12 research outputs found
Parity transitions in the superconducting ground state of hybrid InSb-Al Coulomb islands
The number of electrons in small metallic or semiconducting islands is
quantized. When tunnelling is enabled via opaque barriers this number can
change by an integer. In superconductors the addition is in units of two
electron charges (2e), reflecting that the Cooper pair condensate must have an
even parity. This ground state (GS) is foundational for all superconducting
qubit devices. Here, we study a hybrid superconducting-semiconducting island
and find three typical GS evolutions in a parallel magnetic field: a robust
2e-periodic even-parity GS, a transition to a 2e-periodic odd-parity GS,and a
transition from a 2e- to a 1e-periodic GS. The 2e-periodic odd-parity GS
persistent in gate-voltage occurs when a spin-resolved subgap state crosses
zero energy. For our 1e-periodic GSs we explicitly show the origin being a
single zero-energy state gapped from the continuum, i.e. compatible with an
Andreev bound states stabilized at zero energy or the presence of Majorana zero
modes
Electric field tunable superconductor-semiconductor coupling in Majorana nanowires
We study the effect of external electric fields on
superconductor-semiconductor coupling by measuring the electron transport in
InSb semiconductor nanowires coupled to an epitaxially grown Al superconductor.
We find that the gate voltage induced electric fields can greatly modify the
coupling strength, which has consequences for the proximity induced
superconducting gap, effective g-factor, and spin-orbit coupling, which all
play a key role in understanding Majorana physics. We further show that level
repulsion due to spin-orbit coupling in a finite size system can lead to
seemingly stable zero bias conductance peaks, which mimic the behavior of
Majorana zero modes. Our results improve the understanding of realistic
Majorana nanowire systems.Comment: 10 pages, 5 figures, supplemental information as ancillary fil
Quantized Majorana conductance
Majorana zero-modes hold great promise for topological quantum computing.
Tunnelling spectroscopy in electrical transport is the primary tool to identify
the presence of Majorana zero-modes, for instance as a zero-bias peak (ZBP) in
differential-conductance. The Majorana ZBP-height is predicted to be quantized
at the universal conductance value of 2e2/h at zero temperature. Interestingly,
this quantization is a direct consequence of the famous Majorana symmetry,
'particle equals antiparticle'. The Majorana symmetry protects the quantization
against disorder, interactions, and variations in the tunnel coupling. Previous
experiments, however, have shown ZBPs much smaller than 2e2/h, with a recent
observation of a peak-height close to 2e2/h. Here, we report a quantized
conductance plateau at 2e2/h in the zero-bias conductance measured in InSb
semiconductor nanowires covered with an Al superconducting shell. Our
ZBP-height remains constant despite changing parameters such as the magnetic
field and tunnel coupling, i.e. a quantized conductance plateau. We distinguish
this quantized Majorana peak from possible non-Majorana origins, by
investigating its robustness on electric and magnetic fields as well as its
temperature dependence. The observation of a quantized conductance plateau
strongly supports the existence of non-Abelian Majorana zero-modes in the
system, consequently paving the way for future braiding experiments.Comment: 5 figure
Observation of Conductance Quantization in InSb Nanowire Networks
International audienceMajorana zero modes (MZMs) are prime candidates for robust topological quantum bits, holding a great promise for quantum computing. Semiconducting nanowires with strong spin orbit coupling offer a promising platform to harness one-dimensional electron transport for Majorana physics. Demonstrating the topological nature of MZMs relies on braiding, accomplished by moving MZMs around each other in a certain sequence. Most of the proposed Majorana braiding circuits require nanowire networks with minimal disorder. Here, the electronic transport across a junction between two merged InSb nanowires is studied to investigate how disordered these nanowire networks are. Conductance quantization plateaus are observed in most of the contact pairs of the epitaxial InSb nanowire networks: the hallmark of ballistic transport behavior
Observation of Conductance Quantization in InSb Nanowire Networks
Majorana
zero modes (MZMs) are prime candidates for robust topological
quantum bits, holding a great promise for quantum computing. Semiconducting
nanowires with strong spin orbit coupling offer a promising platform
to harness one-dimensional electron transport for Majorana physics.
Demonstrating the topological nature of MZMs relies on braiding, accomplished
by moving MZMs around each other in a certain sequence. Most of the
proposed Majorana braiding circuits require nanowire networks with
minimal disorder. Here, the electronic transport across a junction
between two merged InSb nanowires is studied to investigate how disordered
these nanowire networks are. Conductance quantization plateaus are
observed in most of the contact pairs of the epitaxial InSb nanowire
networks: the hallmark of ballistic transport behavior
InSb Nanowires with Built-In Ga x In 1â x Sb Tunnel Barriers for Majorana Devices
International audienceMajorana zero modes (MZMs), prime candidates for topological quantum bits, are detected as zero bias conductance peaks (ZBPs) in tunneling spectroscopy measurements. Implementation of a narrow and hightunnel barrier in the next generation of Majorana devices can help to achieve the theoretically predicted quantized height of the ZBP.We propose a material-oriented approach to engineer a sharp and narrow tunnel barrier by synthesizing a thin axial segment of GaxIn1-xSb within an InSb nanowire. By varying the precursor molar fraction and the growth time, we accurately control the composition and the length of the barriers. Theheight and the width of the GaxIn1-xSbtunnel barrier areextracted from the Wentzel-Kramers-Brillouin (WKB)-fits to the experimentalI-V trace
InSb Nanowires with Built-In Ga<sub><i>x</i></sub>In<sub>1â<i>x</i></sub>Sb Tunnel Barriers for Majorana Devices
Majorana
zero modes (MZMs), prime candidates for topological quantum bits,
are detected as zero bias conductance peaks (ZBPs) in tunneling spectroscopy
measurements. Implementation of a narrow and high tunnel barrier in
the next generation of Majorana devices can help to achieve the theoretically
predicted quantized height of the ZBP. We propose a material-oriented
approach to engineer a sharp and narrow tunnel barrier by synthesizing
a thin axial segment of Ga<sub><i>x</i></sub>In<sub>1â<i>x</i></sub>Sb within an InSb nanowire. By varying the precursor
molar fraction and the growth time, we accurately control the composition
and the length of the barriers. The height and the width of the Ga<sub><i>x</i></sub>In<sub>1â<i>x</i></sub>Sb
tunnel barrier are extracted from the WentzelâKramers-Brillouin
(WKB) fits to the experimental <i>I</i>â<i>V</i> traces