Demystifying the growth of superconducting Sr2RuO4 thin films

Abstract

We report the growth of superconducting Sr2RuO4 thin films by molecular-beam epitaxy on (110) NdGaO3 substrates with transition temperatures of up to 1.8 K. We calculate and experimentally validate a thermodynamic growth window for the adsorption-controlled growth of superconducting Sr2RuO4 epitaxial thin films. The growth window for achieving superconducting Sr2RuO4 thin films is narrow in growth temperature, oxidant pressure, and ruthenium-to-strontium flux ratio.

Ferromagnetism and Conductivity in Atomically Thin SrRuO3

“…MBE enables excellent ruthenium stoichiometry control, including the minimization of ruthenium vacancies, the crucial ingredient for high-quality SrRuO 3 layers [39]. Superconducting films of the closely related compound Sr 2 RuO 4 with the highest transition temperature are also achieved by MBE [40]. For our samples, the growth parameters are optimized such that the correct ruthenium stoichiometry is obtained in thick films, as evidenced by the high residual resistivity ratio of 40 [41].…”

Realization of Epitaxial Thin Films of the Topological Crystalline Insulator Sr3SnO

“…Recent advances in materials chemistry and thermodynamic modeling relevant to synthesis have enabled remarkably accurate guidance for engineering various complex oxides by adsorption‐controlled growth. [ 26,27 ] To produce more optimal TCI thin films, we investigated thermodynamic conditions amenable to the adsorption‐controlled growth of Sr 3 SnO using a combination of thermodynamic data from the literature together with density functional theory (DFT) and phonon calculations for Sr 3 SnO (see Figure and the Supporting Information for more details). In our computational model, by considering the equilibrium states of strontium and the balance of the reaction between Sr and SnO, we identified the adsorption‐controlled growth regime for generating phase‐pure Sr 3 SnO (the shaded area in Figure 1): Sr is more volatile than SnO.…”

“…To produce the desired growth conditions in MBE experiments, a molecular beam of Sr was produced by evaporating Sr from an effusion cell, while a SnO molecular beam was formed through the thermal decomposition of SnO 2 contained within an effusion cell at elevated temperature. [ 25,26 ] During the deposition, while the Sr flux was varied between 1.9 and 40 Å s −1 as monitored by a quartz crystal microbalance (QCM), the ratio between the Sr and SnO flux was maintained to be between 13: 1 and 17: 1. The proposed growth window was validated by experiments and the conditions of all the synthesized single‐crystal Sr 3 SnO samples have been found in the predicted range (blue markers in Figure 1).…”

Electronic and vibrational signatures of ruthenium vacancies in Sr2RuO4 thin films

“…Since ruthenium deficiency in Sr 2 RuO 4 (SRO) thin films is strongly dependent on the growth conditions, the adsorption-controlled growth that employs a large flux of ruthenium is an appropriate way to control the stoichiometry 15 . For adsorption-controlled growth of oxides, an oxidation agent is required to evaporate excessive ruthenium as some form of RuO x (g) and to fully oxidize the films.…”

“…Superconductivity in Sr 2 RuO 4 is extremely sensitive to defects, such as nonmagnetic impurities and lattice imperfections and thus it requires high quality samples 24,25 . In order to overcome the volatility of ruthenium oxides, some of us have recently used an adsorption-controlled growth technique to synthesize ruthenate thin films showing superconductivity and unprecedentedly high residual resistivity ratios, defined as the ratio of the resistivities at 300 and 4K 14,15 . Related results have also been reported by other groups where the growth of Sr 2 RuO 4 films was carried out by means of molecular beam epitaxy 16,18 .…”