32 research outputs found
Charge Berezinskii-Kosterlitz-Thouless transition in superconducting NbTiN films
A half-century after the discovery of the superconductor-insulator transition
(SIT), one of the fundamental predictions of the theory, the charge
Berezinskii-Kosterlitz-Thouless (BKT) transition that is expected to occur at
the insulating side of the SIT, has remained unobserved. The charge BKT
transition is a phenomenon dual to the vortex BKT transition, which is at the
heart of the very existence of two-dimensional superconductivity as a
zero-resistance state appearing at finite temperatures. The dual picture points
to the possibility of the existence of a superinsulating state endowed with
zero conductance at finite temperature. Here, we report the observation of the
charge BKT transition on the insulating side of the SIT, identified by the
critical behavior of the resistance. We find that the critical temperature of
the charge BKT transition depends on the magnetic field exhibiting first the
fast growth and then passing through the maximum at fields much less than the
upper critical field. Finally, we ascertain the effects of the finite
electrostatic screening length and its divergence at the magnetic field-tuned
approach to the superconductor-insulator transition.Comment: 9 pages, 6 figure
Reply to Comment on \u27Counterintuitive Consequence of Heating in Strongly-Driven Intrinsic Junctions of Bi₂Sr₂CaCu₂O \u3csub\u3e8+δ\u3c/sub\u3e Mesas\u27
The main criticism raised in the preceding Comment concerns our suggestion that sharp conduction peaks in Bi2Sr2CaCu2O 8+δ mesas, along with absent dip-hump features, may, in general, be a result of self-heating. The author points to the variety of experimental configurations, matrix-element effects, and doping dependencies that might allow a diversity of conductance spectra. We argue that numerous mesa studies (with fixed matrix elements) firmly establish the systematic development of sharp conductance peaks with increased self-heating, and thus, the issue of nonuniversality of tunneling characteristics is not relevant. The author mentions a number of studies that show that the mesa is superconducting near the conductance peak voltage. This is not in dispute and indicates a misinterpretation of our analysis that is clarified here. To address further comments on the technical details of our heating model, we reiterate that our conclusions are independent of our model but rather are based solely on experimental data that are not in dispute
Counterintuitive Consequence of Heating in Strongly-Driven Intrinsic Junctions of Bi₂Sr₂CaCu₂O\u3csub\u3e8+δ\u3c/sub\u3e mesas
Anomalously high and sharp peaks in the conductance of intrinsic Josephson junctions in Bi2 Sr2 CaCu2 O 8+δ (Bi2212) mesas have been commonly interpreted as superconducting energy gaps but here we show they are a result of strong self-heating. This conclusion follows directly from a comparison to the equilibrium gap measured by tunneling in single break junctions on equivalent crystals. As the number of junctions in the mesa, N, and thus heating increase, the peak voltages decrease and the peak width abruptly sharpens for N≥12. Clearly these widely variable features vs N cannot all represent the equilibrium properties. Our data imply that the sharp peaks represent a transition to the normal state. That it occurs at the same dissipated power for N=12-30 strongly implicates heating as the cause. Although peak sharpening due to heating is counterintuitive, as tunneling spectra usually broaden at higher temperatures, a lateral temperature gradient, leading to coexistence of normal hot spots and superconductive regions, qualitatively explains the behavior. However, a more uniform temperature profile cannot be ruled out. As the peak\u27s width and voltage in our shortest mesa (N=6) are more consistent with the break junction data, we propose a figure of merit for Bi2212 mesas, the relative conductance peak width, such that small values signal a crossover into the strong self-heating regime