arXiv subjects

J. Mravlje

Publications and source records attributed to J. Mravlje.

At least 19 recordsLinked to original sources

arXiv2023

The fate of quasiparticles at high-temperature

We study the temperature evolution of quasiparticles in the correlated metal Sr$_2$RuO$_4$. Our angle resolved photoemission data show that quasiparticles persist up to temperatures above 200~K, far beyond the Fermi liquid regime. Extracting the quasiparticle self-energy we demonstrate that the quasiparticle residue $Z$ increases with increasing temperature. Quasiparticles eventually disappear on approaching the bad metal state of Sr$_2$RuO$_4$ not by losing weight but via excessive broadening from super-Planckian scattering. We further show that the Fermi surface of Sr$_2$RuO$_4$ - defined as the loci where the spectral function peaks - deflates with increasing temperature. These findings are in semi-quantitative agreement with dynamical mean field theory calculations.

cond-mat.str-el↗

arXiv2023

Hund bands in spectra of multiorbital systems

Spectroscopy experiments are routinely used to characterize the behavior of strongly correlated systems. An in-depth understanding of the different spectral features is thus essential. Here, we show that the spectrum of the multiorbital Hubbard model exhibits unique Hund \ms{bands} that occur at energies given only by the Hund coupling $J_\mathrm{H}$, as distinct from the Hubbard satellites following the interaction $U$. We focus on experimentally relevant single-particle and optical spectra that we calculate for a model related to iron chalcogenide ladders. The calculations are performed via the density-matrix renormalization group and Lanczos methods. The generality of the implications is verified by considering a generic multiorbital model within dynamical mean-field theory.

cond-mat.str-el↗

arXiv2022

Lattice vibrational modes in changchengite from Raman spectroscopy and first principles electronic structure

We measured room-temperature phonon Raman spectra of changchengite (IrBiS) and compared the experimental phonon wavenumbers to the theoretical ones obtained by means of the \emph{ab initio} density-functional-theory calculations in the presence and absence of the spin-orbit coupling effects. Combining two different excitation photon energies all the symmetry predicted Raman modes are experimentally observed. The electronic properties of IrBiS are found to be similar to the recently studied isostructural compound IrBiSe showing a large Dresselhaus spin-orbit valence band splitting. A good agreement between the experimental and theoretically predicted Raman phonon wavenumbers is found only when the lattice parameter is constrained to the experimental value. The inclusion of the spin orbit coupling does not significantly affect the phonon wavenumbers.

cond-mat.mtrl-sci↗

arXiv2021

Seebeck coefficient in a cuprate superconductor: particle-hole asymmetry in the strange metal phase and Fermi surface transformation in the pseudogap phase

We report measurements of the Seebeck effect in both the $ab$ plane ($S_{\rm a}$) and along the $c$ axis ($S_{\rm c}$) of the cuprate superconductor La$_{1.6-x}$Nd$_{0.4}$Sr$_{x}$CuO$_4$ (Nd-LSCO), performed in magnetic fields large enough to suppress superconductivity down to low temperature. We use the Seebeck coefficient as a probe of the particle-hole asymmetry of the electronic structure across the pseudogap critical doping $p^{\star} = 0.23$. Outside the pseudogap phase, at $p = 0.24 > p^{\star}$, we observe a positive and essentially isotropic Seebeck coefficient as $T \rightarrow 0$. That $S > 0$ at $p = 0.24$ is at odds with expectations given the electronic band structure of Nd-LSCO above $p^{\star}$ and its known electron-like Fermi surface. We can reconcile this observation by invoking an energy-dependent scattering rate with a particle-hole asymmetry, possibly rooted in the non-Fermi liquid nature of cuprates just above $p^{\star}$. Inside the pseudogap phase, for $ p < p^{\star}$, $S_{\rm a}$ is seen to rise at low temperature as previously reported, consistent with the drop in carrier density $n$ from $n \simeq 1 + p$ to $n \simeq p$ across $p^{\star}$ as inferred from other transport properties. In stark contrast, $S_{\rm c}$ at low temperature becomes negative below $p^{\star}$, a novel signature of the pseudogap phase. The sudden drop in $S_{\rm c}$ reveals a change in the electronic structure of Nd-LSCO upon crossing $p^{\star}$. We can exclude a profound change of the scattering across $p^{\star}$ and conclude that the change in the out-of-plane Seebeck coefficient originates from a transformation of the Fermi surface.

cond-mat.str-el↗

arXiv2020

Charge transport in the Hubbard model at high temperatures: triangular versus square lattice

High-temperature bad-metal transport has been recently studied both theoretically and in experiments as one of the key signatures of strong electronic correlations. Here we use the dynamical mean field theory (DMFT) and its cluster extensions, as well as the finite-temperature Lanczos method (FTLM) to explore the influence of lattice frustration on the thermodynamic and transport properties of the Hubbard model at high temperatures. We consider the triangular and the square lattice at half-filling and at 15\% hole-doping. We find that for $T \gtrsim 1.5t$ the self-energy becomes practically local, while the finite-size effects become small at lattice-size $4 \times 4$ for both lattice types and doping levels. The vertex corrections to optical conductivity, which are significant on the square lattice even at high temperatures, contribute less on the triangular lattice. We find approximately linear temperature dependence of dc resistivity in doped Mott insulator for both types of lattices.

cond-mat.str-el↗

arXiv2020

Electronic correlations and transport in iron at Earth's core conditions

The transport properties of iron under Earth's inner core conditions are essential input for the geophysical modelling but are poorly constrained experimentally. Here we show that the thermal and electrical conductivity of iron at those conditions remains high even if the electron-electron-scattering (EES) is properly taken into account. This result is obtained by ab initio simulations taking into account consistently both thermal disorder and electronic correlations. Thermal disorder suppresses the non-Fermi-liquid behavior of the body-centered cubic iron phase, hence, reducing the EES; the total calculated thermal conductivity of this phase is 220 Wm$^{-1}$K$^{-1}$ with the EES reduction not exceeding 20%. The EES and electron-lattice scattering are intertwined resulting in breaking of the Matthiessen's rule with increasing EES. In the hexagonal close-packed iron the EES is also not increased by thermal disorder and remains weak. Our main finding thus holds for the both likely iron phases in the inner core.

cond-mat.str-el↗

arXiv2016

Fermi-liquid behavior and thermal conductivity of ε-iron at Earth's core conditions

The electronic state and transport properties of hot dense iron are of the utmost importance to geophysics. Combining the density functional and dynamical mean field theories we study the impact of electron correlations on electrical and thermal resistivity of hexagonal close-packed $ε$-Fe at Earth's core conditions. $ε$-Fe is found to behave as a nearly perfect Fermi liquid. The quadratic dependence of the scattering rate in Fermi liquids leads to a modification of the Wiedemann-Franz law with suppression of the thermal conductivity as compared to the electrical one. This significantly increases the electron-electron thermal resistivity which is found to be of comparable magnitude to the electron-phonon one. The implications of this effect on the dynamics of Earth's core is discussed.

cond-mat.str-el↗

arXiv2015

Optical spectroscopy and the nature of the insulating state of rare-earth nickelates

Using a combination of spectroscopic ellipsometry and DC transport measurements, we determine the temperature dependence of the optical conductivity of NdNiO$_3$ and SmNiO$_{3}$ films. The optical spectra show the appearance of a characteristic two-peak structure in the near-infrared when the material passes from the metal to the insulator phase. Dynamical mean-field theory calculations confirm this two-peak structure, and allow to identify these spectral changes and the associated changes in the electronic structure. We demonstrate that the insulating phase in these compounds and the associated characteristic two-peak structure are due to the combined effect of bond-disproportionation and Mott physics associated with half of the disproportionated sites. We also provide insights into the structure of excited states above the gap.

cond-mat.str-el↗

arXiv2014

Optical Response of Sr$_2$RuO$_4$ Reveals Universal Fermi-liquid Scaling and Quasiparticles Beyond Landau Theory

We report optical measurements demonstrating that the low-energy relaxation rate ($1/τ$) of the conduction electrons in Sr$_2$RuO$_4$ obeys scaling relations for its frequency ($ω$) and temperature ($T$) dependence in accordance with Fermi-liquid theory. In the thermal relaxation regime, $1/τ\propto (\hbarω)^2 + (pπ\kB T)^2$ with $p=2$, and $ω/T$ scaling applies. Many-body electronic structure calculations using dynamical mean-field theory confirm the low-energy Fermi-liquid scaling, and provide quantitative understanding of the deviations from Fermi-liquid behavior at higher energy and temperature. The excess optical spectral weight in this regime provides evidence for strongly dispersing "resilient" quasiparticle excitations above the Fermi energy.

cond-mat.str-el↗

arXiv2014

Electronic correlations and Hund's coupling effects in SrMoO$_3$ revealed by photoemission spectroscopy

We investigate the electronic structure of a perovskite-type Pauli paramagnet SrMoO3 (t2g2) thin film using hard x-ray photoemission spectroscopy and compare the results to the realistic calculations that combine the density functional theory within the local-density approximation (LDA) with the dynamical-mean field theory (DMFT). Despite the clear signature of electron correlations in the electronic specific heat, the narrowing of the quasiparticle bands is not observed in the photoemission spectrum. This is explained in terms of the characteristic effect of Hund's rule coupling for partially-filled t2g bands, which induces strong quasiparticle renormalization already for values of Hubbard interaction which are smaller than the bandwidth. The interpretation is supported by additional model DMFT calculations including Hund's rule coupling, that show renormalization of low-energy quasiparticles without affecting the overall bandwidth. The photoemission spectra show additional spectral weight around -2 eV that is not present in the LDA+DMFT. We interpret this weight as a plasmon satellite, which is supported by measured Mo, Sr and Oxygen core-hole spectra that all show satellites at this energy.

cond-mat.str-el↗

arXiv2013

Low-energy electronic properties of clean CaRuO$_3$: elusive Landau quasiparticles

We have prepared high-quality epitaxial thin films of CaRuO$_3$ with residual resistivity ratios up to 55. Shubnikov-de Haas oscillations in the magnetoresistance and a $T^2$ temperature dependence in the electrical resistivity only below 1.5 K, whose coefficient is substantially suppressed in large magnetic fields, establish CaRuO$_3$ as a Fermi liquid (FL) with anomalously low coherence scale. Non-Fermi liquid (NFL) $T^{3/2}$ dependence is found between 2 and 25 K. The high sample quality allows access to the intrinsic electronic properties via THz spectroscopy. For frequencies below 0.6 THz, the conductivity is Drude-like and can be modeled by FL concepts, while for higher frequencies non-Drude behavior, inconsistent with FL predictions, is found. This establishes CaRuO$_3$ as a prime example of optical NFL behavior in the THz range.

cond-mat.str-el↗

arXiv2013

Impact of electronic correlations on the equation of state and transport in $ε$-Fe

We have obtained the equilibrium volumes, bulk moduli, equations of state of the ferromagnetic cubic $α$ and paramagnetic hexagonal $ε$ phases of iron in close agreement with experiment using an ab initio dynamical mean-field theory approach. The local dynamical correlations are shown to be crucial for a successful description of the ground-state properties of paramagnetic $ε$-Fe. Moreover, they enhance the effective mass of the quasiparticles and reduce their lifetimes across the $α\to ε$ transition leading to a step-wise increase of the resistivity, as observed in experiment. The calculated magnitude of the jump is significantly underestimated, which points to non-local correlations. The implications of our results for the superconductivity and non-Fermi-liquid behavior of $ε$-Fe are discussed.

cond-mat.str-el↗

arXiv2013

Extremely correlated Fermi liquid theory meets Dynamical mean-field theory: Analytical insights into the doping-driven Mott transition

We consider a doped Mott insulator in the large dimensionality limit within both the recently developed Extremely Correlated Fermi Liquid (ECFL) theory and the Dynamical Mean-Field Theory (DMFT). We show that the general structure of the ECFL sheds light on the rich frequency-dependence of the DMFT self-energy. Using the leading Fermi-liquid form of the two key auxiliary functions introduced in the ECFL theory, we obtain an analytical ansatz which provides a good quantitative description of the DMFT self-energy down to hole doping level 0.2. In particular, the deviation from Fermi-liquid behavior and the corresponding particle-hole asymmetry developing at a low energy scale are well reproduced by this ansatz. The DMFT being exact at large dimensionality, our study also provides a benchmark of the ECFL in this limit. We find that the main features of the self-energy and spectral line-shape are well reproduced by the ECFL calculations in the O(λ^2) `minimal scheme', for not too low doping level >0.3. The DMFT calculations reported here are performed using a state-of-the-art numerical renormalization-group impurity solver, which yields accurate results down to an unprecedentedly small doping level 0.001.

cond-mat.str-el↗

arXiv2012

Origin of the high Neel temperature in SrTcO3

We investigate the origin of the high Neel temperature recently found in Tc perovskites. The electronic structure in the magnetic state of SrTcO3 and its 3d analogue SrMnO3 is calculated within a framework combining band-structure and many-body methods. In agreement with experiment, the Neel temperature of SrTcO3 is found to be four times larger than that of SrMnO3. We show that this is because the Tc-compound lies on the verge of the itinerant-to-localized transition, and also has a larger bandwidth, while the Mn-compound lies deeper into the localized side. For SrTcO3 we predict that the Neel temperature depends weakly on applied pressure, in clear violation of Bloch's rule, signaling the complete breakdown of the localized picture.

cond-mat.str-el↗

arXiv2009

Electron transport through molecules in the Kondo regime: the role of molecular vibrations

We discuss the electronic transport through molecules in the Kondo regime. We concentrate here on the influence of molecular vibrations. Two types of vibrations are investigated: (i) the breathing internal molecular modes, where the coupling occurs between the molecular deformation and the charge density, and (ii) the oscillations of molecule between the contacts, where the displacement affects the tunneling. The system is described by models which are solved numerically using Schoenhammer-Gunnarsson's projection operators and Wilson's numerical renormalization group methods. Case (i) is considered within the Anderson-Holstein model. Here the influence of the phonons is mainly to suppress the repulsion between the electrons at the molecular orbital. Case (ii) is described by a two-channel Anderson model with phonon-assisted hybridization. In both cases, the coupling to electrons softens the vibrational mode and in the strong coupling regime makes the displacement unstable to perturbations that break the symmetry of the confining potential. For instance, in case (ii) when the frequency of oscillations decreases below the magnitude of perturbation breaking the left-right symmetry, the molecule will be abruptly attracted to one of the electrodes. In this regime, the Kondo temperature increases but the conductance through the molecule is suppressed.

cond-mat.mes-hall↗

arXiv2009

Entanglement of electron pairs extracted from a many-body system

Entanglement of spins is analyzed for two electrons extracted from a mixed many electron state by projecting onto the two-electron subspace. The concurrence formulae are expressed in a compact form for states with a well defined square of the total spin projection. As an example, the thermal entanglement for a qubit pair with an anisotropic Heisenberg and the Dzyaloshinskii-Moriya interactions in an inhomogeneous magnetic field is given analytically. Remarkably, the concurrence of a pair of electrons with antiparallel spins and in a delocalised orbital state is given by the scalar product of the state with its spin-flipped state and not with the time-reversed state.

cond-mat.mes-hall↗

arXiv2008

Kondo effect and channel mixing in oscillating molecules

We investigate the electronic transport through a molecule in the Kondo regime. The tunneling between the electrode and the molecule is asymmetrically modulated by the oscillations of the molecule, i.e., if the molecule gets closer to one of the electrodes the tunneling to that electrode will increase while for the other electrode it will decrease. The system is described by a two-channel Anderson model with phonon-assisted hybridization, which is solved with the Wilson numerical renormalization group method. The results for several functional forms of tunneling modulation are presented. For a linearized modulation the Kondo screening of the molecular spin is caused by the even or odd conduction channel. At the critical value of the electron-phonon coupling an unstable two-channel Kondo fixed point is found. For a realistic modulation the spin at the molecular orbital is Kondo screened by the even conduction channel even in the regime of strong coupling. A universal consequence of the electron-phonon coupling is the softening of the phonon mode and the related instability to perturbations that break the left-right symmetry. When the frequency of oscillations decreases below the magnitude of such perturbation, the molecule is abruptly attracted to one of the electrodes. In this regime, the Kondo temperature is enhanced and, simultaneously, the conductance through the molecule is suppressed.

cond-mat.mes-hall↗

arXiv2008

Quantum entanglement of space domains occupied by interacting electrons

Spin-entanglement of two electrons occupying two spatial regions -- domains -- is expressed in a compact form in terms of spin-spin correlation functions. The power of the formalism is demonstrated on several examples ranging from generation of entanglement by scattering of two electrons to the entanglement of a pair of qubits represented by a double quantum dot coupled to leads. In the latter case the collapse of entanglement due to the Kondo effect is analyzed.

cond-mat.mes-hall↗