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Register a new userExperimental determination of the number of flux lines trapped by micro-holes in superconducting samples
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Added by
Alejandro Vladimiro Silhanek
Publication date
2004
fields
Physics
and research's language is
English
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The influence of a periodic landscape of pinning sites on the vortex dynamics in Pb thin films is explored by ac-susceptibility measurements. For different amplitudes h of the ac-drive, the ac-susceptibility x=x+ix exhibits a complex field dependence associated with different dynamic regimes. At very low ac-drives where both, multiquanta vortices trapped by the antidots and interstitial vortices oscillate inside the pinning potential (intra-valley motion), a small kink in x(H) together with a very low dissipation is observed. At intermediate ac-excitations such that vortices in the antidots remain pinned whereas interstices are driven out of the pinning well, a more pronounced kink in the screening coinciding with the onset of dissipation (x(H) ~ 0) indicates the entrance of interstitial vortices. Eventually, at high enough amplitudes all vortices are set in motion and the penetration of interstitial vortices appears as a sudden reduction of the shielding power. We show that these distinctive features allow us to clearly identify the maximum number of flux quanta per hole regardless the vortex dynamic regime.
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The magnetic moment in the superconducting and normal state of a crystalline FeTe0.65Se0.35 superconductor, grown by the Bridgmans method with relatively high growth rate, was measured. The temperature and magnetic field dependences of magnetization and its relaxation time were determined. Studied crystal, being non-uniform due to high growth rate of 5 mm/h, exhibits smaller width of superconducting transition in comparison with an ideal crystal grown with velocity of 1 mm/h, and the difference in magnetic properties of crystals grown with various growth rate, related to their microstructure, is discussed.
Surface distributions of two level system (TLS) defects and magnetic vortices are limiting dissipation sources in superconducting quantum circuits. Arrays of flux-trapping holes are commonly used to eliminate loss due to magnetic vortices, but may increase dielectric TLS loss. We find that dielectric TLS loss increases by approximately 25% for resonators with a hole array beginning 2 $mu text{m}$ from the resonator edge, while the dielectric loss added by holes further away was below measurement sensitivity. Other forms of loss were not affected by the holes. Additionally, we estimate the loss due to residual magnetic effects to be $9times 10^{-10} /mutext{T} $ for resonators patterned with flux-traps and operated in magnetic fields up to $5$ $mutext{T}$. This is orders of magnitude below the total loss of the best superconducting coplanar waveguide resonators.
We have measured upper-critical-field $H_{text c2}$, specific heat C, and tunneling spectra of the intermetallic perovskite superconductor MgCNi${}_3$ with a superconducting transition temperature $T_{text c}approx 7.6$ K. Based on these measurements and relevant theoretical relations, we have evaluated various superconducting parameters for this material, including the thermodynamic critical field $H_{text c}$(0), coherence length $xi$(0), penetration depth $lambda$(0), lower-critical-field $H_{text c1}$(0), and Ginsberg-Landau parameter $kappa$(0). From the specific heat, we obtain the Debye temperature $it Theta_{text D} approx$ 280 K. We find a jump of $Delta C/gamma T_{text c}$=2.3 at $T_{text c}$ (where $it gamma$ is the normal state electronic specific coefficient), which is much larger than the weak coupling BCS value of 1.43. Our tunneling measurements revealed a gap feature in the tunneling spectra at $it Delta$ with $2it {Delta}/{text k}_{text B}T_{text c}approx$ 4.6, again larger than the weak-coupling value of 3.53. Both findings indicate that MgCNi$_3$ is a strong-coupling superconductor. In addition, we observed a pronounced zero-bias conductance peak (ZBCP) in the tunneling spectra. We discuss the possible physical origins of the observed ZBCP, especially in the context of the pairing symmetry of the material.
The stannide family of materials A3T4Sn13 (A = La,Sr,Ca, T = Ir,Rh) is interesting due to the interplay between a tunable lattice instability and phonon-mediated superconductivity with Tc ~ 5-7 K. In Sr3Ir4Sn13 a structural transition temperature T* ~ 147 K associated with this instability has been reported, which is believed to result from a superlattice distortion of the high temperature phase on cooling. Here we report the first experimental study of the electronic structure of a member of this material family - Sr3Ir4Sn13 through measurements of quantum oscillations and comparison with density functional theory calculations. Our measurements reveal good agreement with theory using the lattice parameters consistent with a body-centred cubic lattice of symmetry I-43d of the low temperature phase. The study of the fermiology of Sr3Ir4Sn13 we present here should help inform models of multiband superconductivity in the superconducting stannides.
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