92 research outputs found
Demonstration of a superconducting diode-with-memory, operational at zero magnetic field with switchable nonreciprocity
Diode is one of basic electronic components. It has a nonreciprocal current
response, associated with a broken space/time reversal symmetry. Here we
demonstrate prototypes of superconducting diodes operational at zero magnetic
field. They are based on conventional niobium planar Josephson junctions, in
which space/time symmetry is broken by a combination of self-field effect from
nonuniform bias and stray fields from a trapped Abrikosov vortex. We
demonstrate that nonreciprocity of critical current in such diodes can reach an
order of magnitude and rectification efficiency can exceed 70. Furthermore,
we can easily change the diode polarity and switch nonreciprocity on/off by
changing bias configuration and by trapping/removing a vortex. This facilitates
memory functionality. We argue that such diode-with-memory can be used for a
future generation of in-memory superconducting computers.Comment: 8 pages, 5 figure
Anomalous Hall effect in NiPt thin films
We study Hall effect in sputtered NixPt1-x thin films with different Ni
concentrations. Temperature, magnetic field and angular dependencies are
analyzed and the phase diagram of NiPt thin films is obtained. It is found that
films with sub-critical Ni concentration exhibit cluster-glass behavior at low
temperatures with a perpendicular magnetic anisotropy below the freezing
temperature. Films with over-critical Ni concentration are ferromagnetic with
parallel anisotropy. At the critical concentration the state of the film is
strongly frustrated. Such films demonstrate canted magnetization with the easy
axis rotating as a function of temperature. The magnetism appears via
consecutive paramagnetic - cluster glass - ferromagnetic transitions, rather
than a single second-order phase transition. But most remarkably, the
extraordinary Hall effect changes sign at the critical concentration. We
suggest that this is associated with a reconstruction of the electronic
structure of the alloy at the normal metal - ferromagnet quantum phase
transition.Comment: 12 pages, 17 figure
Anticorrelation between temperature and fluctuations in moderately damped Josephson junctions
We study the influence of dissipation on the switching current statistics of
moderately damped Josephson junctions. Different types of both low- and high-
junctions with controlled damping are studied. The damping parameter of
the junctions is tuned in a wide range by changing temperature, magnetic field,
gate voltage, introducing a ferromagnetic layer or in-situ capacitive shunting.
A paradoxical collapse of switching current fluctuations occurs with increasing
in all studied junctions. The phenomenon critically depends on dissipation
in the junction and is explained by interplay of two counteracting consequences
of thermal fluctuations, which on the one hand assist in premature switching
into the resistive state and on the other hand help in retrapping back to the
superconducting state. This is one of the rare examples of anticorrelation
between temperature and fluctuation amplitude of a physically measurable
quantity.Comment: 17 pages, 20 figure
Nonlocal long-range synchronization of planar Josephson junction arrays
We study arrays of planar Nb Josephson junctions with contacts to
intermediate electrodes, which allow measurements of individual junctions and,
thus, provide an insight into intricate array dynamics. We observe a robust
phase-locking of arrays, despite a significant inter-junction separation.
Several unusual phenomena are reported, such as a bi-stable critical current
with re-entrant superconductivity upon switching of nearby junctions; and
incorrect Shapiro steps, occurring at mixing frequencies between the external
RF radiation and the internal Josephson frequency in nearby junctions. Our
results reveal a surprisingly strong and long-range inter-junction interaction.
It is attributed to nonlocality of planar junction electrodynamics, caused by
the long-range spreading of stray electromagnetic fields. The nonlocality
greatly enhances the high-frequency interjunction coupling and enables
large-scale synchronization. Therefore, we conclude that planar geometry is
advantageous for realization of coherent Josephson electronics.Comment: 8 pages, 5 figure
Growth and nanofabrication of all-perovskite superconducting/ferromagnetic/superconducting junctions
We fabricate and study experimentally all-perovskite-oxide superconductor/ferromagnetic insulator/superconductor (S/FI/S) tunnel junctions made out of the high-temperature cuprate superconductor YBa2Cu3O7−y (YBCO) and the colossal magnetoresistive manganite LaMnO3 (LMO) in the ferromagnetic insulator state. YBCO/LMO/YBCO heterostructures with different LMO thicknesses (5, 10, and 20 nm) are grown epitaxially via pulsed laser deposition. Nanoscale S/FI/S junctions with sizes down to 300 nm are made by three-dimensional nano-sculpturing with focused ion beam. Junctions with a thick (20 nm) LMO barrier exhibit a large negative magnetoresistance below TCurie∼160 K, typical for colossal magnetoresistive manganites, as well as a kink in the current-voltage characteristics at large bias (V∼1–2 Volts), attributed to Zener-type tunneling. However, they do not show a measurable Josephson current. On the contrary, junctions with the thinnest 5- nm LMO barrier exhibit a large supercurrent and no signs of magnetism. The latter may indicate the presence of pinholes due to thickness inhomogeneity and/or a ∼ 2 nm dead magnetic layer at the YBCO / LMO interface caused, e.g., by interdiffusion or strain. The junction with an intermediate 10-nm LMO barrier exhibited a desired S/FI/S junction behavior with significant negative magnetoresistance and signatures of a small Josephson current
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