arXiv subjects

Andrzej Ptok

Publications and source records attributed to Andrzej Ptok.

At least 37 records · Page 2Linked to original sources

arXiv2025

Electronic structure in a rare-earth based nodal-line semimetal candidate PrSbTe

Nodal line semimetals feature topologically protected band crossings between the bulk valence and conduction bands that extend along a finite dimension in the form of a line or a loop. While ZrSiS and similar materials have attracted extensive research as hosts for the nodal line semimetallic phase, an alternative avenue has emerged in the form of isostructural rare-earth (RE) based RESbTe materials. Such systems possess intriguing potentialities for harboring elements of magnetic ordering and electronic correlations owing to the presence of 4f electrons intrinsic to the RE elements. In this study, we have carried out angle resolved photoemission spectroscopy (ARPES) and thermodynamic measurements in conjunction with first principles computations on PrSbTe to elucidate its electronic structure and topological characteristics. Magnetic and thermal characterizations indicate the presence of well-localized 4f states with the absence of any discernible phase transition down to 2 K. The ARPES results reveal the presence of gapless Dirac crossings that correspond to a nodal-line along the XR direction in the three-dimensional Brillouin zone. Furthermore, Dirac crossing that makes up nodal line, which forms a diamond-shaped nodal plane centered at the center of the Brillouin zone is also identified within the experimental resolution. This study on the electronic structure of PrSbTe contributes to the understanding of the pivotal role played by spin-orbit coupling in the context of the RESbTe family of materials

cond-mat.mtrl-sci↗

arXiv2025

Topological in-gap chiral edge states in superconducting Haldane model with spin-orbit coupling

Topological superconductivity is currently one of the prime interests, given the properties of its exotic nature of chiral edge states. A broken time-reversal symmetry (TRS) is an essential ingredient in the recipe of a chiral edge state. The Haldane model is one of the many factors that can break TRS in a system. Thus, we explore the possibility of topological superconductivity in the Haldane model under the influence of a conventional superconductor. The edge states originating from such recipes mostly remain outside the superconducting gap. Contrary to this, in the presence of spin-orbit coupling, the edge modes lie within the superconducting gap, and can lead to a gapless state for some range of parameters. Moreover, we use band inversion and projection on the real-space lattice to confirm the topological and chiral nature of the obtained edge states.

cond-mat.supr-con↗

arXiv2025

Landau levels in Weyl semimetal under uniaxial strain

The external strain can lead to the similar effect to the external applied magnetic field. Such pseudomagnetic field can be larger than typical magnetic fields, what gives the opportunity to experimentally study the Landau levels. In this paper we study the effects of uniaxial strain on the Weyl nodes, using continuum and lattice model. In the continuum model we show that the uniaxial strain leads to magnetic field renormalization, which in practice corresponds to the shift of the Landau levels to higher energy. We also investigate type-I and type-II Weyl nodes using lattice model. In this case, the magnetic field is introduced by the Pierels substitution, while uniaxial strain by the direction dependence of hopping integrals. This allowed us to probe the Landau level and system spectrum which takes form of Hofstadter butterfly. We show that the renormalization of magnetic field, similar to this observed in the continuum model, emerges.

cond-mat.mes-hall↗

arXiv2025

Unveiling the interplay of magnetic order and electronic band structure on the evolution of anomalous Hall effect in MnPtGa single crystal

The recent studies on the anomalous Hall effect (AHE) have revealed an intrinsic relationship between the topological band structure and the experimentally observed transverse conductivity. Consequently, this has led to a heightened focus on examining the topological aspects of AHE. Here we have studied sign reversal of anomalous Hall conductivity with temperature in the single crystalline MnPtGa (space group: $P6_3/mmc$). From the interdependence of the linear resistance, we claim that the origin of such behavior is intrinsic. By systematically studying the electronic band structure and Berry curvature of MnPtGa using first principle calculations supported by magnetic susceptibility and isothermal magnetization measurements we demonstrate that the temperature dependent complex magnetic structure plays a significant role and leads to the sign reversal of anomalous Hall conductivity. We proposed a continuous evolution of the magnetic structure, supported by the ab initio calculations, which is consistent with the experimental data. Our studies have established that the critical temperature ($\approx$110 K), where the sign reversal appears is associated with the magnetic structure and the magnitude of Mn moments.

cond-mat.mtrl-sci↗

arXiv2025

Insulating Half-Heusler TmPdSb with Unusual Band Order and Metallic Surface States

We present theoretical and experimental results exploring a half-Heusler compound TmPdSb with unusual band order and metallic surface states. Typically, the half-Heusler systems exhibit topological features in a semimetallic state, and trivial ones in an insulating state. Topological properties of the most of half-Heusler systems are related to the band inversion around the Fermi level, similar to this observed in CdTe/HgTe systems. In the case of TmPdSb we observed the gapped electronic band structure with ``band inversion'' in the conductance band, while the slab-like system realized metallic surface states. The bulk insulating nature of the compound was corroborated by means of electrical transport measurements. The experimental data revealed several features due to the presence of metallic surface states, such as linear magnetoresistance and weak-antilocalization effect, characterized by enhanced coherence length and a very large number of surface conductive channels. Our findings reveal new features of the rare-earth half-Heusler.

cond-mat.mtrl-sci↗

arXiv2025

Comment on "Fully gapped superconductivity and topological aspects of the noncentrosymmetric superconductor TaReSi"

In a recent paper [T. Shang et al., Phys. Rev. B 107, 224504 (2023)], the authors study the physical properties of TaReSi compounds having Ima2 structure. This noncentrosymmetric structure is proposed to be the source of topological properties for mentioned compound. However, for a correct description of topological features, it is important to recognize the correct structure of the compound at low temperature. In this Comment, we show that Ima2 cannot be realized by TaReSi and is unstable at low temperature. The Ima2 structure contains the soft modes at S (1/2,0,0) point, which leads to the stable structure with Cm symmetry. Notably, the stable Cm system also has a noncentrosymmetric structure, which can be the actual source of topological properties.

cond-mat.supr-con↗

arXiv2025

Lattice dynamics study of electron-correlation-induced charge density wave in antiferromagnetic kagome metal FeGe

Electron-correlation-driven phonon soft modes have been recently reported in the antiferromagnetic kagome FeGe compound and associated with the observed charge density wave (CDW). In this paper, we present a systematic investigation of the CDW origin in the context of the ab initio lattice dynamics study. Performing the group theory analysis of the mentioned soft mode, we found that the stable structure has the Immm symmetry and can be achieved by shifts of Ge atoms. Additionally, we show that the final structure realizes a distorted honeycomb Ge lattice as well as a non-flat kagome-like Fe net. For completeness, we present the electronic properties calculations. From the theoretical STM topography simulation, we indicate that the observed CDW occurs in the deformed honeycomb Ge sublattice.

cond-mat.mtrl-sci↗

arXiv2025

Low temperature phase of AuSn$_{4}$ induced by the van der Waals interactions

AuSn$_{4}$ is the example of an compound that exhibits topological properties. Recent XRD measurements reveal an ambiguous nature of the crystal structure, as it can be realized with either Aea2 or Ccca symmetry. Motivated by this, we analyze the dynamical stability of the compound. We discuss the role of van der Waals (vdW) corrections within the ab initio calculation. Interestingly, our main result indicates that AuSn$_{4}$ can be unstable with both Aea2 and Ccca symmetries, due to the soft modes in the phonon spectra. From the soft mode analyses we find dynamically stable Pc structure. This structure has always smaller energy than Aea2 or Ccca crystal and it stays independent of the vdW correction. We also show that the comparison of theoretical electronic properties with the experimental ARPES measurements. Our findings may be valuable in the future investigations of AuSn$_{4}$-like compounds.

cond-mat.mtrl-sci↗

arXiv2025

Type-II Weyl nodes, flat bands, and evidence for a topological Hall-effect in the new ferromagnet FeCr$_3$Te$_6$

The interplay between linearly dispersing or Dirac-like, and flat electronic bands, for instance, in the kagome ferromagnets, has attracted attention due to a possible interplay between topology and electronic correlations. Here, we report the synthesis, structural, electrical, and magnetic properties of a single-crystalline ferromagnetic compound, namely Fe$_{1/3}$CrTe$_2$ or FeCr$_3$Te$_6$, which crystallizes in the $P\bar{3}m1$ space group instead of the $I2/m$ previously reported for FeCr$_2$Te$_4$. Electronic band structure calculations reveal type-II Dirac nodes and relatively flat bands near the Fermi level ($\varepsilon_F$). This compound shows onset Curie temperature $T_{\text{c}}\simeq 120$ K, followed by an additional ferromagnetic transition near $T_{\text{c2}} \sim 92.5 $ K. Below $T_{\text{c}}$, FeCr$_3$Te$_6$ displays a pronounced anomalous Hall effect, as well as sizable coercive fields that exceed $μ_0H = 1$~T at low $T$s. However, a scaling analysis indicates that the anomalous Hall effect results from a significant intrinsic contribution, as expected from the calculations, but also from the extrinsic mechanism, i.e., scattering. The extrinsic contribution probably results from occupational disorder at the 1b Fe-site within the van der Waals gap of the CrTe$_2$ host. We also observe evidence for a topological Hall component superimposed onto the overall Hall response, suggesting the presence of chiral spin textures akin to skyrmions in this centrosymmetric system. Their possible presence will require experimental confirmation.

cond-mat.other↗

arXiv2025

Low-lying Electronic Structure of Rare-Earth Based Topological Nodal Line Semimetal Candidate DySbTe

Lanthanide (Ln) based LnSbTe materials have garnered significant attention due to rich interplay of long range magnetic ordering and topological properties, driven by unique crystalline symmetry, 4f electron interactions, and pronounced spin-orbit coupling (SOC) effects. DySbTe, as a heavier lanthanide-based member of the LnSbTe family, stands out with its SOC and larger on site interactions on its 4f electrons, which arise due to the heavier Dy element. Here, we present a comprehensive study on the low-temperature bulk physical properties and the electronic structure of DySbTe using magnetic susceptibility, heat capacity, and electrical resistivity measurements, along with high-resolution angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy and spectroscopy (STM/S), and density functional theory calculations. Our thermodynamic measurements revealed an antiferromagnetic ordering below TN = 7.45 K and a subsequent magnetic phase transition at TN1 = 7.15 K. Our transport studies indicate a semimetallic behavior with unusual feature in the ordered state. Our ARPES measurements revealed a diamond-shaped Fermi pocket centered at the G point, with band features that evolve distinctly across various binding energies. STM/S results indicate a minimum in the density of states at around 100 meV below the Fermi level, and ARPES measurements reveal a significant gap present around the X point, differentiating DySbTe from other LnSbTe compounds. These findings enhance our understanding of the SOC effects on the electronic structure and topological properties in the LnSbTe family, highlighting DySbTe as a promising candidate for exploring the interplay between topology and magnetism.

cond-mat.mes-hall↗

arXiv2025

Origin of $A$-type antiferromagnetism and chiral split magnons in altermagnetic $α$-MnTe

The origin of the $A$-type antiferromagnetic ordering, characterized by ferromagnetic layers coupling antiferromagnetically, in the prototype semiconductor altermagnet $α$-MnTe has been a topic of ongoing debate. Experimentally, $α$-MnTe exhibits an in-plane ferromagnetic exchange interaction, whereas previous \emph{ab initio} calculations predicted an antiferromagnetic interaction. In this paper, we resolve this discrepancy by considering an expanded set of magnetic configurations, which reveals a ferromagnetic in-plane exchange interaction in agreement with experimental findings. Additionally, we demonstrate that the 10th nearest-neighbor exchange interaction is directionally dependent, inducing a nonrelativistic chiral splitting in the magnon bands, as recently observed experimentally. We further show that applying a compressive strain may significantly enhance both nonrelativistic spin and chiral magnon splittings. The strain can also change the sign of the in-plane exchange interaction. Computing magnetic susceptibility, we show that strain enhances the N{é}el temperature, significantly. Our results highlight the critical importance of convergence in the number of magnetic configurations for spin interactions in antiferromagnetic materials.

cond-mat.mtrl-sci↗

arXiv2025

Correlation stabilized ferromagnetic MnRuAs with distorted kagome lattice

We present an in-depth analysis of MnRuAs, a compound crystallizing in the P$\bar{6}$2m symmetry with a distorted kagome lattice, revealing its distinctive structural, magnetic, and electronic properties through state-of-the-art ab initio calculations. By incorporating strong correlation effects using the DFT+U approach, we demonstrate the stabilization of MnRuAs, transforming its inherent dynamical instability into a robust ferromagnetic state with significant coupling along the $c$ axis. The calculated magnon dispersion reveals a parabolic profile with a minimum at the $Γ$ point, indicative of ferromagnetic behavior. Furthermore, MnRuAs exhibits intriguing electronic properties, including quasi-one-dimensional Fermi surface and the formation of nodal sphere. Our study also delves into the electronic surface states and constant energy contours, offering valuable insights into the complex physics of this material.

cond-mat.mtrl-sci↗

arXiv2025

Evidences for local non-centrosymmetricity and strong phonon anomaly in EuCu2As2: A Raman spectroscopy and lattice dynamics study

Phonon modes and their association with the electronic states have been investigated for the metallic EuCu$_{2}$As$_{2}$ system. In this work, we present the Raman spectra of this pnictide system which clearly shows the presence of seven well defined peaks above $100$~cm$^{-1}$ that is consistent with the locally non-centrosymmetric {\it P4/nmm} crystal structure, contrary to that what is expected from the accepted symmorphic {\it I4/mmm} structure. Lattice dynamics calculations using the {\it P4/nmm} symmetry attest that there is a commendable agreement between the calculated phonon spectra at the $Γ$ point and the observed Raman mode frequencies, with the most intense peak at $\sim 232$~cm$^{-1}$ being ascribed to the A$_{1g}$ mode. Temperature dependent Raman measurements show that there is a significant deviation from the expected anharmonic behaviour around $165$~K for the A$_{1g}$ mode, with anomalies being observed for several other modes as well, although to a lesser extent. Attempts are made to rationalize the observed anomalous behavior related to the hardening of the phonon modes, with parallels being drawn from metal dichalcogenide and allied systems. Similarities in the evolution of the Raman peak frequencies with temperature seem to suggest a strong signature of a subtle electronic density wave instability below $165$~K in this compound.

cond-mat.str-el↗

arXiv2024

Electronic properties and surface states of RbNi$_2$Se$_2$

Iron-based superconductors, with the ThCr$_{2}$Si$_{2}$-type tetragonal structure (122 family), due to the iron arsenide/selenide layers exhibit several characteristic electronic properties. For example, multiband character mosty associated with the $d$-orbitals of iron and the quasi-two-dimensional (2D) cylindrical Fermi surface. Moreover, external hydrostatic pressure leads to the isostructural phase transition from the tetragonal to collapsed-tetragonal phase. In this paper, in relation to the iron-based superconductors, we discuss the electronic properties of novel 122-family member RbNi$_{2}$Se$_{2}$ [Liu H. et al., Phys. Rev. B 106, 094511 (2022)]. We show that the two Fermi pockets exhibit quasi-2D character. Calculation of the surface spectral function for the (001) surface shows that the surface states are realized independently on the surface termination. Additionally, contrary to the iron-based 122 compounds, RbNi$_{2}$Se$_{2}$ exhibits extraordinary multiple isostructural phase transitions under pressure. Moreover, the Lifshizt transition occurs under external pressure, which results into a strong modification of the shapes of the Fermi pockets.

cond-mat.supr-con↗

arXiv2024

Dirac Dispersions and Fermi Surface Nesting in LaCuSb$_{2}$

LaCuSb$_{2}$ is a superconductor with a transition temperature of about $T_\text{c} = 0.9$K and is a potential platform where Dirac fermions can be experimentally observed. In this paper, we report systematic high-resolution studies of its electronic structure using the angle-resolved photoemission spectroscopy (ARPES) technique supported by the DFT calculation. The Fermi surface consists of four branches, of which the two inner ones are more 3-dimensional and the theoretical calculations reproduce well the experiment. We observe several linear dispersions forming Dirac-like structures. The nodal lines are present in the system along ${\text{M}}$-${\text{A}}$ and ${\text{X}}$-${\text{R}}$ and Dirac crossings along ${\text{X}}$-${\text{R}}$ are observed by ARPES. Finally, the nesting between external Fermi surface pockets, which corresponds to charge density wave (CDW) modulation vector is enhanced in LaCuSb$_{2}$ as compared to LaAgSb$_{2}$, while CDW appears in the latter system.

cond-mat.mtrl-sci↗

arXiv2024

Electronic and dynamical properties of cobalt monogermanide CoGe phases under pressure

We present the pressure dependence of the electronic and dynamical properties of six different CoGe phases: orthorhombic Cmmm, hexagonal P6/mmm and P$\bar{6}$2m, monoclinic C2/m, cubic P2$_{1}$3, and orthorhombic Pnma. Using first-principles DFT calculations and the direct force-constants method, we study the dynamical stability of individual phases under external pressure. We show that the orthorombic Cmmm and hexagonal P6/mmm structures are unstable over a broad pressure range and most pronounced imaginary phonon soft mode in both cases leads to a stable hexagonal P$\bar{6}$2m structure of the lowest ground-state energy of all studied phases at ambient and low (below $\sim 3$ GPa) external pressure. Under these conditions, the cubic P2$_{1}$3 phase has the highest energy, however, together with monoclinic C2/m and orthorombic Pnma it is dynamically stable and all these three structures can potentially coexist as meta-stable phases. Above $\sim 3$ GPa, the cubic P2$_{1}$3 phase becomes the most energetically favorable. Fitting the Birch--Murnaghan equation of state we derive bulk modulus for all mentioned phases, which indicate relatively high resistance of CoGe to compression. Such conclusions are confirmed by band structure calculations. Additionally, we show that electronic bands of the hexagonal P$\bar{6}$2m phase reveal characteristic features of the kagome-like structure, while in the cubic P2$_{1}$3 phase spectrum, one can locate spin-1 and double Weyl fermions. In both cases, the external pressure induces the Lifshitz transition, related to the modification of the Fermi surface topology.

cond-mat.mtrl-sci↗

arXiv2024

Lattice dynamics of altermagnetic ruthenium oxide RuO$_{2}$

Altermagnetic ruthenium oxide RuO$_{2}$ crystallizes with P4$_{2}$/mnm symmetry. Here we discuss the lattice dynamics of this structure. We show and discuss the phonon dispersion and density of states. The phonon dispersion curves contain several Dirac nodal lines and highly degenerate Dirac points. We present the characteristic frequencies and their irreducible representations at the $Γ$ point. Theoretically obtained frequencies of the Raman active modes nicely reproduce the ones reported experimentally.

cond-mat.mtrl-sci↗

arXiv2023

Complex Fermiology and Electronic Structure of Antiferromagnet EuSnP

We studied the electronic structure of a layered antiferromagnetic metal, EuSnP, in the paramagnetic and in the antiferromagnetic phase using angle resolved photoemission spectroscopy (ARPES) alongside density functional theory (DFT) based first principles calculations. The temperature dependence of the magnetic susceptibility measurements exhibits an antiferromagnetic transition at a Neel temperature of 21 K. Employing high resolution ARPES, the valence band structure was measured at several temperatures above and below the Neel temperature, which produced identical spectra independent of temperature. Through analysis of the ARPES results presented here, we attribute the temperature independent spectra to the weak coupling of the Sn, and P conduction electrons with Eu 4f states.

cond-mat.mes-hall↗