88 research outputs found
A Tunable Monolithic SQUID in Twisted Bilayer Graphene
Magic-angle twisted bilayer graphene (MATBG) hosts a number of correlated
states of matter that can be tuned by electrostatic doping. Superconductivity
has drawn considerable attention and the mechanism behind it is a topic of
active discussion. MATBG has been experimentally characterized by numerous
transport and scanning-probe experiments. The material has also emerged as a
versatile platform for superconducting electronics, as proven by the
realization of monolithic Josephson junctions. However, even though
phase-coherent phenomena have been measured, no control of the superconducting
phase has been demonstrated so far. Here, we present a Superconducting Quantum
Interference Device (SQUID) in MATBG, where the superconducting phase
difference is controlled through the magnetic field. We observe
magneto-oscillations of the critical current, demonstrating long-range
coherence agreeing with an effective charge of 2e for the superconducting
charge carriers. We tune to both asymmetric and symmetric SQUID configurations
by electrostatically controlling the critical currents through the junctions.
With this tunability, we study the inductances in the device, finding values of
up to 2{\mu}H. Furthermore, we directly observe the current-phase relation of
one of the Josephson junctions of the device. Our results show that
superconducting devices in MATBG can be scaled up and used to reveal properties
of the material. We expect this to foster a more systematic realization of
devices of this type, increasing the accuracy with which microscopic
characteristics of the material are extracted. We also envision more complex
devices to emerge, such as phase-slip junctions or high kinetic inductance
detectors.Comment: Supplementary Information is included in the .pd
Tunable quantum interferometer for correlated moir\'e electrons
Magic-angle twisted bilayer graphene (MATBG) can host an intriguing variety
of gate-tunable correlated states, including superconducting and correlated
insulator states. Junction-based superconducting devices, such as Josephson
junctions and SQUIDs, have been introduced recently and enable the exploration
of the charge, spin, and orbital nature of superconductivity and the coherence
of moir\'e electrons in MATBG. However, complementary fundamental coherence
effects - in particular, the Little-Parks effect in a superconducting and the
Aharonov-Bohm effect in a normal conducting ring - remained to be observed.
Here, we report the observation of both these phenomena in a single
gate-defined ring device where we can embed a superconducting or normal
conducting ring in a correlated or band insulator. We directly observe the
Little-Parks effect in the superconducting phase diagram as a function of
density and magnetic field, confirming the effective charge of . By
measuring the Aharonov-Bohm effect, we find that in our device, the coherence
length of normal conducting moir\'e electrons exceeds a few microns at 50 mK.
Surprisingly, we also identify a regime characterized by -periodic
oscillations but with superconductor-like nonlinear transport. Taken together,
these experiments establish a novel device platform in MATBG, and more
generally in tunable 2D materials, to unravel the nature of superconductivity
and other correlated quantum states in these materials
High mobility transport in isotopically-enriched C and C exfoliated graphene
Graphene quantum dots are promising candidates for qubits due to weak
spin-orbit and hyperfine interactions. The hyperfine interaction, controllable
via isotopic purification, could be the key to further improving the coherence.
Here, we use isotopically enriched graphite crystals of both C and
C grown by high-pressure-high-temperature method to exfoliate graphene
layers. We fabricated Hall bar devices and performed quantum transport
measurements, revealing mobilities exceeding and a
long mean free path of microns, which are as high as natural graphene.
Shubnikov-de Haas oscillations, quantum Hall effect up to the filling factor of
one, and Brown-Zak oscillations due to the alignment of hBN and graphene are
observed thanks to the high mobility. These results constitute a material
platform for physics and engineering of isotopically-enriched graphene qubits.Comment: 6 pages, 2 figure
Characterization of Ion Cyclotron Wall Conditioning Using Material Probes in LHD
The ion cyclotron wall conditioning (ICWC) is one of the conditioning methods to reduce impurities and to remove tritium from the plasma facing components. Among the advantages of ICWC are the possible operation under strong magnetic field for fully torus area based on the charge exchange damage observed in thin SS samples arranged on a hexahxedron block holder with three different facings, the areas influenced by ICWC is estimated. On the plasma facing area of the material holder, high density of helium bubbles is observed by transmission electron microscope (TEM). But the other areas show no observable damage. The fact that the bubble were observed only in a sample facing the plasma implies that the effective particles, most probably charge exchange neutrals come to the wall straightly Thus, cleaning of the surfaces un-exposed to plasma directly and those in shadow area is difficult by ICWC
The X-ray Polarization Probe mission concept
The X-ray Polarization Probe (XPP) is a second generation X-ray polarimeter
following up on the Imaging X-ray Polarimetry Explorer (IXPE). The XPP will
offer true broadband polarimetery over the wide 0.2-60 keV bandpass in addition
to imaging polarimetry from 2-8 keV. The extended energy bandpass and
improvements in sensitivity will enable the simultaneous measurement of the
polarization of several emission components. These measurements will give
qualitatively new information about how compact objects work, and will probe
fundamental physics, i.e. strong-field quantum electrodynamics and strong
gravity.Comment: submitted to Astrophysics Decadal Survey as a State of the Profession
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