arXiv subjects

Claudia Felser

Publications and source records attributed to Claudia Felser.

At least 37 records · Page 2Linked to original sources

arXiv2026

Efficient spin-pumping and spin transport across epitaxial Mn$_3$Sn(0001) noncollinear antiferromagnet/permalloy interfaces

The generation and control of spin currents are crucial for advancing next-generation spintronic technologies. These technologies depend on materials capable of efficiently sourcing and interconverting spin and charge currents, while overcoming some limitations associated with conventional ferromagnets and heavy metals. Kagome topological antiferromagnetic Weyl semimetals, such as Mn3Sn, present unique advantages owing to their distinct magnetic order and significant Berry curvature-driven transport phenomena. In this study, we systematically investigate spin current generation and spin-to-charge conversion phenomena in epitaxial (0001)-oriented Mn$_3$Sn thin films. Our findings reveal a spin Hall angle of 0.9$\%$ and a nearly isotropic in-plane spin Hall conductivity of ~44.4 ($\hbar$/e) $Ω^{-1}$.cm$^{-1}$ at room temperature, originating from a combination of intrinsic and extrinsic contributions, as discussed in light of first-principle calculations. Furthermore, in Mn$_3$Sn(0001)/Ni$_{81}$Fe$_{19}$ heterostructures, we observe a high spin-mixing conductance of 28.52 nm$^{-2}$ and an interfacial spin-transparency of approximately 72$\%$. Notably, we also find that the spin diffusion length in Mn$_3$Sn(0001) epitaxial films exceeds 15 nm at room temperature. Our results highlight the potential, and limitations, of the topological Weyl noncollinear antiferromagnet Mn$_3$Sn as an efficient material for spin transport and conversion in prospective spintronic applications.

cond-mat.mtrl-sci↗

arXiv2026

Detecting the full photoemission cone from laser-based ARPES experiments by leveraging deflector technology

Angle-resolved photoemission spectroscopy (ARPES) provides a direct access to the electronic band structure of solid and molecular systems. The momentum range accessible by this technique depends directly on the photon energy used, and low-photon-energy sources are insufficient to photoemit electrons over the full Brillouin zone of most quantum materials. In addition, while electrons are emitted over a 2$π$ solid angle, conventional hemispherical analyzers only collect a small subset of those electrons. A previous work [RSI 92, 123907 (2021)] demonstrated that electrons emitted over a larger field-of-view can be acquired in one fixed configuration by accelerating them towards the analyzer with a bias voltage. Here, we extend this work by leveraging the deflector technology of novel ARPES hemispherical analyzers. We demonstrate the ability to detect all $2π$ photoemitted electrons in a fixed configuration for various materials such as gold, cuprates and transition-metal dichalcogenides. This approach is especially advantageous for time-resolved ARPES, as electron dynamics over a large momentum range can be accessed with identical measurement conditions.

cond-mat.mtrl-sci↗

arXiv2026

Magneto-optic phonon resonances in magnetic topological EuCd2As2 via helical Raman spectroscopy

EuCd2As2 materials have two magnetic ordering states: antiferromagnetic (AFM) and ferromagnetic (FM) when their chemical tunability is utilized. While AFM-EuCd2As2 has a nonzero magnetoelectric response due to its symmetry breaking with spin configuration, FM-EuCd2As2 is an ideal candidate for studies of Weyl physics because of its minimum number of Weyl points with opposite chirality. In this article, we examine cryogenic low-frequency Raman spectroscopy of phonon modes in FM-EuCd2As2 crystals using circular polarization configurations, with support from density functional theory calculations, and investigate in-plane magneto-anisotropy by linear polarization configuration below the Curie temperature (Tc = 26 K). We attribute the anomalous enhancements in Raman intensities below the Curie temperature are due to spin-phonon coupling. Furthermore, we see that A-mode peaks can be distinguished by magneto-helical Raman spectroscopy through the magneto-optic effect and that the degree of circular polarization (DCP) of 12.5 meV peak reaches 60% at 4.2 K and becomes saturated. We also examine AFM-EuCd2As2 below Néel temperature (TN = 9 K) to compare with FM-EuCd2As2, but we hardly observe spin-phonon coupling and find negligible DCP values due to almost zero net magnetization. Our results contribute to the understanding of the phonon dynamics and the interplay between topology and magnetism in FM-EuCd2As2, through helical light and external magnetic fields. This lays the foundation for utilizing state-of-the-art Weyl systems for applications in thermoelectrics, phononic devices, and topological quantum computing.

cond-mat.mtrl-sci↗

arXiv2026

Emergent chirality and enantiomeric selectivity in layered NbOX$_2$ crystals

The spontaneous emergence of chirality in crystalline solids has profound implications for electronic, optical, and topological properties, making the control of chiral phases a central challenge in materials design. Here, we investigate the structural and electronic properties of a new family of layered compounds, $\mathrm{NbOX_2}$, and explore the connection between their achiral $I m m m$ phase and chiral $C 2$. Through first-principles calculations, we identify an intermediate achiral $C 2/m$ phase that bridges the high- and low-symmetry phases within a three-dimensional order parameter space. By analyzing the Born-Oppenheimer energy surfaces, we find that the shallow energy minima of the $C2/m$ phase suggest it may be stabilized either by external factors such as pressure, as demonstrated here, or by ionic quantum or thermal fluctuations and the resulting lattice anharmonicity. Additionally, we show how an external electric field, by breaking the necessary symmetries, biases the system toward a preferred chirality by lifting the energy degeneracy between the two enantiomers. This, combined with the small energy barrier between the enantiomers in the $C 2$ phase, enables handedness control and allows us to propose a mechanism for selective handedness stabilization by leveraging electric fields and pressure or temperature-dependent anharmonic effects. Our findings establish a framework for understanding chirality emergence in layered materials and offer a pathway for designing systems with tunable enantiomeric populations.

cond-mat.mtrl-sci↗

arXiv2026

Phonon collapse and anharmonic melting of the 3D charge-density wave in kagome metals

The charge-density wave (CDW) mechanism and resulting structure of the AV3Sb5 family of kagome metals has posed a puzzling challenge since their discovery four years ago. In fact, the lack of consensus on the origin and structure of the CDW hinders the understanding of the emerging phenomena. Here, by employing a non-perturbative treatment of anharmonicity from first-principles calculations, we reveal that the charge-density transition in CsV3Sb5 is driven by the large electron-phonon coupling of the material and that the melting of the CDW state is attributed to ionic entropy and lattice anharmonicity. The calculated transition temperature is in very good agreement with experiments, implying that soft mode physics are at the core of the charge-density wave transition. Contrary to the standard assumption associated with a pure kagome lattice, the CDW is essentially three-dimensional as it is triggered by an unstable phonon at the L point. The absence of involvement of phonons at the M point enables us to constrain the resulting symmetries to six possible space groups. The unusually large electron-phonon linewidth of the soft mode explains why inelastic scattering experiments did not observe any softened phonon. We foresee that large anharmonic effects are ubiquitous and could be fundamental to understand the observed phenomena also in other kagome families.

cond-mat.mtrl-sci↗

arXiv2026

Observation of the Magnus Nonlinear Hall effect from Chiral Weyl Monopoles

The nonlinear Hall effect (NLHE) connects crystalline symmetry to quantum geometry, offering a probe of band topology beyond linear transport. While most studies have focused on the Berry curvature dipole in low-symmetry crystals, mechanisms that directly probe Berry monopoles in higher-symmetry chiral lattices remain unexplored. Here, we report the observations of the NLHE in the chiral Weyl semimetal CoSi, a platform where the Berry curvature dipole is symmetry-forbidden. By employing focused ion beam-fabricated crossbar devices, we detect a robust second-harmonic Hall voltage under zero magnetic field, hosting all key signatures of the NLHE. Theoretical analysis attributes the nonlinear Hall conductivity to skew scattering of self-rotating electron wave packets, whose chirality is dictated by the underlying band topology, a process reminiscent of the classical Magnus effect. Furthermore, the NLHE signal exhibits a temperature-dependent sign reversal, and a strong, linearly field-dependent modulation that grows with carrier mobility, directly reflecting the topological Weyl nodes distribution near the Fermi level. These findings establish CoSi as a platform for Berry monopole-driven nonlinear transport, demonstrating a skew-scattering route to topological nonlinear Hall responses that bypasses conventional symmetry constraints.

cond-mat.mes-hall↗

arXiv2026

Interpretation of Crystal Energy Landscapes with Kolmogorov-Arnold Networks

Characterizing crystalline energy landscapes is essential to predicting thermodynamic stability, electronic structure, and functional behavior. While machine learning (ML) enables rapid property predictions, the "black-box" nature of most models limits their utility for generating new scientific insights. Here, we introduce Kolmogorov-Arnold Networks (KANs) as an interpretable framework to bridge this gap. Unlike conventional neural networks with fixed activation functions, KANs employ learnable functions that reveal underlying physical relationships. We developed the Element-Weighted KAN, a composition-only model that achieves state-of-the-art accuracy in predicting formation energy, band gap, and work function across large-scale datasets. Crucially, without any explicit physical constraints, KANs uncover interpretable chemical trends aligned with the periodic table and quantum mechanical principles through embedding analysis, correlation studies, and principal component analysis. These results demonstrate that KANs provide a powerful framework with high predictive performance and scientific interpretability, establishing a new paradigm for transparent, chemistry-based materials informatics.

cond-mat.dis-nn↗

arXiv2026

Quantum Oscillations and Superconductivity in YPtBi Under Pressure

The topological semimetal YPtBi has attracted considerable attention, owing to its novel superconducting and normal state properties. A strong band inversion from spin-orbit coupling allows the existence of $j=3/2$ quasiparticles near the Fermi level, which form Cooper pairs with angular momentum potentially higher than single or triplet states. In this report, we present high-pressure magnetotransport and Shubnikov-de Haas effect measurements on high-quality YPtBi up to $P = 2.08$ GPa. As a function of pressure, we observe a trend toward more insulating resistivity at low temperatures concomitant with a suppression of quantum oscillation amplitude. Together with a decrease of the upper critical field and significant increase in the Dingle temperature, the pressure-induced changes point to a weakening of the band inversion and potential tuning of the topological nature of YPtBi, suggesting pressure as a useful tool for understanding the nature of topology in other related half-Heusler compounds.

cond-mat.supr-con↗

arXiv2026

Programmable, Spontaneous Superlattice Memory in a Monolayer Topological Insulator

Memory is a foundational concept across disciplines, from neurobiology and electronics to artificial intelligence and quantum gravity. In materials, memory effects typically arise from ferroic orders, such as ferroelectricity and ferromagnetism, where information is stored in charge or spin degrees of freedom. Here, we report a surprising discovery of a nonvolatile superlattice memory effect in monolayer TaIrTe4, a dual quantum spin Hall insulator, where information is encoded through sharply contrasting lattice periodicities. In particular, in a pristine monolayer, we observe the spontaneous emergence of a long-period superlattice that can be programmed ON and OFF in a nonvolatile manner by electrostatic tuning of low-energy electronic states. This switching toggles the system between two structural configurations with unit cell areas differing by nearly two orders of magnitude. Mechanistically, our results reveal two independent and distinct instabilities, one in the lattice and the other in the QSH electrons, which are coupled, leading to electrostatic control of lattice configurations with nonvolatile memory. This finding is enabled by combining linear and nonlinear transport measurements, Raman spectroscopy, and scanning tunneling microscopy, which probe complementary aspects of the underlying orders. Remarkably, this nonvolatile memory effect stabilizes a spontaneous superlattice with a periodicity on the few-nanometer scale that remains robust across a wide doping range, persists over days, and survives above 70 K. Combined with the QSH topology, this stability offers a promising route to nonvolatile memory control of topological flat bands and their filling enabled quantum states. Our preliminary data indeed show the emergence of new insulating states at fractional superlattice fillings, which can be clearly switched ON and OFF together with the superlattice.

cond-mat.mes-hall↗

arXiv2026

Quantifying quasiparticle chirality in a chiral topological semimetal

Recently, the projection of the electron's spin on its crystal momentum has been proposed as a metric to quantify electronic chirality of Bloch states in crystals, which is expected to affect a wide range of physical properties, such as magnetoelectric and optical responses. However, a direct experimental quantification of this chirality metric over an entire iso-energy surface has remained elusive. Here, we have used spin- and angle-resolved photoemission spectroscopy to directly probe the electronic chirality by measuring the bulk spin texture of Kramers-Weyl and Weyl cones in RhSi, a chiral topological semimetal with strong spin-orbit coupling (SOC). After quantifying the SOC splitting of Weyl cones, we determine their spin direction along different azimuthal angles to extract energy dependent the deviations (up to ~40°) from perfect parallel spin-momentum locking. From these deviations we define an energy-dependent normalized electron chirality density (NECD), a directly accessible metric of bulk electronic chirality. In RhSi, the NECD decreases from 1 at the Kramers-Weyl point to ~0.8 at ~200 meV below it. Finally, we show that this experimentally grounded NECD provides predictive power for magneto-optical and transport responses of chiral materials, exemplified by the longitudinal Edelstein effect.

cond-mat.mes-hall↗

arXiv2026

Identifying field-tunable surface resonance states on black phosphorus

Surface resonance states are electronic states localized near the surface while remaining hybridized with bulk bands. These states can strongly modify the electric-field response of semiconductors. Here, we demonstrate using scanning tunneling spectroscopy that on black phosphorus, surface resonance states near the valence-band edge dominate the screening of a strong external electric field. We observe in the tunneling conductance spectrum a pronounced dip with an energy continuously tunable by the local electric field in the tunneling junction. Meanwhile, we also notice that the bulk band edges remain effectively pinned, indicating efficient surface screening and suppression of bulk band bending. We interpret the conductance dip as the consequence of a field-dependent tunneling barrier: as the external electric field drives the surface resonance band into the band gap, the coupling between the surface resonance states and the bulk states is suppressed, leading to a reduced tunneling probability. Our simplified model based on this mechanism reproduces our main experimental findings. Our results highlight surface-localized states as a critical component in the electrostatic response of semiconductors, which must be taken into consideration in the design and operation of nanoscale semiconductor devices.

cond-mat.mes-hall↗

arXiv2026

Chiralometer: Direct Torque Detection of Crystal Chirality

Chirality governs phenomena ranging from chemical reactions to the topology of quasiparticle charge carriers. However, a direct macroscopic probe for crystal chirality remains a significant challenge, especially in time reversal symmetric systems with weak circular dichroism signal. Here, we propose the ``Chiralometer'', a mechanical detection method that probes chirality by driving angular momentum carriers out of equilibrium. Using first-principles calculations and semiclassical transport theory, we demonstrate that a temperature gradient in insulators or an electric field in metals induces uncompensated angular momentum in phonons and electrons, respectively. This imbalance generates a macroscopic mechanical torque ($τ\sim 10^{-11} N \cdot m$) well within the sensitivity of modern torque magnetometry and cantilever-based sensors. We identify robust signatures in chiral crystals such as Te, SiO$_2$, and the topological semimetal CoSi. Our work establishes mechanical torque as a fundamental order parameter for chirality, offering a transformative tool for orbitronics and chiral quantum materials.

cond-mat.mtrl-sci↗

arXiv2026

Anisotropic anomalous Hall effect in distorted kagome GdTi3Bi4

Topological kagome magnets offer a rich landscape for exploring the intricate interplay of quantum interactions among geometry, topology, spin, and correlation. GdTi3Bi4 crystallizes in layered Ti based kagome nets intertwined with zigzag Gd chains along the a axis and orders antiferromagnetically below 15 K. Here, we present the temperature and field dependent electrical transport of GdTi3Bi4 in different directions. The material exhibits anomalous Hall conductivity (AHC) of 410 S cm-1 at 2 K for B parallel c and it is completely absent for B parallel a, despite the similar magnetization observed in both orientations. This behavior is quite contradictory, as anomalous Hall effect (AHE) typically scales with the magnetization. Through first principles calculations, it is demonstrated that in the presence of time reversal symmetry broken by the Gd 4f sublattice and spin orbit coupling, the magnetization direction controls the orbital mixing in the Ti t2g bands, relocating Berry curvature hot spots and producing the observed orientation selective AHC. The results establish GdTi3Bi4 as platform for investigating new avenues of AHE, such as directional AHE, and thus shed new light on the intricate coupling between magnetic and electronic structures, paving the way for exploring novel quantum phenomena.

cond-mat.mtrl-sci↗

arXiv2025

First-principles study of magnetic and spin-dependent transport properties of Mn2VZ (Z = Al, Ga) with negative spin polarization using a disordered local moment approach at finite temperatures

First-principles studies were performed on two Mn-based ferrimagnetic Heusler compounds with L21 and B2 structures, that is, Mn2VZ (Z = Al or Ga). The aim was to investigate their magnetic properties, electronic structures, and spin-resolved longitudinal conductivity at finite temperatures. Density functional theory (DFT) and functional integral theory were used. This approach incorporates transverse spin fluctuations through a disordered local moment method and the coherent potential approximation. In all cases, the calculated theoretical Curie temperatures were lower than the experimental values. Alloys with a B2 structures exhibit higher Curie temperatures compared to compounds with an L21 structures. Calculations of the temperature dependence of the density of states (DOS) indicate that the half-metallic electronic structure collapses owing to the renormalization of transverse spin fluctuations at a finite temperatures. However, the spin-resolved longitudinal conductivities demonstrated an improved spin polarization, particularly for Mn2VGa with an L21 structure. This result contradicts predictions based on the temperature-dependent DOS. The competition between the metallic transitions, which are caused by a modification of the DOS, and scattering coming from spin-disorder explains this phenomenon. Both of these effects are induced by transverse spin fluctuations. Additionally, the results show that half-metallicity, as defined by the DOS or conductivity, is inconsistent at finite temperatures. Finally, the total energy landscape of the paramagnetic state was calculated using the fixed spin moment method to investigate the strength of the longitudinal spin fluctuations. These results suggest that the alloys may exhibit strong longitudinal spin fluctuations.

cond-mat.mtrl-sci↗

arXiv2025

Anomalous impurity-induced charge modulations in black phosphorus

We observe anomalous charge modulations induced by ionized indium impurities on the surface of the semiconductor black phosphorus by scanning tunneling microscopy (STM). When the impurities are switched into a negatively charged state by the STM tip, periodic charge modulations emerge around the impurity center, but strictly confined by the nanoscale impurity potential. These modulations form a distorted triangular pattern, whose periodicity remains unchanged in a wide range of positive bias. Furthermore, these local charge orders exhibit an anisotropy opposite to that expected based on the anisotropy of the Fermi surface, challenging a simple band-structure interpretation. Our experiment demonstrates the possibility of creating and manipulating macroscopic charge orders through impurity engineering.

cond-mat.str-el↗

arXiv2025

Non-collinear magnetism contra frustration: Magnetic order and anisotropy in hexagonal MnPtGa

MnPtGa is a hexagonal intermetallic compound with a rich variety of magnetic order. Its magnetic state is reported to range from collinear ferromagnetism, to non-collinear skyrmion type order. MnPtGa is a system with strongly localized magnetic moments at the Mn atoms as was demonstrated using calculations for disordered local moments. The magnetic moments at the Mn sites stay at about 3.9 bohr even above the calculated magnetic transition temperatures (TN = 220 K or TC = 285 K). In the present work, a special emphasis was focused on the possible non-collinear magnetic order using first principles calculations. The investigations included magnetic anisotropy, static noncollinear order in form of spin canting and dynamic non-collinearity in spin spirals. It is found that the energy differences between ferromagnetic, antiferromagnetic, canted, or spiral magnetic order are in the order of not more than 30 meV, which is in the order of thermal energies at ambient temperature. This hints that a particular magnetic state - including skyrmions, antiskyrmions or spin glass transitions - may be forced when an external field is applied at finite temperature.

cond-mat.mtrl-sci↗

arXiv2025

Broadband nonlinear Hall response and multiple wave mixing in a room temperature altermagnet

Crystalline symmetries determine the linear and nonlinear response of materials to external stimuli such as mechanical pressure and electromagnetic fields, governing phenomena such as piezoelectricity, optical activity, and multiple wave mixing with wide ranging technological applications. Altermagnets present a new class of materials with magnetic crystalline order where specific crystal symmetry operations connect antiferromagnetic sublattices, leading to non-relativistic spin-splitting of the electronic band structure. Hence, the electric material properties of altermagnets should uniquely mirror these underlying symmetry properties, potentially giving rise to novel phenomena in response to external driving fields. Here, we report the discovery of a broadband third-order nonlinear anomalous Hall effect in altermagnetic CrSb at room temperature. The comparison of our observations with symmetry analyses and model calculations shows that this nonlinear Hall response is induced by the nonlinear electric susceptibility of a Berry curvature quadrupole, which exists within the spin-split band structure of CrSb and is characterized by the underlying crystalline and magnetic symmetries. We then utilize this third-order nonlinear electric susceptibility of CrSb to realize a multiple wave mixing device with pronounced four wave mixing output, which could, in principle, be extended to THz frequencies. Our study discovers that the crystalline magnetic order of altermagnets determines their nonlinear electric material properties, which could facilitate applications in high-frequency electronics, THz generation, communication networks, and energy harvesting.

cond-mat.mes-hall↗

arXiv2025

High Resolution Polar Kerr Effect Studies of Cs3Sb5 and ScV6Sn6 Below the Charge Order Transition

We report high resolution polar Kerr effect measurements on CsV3Sb5 and ScV6Sn6 single crystals in search for signatures of spontaneous polar Kerr effect (PKE) below the charge order transitions of these materials. Utilizing two separate zero-area loop Sagnac interferometers operating at 1550 nm and 830 nm wavelengths, we studied the temperature dependence of possible PKE after training with magnetic field. While a finite field Kerr measurement yielded optical rotation expected from the Pauli susceptibility of the itinerant carriers, no signal was detected at zero-field to within the noise floor limit of the apparatus of below $\sim$100 nanoradians. Simultaneous coherent reflection measurements confirm the sharpness of the charge order transition in the same optical volume as the Kerr measurements. Application of strain to reveal a hidden flux-ordered magnetic state did not result in a finite Kerr effect.

cond-mat.str-el↗