ABSTRACT
In this work, we resolve conflicting experimental and theoretical findings related to the dynamical stability and superconducting properties of [Formula: see text]-LuH3, which was recently suggested as the parent phase harboring room-temperature superconductivity at near-ambient pressures. Including temperature and quantum anharmonic lattice effects in our calculations, we demonstrate that the theoretically predicted structural instability of the [Formula: see text] phase near ambient pressures is suppressed for temperatures above 200 K. We provide a p-T phase diagram for stability up to pressures of 6 GPa, where the required temperature for stability is reduced to T > 80 K. We also determine the superconducting critical temperature Tc of [Formula: see text]-LuH3 within the Migdal-Eliashberg formalism, using temperature- and quantum-anharmonically-corrected phonon dispersions, finding that the expected Tc for electron-phonon mediated superconductivity is in the range of 50-60 K, i.e., well below the temperatures required to stabilize the lattice. When considering moderate doping based on rigidly shifting the Fermi level, Tc decreases for both hole and electron doping. Our results thus provide evidence that any observed room-temperature superconductivity in pure or doped [Formula: see text]-LuH3, if confirmed, cannot be explained by a conventional electron-phonon mediated pairing mechanism.
ABSTRACT
Motivated by the recent report of room-temperature superconductivity at near-ambient pressure in N-doped lutetium hydride, we performed a comprehensive, detailed study of the phase diagram of the Lu-N-H system, looking for superconducting phases. We combined ab initio crystal structure prediction with ephemeral data-derived interatomic potentials to sample over 200,000 different structures. Out of the more than 150 structures predicted to be metastable within ~50 meV from the convex hull we identify 52 viable candidates for conventional superconductivity, for which we computed their superconducting properties from Density Functional Perturbation Theory. Although for some of these structures we do predict a finite superconducting Tc, none is even remotely compatible with room-temperature superconductivity as reported by Dasenbrock et al. Our work joins the broader community effort that has followed the report of near-ambient superconductivity, confirming beyond reasonable doubt that no conventional mechanism can explain the reported Tc in Lu-N-H.
ABSTRACT
We present structural, electrical, and thermoelectric potential measurements on high-quality single crystals of ZrTe1.8 grown from isothermal chemical vapor transport. These measurements show that the Te-deficient ZrTe1.8, which forms the same structure as the nonsuperconducting ZrTe2, is superconducting below 3.2 K. The temperature dependence of the upper critical field (H c2) deviates from the behavior expected in conventional single-band superconductors, being best described by an electron-phonon two-gap superconducting model with strong intraband coupling. For the ZrTe1.8 single crystals, the Seebeck potential measurements suggest that the charge carriers are predominantly negative, in agreement with the ab initio calculations. Through first-principles calculations within DFT, we show that the slight reduction of Te occupancy in ZrTe2 unexpectedly gives origin to density of states peaks at the Fermi level due to the formation of localized Zr-d bands, possibly promoting electronic instabilities at the Fermi level and an increase at the critical temperature according to the standard BCS theory. These findings highlight that the Te deficiency promotes the electronic conditions for the stability of the superconducting ground state, suggesting that defects can fine-tune the electronic structure to support superconductivity.
ABSTRACT
Salinity is a major issue affecting photosynthesis and crop production worldwide. High salinity induces both osmotic and ionic stress in plant tissues as a result of complex interactions among morphological, physiological, and biochemical processes. Salinity, in turn, can provoke inactivation of some enzymes in the Calvin-Benson cycle and therefore affect the fine adjustment of electron transport in photosystem I and carbon related reactions. Here, we used three contrasting Jatropha curcas genotypes namely CNPAE183 (considered tolerant to salinity), CNPAE218 (sensible), and JCAL171 (intermediate) to understand salinity responses. By performing a long-term (12 months) experiment in land conditions, we investigated distinct mechanisms used by J. curcas to cope with threatening salinity effects by analyzing gas exchange, mineral nutrition and metabolic responses. First, our results highlighted the plasticity of stomatal development and density in J. curcas under salt stress. It also demonstrated that the CNPAE183 presented higher salt-tolerance whereas CNPAE218 displayed a more sensitive salt-tolerance response. Our results also revealed that both tolerance and sensitivity to salinity were connected with an extensive metabolite reprogramming in the Calvin-Benson cycle and Tricarboxylic Acid cycle intermediates with significant changes in amino acids and organic acids. Collectively, these results indicate that the CNPAE183 and CNPAE218 genotypes demonstrated certain characteristics of salt-tolerant-like and salt-sensitive-like genotypes, respectively. Overall, our results highlight the significance of metabolites associated with salt responses and further provide a useful selection criterion in during screening for salt tolerance in J. curcas in breeding programmes.
