478 research outputs found

### Scanning microSQUID Force Microscope

A novel scanning probe technique is presented: Scanning microSQUID Force
microscopy (SSFM). The instrument features independent topographic and magnetic
imaging. The SSFM operates in a dilution refrigerator in cryogenic vacuum.
Sample and probe can be cooled to 0.45 K. The probe consists of a microSQUID
placed at the edge of a silicon chip attached to a quartz tuning fork. A
topographic vertical resolution of 0.02 micrometer is demonstrated and magnetic
flux as weak as $10^{-3} \Phi_{0}$ is resolved with a 1 micrometer diameter
microSQUID loop.Comment: submitted to Review of Scientific Instrument

### Measurement of the Current-Phase Relation in Josephson Junctions Rhombi Chains

We present low temperature transport measurements in one dimensional
Josephson junctions rhombi chains. We have measured the current phase relation
of a chain of 8 rhombi. The junctions are either in the classical phase regime
with the Josephson energy much larger than the charging energy, $E_{J}\gg
E_{C}$, or in the quantum phase regime where $E_{J}/E_{C}\approx 2$. In the
strong Josephson coupling regime ($E_{J}\gg E_{C} \gg k_{B}T$) we observe a
sawtooth-like supercurrent as a function of the phase difference over the
chain. The period of the supercurrent oscillations changes abruptly from one
flux quantum $\Phi_{0}$ to half the flux quantum $\Phi_{0}/2$ as the rhombi are
tuned in the vicinity of full frustration. The main observed features can be
understood from the complex energy ground state of the chain. For
$E_{J}/E_{C}\approx 2$ we do observe a dramatic suppression and rounding of the
switching current dependence which we found to be consistent with the model
developed by Matveev et al.(Phys. Rev. Lett. {\bf 89}, 096802(2002)) for long
Josephson junctions chains.Comment: to appear in Phys. Rev.

### Observation of two species of vortices in the anisotropic spin-triplet superconductor $Sr_2 Ru O_4$

Magnetic flux structures in single crystals of the layered spin triplet
superconductor Sr$\_{2}$RuO$\_{4}$ are studied by scanning micro SQUID Force
microscopy. Vortex chains appear as the applied field is tilted along the
in-plane direction of the superconductor. The vortex chains align along the
direction of the in-plane component of the applied magnetic field. The
decoration of in-plane vortices by crossing Abrikosov vortices is observed: two
vortex orientations are apparent simultaneously, one along the layers and the
other perpendicular to the layers. The crossing vortices appear preferentially
on the in-plane vortices

### Magnetism of Superconducting UPt3

The phase diagram of superconducting $U\!Pt_{3}$ in pressure-temperature
plane, together with the neutron scattering data is studied within a two
component superconducting order parameter scenario. In order to give a
qualitative explanation to the experimental data a set of two linearly
independent antiferromagnetic moments which emerge appropriately at the
temperature \mbox{$T_{N}\sim 10\cdot T_{c}$} and \mbox{$T_{m}\sim T_{c}$} and
couple to superconductivity is proposed. Several constraints on the fourth
order coefficients in the Ginzburg-Landau free energy are obtained.Comment: 17 pages, figures available on request to
[email protected]

### MicroSQUID Force microscopy in a dilution refrigerator

We present a new generation of a scanning MicroSQUID microscope operating in
an inverted dilution refrigerator. The MicroSQUIDs have a size of 1.21$ \
\mum\textsuperscript{2} and a magnetic flux sensitivity of 120 \mu\Phi_{0} /
\sqrt{\textrm{Hz}}$and thus a field sensitivity of %$550^{-6} \ \Phi_{0} /
\sqrt{\textrm{Hz}}$550$ \ \mu \textrm{G}/ \sqrt{\textrm{Hz}}$. The scan range
at low temperatures is about 80$\mu$m and a coarse displacement of 5 mm in x
and y direction has been implemented. The MicroSQUID-to-sample distance is
regulated using a tuning fork based force detection. A MicroSQUID-to-sample
distance of 420 nm has been obtained. The reliable knowledge of this distance
is necessary to obtain a trustworthy estimate of the absolute value of the
superconducting penetration depth. An outlook will be given on the ongoing
direction of development

### Visualization by scanning SQUID microscopy of the intermediate state in the superconducting Dirac semimetal PdTe${}_2$

The Dirac semimetal PdTe${}_2$ becomes superconducting at a temperature
$T_{c}=1.6$~K. Thermodynamic and muon spin rotation experiments support type-I
superconductivity, which is unusual for a binary compound. A key property of a
type-I superconductor is the intermediate state which presents a coexistence of
superconducting and normal domains (flux structures) at magnetic fields lower
than the thermodynamic critical field $H_{c}$. By means of scanning SQUID
microscopy (SSM) we observe flux structures in the superconducting state of
PdTe${}_2$. The flux structures are strongly history dependent with a
transition from round shapes to laminar shapes as the magnetic field is more
and more increased. The field amplitudes measured at the surface are indicative
for the presence of Landau branching. The domain wall width in the intermediate
state has been determined.Comment: 8 pages 5 figure

### Silicon Superconducting Quantum Interference Device

We have studied a Superconducting Quantum Interference SQUID device made from
a single layer thin film of superconducting silicon. The superconducting layer
is obtained by heavily doping a silicon wafer with boron atoms using the Gas
Immersion Laser Doping (GILD) technique. The SQUID device is composed of two
nano-bridges (Dayem bridges) in a loop and shows magnetic flux modulation at
low temperature and low magnetic field. The overall behavior shows very good
agreement with numerical simulations based on the Ginzburg-Landau equations.Comment: Published in Applied Physics Letters (August 2015

### Density of States and NMR Relaxation Rate in Anisotropic Superconductivity with Intersecting Line Nodes

We show that the density of states in an anisotropic superconductor with
intersecting line nodes in the gap function is proportional to $E log (\alpha
\Delta_0 /E)$ for $|E| << \Delta_0$, where $\Delta_0$ is the maximum value of
the gap function and $\alpha$ is constant, while it is proportional to $E$ if
the line nodes do not intersect. As a result, a logarithmic correction appears
in the temperature dependence of the NMR relaxation rate and the specific heat,
which can be observed experimentally. By comparing with those for the heavy
fermion superconductors, we can obtain information about the symmetry of the
gap function.Comment: 7 pages, 4 PostScript Figures, LaTeX, to appear in J. Phys. Soc. Jp

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