Kavli Affiliate: Grace Xing
| First 5 Authors: Anand Ithepalli, Amit Rohan Rajapurohita, Arjan Singh, Rishabh Singh, John Wright
| Summary:
Two single crystal phases of tantalum nitride were stabilized on c-plane
sapphire using molecular beam epitaxy. The phases were identified to be
$delta$-TaN with a rocksalt cubic structure and $gamma$-Ta$_2$N with a
hexagonal structure. Atomic force microscopy scans revealed smooth surfaces for
both the films with root mean square roughnesses less than 0.3 nm. Phase-purity
of these films was determined by x-ray diffraction. Raman spectrum of the
phase-pure $delta$-TaN and $gamma$-Ta$_2$N obtained will serve as a future
reference to determine phase-purity of tantalum nitride films. Further, the
room-temperature and low-temperature electronic transport measurements
indicated that both of these phases are metallic at room temperature with
resistivities of 586.2 $muOmega$-cm for the 30 nm $delta$-TaN film and 75.5
$muOmega$-cm for the 38 nm $gamma$-Ta$_2$N film and become superconducting
below 3.6 K and 0.48 K respectively. The superconducting transition temperature
reduces with applied magnetic field as expected. Ginzburg-Landau fitting
revealed a 0 K critical magnetic field and coherence length of 18 T and 4.2 nm
for the 30 nm $delta$-TaN film and 96 mT and 59 nm for the 38 nm
$gamma$-Ta$_2$N film. These tantalum nitride films are of high interest for
superconducting resonators and qubits.
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