arXiv subjects

Dominik Spath

Publications and source records attributed to Dominik Spath.

4 recordsLinked to original sources

arXiv2026

Ab initio thermodynamic statistical modeling of the miscibility gap and the metal-insulator phase transition in SrTi$_{1-x}$V$_x$O$_{3}$

The substitutional alloy SrTi$_{1-x}$V$_x$O$_3$ interpolates between the band insulator SrTiO$_3$ and the correlated metal SrVO$_3$, exhibiting a composition-driven metal--insulator transition whose origin combines Mott physics with local chemical disorder. Previous first-principles studies relied on individual supercells, which cannot capture the thermally disordered solid solution, since configurations of identical composition can display very different electronic properties. Here we treat the alloy within a generalized quasi-chemical approximation, a thermodynamically consistent statistical framework in which every property is obtained as an ensemble average over all symmetry-inequivalent clusters, weighted by occurrence probabilities that minimize the Gibbs mixing free energy. This provides a well-defined procedure to average over different supercells, and places the structural and electronic descriptions on an equal footing. From the mixing thermodynamics we obtain a miscibility gap with a critical temperature of 1443 K, consistent with experimental evidence. Combining the cluster ensemble with dynamical mean-field theory, we track the density of states at the Fermi level across the full composition range: whereas density-functional theory alone predicts a metal for all $x>0$, the correlated spectral function reproduces the transition, evolving from insulating below $x\approx0.3$ to metallic near $x=1$. Finally, classifying clusters as metallic or insulating and performing site percolation on a simple cubic lattice yields a sharp onset of system-spanning conduction near $x\approx0.4$. These results establish a thermodynamically consistent, configuration--averaged framework applicable to the broader class of correlated materials.

cond-mat.str-el↗

arXiv2026

Ultrafast dynamics and light-induced superconductivity from first principles

Experiments on superconducting materials have unveiled unique emergent properties when they are driven far from equilibrium. However, a quantitative first-principles treatment that describes experimental observations is lacking. In this work, we develop an ab-initio model for the nonequilibrium response of optically irradiated superconducting films within the framework of conventional electron-phonon-mediated superconductivity, leveraging new numerical techniques to solve the Migdal-Eliashberg equations directly on the real-frequency axis. This enables us to quantitatively reproduce the optical response of superconducting films in pump-probe experiments and validate our approach on measurements of the differential reflectance of Pb and LaH$_{10}$ in response to a pump excitation. Similar calculations performed on the alkali-doped fulleride K$_3$C$_{60}$ reveal that a photo-induced superconducting state is generated after irradiation by an ultrafast mid-infrared pulse of sufficient intensity, as reported in prior experimental work. The enhancement in this framework is attributed to the excitation of quasiparticles to energies resonant with the strongest electron-phonon coupling in K$_3$C$_{60}$, in close analogy to the mechanism for enhancement of superconductivity under microwave irradiation, explaining the nature of the photo-induced superconducting state and elucidating the subsequent quasiparticle and phonon dynamics. Our results suggest that photo-induced superconductivity is accessible in more materials than previously recognized. We demonstrate this by performing calculations on calcium-intercalated graphite, CaC$_6$, and predict a similar photo-induced superconducting gap.

cond-mat.supr-con↗

arXiv2026

Fast Real-Axis Eliashberg Calculations: Full-bandwidth solutions beyond the constant density of states approximation

Experimentally relevant signatures of superconductivity require access to real-frequency quantities, such as the spectral functions, optical response, and transport properties, yet Migdal-Eliashberg calculations are commonly performed on the imaginary axis and then analytically continued, a step that is numerically delicate and can obscure physically relevant spectral features. Here we present a practical route to solving the finite-temperature Migdal-Eliashberg equations directly on the real-frequency axis, while retaining the effects from the full-bandwidth electronic structure. Our formulation accounts for particle-hole asymmetry through an energy-dependent electronic density of states, avoiding the constant density of states approximation often used in real-axis calculations, and includes a static screened Coulomb contribution. We introduce an efficient numerical technique to solve the Migdal-Eliashberg integrals whose computational cost scales linearly with the real-frequency grid, making high-resolution, full-bandwidth real-axis calculations feasible and providing direct access to the interacting Green's function and derived observables without analytic continuation. As an illustration, we apply the method to H$_{3}$S, where a van-Hove singularity near the Fermi level produces strong particle-hole asymmetry. The full-bandwidth solution yields noticeably different spectra than the constant density of states approximation and brings the superconducting gap and lineshapes into closer agreement with experiment, highlighting when band-structure details are essential. Furthermore, the methods presented here open the door to time-dependent, nonequilibrium simulations within Eliashberg theory.

cond-mat.supr-con↗

arXiv2025

IsoME: Streamlining High-Precision Eliashberg Calculations

This paper introduces the Julia package IsoME, an easy-to-use yet accurate and robust computational tool designed to calculate superconducting properties. Multiple levels of approximation are supported, ranging from the basic McMillan-Allen-Dynes formula and its machine learning-enhanced variant to Eliashberg theory including static Coulomb interactions derived from $GW$ calculations, offering a fully ab initio approach to determine superconducting properties, such as the critical superconducting temperature ($T_\text{c}$) and the superconducting gap function ($\Delta$). We validate IsoME by benchmarking it against various materials, demonstrating its versatility and performance across different theoretical levels. The findings indicate that the previously held assumption that Eliashberg theory overestimates $T_\text{c}$ is no longer valid when $\mu^*$ is appropriately adjusted to account for the finite Matsubara frequency cutoff. Furthermore, we conclude that the constant density of states (DOS) approximation remains accurate in most cases. By unifying multiple approximation schemes within a single framework, IsoME combines first-principles precision with computational efficiency, enabling seamless integration into high-throughput workflows through its $T_\text{c}$ search mode. This makes IsoME a powerful and reliable tool for advancing superconductivity research.

cond-mat.supr-con↗