2026/07/16 by Anand Ithepalli, Haoran Lu, Eegene Clara Chung +9
#cond-mat.supr-con #cond-mat.mtrl-sci
Using molecular beam epitaxy, we have realized thin films of titanium nitride (TiN) on c-plane sapphire that exhibit the lowest observed full-width at half maximum X-ray rocking curve width of 18 arcsec. Though the (111) oriented TiN exhibits an abrupt and crystalline interface with sapphire, for the first time we observe sub-surface defects in the sapphire substrate, which nucleate structural defects in the epitaxial TiN layer. Using quarter-wavelength coplanar waveguide (CPW) resonators in a 3 \textmu m/6 \textmu m/3 \textmu m gap/strip/gap lines in a hanger geometry, we find the internal quality factor of the TiN resonators to be >106 in the single-photon ⟨ n ⟩ ∼ 1 limit at 5.8 GHz and 10 mK, rising to >20 × 106 at ⟨ n ⟩ ∼ 106. The results are of high interest for applications of superconducting TiN in several areas, and provide a path towards epitaxial Josephson junctions with crystalline barriers in the future for high coherence qubits.