Scanning-tunneling microscopy/spectroscopy and break-junction tunneling spectroscopy of FeSe1–xTex

Abstract

The iron-chalcogenide superconductor FeSe 1-x Te x (0.5 < x < 1) was investigated by scanning-tunneling microscopy/spectroscopy (STM/STS) and break-junction techniques. In the STM topography of the samples, randomly distributed Te and Se surface atomic structure patterns correlate well with the bulk composition, demonstrating that nanoscale surface features directly reflect bulk properties. The high-bias STS measurements clarified the gap-like structure at ≈ 100-300 meV, which is consistent with the break-junction data. These highenergy structures were also found in sulfur substituted FeS 0.1 Te 0.9 . Possible origin of such spectral peculiarities is discussed. The superconducting gap 2Δ ≈ 3.4 ± 0.2 meV at temperature T = 4.2 K was found in the break junction of

The spatial distributions of large gap-like structure on Fe(Se,Te) single crystals observed by STM/STS

“…2(a) shows the averaged dI/dV spectra up to the high bias range |V| < 600 mV for the various FeSe 1Àx Te x (x = 0.5, 0.6, 0.7) at T = 4.9 K. The broad pseudogap-like structures (V PG ) were clearly observed at the negative biases of V = À200 to À400 mV in all the samples. These gap-like peaks V PG were also reproduced in the sulfur-substituted compound FeS 0.1 Te 0.9 [7]. Hence, the V PG peaks were commonly observed in iron chalcogenide superconductors.…”

“…From the fitting curve, the estimated gap energy was about D $ 7 meV with the large broadening parameter C $ 5 meV. The gap magnitude was apparently larger than the SC gaps of our previous break-junction tunneling and STS results, D = 1-3 meV [4][5][6][7]9]. According to the ARPES measurement, the maximum size of SC gap among the multiple-Fermi surfaces was estimated as $4 mV on FeSe 0.3 Te 0.7 [14], which is roughly similar to our present results.…”

“…After that, the samples were annealed at 673 K for 100 h in low vacuum atmospheres of several Pa [11]. Details of the synthesis procedures were described elsewhere [7,8]. The actual compositions of the specimens measured by the electron probe micro analyzer (EPMA) were Fe 1.10 Se 0.28 Te 0.72 (x = 0.7), Fe 1.05 Se 0.38 Te 0.62 (x = 0.6), and Fe 1.08 Se 0.41 Te 0.59 (x = 0.5) [7] (hereafter, we denote as FeSe 1Àx Te x ).…”

“…Details of the synthesis procedures were described elsewhere [7,8]. The actual compositions of the specimens measured by the electron probe micro analyzer (EPMA) were Fe 1.10 Se 0.28 Te 0.72 (x = 0.7), Fe 1.05 Se 0.38 Te 0.62 (x = 0.6), and Fe 1.08 Se 0.41 Te 0.59 (x = 0.5) [7] (hereafter, we denote as FeSe 1Àx Te x ). The STM equipment used in this experiment was commercially supplied system (Omicron LT-UHV-STM) with upgraded modifications [12].…”

“…Hence, the 11-type is very suitable for the scanning tunneling microscopy/spectroscopy (STM/STS) studies, which provide direct information on the electronic density of states. For understanding the superconductivity mechanism, the superconducting (SC) gap is a very important quantity [4][5][6][7][8]. However, the gap structures observed by the STS measurements are usually obscured with a few exceptions [6,9].…”