اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSe content $x$ dependence of electron correlation strength in Fe$_{1+y}$Te$_{1-x}$Se$_{x}$
204
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
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 behaviors, we have performed ARPES studies of Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ ($x$ = 0, 0.1, 0.2, and 0.4). The obtained mass renormalization factors for different energy bands are qualitatively consistent with DFT + DMFT calculations. Our results provide evidence for strong orbital dependence of mass renormalization, and systematic data which help us to resolve inconsistencies with other experimental data. The unusually strong orbital dependence of mass renormalization in Te-rich Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ arises from the dominant contribution to the Fermi surface of the $d_{xy}$ band, which is the most strongly correlated and may contribute to the suppression of superconductivity.
قيم البحث
اقرأ أيضاً
Using angle-resolved photoemission spectroscopy we have studied the low-energy electronic structure and the Fermi surface topology of Fe$_{1+y}$Te$_{1-x}$Se$_x$ superconductors. Similar to the known iron pnictides we observe hole pockets at the cente
r and electron pockets at the corner of the Brillouin zone (BZ). However, on a finer level, the electronic structure around the $Gamma$- and $Z$-points in $k$-space is substantially different from other iron pnictides, in that we observe two hole pockets at the $Gamma$-point, and more interestingly only one hole pocket is seen at the $Z$-point, whereas in $1111$-, $111$-, and $122$-type compounds, three hole pockets could be readily found at the zone center. Another major difference noted in the Fe$_{1+y}$Te$_{1-x}$Se$_x$ superconductors is that the top of innermost hole-like band moves away from the Fermi level to higher binding energy on going from $Gamma$ to $Z$, quite opposite to the iron pnictides. The polarization dependence of the observed features was used to aid the attribution of the orbital character of the observed bands. Photon energy dependent measurements suggest a weak $k_z$ dispersion for the outer hole pocket and a moderate $k_z$ dispersion for the inner hole pocket. By evaluating the momentum and energy dependent spectral widths, the single-particle self-energy was extracted and interestingly this shows a pronounced non-Fermi liquid behaviour for these compounds. The experimental observations are discussed in context of electronic band structure calculations and models for the self-energy such as the spin-fermion model and the marginal-Fermi liquid.
We present a systematic study of the nematic fluctuations in the iron chalcogenide superconductor Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ ($0 leq x leq 0.53$) using the elastoresistivity technique. Near $x = 0$, in proximity to the double-stripe magnetic order
of Fe$_{1+y}$Te, a diverging $B_{1g}$ nematic susceptibility is observed. Upon increasing $x$, despite the absence of magnetic order, the $B_{2g}$ nematic susceptibility increases and becomes dominant, closely following the strength of the $(pi, pi)$ spin fluctuations. Over a wide range of compositions ($0.17 leq x leq 0.53$), while the $B_{2g}$ nematic susceptibility follows a Curie temperature dependence (with zero Weiss temperature) at low temperatures, it shows deviations from Curie-Weiss behavior for temperatures higher than $50K$. This is the opposite of what is observed in typical iron pnictides, where Curie-Weiss deviations are seen at low temperatures. We attribute this unusual temperature dependence to a loss of coherence of the $d_{xy}$ orbital, which is supported by our theoretical calculations. Our results highlight the importance of orbital differentiation on the nematic properties of iron-based materials.
We report an investigation of the lattice dynamical properties in a range of Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ compounds, with special emphasis on the c-axis polarized vibration of Fe with B$_{1g}$ symmetry, a Raman active mode common to all families of F
e-based superconductors. We have carried out a systematic study of the temperature dependence of this phonon mode as a function of Se $x$ and excess Fe $y$ concentrations. In parent compound Fe$_{1+y}$Te, we observe an unconventional broadening of the phonon between room temperature and magnetic ordering temperature $T_N$. The situation smoothly evolves towards a regular anharmonic behavior as Te is substituted for Se and long range magnetic order is replaced by superconductivity. Irrespective to Se contents, excess Fe is shown to provide an additional damping channel for the B$_{1g}$ phonon at low temperatures. We performed Density Functional Theory (DFT) ab-initio calculations within the local density approximation (LDA) to calcuate the phonon frequencies including magnetic polarization and Fe non-stoichiometry in the Virtual Crystal Approximation (VCA). We obtained a good agreement with the measured phonon frequencies in the Fe-deficient samples, while the effects of Fe excess are poorly reproduced. This may be due to excess Fe-induced local magnetism and low energy magnetic fluctuations that can not be treated accurately within these approaches. As recently revealed by neutron scattering and $mu$-SR studies, these phenomena occur in the temperature range where anomalous decay of the B$_{1g}$ phonon is observed, and suggests a peculiar coupling of this mode with local moments and spin fluctuations in Fe$_{1+y}$Te$_{1-x}$Se$_{x}$.
We compare the superconducting phase-diagram under high magnetic fields (up to $H = 45$ T) of Fe$_{1+y}$Se$_{0.4}$Te$_{0.6}$ single crystals originally grown by the Bridgman-Stockbarger (BRST) technique, which were annealed to display narrow supercon
ducting transitions and the optimal transition temperature $T_c gtrsim 14$ K, with the diagram for samples of similar stoichiometry grown by the traveling-solvent floating-zone technique as well as with the phase-diagram reported for crystals grown by a self-flux method. We find that the so-annealed samples tend to display higher ratios $H_{c2}/T_c$, particularly for fields applied along the inter-planar direction, where the upper critical field $H_{c2}(T)$ exhibits a pronounced downward curvature followed by saturation at lower temperatures $T$. This last observation is consistent with previous studies indicating that this system is Pauli limited. An analysis of our $H_{c2}(T)$ data using a multiband theory suggests the emergence of the Farrel-Fulde-Larkin-Ovchnikov state at low temperatures. A detailed structural x-ray analysis, reveals no impurity phases but an appreciable degree of mosaicity in as-grown BRST single-crystals which remains unaffected by the annealing process. Energy-dispersive x-ray analysis showed that the annealed samples have a more homogeneous stoichiometric distribution of both Fe and Se with virtually the same content of interstitial Fe as the non-annealed ones. Thus, we conclude that stoichiometric disorder, in contrast to structural disorder, is detrimental to the superconducting phase diagram of this series under high magnetic fields. Finally, a scaling analysis of the fluctuation conductivity in the superconducting critical regime, suggests that the superconducting fluctuations have a two-dimensional character in this system.
Neutron scattering has played a significant role in characterizing magnetic and structural correlations in Fe$_{1+y}$Te$_{1-x}$Se$_x$ and their connections with superconductivity. Here we review several key aspects of the physics of iron chalcogenide
superconductors where neutron studies played a key role. These topics include the phase diagram of Fe$_{1+y}$Te$_{1-x}$Se$_{x}$, where the doping-dependence of structural transitions can be understood from a mapping to the anisotropic random field Ising model. We then discuss orbital-selective Mott physics in the Fe chalcogenide series, where temperature-dependent magnetism in the parent material provided one of the earliest cases for orbital-selective correlation effects in a Hunds metal. Finally, we elaborate on the character of local magnetic correlations revealed by neutron scattering, its dependence on temperature and composition, and the connections to nematicity and superconductivity.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
