Temperature Dependence Of Critical Field Research Articles

Localization effects on superconductivity in homogeneous metallic glasses.

It is pointed out that localization effects on bulk superconductivity do exist and can be significant in homogeneous amorphous alloys (or typical metallic glasses) whose upper critical fields appear to follow the standard Werthamer-Helfand-Hohenberg-Maki (WHHM) curves. Owing to the similarity in the temperature dependence of critical fields predicted by the Fukuyama-Ebisawa-Maekawa theory of the weakly localized regime and the WHHM results over a very wide temperature range, these effects have escaped notice heretofore. Comparison of the electronic density of states obtained from specific-heat measurement (absence of field-induced delocalization effects) and the ``apparent'' one derived from fitting critical-field data reveals the aforementioned effects.

Comparison of superconducting parameters of A 15- and σ-phases of Nb−Pt

The superconducting properties of A 15- and σ-phases of the system Nb−Pt were investigated. Alloys of compositions Nb3Pt, Nb2Pt, and Nb62Pt38 were prepared by arc melting and subjected to optical microscopic and x-ray analysis for structure determination. The transition temperatures were measured inductively as well as resistively. The temperature dependences of critical fields were measured up to 35 kG. The A 15-phase has aT c value of 8.97K and a zero temperature upper critical fieldH c2(0) of 100 kG as compared to aT c value of 2.14K and anH c2(0) value of 14kG for the σ-phase. A comparison with theoretical upper critical field values seems to indicate that a spin-orbit coupling mechanism is responsible for the higher value ofH c2(0) in the case of the A 15-phase alloy. The temperature dependent resistance up to 300 K is also measured and discussed for both the phases.

High-field effects in chalcogenide switching glasses

The current-electric field and transient current characteristics have been measured at high fields for a number of chalcogenide switching glasses, over a range of temperatures. Pulses between 2.5 and 50 ns wide were used so that it could be assumed that the Joule heating was adiabatic in the active layer of the devices tested. A high offstate current region associated with a rise in the current transient is observed at fields above a temperature-dependent critical field. This behaviour has been interpreted as the result of impact ionisation of Zener breakdown and, in the absence of a radial temperature gradient, can be considered as evidence supporting an electronic switching mechanism.

Magnetoresistance of Hexagonal FeGe Single Crystals between 4.2 K and 30 K

The low field transverse magnetoresistance of hexagonal FeGe has been measured for the field in the basal plane with current both parallel and perpendicular to the c-axis. At a temperature dependent critical field (Δϱ/ϱ0) // c shows a sharp peak, then decreases rapidly until it levels off at a second critical field. (Δϱ/ϱ0) ⊥ c exhibits a sharp dip at the first critical field followed by rising magnetoresistance with increasing field until the second critical field, where it levels off. The observed anomalies are related to changes in the spin structure and magnetic superzone effects. The possibilities of itinerant antiferromagnetism are also considered.

Magnetically Controllable Cooperative Jahn-Teller Distortion in TmAsO4

TmAs${\mathrm{O}}_{4}$ undergoes a cooperative Jahn-Teller distortion at 6.0 K. At $Tl6$ K there is a temperature-dependent critical field ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}}_{c}$ at which a cooperative distortion back to the high-temperature phase occurs. For $Bl{B}_{c}$, the distortion directions in the basal plane are the (110) and the ($1\overline{1}0$) directions and are magnetically controllable.

The temperature dependence of the critical field H c2 in solid solution Nb-Ta alloys

The temperature dependence of the upper critical field H c2 is studied on the whole composition range of Nb-Ta alloys. The results are in accord with the theoretical prediction made by Maki.

Temperature dependence of critical fields in high field superconductors

The temperature dependence of critical fields is calculated for high field superconductors if the phase transition into the normal state is of first order. The effect of superheating is discussed.