Effect of disorder on magnetoresistance oscillations in nanoperforated superconducting TiN films

The low-temperature transport properties of nanoperforated superconducting TiN films have been experimentally studied. A periodic dependence of the resistance on an external magnetic field, with a period corresponding to a magnetic flux quantum per cell, is observed. An anomalous temperature dependence of the oscillation amplitude is found. The role of the effects of electron-electron interaction and localization in the physical properties of arrays of weak links, based on strongly disordered superconducting films, is discussed.     

Slow oscillations of magnetoresistance in quasi-two-dimensional metals

Slow oscillations of the interlayer magnetoresistance observed in the layered organic metal beta-(BEDT-TTF)(2)IBr(2) are shown to originate from the slight warping of its Fermi surface rather than from independent small cyclotron orbits. Unlike the usual Shubnikov-de Haas effect, these oscillations are not affected by the temperature smearing of the Fermi distribution and can therefore become dominant at high enough temperatures. We suggest that the slow oscillations are a general feature of clean quasi-two-dimensional metals and discuss possible applications of the phenomenon.     

Tunnel magnetoresistance oscillations in a ferromagnet-insulator-ferromagnet system

A model of spin-dependent transport of electrons through a ferromagnet-insulator-ferromagnet structure is developed. It takes into account the image forces, tunnel barrier parameters, and effective masses of an electron tunneling in the barrier and in the ferromagnetic electrode in the free electron approximation. Calculations for an iron-aluminum oxide-iron structure show that, with an increase in the bias voltage, the tunnel magnetoresistance decreases monotonically and then breaks into damped oscillations caused by the interference of the electrons’ wave functions in the conduction region of the potential barrier. The image forces increase the tunnel magnetoresistance by two or three times.     

Magnetophonon oscillations in the magnetoresistance of epitaxial n-GaAs

The longitudinal and transverse magnetoresistance of epitaxial n-GaAs of mobility 2.8 × 10⁴ and 7.8 × × 10⁴ cm²/V-sec (77°K) exhibit oscillations due to the scattering of electrons on optical and acoustic phonons. These oscillations are investigated in magnetic fields up to 170 kG and in the temperature range 80°K to 200°K.     

Plasma oscillations in spheres and the magnetoresistance of potassium

We have observed in potassium the spectrum of the longitudinal helicon oscillations. We have used these oscillations to measure the magnetoresistance and Hall coefficient. In addition, a low frequency method for the measurement of magnetoresistance in metals is demonstrated with experiments on single crystal potassium spheres. The magnetoresistance saturates, but its magnitude depends upon sample history.     

Steps in the phase transition of superconducting Pb-film strips

We studied voltage steps in the transition curve U(T) of superconducting Pb-film strips. The steps strongly depend on the thermal conductivity of the substrate and indicate the formation of phase-slip centers and hot spots.     

Angular magnetoresistance oscillations in bilayers in tilted magnetic fields

Angular magnetoresistance oscillations (AMRO) were originally discovered in organic conductors and then found in many other layered metals. It should be possible to observe AMRO to semiconducting bilayers as well. Here we present an intuitive geometrical interpretation of AMRO as the Aharonov–Bohm interference effect, both in real and momentum spaces, for balanced and imbalanced bilayers. Applications to the experiments with bilayers in tilted magnetic fields in the metallic state are discussed. We speculate that AMRO may be also observed when each layer of the bilayer is in the composite-fermion state.     

Quantum theory of dynamic magnetoresistance

The connected-diagram expansion method is applied in the evaluation of the dynamic conductivity of an electron-impurity system subjected to a constant magnetic field B. This method treats the two cases, B ≠ 0 and B = 0, on the same footing such that the differences appear at the final stage of calculation. A clear physical picture is sustained throughout because no extraneous arguments about the splitting of a density operator into diagonal and non-diagonal parts in freeelectron states, which appeared in most of the past literatures, are used. A transport equation in the limits of low impurity density n_s, and small coupling λ is given explicitly. This equation is meant to describe the dynamic conductivity at an arbitrary frequency ω of an applied electric field and at an arbitrary magnitude of B. It reduces to the transport equation of Argyres in the limit of zero frequency and to that of Yamada-Ron in the limit of zero field. The conductivity in the limits of large ω large B, smalln_s and small λ, is calculated explicitly. The limiting forms of the new expressions are in agreement with the result of Titeica (B ≠0, ω = 0) and with that of Yamada-Ron (B = 0, ω ≠ 0). The expression explicitly indicates that the dynamical response can be no longer interpreted in terms of scattering cross section. The conductivity of an electron-phonon system is discussed briefly.     

Radiation-induced magnetoresistance oscillations in a 2D electron gas

Recent measurements of a 2D electron gas subjected to microwave radiation reveal a magnetoresistance with an oscillatory dependence on the ratio of radiation frequency to cyclotron frequency. We perform a diagrammatic calculation and find radiation-induced resistivity oscillations with the correct period and phase. Results are explained via a simple picture of current induced by photoexcited disorder-scattered electrons. The oscillations increase with radiation intensity, easily exceeding the dark resistivity and resulting in negative-resistivity minima. At high intensity, we identify additional features, likely due to multiphoton processes, which have yet to be observed experimentally.     

Surface acoustic-wave-induced magnetoresistance oscillations in a two-dimensional electron gas

We study the geometrical commensurability oscillations imposed on the resistivity of 2D electrons in a perpendicular magnetic field by a propagating surface acoustic wave (SAW). We show that, for omega相似文献   

Critical current behavior in locally illuminated superconducting lead strips

We have used guided optical waves to locally illuminate superconducting thin lead strips and measured the critical current as a function of optical power. The measured results resemble the predictions of a simple heating model more closely than the Parker T¹ model in the temperature range investigated (5.5 K to T_c) and several possible reasons for this behavior are discussed.     

Dispersive photon blockade in a superconducting circuit

Mediated photon-photon interactions are realized in a superconducting coplanar waveguide cavity coupled to a superconducting charge qubit. These nonresonant interactions blockade the transmission of photons through the cavity. This so-called dispersive photon blockade is characterized by measuring the total transmitted power while varying the energy spectrum of the photons incident on the cavity. A staircase with four distinct steps is observed and can be understood in an analogy with electron transport and the Coulomb blockade in quantum dots. This work differs from previous efforts in that the cavity-qubit excitations retain a photonic nature rather than a hybridization of qubit and photon and provides the needed tolerance to disorder for future condensed matter experiments.     

Giant magnetoresistance oscillations caused by cyclotron resonance harmonics

For high-mobility two-dimensional electrons at a GaAs/AlGaAs heterojunction, we have studied, both experimentally and theoretically, the recently discovered giant magnetoresistance oscillations with nearly zero resistance in the oscillation minima which appear under microwave radiation. We have proposed a model based on nonequilibrium occupation of Landau levels caused by radiation which describes the oscillation picture.     

Superconductivity and normal state magnetoresistance in superconducting FeSe:Sb

We prepared a series of β-FeSe samples with a nominal composition of Fe1.11Se1-xSbx(0≤x≤0.5).The X-ray diffraction,transport and magnetic measurements were performed on these samples to investigate the structure,the superconducting properties and the normal state transport and magnetic properties.Although the X-ray diffraction data suggested that Sb atoms were not incorporated into the β-FeSe phase,the transport data showed observable changes of superconductivity,normal state resistivity and magnetoresistance.This was represented by the increase in the superconducting transition temperature and the upper critical field.Also,for the samples with a low level of Sb content,a clear decrease of the normal state resistivity and a substantial increase of the residual resistance ratio were observed.Furthermore,the samples showed a significant increase of the normal state magnetoresistance that appeared not to follow the Kohler's rule.The results were discussed in the frame of reduction of excess Fe at interstitial sites of β-FeSe.