204 research outputs found
Subtle leakage of a Majorana mode into a quantum dot
We investigate quantum transport through a quantum dot connected to source
and drain leads and side-coupled to a topological superconducting nanowire
(Kitaev chain) sustaining Majorana end modes. Using a recursive Green's
function approach, we determine the local density of states (LDOS) of the
system and find that the end Majorana mode of the wire leaks into the dot thus
emerging as a unique dot level {\it pinned} to the Fermi energy
of the leads. Surprisingly, this resonance pinning, resembling in this sense a
"Kondo resonance", occurs even when the gate-controlled dot level
is far above or far below . The
calculated conductance of the dot exhibits an unambiguous signature for the
Majorana end mode of the wire: in essence, an off-resonance dot
[], which should have ,
shows instead a conductance over a wide range of , due to this
pinned dot mode. Interestingly, this pinning effect only occurs when the dot
level is coupled to a Majorana mode; ordinary fermionic modes (e.g., disorder)
in the wire simply split and broaden (if a continuum) the dot level. We discuss
experimental scenarios to probe Majorana modes in wires via these leaked/pinned
dot modes.Comment: 3 figures, 5 pages, published in Phys. Rev. B (Editors' suggestion
Helical edge states in multiple topological mass domains
The two-dimensional topological insulating phase has been experimentally
discovered in HgTe quantum wells (QWs). The low-energy physics of
two-dimensional topological insulators (TIs) is described by the
Bernevig-Hughes-Zhang (BHZ) model, where the realization of a topological or a
normal insulating phase depends on the Dirac mass being negative or positive,
respectively. We solve the BHZ model for a mass domain configuration, analyzing
the effects on the edge modes of a finite Dirac mass in the normal insulating
region (soft-wall boundary condition). We show that at a boundary between a TI
and a normal insulator (NI), the Dirac point of the edge states appearing at
the interface strongly depends on the ratio between the Dirac masses in the two
regions. We also consider the case of multiple boundaries such as NI/TI/NI,
TI/NI/TI and NI/TI/NI/TI.Comment: 11 pages, 15 figure
Evolution of a Streamer-Blowout CME as Observed by Imagers on Parker Solar Probe and the Solar Terrestrial Relations Observatory
Context: On 26-27 January 2020, the wide-field imager WISPR on Parker Solar
Probe (PSP) observed a coronal mass ejection (CME) from a distance of
approximately 30 solar radii as it passed through the instrument's 95 degree
field-of-view, providing an unprecedented view of the flux rope morphology of
the CME's internal structure. The same CME was seen by STEREO, beginning on 25
January.
Aims: Our goal was to understand the origin and determine the trajectory of
this CME.
Methods: We analyzed data from three well-placed spacecraft: Parker Solar
Probe (PSP), Solar Terrestrial Relations Observatory-Ahead (STEREO-A), and
Solar Dynamics Observatory (SDO). The CME trajectory was determined using the
method described in Liewer et al. (2020) and verified using simultaneous images
of the CME propagation from STEREO-A. The fortuitous alignment with STEREO-A
also provided views of coronal activity leading up to the eruption.
Observations from SDO, in conjunction with potential magnetic field models of
the corona, were used to analyze the coronal magnetic evolution for the three
days leading up to the flux rope ejection from the corona on 25 January.
Results: We found that the 25 January CME is likely the end result of a slow
magnetic flux rope eruption that began on 23 January and was observed by
STEREO-A/Extreme Ultraviolet Imager (EUVI). Analysis of these observations
suggest that the flux rope was apparently constrained in the corona for more
than a day before its final ejection on 25 January. STEREO-A/COR2 observations
of swelling and brightening of the overlying streamer for several hours prior
to eruption on January 25 led us to classify this as a streamer-blowout CME.
The analysis of the SDO data suggests that restructuring of the coronal
magnetic fields caused by an emerging active region led to the final ejection
of the flux rope.Comment: 12 pages, 12 figures. Accepted in A&
Helical edge states in multiple topological mass domains
The two-dimensional topological insulating phase has been experimentally
discovered in HgTe quantum wells (QWs). The low-energy physics of
two-dimensional topological insulators (TIs) is described by the
Bernevig-Hughes-Zhang (BHZ) model, where the realization of a topological or a
normal insulating phase depends on the Dirac mass being negative or positive,
respectively. We solve the BHZ model for a mass domain configuration, analyzing
the effects on the edge modes of a finite Dirac mass in the normal insulating
region (soft-wall boundary condition). We show that at a boundary between a TI
and a normal insulator (NI), the Dirac point of the edge states appearing at
the interface strongly depends on the ratio between the Dirac masses in the two
regions. We also consider the case of multiple boundaries such as NI/TI/NI,
TI/NI/TI and NI/TI/NI/TI.Comment: 11 pages, 15 figure
Scanning Tunneling Microscope Operating as a Spin-diode
We theoretically investigate spin-polarized transport in a system composed of
a ferromagnetic Scanning Tunneling Microscope (STM) tip coupled to an adsorbed
atom (adatom) on a host surface. Electrons can tunnel directly from the tip to
the surface or via the adatom. Since the tip is ferromagnetic and the host
surface (metal or semiconductor) is non-magnetic we obtain a spin-diode effect
when the adatom is in the regime of single occupancy. This effect leads to an
unpolarized current for direct bias (V > 0) and polarized current for reverse
(V < 0) bias voltages, if the tip is nearby the adatom. Within the
nonequilibrium Keldysh technique we analyze the interplay between the lateral
displacement of the tip and the intra adatom Coulomb interaction on the
spindiode effect. As the tip moves away from the adatom the spin-diode effect
vanishes and the currents become polarized for both V > 0 and V < 0. We also
find an imbalance between the up and down spin populations in the adatom, which
can be tuned by the tip position and the bias. Finally, due to the presence of
the adsorbate on the surface, we observe spin-resolved Friedel oscillations in
the current, which reflects the oscillations in the calculated LDOS of the
subsystem surface+adatom.Comment: 11 pages, 4 figures. Submitte
Efeito de diferentes emulsificantes na germinação dos conídios do fungo entomopatogênico Verticillium lecanii (Zimm.) Viégas.
Resumo
Seleção de isolados de Verticillium lecanii (Zimm.) Viégas para o controle do pulgão do pínus Cinara atlantica (Hemiptera: aphididae).
Organizado por Patricia Póvoa de Mattos, Celso Garcia Auer, Rejane Stumpf Sberze, Katia Regina Pichelli e Paulo César Botosso
Patogenicidade de cepas do fungo Verticillium lecanii (Zimm.) Viégas cultivado em meio sólido e meio líquido para controle de Cinara atlantica (Wilson, 1919) (Hemiptera: Aphididae).
Resumo
Impacto do fungo entomopatogênico Verticillium lecanii (Zimm.) Viègas sobre larvas do predador Syrphus phaeostigma Wiedemann (Diptera: Syrphidae).
Resumo
Avaliação da produção de Verticillium lecanii (Zimm.) Viégas em diferentes meios de cultura sólidos.
Organizado por Patricia Póvoa de Mattos, Celso Garcia Auer, Rejane Stumpf Sberze, Katia Regina Pichelli e Paulo César Botosso
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