We demonstrate the first STM evaluation of the Young's modulus (E) of nanoparticles (NPs) of different sizes. The sample deformation induced by tip-sample interaction has been determined using current-distance (I-Z) spectroscopy. As a result of tip-sample interaction, and the induced surface deformations, the I-z curves deviates from pure exponential dependence. Normally, in order to analyze the deformation quantitatively, the tip radius must be known. We show, that this necessity is eliminated by measuring the deformation on a substrate with a known Young's modulus (Au(111)) and estimating the tip radius, and afterwards, using the same tip (with a known radius) to measure the (unknown) Young's modulus of another sample (nanoparticles of CdS). The Young's modulus values found for 3 NP's samples of average diameters of 3.7, 6 and 7.5 nm, were E similar to 73%, 78% and 88% of the bulk value, respectively. These results are in a good agreement with the theoretically predicted reduction of the Young's modulus due to the changes in hydrostatic stresses which resulted from surface tension in nanoparticles with different sizes. Our calculation using third order elastic constants gives a reduction of E which scales linearly with 1/r (r is the NP's radius). This demonstrates the applicability of scanning tunneling spectroscopy for local mechanical characterization of nanoobjects. The method does not include a direct measurement of the tip-sample force but is rather based on the study of the relative elastic response. (C) 2014 Elsevier B.V. All rights reserved.

Superconductors are considered in view of applications to atom chip devices. The main features of magnetic traps based on superconducting wires in the Meissner and mixed states are discussed. The former state may mainly be interesting for improved atom optics, while in the latter, cold atoms may provide a probe of superconductor phenomena. The properties of a magnetic side guide based on a single superconducting strip wire placed in an external magnetic field are calculated analytically and numerically. In the mixed state of type II superconductors, inhomogeneous trapped magnetic flux, relaxation processes and noise caused by vortex motion are posing specific challenges for atom trapping.

We analyze atom-surface magnetic interactions on atom chips where the magnetic trapping potentials are produced by current carrying wires made of electrically anisotropic materials. We discuss a theory for time dependent fluctuations of the magnetic potential, arising from thermal noise originating from the surface. It is shown that using materials with a large electrical anisotropy results in a considerable reduction of heating and decoherence rates of ultra-cold atoms trapped near the surface, of up to several orders of magnitude. The trap loss rate due to spin flips is expected to be significantly reduced upon cooling the surface to low temperatures. In addition, the electrical anisotropy significantly suppresses the amplitude of static spatial potential corrugations due to current scattering within imperfect wires. Also the shape of the corrugation pattern depends on the electrical anisotropy: the preferred angle of the scattered current wave fronts can be varied over a wide range. Materials, fabrication, and experimental issues are discussed, and specific candidate materials are suggested.

We discuss the influence of the material type in metal wires to the electromagnetic fluctuations in magnetic microtraps close to the surface of an atom chip. We show that significant reduction of the magnetic noise can be achieved by replacing the pure noble metal wires with their dilute alloys. The alloy composition provides an additional degree of freedom which enables a, controlled reduction of both magnetic noise and resistivity if the atom chip is cooled. In addition, we provide a careful re-analysis of the magnetically induced trap loss observed by Yu-Ju Lin et al. [Phys. Rev. Lett. 92 050404 (2004)] and find good agreement with an improved theory.

To determine the magnetic field inside a superconductor, we have measured the distribution of the ac magnetic field in a narrow gap between two BSCCO superconducting cylinders with a set of Hall probes. Numerical simulations showed a close agreement between the magnetic field distributions inside the superconductor and the gap. Bean’s model was used for setting the current density distribution inside the superconductor. It was found that at low currents, the field distribution inside the superconductors could be described by Bean’s model. Marked difference observed at higher currents can be explained by flux creep and flux flow.

Deterministic oscillations of current-induced metastable resistivity in changing voltage have been detected in La0.82Ca0.18MnO3 single crystals. At low temperatures, below the Curie point, application of specific bias procedures switches the crystal into a metastable resistivity state characterized by the appearance of pronounced reproducible and random structures in the voltage dependence of the differential conductivity. In a certain bias range equally spaced broad conductivity peaks have been observed. The oscillating conductivity has been tentatively ascribed to resonances in a quantum well within the double-tunnel barrier of intrinsic weak links associated with twinlike defect boundaries.

Microwave transmission through HTSC circular waveguides close to the cutoff conditions has been investigated. Applicative consequences of a sharp decrease in the transmitted power observed in the vicinity of the superconducting transition are discussed.

Random telegraph fluctuations of the resistivity exceeding 10% have been observed in current induced low resistive metastable state of low-dopped La 1-x Ca x MnO 3 single crystal at temperatures below the Curie point. Telegraph amplitudes and average life-times depend on dc bias. Near the characteristic minimum in the resistance vs current curve the bias dependent duty cycle of the telegraph signal crosses 0.5. The pronounced telegraph fluctuations are tentatively associated with fluctuating conductivity of intrinsic tunnel barriers between ferromagnetic domains joined by antiferromagnetic insulating matrix in percolating paths of the phase separated manganite.

The influence of dc current flow on the resistivity and phase transitions in low-doped ${\mathrm{La}}_{0.82}{\mathrm{Ca}}_{0.18}{\mathrm{MnO}}_{3}$ single crystals has been investigated. At low temperatures, where the resistivity strongly increases with decreasing temperature, dc current depresses resistivity in a way consistent with the domination of tunneling-conduction mechanisms. Current flow exceeding some threshold currents results in resistivity switching and metastability. Bipolar current sweep exceeding threshold currents in both positive and negative direction creates low-resistivity states in the sample. The low-resistivity state converts into a very-low- and stable-resistivity state under a stronger bipolar current sweep. Current-induced low-resistivity states are characterized by long-term memory persisting even after storing the sample for a few days at room temperature. The memory can be erased by ac current flow at high temperatures. The results are interpreted in terms of a spin-polarized tunnel conduction mechanism, which modifies phase-separation conditions along the percolation path.

It is well known that the boundary conditions of the electromagnetic fields on the surface of a superconductor are influenced by the field penetration into the material. In a series of recent publications, it has been suggested that this effect substantially influences the wave propagation in high-temperature superconducting waveguides, to the extent that the mode order becomes different than that predicted for perfect conductor waveguides. In this paper, we present experimental investigation of this effect. We show that the effect of superconductivity on the wave propagation in waveguides is very small for temperatures well below the transition temperature and away from cutoff. We also discuss the behavior of the waveguide near cutoff and very close to the transition temperature.

The normal-state transverse magnetoresistance (\ensuremath{\Delta}R/${\mathit{R}}_{0}$) has been studied in the ab plane of three ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{x}}$ single crystals with oxygen indices x=6.95, 6.88, and 6.62. A linear quadratic-field dependence \ensuremath{\Delta}R/${\mathit{R}}_{0}$=${\mathit{AH}}^{2}$+BH has been found up to 15 T in the temperature region where superconducting fluctuations are negligible. The linear component dominating in oxygen-deficient samples is probably related to the interaction between charge carriers and dynamic antiferromagnetic spin fluctuations in ${\mathrm{CuO}}_{2}$ layers of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{x}}$.