Hot-spot formation in stacks of intrinsic Josephson junctions in Bi2Sr2CaCu2O

B. Gross

¹

,

Stefan Guénon

²

,

Jie Yuan

³

et al.

Direct imaging of hot spots in Bi2Sr2CaCu2O8+δ mesa terahertz sources

“…A broad temperature maximum appears in the center of the mesa, in good qualitative agreement with numerical solutions of the heat diffusion equations. 5,6 The sharp, step-like feature visible in the middle of the longitudinal profiles ( Fig. 5(a)) marks the edge of the Au-current lead evaporated onto the mesa.…”

“…The inset of Fig. 3(a) shows currentvoltage characteristic measured on decreasing current bias at temperature intervals of 5 K between 10 K and 100 K. The pronounced back-bending of the IV-curve, particularly at the lowest temperatures, is commonly seen on this type of sample [4][5][6] and is the hallmark of strong self-heating. At temperatures below 45 K, re-trapping occurs at currents low enough such that the c-axis resistance can be estimated from the sub-gap voltage as indicated by the solid lines.…”

“…3 Extensive studies have shown that due to the low thermal conductivity along the crystallographic c-axis, Bi-2212 mesas are prone to self-heating when electrically biased to currentvoltage conditions at which THz-emission is expected. [4][5][6] This problem is particularly serious in the relatively large mesas commonly used for THz-generation. Low-temperature scanning laser microscopy (LTSLM) experiments in which a modulated laser pulse induces a local variation in the c-axis resistivity and/or critical current of Bi-2212 indicate that the self-heating is not uniform, but rather takes the form of one or more localized hot spots.…”

“…[7][8][9] This is broadly consistent with recent thermal images of the surface temperature of BSCCO mesas 10 and with theoretical calculations for Bi-2212 mesas of this type, which predict non-uniform self-heating of the order of tens of Kelvin. 5,6 Furthermore, it is possible that hot spots form a shunt between the stacked Josephson junctions, thereby promoting their synchronization. 5,11 This is consistent with studies, which find a narrower THz radiation line width from mesas with comparatively high DC power dissipation.…”

Control of circularly polarized THz wave from intrinsic Josephson junctions by local heating

“…Stacks of these natural Josephson junctions, which are referred to as intrinsic Josephson junctions (IJJs), can generate an AC Josephson current in the THz frequency range by application of a voltage, and the THz wave emission is attributed to the generation of this current. Intense THz emissions have been reported for IJJs fabricated in a mesa geometry, which itself behaves as a cavity resonator, and thus, a number of studies on such IJJ mesas have been carried out both experimentally [4][5][6][7][8][9][10][11][12][13][14][15] and theoretically [16][17][18][19][20][21][22][23][24][25][26]. However, in the previous studies, little attention was given to the state of the polarization of the THz waves.…”