Microwave Impedance of Thin-Film Superconductor–Normal Metal Hybrid Structures with a High Conductivity Ratio

Physics of the Solid State - The temperature dependence of the linear electrodynamic response of thin-film superconductor (MoN)–normal metal (Al) hybrid structures with a high conductivity...     

Superconductor–Insulator Transition in NbTiN Films

Experimental results indicating a direct disorder-induced superconductor–insulator transition in NbTiN thin films have been reported. It has been shown that an increase in the resistance per square in the normal state is accompanied by the suppression of the critical temperature of the superconducting transition T_c according to the fermion mechanism of suppression of superconductivity by disorder. At the same time, the temperature of the Berezinskii–Kosterlitz–Thouless transition is completely suppressed at a nonzero critical temperature and, then, the ground state changes to insulating, which is characteristic of the boson model of suppression of superconductivity by disorder. It has been shown that the temperature dependences of the resistance of insulating films follow the Arrhenius activation law.     

Terahertz Detection with Twin Superconductor-Insulator-Superconductor Tunnel Junctions

Terahertz detection with twin superconductor-insulator-superconductor （SIS） tunnel junctions, which are connected in parallel via an inductive thin-film superconducting microstrip line, is mainly studied. Firstly, we investigate the direct-detection response of a superconducting twin-junction device by means of a Fourier transform spectrometer. Secondly, we construct a direct-detection model of twin SIS tunnel junctions. The superconducting twin-junction device is then simulated in terms of the constructed model. The simulation result is found to be in good agreement with the measured one. In addition, we observe that the direct-detection response of the device is consistent with the noise temperature behaviour.     

Microdischarges Near Metal–Insulator Interfaces

Some statistical features of microdischarges running near the metal-insulator interfaces have been discussed. The study has verified an exponential character of statistical distributions of the time intervals between microdischarge pulses, power-law distribution of voltage peaks of these pulses (height of pulses) and very weak correlation effects among pulses, i.e. weak time-height correlation, time autocorrelation and height autocorrelation. A statistical parameter of the power law distribution of the heights of microdischarge pulses proved to be sensitive to the voltage load of the insulating interface metal-insulator.     

Peculiarities of the Nonlinear Response of a Superconductor–Normal Metal Structure with a Large Ratio of Resistivities

Physics of the Solid State - Using the near-field microwave microscopy method, the temperature dependence of third harmonics power P3ω(T) of the MoN/Al superconductor–normal metal...     

Negative Differential Resistance and Other Features of Spin-Dependent Electron Transport in Double-Barrier Hybrid Superconductor–Ferromagnetic Metal–Normal Metal Structures

Spin-dependent electronic transport is theoretically investigated for double-barrier hybrid structures S–IF–F–IF–N and S–IF–N–IF–N, where S is a superconductor; F and N are ferromagnetic and normal metals, respectively; and IF is the spin-active barrier. It is shown that in the case of strong superconducting proximity effect and sufficiently thin F layers, the differential resistance of such structures can become negative at some voltages, and the voltage dependence of the current can have an N-shaped form. Characteristic feature of the differential resistance is its asymmetric dependence on voltage, which is most clearly manifested at strong polarization of at least one of the barriers. The influence of impurity spin–orbit scattering processes in the N-layer located between the barriers is investigated. The study was carried out for the case of diffusion electron transport.     

Magnetic Tunnel Junctions with MgO／Al-O Composite Barriers

Magnetic tunnel junctions (MTJs) with structures of Ta(5 nm)/Cu(30nm)/Ta(5 nm)/Ni79Fe21 (5 nm)/Ir22Mn78 (12 nm)/Co62Fe20B18 (4 nm)/MgO(d)/Al(0.8 nm)-oxide/Co62Fe20B18 (6 nm)/Cu(30 nm)/Ta(5 nm) on a thermally oxidized Si wafer substrate were fabricated by magnetron sputtering and photolithographic patterning method. The tunnel magnetoresistance (TMR) and the bias dependence of TMR at room temperature for the MTJs with different thickness d of MgO are investigated. TMR values of over 50% as high as those of the MTJs with pure Al-O barrier and the TMR-voltage curve asymmetries, which vary with the increase of d, are observed in the MTJs with hybrid barriers after annealing at 265℃ for an hour. The dependences of TMR, resistance and coercivity of the MTJs with composite barriers on temperature are also investigated.     

Reliability Characteristics of Diamond-Like Carbon as Gate Insulator for Metal–Insulator–Semiconductor Application

Physics of the Solid State - This study presents the reliability of diamond-like carbon (DLC) ultrathin films fabricated by DC magnetron sputtering as the gate dielectric layer in...     

Holographic Insulator/Superconductor Phase Transition in Born–Infeld Electrodynamics

We study holographic insulator/superconductor phase transition in the framework of Born–Infeld electrodynamics both numerically and analytically. First we numerically study the efects of the Born–Infeld electrodynamics on the phase transition, find that when the Born–Infeld parameter increases, the critical chemical potential keeps invariant but the gap frequency becomes larger. Then we employ the variational method for the Sturm–Liouville eigenvalue problem to study the phase transition analytically. The analytical results obtained are found to be consistent with the numerical results.     

Field-Induced Metal–Insulator Transition in β-EuP_3

Metal-insulator transition(MIT) is one of the most conspicuous phenomena in correlated electron systems.However such a transition has rarely been induced by an external magnetic field as the field scale is normally too small compared with the charge gap.We present the observation of a magnetic-field-driven MIT in a magnetic semiconductor β-EuP_3.Concomitantly,we find a colossal magnetoresistance in an extreme way:the resistance drops billionfold at 2K in a magnetic field less than 3T.We ascribe this striking MIT as a field-driven transition from an antiferromagnetic and paramagnetic insulator to a spin-polarized topological semimetal,in which the spin configuration of Eu~(2+)cations and spin-orbital coupling play a crucial role.As a phosphorene-bearing compound whose electrical properties can be controlled by the application of field,β-EuP_3 may serve as a tantalizing material in the basic research and even future electronics.     

Gaseous Metal and the Problem of Vapor–Liquid (Insulator–Metal) Transition in Metal Vapors

Journal of Experimental and Theoretical Physics - We consider the main properties of a gaseous metal, viz., the state of metal vapor adjoining the vapor–fluid transition binodal. The gaseous...     

Metal–Insulator Phase Transition in Iron-Doped Vanadium Dioxide Thin Films

Physics of the Solid State - The electrical conductivity of polycrystalline V(1 – x)FexO2 films has been investigated in a wide temperature range, which covers both the...     

Mesoscopic Transport Characteristics of a Normal—Metal—Superconducting—Grain—Superconductor System

We investigate transport properties of a normal-metal-superconducting-grain-superconductor system by the use of the equivalent single-particle multi-channel networks, taking into account the multi-level structure, the Coulomb interaction, and the pair potential on the grain. The dependence of the current on the gate voltage show oscillating behaviour with a period related to 2e of the charge on the grain, reflecting the charge transfer in units of Cooper pairs. The conductance can be enhanced when the pairing parameter is near the Coulomb energy e^2/2C, due to the resonance of the Andreev reflection through the grain. The magnitude of the Andreev reflection as a function of the bias voltage exhibits complicated structures, reflecting the multiple levels, the spin orientations, and the interaction energy on the grain.     

Metal–Insulator Phase Transition in Tungsten-Doped Vanadium Dioxide Thin Films

Physics of the Solid State - The electrical conductivity of thin polycrystalline V(1 – x)WxO2 has been studied in a wide temperature range, which covers the regions of both...     

Detection of the Ferromagnetic Properties of Si:P in the Region of an Insulator–Metal Phase Transition

JETP Letters - The ferromagnetic properties of Si:P in the region of a concentration insulator–metal phase transition at liquid helium temperatures have been detected and studied. To...     

Nonlinear Screening and the Metal–Insulator Transition in a Two-Dimensional Electron Gas

Russian Physics Journal - The density functional theory is used to study the nonlinear screening properties of a two-dimensional electron gas in a strong magnetic field. The Kohn-Sham equations for...     

Metal–Insulator Phase Transition in Thin Films of a Nickel-Doped Vanadium Dioxide

Physics of the Solid State - The electrical conductivity of thin polycrystalline VNixO2 films has been studied in a wide range of temperatures, which covers the regions of both metallic and...     

Rigorous Spectral Analysis of the Metal–Insulator Transition in a Limit-Periodic Potential

We consider the limit-periodic Jacobi matrices associated with the real Julia sets of f (z)=z ²– for which [2, ) can be seen as the strength of the limit-periodic coefficients. The typical local spectral exponent of their spectral measures is shown to be a harmonic function in decreasing logarithmically from 1 to 0.     

Fabrication of Intrinsic Josephson Junctions on BI2Sr2CaCu2O8＋δ Single Crystals with Reproducible Surface Junctions

Intrinsic Josephson junctions on Bi2Sr2CaCu2O8 δ single crystals are successfully fabricated using photolithography and Ar jon milling .Here we discuss the properties of the surface CuO2/metal bilayers and surface junctions prepared with different crystal cleavage conditions and metal film deposition techniques.We show that,by cleaving the crystal at liquid nitrogen temperature in vacuum,the contents of the (interstitial) oxygen in the Bi-O layers become stable upon cleavage,leading to a CuO2/metal bilayer and to surface junctions with reproducible properites,These results can be useful for practical device fabrications as well as for the studies of the contact properties between high Tc superconductors and normal metals.     

Edge States of an Excitonic Insulator with the Spin—Orbit Interaction

JETP Letters - The effect of the spin-orbit and Coulomb interactions on the symmetry and topological properties of the s, p, d, and s + d phases of an excitonic insulator has been considered by...