Single gap superconductivity in beta-Bi2Pd

beta-Bi2Pd compound has been proposed as another example of a multi-gap superconductor [Y. Imai et al., J. Phys. Soc. Jap. 81, 113708 (2012)]. Here, we report on measurements of several important physical quantities capable to show a presence of multiple energy gaps on our superconducting single crystals of beta-Bi2Pd with the critical temperature Tc close to 5 K. The calorimetric study via a sensitive ac technique shows a sharp anomaly at the superconducting transition, however only a single energy gap is detected. Also other characteristics inferred from calorimetric measurements as the field dependence of the Sommerfeld coefficient and the temperature and angular dependence of the upper critical magnetic field point unequivocally to standard single s-wave gap superconductivity. The Hall-probe magnetometry provides the same result from the analysis of the temperature dependence of the lower critical field. A single-gapped BCS density of states is detected by the scanning tunneling spectroscopy measurements. Then, the bulk as well as the surface sensitive probes evidence a standard conventional superconductivity in this system where the topologically protected surface states have been recently detected by ARPES [M. Sakano et al., Nature Comm. 6, 8595 (2015)] .Comment: 7 pages, 4 figures, 1 tabl

Study of Tip-Induced Ti-Film Oxidation in Atomic Force Microscopy Contact and Non-Contact Mode

Local anodic oxidation of metals using scanning probe techniques is mostly used for fabrication of isolated gates. The high-resistance oxide created in such a manner divides a thin metallic film into isolated regions. The tip-induced metallic oxide has not so far been used in nanolithography processes as a masking material. The aim of this contribution is to study the technological potential of a TiO$\text{}_{x}$ mask prepared by the local anodic oxidation of a Ti film. Such a mask can be used to complete a nanotechnology process using atomic force microscopy, which can be easily combined with standard optical lithography techniques. We have found that the insulating properties of the oxides prepared in contact and non-contact modes differ strongly - they represent an energy barrier of 200 meV and 400 meV, respectively

IV characteristics in structures prepared by tip induced oxidation

We have studied transport of a two-dimensional electron gas through an energy barrier prepared by local anodic oxidation with an AFM tip. Experimental IV curves are first explained by a simple model in which the built-in potential is of tapered shape. Then we use computer simulations, ensemble Monte Carlo method with molecular dynamics included, to explain the details of the 2D electron transport in the system. The simulations show the influence of the carrier concentration, applied voltage, and barrier width, on the effective barrier height. We show that few ionized donors can influence the 2D electron transport in the system significantly. In a similar way the confinement of 2D electrons in nanometer-sized devices (quantum dots, wires, single-electron transistors) can be reduced?

Study of Magnetic Micro-Ellipses by Cantilever Sensor

In this paper, we propose a method for prototyping cantilever sensors by means of a modification of commercial atomic force microscopy cantilevers, using electron beam lithography and focused ion beam milling. To overcome obstacles with resist coating related to spin-coating of nonplanar 3D substrates, in this case of free-standing cantilevers, we propose a modified method based on spin-coating technique. An auxiliary atomic force microscopy chip was inserted below the cantilever to quasi-planarize the surface during spin-coating of electron beam resist. Magnetic micro-ellipses were prepared at the free-end of the cantilever by electron beam lithography. We propose a design of a cantilever sensor for the study of magnetic coupling between two cantilevers, prepared by focused ion beam milling. In ideal case, the coupling could be detected by a shift in resonance peaks. Attractive and repulsive forces between magnetic structures were shown by magnetic force microscopy

High Resolution Tips for Switching Magnetization MFM

Switching magnetization magnetic force microscopy (SM-MFM) is based on two-pass magnetic force microscopy with opposite orientation of tip magnetization between two scans. The sum of the scanned data with reversed tip magnetization depicts local van der Waals forces, and their difference maps the local magnetic forces. Tip magnetization can be easily reversed in external magnetic field during the scanning. The separation of the forces mapped enables scanning in close proximity of the sample (~5 nm). Therefore, extremely high spatial resolution (10 nm) is achievable by the SM-MFM. Image phase resolution of the MFM method depends on various geometric parameters of the tip, such as tip length, its apex radius and taper angle. The parameters are determined by the evaporation process, within which the standard atomic force microscopy tips are coated with magnetic layer. In this work we show that the thickness of the coated layer is important for the SM-MFM spatial resolution

Magnetization Studies of Cu0.058TiSe2Cu_{0.058}TiSe_{2} Near a Quantum Critical Point

We study superconducting properties of highly underdoped $Cu_{0.058}TiSe_{2}$ single crystal by means of bulk magnetization measurements. We extract the upper critical field, $H_{c2}$, for magnetic field applied parallel, as well as perpendicular to the sample planes. Obtained values, $H_{c2}^{ab}(0)$=1.03 T and $H_{c2}^c(0)$=0.54 T, define a moderate anisotropy of the upper critical fields of 1.90. From the upper and lower critical fields we extract the Ginzburg-Landau parameters $κ_{ab}(0)$=26.3, and $κ_c(0)$=12.6 that classify $Cu_{0.058}TiSe_{2}$ as an extreme type II superconductor

Individual vortex nucleation/annihilation in ferromagnetic nanodots with broken symmetry observed by micro-Hall magnetometry

We studied vortex nucleation/annihilation process and its temperature dependence in micromagnetic objects with lowered symmetry using micro-Hall magnetometry. Magnetization reversal curves were obtained for the Pacman-like nanodots placed directly on Hall probes. Lowered symmetry of the object leads to good control of its chirality. Vortex nucleation and annihilation fields strongly depend on the angle of the external in-plane magnetic field with respect on the nanodot symmetry. The micromagnetic simulations support the experimental results - the vortex nucleation fields are controlled by local magnetization configurations present in the object (C-, S-, and double S-states) for field just above vortex nucleation field. The experiments also confirm that the vortex nucleation proceeds via thermal activation over an energy barrier

One or two gaps in Mo₈Ga₄₁ superconductor? Local Hall-probe magnetometry study

The magnetization properties of the endohedral cluster superconductor Mo8Ga41 are studied by sensitive Hall-probe magnetometry. The temperature dependence of the lower critical magnetic field H-c1 is obtained and compared to theoretical models accounting for single-gap and two-gap superconductivity. Data can be described by both models with minor differences. These results are confronted with our previous measurements which evidence that the system is inherently single-gap s-wave superconductor but minor additional phases are present also in seemingly perfect samples. We discuss how presence of such additional phases with varying size of the penetration depth and H-c1 field is reflected in magnetization measurements which could lead to misinterpretation of the multigap superconductivity in Mo8Ga41