scholarly journals Electronic and Lattice Dynamical Properties of the Iron-Based Superconductors LiFeAs and NaFeAs

2010 ◽  
Vol 2010 ◽  
pp. 1-6 ◽  
Author(s):  
R. A. Jishi ◽  
H. M. Alyahyaei
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Superconducting Transition ◽  
Phonon Coupling ◽  
Functional Theory ◽  
Iron Based Superconductors ◽  
Electron Phonon Coupling ◽  
Dynamical Properties ◽  
Iron Based ◽  
Conventional Type

The electronic structure and lattice vibrational frequencies of the newly discovered superconductors, LiFeAs and NaFeAs, are calculated within density functional theory. We show that, in the vicinity of the Fermi energy, the density of states is dominated by contributions from Fe 3d states. We also calculate the electron-phonon coupling strength and show that it is too weak to account for the observed values of the superconducting transition temperatures. This seems to indicate that the iron-based superconductors are not of the conventional type.

scholarly journals Singlet and triplet excitons and charge polarons in cycloparaphenylenes: a density functional theory study

2015 ◽  
Vol 17 (22) ◽  
pp. 14613-14622 ◽  
Author(s):  
Jin Liu ◽  
Lyudmyla Adamska ◽  
Stephen K. Doorn ◽  
Sergei Tretiak
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Spatial Localization ◽  
Molecular Geometry ◽  
Density Functional Theory Study ◽  
Phonon Coupling ◽  
Functional Theory ◽  
Electron Phonon Coupling ◽  
Electronic Wavefunction ◽  
Triplet Excitons

Upon excitation, electron–phonon coupling leads to spatial localization of the electronic wavefunction and distortion of molecular geometry.

Superconductivity of lithium-doped hydrogen under high pressure

2014 ◽  
Vol 70 (2) ◽  
pp. 104-111 ◽  
Author(s):  
Yu Xie ◽  
Quan Li ◽  
Artem R. Oganov ◽  
Hui Wang
Keyword(s):  
Density Functional Theory ◽  
High Pressure ◽  
Fermi Level ◽  
Density Of States ◽  
Lattice Dynamics ◽  
Density Functional ◽  
Phonon Coupling ◽  
Critical Temperatures ◽  
Functional Theory ◽  
Electron Phonon Coupling

The high-pressure lattice dynamics and superconductivity of newly proposed lithium hydrides (LiH2, LiH6and LiH8) have been extensively studied using density functional theory. The application of the Allen–Dynes modified McMillan equation and electron–phonon coupling calculations show that LiH6and LiH8are superconductors with critical temperatures (Tc) of 38 K at 150 GPa for LiH6and 31 K at 100 GPa for LiH8, while LiH2is not a superconductor. TheTcof LiH6increases rapidly with pressure and reaches 82 K at 300 GPa due to enhancement of the electron–phonon coupling and the increased density of states at the Fermi level, while theTcof LiH8remains almost constant.

scholarly journals Strong enhancement of magnetic order from bulk to stretched monolayer FeSe as Hund’s metals

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Chang-Youn Moon
Keyword(s):  
Density Functional ◽  
Magnetic Order ◽  
Mean Field Theory ◽  
Mean Field ◽  
Comprehensive Understanding ◽  
Functional Theory ◽  
Iron Based Superconductors ◽  
Magnetic Orders ◽  
Spatial Isolation ◽  
Iron Based

Abstract Despite of the importance of magnetism in possible relation to other key properties in iron-based superconductors, its understanding is still far from complete especially for FeSe systems. On one hand, the origin of the absence of magnetic orders in bulk FeSe is yet to be clarified. On the other hand, it is still not clear how close monolayer FeSe on SrTiO3, with the highest transition temperature among iron-based superconductors, is to a magnetic instability. Here we investigate magnetic properties of bulk and monolayer FeSe using dynamical mean-field theory combined with density-functional theory. We find that suppressed magnetic order in bulk FeSe is associated with the reduction of interorbital charge fluctuations, an effect of Hund’s coupling, enhanced by a larger crystal-field splitting. Meanwhile, spatial isolation of Fe atoms in expanded monolayer FeSe leads into a strong magnetic order, which is completely destroyed by a small electron doping. Our work provides a comprehensive understanding of the magnetic order in iron-based superconductors and other general multi-orbital correlated systems as Hund’s metals.

scholarly journals Higher superconducting transition temperature by breaking the universal pressure relation

2019 ◽  
Vol 116 (6) ◽  
pp. 2004-2008 ◽  
Author(s):  
Liangzi Deng ◽  
Yongping Zheng ◽  
Zheng Wu ◽  
Shuyuan Huyan ◽  
Hung-Cheng Wu ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
High Temperature ◽  
Transition Temperature ◽  
Density Functional ◽  
High Temperature Superconductors ◽  
Density Functional Theory Calculations ◽  
Universal Relation ◽  
Superconducting Transition ◽  
Functional Theory ◽  
A Charge

By investigating the bulk superconducting state via dc magnetization measurements, we have discovered a common resurgence of the superconducting transition temperatures (Tcs) of the monolayer Bi2Sr2CuO6+δ(Bi2201) and bilayer Bi2Sr2CaCu2O8+δ(Bi2212) to beyond the maximum Tcs (Tc-maxs) predicted by the universal relation between Tcand doping (p) or pressure (P) at higher pressures. The Tcof underdoped Bi2201 initially increases from 9.6 K at ambient to a peak at 23 K at 26 GPa and then drops as expected from the universal Tc-P relation. However, at pressures above 40 GPa, Tcrises rapidly without any sign of saturation up to 30 K at 51 GPa. Similarly, the Tcfor the slightly overdoped Bi2212 increases after passing a broad valley between 20 and 36 GPa and reaches 90 K without any sign of saturation at 56 GPa. We have, therefore, attributed this Tcresurgence to a possible pressure-induced electronic transition in the cuprate compounds due to a charge transfer between the Cu 3dx2−y2and the O 2pbands projected from a hybrid bonding state, leading to an increase of the density of states at the Fermi level, in agreement with our density functional theory calculations. Similar Tc-P behavior has also been reported in the trilayer Br2Sr2Ca2Cu3O10+δ(Bi2223). These observations suggest that higher Tcs than those previously reported for the layered cuprate high-temperature superconductors can be achieved by breaking away from the universal Tc-P relation through the application of higher pressures.

ELECTRONIC AND DYNAMICAL PROPERTIES OF MgB2 AND RELATED COMPOUNDS

2002 ◽  
Vol 16 (11n12) ◽  
pp. 1563-1569 ◽  
Author(s):  
G. PROFETA ◽  
A. CONTINENZA ◽  
F. BERNARDINI ◽  
G. SATTA ◽  
S. MASSIDDA
Keyword(s):  
Density Functional Theory ◽  
Local Density Approximation ◽  
Density Functional ◽  
Local Density ◽  
Density Approximation ◽  
Superconducting Properties ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Dynamical Properties ◽  
Related Compounds

We report a detailed study of the electronic and dynamical properties of MgB2 , BeB2 and of the AlMgB4 superlattice, within the local density approximation to the density functional theory. On the basis of our results we discuss the superconducting properties of these systems, and point to the high T c in MgB2 as a fortunate combination of events.

ELECTRONIC STRUCTURE OF K0.8Fe2Se2 FROM DENSITY FUNCTIONAL THEORY GW METHOD SIMULATION

2013 ◽  
Vol 27 (15) ◽  
pp. 1362017
Author(s):  
LIUXI TAN ◽  
RUI GUO ◽  
SHIZHONG YANG ◽  
EBRAHIM KHOSRAVI ◽  
GUANG-LIN ZHAO ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Electric Dipole ◽  
First Principles ◽  
Density Functional ◽  
Lattice Distortion ◽  
The Novel ◽  
Functional Theory ◽  
Density Analysis ◽  
Iron Based

First principles density functional theory — based (GW) method — was used to simulate the electronic structure of the novel iron-based superconductor K 0.8 Fe 2 Se 2. The calculated band gap of K 0.8 Fe 2 Se 2 at the Γ point is 0.15 eV, which is significantly lower than the 0.61 eV of vacancy free crystal KFe 2 Se 2. The d-orbital of Fe atom is overlapped with the p-orbital of Se atom. Charge density analysis shows strong lattice distortion and vacancy related electric dipole and quadruple near the K vacancy. The reflectivity is anisotropic in three coordinate directions.

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