arXiv subjects

Armin Sahinovic

Publications and source records attributed to Armin Sahinovic.

4 recordsLinked to original sources

arXiv2026

Delafossites as an unexpected competing phase to infinite-layer oxides

Motivated by the discovery of superconductivity in Sr-doped infinite-layer nickelate films on SrTiO$_3$(001), we explore the broader landscape of $AB$O$_2$ oxides through comprehensive high-throughput first-principles simulations. Specifically, delafossites and their ordered rock-salt (111) variants stand out as intriguing layered oxides that share the infinite-layer $AB$O$_2$ stoichiometry and simultaneously retain a perovskite-like octahedral motif. This positions them as a unique structural bridge between these two phases and as promising candidates for novel correlated electronic states. We compile a phase diagram that compares the relative stability of these four distinct oxides across the periodic table. Surprisingly, we find that the delafossite structure rivals the infinite-layer phase in thermodynamic stability for the nickelates, and even more for the recently suggested palladate and platinate analogs. Comparison of the respective electronic structures reveals that the delafossite compounds, which we find to be characterized by reversed cation order, exhibit a strongly $d_{z^2}$-dominated Fermi surface, in stark contrast to the $d_{x^2-y^2}$ character observed in the infinite-layer phases. Among all candidates, the La-Ni combination stands out as a thermodynamic optimum for stabilizing the infinite-layer motif. Furthermore, we show that hole doping via Ca, Sr, and Ba systematically enhances the stability of the infinite-layer phase in all three transition-metal families. These results reveal fundamental challenges in realizing bulk substrate-free infinite-layer oxides, and simultaneously offer guidance for future experimental synthesis efforts targeting novel superconducting compounds.

cond-mat.mtrl-sci↗

arXiv2026

Engineering the band structure of few-layer graphene by S-doping: from linear dispersion to impurity flat bands

Motivated by the technological relevance of S-doped few-layer graphene (FLG) in battery applications and in the oxygen reduction reaction, we systematically explore the effect of basal plane S-doping on the electronic properties of mono-, bi-, and four-layer graphene, using first-principles calculations with van der Waals corrections. In the monolayer we find a variety of effects ranging from a sustained Dirac cone with localized impurity bands away from the Fermi level for thiophenic doping (2V1S) to a band gap opening of 0.4 eV and impurity flat bands close to the Fermi-level for graphitic doping (1V1S) and an additional $n$-type doping together with spin-polarization for thiopyranic doping (4V3S). Incorporation in FLG leads to modification of the Dirac cone into a set of hyperbolic touching bands in 2V1S; reduction (bilayer) and closing of the band gap with additional hyperbolic touching bands in conjunction with an impurity flat band at the Fermi level in 1V1S and 4V3S and a reduction of spin polarization in the latter. Overall, S-doping enables design of the band structure and tuning the electronic behavior of FLG from metallic to insulating and from linear dispersion to impurity flat bands that makes S-doped FLG a promising material for versatile technological applications.

cond-mat.mtrl-sci↗

arXiv2023

Nature of the magnetic coupling in infinite-layer nickelates versus cuprates

In contrast to the cuprates, where the proximity of antiferromagnetism (AFM) and superconductivity is well established, first indications for AFM interactions in superconducting infinite-layer nickelates were only recently obtained. Here, we explore, based on first-principles simulations, the nature of the magnetic coupling in NdNiO2 as a function of the on-site Coulomb and exchange interaction, varying the explicit hole doping and the treatment of the Nd $4f$ electrons. The $U$-$J$ phase diagrams for undoped nickelates and cuprates indicate $G$-type ordering, yet show different $U$ dependency. By either Sr hole doping or explicit treatment of the Nd $4f$ electrons, we find a transition to a Ni $C$-type AFM ground state. We trace the effect of Sr doping back to a distinct accommodation of the holes by the Ni versus Cu $e_g$ orbitals. The interaction between Nd $4f$ and Ni $3d$ states stabilizes $C$-type AFM order on both sublattices. Though spin-orbit interactions induce a band splitting near the Fermi energy, the bad-metal state is retained even under epitaxial strain. These results establish the distinct role of the magnetic interactions in the nickelates versus the cuprates and suggest the former as a unique platform to investigate the relation to unconventional superconductivity.

cond-mat.supr-con↗

arXiv2021

Active learning and element embedding approach in neural networks for infinite-layer versus perovskite oxides

Combining density functional theory simulations and active learning of neural networks, we explore formation energies of oxygen vacancy layers, lattice parameters, and their correlations in infinite-layer versus perovskite oxides across the periodic table, and place the superconducting nickelate and cuprate families in a comprehensive statistical context. We show that neural networks predict these observables with high precision, using only 30-50% of the data for training. Element embedding autonomously identifies concepts of chemical similarity between the individual elements in line with human knowledge. Based on the fundamental concepts of entropy and information, active learning composes the training set by an optimal strategy without a priori knowledge and provides systematic control over the prediction accuracy. This offers key ingredients to considerably accelerate scans of large parameter spaces and exemplifies how artificial intelligence may assist on the quantum scale in finding novel materials with optimized properties.

cond-mat.supr-con↗