Inhomogeneous superconductivity in thin crystals of FeSe_1−xTe_x (x = 1.0, 0.95, and 0.9)

Abstract

We investigated the temperature dependence of resistivity in thin crystals of FeSe 1−x Te x (x=1.0, 0.95, and 0.9), though bulk crystals with 1.0 × 0.9 are known to be non-superconducting. With decreasing thickness of the crystals, the resistivity of x=0.95 and 0.9 decreases and reaches zero at a low temperature, which indicates a clear superconducting transition. The anomaly of resistivity related to the structural and magnetic transitions completely disappears in 55-to 155-nm-thick crystals of x=0.9, resulting in metallic behavior in the normal state. Microbeam x-ray diffraction measurements were performed on bulk single crystals and thin crystals of FeSe

Observation of a superconducting state of a topological superconductor candidate, FeTe0.6Se0.4, equipping ferromagnetic electrodes with perpendicular magnetic anisotropy

“…Here, salient resistance increase was observed at approximately 90 K. Li et al 24) reported that the increase in resistance is ascribed to the first-order magnetic and structural phase transition originating from FeTe. Furthermore, Eguchi et al 22) observed a similar resistance increase in FeTeSe, although they used non-magnetic electrodes. Therefore, the anomalous resistance increase is not attributed to the adjacent PMA electrodes.…”

“…The perpendicular magnetic field dependence of the Hall voltage (V Hall ) was measured by An FTS bulk single crystal was synthesized using the chemical vapor transport method, and an FTS thin film was mechanically exfoliated and transferred onto a SiO 2 (100 nm)/Si substrate using the scotch tape method. 21,22) Ar + milling was implemented to remove a possible oxidized layer on the FTS surface. The optical microscopy image of FTS after Ar + milling is shown in Fig.…”

“…3(a) and shows the resistance of FTS from 6 to 20 K. The unequivocal transition from a normal to a superconducting state was observed and the midpoint superconducting transition temperature (T c mid ) was determined to be 15.0 K. The observed T c mid is consistent with that observed in previous studies using bulk FeTe 0.6 Se 0.4 and thin film FeTe x Se 1−x (x = 1, 0.95, and 0.9) equipping non-magnetic electrodes as contacts. 22,23) Therefore, it can be concluded that the superconducting state is realized in mechanically exfoliated FTS equipping ferromagnetic PMA electrodes, i.e. stray fields from the ferromagnetic electrode layers and the ferromagnetic Co adjacent to the superconducting FTS do not destroy the superconducting state in FTS and the state can exist even beneath the ferromagnet.…”

Hydrothermally Obtaining Superconductor Single Crystal of FeSe0.2Te0.8 without Interstitial Fe

“…[6][7][8] It is essential to synthesize high-quality FeSe1−𝑥Te𝑥 single crystals with bulk superconductivity for investigating the intrinsic physical properties. [9][10][11][12][13][14][15][16] The as-grown Fe 1+𝛿 Se1−𝑥Te𝑥 single crystals with the self-flux method inherently contains excess Fe atoms (𝛿 in quantity) for Te substitution 𝑥 > 0.5, which occupy the interstitial sites of the Fe(Se,Te) layers. [17] These interstitial irons are found to strongly suppress superconductivity and cause the physical properties to vary from sample to sample, [7,10,14,[18][19][20] interfering with a consistent understanding of the intrinsic physics.…”