arXiv subjects

Jernej Mravlje

Publications and source records attributed to Jernej Mravlje.

At least 19 recordsLinked to original sources

arXiv2026

Criticality and Quench Dynamics at the Anderson Transition of a Chern Insulator

We study the critical properties of the topological Anderson phase transition in a strongly disordered Chern insulator, separating the topological phase from a trivial Anderson insulator. We show that the transition is characterized by a non-zero electrical conductance and by the emergence of a critical length scale in the real-space profile of the local Chern marker. From this, we extract the correlation-length and the dynamical critical exponents, which are consistent with those of non-interacting models of the integer quantum Hall effect. We then ramp the disorder strength across the transition and study the ensuing dynamics. In contrast to clean topological systems, we find that the excitation density does not follow the Kibble-Zurek scaling. The non-equilibrium length scale associated with the local Chern marker is decoupled from the generation of excitations. For studied system sizes, we find it to be close to the Kibble-Zurek prediction for the topological-to-trivial quench, while it deviates from it for the reverse direction.

cond-mat.str-el↗

arXiv2026

Local topological markers for Chern insulators in ribbon geometry

Local topological markers are used to characterize Chern insulators in the presence of spatial inhomogeneities, such as boundaries and disorder. In this paper, we study the local Chern marker in systems with partial translational symmetry. We express the local Chern marker in the hybrid position-momentum basis for both open and periodic boundary conditions. We calculate the local Chern marker for a Haldane model ribbon. We show that the behavior at the two boundaries is qualitatively different from fully open geometries. We further compare the local Chern marker with the local Středa marker and show agreement in the bulk and small deviations at the boundaries that diminish with increasing system size. The correspondence between the two markers remains good if disorder is introduced, provided its magnitude remains below large values that cause substantial change of the Chern number due to Anderson physics. Finally, by exploiting the numerical efficiency due to partial translational symmetry, we study equilibrium critical behavior and the Kibble-Zurek mechanism in a weakly disordered Qi-Wu-Zhang Chern insulator. We extract relevant scaling exponents from the local Chern marker configuration and show that they converge to the analytically predicted values with increasing system size.

cond-mat.mes-hall↗

arXiv2025

2D coherent spectroscopy signatures of exciton condensation in Ta$_2$NiSe$_5$

We show that the nonlinear optical response probed by two-dimensional coherent spectroscopy (2DCS) can discriminate between excitonic and lattice driven order. In the excitonic regime of a realistic model of Ta$_2$NiSe$_5$, the third order 2DCS signals are strongly enhanced by the condensate's amplitude and phase modes, with negligible contributions from single-particle excitations. In the linear optical response, in contrast, single-particle and collective-mode contributions overlap. With increasing electron-phonon coupling, the amplitude mode contribution to 2DCS initially remains robust, but then drops rapidly and remains small in the phonon-dominated regime -- even in systems with large order parameter. 2DCS also aids the detection of the massive relative phase mode, which is analogous to the Leggett mode in superconductors. Our analysis, based on the time-dependent Hartree-Fock approach, demonstrates that 2DCS can track the emergence of the symmetry-broken state and the crossover from Coulomb-driven to phonon-driven order.

cond-mat.str-el↗

arXiv2025

Insulating transport in anisotropic metals: breakdown of Drude transport and the puzzling $c$-axis resistivity of Sr$_2$RuO$_4$ and other layered oxides

We reveal a mechanism that may explain the non-metallic out-of-plane resistivity in layered metals. By carefully examining how the Drude-Boltzmann expression for the $c$-axis conductivity emerges out of the Kubo formula, we find, besides the standard metallic term proportional to the carrier lifetime $τ$, a non-Drude contribution proportional to $1/τ$. The Drude behavior breaks down when $1/τ> 2 η^*$, the crossover value $η^*$ being small (and hence observable) when the $c$-axis velocities vary rapidly with the distance from the Fermi surface. We consider the Hund metal Sr$_2$RuO$_4$ as a test case, which we study within a realistic dynamical mean-field theory approach. The non-Drude behavior observed experimentally in $c$-axis transport is reproduced and explained by our considerations, showing that earlier invoked extrinsic mechanisms that involve either impurities or phonons are unnecessary. We point out that the small value of $η^*$ is due to a peculiar accidental cancellation due to destructive interference characteristic of body-centered tetragonal lattices.

cond-mat.str-el↗

arXiv2025

Quantum anomalous Hall domains in a Quenched Topological Mott Insulator

We study an interacting spinless quadratic band touching model that realizes a topological Mott insulating state. We quench the interaction from a value corresponding to the nematic insulator to that of the quantum anomalous Hall (QAH) ordered phase. We perform time-dependent Hartree-Fock simulations and show that after the quench the system realizes an excited Dirac semimetal state, which is however unstable and spontaneously evolves to a state with inhomogeneous nematic and QAH order parameters. The modulations form a stripe pattern that grows exponentially with time until the local Chern marker reaches unity. The alternating QAH order defines a domain structure with boundaries that host chiral sublattice currents.

cond-mat.str-el↗

arXiv2025

Respective Roles of Electron-Phonon and Electron-Electron Interactions in the Transport and Quasiparticle Properties of SrVO$_3$

The spectral and transport properties of strongly correlated metals, such as SrVO$_3$ (SVO), are widely attributed to electron-electron ($e$-$e$) interactions, with lattice vibrations (phonons) playing a secondary role. Here, using first-principles electron-phonon ($e$-ph) and dynamical mean field theory calculations, we show that $e$-ph interactions play an essential role in SVO: they govern the electron scattering and resistivity in a wide temperature range above 30 K, and induce an experimentally observed kink in the spectral function. In contrast, the $e$-$e$ interactions control quasiparticle renormalizations and low temperature transport, and enhance the $e$-ph coupling. We clarify the origin of the near $T^2$ temperature dependence of the resistivity by analyzing the $e$-$e$ and $e$-ph limited transport regimes. Our work disentangles the electronic and lattice degrees of freedom in a prototypical correlated metal, revealing the dominant role of $e$-ph interactions in SVO.

cond-mat.mtrl-sci↗

arXiv2025

Strong effects of thermally induced low-spin-to-high-spin crossover on transport properties of correlated metals

We use dynamical mean-field theory to study how electronic transport in multi-orbital metals is influenced by correlated (nominally) empty orbitals that are in proximity to the Fermi level. Specifically, we study 2 + 1 orbital and 3 + 2 orbital (i.e. t2g + eg ) models on a Bethe lattice with a crystal field that is set so that the higher lying orbitals are nearly empty at low temperatures but get a non-negligible occupancy at elevated temperature. The high temperature regime is characterized by thermal activation of carriers leading to higher magnetic response (i.e., thermally induced low-spin to high-spin transition) and substantial influence on resistivity, where one can distinguish two counteracting effects: increased scattering due to formation of high spin and increased scattering phase space on one hand, and additional parallel conduction channel on the other. The former effect is stronger and one may identify cases where resistivity increases by a factor of three at high temperatures even though the occupancy of the unoccupied band remains small (< 10%). We discuss implications of our findings for transport properties of correlated materials.

cond-mat.str-el↗

arXiv2024

Collective modes and Raman response in Ta$_2$NiSe$_5$

We explore the collective response in an excitonic insulator phase in Ta$_2$NiSe$_5$ using a semirealistic model including relevant lattice and electronic instabilities. We calculate order-parameter susceptibility and Raman response within a time-dependent Hartree-Fock approach. Contrary to the standard expectations, the amplitude mode frequency does not coincide with the single-particle gap but has a higher frequency. We find a phase mode that is massive because the excitonic condensation breaks a discrete symmetry only and that becomes heavier as the electron-lattice coupling is increased. These features are expected to apply to generic realistic excitonic insulators. We discuss scenarios under which the phase mode does not appear as a sharp in-gap resonance.

cond-mat.str-el↗

arXiv2024

High-harmonic generation in semi-Dirac and Weyl semimetals with broken time-reversal symmetry: Exploring merging of Weyl nodes

We explore anomalous high-harmonic generation in a model that realizes a transition from a broken time-reversal symmetry Weyl-semimetal to a semi-Dirac regime, i.e. a gapless semimetal with dispersion that is parabolic in one direction and conical in the other two. We point out the intensity of the induced anomalous high harmonics is high in the semi-Dirac regime. For Weyl semimetals, we reveal anomalous high harmonics are due to excitations at momenta where the dispersion is not strictly linear and that in the linearized low-energy theory the anomalous response is harmonic only. Our findings aid experimental characterization of Weyl, Dirac, and semi-Dirac semimetals.

cond-mat.mes-hall↗

arXiv2023

Signatures of Hund Metal and finite-frequency nesting in Sr$_2$RuO$_4$ Revealed by Electronic Raman Scattering

We investigate the electronic Raman scattering of Sr$_2$RuO$_4$ using a material-realistic dynamical mean-field theory approach. We identify the low-energy Fermi liquid behavior and point out that the enhanced Raman response at higher energies is a fingerprint of Hund metals. These signatures originate in the two-stage coherence of Hund metals and associated quasiparticle `unrenormalization'. In agreement with recent experimental observations, we find the $\mathrm{B}_{1g}$ and $\mathrm{B}_{2g}$ responses differ, but our calculations suggest a novel interpretation of this dichotomy. The $\mathrm{B}_{1g}$ response is dominated by the $xy$ orbital and the $\mathrm{B}_{2g}$ response receives contributions from all orbitals and is strongly affected by previously unnoticed finite-frequency interband nesting. We calculate the vertex-corrections to Raman response and show that their effect is nonvanishing but small.

cond-mat.str-el↗

arXiv2023

Thermoelectric effect on diffusion in the two-dimensional Hubbard model

We study charge and heat transport in the square lattice Hubbard model at strong coupling using the finite-temperature Lanczos method. We construct the diffusion matrix and estimate the effect of thermoelectric terms on diffusive and hydrodynamic time evolution. The thermoelectric terms prevent the interpretation of the diffusion in terms of a single time scale. We discuss our results in relation to cold-atom experiments and measurements of heat conductivity based on the measurements of heat diffusion.

cond-mat.str-el↗

arXiv2023

Combining Electron-Phonon and Dynamical Mean-Field Theory Calculations of Correlated Materials: Transport in the Correlated Metal Sr$_2$RuO$_4$

Electron-electron ($e$-$e$) and electron-phonon ($e$-ph) interactions are challenging to describe in correlated materials, where their joint effects govern unconventional transport, phase transitions, and superconductivity. Here we combine first-principles $e$-ph calculations with dynamical mean field theory (DMFT) as a step toward a unified description of $e$-$e$ and $e$-ph interactions in correlated materials. We compute the $e$-ph self-energy using the DMFT electron Green's function, and combine it with the $e$-$e$ self-energy from DMFT to obtain a Green's function including both interactions. This approach captures the renormalization of quasiparticle dispersion and spectral weight on equal footing. Using our method, we study the $e$-ph and $e$-$e$ contributions to the resistivity and spectral functions in the correlated metal Sr$_2$RuO$_4$. In this material, our results show that $e$-$e$ interactions dominate transport and spectral broadening in the temperature range we study (50$-$310~K), while $e$-ph interactions are relatively weak and account for only $\sim$10\% of the experimental resistivity. We also compute effective scattering rates, and find that the $e$-$e$ interactions result in scattering several times greater than the Planckian value $k_BT$, whereas $e$-ph interactions are associated with scattering rates lower than $k_BT$. Our work demonstrates a first-principles approach to combine electron dynamical correlations from DMFT with $e$-ph interactions in a consistent way, advancing quantitative studies of correlated materials.

cond-mat.mtrl-sci↗

arXiv2023

Influence of oxygen on electronic correlation and transport in iron in the outer Earth's core

Knowing the transport properties of iron under realistic conditions present in the Earth's core is essential for the geophysical modeling of Earth's magnetic field generation. Besides by extreme pressures and temperatures, transport may be influenced importantly also by the presence of light elements. Using a combination of molecular dynamics, density functional theory, and dynamical mean-field theory methods we investigate how oxygen impurities influence the electronic correlations and transport in the liquid outer Earth's core. We consider a case with an oxygen content of ~10 atomic%, a value that is believed to be close to the composition of the core. We find that the electronic correlations are enhanced but their effect on conductivities is moderate (compared to pure Fe, electrical conductivity drops by 10% and thermal conductivity by 18%). The effect of electron-electron scattering alone, whereas not large, is comparable to effects of the compositional disorder. We reveal the mechanism behind the larger suppression of the thermal conductivity and associated reduction of the Lorenz ratio and discuss its geophysical significance.

cond-mat.str-el↗

arXiv2022

Thermal conductivity and heat diffusion in the two-dimensional Hubbard model

We study the electronic thermal conductivity $κ_\textrm{el}$ and the thermal diffusion constant $D_\textrm{Q,el}$ in the square lattice Hubbard model using the finite-temperature Lanczos method. We exploit the Nernst-Einstein relation for thermal transport and interpret the strong non-monotonous temperature dependence of $κ_\textrm{el}$ in terms of that of $D_\textrm{Q,el}$ and the electronic specific heat $c_\textrm{el}$. We present also the results for the Heisenberg model on a square lattice and ladder geometries. We study the effects of doping and consider the doped case also with the dynamical mean-field theory. We show that $κ_\textrm{el}$ is below the corresponding Mott-Ioffe-Regel value in almost all calculated regimes, while the mean free path is typically above or close to lattice spacing. We discuss the opposite effect of quasi-particle renormalization on charge and heat diffusion constants. We calculate the Lorenz ratio and show that it differs from the Sommerfeld value. We discuss our results in relation to experiments on cuprates. Additionally, we calculate the thermal conductivity of overdoped cuprates within the anisotropic marginal Fermi liquid phenomenological approach.

cond-mat.str-el↗

arXiv2022

Spin Seebeck coefficient and spin-thermal diffusion in the two-dimensional Hubbard model

We investigate the spin Seebeck coefficient $S_s$ in the square lattice Hubbard model at high temperatures of relevance to cold-atom measurements. We solve the model with the finite-temperature Lanczos and with the dynamical mean-field theory methods and find they give similar results in the considered regime. $S_s$ exceeds the atomic 'Heikes' estimates and the Kelvin entropic estimates drastically. We analyze the behavior in terms of a mapping onto the problem of a doped attractive model and derive an approximate expression that allows relating the enhancement of $S_s$ to distinct scattering of the spin-majority and the spin-minority excitations. Our analysis reveals the limitations of entropic interpretations of Seebeck coefficient even in the high-temperature regime. Large values of $S_s$ could be observed on optical lattices. We also calculate the full diffusion matrix. We quantify the spin-thermal diffusion, that is, the extent of the mixing between the spin and the thermal diffusion and discuss the results in the context of recent measurements of the spin-diffusion constant in cold atoms.

cond-mat.str-el↗

arXiv2021

Skewed Non-Fermi Liquids and the Seebeck Effect

We consider non-Fermi liquids in which the inelastic scattering rate has an intrinsic particle-hole asymmetry and obeys $ω/T$ scaling. We show that, in contrast to Fermi liquids, this asymmetry influences the low-temperature behaviour of the thermopower even in the presence of impurity scattering. Implications for the unconventional sign and temperature dependence of the thermopower in cuprates in the strange metal (Planckian) regime are emphasized.

cond-mat.str-el↗

arXiv2021

BaOsO$_3$: A Hund's metal in the presence of strong spin-orbit coupling

We investigate the 5d transition metal oxide BaOsO$_3$ within a combination of density functional theory (DFT) and dynamical mean-field theory (DMFT), using a matrix-product-state impurity solver. BaOsO$_3$ has 4 electrons in the t$_{2g}$ shell akin to ruthenates but stronger spin-orbit coupling (SOC) and is thus expected to reveal an interplay of Hund's metal behavior with SOC. We explore the paramagnetic phase diagram as a function of SOC and Hubbard interaction strengths, identifying metallic, band (van-Vleck) insulating and Mott insulating regions. At the physical values of the two couplings we find that BaOsO$_3$ is still situated inside the metallic region and has a moderate quasiparticle renormalization $m^*/m \approx 2$; consistent with specific heat measurements. SOC plays an important role in suppressing electronic correlations (found in the vanishing SOC case) through the splitting of a van-Hove singularity (vHs) close to the Fermi energy, but is insufficient to push the material into an insulating van-Vleck regime. In spite of the strong effect of SOC, BaOsO$_3$ can be best pictured as a moderately correlated Hund's metal.

cond-mat.str-el↗

arXiv2021

Spin diffusion and spin conductivity in the 2d Hubbard model

We study the spin diffusion and spin conductivity in the square lattice Hubbard model by using the finite-temperature Lanczos method. We show that the spin diffusion behaves differently from the charge diffusion and has a nonmonotonic $T$ dependence. This is due to a progressive liberation of charges that contribute to spin transport and enhance it beyond that active at low temperature due to the Heisenberg exchange. We further show that going away from half-filling and zero magnetization increases the spin diffusion, but that the increase is insufficient to reconcile the difference between the model calculations and the recent measurements on cold-atoms.

cond-mat.str-el↗