Based on first-principle FLAPW-GGA calculations, we have investigated the systematic trends in structural and electronic properties of a newly discovered group of ThCr2Si2-like arsenides: SrRu2As2, BaRu2As2, SrRh2As2 and BaRh2As2. Our results show that the replacement of an alkaline earth metal (Sr - Ba) and 4d metal (Ru - Rh) leads to various types of anisotropic deformations of the crystal structure caused by strong anisotropy of inter-atomic bonds.
The band structure, density of states and Fermi surfaces have been evaluated and discussed. Appreciable changes in the near-Fermi bands and the Fermi surface topology found as going from (Sr,Ba)Ru2As2 to (Sr,Ba)Rh2As2 reflect the growth of the 3D-like type of dispersion for these systems, which is accompanied by an increase in the near-Fermi density of states. The inter-atomic bonding in (Sr,Ba)(Ru,Rh)2As2 phases adopts a complex anisotropic character, where the bonding in [(Ru,Rh)2As2] blocks is of a mixed metallic-ionic-covalent type whereas between adjacent [(Ru,Rh)2As2] blocks and (Sr,Ba) atomic sheets, ionic interactions emerge; thus these systems may be classified as ionic metals.
LiB, a predicted layered compound analogous to the MgB$_2$ superconductor, has been recently synthesized via cold compression and quenched to ambient pressure, yet its superconducting properties have not been measured. According to prior isotropic superconductivity calculations, the critical temperature ($T_{\rm{c}}$) was expected to be only 10$-$15 K. Using the anisotropic Migdal-Eliashberg formalism, we show that the $T_{\rm{c}}$ may actually exceed 32 K. Our analysis of the contribution from different electronic states helps explain the detrimental effect of pressure and doping on the compo…
We applied $ab$ $initio$ phonon analysis to layered titanium-oxypnictides, Na$_2$Ti$_2Pn_2$O ($Pn$ = As, Sb), and found a clear contrast between the cases with lighter/heavier pnictogen in comparisons with experiments. The result completely explains the experimental structure, $C$2/$m$ for $Pn$ = As, within the conventional electron-phonon framework, while there arise discrepancies when the pnictogen gets heavier, being in the same trend for the BaTi$_2Pn_2$O ($Pn$ = As, Sb, Bi) case. The fact implies a systematic dependence on pnictogen to tune the mechanism of the phase transition and superc…
High magnetic field transport measurements and ab initio calculations on the layered superconductor TaSe3 have provided compelling evidences for the existence of a three-dimensional strong topological insulator state. Longitudinal magnetotransport measurements up to ~ 33 T unveiled striking Shubnikov-de Hass oscillations with two fundamental frequencies at 100 T and 175 T corresponding to a nontrivial electron Fermi pocket at the B point and a nontrivial hole Fermi pocket at the Γ point respectively in the Brillouin zone. However, calculations revealed one more electron pocket at the B point, …
We explore the layered palladium oxides La$_2$PdO$_4$, LaPdO$_2$ and La$_4$Pd$_3$O$_8$ via ab initio calculations. La$_2$PdO$_4$, being low spin $d^8$, is quite different from its high spin nickel analog. Hypothetical LaPdO$_2$, despite its $d^9$ configuration, has a paramagnetic electronic structure very different from cuprates. On the other hand, the hypothetical trilayer compound La$_4$Pd$_3$O$_8$ ($d^{8.67}$) is more promising in that its paramagnetic electronic structure is very similar to that of overdoped cuprates. But even in the $d^9$ limit (achieved by partial substitution of La with…
In this work we probe the possibility of high-temperature conventional superconductivity in the boron-carbon system, using ab-initio screening. A database of 320 metastable structures with fixed composition (50$\%$/50$\%$) is generated with the Minima-Hopping method, and characterized with electronic and vibrational descriptors. Full electron-phonon calculations on sixteen representative structures allow to identify general trends in $T_{\textrm{c}}$ across and within the four families in the energy landscape, and to construct an approximate $T_{\textrm{c}}$ predictor, based on transparently i…
The intriguing coexistence of the charge density wave (CDW) and superconductivity in SrPt$_2$As$_2$ and LaPt$_2$Si$_2$ has been investigated based on the {\it ab initio} density functional theory band structure and phonon calculations. We have found that the local split distortions Pt atoms in the [As-Pt-As] layers play an essential role in driving the five-fold supercell CDW instability as well as the phonon softening instability in SrPt$_2$As$_2$. By contrast, the CDW and phonon softening instabilities in LaPt$_2$Si$_2$ occur without split distortions of Pt atoms, indicating that the driving…
SnTaS2 is a recently discovered layered semimetal exhibiting type-II low transition temperature superconductivity. Except some superconductivity related parameters, most of the physical properties, namely, elastic, mechanical, bonding, phonon dispersion, acoustic, thermophysical, and optical properties of SnTaS2 are unexplored till now. In this study, we have investigated these hitherto unexplored properties of SnTaS2 for the first time employing density functional theory (DFT) based first-principles method. SnTaS2 is a mechanically stable, elastically anisotropic compound with strongly layere…
Layered magnetic transition-metal thiophosphate NiPS3 has unique two-dimensional (2D) magnetic properties and electronic behavior. The electronic band structure and corresponding magnetic state are expected to sensitive to the interlayer interaction, which can be tuned by external pressure. Here, we report an insulator-metal transition accompanied with magnetism collapse during the 2D-3D crossover in structure induced by hydrostatic pressure. A two-stage phase transition from monoclinic (C2=m) to trigonal (P-31m) lattice is identified by ab initio simulation and confirmed by high-pressure XRD …
Besides the chemical constituents, it is the lattice geometry that controls the most important material properties. In many interesting compounds, the arrangement of elements leads to pronounced anisotropies, which reflect into a varying degree of quasi two-dimensionality of their low-energy excitations. Here, we start by classifying important families of correlated materials according to a simple measure for the tetragonal anisotropy of their ab initio electronic (band) structure. Second, we investigate the impact of a progressively large anisotropy in driving the non-locality of many-body ef…
General trends of electronic structures, superconducting pairing, and magnetic correlations in the Ruddlesden-Popper nickelate $m$-layered superconductors La$_{m+1}$Ni$_{m}$O$_{3m+1}$
