Growth of superconducting FeSe0.5Te0.5 thin films by pulsed-laser deposition

Iron chalcogenide superconductors FeSe1−xTex are important materials for investigating the relation be-tween the superconductivity and the orbital and/or electronic nematic order, because the end member material FeSe exhibits a structural transition without a magnetic phase transition. However, the phase separation occurs in the region of 0.1 ≤ x ≤ 0.4 for bulk samples, and it prevents the complete understanding of this system. Here, we report the successful fabrication of epitaxial thin films of FeSe1−xTex with 0 ≤ x ≤ 0.7, which includes the phase-separation region, on LaAlO3 substrates via pulsed laser deposition. In the temperature dependences of differential resistivity for these films with 0 ≤ x ≤ 0.3, the dip- or peak- anomalies, which are well-known to be originated from the structural transition in FeSebulk samples, are observed at the characteristic temperatures, T*. The doping-temperature (x–T) phase diagram of FeSe1−xTex films clearly shows that T* decreases with increasing x, and that Tc suddenly changes at a certain Te content where T* disappears, which turns out to be commonly observed for both films on LaAlO3 and CaF2. These indicate the importance of controlling the structural transition to achieve high Tc in iron chalcogenides.

“…All of the films in this study were grown by the PLD method with a KrF laser627. FeSe 1− x Te x polycrystalline pellets ( x = 0–0.7) were used as targets.…”

Section: Methodsmentioning

confidence: 99%

Control of structural transition in FeSe1−xTex thin films by changing substrate materials

Imai

Sawada

Nabeshima

et al. 2017

“…and FeSe0.8Te0.2 thin films were deposited by means of pulsed laser deposition (PLD) with a KrF eximer laser and an FeSe or FeSe0.8Te0.2 polycrystalline target. The fabrication conditions are described in detail elsewhere 30,31. We used a commercially available STO (001) substrate with a step-and-terrace surface, a LAO (001) substrate and a CaF2 (001) substrate.…”

mentioning

confidence: 99%

Superconductivity at 38 K at an electrochemical interface between an ionic liquid and FeSe0.8Te0.2 on various substrates

Kouno

Sato

Katayama

et al. 2018

Superconducting FeSe0.8Te0.2 thin films on SrTiO3, LaAlO3 and CaF2 substrates were electrochemically etched in an ionic liquid, DEME-TFSI, electrolyte with a gate bias of 5 V. Superconductivity at 38 K was observed on all substrates after the etching of films with a thickness greater than 30 nm, despite the different Tc values of 8 K, 12 K and 19 K observed before etching on SrTiO3, LaAlO3 and CaF2 substrates, respectively. Tc returned to its original value with the removal of the gate bias. The observation of Tc enhancement for these thick films indicates that the Tc enhancement is unrelated to any interfacial effects between the film and the substrate. The sheet resistance and Hall coefficient of the surface conducting layer were estimated from the gate bias dependence of the transport properties. The sheet resistances of the surface conducting layers of the films on LaAlO3 and CaF2 showed identical temperature dependence, and the Hall coefficient was found to be almost independent of temperature and to take values of −0.05 to −0.2 m2/C, corresponding to 4–17 electrons per FeSe0.8Te0.2 unit cell area in two dimensions. These common transport properties on various substrates suggest that the superconductivity at 38 K appears in the surface conducting layer as a result of an electrochemical reaction between the surface of the FeSe0.8Te0.2 thin film and the ionic liquid electrolyte.

“…It has been shown that superconductivity can be modulated by ferroelectric field effect23 or biaxial strain related to the converse piezoelectric effect of FE4. For biaxial-strain-effect study, substrates with different mismatches with the film have been widely used5678. In this case, besides the biaxial strain effect, other effects may be induced due to the different interfaces and mismatch-related defects, etc 4…”

mentioning

confidence: 99%

Quasi-two-dimensional superconductivity in FeSe0.3Te0.7 thin films and electric-field modulation of superconducting transition

Zhu

Mei

Wei

et al. 2015

We report the structural and superconducting properties of FeSe0.3Te0.7 (FST) thin films with different thicknesses grown on ferroelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates. It was shown that the FST films undergo biaxial tensile strains which are fully relaxed for films with thicknesses above 200 nm. Electrical transport measurements reveal that the ultrathin films exhibit an insulating behavior and superconductivity appears for thicker films with Tc saturated above 200 nm. The current-voltage curves around the superconducting transition follow the Berezinskii-Kosterlitz-Thouless (BKT) transition behavior and the resistance-temperature curves can be described by the Halperin–Nelson relation, revealing quasi-two-dimensional phase fluctuation in FST thin films. The Ginzburg number decreases with increasing film thickness indicating the decrease of the strength of thermal fluctuations. Upon applying electric field to the heterostructure, Tc of FST thin film increases due to the reduction of the tensile strain in FST. This work sheds light on the superconductivity, strain effect as well as electric-field modulation of superconductivity in FST films.