Anomalous isotope effect in iron-based superconductors

Abstract

The role of electron-phonon interactions in iron-based superconductor is currently under debate with conflicting experimental reports on the isotope effect. To address this important issue, we employ the renormalization-group method to investigate the competition between electron-electron and electron-phonon interactions in these materials. The renormalization-group analysis shows that the ground state is a phonon-dressed unconventional superconductor: the dominant electronic interactions account for pairing mechanism while electron-phonon interactions are subdominant. Because of the phonon dressing, the isotope effect of the critical temperature can be normal or reversed, depending on whether the retarded intra- or inter-band interactions are altered upon isotope substitutions. The connection between the anomalous isotope effect and the unconventional pairing symmetry is discussed at the end.

Study of the Isotope Effects of Novel Superconducting LaH<sub>10</sub>-LaD<sub>10</sub> and H<sub>3</sub>S-D<sub>3</sub>S Systems

“…The value of the Coulomb potential μ * = 0.1 was assumed. For R3m structure, the values of α from Equation (8) are almost constant with the compressed pressure values and equal to 0.49 as shown in Table 2. On the other hand, when using the Equation (11) in calculating the values of α, it was noticed that the average value of α was equal to Table 2.…”

“…Such an effect can be considered as the hallmark of phonon-induced superconductivity in conventional superconductors. Inspired by anomalous isotope effect in iron-based superconductors [8], it is helpful to investigate the competitions between electron-electron and electron-phonon interaction. While phonons are central in explaining the mechanism of conventional superconductors, their role should be taken into accounts for explaining high T c superconductors, as well.…”

“…The Coulomb pseudopotential μ * = 0.2 was assumed. The isotope coefficient α was determined by using the EM-model, Equation(8) and the GK-model, Equation(11). Both models mainly depend on the values of the critical temperatures, but new variables, acoustic phonon frequency and the acoustic coupling coefficient were added in the GK model.…”

Role of nematicity in controlling spin fluctuations and superconducting Tc in bulk FeSe

“…The precise nature of the boson that is a Cooper pair in FeSe is debated, though generally the primary mechanism is believed to be magnetic fluctuations. This is supported by the observation of a negligible isotope effect in bulk FeSe [34]. Since the normal phase just above critical temperature T c = 8 K is orthorhombic, there has been much speculation that nematicity can be the mechanism driving superconductivity, though heavily debated.…”

Natural Extracts for Antibacterial Applications

“…The earliest natural extracts were obtained from plants, especially vegetal extracts with antibacterial properties, [33][34][35] a common practice for millennia. For example, powders or extracts of allium, [36,37] garlic, [38,39] ginger, [40,41] carica papaya leaf, [42,43] onions, [44,45] mint, [46] bay leaf, black pepper, coriander (seed and leaf), cumin, mustard, onion, and turmeric [47] all can function as fungicides capable of treating diseases. Most importantly, most extracts have excellent biocompatibility and nontoxicity, but can combat pathogenic bacteria.…”