Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userUnderlying mechanism of charge transfer in Li-doped MgH$_{16}$ at high pressure
183
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
A lithium-doped magnesium hydride Li$_2$MgH$_{16}$ was recently reported [Y. Sun $et$ $al$., Phys. Rev. Lett. {bf 123}, 097001 (2019)] to exhibit the highest ever predicted superconducting transition temperature $T_{rm c}$ under high pressure. Based on first-principles density-functional theory calculations, we reveal that the Li dopants locating in the pyroclore lattice sites give rise to the excess electrons distributed in interstitial regions. Such loosely bound anionic electrons are easily captured to stabilize a clathrate structure consisting of H cages. This addition of anionic electrons to H cages enhances the H-derived electronic density of states at the Fermi level, thereby leading to a high-$T_{rm c}$ superconductivity. We thus propose that the electride nature of Li dopants is an essential ingredient in the charge transfer between Li dopants and H atoms. Our findings offer a deeper understanding of the underlying mechanism of charge transfer in Li$_2$MgH$_{16}$ at high pressure.
rate research
Read More
The Fermi surface topology of $cI$16 Li at high pressures is studied using a recently developed first-principles unfolding method. We find the occurrence of a Lifshitz transition at $sim$43 GPa, which explains the experimentally observed anomalous onset of the superconductivity enhancement toward lowered pressure. Furthermore we identify, in comparison with previous reports, additional nesting vectors that contribute to the $cI$16 structural stability. Our study highlights the importance of three-dimensional unfolding analyses for first-principles studies of Fermi surface topologies and instabilities in general.
We investigate the possibility of achieving high-temperature superconductivity in hydrides under pressure by inducing metallization of otherwise insulating phases through doping, a path previously used to render standard semiconductors superconducting at ambient pressure. Following this idea, we study H$_2$O, one of the most abundant and well-studied substances, we identify nitrogen as the most likely and promising substitution/dopant. We show that for realistic levels of doping of a few percent, the phase X of ice becomes superconducting with a critical temperature of about 60 K at 150GPa. In view of the vast number of hydrides that are strongly covalent bonded, but that remain insulating until rather large pressures, our results open a series of new possibilities in the quest for novel high-temperature superconductors.
This work investigates the high-pressure structure of freestanding superconducting ($T_{c}$ = 4.3,K) boron doped diamond (BDD) and how it affects the electronic and vibrational properties using Raman spectroscopy and x-ray diffraction in the 0-30,GPa range. High-pressure Raman scattering experiments revealed an abrupt change in the linear pressure coefficients and the grain boundary components undergo an irreversible phase change at 14,GPa. We show that the blue shift in the pressure-dependent vibrational modes correlates with the negative pressure coefficient of $T_{c}$ in BDD. The analysis of x-ray diffraction data determines the equation of state of the BDD film, revealing a high bulk modulus of $B_{0}$=510$pm$28,GPa. The comparative analysis of high-pressure data clarified that the sp$^{2}$ carbons in the grain boundaries transform into hexagonal diamond.
In this work, we show that the same theoretical tools that successfully explain other hydrides systems under pressure seem to be at odds with the recently claimed conventional room temperature superconductivity of the carbonaceous sulfur hydride. We support our conclusions with I) the absence of a dominant low-enthalpy stoichiometry and crystal structure in the ternary phase diagram. II) Only the thermodynamics of C-doping phases appears to be marginally competing in enthalpy against H$_3$S. III) Accurate results of the transition temperature given by ab initio Migdal-Eliashberg calculations differ by more than 110 K to recently theoretical claims explaining the high-temperature superconductivity in carbonaceous-hydrogen sulfide. A novel mechanism of superconductivity or a breakdown of current theories in this system is possibly behind the disagreement.
Polycrystalline Eu0.5La0.5BiS2F was synthesized by solid state reaction which crystallizes in the tetragonal CeOBiS2 structure (P4/nmm). We report here enhancement of Tc to 2.2 K in Eu0.5La0.5BiS2F (by electron doping in EuBiS2F with Tc ~ 0.3 K). Eu0.5La0.5BiS2F is semiconducting down to 3 K and an onset of superconductivity is seen at 2.2 K at ambient pressure. Upon application of pressure the Tc could be enhanced upto 10 K. Step like features are seen in the resistivity curves at intermediate pressures (0.5 - 1 GPa) which hints towards the possible existence of two phases with different Tc. At a pressure above 1.38GPa, the Tconset remains invariant at 10 K but the Tc(r{ho}=0) is increased to above 8.2 K. There is a possible transformation from a low Tc phase to a high Tc phase by application of pressure.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
