GROWTH AND STUDY OF STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF Fe (Te, Se) THIN FILMS AND SINGLE CRYSTALS

Abstract

Superconductivity is a remarkable phenomenon in condensed matter physics, was first observed in mercury by H. K. Onnes in 1911. Over the years, numerous efforts have been made to improve superconducting transition temperature (TC). Until 1986, the highest TC achieved was approximately 23 K in the Nb3Ge compound. Bednorz and Muller discovered the superconductivity in Sr/Ba doped La2CuO4, which exhibited a TC of around 35 K. This remarkable finding sparked extensive research efforts to identify new superconductors with high-transition temperature. Subsequently, a series of unpredicted superconductors were found in cuprate materials after Bednorz and Muller's discovery. In 2006, the discovery of iron-based superconductors (IBSs) opened a new era of superconductivity. These materials exhibit a fascinating combination of superconductivity and magnetism, offering a wide range of compounds with multiband electronic structures. The IBSs possess a layered structure consisting of FeCh (Ch=Se, Te) or FePn (Pn=As, P) planes, similar to the CuO2 planes in cuprate superconductors. The simplest crystal structure, along with the less toxicity compared to arsenic, makes 11-type compounds as promising candidates for understanding the mechanism of superconductivity in these compounds. This thesis focuses on the synthesis, characterization, and investigation of the structural, transport, and magnetic properties of Fe (Te, Se) thin films and single crystals. The synthesis process involves the growth of Fe (Te, Se) single crystals via self-flux method and thin films using Pulsed Laser Deposition (PLD) technique. To examine the structural and morphological properties of the synthesized samples, the X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), and High-resolution transmission electron microscopy (HRTEM) techniques were employed. Additionally, X-ray photoemission spectroscopy (XPS) has been utilized to investigate the chemical state of the elements within the samples. In order to gain a deeper understanding of the superconducting properties of Fe (Te, Se) samples, we conducted three key measurements: (1) resistivity, (2) magnetization (3) specific heat measurements. The resistivity measurements were performed at different temperatures and magnetic fields to investigate the magneto-transport properties of the samples.