junction
separating islands
Relaxation and edge reconstruction in integer quantum Hall systems
The interplay between the confinement potential and electron-electron
interactions causes reconstructions of Quantum Hall edges. We study the
consequences of this edge reconstruction for the relaxation of hot electrons
injected into integer quantum Hall edge states. In translationally invariant
edges, the relaxation of hot electrons is governed by three-body collisions
which are sensitive to the electron dispersion and thus to reconstruction
effects. We show that the relaxation rates are significantly altered in
different reconstruction scenarios.Comment: 8 pages, 3 figure
Exciton-polariton topological insulator
The authors thank R. Thomale for fruitful discussions. S.K. acknowledges the European Commission for the H2020 Marie SkĆodowska-Curie Actions (MSCA) fellowship (Topopolis). S.K., S.H. and M.S. are grateful for financial support by the JMU-Technion seed money program. S.H. also acknowledges support by the EPSRC âHybrid Polaritonicsâ Grant (EP/M025330/1). The WĂŒrzburg group acknowledges support by the ImPACT Program, Japan Science and Technology Agency and the State of Bavaria. T.C.H.L. and R. G. were supported by the Ministry of Education (Singapore) Grant No. 2017-T2-1-001Topological insulatorsâmaterials that are insulating in the bulk but allow electrons to flow on their surfaceâare striking examples of materials in which topological invariants are manifested in robustness against perturbations such as defects and disorder1. Their most prominent feature is the emergence of edge states at the boundary between areas with different topological properties. The observable physical effect is unidirectional robust transport of these edge states. Topological insulators were originally observed in the integer quantum Hall effect2 (in which conductance is quantized in a strong magnetic field) and subsequently suggested3,4,5 and observed6 to exist without a magnetic field, by virtue of other effects such as strong spinâorbit interaction. These were systems of correlated electrons. During the past decade, the concepts of topological physics have been introduced into other fields, including microwaves7,8, photonic systems9,10, cold atoms11,12, acoustics13,14 and even mechanics15. Recently, topological insulators were suggested to be possible in exciton-polariton systems16,17,18 organized as honeycomb (graphene-like) lattices, under the influence of a magnetic field. Exciton-polaritons are part-light, part-matter quasiparticles that emerge from strong coupling of quantum-well excitons and cavity photons19. Accordingly, the predicted topological effects differ from all those demonstrated thus far. Here we demonstrate experimentally an exciton-polariton topological insulator. Our lattice of coupled semiconductor microcavities is excited non-resonantly by a laser, and an applied magnetic field leads to the unidirectional flow of a polariton wavepacket around the edge of the array. This chiral edge mode is populated by a polariton condensation mechanism. We use scanning imaging techniques in real space and Fourier space to measure photoluminescence and thus visualize the mode as it propagates. We demonstrate that the topological edge mode goes around defects, and that its propagation direction can be reversed by inverting the applied magnetic field. Our exciton-polariton topological insulator paves the way for topological phenomena that involve lightâmatter interaction, amplification and the interaction of exciton-polaritons as a nonlinear many-body system.PostprintPeer reviewe
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