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تسجيل مستخدم جديدThermoelectric response of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$: evidence for strong correlation and low carrier density
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We present a study of the Seebeck and Nernst coefficients of Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ extended up to 28 T. The large magnitude of the Seebeck coefficient in the optimally doped sample tracks a remarkably low normalized Fermi temperature, which, like other correlated superconductors, is only one order of magnitude larger than T$_c$. We combine our data with other experimentally measured coefficients of the system to extract a set of self-consistent parameters, which identify Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ as a low-density correlated superconductor barely in the clean limit. The system is subject to strong superconducting fluctuations with a sizeable vortex Nernst signal in a wide temperature window.
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It has been clarified that bulk superconductivity in Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ can be induced by annealing in an appropriate atmosphere to remove the harmful effects of excess iron. In order to clarify the details of the annealing process, we st
udied the changes in the physical properties and reaction products of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ annealed in pnictogen (P, As, Sb) atmospheres. Crystals annealed in a pnictogen atmosphere show bulk superconductivity and the values of $T_{c}$ and $J_{c}$ are about $14~$K and 2-4 $times 10{^5}~$A/cm$^2$ ($2~$K, self-field), respectively. It is also found that the reaction rate increases with the increase in the saturated vapor pressure of the pnictogen. Unexpectedly, the reaction products of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ after annealing in a P atmosphere mainly consist of FeTe$_2$. In addition, the amount of P required to obtain the optimal $T_{c}$ is much smaller than the amount of excess iron, which is similar to the case of oxygen annealing. P, oxygen, and to some extent As could serve as catalysts to form FeTe$_2$ to remove excess iron.
We study Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ multi-band superconductor with $T_c=14$K by polarization-resolved Raman spectroscopy. Deep in the superconducting state, we detect pair-breaking excitation at 45cm$^{-1}$ ($2Delta=5.6$meV) in the $XY$($B_{2g}$)
scattering geometry, consistent with twice of the superconducting gap energy (3 meV) revealed by ARPES on the hole-like Fermi pocket with $d_{xz}/d_{yz}$ character. We analyze the superconductivity induced phonon self-energy effects for the $B_{1g}$(Fe) phonon and estimate the electron-phonon coupling constant $lambda^Gamma approx 0.026$, which is insufficient to explain superconductivity with $T_c=14$K.
Iron chalcogenide Fe(Te,Se) attracted much attention due to its simple structure, which is favorable for probing the superconducting mechanism. Its less toxic nature compared with iron arsenides is also advantageous for applications of iron-based sup
erconductors. By intercalating spacer layers, superconducting transition temperature has been raised over 40 K. On the other hand, the presence of excess Fe is almost unavoidable in Fe(Te,Se) single crystals, which hinders the appearance of bulk superconductivity and causes strong controversies over its fundamental properties. Here we report a systematical study of O$_2$-annealing dynamics in Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ by controlling the amount of O$_2$, annealing temperature, and time. Bulk superconductivity can be gradually induced by increasing the amount of O$_2$ and annealing time at suitable temperatures. The optimally annealed crystals can be easily obtained by annealing with ~ 1.5% molar ratio of oxygen at 400 $^{circ}$C for more than 1 hour. Superconductivity was witnessed to evolve mainly from the edge of the crystal to the central part. After the optimal annealing, the complete removal of excess Fe was demonstrated via STM measurements. Some fundamental properties were recharacterized and compared with those of as-grown crystals to discuss the influence of excess Fe.
We report a systematic study of the superconducting (SC) and normal-state anisotropy of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ single crystals with controlled amounts of excess Fe ($y$ = 0, 0.07, and 0.14). The SC state anisotropy $gamma_{H}$ was obtained by
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The iron chalcogenide Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ on the Te-rich side is known to exhibit the strongest electron correlations among the Fe-based superconductors, and is non-superconducting for $x$ < 0.1. In order to understand the origin of such beh
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