Journal Article

Terahertz Absorption Spectroscopy in Bicrystal Josephson Junctions Formed from Mutually Tilted Ic/I-Axes YBasub.2Cusub.3Osub.7−x Films

Divin, Yuriy

2023

Overview

Spectral analysis of terahertz (THz) and sub-THz emission from quantum cascade lasers has been recently demonstrated using conventional YBa[sub.2]Cu[sub.3]O[sub.7−x] bicrystal Josephson junctions made from c-axes thin films. Josephson frequencies of alternative bicrystal junctions made from YBa[sub.2]Cu[sub.3]O[sub.7−x] films with mutually tilted c-axes extend further into the THz range. However, these THz oscillations can weaken due to new absorption channels in the junction environment. Here, using Josephson admittance spectroscopy, THz losses in YBa[sub.2]Cu[sub.3]O[sub.7−x] bicrystal junctions with mutually tilted c-axes are studied. Absorption maximizes at a reproducible set of THz frequencies close to those of collective modes in bulk YBa[sub.2]Cu[sub.3]O[sub.7−x] recovered by Fourier spectroscopy. Annealing junctions in atomic oxygen reduces the losses at frequencies of 2.7 and 3.6 THz, while the losses increase at frequencies of 2.3 and 4.6 THz. Thus, as a THz spectrum analyzer, YBa[sub.2]Cu[sub.3]O[sub.7−x] bicrystal junctions require post-fabrication correction of the oxygen content. In addition, the fine structure of the absorption spectrum appears at frequencies near 4.6 THz. Significant absorption near 2.3 THz may be due to effects associated with the second Josephson harmonic or second-order nonlinearity of the susceptibility in YBa[sub.2]Cu[sub.3]O[sub.7−x]. This work paves the way towards probing collective modes in high-Tc materials in situ using the Josephson oscillations.

• Publisher: MDPI AG
• Subject: Grain boundaries / Tokamaks