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Probes the high-frequency behavior and partial phase coherence of current-induced excitations. Determination of the magnon spectrum; Investigation of how the magnon frequency and amplitude vary with the exciting current; Observations, which support the feasability of a spin-wave maser or spin-wave amplification by stimulated emission of radiation (SWASER).

Magnetotransport measurements are presented on polycrystalline MgB2 samples. The `resistive'' upper critical magnetic field reveals a temperature dependence with a positive curvature from Tc=39.3 K down to about 20 K, then changes to a slightly negative curvature reaching 25 T at 1.5 K. The 25-T upper critical field is much higher than what is known so far on polycrystals of MgB2 but it is in agreement with recent data obtained on epitaxial MgB2 films. The deviation of Bc2(T) from standard BCS might be due to the proposed two-gap superconductivity in this compound. The observed quadratic normal-state magnetoresistance with validity of Kohler''s rule can be ascribed to classical trajectory effects in the low-field limit. [Copyright &y& Elsevier]

Abstract: We present the experimental observation of hysteresis in high quality single crystals with different sample shapes of the simple metal beryllium. The hysteresis itself turns out to be very small. Here, Hall probe measurements at very low modulation frequency prove that the hysteresis is not due to eddy current effects. Furthermore, the hysteresis effect is measured using a standard AC method with various modulation levels and frequencies, and for samples with different demagnetization factors. We demonstrate that previously in rod-like samples observed effect is also present in a plate-like sample. The irreversible behavior of the magnetization occurs at the paramagnetic part of the de Haas–van Alphen (dHvA) period in case of Condon domain formation arising if the dHvA amplitude is strong enough. Moreover, we show that the resulting, extremely nonlinear response to a very small modulation field offers a simple way to find the Condon domain phase diagram. [Copyright &y& Elsevier]

Abstract We report on the fabrication of a clean, stable in room atmosphere and superconducting surface consisting of graphene on tantalum carbide (TaC) obtained by high-temperature annealing of a tantalum thin film on SiC. Low temperature scanning tunnelling spectroscopy reveals that the surface is superconducting with a superconducting order parameter up to 1.6 meV. In addition, atomically-resolved imaging establishes the chemical inertness of the surface. This result is achieved because few graphene layers protect the surface superconductivity of the buried superconducting TaC formed during the high-temperature annealing. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Establishing good electrical contacts to nanoscale devices is a major issue for modern technology and contacting 2D materials is no exception to the rule. One-dimensional edge-contacts to graphene were recently shown to outperform surface contacts but the method remains difficult to scale up. We report a resist-free and scalable method to fabricate few graphene layers with electrical contacts in a single growth step. This method derives from the discovery reported here of the growth of few graphene layers on a metallic carbide by thermal annealing of a carbide forming metallic film on SiC in high vacuum. We exploit the combined effect of edge-contact and partially-covalent surface epitaxy between graphene and the metallic carbide to fabricate devices in which low contact-resistance and Josephson effect are observed. Implementing this approach could significantly simplify the realization of large-scale graphene circuits. [ABSTRACT FROM AUTHOR]

Provides information on experiments performed to test the susceptibility to strong magnetic fields of electron tunneling in normal metal-based nanostructures for Coulomb blockade primary thermometry. Methodology used to conduct the experiments; Description of the fabrication of the Coulomb blockade primary thermometry (CBT); Suppression of superconductivity in CBT arrays; Results of the experiments.

The epitaxial growth of graphene by the sublimation of Si-terminated silicon carbide (SiC) is studied inside a graphite enclosure in a radio-frequency furnace by comparing different in situ processes involving hydrogen etching or not and different growth conditions. For the growth under vacuum, even with the surface preparation of hydrogen etching, the morphology of the synthesized graphene is found full of voids and defects in the form of a multilayer graphene film. For the growth under Ar, the hydrogen etching plays a vital role to improve the graphene quality in terms of surface roughness, the number of graphene layers and the domain size. For the graphene samples grown with the proposed protocol, the original combination of micro-probe Raman spectroscopy and simultaneous optical transmission and reflection measurements reveals a detailed spatially resolved image of the graphene domains with monolayer domain size of ~5×5 µm 2 on about 2/3 of the total sample surface. The magnetotransport data yield charge-carrier mobilities up to 2900 cm 2 /Vs as found for high quality graphene on the Si-face of SiC. The observed magnetoquantum oscillations in the magnetoresistance confirm the expected behavior of single-layer graphene. [ABSTRACT FROM AUTHOR]

Abstract: The structural transitions in ferronematic based on 8CB and 6CHBT, exposed to combined electric and magnetic fields, are investigated. The influence of the presence of magnetic admixture on the Fredericksz transition threshold is studied. Using the found dependencies of critical fields on increasing magnetic particles volume concentration the type of anchoring was determined as soft with m ⊥ n in 8CB and m ∥ n in 6CHBT-based ferronematics. [Copyright &y& Elsevier]

Using high angular resolution (up to 10−4 degree) resistive measurements we studied a YBa2Cu3O6.5 single crystal for the magnetic field (B<28 T) direction closely parallel (within the lock-in angle of 0.3°) to the crystal CuO-planes. Our data show that the vortices become confined between the CuO-planes below a well-defined temperature Tcf. Using a pseudo-flux transformer geometry for electrical transport measurements we demonstrate directly a smectic-like vortex movement for temperatures below TS. Our measurements reveal a rich phase diagram for magnetic field orientation B&par;CuO, originating from the inter-play between pinning by the CuO-planes, point-like disorder from oxygen vacancies and temperature fluctuations. Commensurability between the inter-vortex distance and the CuO-layer period causes a pronounced oscillatory behaviour dominated by in-plane vortex movement. [Copyright &y& Elsevier]

We use magneto-transport spectroscopy to study a dramatic instability between a low and high conductivity mode in Si/SiGe-based resonant tunneling diodes with an embedded layer of self-assembled Ge hut cluster quantum dots in the Si barrier. In the low current regime a simple activation-type behavior with an astonishingly low activation energy in the order of 0.1 meV is determined. In the high current regime a region of negative differential conduction can be observed. We discuss the influence of different layer structures and magnetic fields. [Copyright &y& Elsevier]

Our Andreev reflection measurements (Phys. Rev. Lett. 87 (2001) 137005) along with other experiments have led to a general consensus that MgB2 is a multiband superconductor with two main superconducting gaps closing at the same Tc. Here we show the behavior of the small gap as a function of the temperature and magnetic field. This gap is isotropic with Tc of the bulk material but with a specific small (crossover) critical magnetic field of about 1 T much lower than the real Hc2. The latter field is anisotropic and is rather governed by the large gap and strongly anisotropic Fermi surface of the material. [Copyright &y& Elsevier]

Point-contact spectroscopy measurements on magnesium diboride reveal the existence of two superconducting energy gaps closing at the same transition temperature in line with the multi-band model of superconductivity. The sizes of the two gaps (Δπ=2.8 meV and Δσ=6.5–7 meV) are respectively smaller and larger than the expected weak coupling value of the one-gap superconductor. The smaller gap is rapidly filled by a small magnetic field of about 1–2 T much lower than the real upper critical field Hc2. The larger gap is closed at the anisotropic Hc2. Above the gap energies reproducible non-linearities are observed at the characteristic phonon energies of MgB2. [Copyright &y& Elsevier]

The superconducting phase diagram of single-crystal MgB2 has been determined using magnetization, magneto-transport and specific heat measurements. A value of 9.4 nm is found for the zero-temperature in-plane coherence length. The superconducting anisotropy coefficient, γ, increases monotonously from a value around 2 near Tc to 4.5 at low temperature. The current dependence and angular dependence of the resistive transitions give evidence for a surface superconducting state for H&par;c which might account for the wide spread in reported values of the superconducting anisotropy. [Copyright &y& Elsevier]

The three-dimensional to two-dimensional (2D) crossover of the superconducting state is presented for the naturally layered single crystal of (LaSe)1.14(NbSe2) with the critical temperature Tc of 1.23 K. Namely, the temperature dependence of the upper critical magnetic field Bc2 parallel to the layers reveals an upturn at the crossover temperature T* due to the vortex confinement between the superconducting layers. Below this temperature in the 2D regime the angular dependence of Bc2 displays a cusp at the field parallel to the layers. In the superconducting state the interlayer transport is accomplished in this system by the tunneling of quasiparticles and Cooper pairs. [Copyright &y& Elsevier]

We have measured the magnetoresistance of a trench-like modulated two-dimensional electron gas in a parallel magnetic field in comparison with an unstructured reference sample. We observe a step-like increase in the magnetoresistance of the trench sample that is not present in the reference. We attribute this to different numbers of edge channels being transported through the trench structure. [Copyright &y& Elsevier]

Quantum oscillation (QO) experiments on two organic metals, the highly two-dimensional (2D) electronic system κ-(BEDT-TTF)2I3 and the quasi-2D (Q2D) system (BEDT-TTF)4[Ni(dto)2] are discussed. The influence of the more or less pronounced two-dimensionality onto their electronic properties can be studied as best in the special magnetic field orientation exactly perpendicular to the conducting planes. [Copyright &y& Elsevier]

Selected proton sites were substituted by methyl groups in the quantum spin system CuHpCl, in order to elucidate the magnetic structure of this material, previously considered as a prototypal spin ladder. Magnetization measurements show that the spin gap is weakened or even suppressed upon methyl substitution. This strongly suggests that the main magnetic exchange of these systems does not occur within the Cu–Cl–Cu dimer unit. [Copyright &y& Elsevier]

The point-contact spectroscopy data reveal the existence of two distinct superconducting energy gaps in the Andreev reflection of quasiparticles between MgB2 and a copper counterelectrode. Above the gap energies reproducible nonlinearities are observed at the characteristic phonon energies of MgB2. The strength and position of the observed nonlinearities due to the electron–phonon interaction do not reveal any renormalization when the point contact undergoes the transition from the superconducting to the normal state. [Copyright &y& Elsevier]