38 research outputs found
Dissipationless Nonlinearity in Quantum Material Josephson Diodes
Dissipationless nonlinearities for three-wave mixing are a key component of
many superconducting quantum devices, such as amplifiers and bosonic qubits. So
far, such third-order nonlinearities have been primarily achieved with circuits
of concatenated Josephson tunnel junctions. In this work, we theoretically
develop an alternative approach to realize third-order nonlinearities from
gate-tunable and intrinsically symmetry-broken quantum material Josephson
junctions. We illustrate this approach on two examples, an Andreev
interferometer and a magnetic Josephson junction. Our results show that both
setups enable Kerr-free three-wave mixing for a broad range of frequencies, an
attribute that is highly desirable for amplifier applications. Moreover, we
also find that the magnetic junction constitutes a paradigmatic example for
three-wave mixing in a minimal single-junction device without the need for any
external biases. We hope that our work will guide the search of dissipationless
nonlinearities in quantum material superconducting devices and inspire new ways
of characterizing symmetry-breaking in quantum materials with microwave
techniques
Double-Fourier engineering of Josephson energy-phase relationships applied to diodes
We present a systematic method to design arbitrary energy-phase relations
using parallel arms of two series Josephson tunnel junctions each. Our approach
employs Fourier engineering in the energy-phase relation of each arm and the
position of the arms in real space. We demonstrate our method by engineering
the energy-phase relation of a near-ideal superconducting diode, which we find
to be robust against the imperfections in the design parameters. Finally, we
show the versatility of our approach by designing various other energy-phase
relations.Comment: 13 pages, 8 figure
Tunneling in graphene-topological insulator hybrid devices
Hybrid graphene-topological insulator (TI) devices were fabricated using a
mechanical transfer method and studied via electronic transport. Devices
consisting of bilayer graphene (BLG) under the TI BiSe exhibit
differential conductance characteristics which appear to be dominated by
tunneling, roughly reproducing the BiSe density of states. Similar
results were obtained for BLG on top of BiSe, with 10-fold greater
conductance consistent with a larger contact area due to better surface
conformity. The devices further show evidence of inelastic phonon-assisted
tunneling processes involving both BiSe and graphene phonons. These
processes favor phonons which compensate for momentum mismatch between the TI
and graphene points. Finally, the utility of these tunnel
junctions is demonstrated on a density-tunable BLG device, where the
charge-neutrality point is traced along the energy-density trajectory. This
trajectory is used as a measure of the ground-state density of states
Enhanced Superconductivity and Suppression of Charge-density Wave Order in 2H-TaS in the Two-dimensional Limit
As superconductors are thinned down to the 2D limit, their critical
temperature typically decreases. Here we report the opposite behavior, a
substantial enhancement of with decreasing thickness, in 2D crystalline
superconductor 2H-TaS. Remarkably, in the monolayer limit, increases
to 3.4 K compared to 0.8 K in the bulk. Accompanying this trend in
superconductivity, we observe suppression of the charge-density wave (CDW)
transition with decreasing thickness. To explain these trends, we perform
electronic structure calculations showing that a reduction of the CDW amplitude
results in a substantial increase of the density of states at the Fermi energy,
which contributes to the enhancement of . Our results establish ultra-thin
2H-TaS as an ideal platform to study the competition between CDW order and
superconductivity
Magnetoresistance and quantum oscillations of an electrostatically tuned semimetal-to-metal transition in ultrathin WTe 2
We report on electronic transport measurements of electrostatically gated nanodevices of the semimetal WTe[subscript 2]. High mobility metallic behavior is achieved in the 2D limit by encapsulating thin flakes in an inert atmosphere. At low temperatures, we find that a large magnetoresistance can be turned on and off by electrostatically doping the system between a semimetallic state and an electron-only metallic state, respectively. We confirm the nature of the two regimes by analyzing the magnetoresistance and Hall effect with a two-carrier model, as well as by analysis of Shubnikov-de Haas oscillations, both of which indicate depletion of hole carriers via the electrostatic gate. This confirms that semiclassical transport of two oppositely charged carriers accurately describes the exceptional magnetoresistance observed in this material. Finally, we also find that the magnetoresistance power law is subquadratic and density independent, suggesting new physics specifically in the semimetallic regime.United States. Dept. of Energy. Office of Basic Energy Science. Division of Materials Sciences and Engineering (Award DE-SC0006418)United States. Air Force Office of Scientific Research (Grant FA9550-16-1-0382)Gordon and Betty Moore Foundation (EPiQS Initiative Grant GBMF4541
Chiral adiabatic transmission protected by Fermi surface topology
We demonstrate that Andreev modes that propagate along a transparent
Josephson junction have a perfect transmission at the point where three
junctions meet. The chirality and the number of quantized transmission channels
is determined by the topology of the Fermi surface and the vorticity of the
superconducting phase differences at the trijunction. We explain this chiral
adiabatic transmission (CAT) as a consequence of the adiabatic evolution of the
scattering modes both in momentum and real space. We identify an effective
energy barrier that guarantees quantized transmission. We expect that CAT is
observable in nonlocal conductance and thermal transport measurements.
Furthermore, because it does not rely on particle-hole symmetry, CAT is also
possible to observe directly in metamaterials.Comment: 12 pages, 7 figure
Coexistence of nonequilibrium density and equilibrium energy distribution of quasiparticles in a superconducting qubit
The density of quasiparticles typically observed in superconducting qubits
exceeds the value expected in equilibrium by many orders of magnitude. Can this
out-of-equilibrium quasiparticle density still possess an energy distribution
in equilibrium with the phonon bath? Here, we answer this question
affirmatively by measuring the thermal activation of charge-parity switching in
a transmon qubit with a difference in superconducting gap on the two sides of
the Josephson junction. We then demonstrate how the gap asymmetry of the device
can be exploited to manipulate its parity.Comment: Updated acknowledgements, corrected typo