arXiv subjects

Piotr Chudzinski

Publications and source records attributed to Piotr Chudzinski.

16 recordsLinked to original sources

arXiv2025

Effect of pressure, doping and magnetism on electronic structure and phonon dispersion of FeSe

We present a Density Functional Theory (DFT) based first-principles study on iron chalcogenides superconductor FeSe, systematically investigating pressure and doping induced modifications to its electronic, magnetic, and lattice dynamical properties. Our constrained-DFT calculations in striped antiferromagnetic and staggered dimer phase reveal a non-trivial dependence of the electronic structure on the local magnetic moment at all pressures. Sulpher (S) and tellurium (Te) doping exert opposing effects on the electronic structure, attributable to their contrasting chemical pressure effects (negative for S, positive for Te). Lattice dynamics calculations divulge distinct dependence of different phonon modes on local magnetic moment in different magnetic phases. We identify pressure and magnetic moment-dependent dynamical instability in certain magnetic phases, underscoring the intricate interplay of structural, electronic, and magnetic properties in this system. Investigation of spin-phonon coupling for different phonon modes shows the presence of strong magneto-elastic coupling in FeSe with pressure distinctly affecting prominent optical phonon modes -- pure iron derived $B_{1g}$ and pure selenium derived $A_{1g}$. A clear indication of the change in spin-phonon coupling with pressure is visible, especially for the $B_{1g}$ mode.

cond-mat.mtrl-sci↗

arXiv2025

Generalized incommensurability: the role of anomalously strong spin-orbit coupling for the spin ordering in a quasi-2D system, FeSe

We study 2D spin and orbital systems, in a classical limit, in a regime where their coupling is so strong that orbital fluctuations are able to change sign of spin-exchange. Our aim is to understand how different phases in the orbital sector determine the ordering in the spin sector. The existence of intermediate vortex crystal (VC) phases, beside the canonical Kosterlitz and Thouless (KT) phases is now a well-established fact. Recently, we found [Phys. Rev. Research 6, 043154] that such a phase can explain phase diagram of FeSe. Motivated by this, here we develop a Renormalization Group (RG) method which can capture the formation of the VC phase. We achieve it by incorporating orbital vortex-vortex interactions through space-dependent incommensurability. Simultaneously, we incorporate the coupling with the spin sector for both short- and long-range interactions. We then derive a phase diagram including the effects of long-range interactions and spin-orbit coupling. The presence of the intermediate VC phase in the orbital sector changes the scaling of long-range spin-spin interactions, making them relevant under specific conditions. We thus find that the regular arrangement of orbital vortices can induce a long-range order in the 2D spin system.

cond-mat.str-el↗

arXiv2024

Exact correlation functions at finite temperatures in Tomonaga-Luttinger liquid with an open end

The paradigmatic state of a 1D collective metal, the Tomonaga-Luttinger liquid (TLL), offers us an exact analytic solution for a strongly interacting quantum system not only for infinite systems at zero temperature but also at finite temperature and with a boundary. Potentially, these results are of high relevance for technology as they could lay the foundation for a many-body description of various nanostructures. For this to happen, we need expressions for local (i.e., spatially resolved) correlations as a function of frequency. In this study, we find such expressions and study their outcome. Based on our analytic expressions we are able to identify two distinct cases of TLL which we call Coulomb metal and Hund metal, respectively. We argue that these two cases span all the situations possible in nanotubes made out of p-block elements. From an applications viewpoint, it is crucial to capture the fact that the end of the 1D system can be coupled with the external environment and emit electrons into it. We discuss such coupling on two levels for both Coulomb and Hund metals: i) in the zeroth order approximation, the coupling modifies the 1D system's boundary conditions; ii) stronger coupling, when the environment can self-consistently modify the 1D system, we introduce spatially dependent TLL parameters. In case ii) we were able to capture the presence of plasmon-polariton particles, thus building a link between TLL and the field of nano-optics.

cond-mat.str-el↗

arXiv2024

Tomonaga-Luttinger Liquid parameters in Multi-wall Nanotubes

Tomonaga-Luttinger liquid (TLL) theory is a canonical formalism used to describe one-dimensional (1D) metals, where the low energy physics is determined by collective bosonic excitations. In this work, we present a theoretical model to compute the parameters of Tomonaga-Luttinger liquid (TLL) in multi-wall nanotubes (MWNTs). MWNTs introduce additional complexity to the usual fermionic chains due to interactions and hybridization between their multiple coaxial shells. We consider a model in which conducting paths along the length of the MWNTs are randomly distributed among the shells. Since the valley degree of freedom remains a good quantum number, the TLL description in addition to spin and charge, contains also valley degree of freedom, hence four mode description applies. The values of all four TLL parameters are obtained for this model. A surprising outcome is that the compressibility of the holon mode becomes a universal quantity, while the parameters of neutral modes will depend on the details of inter-shell coupling. Finally, we propose experiments where our predictions can be tested.

cond-mat.mtrl-sci↗

arXiv2024

A first-principles study and mesoscopic modeling of two-dimensional spin and orbital fluctuations in FeSe

We calculated the structural, electronic and magnetic properties of FeSe within density-functional theory at the generalized gradient approximation level. First, we studied how the bandwidth of the d-bands at the Fermi energy are renormalized by adding simple corrections: Hubbard U, Hunds J and by introducing long-range magnetic orders. We found that introducing either a striped or a staggered dimer antiferromagnetic order brings the bandwidths -- which are starkly overestimated at the generalized gradient approximation level -- closer to those experimentally observed. Second, for the ferromagnetic, the striped, checkerboard and the staggered dimer antiferromagnetic order, we investigate the change in magnetic formation energy with local magnetic moment of Fe at a pressure up to 6 GPa. The bilinear and biquadratic exchange energies are derived from the Heisenberg model and noncollinear first-principles calculations, respectively. We found a non-trivial behavior of the spin-exchange parameters on the magnetization, and we put forward a field-theory model that rationalizes these results in terms of two-dimensional spin and orbital fluctuations. The character of these fluctuations can be either that of a standard density wave or a topological vortex. Topological vortexes can result in mesoscopic magnetization structures.

cond-mat.mtrl-sci↗

arXiv2022

Thermal topological phase transition in SnTe from \emph{ab-initio} calculations

One of the key issues in the physics of topological insulators is whether the topologically non-trivial properties survive at finite temperatures and, if so, whether they disappear only at the temperature of topological gap closing. Here, we study this problem, using quantum fidelity as a measure, by means of \emph{ab-initio} methods supplemented by an effective dissipative theory built on the top of the \emph{ab-initio} electron and phonon band structures. In the case of SnTe, the prototypical crystal topological insulator, we reveal the presence of a characteristic temperature, much lower than the gap-closing one, that marks a loss of coherence of the topological state. The transition is not present in a purely electronic system but it appears once we invoke coupling with a dissipative bosonic bath. Features in the dependence with temperature of the fidelity susceptibility can be related to changes in the band curvature, but signatures of a topological phase transition appear in the fidelity only though the non-adiabatic coupling with soft phonons. Our argument is valid for valley topological insulators, but in principle can be generalized to the broader class of topological insulators which host any symmetry-breaking boson.

cond-mat.mtrl-sci↗

arXiv2022

Generalizing Fowler-Nordheim Tunneling Theory for an Arbitrary Power Law Barrier

Herein, the canonical Fowler-Nordheim theory is extended by computing the zero-temperature transmission probability for the more general case of a barrier described by a fractional power law. An exact analytical formula is derived, written in terms of Gauss hypergeometric functions, that fully capture the transmission probability for this generalized problem, including screened interaction with the image potential. First, the quality of approximation against the so far most advanced formulation of Fowler-Nordheim, where the transmission is given in terms of elliptic integrals, is benchmarked. In the following, as the barrier is given by a power law, in detail, the dependence of the transmission probability on the exponent of the power law is analyzed. The formalism is compared with results of numerical calculations and its possible experimental relevance is discussed. Finally, it is discussed how the presented solution can be linked in some specific cases with an exact quantum-mechanical solution of the quantum well problem.

cond-mat.mtrl-sci↗

arXiv2022

ARPES in strongly disordered systems -- theory of electronic bands melting

It is well known that translational symmetry-breaking disorder will disrupt ARPES spectra up to the point where they become invisible. However, a theoretical framework to capture this phenomenon has been largely missing. Here, based on a rigorous theory of the ARPES process, we provide this much-needed framework. In particular, we show how the frequently used sudden electron approximation has to be modified in this situation. Our main result is an argument that links the photoemission line broadening with an operator content of a disorder operator and so with the criticality of the corresponding order-disorder phase transition. For concreteness, we focus here on the frustrated 2D trigonal (pseudo-)spin model, with Ising order-disorder operators behind the transition. Still, our formalism is general and can be applied in a much broader context.

cond-mat.str-el↗

arXiv2022

Temperature dependent ARPES of the metallic-like bands in Si(553)-Au

We conducted a thorough investigation into the temperature dependence of the metallic-like bands of Si(553)-Au using angular-resolved photoemission spectroscopy (ARPES). Our study addresses the challenges posed by the short-term stability of the surface and photo-voltage effects, which we overcame to extract changes in the band-filling and Fermi-velocity. Our findings shed light on the low-temperature phase of the step edge in Si(553)-Au, which has been a topic of ongoing debate regarding its structural or electronic nature. Through comparison with theoretical predictions of a structural-related low-temperature to high-temperature phase transition, we discovered that the band-filling and Fermi-velocity do not change accordingly, thereby ruling out this scenario. Our study contributes to a better understanding of this material system and provides an important reference for future research.

cond-mat.mtrl-sci↗

arXiv2020

Thermal conductivity of porous polycrystalline PbTe

PbTe is a leading thermoelectric material at intermediate temperatures, largely thanks to its low lattice thermal conductivity. However, its efficiency is too low to compete with other forms of power generation. This efficiency can be effectively enhanced by designing nanostructures capable of scattering phonons over a wide range of length scales to reduce the lattice thermal conductivity. The presence of grain boundaries can reduce the thermal conductivity to $\sim 0.5$ Wm$^{-1}$K$^{-1}$ for small vacancy concentrations and grain sizes. However, grains anneal at finite temperature, and equilibrium and metastable grain size distributions determine the extent of the reduction in thermal conductivity. In the present work, we propose a phase-field model informed by molecular dynamics simulations to study the annealing process in PbTe and how it is affected by the presence of grain boundaries and voids. We find that the thermal conductivity of PbTe is reduced by up to 35\% in the porous material at low temperatures. We observe that a phase transition at a finite density of voids governs the kinetics of impeding grain growth by Zener pinning.

cond-mat.mes-hall↗

arXiv2020

Towards temperature-induced topological phase transition in SnTe: A first principles study

The temperature renormalization of the bulk band structure of a topological crystalline insulator, SnTe, is calculated using first principles methods. We explicitly include the effect of thermal-expansion-induced modification of electronic states and their band inversion on electron-phonon interaction. We show that the direct gap decreases with temperature, as both thermal expansion and electron-phonon interaction drive SnTe towards the phase transition to a topologically trivial phase as temperature increases. The band gap renormalization due to electron-phonon interaction exhibits a non-linear dependence on temperature as the material approaches the phase transition, while the lifetimes of the conduction band states near the band edge show a non-monotonic behavior with temperature. These effects should have important implications on bulk electronic and thermoelectric transport in SnTe and other topological insulators.

cond-mat.mtrl-sci↗

arXiv2016

Time evolution during and after finite-time quantum quenches in Luttinger liquids

We consider finite-time quantum quenches in the interacting Tomonaga--Luttinger model, for example time-dependent changes of the nearest-neighbour interactions for spinless fermions. We use the exact solutions for specific protocols including the linear and cosine ramps (or, more generally, periodic pumping). We study the dynamics of the total and kinetic energy as well as the Green functions during as well as after the quench. For the latter we find that the light-cone picture remains applicable, however, the propagating front is delayed as compared to the sudden quench. We extract the universal behaviour of the Green functions and in particular provide analytic, non-perturbative results for the delay applicable to quenches of short to moderate duration but arbitrary time dependency.

cond-mat.str-el↗

arXiv2015

Spin-orbit coupling and proximity effects in metallic carbon nanotubes

We study spin-orbit coupling in metallic carbon nanotubes (CNTs) within the many-body Tomonaga-Luttinger liquid (TLL) framework. For a well defined sub-class of metallic CNTs, that contains both achiral zig-zag as well as a sub-set of chiral tubes, an effective low energy field theory description is derived. We aim to describe system at finite dopings, but close to the charge neutrality point (commensurability). A new regime is identified where spin-orbit coupling leads to an inverted hierarchy of mini-gaps of bosonic modes. We then add a proximity coupling to a superconducting (SC) substrate and show that the only order parameter that is supported within the novel, spin-orbit induced phase is a topologically trivial s-SC.

cond-mat.str-el↗

arXiv2014

The two classes of low energy spectra in finite carbon nanotubes

Electrons in carbon nanotubes (CNTs) possess spin and orbital degrees of freedom. The latter is inherited from the bipartite graphene lattice with two inequivalent Dirac points. The electronic spectra obtained in several transport experiments on CNT quantum dots in parallel magnetic field often show an anticrossing of spectral lines assigned to the opposite Dirac valleys. So far this valley mixing has been attributed to the disorder, with impurity induced scattering. We show that this effect can arise also in ultraclean CNTs of the armchair class and it can be caused solely by the presence of the boundaries. In contrast, in CNTs of the zigzag class it does not occur. These two fundamentally different classes of spectra arise because of different symmetries of the low energy eigenstates of the two types of CNTs. The magnitude of the level splitting depends in a nonmonotonous way on the distance of the involved energy levels from the charge neutrality point.

cond-mat.mes-hall↗

arXiv2014

Magnetoplasmon resonances in polycrystalline bismuth as seen via terahertz spectroscopy

We report the magnetic field-dependent far-infrared reflectivity of polycrystalline bismuth. We observe four distinct absorptions that we attribute to magnetoplasmon resonances, which are collective modes of an electron-hole liquid in magnetic field and become optical and acoustic resonances of the electron-hole system in the small-field limit. The acoustic mode is expected only when the masses of distinct components are very different, which is the case in bismuth. In a polycrystal, where the translational symmetry is broken, a big shift of spectral weight to acoustic plasmon is possible. This enables us to detect an associated plasma edge. Although the polycrystal sample has grains of randomly distributed orientations, our reflectivity results can be explained by invoking only two, clearly distinct, series of resonances. In the limit of zero field, the optical modes of these two series converge onto plasma frequencies measured in monocrystal along the main optical axes.

cond-mat.str-el↗

arXiv2012

Magnetic phases in the one-dimensional Kondo chain on a metallic surface

We study the low-temperature properties of a one-dimensional spin-1/2 chain of magnetic impurities coupled to a (normal) metal environment by means of anisotropic Kondo exchange. In the case of easy-plane anisotropy, we obtain the phase diagram of this system at T=0. We show that the in-plane Kondo coupling destabilizes the Tomonaga-Luttinger phase of the spin-chain, and leads to two different phases: i) At strong Kondo coupling, the spins in the chain form Kondo singlets and become screened by the metallic environment, and ii) At weak and intermediate Kondo coupling, we find a novel dissipative phase characterized by diffusive gapless spin excitations. The two phases are separated by a quantum critical point of the Wilson-Fisher universality class with dynamical exponent $z\simeq2$.

cond-mat.mes-hall↗