13 research outputs found
Enhanced proximity effect in zigzag-shaped Majorana Josephson junctions
High density superconductor-semiconductor-superconductor junctions have a
small induced superconducting gap due to the quasiparticle trajectories with a
large momentum parallel to the junction having a very long flight time. Because
a large induced gap protects Majorana modes, these long trajectories constrain
Majorana devices to a low electron density. We show that a zigzag-shaped
geometry eliminates these trajectories, allowing the robust creation of
Majorana states with both the induced gap and the Majorana
size improved by more than an order of magnitude for realistic
parameters. In addition to the improved robustness of Majoranas, this new
zigzag geometry is insensitive to the geometric details and the device tuning.Comment: 5 pages, 4 figure
InAs-Al Hybrid Devices Passing the Topological Gap Protocol
We present measurements and simulations of semiconductor-superconductor
heterostructure devices that are consistent with the observation of topological
superconductivity and Majorana zero modes. The devices are fabricated from
high-mobility two-dimensional electron gases in which quasi-one-dimensional
wires are defined by electrostatic gates. These devices enable measurements of
local and non-local transport properties and have been optimized via extensive
simulations for robustness against non-uniformity and disorder. Our main result
is that several devices, fabricated according to the design's engineering
specifications, have passed the topological gap protocol defined in Pikulin
{\it et al.}\ [arXiv:2103.12217]. This protocol is a stringent test composed of
a sequence of three-terminal local and non-local transport measurements
performed while varying the magnetic field, semiconductor electron density, and
junction transparencies. Passing the protocol indicates a high probability of
detection of a topological phase hosting Majorana zero modes. Our experimental
results are consistent with a quantum phase transition into a topological
superconducting phase that extends over several hundred millitesla in magnetic
field and several millivolts in gate voltage, corresponding to approximately
one hundred micro-electron-volts in Zeeman energy and chemical potential in the
semiconducting wire. These regions feature a closing and re-opening of the bulk
gap, with simultaneous zero-bias conductance peaks at {\it both} ends of the
devices that withstand changes in the junction transparencies. The measured
maximum topological gaps in our devices are 20-eV. This demonstration
is a prerequisite for experiments involving fusion and braiding of Majorana
zero modes.Comment: Fixed typos. Fig. 3 is now readable by Adobe Reade