Single crystal growth, transport and scanning tunneling microscopy and spectroscopy of FeSe 1−x S x

• Published in: CrystEngComm 2018, Vol.20 (17), p.2449-2454
• Main Authors: Chareev, Dmitriy, Ovchenkov, Yevgeniy, Shvanskaya, Larisa, Kovalskii, Andrey, Abdel-Hafiez, Mahmoud, Trainer, Dan J., Lechner, Eric M., Iavarone, Maria, Volkova, Olga, Vasiliev, Alexander
• Format: Article
• Language: English
• Subjects: Chemistry; Crystallography
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/C8CE00074C

Single crystals of sulfur-substituted iron selenide, FeSe 1−x S x , were grown within eutectics of molten halides, AlCl 3 /KCl, AlCl 3 /KCl/NaCl or AlCl 3 /KBr, under permanent temperature gradient. The innovative “ampoule in ampoule” design of a crystallization vessel allows obtaining mm-sized plate-like single crystals with a sulfur content up to x ∼ 0.19. The sharp anomalies in the physical properties indicate the superconducting and nematic phase transitions in FeSe 0.96 at T C = 8.4 K and T N = 90 K, respectively. Scanning tunneling microscopy reveals the presence of dumbbell defects associated with Fe vacancies and dark defects at the chalcogen site associated with S within the FeSe 1−x S x series of compounds. Scanning tunneling spectroscopy shows the presence of two different superconducting gaps at both hole and electron pockets of the Fermi surface for low S content levels. As a function of sulfur content, T C follows the conventional dome-shaped curve while T N decreases with x . The overall appearance of the T – x phase diagram of FeSe 1−x S x suggests the importance of nematic fluctuations for the formation of the superconducting state in these compounds.