scholarly journals Magnetoresistance, Gating and Proximity Effects in Ultrathin NbN-Bi2Se3 Bilayers

2017 ◽  
Author(s):  
Gad Koren
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Topological Insulator ◽  
Proximity Effects ◽  
S Wave ◽  
Flux Flow ◽  
Pseudogap Phase ◽  
Topological Superconductors ◽  
Vortex Physics ◽  
Proximity Coupling

Ultrathin Bi2Se3-NbN bilayers comprise a simple proximity system of a topological insulator and an s-wave superconductor for studying gating effects on topological superconductors. Here we report on 3 nm thick NbN layers of weakly connected superconducting islands, overlayed with 10 nm thick Bi2Se3 film which facilitates enhanced proximity coupling between them. Resistance versus temperature of the most resistive bilayers shows insulating behavior but with signs of superconductivity. We measured the magnetoresistance (MR) of these bilayers versus temperature with and without a magnetic field H normal to the wafer (MR=[R(H)-R(0)]/\{[R(H)+R(0)]/2\}), and under three electric gate-fields of 0 and ±2 MV/cm. The MR results showed a complex set of gate sensitive peaks which extended up to about 30 K. The results are discussed in terms of vortex physics, and the origin of the different MR peaks is identified and attributed to flux-flow MR in the isolated NbN islands and the different proximity regions in the Bi2Se3 cap-layer. The dominant MR peak was found to be consistent with enhanced proximity induced superconductivity in the topological edge currents regions. The high temperature MR data suggest a possible pseudogap phase or a highly extended fluctuation regime.

The activation energy U(T,B) in high temperature superconductor

2020 ◽  
Vol 92 (2) ◽  
pp. 20601
Author(s):  
Abdelaziz Labrag ◽  
Mustapha Bghour ◽  
Ahmed Abou El Hassan ◽  
Habiba El Hamidi ◽  
Ahmed Taoufik ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Activation Energy ◽  
Phase Diagram ◽  
High Temperature ◽  
Apparent Activation Energy ◽  
High Temperature Superconductor ◽  
Flux Flow ◽  
Resistivity Measurements ◽  
Vortex Phase ◽  
The Magnetic Field

It is reported in this paper on the thermally assisted flux flow in epitaxial YBa2Cu3O7-δ deposited by Laser ablation method on the SrTiO3 substrate. The resistivity measurements ρ (T, B) of the sample under various values of the magnetic field up to 14T in directions B∥ab-plane and B∥c-axis with a dc weak transport current density were investigated in order to determine the activation energy and then understand the vortex dynamic phenomena and therefore deduce the vortex phase diagram of this material. The apparent activation energy U0 (B) calculated using an Arrhenius relation. The measured results of the resistivity were then adjusted to the modified thermally assisted flux flow model in order to account for the temperature-field dependence of the activation energy U (T, B). The obtained values from the thermally assisted activation energy, exhibit a behavior similar to the one showed with the Arrhenius model, albeit larger than the apparent activation energy with ∼1.5 order on magnitude for both cases of the magnetic field directions. The vortex glass model was also used to obtain the vortex-glass transition temperature from the linear fitting of [d ln ρ/dT ] −1 plots. In the course of this work thanks to the resistivity measurements the upper critical magnetic field Hc2 (T), the irreversibility line Hirr (T) and the crossover field HCrossOver (T) were located. These three parameters allowed us to establish a phase diagram of the studied material where limits of each vortex phase are sketched in order to optimize its applicability as a practical high temperature superconductor used for diverse purposes.

scholarly journals Coherent spin transport through helical edge states of topological insulator

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
R. A. Niyazov ◽  
D. N. Aristov ◽  
V. Yu. Kachorovskii
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Topological Insulator ◽  
Spin Transport ◽  
Magnetic Impurity ◽  
Quantum Calculations ◽  
Edge States ◽  
Level Spacing ◽  
Aharonov Bohm ◽  
Coherent Spin

AbstractWe study coherent spin transport through helical edge states of topological insulator tunnel-coupled to metallic leads. We demonstrate that unpolarized incoming electron beam acquires finite polarization after transmission through such a setup provided that edges contain at least one magnetic impurity. The finite polarization appears even in the fully classical regime and is therefore robust to dephasing. There is also a quantum magnetic field-tunable contribution to the polarization, which shows sharp identical Aharonov-Bohm resonances as a function of magnetic flux—with the period hc/2e—and survives at relatively high temperature. We demonstrate that this tunneling interferometer can be described in terms of ensemble of flux-tunable qubits giving equal contributions to conductance and spin polarization. The number of active qubits participating in the charge and spin transport is given by the ratio of the temperature and the level spacing. The interferometer can effectively operate at high temperature and can be used for quantum calculations. In particular, the ensemble of qubits can be described by a single Hadamard operator. The obtained results open wide avenue for applications in the area of quantum computing.

Magnetoresistance investigation in the mixed state of a high temperature superconductor

2020 ◽  
Author(s):  
Mustapha Bghour ◽  
A. Labrag ◽  
H. El hamidi ◽  
A. Abou El hassan ◽  
A. Taoufik
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Mixed State ◽  
High Temperature Superconductor ◽  
Scaling Law ◽  
Good Alternative ◽  
Magnetic Field Direction ◽  
Flux Flow ◽  
The Magnetic Field ◽  
Good Agreement

In this work we analyze the behavior of magnetoresistance R(H,T) of a high temperature superconductor YBa2Cu3O7-delta thin film optimally doped. Measurements of magnetoresistance were carried out in the mixed state for a magnetic field up to 14T applied in the c-axis then parallel to ab-plane with a DC transport current of 100 and 500nA, 0.1 and 0.3mA perpendicular to the magnetic field direction in both cases. The obtained results show that the magnetoresistance is in a good agreement with the thermally assisted flux creep. However, the magnetoresistance in the flux flow regime cannot be described by the Barden-Stephen model which conjecture another origin of these results. In this sense, the quantum fluctuations of the order be parameter is a good alternative to understanding the shape of the magnetoresistance. The comparison of the magnetoresistance of the two directions shows that Rc(H,T) is larger than Rab(H,T) with anisot-ropy factor gamma=Rc/Rab depending on temperature and magnetic field. The irreversibility line Hirr(T) as well as Hc2(T) are determined and the first one is adjusted with the phenomenological model Hirr(T)=Hirr(0)(1-T/T0)^alpha where Hirr(0), T0 and alpha are parameters obtained from the fit. The investigation of the scaling law allows us to prove that a crossover from 3D to 2D behavior is a feature of our sample which justifies the existence of the decoherence effect.

scholarly journals Pseudogap Isotope Effect as a Probe of Bipolaron Mechanism in High Temperature Superconductors

Materials ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 4973
Author(s):  
Victor D. Lakhno
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Isotope Effect ◽  
High Temperature Superconductors ◽  
Translation Invariant ◽  
Pseudogap Phase ◽  
The Magnetic Field

A theory of a pseudogap phase of high-temperature superconductors where current carriers are translation invariant bipolarons is developed. A temperature of T* a transition from a pseudogap phase to a normal one is calculated. For the temperature of a transition to the pseudogap phase, the isotope coefficient is found. It is shown that the results obtained, in particular, the possibility of negative values of the isotope coefficient, are consistent with the experiment. New experiments on the influence of the magnetic field on the isotope coefficient are proposed.

scholarly journals Measurements and Analysis of AC Losses in HTS Windings of Electrical Machine for Different Operation Modes

2021 ◽  
Vol 11 (6) ◽  
pp. 2741
Author(s):  
Sergey Zanegin ◽  
Nikolay Ivanov ◽  
Vasily Zubko ◽  
Konstantin Kovalev ◽  
Ivan Shishov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
High Temperature Superconductor ◽  
High Temperature Superconductors ◽  
Transport Current ◽  
Operating Conditions ◽  
Ac Losses ◽  
Electrical Machine ◽  
2Nd Generation ◽  
Motor Mode

The article is devoted to the study of losses in devices based on high-temperature superconductors of the 2nd generation. The complexity of the devices under study increases from a single rack coil to a winding assembled from several coils, and finally to an electric machine operating in generator mode. This is the way to experimentally study the behavior of 2nd generation high temperature superconductor (2G HTS) carrying a transport current in various conditions: self-field, external DC, and AC magnetic field. Attention is also paid to the losses in the winding during its operation from the inverter, which simulates the operating conditions in the motor mode of a propulsion system.

An application of high-temperature superconductors YBCO to magnetic separation

2017 ◽  
Vol 31 (25) ◽  
pp. 1745001 ◽  
Author(s):  
Qiudong Guo ◽  
Peng Zhang ◽  
Lin Bo ◽  
Guibin Zeng ◽  
Dengqian Li ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Magnetic Separation ◽  
High Magnetic Field ◽  
Low Cost ◽  
Rapid Development ◽  
High Temperature Superconductors ◽  
New Approach ◽  
Industrial Areas ◽  
Ybco Tape

With the rapid development of manufacturing technology of high temperature superconductive YB[Formula: see text]Cu3O[Formula: see text] YBCO materials and decreasing in cost of production, YBCO is marching into industrial areas with its good performances as source of high-magnetic field and rather low cost in reaching superconductivity. Based on analysis of the performance of high temperature superconductors YBCO and development of technology in superconductive magnetic separation both home and abroad, we propose a new approach of taking YBCO tape to make a solenoid as the source of a high magnetic field of magnetic separatior of ores. The paper also looks into the future of the YBCO high temperature superconductive magnetic separation from the perspective of technology and cost, as well as its applications in other industries.

scholarly journals Induced unconventional superconductivity on the surface states of Bi2Te3 topological insulator

2017 ◽  
Vol 8 (1) ◽  
Author(s):  
Sophie Charpentier ◽  
Luca Galletti ◽  
Gunta Kunakova ◽  
Riccardo Arpaia ◽  
Yuxin Song ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Topological Insulator ◽  
Quantum Interference ◽  
Order Parameter ◽  
Thermal Strain ◽  
Surface States ◽  
Field Pattern ◽  
Key Factors ◽  
Ordered Phases ◽  
Simultaneous Existence

Abstract Topological superconductivity is central to a variety of novel phenomena involving the interplay between topologically ordered phases and broken-symmetry states. The key ingredient is an unconventional order parameter, with an orbital component containing a chiral p x  + ip y wave term. Here we present phase-sensitive measurements, based on the quantum interference in nanoscale Josephson junctions, realized by using Bi2Te3 topological insulator. We demonstrate that the induced superconductivity is unconventional and consistent with a sign-changing order parameter, such as a chiral p x  + ip y component. The magnetic field pattern of the junctions shows a dip at zero externally applied magnetic field, which is an incontrovertible signature of the simultaneous existence of 0 and π coupling within the junction, inherent to a non trivial order parameter phase. The nano-textured morphology of the Bi2Te3 flakes, and the dramatic role played by thermal strain are the surprising key factors for the display of an unconventional induced order parameter.

scholarly journals Motional Stark Effect measurements of the local magnetic field in high temperature fusion plasmas

2015 ◽  
Vol 10 (10) ◽  
pp. P10008-P10008 ◽  
Author(s):  
R.C. Wolf ◽  
A. Bock ◽  
O.P. Ford ◽  
R. Reimer ◽  
A. Burckhart ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Stark Effect ◽  
Local Magnetic Field ◽  
Fusion Plasmas ◽  
Motional Stark Effect
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