Temperature dependence of geometrical and velocity matching resonances in Bi2Sr2CaCu2O8+x intrinsic Josephson junctions

TL;DR

This study investigates how temperature affects resonances and electromagnetic wave velocities in Bi2Sr2CaCu2O8+x intrinsic Josephson junctions, revealing impacts on device coherence and tunability for THz applications.

Contribution

It provides new insights into the temperature dependence of geometrical and velocity-matching resonances, highlighting the effects of self-heating and the potential for frequency tunability.

Findings

Resonance quality factor decreases rapidly above 10 K.

Swihart velocity remains flat at low T, following critical current.

Self-heating limits coherent THz emission power.

Abstract

We study temperature dependence of geometrical (Fiske) and velocity-matching (Eck) resonances in the flux flow state of small Bi2Sr2CaCu2O8+x mesa structures. It is shown that the quality factor of resonances is high at low T, but rapidly decreases with increasing temperature already at T > 10 K. We also study T-dependencies of resonant voltages and the speed of electromagnetic waves (the Swihart velocity). Surprisingly it is observed that the Swihart velocity exhibits a flat T-dependence at low T, following T-dependence of the c-axis critical current, rather than the expected linear T-dependence of the London penetration depth. Our data indicate that self-heating is detrimental for operation of mesas as coherent THz oscillators because it limits the emission power via suppression of the quality factor. On the other hand, significant temperature dependence of the Swihart velocity allows broad-range tunability of the output frequency.