Eunsung's paper published in Applied Physics Letters
Congratulation to Eunsung for his paper published in Applied Physics Letters (Appl. Phys. Lett. 101, 042601 (2012)). Below is a brief summary of the article:
Thin film study of the recently discovered Fe-base superconductors is important not only in its application to superconducting (SC) technology, but also in elucidating its mechanism for superconductivity. Strain effects in thin films have been also shown to be an effective way to raise the SC transition temperature beyond its bulk-crystal counterpart. Despite the ever growing interest in thin film study, however, high volatility of the constituent elements of the Fe-based superconductors makes it difficult to fabricate high-quality thin films, especially for the hole-doped ones. This Letter reports the pressure dependence of the superconducting properties of K-doped BaFe2As2 thin films (optimally hole doped) on the LaAlO3 substrate, where Tc is 39.95 K, the SC transition width is 1.30 K, and RRR = 38, indicating high quality of the film. Unlike single crystals with similar stoichiometry, Tc of the thin film with optimal potassium concentration gradually increases to 40.8 K at 11.8 kbar (Pc), the highest for this compound, and decreases with further increasing pressure, showing a dome shape. The unusual pressure dependence of the Tc is ascribed to lattice mismatch between the LAO substrate and thin film, where applied hydrostatic pressure effectively acts as the uniaxial pressure along the crystalline c-axis of the film. Observation of a funnel-shape topology of the resistivity near the optimal pressure Pc indicates that the high-temperature superconductivity in this compound is relevant to the quantum fluctuations from a quantum critical point at Pc. Through the systematic control of external applied pressure, the current work paves a way to sensitively study the effects of the substrate to the high SC transition temperature in the thin films and its SC mechanism.