13 research outputs found
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Exchange biased anomalous Hall effect driven by frustration in a magnetic kagome lattice.
Co[Formula: see text]Sn[Formula: see text]S[Formula: see text] is a ferromagnetic Weyl semimetal that has been the subject of intense scientific interest due to its large anomalous Hall effect. We show that the coupling of this material's topological properties to its magnetic texture leads to a strongly exchange biased anomalous Hall effect. We argue that this is likely caused by the coexistence of ferromagnetism and geometric frustration intrinsic to the kagome network of magnetic ions, giving rise to spin-glass behavior and an exchange bias
Electrically tunable multi-terminal SQUID-on-tip
We present a new nanoscale superconducting quantum interference device
(SQUID) whose interference pattern can be shifted electrically in-situ. The
device consists of a nanoscale four-terminal/four-junction SQUID fabricated at
the apex of a sharp pipette using a self-aligned three-step deposition of Pb.
In contrast to conventional two-terminal/two-junction SQUIDs that display
optimal sensitivity when flux biased to about a quarter of the flux quantum,
the additional terminals and junctions allow optimal sensitivity at arbitrary
applied flux, thus eliminating the magnetic field "blind spots". We demonstrate
spin sensitivity of 5 to 8 over a continuous field
range of 0 to 0.5 T, with promising applications for nanoscale scanning
magnetic imaging
Nanoscale imaging of equilibrium quantum Hall edge currents and of the magnetic monopole response in graphene
The recently predicted topological magnetoelectric effect and the response to
an electric charge that mimics an induced mirror magnetic monopole are
fundamental attributes of topological states of matter with broken time
reversal symmetry. Using a SQUID-on-tip, acting simultaneously as a tunable
scanning electric charge and as ultrasensitive nanoscale magnetometer, we
induce and directly image the microscopic currents generating the magnetic
monopole response in a graphene quantum Hall electron system. We find a rich
and complex nonlinear behavior governed by coexistence of topological and
nontopological equilibrium currents that is not captured by the monopole
models. Furthermore, by utilizing a tuning fork that induces nanoscale
vibrations of the SQUID-on-tip, we directly image the equilibrium currents of
individual quantum Hall edge states for the first time. We reveal that the edge
states that are commonly assumed to carry only a chiral downstream current, in
fact carry a pair of counterpropagating currents, in which the topological
downstream current in the incompressible region is always counterbalanced by
heretofore unobserved nontopological upstream current flowing in the adjacent
compressible region. The intricate patterns of the counterpropagating
equilibrium-state orbital currents provide new insights into the microscopic
origins of the topological and nontopological charge and energy flow in quantum
Hall systems
Hidden spin-texture at topological domain walls drive exchange bias in a Weyl semimetal
Exchange bias is a phenomenon critical to solid-state technologies that
require spin valves or non-volatile magnetic memory. The phenomenon is usually
studied in the context of magnetic interfaces between antiferromagnets and
ferromagnets, where the exchange field of the former acts as a means to pin the
polarization of the latter. In the present study, we report an unusual instance
of this phenomenon in the topological Weyl semimetal Co3Sn2S2, where the
magnetic interfaces associated with domain walls suffice to bias the entire
ferromagnetic bulk. Remarkably, our data suggests the presence of a hidden
order parameter whose behavior can be independently tuned by applied magnetic
fields. For micron-size samples, the domain walls are absent, and the exchange
bias vanishes, suggesting the boundaries are a source of pinned uncompensated
moment arising from the hidden order. The novelty of this mechanism suggests
exciting opportunities lie ahead for the application of topological materials
in spintronic technologies.Comment: Main text: 11 pages, 4 figures. Supplementary information: 7 pages, 6
figures. Supplementary videos:
Systematic Improvements in Transmon Qubit Coherence Enabled by Niobium Surface Encapsulation
We present a novel transmon qubit fabrication technique that yields
systematic improvements in T coherence times. We fabricate devices using an
encapsulation strategy that involves passivating the surface of niobium and
thereby preventing the formation of its lossy surface oxide. By maintaining the
same superconducting metal and only varying the surface structure, this
comparative investigation examining different capping materials and film
substrates across different qubit foundries definitively demonstrates the
detrimental impact that niobium oxides have on the coherence times of
superconducting qubits, compared to native oxides of tantalum, aluminum or
titanium nitride. Our surface-encapsulated niobium qubit devices exhibit T
coherence times 2 to 5 times longer than baseline niobium qubit devices with
native niobium oxides. When capping niobium with tantalum, we obtain median
qubit lifetimes above 200 microseconds. Our comparative structural and chemical
analysis suggests that amorphous niobium suboxides may induce higher losses.
These results are in line with high-accuracy measurements of the niobium oxide
loss tangent obtained with ultra-high Q superconducting radiofrequency (SRF)
cavities. This new surface encapsulation strategy enables further reduction of
dielectric losses via passivation with ambient-stable materials, while
preserving fabrication and scalable manufacturability thanks to the
compatibility with silicon processes
Exchange biased anomalous Hall effect driven by frustration in a magnetic kagome lattice.
Exchange biased anomalous Hall effect driven by frustration in a magnetic kagome lattice.
Recommended from our members
Exchange biased anomalous Hall effect driven by frustration in a magnetic kagome lattice.
Co[Formula: see text]Sn[Formula: see text]S[Formula: see text] is a ferromagnetic Weyl semimetal that has been the subject of intense scientific interest due to its large anomalous Hall effect. We show that the coupling of this materials topological properties to its magnetic texture leads to a strongly exchange biased anomalous Hall effect. We argue that this is likely caused by the coexistence of ferromagnetism and geometric frustration intrinsic to the kagome network of magnetic ions, giving rise to spin-glass behavior and an exchange bias
Recommended from our members
Electrically Tunable Multiterminal SQUID-on-Tip.
We present a new nanoscale superconducting quantum interference device (SQUID) whose interference pattern can be shifted electrically in situ. The device consists of a nanoscale four-terminal-four-junction SQUID fabricated at the apex of a sharp pipet using a self-aligned three-step deposition of Pb. In contrast to conventional two-terminal-two-junction SQUIDs that display optimal sensitivity when flux biased to about a quarter of the flux quantum, the additional terminals and junctions allow optimal sensitivity at arbitrary applied flux, thus eliminating the magnetic field "blind spots". We demonstrate spin sensitivity of 5 to 8 μB/Hz1/2 over a continuous field range of 0 to 0.5 T with promising applications for nanoscale scanning magnetic imaging