Direct observation of vortices in an array of holes at low temperature: temperature dependance and first visualization of localized superconductivity

A scanning micro superconducting quantum interference device (microSQUID) microscope is used to directly image vortices in a superconducting Al thin film. We observe the temperature dependence of the vortex distribution in a regular defect (hole) array patterned into the Al film. The first direct observation of the localized superconducting state around the holes is shown as well as the effect of the hole size on nucleation of the superconducting state

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

Cuando los módems sean más rápidos que los módems

Peer Reviewe

Observation of two species of vortices in the anisotropic spin-triplet superconductor Sr2RuO4Sr_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

Modified Sagnac experiment for measuring travel-time difference between counter-propagating light beams in a uniformly moving fiber

A fiber optic conveyor has been developed for investigating the travel-time difference between two counter-propagating light beams in uniformly moving fiber. Our finding is that there is a travel-time difference Deltat=2vDeltal/c^2 in a fiber segment of length Deltal moving with the source and detector at a speed v, whether the segment is moving uniformly or circularly.Comment: 4 pages, including 4 figure

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.