7 research outputs found
Continuous Transition between Antiferromagnetic Insulator and Paramagnetic Metal in the Pyrochlore Iridate Eu2Ir2O7
Our single crystal study of the magneto-thermal and transport properties of
the pyrochlore iridate Eu2Ir2O7 reveals a continuous phase transition from a
paramagnetic metal to an antiferromagnetic insulator for a sample with
stoichiometry within ~1% resolution. The insulating phase has strong proximity
to an antiferromagnetic semimetal, which is stabilized by several % level of
the off-stoichiometry. Our observations suggest that in addition to electronic
correlation and spin-orbit coupling the magnetic order is essential for opening
the charge gap.Comment: 6 pages, 6 figure
Dispersive sensing in hybrid InAs/Al nanowires
Dispersive charge sensing is realized in hybrid semiconductor-superconductor
nanowires in gate-defined single- and double-island device geometries.
Signal-to-noise ratios (SNRs) were measured both in the frequency and time
domain. Frequency-domain measurements were carried out as a function of
frequency and power and yield a charge sensitivity of for an 11 MHz measurement bandwidth. Time-domain measurements
yield SNR > 1 for 20 s integration time. At zero magnetic field,
photon-assisted tunneling was detected dispersively in a double-island
geometry, indicating coherent hybridization of the two superconducting islands.
At an axial magnetic field of 0.6 T, subgap states are detected dispersively,
demonstrating the suitability of the method for sensing in the topological
regime
Radio-frequency methods for Majorana-based quantum devices: fast charge sensing and phase diagram mapping
Radio-frequency (RF) reflectometry is implemented in hybrid
semiconductor-superconductor nanowire systems designed to probe Majorana zero
modes. Two approaches are presented. In the first, hybrid nanowire-based
devices are part of a resonant circuit, allowing conductance to be measured as
a function of several gate voltages ~40 times faster than using conventional
low-frequency lock-in methods. In the second, nanowire devices are capacitively
coupled to a nearby RF single-electron transistor made from a separate
nanowire, allowing RF detection of charge, including charge-only measurement of
the crossover from 2e inter-island charge transitions at zero magnetic field to
1e transitions at axial magnetic fields above 0.6 T, where a topological state
is expected. Single-electron sensing yields signal-to-noise exceeding 3 and
visibility 99.8% for a measurement time of 1 {\mu}s
Scaling of Majorana Zero-Bias Conductance Peaks
We report an experimental study of the scaling of zero-bias conductance peaks
compatible with Majorana zero modes as a function of magnetic field, tunnel
coupling, and temperature in one-dimensional structures fabricated from an
epitaxial semiconductor-superconductor heterostructure. Results are consistent
with theory, including a peak conductance that is proportional to tunnel
coupling, saturates at , decreases as expected with field-dependent
gap, and collapses onto a simple scaling function in the dimensionless ratio of
temperature and tunnel coupling.Comment: Accepted in Physical Review Letter
Photon Assisted Tunneling of Zero Modes in a Majorana Wire
Hybrid nanowires with proximity-induced superconductivity in the topological
regime host Majorana zero modes (MZMs) at their ends, and networks of such
structures can produce topologically protected qubits. In a double-island
geometry where each segment hosts a pair of MZMs, inter-pair coupling mixes the
charge parity of the islands and opens an energy gap between the even and odd
charge states at the inter-island charge degeneracy. Here, we report on the
spectroscopic measurement of such an energy gap in an InAs/Al double-island
device by tracking the position of the microwave-induced quasiparticle (qp)
transitions using a radio-frequency (rf) charge sensor. In zero magnetic field,
photon assisted tunneling (PAT) of Cooper pairs gives rise to resonant lines in
the 2e-2e periodic charge stability diagram. In the presence of a magnetic
field aligned along the nanowire, resonance lines are observed parallel to the
inter-island charge degeneracy of the 1e-1e periodic charge stability diagram,
where the 1e periodicity results from a zero-energy sub-gap state that emerges
in magnetic field. Resonant lines in the charge stability diagram indicate
coherent photon assisted tunneling of single-electron states, changing the
parity of the two islands. The dependence of resonant frequency on detuning
indicates a sizable (GHz-scale) hybridization of zero modes across the junction
separating islands