arXiv subjects

Magdalena Birowska

Publications and source records attributed to Magdalena Birowska.

18 recordsLinked to original sources

arXiv2026

Evidence for Many-Body States in NiPS$_3$ Revealed by Angle-Resolved Photoelectron Spectroscopy

We present $\mu$-ARPES spectra of the Mott-insulating van der Waals antiferromagnet NiPS$_3$. Signatures of strong correlations -- such as the onset of atomic or atomic-ligand multiplets and spin-orbit-entangled exciton have been observed in this material by various two-particle spectroscopies, but not previously in photoemission. Our measurements reveal a weakly dispersive feature at the valence-band edge that is absent in DFT+$U$ calculations and remains unchanged across the N\'eel transition. After critically examining and ruling out alternative interpretations, we show that an exact diagonalization of a NiS$_6$ cluster yields low-energy final-state configurations of mixed multiplet $d^7$ and $d^8\underline{L}$ character, whose energy differences are consistent with the observed additional feature. This implies that ARPES directly accesses local Ni-S multiplet physics in NiPS$_3$, revealing a many-body structure beyond mean-field theory. Our results confirm that NiPS$_3$ is an excellent model platform in which strong correlations, reduced dimensionality, and covalent metal-ligand bonding jointly shape both two- and single-particle spectroscopies, underscoring the need for a genuinely quantum many-body description of two-dimensional quantum materials.

cond-mat.str-el↗

arXiv2025

Symmetry-Breaking Phenomena in MnPS3/TMDC Heterostructures: Non-relativistic Spin Splitting, Altermagnetism and Spin-Valley Effects

We explore symmetry-breaking phenomena in MnPS3/TMDC (MoS2, WS2, MoSe2, WSe2) heterostructures using first-principles calculations, considering two high-symmetry stacking configurations, S1 and S2, which differ not only by their interfacial registry but also by a 30{\deg} twist between the layers. Depending on the stacking geometry, the systems exhibit two distinct types of nonrelativistic spin splitting (NRSS): S2 hosts altermagnetic-like band crossings, while S1 shows global spin splitting characteristic of symmetry-breaking NRSS. Magnetic exchange and anisotropy parameters indicate that the intrinsic magnetic properties of MnPS3 are largely preserved upon interfacing. Including spin-orbit coupling, we find tunable conduction-valley splitting controlled by the MnPS3 spin orientation. Our results identify MnPS3 as a symmetry-tunable antiferromagnetic substrate capable of inducing and controlling spin and valley effects in 2D heterostructures without relying on net magnetization or strong SOC, offering a route toward nonvolatile valleytronic functionalities.

cond-mat.mtrl-sci↗

arXiv2025

Probing the band structure of the strongly correlated antiferromagnet NiPS3 across its phase transition

NiPS3 is an exfoliable van-der-Waals intralayer antiferromagnet with zigzag-type spin arrangement. It is distinct from other TMPS3 (TM: transition metal) materials by optical excitations into a strongly correlated state that is tied to the magnetic properties. However, the related, fundamental band structure across the antiferromagnetic phase transition has not been probed yet. Here, we use angular-resolved photoelectron spectroscopy with {\mu}m resolution in combination with DFT+U calculations for that purpose. We identify a characteristic band shift across TN. It is attributed to bands of mixed Ni and S character related to the superexchange interaction of Ni 3t2g orbitals. Moreover, we find a structure above the valence band maximum with little angular dispersion that could not be reproduced by the calculations. The discrepancy suggests the influence of many-body interactions beyond the DFT+U approximations in striking contrast to the results on MnPS3 and FePS3, where these calculations were sufficient for an adequate description.

cond-mat.str-el↗

arXiv2024

Direct Optical Probing of the Magnetic Properties of the Layered Antiferromagnet CrPS$_4$

Unusual magnetic properties of Van der Waals type antiferromagnetic semiconductors make them highly attractive for spintronics and optoelectronics. A link between the magnetic and optical properties of those materials, required for practical applications, has not been, however, established so far. Here, we report on a combined experimental and theoretical study of magnetic, optical, and structural properties of bulk CrPS$_{4}$ samples. We find that the magnetic-field-dependent circular polarization degree of the photoluminescence is a direct measure of the net magnetization of CrPS$_{4}$. Complementary, Raman scattering measured as a function of magnetic field and temperature enables the determination of the magnetic susceptibility curve of the material. Our experimental results are backed by Our experimental results are supported by density functional theory calculations that take as input the lattice parameters determined from temperature-dependent X-ray diffraction measurements. This allows us to explain the impact of spin ordering on the spectral position of Raman transitions in CrPS$_4$, as well as anomalous temperature shifts of selected of them. The presented method for all-optical determination of the magnetic properties is highly promising for studies of spin ordering and magnetic phase transitions in single- or a few-layer samples of magnetic layered materials, for which a poor signal-to-noise ratio precludes any reliable neutron scattering or magnetometry measurements.

cond-mat.mtrl-sci↗

arXiv2024

Tuning Magnetic and Optical Properties in MnxZn1-xPS3 Single Crystals by the Alloying Composition

The exploration of two-dimensional (2D) antiferromagnetic (AFM) materials has shown great promise and interest in tuning the magnetic and electronic properties as well as studying magneto-optical effects. The current work investigates the control of magneto-optical interactions in alloyed MnxZn1-xPS3 lamellar semiconductor single crystals, with the Mn/Zn ratio regulating the coupling strength. Magnetic susceptibility results show a retention of AFM order followed by a decrease in N\'eel temperatures down to ~ 40% Mn concentration, below which a paramagnetic behavior is observed. Absorption measurements reveal an increase in bandgap energy with higher Zn(II) concentration, and the presence of Mn(II) d-d transition below the absorption edge. DFT+U approach qualitatively explained the origin and the position of the experimentally observed mid band-gap states in pure MnPS3, and corresponding peaks visible in the alloyed systems MnxZn1-xPS3. Accordingly, emission at 1.3 eV in all alloyed compounds results from recombination from a 4T1g Mn(II) excited state to a hybrid p-d state at the valence band. Most significant, temperature-dependent photoluminescence (PL) intensity trends demonstrate strong magneto-optical coupling in compositions with x > 0.65. This study underscores the potential of tailored alloy compositions as a means to control magnetic and optical properties in 2D materials, paving the way for advances in spin-based technologies.

cond-mat.mtrl-sci↗

arXiv2023

Magneto-optical anisotropies of 2D antiferromagnetic MPX$_3$ from first principles

Here we systematically investigate the impact of the spin direction on the electronic and optical properties of transition metal phosphorus trichalcogenides (MPX$_3$, M=Mn, Ni, Fe; X=S, Se) exhibiting various antiferromagnetic arrangement within the 2D limit. Our analysis based on the density functional theory and versatile formalism of Bethe-Salpeter equation reveals larger exciton binding energies for MPS$_3$ (up to 1.1 eV in air) than MPSe$_3$(up to 0.8 eV in air), exceeding the values of transition metal dichalcogenides (TMDs). For the (Mn,Fe)PX$_3$ we determine the optically active band edge transitions, revealing that they are sensitive to in-plane magnetic order, irrespective of the type of chalcogen atom. We predict the anistropic effective masses and the type of linear polarization as an important fingerprints for sensing the type of magnetic AFM arrangements. Furthermore, we identify the spin-orientation-dependent features such as the valley splitting, the effective mass of holes, and the exciton binding energy. In particular, we demonstrate that for MnPX$_3$ (X=S, Se) a pair of non equivalent K+ and K- points exists yielding the valley splittings that strongly depend on the direction of AFM aligned spins. Notably, for the out-of-plane direction of spins, two distinct peaks are expected to be visible below the absorption onset, whereas one peak should emerge for the in-plane configuration of spins. These spin-dependent features provide an insight into spin flop transitions of 2D materials. Finally, we propose a strategy how the spin valley polarization can be realized in 2D AFM within honeycomb lattice.

cond-mat.mtrl-sci↗

arXiv2023

Recent progress in thermoelectric MXene-based structures versus other 2D materials

Thermoelectricity is a next-generation solution for efficient waste heat management. Although various thermoelectric materials exist, there is still a lot of scope for advancement, especially in room temperature applications. Recently, two-dimensional (2D) materials, including MXenes, showed promise as thermoelectric materials. On the other hand, MXenes generally exhibit metallic behavior that can hinder thermoelectric performance. Nevertheless, the variety of MXene's chemical composition and surface functionalization facilitate the research path based on energy band engineering, carrier concentration, and mobility. Multiple strategies to enhance the thermoelectric properties of layered MXenes materials, including structural modifications, defects, band gap engineering, etc. have been comprehensively demonstrated. In addition, advanced structural engineering such as nanostructuring MXenes with materials of different dimensions, creating van der Waals heterostructures, alloying, and utilizing MXenes as nanoinclusions or nanocomposites is presented. The thermoelectric efficiency of MXenes over the landscape of other 2D and conventional thermoelectric materials has been systematically compared. Meanwhile, a future approach has been proposed to enhance the thermoelectric properties of novel members of the flatland, MBenes exhibiting an incredible diversity of structures and crystal symmetries. Finally, potential applications in thermoelectrics and future prospects of MXenes are discussed. This article provides a timely and unique review of MXenes advantages and limitations that have never been so well understood and established. This creates a comfort zone for rational tailoring of their structure-property-performance relationship, which is crucial concerning the thermoelectric performance, widely covered in this review.

cond-mat.mtrl-sci↗

arXiv2022

Electronic band structure changes across the antiferromagnetic phase transition of exfoliated MnPS$_3$ probed by $\mu$-ARPES

Exfoliated magnetic 2D materials enable versatile tuning of magnetization, e.g., by gating or providing proximity-induced exchange interaction. However, their electronic band structure after exfoliation has not been probed, most likely due to their photochemical sensitivity. Here, we provide micron-scale angle-resolved photoelectron spectroscopy of the exfoliated intralayer antiferromagnet MnPS$_3$ above and below the N\'{e}el temperature down to one monolayer. The favorable comparison with density functional theory calculations enables to identify the orbital character of the observed bands. Consistently, we find pronounced changes across the N\'{e}el temperature for bands that consist of Mn 3d and 3p levels of adjacent S atoms. The deduced orbital mixture indicates that the superexchange is relevant for the magnetic interaction. There are only minor changes between monolayer and thicker films demonstrating the predominant 2D character of MnPS$_3$. The novel access is transferable to other MPX$_3$ materials (M: transition metal, P: phosphorus, X: chalcogenide) providing a multitude of antiferromagnetic arrangements.

cond-mat.mtrl-sci↗

arXiv2022

Stress-Tuned Optical Transitions in Layered 1T-MX2 (M= Hf, Zr, Sn; X= S, Se) Crystals

Optical measurements under externally applied stresses allow us to study the materials' electronic structure by comparing the pressure evolution of optical peaks obtained from experiments and theoretical calculations. We examine the stress-induced changes in electronic structure for the thermodynamically stable 1T polytype of selected MX2 compounds (M=Hf, Zr, Sn; X=S, Se), using the density functional theory. We demonstrate that considered 1T-MX2 materials are semiconducting with indirect character of the band gap, irrespective to the employed pressure as predicted using modified Becke-Johnson potential. We determine energies of direct interband transitions between bands extrema and in band-nesting regions close to Fermi level. Generally, the studied transitions are optically active, exhibiting in-plane polarization of light. Finally, we quantify their energy trends under external hydrostatic, uniaxial, and biaxial stresses by determining the linear pressure coefficients. Generally, negative pressure coefficients are obtained implying the narrowing of the band gap. The semiconducting-to-metal transition are predicted under hydrostatic pressure. We discuss these trends in terms of orbital composition of involved electronic bands. In addition, we demonstrate that the measured pressure coefficients of HfS2 and HfSe2 absorption edges are in perfect agreement with our predictions. Comprehensive and easy-to-interpret tables containing the optical features are provided to form the basis for assignation of optical peaks in future measurements.

cond-mat.mtrl-sci↗

arXiv2022

Crystal anisotropy implications on the intrinsic magnetic and optical properties in van der Waals FePS3

Antiferromagnetic (AFM) FePS3 has gained significant interest recently for its potential applications in spin-related devices. A single layer is comprised of a honeycomb network, stabilized by long-range spin-exchange interactions, with a zigzag or Neel arrangement of the Fe-atoms. This study exposed, for the first time, a strong impact of lateral crystal distortion on the magnetic arrangement and optical properties of FePS3. This impact was deciphered by correlating photoluminescence (PL) observations with single-crystal XRD which uncovered anisotropy in the a/b crystallographic plane. Thus, induceing a breakage in the inversion symmetry in FePS3 causing changes in it's electronic and optical transitions. The MPL observations exhibited an unexpected band-edge circularly polarized recombination emission, while off-band-edge transitions were linearly polarized. Also, temperature-dependent MPL measurements reflected zigzag-AFM at low temperatures and the coexistence of zigzag or Neel at mid temperatures. Theoretical calculation implementing anisotropy in spin-exchange interactions among Fe atom's nearest neighbors revealed stabilized zigzag arrangement tilted away from the a-axis. Furthermore, DFT calculations of the electronic band-edge predicted split states in degenerate symmetric points (K+/K-) for zigzag structure and non-degenerate for the Neel arrangement. Highlighting the importance of the inclusion of a crystallographic anisotropy parameter for the simulation of the experimental observations.

cond-mat.mtrl-sci↗

arXiv2022

Anisotropic Magnetodielectric Coupling in Layered Antiferromagnetic FePS$_3$

We report anisotropic magnetodielectric (MD) coupling in layered van der Waals (vdW) antiferromagnetic (AFM) FePS$_3$ (N\'eel temperature $T_{\mathrm{N}}$ $\sim$ 120K) with perpendicular anisotropy. Above $T_N$, while dielectric response function along \textit{c}-axis shows frequency dependent relaxations, in-plane data is frequency independent and reveals a deviation from phonon-anharmonicity in the ordered state, thereby implying a connection to spin-phonon coupling known to be indicative of onset of magnetic ordering. At low temperature (below 40 K), atypical anomaly in the dielectric constant is corroborated with temperature dependent DC and AC susceptibility. The magnetodielectric response across this anomaly differs significantly for both, in-plane and out-of-plane cases. We have explained this in terms of preferential orientation of magnetic AFM-z alignment, implied by the in-plane structural anisotropy as confirmed by \textit{ab-initio} calculations. Controlling relative strength of magnetodielectric coupling with magnetic anisotropy opens up a strategy for tracking subtle modifications of structure, such as in-plane anisotropy, with potential application to spintronic technologies.

cond-mat.mes-hall↗

arXiv2021

Limited ferromagnetic interactions in monolayers of MPS$_3$ (M=Mn, Ni)

We present a systematic study of the electronic and magnetic properties of two-dimensional ordered alloys, consisting of two representative hosts (MnPS$_3$ and NiPS$_3$) of transition metal phosphorus trichalcogenides doped with $3d$ elements. For both hosts our DFT+U calculations are able to qualitatively reproduce the ratios and signs of all experimentally observed magnetic couplings. The relative strength of all antiferromagnetic exchange couplings, both in MnPS$_3$ as well as in NiPS$_3$, can successfully be explained using an effective direct exchange model: they reveal that the third-neighbor exchange dominates in NiPS$_3$ due to the filling of the $t_{2g}$ subshell, whereas for MnPS$_3$ the first neighbor exchange is prevailed owing to the presence of the $t_{2g}$ magnetism. On the other hand, the nearest neighbor ferromagnetic coupling in NiPS$_3$ can only be explained using a more complex superexchange model and is (also) largely triggered by the absence of the $t_{2g}$ magnetism. For the doped systems, the DFT+U calculations revealed that magnetic impurities do not affect the magnetic ordering observed in the pure phases and thus in general in these systems ferromagnetism may not be easily induced by such a kind of elemental doping. However, unlike for the hosts, the first and second (dopant-host) exchange couplings are of similar order of magnitude. This leads to frustration in case of antiferromagnetic coupling and may be one of the reasons of the observed lower magnetic ordering temperature of the doped systems.

cond-mat.mtrl-sci↗

arXiv2021

Spectroscopy and structural investigation of iron phosphorus trisulfide -- FePS$_3$

Lamellar structures of transition metal phosphorus trisulfides possess strong intralayer bonding, albeit adjacent layers are held by weak van der Waals interactions. Those compounds received enormous interest due to their unique combination of optical and long-range magnetic properties. Among them, iron phosphorus trisulfide (FePS$_3$) gathered special attention for being a semiconductor with an absorption edge in the near-infrared, as well as showing an Ising-like anti-ferromagnetism. We report a successful growth of centimeter size bulk FePS$_3$ crystals with a chemical yield above 70%, whose crystallographic structure and composition were carefully identified by advanced electron microscopy methodologies, including atomic resolution elemental mapping, along with photoelectron spectroscopy. The knowledge on the optical activity of FePS$_3$ is extended utilizing temperature-dependent absorption and photoacoustic spectroscopies, while measurements were corroborated with density-functional theory calculations. Temperature-dependent experiments showed a small and monotonic band-edge energy shift down to 115 K and exposed the interconnected importance of electron-phonon coupling. Most of all, the correlation between the optical behavior and the magnetic phase transition is revealed, which shows the practical utilization of temperature-dependent optical absorption to investigate magnetic interactions.

cond-mat.mtrl-sci↗

arXiv2020

Large exciton binding energies in MnPS$_3$ as a case study of vdW layered magnet

Stable excitons in semiconductor monolayers such as transition-metal dichalcogenides (TMDCs) enable and motivate fundamental research as well as the development of room-temperature optoelectronics applications. The newly discovered layered magnetic materials present a unique opportunity to integrate optical functionalities with magnetism. We predict that a large class of antiferromagnetic semiconducting monolayers of the MPX$_3$ family exhibit giant excitonic binding energies, making them suitable platforms for magneto-optical investigations and optospintronics applications. Indeed, our investigations, based on first principles methods combined with an effective-model Bethe-Salpeter solver, show that excitons in bare Neel-MnPS$_3$ are bound by more than 1 eV, which is twice the excitonic energies in TMDCs. In addition, the antiferromagnetic ordering of monolayer samples can be inferred indirectly using different polarization of light.

cond-mat.mtrl-sci↗

arXiv2020

Supercell-core software: a useful tool to generate an optimal supercell for vertically stacked nanomaterials

Vertically oriented materials, such as van der Waals heterostructures, that have novel hybrid properties are crucial for fundamental scientific research and the design of new nano-devices. Currently, most available theoretical methods require applying a supercell approach with periodic boundary conditions to explore the electronic properties of such nanomaterials. Herein, we present supercell-core software, which provides a way to determine the supercell of non-commensurate lattices, in particular, van der Waals heterostructures. Although this approach is very common, most of the reported work still uses supercells that are constructed 'by hand' and on a temporary basis. The developed software is designed to facilitate finding and constructing optimised supercells (i.e., with small size and minimal strain accumulation in adjacent layers) of vertically stacked lattices.

cond-mat.mtrl-sci↗

arXiv2020

The impact of hexagonal boron nitride encapsulation on the structural and vibrational properties of few layer black phosphorus

The encapsulation of two-dimensional layered materials such as black phosphorus is of paramount importance for their stability in air. However, the encapsulation poses several questions, namely, how it affects, via the weak van der Waals forces, the properties of the black phosphorus and whether these properties can be tuned on demand. Prompted by these questions, we have investigated the impact of hexagonal boron nitride encapsulation on the structural and vibrational properties of few layer black phosphorus, using a first-principles method in the framework of density functional theory. We demonstrate that the encapsulation with hexagonal boron nitride imposes biaxial strain on the black phosphorus material, flattening its puckered structure, by decreasing the thickness of the layers via the increase of the puckered angle and the intra-layer P-P bonds. This work exemplifies the evolution of structural parameters in layered materials after the encapsulation process. We find that after encapsulation, phosphorene (single layer black phosphorous) contracts by 1.1% in the armchair direction and stretches by 1.3% in the zigzag direction, whereas few layer black phosphorus mainly expands by up to 3% in the armchair direction. However, these relatively small strains induced by the hexagonal BN, lead to significant changes in the vibrational properties of black phosphorus, with the redshifts of up to 10 cm$^{-1}$ of the high frequency optical mode $A_g^1$. In general, structural changes induced by the encapsulation process open the door to substrate controlled strain engineering in two-dimensional crystals.

cond-mat.mtrl-sci↗

arXiv2018

Nematicity of correlated systems driven by anisotropic chemical phase separation

The origin of nematicity, i.e., in-plane rotational symmetry breaking, and in particular the relative role played by spontaneous unidirectional ordering of spin, orbital, or charge degrees of freedom, is a challenging issue of magnetism, unconventional superconductivity, and quantum Hall effect systems, discussed in the context of doped semiconductor systems, such as Ga$_{1-x}$Mn$_x$As, Cu$_x$Bi$_2$Se$_3$, and Ga(Al)As/Al$_x$Ga$_{1-x}$As quantum wells, respectively. Here, guided by our experimental and theoretical results for In$_{1-x}$Fe$_x$As, we demonstrate that spinodal phase separation at the growth surface (that has a lower symmetry than the bulk) can lead to a quenched nematic order of alloy components, which then governs low temperature magnetic and magnetotransport properties, in particular the magnetoresistance anisotropy whose theory for the $C_{2v}$ symmetry group is advanced here. These findings, together with earlier data for Ga$_{1-x}$Mn$_x$As, show under which conditions anisotropic chemical phase separation accounts for the magnitude of transition temperature to a collective phase or merely breaks its rotational symmetry. We address the question to what extent the directional distribution of impurities or alloy components setting in during the growth may account for the observed nematicity in other classes of correlated systems.

cond-mat.mtrl-sci↗

arXiv2017

Assessment of approaches for dispersive forces employing graphone as a case study

We have studied two interchange layer systems, (i) free standing partly hydrogenated graphene (graphone), and (ii) graphone on the Nickel (111) surface, to assess various density functional theory based computational schemes incorporating van der Waals forces. The various van der Waals methods have been employed ranging from the semiempirical force-field-like correction of Grimme, through non-local van der Waals density functionals, up to the functionals involving exact exchange and the random phase approximation for the correlation. Generally, all computational schemes lead to a similar qualitative picture of hydrogen layer physisorption and chemisorption to graphene. The largest discrepancies between the approaches emerge for the energetics of the investigated systems. Our studies shed light on the physical mechanisms of graphene hydrogenation both in vacuum and in the proximity of metallic surface. In particular, it is revealed that the adsorption of hydrogen atoms affects the nature of the bonding between graphene and the Ni(111) surface, from the weak to strong semi-covalent bonding. On the other hand, it turns out that the adsorption of hydrogen layer to graphene is stronger in the presence of the metallic surface.

cond-mat.mtrl-sci↗