Núria Alcalde Herraiz, Avdelningen för kvantkomponentfysik

Sammanfattning:

The breakdown of the quasiparticle paradigm in strongly correlated systems, such as the strange metal phase of high-temperature superconductor (HTSs), challenges conventional understanding of charge transport. Unlike Fermi liquids, these materials exhibit anomalous linear-in-temperature resistivity from room temperature down to superconducting transition and ultrafast energy dissipation, suggesting collective, hydrodynamic character of charge flow. 

To probe this regime, we fabricated nanometric Tesla valves on the overdoped HTS YBa2Cu3O7-δ (YBCO), which exhibits the strange metal phase above its critical temperature. These structures exploit directional flow to detect turbulence-induced anisotropies in resistance. Our DC measurements on 50 nm thick devices revealed only very small relative asymmetries in the current voltage characteristics, on the order of 10-4 mV, which is close to the resolution limit of our setup and prevents a definite assessment of hydrodynamic flow.

In addition to direction-dependent electronic transport in the dc regime, hydrodynamic instabilities in the strange metal phase may also manifest in nonlinear THz responses. To investigate this possibility, we conducted harmonic mixing experiments in YBCO nanobridges. Although no measurable harmonic generation was observed in the strange metal regime, our exploration of hydrodynamic transport unexpectedly revealed a promising application of YBCO’s nanobridges for THz detection upon entering the superconducting state. Specifically, in the superconducting phase, we detected harmonic mixing above 1 THz at 60 K, attributed to nonlinearities in the current-phase relation of the nanobridges. These findings underscore the potential of HTS nanostructures not only for probing exotic transport regimes but also for advancing THz detection technologies near liquid nitrogen temperatures, highlighting how fundamental research can lead to unforeseen technological innovations.

Diskussionsledare: Samuel Avila-Lara, Associate Professor