arXiv subjects

K. R. Pakuszewski

Publications and source records attributed to K. R. Pakuszewski.

7 recordsLinked to original sources

arXiv2025

Evidence for a field-induced Lifshitz transition in the Weyl semimetal CeAlSi

The Weyl semimetal CeAlSi crystallises in the noncentrosymmetric tetragonal space group $I4_1md$ and exhibits ferromagnetic order below 8 K, thereby breaking both spatial inversion and time-reversal symmetries. This unique combination of properties establishes CeAlSi as a model system for studying the interplay between non-trivial topological states and strong electron correlations. In this work, we report observations of Shubnikov-de Haas oscillations in the electrical resistivity under magnetic fields up to 68 T applied parallel to the [001] crystallographic axis. Our measurements reveal an abrupt change in the oscillation frequencies near 14 T, which is indicative of a field-induced Lifshitz transition. Additionally, our results are consistent with the ferromagnetic order bringing the Weyl nodes closer to the Fermi level in CeAlSi. Furthermore, they suggest that the RKKY interaction plays an important role.

cond-mat.str-el↗

arXiv2025

Orbital-Selective Band Structure Evolution in BaFe$_{2-x}$M$_x$As$_2$ (M = Cr, Co, Cu, Ru and Mn) Probed by Polarization-Dependent ARPES

We present a systematic study of the evolution of the band structure in the Fe-based superconductor family BaFe$_{2-x}$M$_x$As$_2$ (M = Cr, Co, Cu, Ru and Mn) using polarization-dependent angle-resolved photoemission spectroscopy (ARPES). Low-substituted samples, with comparable spin-density wave transition temperatures ($T_\text{SDW}$), were chosen to facilitate controlled comparisons. The sizes of the central hole pockets ($\alpha$, $\beta$, and $\gamma$) remain largely unchanged across different substitutions, showing no clear correlation with either $T_\text{SDW}$ or the As height relative to the Fe planes. However, subtle trends are observed: a modest increase in the size of the $\eta_\text{X}$ electron pocket correlates with the suppression of $T_\text{SDW}$. Furthermore, the contraction of the $\eta_\text{X}$ pocket appears to be linked to an increase in the As height relative to the Fe planes. Our results suggest that the suppression of $T_\text{SDW}$ is primarily driven by changes in the Fe-As bond length, with the effect being more pronounced in electronic states with planar character. These findings provide insight into the electronic structure of BaFe$_{2-x}$M$_x$As$_2$.

cond-mat.supr-con↗

arXiv2025

YNiSn$_2$: A candidate Dirac semimetal

We report the synthesis and physical properties of the new compound YNiSn$_2$, which crystallizes in the orthorhombic \textit{Cmcm} structure. The material exhibits semimetallic behavior and develops a giant positive magnetoresistance approaching 1200\% at $B = 16$ T. Pronounced de Haas-van Alphen and Shubnikov-de Haas oscillations reveal a dominant quasi-two-dimensional Fermi surface with an exceptionally small cyclotron effective mass of $m^{*} = 0.08 m{0}$, indicating light carriers and a tiny Fermi surface pocket. The strong anisotropy revealed by Shubnikov-de Haas quantum oscillation measurements highlights the low-dimensional electronic character of YNiSn$_2$, positioning it as a promising Dirac semimetal candidate.

cond-mat.str-el↗

arXiv2023

Hole doping and electronic correlations in Cr-substituted BaFe$_{2}$As$_{2}$

Superconductivity (SC) is absent in Cr-substituted BaFe$_{2}$As$_{2}$ (CrBFA), a well-established but poorly understood topic. Additionally, the suppression of the spin density wave transition temperature ($T_{\text{SDW}}$) in CrBFA and Mn-substituted BaFe$_{2}$As$_{2}$ (MnBFA) coincides as a function of Cr/Mn content, despite the distinct electronic effects of these substitutions. In this work, we employ angle-resolved photoemission spectroscopy (ARPES) and combined density functional theory plus dynamical mean field theory calculations (DFT+DMFT) to address the evolution of the Fermi surface (FS) and electronic correlations in CrBFA. Our findings reveal that incorporating Cr leads to an effective hole doping of the states near the FS, which is well described within the virtual crystal approximation (VCA). We analyzed the electronic band spectra with main $d_{yz}$-orbital character and found a fractional scaling of the imaginary part of self-energy as a function of the binding energy, a signature property of Hund's correlations. We conclude that CrBFA is a correlated electron system and the changes in the FS as a function of Cr are unrelated to the suppression of $T_{\text{SDW}}$. We suggest that the absence of SC is primarily due to the competition between Cr local moments and the Fe-derived itinerant spin fluctuations.

cond-mat.str-el↗

arXiv2023

Topological Hall effect in CeAlGe

The Weyl semimetal CeAlGe is a promising material to study nontrivial topologies in real and momentum space due to the presence of a topological magnetic phase. Our results at ambient pressure show that the electronic properties of CeAlGe are extremely sensitive to small stoichiometric variations. In particular, the topological Hall effect (THE) present in CeAlGe is absent in some samples of almost identical chemical composition. The application of external pressure favors the antiferromagnetic ground state. It also induces a THE where it was not visible at ambient pressure. Furthermore, a small pressure is sufficient to drive the single region of the THE in magnetic fields into two different ones. Our results reveal an extreme sensitivity of the electronic properties of CeAlGe to tiny changes in its chemical composition, leading to a high tunability by external stimuli. We can relate this sensitivity to a shift in the Fermi level and to domain walls.

cond-mat.str-el↗

arXiv2022

Orbital localization and the role of the Fe and As $4p$ orbitals in BaFe$_{2}$As$_{2}$ probed by XANES

The polarization dependence of the near edge x-ray absorption spectroscopy (XANES) is an element specific probe to the real-space distribution of the density of unoccupied states in solid-state materials. In this paper, we present Fe and As $K$-edge experiments of Ba(Fe$_{1-x}$$M_{x}$)$_{2}$As$_{2}$ ($M=$ Mn, Co and $x=0.0$ and $0.08$). The experiments reveal a strong polarization dependence of the probed XANES spectra, which concerns mainly an increase of the intensity of electronic transitions when the beam polarization is set out of the sample's $ab$ crystallographic plane. The results show that states with $p_{z}$-orbital character dominate the density of unoccupied states close to the Fermi level. Partial substitution of Fe by Co is shown to decrease the intensity anisotropy, suggesting that Co promotes electronic transfer preferentially to states with $p_{z}$-orbital character. On the other hand, Mn substitution causes the increase of the spectra $p_{z}$-orbital anisotropy, which is proposed to take place by means of an enhanced local Fe $3d4p$ mixing, unveiling the role of Fe $4p$ states in the localization of the Fe $3d$ orbitals. Moreover, by comparing our results to previous experiments, we identify the relative mixing between Fe and the pnictide $4p_{x,y,z}$ orbitals as a clear divide between the electronic properties of iron arsenides and selenides. Our conclusions are supported by multiple-scattering theory calculations of the XANES spectra and by quantum chemistry calculations of Fe coordination electronic structure.

cond-mat.str-el↗

arXiv2021

Tuning the nontrivial topological properties of the Weyl semimetal CeAlSi

In the ferromagnetic Weyl semimetal CeAlSi both space-inversion and time-reversal symmetries are broken. We use external pressure as an effective tuning parameter and relate three observations to the presence of a nontrivial topology in its ferromagnetic regime: an exceptional temperature response of the quantum oscillations amplitude, the presence of an anomalous Hall effect (AHE), and the existence of an unusual loop Hall effect (LHE). We find a suppression of the AHE and the LHE with increasing pressure, while the Curie temperature is enhanced. The magnetic structure and the electronic bands exhibit only a negligible pressure effect suggesting the importance of the domain wall landscape for the topological behavior in CeAlSi.

cond-mat.mtrl-sci↗