32 research outputs found
Emission of entangled Kramers pairs from a helical mesoscopic capacitor
The realization of single-electron sources in integer quantum Hall systems
has paved the way for exploring electronic quantum optics experiments in
solid-state devices. In this work, we characterize a single Kramers pair
emitter realized by a driven antidot embedded in a two-dimensional topological
insulator, where spin-momentum locked edge states can be exploited for
generating entanglement. Contrary to previous proposals, the antidot is coupled
to both edges of a quantum spin Hall bar, thus enabling this mesoscopic
capacitor to emit an entangled two-electron state. We study the concurrence
of the emitted state and the efficiency of its
emission as a function of the different spin-preserving and spin-flipping
tunnel couplings of the antidot with the edges. We show that the efficiency
remains very high () even for maximally entangled states
(). We also discuss how the entanglement can be probed by means
of noise measurements and violation of the Clauser-Horne-Shimony-Holt
inequality.Comment: 9 pages, 5 figure
Magnetic AC control of the spin textures in a helical Luttinger liquid
We demonstrate the possibility to induce and control peculiar spin textures
in a helical Luttinger liquid, by means of a time-dependent magnetic scatterer.
The presence of a perturbation that breaks the time-reversal symmetry opens a
gap in the spectrum, inducing single-particle backscattering and a peculiar
spin response. We show that in the weak backscattering regime asymmetric spin
textures emerge at the left and right side of the scatterer, whose spatial
oscillations are controlled by the ratio between the magnetization frequency
and the Fermi energy and by the electron interaction. This peculiar spin
response marks a strong difference between helical and non-helical liquids,
which are expected to produce symmetric spin textures even in the AC regime.Comment: 7 pages, 4 figure
Generating and controlling spin-polarized currents induced by a quantum spin Hall antidot
We study an electrically controlled quantum spin Hall antidot embedded in a
two-dimensional topological insulating bar. Helical edge states around the
antidot and along the edges of the bar are tunnel coupled. The close connection
between spin and chirality, typical of helical systems, allows to generate a
spin-polarized current flowing across the bar. This current is studied as a
function of the external voltages, by varying the asymmetry between the
barriers. For asymmetric setups, a switching behavior of the spin current is
observed as the bias is increased, both in the absence and in the presence of
electron interactions. This device allows to generate and control the
spin-polarized current by simple electrical means.Comment: 7 pages, 6 figure
Time-resolved pure spin fractionalization and spin-charge separation in helical Luttinger liquid based devices
Helical Luttinger liquids, appearing at the edge of two-dimensional
topological insulators, represent a new paradigm of one-dimensional systems,
where peculiar quantum phenomena can be investigated. Motivated by recent
experiments on charge fractionalization, we propose a setup based on helical
Luttinger liquids that allows to time-resolve, in addition to charge
fractionalization, also spin-charge separation and pure spin fractionalization.
This is due to the combined presence of spin-momentum locking and interactions.
We show that electric time-resolved measurements can reveal both charge and
spin properties, avoiding the need of magnetic materials. Although challenging,
the proposed setup could be achieved with nowadays technologies, promoting
helical liquids as interesting playgrounds to explore the effects of
interactions in one dimension.Comment: main text + supplementary materia
Transient dynamics of spin-polarized injection in helical Luttinger liquids
We analyze the time evolution of spin-polarized electron wave packets
injected into the edge states of a two-dimensional topological insulator. In
the presence of electron interactions, the system is described as a helical
Luttinger liquid and injected electrons fractionalize. However, because of the
presence of metallic detectors, no evidences of fractionalization are encoded
in dc measurements, and in this regime the system do not show deviations from
its non-interacting behavior. Nevertheless, we show that the helical Luttinger
liquid nature emerges in the transient dynamics, where signatures of
charge/spin fractionalization can be clearly identified.Comment: Contribution for the special issue of Physica E in memory of Markus
B\"uttiker. 4 figure
Interference induced thermoelectric switching and heat rectification in quantum Hall junctions
Interference represents one of the most striking manifestation of quantum
physics in low-dimensional systems. Despite evidences of quantum interference
in charge transport have been known for a long time, only recently signatures
of interference induced thermal properties have been reported, paving the way
for the phase-coherent manipulation of heat in mesoscopic devices. In this work
we show that anomalous thermoelectric properties and efficient heat
rectification can be achieved by exploiting the phase-coherent edge states of
quantum Hall systems. By considering a tunneling geometry with multiple quantum
point contacts, we demonstrate that the interference paths effectively break
the electron-hole symmetry, allowing for a thermoelectric charge current
flowing either from hot to cold or viceversa, depending on the details of the
tunnel junction. Correspondingly, an interference induced heat current is
predicted, and we are able to explain these results in terms of an intuitive
physical picture. Moreover, we show that heat rectification can be achieved by
coupling two quantum Hall systems with different filling factors, and that this
effect can be enhanced by exploiting the interference properties of the tunnel
junction.Comment: 9 pages, 7 figure
Transport through a quantum spin Hall antidot as a spectroscopic probe of spin textures
We investigate electron transport through an antidot embedded in a narrow
strip of two-dimensional topological insulator. We focus on the most generic
and experimentally relevant case with broken axial spin symmetry.
Spin-non-conservation allows additional scattering processes which change the
transport properties profoundly. We start from an analytical model for
noninteracting transport, which we also compare with a numerical tight-binding
simulation. We then extend this model by including Coulomb repulsion on the
antidot, and we study the transport in the Coulomb-blockade limit. We
investigate sequential tunneling and cotunneling regimes, and we find that the
current-voltage characteristic allows a spectroscopic measurement of the
edge-state spin textures.Comment: 11 pages, 7 figure
Current enhancement through a time dependent constriction in fractional topological insulators
We analyze the backscattering current induced by a time dependent
constriction as a tool to probe fractional topological insulators. We
demonstrate an enhancement of the total current for a fractional topological
insulator induced by the dominant tunneling excitation, contrary to the
decreasing present in the integer case for not too strong interactions. This
feature allows to unambiguously identify fractional quasiparticles.
Furthermore, the dominant tunneling processes, which may involve one or two
quasiparticles depending on the interactions, can be clearly determined.Comment: 6 pages, 3 figure
Coulomb blockade microscopy of spin density oscillations and fractional charge in quantum spin Hall dots
We evaluate the spin density oscillations arising in quantum spin Hall
quantum dots created via two localized magnetic barriers. The combined presence
of magnetic barriers and spin-momentum locking, the hallmark of topological
insulators, leads to peculiar phenomena: a half-integer charge is trapped in
the dot for antiparallel magnetization of the barriers, and oscillations appear
in the in-plane spin density, which are enhanced in the presence of electron
interactions. Furthermore, we show that the number of these oscillations is
determined by the number of particles inside the dot, so that the presence or
the absence of the fractional charge can be deduced from the in-plane spin
density. We show that when the dot is coupled with a magnetized tip, the
spatial shift induced in the chemical potential allows to probe these peculiar
features.Comment: 6 pages, 6 figure