Magnetoconductance Data Research Articles

Nonlocal effect in magnetoconductivity of high-Tc superconductors.

We reanalyze theoretically the fluctuation-induced electric conductivity in high-${\mathit{T}}_{\mathit{c}}$ superconductors, since an early theory proposed by Aronov et al. contains an error. When this error is corrected, we find that the dirty-limit theory cannot describe the magnetoconductance data obtained in a monocrystal of Y-Ba-Cu-O by Matsuda et al. The clean-limit theory, on the other hand, describes the data somewhat better. Finally, inclusion of the nonlocal effect in the clean-limit theory removes most of the discrepancy between theory and experiment.

Anomalous conduction processes in amorphous indium oxide films

A transition in the resistance behavior of amorphous indium oxide In xO y films from a Coulomb-gap variable-range hopping law towards a constant activation energy law has been observed at low temperatures. The magnetoconductance (MC) is strongly positive, linear in magnetic field, and increases with decreasing temperature as T -1.1 in a fixed magnetic field. The MC theories of Schirmacher and of Nguyen, Spivak, and Shklovskii qualitatively describe the MC data.

Weak Localization and Interaction Effects in Thin Disordered Zinc Films

AbstractThe low temperature resistance ΔR(T)/R and magnetoconductance Δσ(H, T) is measured of thin and quasi two‐dimensional disordered zinc films. At low temperatures, the thinnest films show a logarithmic temperature dependence of resistance. This is well explained by the localization and electron–electron interaction theory. The electron–phonon and electron–electron contributions to the resistance are described in detail. From the magnetoconductance data, the inelastic and spin–orbit scattering times are calculated and compared with theoretical values.

Phase coherent length measurements in single-crystal NiSi2 films

The phase coherent length lφ of conduction electrons in single-crystal NiSi2 films has been measured using weak localization phenomena. Logarithmic temperature dependence and logarithmic magnetic-field dependence of the conductivity observed in epitaxially grown NiSi2 single-crystal films with thicknesses from 6 to 40 nm are interpreted in terms of the two-dimensional weak localization with strong spin-orbit interaction. Considerably long-phase coherent lengths are obtained by fitting analyses using magnetoconductance data; lφ=0.8 μm at 4.2 K and 1.5 μm at 2 K. This is due to a very low concentration of magnetic scatterers in NiSi2. Because of its long-phase coherent length, the single-crystal NiSi2 film can be applied to novel quantum interference devices.

Dominating Coulomb-interaction effects in amorphous InxOy films.

Insulating thin three-dimensional (3D) amorphous films of ${\mathrm{In}}_{\mathrm{x}}$${\mathrm{O}}_{\mathrm{y}}$ exhibit the surprising resistance-versus-temperature dependence R\ensuremath{\propto}exp[(${T}_{0}$/T${)}^{1/2}$] between 6 and 106 K. The (1/T${)}^{1/2}$ exponent in the resistance expression, the observed positive magnetoresistance behavior, and the lack of dependence of the magnetoresistance upon magnetic field orientation all suggest a dominating Coulomb electron-electron interaction transport mechanism. Interestingly, the experimental magnetoconductance data could be well described using the 3D electron-electron spin-splitting interaction theory derived for metallic systems, but modified by a simple temperature prescaling factor, 1/exp[(${T}_{0}$/T${)}^{1/2}$]. This prescaling factor accounts for the strong temperature dependence of the conductivity that is present in insulating films.

Magnetoconductance measurements in the variable-range-hopping regime.

Magnetoconductance measurements in the strongly localized regime have been made on a thin 119-A granular In/sub 2/O/sub 3-//sub x/ film which exhibited variable-range hopping in its resistance. Some of the predictions suggested by Sivan, Entin-Wohlman, and Imry where observed in the magnetoconductance (MC) data including the B/sup 2/ dependence of the MC in low magnetic fields and the positive sign of the MC at higher fields. However, there was no tendency for the MC to saturate at higher fields, nor did the MC take on negative values in the more weakly disordered films. Our MC data were in conflict with Faran and Ovadyahu's observations of a T/sup -1/ dependence of the MC. Electron-electron interaction effects dominated the electronic transport properties in the liquid-helium temperature range.

Transport properties of a 100-A

Because of its relatively small electron-carrier concentration per unit volume N\ensuremath{\simeq}${10}^{20}$/${\mathrm{cm}}^{3}$, the electronic transport properties of ${\mathrm{In}}_{2}$${\mathrm{O}}_{3\mathrm{\ensuremath{-}}\mathrm{x}}$ are dominated by electron-electron interaction effects owing to reduced electron screening. Weak localization effects are also important. These two processes well describe the behavior of the magnetoconductance data, the resistance versus temperature data in different perpendicular magnetic fields, and the temperature-dependent Hall-constant data in a 2-T field. The temperature-dependent Hall-constant data exhibited a ln(1/T) dependence and yielded a value of 0.75 for the electron screening constant F. Fits to the low-magnetic-field magnetoconductance data yielded values for the inelastic ${\ensuremath{\tau}}_{i}$, the spin-orbit ${\ensuremath{\tau}}_{\mathrm{so}}$, and the magnetic impurity ${\ensuremath{\tau}}_{s}$ scattering times. Both ${\ensuremath{\tau}}_{\mathrm{so}}$ and ${\ensuremath{\tau}}_{s}$ are long (weak scattering processes) and took on values of ${\ensuremath{\tau}}_{\mathrm{so}=7.6\ifmmode\times\else\texttimes\fi{}{10}^{\mathrm{\ensuremath{-}}11}}$ sec and ${\ensuremath{\tau}}_{s}$=7.3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}11}$ sec, whereas ${\ensuremath{\tau}}_{i}$(sec)=133\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$/T could be well described by the Nyquist formula of Altshuler and co-workers. The high-field, low-temperature, magnetoconductance data were characterized by a negative interaction contribution \ensuremath{\Delta}${\ensuremath{\sigma}}_{\mathrm{int}}$, and experimental values for \ensuremath{\Delta}${\ensuremath{\sigma}}_{\mathrm{int}}$ at 0.5 K agreed well with the interaction theory of Lee and Ramakrishnan. The resistance versus temperature data could be nicely explained using both the 2D interaction and 2D weak localization theories for the conductivity; no adjustable parameters were used in the fitting of the resistance and magnetoconductance data.

Electron inelastic scattering in aluminum films and wires at temperatures near the superconducting transition.

Sensitive magnetoconductance measurements have been made on clean Al films and submicrometer-width wires. Theoretical expressions for the magnetoconductance (MC) provide a good fit to the data only after high-field corrections are made to the Maki-Larkin term. Analysis of the MC data is used to infer the temperature-dependent electron inelastic scattering rate 1/${\ensuremath{\tau}}_{i}$ in the vicinity of the superconducting transition temperature ${T}_{c}$. At temperatures just above ${T}_{c}$, the coupling between electrons and superconducting fluctuations is expected to affect significantly the inelastic scattering rate, producing a rapid rise in 1/${\ensuremath{\tau}}_{i}$ as T approaches ${T}_{c}$ from above. We observe this novel behavior in both one- and two-dimensional samples and find it to be in good quantitative agreement with recent theoretical predictions.

Inelastic electron lifetime in niobium films.

The perpendicular magnetoconductance has been measured for thin niobium films (${R}_{\ensuremath{\square}}$=47--218 \ensuremath{\Omega}) for temperatures from near the superconducting transition temperature ${T}_{c}$ to 20 K. The electron phase-coherence lifetime has been determined by analyzing magnetoconductance data, using the theories of localization and superconducting fluctuation effects in thin films. This electron lifetime is interpreted in terms of electron-electron and electron-phonon scattering mechanisms.

Magnetoconductance of thin-film superconductors near critical disorder

Gauge-invariant approximations are used to derive all diagrams for the current response function to lowest order in the superconducting pair fluctuations. The resulting expression for the magnetoconductance extends the range in temperature and magnetic field over which meaningful comparisons with experimental data can be made. This aspect of the theory is illustrated in an analysis of magnetoconductance data on 100-A\r{}-thick In/${\mathrm{InO}}_{\mathrm{x}}$ superconductors near critical disorder where the transition temperature is rapidly suppressed with increasing sheet resistance. The temperature dependence and magnitude of the derived inelastic scattering rate is in good agreement with theory which includes the effect of superconducting fluctuations on the two-dimensional inelastic electron-electron scattering rate.

Scaling behavior of the magnetoconductance of highly disordered In/InO x thin-films superconductors

Magnetoconductance data on composite amorphous In/InO x thin (100 Å)-film superconductors have been analyzed near critical disorder where the mean-field transition temperature T c0 is rapidly suppressed with increasing normal-state sheet resistance. For a factor of 2.5 decrease in T co, from 2.49 K to 0.97 K, the magnetoconductance data are observed to be scale-invariant with respect to the parameter ratios H/ T, the perpendicular magnetic field divided by the temperature, and T/ T c0, the temperature T normalized to T c0. This behavior is consistent with the functional forms of the Aslamazov-Larkin and Maki-Larkin contributions to the magnetoconductance providing the electron diffusivity is constant and the inelastic scattering rate is linear in temperature. These restrictive conditions are found to be valid for independent experimental determinations. Deviations in the scaling behavior are observed when weak localization contributions dominate at high temperature and when data for films with even lower T co are included in the analysis.

Superconducting-fluctuation conductivity of one-dimensional wires in a magnetic field.

We consider the effects of superconducting fluctuations on the magnetoconductance of narrow wires at temperatures just above the transition temperature T/sub c/. The range of validity of expression for the Maki-Thompson correction to the conductivity is extended to lower reduced temperatures, t = T/T/sub c/, and higher values of the magnetic field H. These extensions allow the determination of inelastic scattering rates, via magnetoconductance measurements, in the physically interesting region of temperatures near T/sub c/. Magnetoconductance data from sub-micrometer-width aluminum wires are found to support the predictions quite well.

Superconducting fluctuations and magnetoconductance measurements of thin films in parallel magnetic fields.

Parallel magnetoconductance measurements have been made on thin Cu-Pb films having different spin-orbit interactions. A theory of parallel magnetoconductance, first proposed by Al'tshuler and Aronov and expanded by Gershenzon, Gubankov, and Zhuravlev gives a qualitative description of the experimental results. However, this theory fails to account for the low-temperature dependence of the magnetoconductance data at low temperatures. The temperature dependence of the conductivity in fixed parallel fields was studied and compared to the theory of Markiewicz; agreement between theory and data was acceptable. Several of the films exhibited superconducting fluctuations; measurements of the parallel magnetoconductance give values of the parameter \ensuremath{\beta}(T/${T}_{c}$) in fair agreement with the theoretical values predicted by Larkin.