Counterintuitive consequence of heating in strongly-driven intrinsic junctions ofBi2Sr2CaCu2O8+δ

Abstract

Anomalously high and sharp peaks in the conductance of intrinsic Josephson junctions in Bi 2 Sr 2 CaCu 2 O 8+␦ ͑Bi2212͒ 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 Ն 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's width and voltage in our shortest mesa ͑N =6͒ 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.

Terahertz wave emission from intrinsic Josephson junctions in high-Tcsuperconductors

“…In figure 5, the contact resistance can be seen in our data below T c due to our three-point measurements: it is usually < 5 except for one sample (w = 40 μm). A recent study on 10×10 μm 2 mesas show the contact resistance to be a superconductor-insulator-normal-metal junction that can be expected to be weakly temperature-dependent above T c and diverge at low temperatures [29]. Values range from 0.00015 to 0.0005 cm 2 .…”

Powerful terahertz emission from Bi2Sr2CaCu2O8+δ mesa arrays

“…2). As can be seen in the plot, the IV-characteristics are strongly influenced by self-heating, to the extent that it is S-shaped, which is typical for mesas of this size [12,15]. For the mesas on this chip, THz emission occurs where dI/dV is very large, or even negative, and it has been suggested [16] that this may be essential for some modes of THz emission in these devices.…”

Eliashberg Analysis of Tunneling Experiments: Support for the Pairing Glue Hypothesis in Cuprate Superconductors

“…We take advantage of a number of studies [19][20][21] that show clearly that the normal state conductance is a smoothly varying function which merges with the superconducting conductance for voltages just beyond that of the hump in the dip or hump spectral feature. Published SIS tunneling conductances [16] have been normalized by generating a normal state conductance which smoothly interpolates between the positive and negative high bias superconducting data just beyond the hump voltage.…”