arXiv subjects

Andrzej Ptok

Publications and source records attributed to Andrzej Ptok.

At least 55 records · Page 3Linked to original sources

arXiv2023

Anisotropic positive linear and sub-linear magnetoresistivity in the cubic type-II Dirac metal Pd$_3$In$_7$

We report a transport study on Pd$_3$In$_7$ which displays multiple Dirac type-II nodes in its electronic dispersion. Pd$_3$In$_7$ is characterized by low residual resistivities and high mobilities, which are consistent with Dirac-like quasiparticles. For an applied magnetic field $(μ_{\text{0}} H)$ having a non-zero component along the electrical current, we find a large, positive, and linear in $μ_{\text{0}} H$ longitudinal magnetoresistivity (LMR). The sign of the LMR and its linear dependence deviate from the behavior reported for the chiral-anomaly-driven LMR in Weyl semimetals. Interestingly, such anomalous LMR is consistent with predictions for the role of the anomaly in type-II Weyl semimetals. In contrast, the transverse or conventional magnetoresistivity (CMR for electric fields $\textbf{E} \bot μ_{\text{0}} \textbf{H}$) is large and positive, increasing by $10^3-10^4$ \% as a function of $μ_{\text{0}}H$ while following an anomalous, angle-dependent power law $ρ_{\text{xx}}\propto (μ_{\text{0}}H)^n$ with $n(θ) \leq 1$. The order of magnitude of the CMR, and its anomalous power-law, is explained in terms of uncompensated electron and hole-like Fermi surfaces characterized by anisotropic carrier scattering likely due to the lack of Lorentz invariance.

cond-mat.mes-hall↗

arXiv2023

Electronic properties and surface states of CeRh$_{2}$As$_{2}$

Locally noncentrosymmetric CeRh$_{2}$As$_{2}$ exhibits characteristic two-phase unconventional $H$--$T$ superconducting phase diagram. The transition from even- to odd-parity superconducting phase is supported by the P4/nmm crystal structure and it can be induced by the external magnetic field. Dual nature of the Ce $f$ electrons and competition between their itinerant and localized nature can be important for its physical proprieties. The existing electronic band structure in this material is still under debate. Energy scale occurring in the system can be important for adequate theoretical description of its supercomputing properties. In this paper, we discuss electronic band structure obtained from {\it ab initio} calculations. We analyze electronic surface states which can be compared with recently obtained angle-resolved photoemission spectroscopy measurement (ARPES). Additionally, we present the analyses of the hopping parameters obtained from the electronic band structure. The As-Rh layers are characterized by much more significant hopping parameters between atoms than these obtained for the Ce-Ce atoms. This suggests need of a revision of the tight binding model necessary for adequate description of the physical properties of CeRh$_{2}$As$_{2}$.

cond-mat.supr-con↗

arXiv2023

Observation of momentum-dependent charge density wave gap in a layered antiferromagnet GdTe3

Charge density wave (CDW) ordering has been an important topic of study for a long time owing to its connection with other exotic phases such as superconductivity and magnetism. The RTe3 (R = rare-earth elements) family of materials provides a fertile ground to study the dynamics of CDW in van der Waals layered materials, and the presence of magnetism in these materials allows to explore the interplay among CDW and long range magnetic ordering. Here, we have carried out a high-resolution angle-resolved photoemission spectroscopy (ARPES) study of a CDW material GdTe3, which is antiferromagnetic below 12 K, along with thermodynamic, electrical transport, magnetic, and Raman measurements. Our Raman spectroscopy measurements show the presence of CDW amplitude mode at room temperature, which remains prominent when the sample is thinned down to 4-layers by exfoliation. Our ARPES data show a two-fold symmetric Fermi surface with both gapped and ungapped regions indicative of the partial nesting. The gap is momentum dependent, maximum along G-Z and gradually decreases going towards G - M. Our study provides a platform to study the dynamics of CDW and its interaction with other physical orders in two- and three-dimensions.

cond-mat.mes-hall↗

arXiv2023

Tuning the topological character of half-Heusler systems: A comparative study on Y$T$Bi ($T$ = Pd, Pt)

Half-Heusler systems host a plethora of different ground states, especially with non-trivial topology. However, there is still a lack of spectroscopic insight into the corresponding band inversion in this family. In this work, we locally explore the half-Heuslers Y$T$Bi ($T =$ Pt and Pd) by means of scanning tunneling microscopy/spectroscopy. From our analysis of the (120) surface plane, we infer that the increase of the spin--orbit coupling upon going from Pd to Pt is the main player in tuning the surface states from trivial to topologically non-trivial. Our measurements unveil a ($2 \times 1$) reconstruction of the (120) surface of both systems. Using density functional theory calculations, we show that the observed different behavior of the local density of states near the Fermi level in these two materials is directly related to the presence of metallic surface states. Our work sheds new light on a well known tunable family of materials and opens new routes to explore the presence of topological states of matter in half-Heusler systems and its microscopic observation.

cond-mat.mtrl-sci↗

arXiv2023

Ruthenium dioxide RuO$_{2}$: effect of the altermagnetism on the physical properties

Ruthenium oxide with the rutile structure is one of example of altermagnets. These systems are characterized by compensated magnetic moments (typical for antiferromagnets) and strong time reversal symmetry breaking (typical for ferromagnets). However, in such cases, the electronic band structure exhibit strong spin splitting along some directions in the momentum space. Occurrence of the compensated magnetic textures allows for realization of surfaces with specific magnetization, which dependent on the surface orientation and/or its termination. Here, we study interplay between the electronic surface states and the surface magnetization. We show that the spin-resolved spectra strongly depends on a direction in reciprocal space. Such properties can be used for the experimental confirmation of the altermagnetism in RuO$_{2}$ within the spectroscopic techniques. Additionally, we show that the most modified orbitals in the system are $d_{z^{2}}$ and $d_{xy}$ orbitals of Ru. Similarly, the Ru $e_{g}$ states are most sensitive on epitaxial strain, what can suggest some link between altermagnetism and strain.

cond-mat.mtrl-sci↗

arXiv2023

Phononic drumhead surface state in distorted kagome compound RhPb

RhPb was initially recognized as one of a CoSn-like compounds with $P6/mmm$ symmetry, containing an ideal kagome lattice of $d$-block atoms. However, theoretical calculations predict the realization of the phonon soft mode which leads to the kagome lattice distortion and stabilization of the structure with $P\bar{6}2m$ symmetry [A. Ptok et al., Phys. Rev. B 104, 054305 (2021)]. Here, we present the single crystal x-ray diffraction results supporting this prediction. Furthermore, we discuss the main dynamical properties of RhPb with $P\bar{6}2m$ symmetry. The bulk phononic dispersion curves contain several flattened bands, Dirac nodal lines, and triple degenerate Dirac points. As a consequence, the phononic drumhead surface state is realized for the (100) surface, terminated by the zigzag-like edge of Pb honeycomb sublattice.

cond-mat.mtrl-sci↗

arXiv2023

Spin-polarized superconducting phase in semiconducting system with next-nearest-neighbor hopping on the honeycomb lattice

The particles in the honeycomb lattice with on-site $s$-wave pairing exhibit many interesting behaviors, which can be described in the framework of the Hubbard model. Among others, at the half-filling, some critical value $|U_c|$ of pairing interaction $U<0$ exists that, for $U<U_c$, the superconducting phase becomes unstable. Introduction of the nonzero hopping $t'$ between next-nearest-neighbor sites strongly modifies the physical properties of the system. Here, we discuss the behavior of the system for $t' \neq 0$ (at the ground state), where the hopping between next-nearest neighbors leads to change of the order of phase transition between superconducting and normal phases from discontinuous to continuous one in the external magnetic field $h$. We show that this behavior is strongly dependent on $t'$ and associated with the Dirac cones in the non-interacting band structure of the system. For non-zero magnetic field and for some range of $t'$, a spin-polarized superconducting phase occurs in the ground state phase diagram (only at the half-filling and for $h\neq 0$).

cond-mat.supr-con↗

arXiv2023

Observation of gapless nodal-line states in NdSbTe

Lanthanide (Ln) based systems in the ZrSiS-type nodal-line semimetals have been subjects of research investigations as grounds for studying the interplay of topology with possible magnetic ordering and electronic correlations that may originate from the presence of Ln 4f electrons. In this study, we carried out a thorough study of a LnSbTe system - NdSbTe - by using angle-resolved photoemission spectroscopy along with first-principles calculations and thermodynamic measurements. We experimentally detect the presence of multiple gapless nodal-line states, which is well supported by first-principles calculations. A dispersive and an almost non-dispersive nodal-line exist along the bulk X-R direction. Another nodal-line is present well below the Fermi level across the G- M direction, which is formed by bands with high Fermi velocity that seem to be sensitive to light polarization. Our study provides an insight into the electronic structure of a new LnSbTe material system that will aid towards understanding the connection of Ln elements with topological electronic structure in these systems.

cond-mat.mes-hall↗

arXiv2023

Chiral phonons in binary compounds $A$Bi ($A$ = K, Rb, Cs) with P2$_1$/c structure

Binary compounds $A$Bi ($A$ = K, Rb, Cs) crystallize in P2$_1$/c structure containing both clockwise and anticlockwise chiral chains of Bi atoms. Electronic band structure exhibits the insulating nature of these systems, with the band gap about $0.25$ eV. The presented study of dynamical properties confirm a stability of the system with P2$_1$/c symmetry. The crystal structure contains the quasi-one-dimensional Bi chains, exhibiting four-fold-like rotational ``local'' symmetry. Nevertheless, the system formally posses two-fold rotational symmetry. Independently of the absence of the three-fold (or higher) rotational symmetry axes for the whole crystal, the chiral modes propagate along the Bi atom chains in these systems. We discuss basic properties of these modes in monoatomic chiral chains. We show that the two-fold rotational symmetry axis affects the main properties of the chiral phonons, which are not realized at the high-symmetry points, but along some paths between them in the reciprocal space. In addition, in the doped system, the chiral phonons possess non-zero total angular momentum.

cond-mat.mtrl-sci↗

arXiv2023

$T_{3}$Pb$_{2}Ch_{2}$ ($T$=Pd,Pt and $Ch$=S,Se) with transition metal kagome net: Dynamical properties, phonon nodal line, phonon surface states, and chiral phonons

Shandite with Ni$_{3}$Pb$_{2}$S$_{2}$ chemical formula and R$\bar{3}$m symmetry, contains the kagome sublattice formed by the transition metal atoms. Recent experimental results confirmed the possibility of successfully synthesizing Pd$_{3}$Pb$_{2}Ch_{2}$ ($Ch$=S,Se) with the same structure. In this paper, we theoretically investigate the dynamical properties of such compounds. Furthermore, we study the possibility of realizing Pt$_{3}$Pb$_{2}Ch_{2}$ with the shandite structure. We show that the Pd$_{3}$Pb$_{2}${\it Ch}$_{2}$ and Pt$_{3}$Pb$_{2}$S$_{2}$ are stable with R$\bar{3}$m symmetry. In the case of Pt$_{3}$Pb$_{2}$S$_{2}$, there is a soft mode, which is the source of the structural phase transition from R$\bar{3}$m to R$\bar{3}$c symmetry, related to the distortion within the kagome sublattice. We discuss realized phonon nodal lines in the bulk phonon dispersions in upper frequency modes. We show that the shandite structure can host the phonon surface states, with strong dependence by the surface kind. Additionally, chiral phonons with circular motion of the Pb atoms around the equilibrium position are realized.

cond-mat.mtrl-sci↗

arXiv2023

Influence of $f$ Electrons on the Electronic Band Structure of Rare-Earth Nickelates

Recently, superconductivity was discovered in the infinite layer of hole-doped nickelates NdNiO$_{2}$. Contrary to this, superconductivity in LaNiO$_{2}$ is still under debate. This indicates the crucial role played by the $f$ electrons on the electronic structure and the pairing mechanism of infinite-layer nickelates. Here we discuss the role of the electron correlations on the $f$ electron states and their influence on the electronic structure. We show that the lattice parameters are in good agreement with the experimental values, independent of the chosen parameters within the DFT+$U$ approach. Increasing Coulomb interaction $U$ tends to shift the $f$ states away from the Fermi level. Surprisingly, independently of the position of $f$ states with respect to the Fermi energy, these states play an important role in the electronic band structure, which can be reflected in the modification of the NdNiO$_{2}$ effective models.

cond-mat.str-el↗

arXiv2022

Theoretical study of dynamical and electronic properties of noncentrosymmetric superconductor NbReSi

The noncentrosymmetric NbReSi superconductor with $T_{c} \simeq 6.5$ K is characterized by the relatively large upper critical magnetic field. Its multigap features were observed experimentally. Recent studies suggested realization of P$\bar{6}$2m or Ima2 symmetry. We discuss the dynamical properties of both symmetries (e.g., phonon spectra). In this paper, using the ab initio techniques, we clarify this ambiguity, and conclude that the Ima2 symmetry is unstable, and P$\bar{6}$2m should be realized. The P$\bar{6}$2m symmetry is also stable in the presence of external hydrostatic pressure. We show that NbReSi with the P$\bar{6}$2m symmetry should host phonon surface states for (100) and (110) surfaces. Additionally, we discuss the main electronic properties of the system with the stable symmetry.

cond-mat.supr-con↗

arXiv2022

Chiral phonon in the cubic system based on the Laves phase of $A$Bi$_{2}$ ($A=$K, Rb, Cs)

$A$B$_{2}$ ($A=$K, Rb, Cs) compounds crystallize in the cubic Laves phase (symmetry Fd$\bar{3}$m). The geometry of the crystal structure allows the realization of chiral phonons, which are associated with the circulation of atoms around their equilibrium positions. Due to the inversion symmetry and time reversal symmetry, total pseudo-angular momentum (PAM) of the system vanishes. We show that the doping of these system can lead to a new phase with symmetry F$\bar{4}3$m. New systems (KRbBi$_{4}$ and RbCsBi$_{4}$) do not exhibit soft modes (are stable dynamically). Due to the inversion symmetry breaking, realized chiral phonon modes posses a non-zero total PAM. In both type of systems the chiral phonons are realized for the wavectors at the edge of the Brillouine zone. This study explores the possibility of chiral phonon engineering via doping, and predicts two new materials. Discussing the problem opens a new way to study the phonon Hall effect.

cond-mat.mtrl-sci↗

arXiv2022

Connection between the semiconductor--superconductor transition and the spin-polarized superconducting phase in the honeycomb lattice

The band structure of noninteracting fermions in the honeycomb lattice exhibits the Dirac cones at the corners of the Brillouin zone. As a consequence, fermions in this lattice manifest a semiconducting behavior below some critical value of the onsite attraction, $U_{c}$. However, above $U_{c}$, the superconducting phase can occur. We discuss an interplay between the semiconductor--superconductor transition and the possibility of realization of the spin-polarized superconductivity (the so-called Sarma phase). We show that the critical interaction can be tuned by the next-nearest-neighbor (NNN) hopping in the absence of the magnetic field. Moreover, a critical value of the NNN hopping exists, defining a range of parameters for which the semiconducting phase can emerge. In the weak coupling limit case, this quantum phase transition occurs for the absolute value of the NNN hopping equal to one third of the hopping between the nearest neighbors. Similarly, in the presence of the magnetic field, the Sarma phase can appear, but only in a range of parameters for which initially the semiconducting state is observed. Both of these aspects are attributed to the Lifshitz transition, which is induced by the NNN hopping as well as the external magnetic field.

cond-mat.supr-con↗

arXiv2022

Termination dependence of the surface states in Pb$_{2}$Pd

Topological properties of systems lead to the emergence of surface states which can be observed experimentally within the angle-resolved photoemission spectroscopy (ARPES) measurements. Recently, the topological properties of Pb$_{2}$Pd were reported. In this paper, we discuss the role of the surface termination on the realized surface states. We discuss the termination dependence of the surface state for (001) and (110) surface. We demonstrate that the Pd terminated (001) surface allow realization of the Dirac cone-like surface state. In the case (110) we observe well visible surface states with parabolic-like dispersion relation in close vicinity of the Fermi level.

cond-mat.mtrl-sci↗

arXiv2022

Majorana bound states in the presence of the half-smeared potential

The Majorana bound state can be realized in one dimensional chain, in form of two well localized and separated states at both ends of the chain. In this paper, we discuss the case when the potential is smeared at one end of the system. In our investigation, we assume the smearing in form of a quadratic function of position. We show that the smearing potential lead to the emergence of extra in-gap states, and effectively decrease the local gap (around the smeared potential). The Majorana states are still preserved in the system, however, their localization depend on the smearing. Moreover, the symmetric localization of the Majorana states from both side of the system is no longer preserved in the presence of the smearing potential.

cond-mat.supr-con↗

arXiv2022

Electronic band structure and surface states in Dirac semimetal LaAgSb$_{2}$

LaAgSb$_{2}$ is a Dirac semimetal showing charge density wave (CDW) order. Previous ARPES results suggest the existence of the Dirac-cone-like structure in the vicinity of the Fermi level along the $Γ$-M direction [X. Shi et al., Phys. Rev. B 93, 081105(R) (2016)]. This paper is devoted to a complex analysis of the electronic band structure of LaAgSb$_{2}$ by means of angle-resolved photoemission spectroscopy (ARPES) and theoretical calculations within the direct ab initio method as well as tight binding model formulation. To investigate the possible surface states we performed the direct DFT slab calculation and the surface Green function calculation for the (001) surface. The appearance of the surface states, which depends strongly on surface, points to the conclusion that LaSb termination is realized in the cleaved crystals. Moreover, the surface states predicted by our calculations at the $Γ$ and $X$ points are found by ARPES. Nodal lines, which exist along X--R and M-A path due to crystal symmetry, are also observed experimentally. The calculations reveal another nodal lines, which originate from vanishing of spin-orbit coupling and are located at X-M-A-R plane at the Brillouin zone boundary. In addition, we analyze band structure along the $Γ$-M path to verify, whether Dirac surface states can be expected. Their appearance in this region is not confirmed.

cond-mat.mtrl-sci↗

arXiv2022

Shiba states in systems with density of states singularities

Magnetic impurities placed in the superconductor can lead to emergence of the Yu-Shiba-Rusinov bound states. Coupling between the impurity and the substrate depends on density of states (DOS) at the Fermi level and can be tuned by DOS singularities. In this paper, we study the role of DOS singularities using the real space Bogoliubov-de Gennes equations for chosen lattice models. To uncover the role of these singularities (Dirac point, van Hove singularity, or the flat band), we study honeycomb, kagome, and Lieb lattices. We show that the properties of the Shiba state strongly depends on the type of lattice. Nevertheless some behaviors are generic, e.g. dependence of the critical magnetic coupling on the DOS at the Fermi level. However, the Shiba states realized in the Lieb lattice exhibit extraordinary properties, which can be explained by the presence of a few nonequivalent sublattices. Depending on the location of the magnetic impurity in the chosen sublattice, the value of critical magnetic coupling $J_\text{c}$ can be reduced or enhanced when the flat band is located at the Fermi level. In this context, we also present differences in the local DOS and coherence lengths for different sublattices in the Lieb lattice.

cond-mat.supr-con↗