Surface resistance of YBa2Cu3O7 films on SrTiO3 and LaGaO3 substrates

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Abstract
Surface resistance measurements of films of YBa2Cu3O7 deposited onto single‐crystal substrates of LaGaO3 and SrTiO3 have been made at a frequency of 22 GHz. The measurements were made in either a copper or niobium cavity by replacing the end wall with the superconducting film. Typical surface resistance at 20 K are 1–2 mΩ for films on LaGaO3 and 6–8 mΩ for films on SrTiO3, as measured in the copper cavity. The LaGaO3 values lie within the sensitivity range of the Cu cavity (∼2 mΩ) and can only be considered upper limits. Similar measurements in a Nb superconducting cavity resulted in a surface resistance value of 0.2±0.1 mΩ at 4 K for the best LaGaO3‐based film. This value is more than an order of magnitude lower than Cu, and suggests that LaGaO3‐based films may offer immediate advantages in a number of applications.