Dresden 2020 – wissenschaftliches Programm
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TT 26.4: Vortrag
Dienstag, 17. März 2020, 14:45–15:00, HSZ 02
Planar GHz resonators on SrTiO3: Suppressed losses at temperatures below 1 K — Vincent T. Engl, Nikolaj G. Ebensperger, Lars Wendel, and •Marc Scheffler — 1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany
The complex dielectric constant є = є1 + i є2 of SrTiO3 reaches high values є1 ≈ 2*104 at cryogenic temperatures, while the dielectric losses (є2) are much stronger than for other crystalline dielectrics. SrTiO3 is a common substrate for oxide thin films, like the superconducting LaAlO3/SrTiO3 system, but the large є1 and є2 restrict high-frequency quantum devices on SrTiO3. Here we present superconducting coplanar Nb resonators on SrTiO3, which we successfully operate in a distant-flip-chip geometry  at frequencies that exceed 1 GHz. We find a pronounced and unexpected increase in resonator quality factor Q at temperatures below 1 K, reaching up to Q ≈ 800. We attribute this to substantial changes of the dielectric losses in SrTiO3 at mK temperatures, and we also detect non-monotonous changes in the temperature-dependent є1. These findings  challenge our present understanding of the dielectric properties of SrTiO3 and at the same time demonstrate that cryogenic high-frequency devices on SrTiO3 are more feasible than previously assumed.
 L. Wendel et al. arXiv:1911.10518 [cond-mat.supr-con]
 V. T. Engl et al. arXiv:1911.11456 [cond-mat.supr-con]