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Walter Schnelle

Publications and source records attributed to Walter Schnelle.

At least 19 recordsLinked to original sources
arXiv2026

Near-Room-Temperature Antiferromagnetic Ordering in the Quadruple Perovskite Sr4NaRu3O12

We report the synthesis, structure and magnetic properties of two 1:3 ordered quadruple perovskites Sr4MRu3O12 (M = Li and Na). Sr4NaRu3O12 crystallizes in the centrosymmetric space group R-3 and Sr4LiRu3O12 appears to be isostructural to the Na compound based on the PXRD data. In Sr4NaRu3O12, both Na and Ru are predominantly ordered at the B sites (here Na/Li and Ru) and the structure contains only corner-connected RuO6 and NaO6 octahedra. This atomic ordering also leads to a rather large unit cell with a = 11.25 {\AA} and c = 27.6 {\AA} compared to the basic 12R structure (a = 5.5 {\AA} and c ~ 27 {\AA}). Magnetic measurements reveal that Sr4NaRu3O12 undergoes a magnetic transition to an antiferromagnetic state below TN ~ 265 K which is confirmed by DSC and neutron diffraction. The Ru moments show a collinear antiferromagnetic spin alignment along the hexagonal c axis with a propagation vector k = (0, 0, 1.5). Interestingly, those Ru moments lying on the three-fold roto-inversion do not significantly contribute to the magnetic order, since they are located between antiferromagnetically coupled Ru atoms and are therefore probably highly frustrated. Band structure calculations on Sr4NaRu3O12 complement the observed magnetic ground state and a semiconducting behavior in the compound. Sr4LiRu3O12 shows a magnetic anomaly below 110 K, possibly associated with competing ferromagnetic and antiferromagnetic interactions.

cond-mat.str-el↗
arXiv2026

Intrinsic magnetotransport and orientation dependent topological Hall effect in EuAuBi

We report the growth of high-quality single crystals of the magnetic topological semimetal EuAuBi using a Pb flux method, which effectively suppresses the formation of secondary Au2Bi impurity phases that were prevalent in the previously reported Bi flux grown crystals. This growth optimization enables reliable investigation of the intrinsic physical properties of EuAuBi. Importantly, Pb flux growth stablilizes c axis oriented single crystals, enabling Hall measurements in a previously unexplored geometry. In this configuration (I parallel to c, B perpendicular to c), a finite residual Hall contribution, known as topological Hall signal emerges below the antiferromagnetic ordering temperature and within a narrow magnetic field range. This Hall contribution coincides with the metamagnetic transitions, anomalies in magnetoresistance, and an additional feature in field-dependent specific heat, indicating strong coupling between the electronic transport and field induced magnetic reconstructions. Consequently, these findings underscore the significance of crystal orientation in uncovering topological transport signatures in magnetic semimetals such as EuAuBi.

cond-mat.str-el↗
arXiv2026

Complex spin dynamics induced metamagnetic phase transitions in Dirac semimetal EuAuBi

We report a comprehensive investigation of the physical properties of the Dirac semimetal compound EuAuBi single crystals, using neutron diffraction, magnetization, electrical transport, and specific heat measurements. EuAuBi crystallizes in a hexagonal structure with space group P63mc (No. 186). First-principles calculations using density functional theory characterize it as a Dirac semimetal, with a notable band-crossing in proximity to the Fermi level (EF ) along the {\Gamma}-A direction. The crystal exhibits three distinct magnetic phases at 4 K (TN1), 3.5 K (TN2), and 2.8 K (TN3)as observed from magnetic and specific heat measurements. However, zero-field neutron diffraction resolves only two magnetic phases: a commensurate antiferromagnetic phase and a canted antiferromagnetic phase. Field-dependent ac and dc magnetization measurements uncover field-induced non-trivial spin textures in the magnetic field range 1.5 to 3 T, manifested as a tilted plateau in the magnetization curves. The interplay between conduction carriers and these spin textures is further evidenced by unique features in the magnetic field-dependent longitudinal resistivity in the system. Finally, we present a comprehensive magnetic phase diagram of EuAuBi, highlighting diverse spin alignments present in the material. EuAuBi thus emerges as a rare material system in which both momentum-space and real-space Berry curvature effects may coexist, providing a unique opportunity to investigate their interplay.

cond-mat.mtrl-sci↗
arXiv2025

Probing orbital magnetism of a kagome metal CsV3Sb5 by a tuning fork resonator

The recently discovered kagome metal CsV$_3$Sb$_5$ exhibits a complex phase diagram that encompasses frustrated magnetism, topological charge density wave (CDW), and superconductivity. One CDW state that breaks time-reversal symmetry was proposed in this compound, while the exact nature of the putative magnetic state remains elusive. To examine the thermodynamic state of CsV$_3$Sb$_5$ and assess the character of the associated magnetism, we conducted tuning fork resonator measurements of magnetotropic susceptibility over a broad range of angles, magnetic fields, and temperature. We found a cascade of phase transition in the CDW phase. Of particular interest is a highly anisotropic magnetic structure that arises below about 30~K, with a magnetic moment along the $c$-axis that has an extremely small magnitude. This magnetic state demonstrates extremely slow dynamics and small saturate field, all suggest that electronic phase below 30~K breaks time reversal symmetry and has an unconventional origin.

cond-mat.mtrl-sci↗
arXiv2025

Ultrafast Electronic Structure Engineering in 1$T$-TaS$_2$: Role of Doping and Amplitude Mode Dynamics

In strongly correlated transition metal dichalcogenides, an intricate interplay of polaronic distortions, stacking arrangement, and electronic correlations determines the nature of the insulating state. Here, we study the response of the electronic structure to optical excitations to reveal the effect of chemical electron doping on this complex interplay. Transient changes in pristine and electron-doped 1$T$ -TaS$_2$ are measured by femtosecond time-resolved photoelectron spectroscopy and compared to theoretical modeling based on non-equilibrium dynamical mean-field theory and density functional theory. The fine changes in the oscillatory signal of the charge density wave amplitude mode indicate phase-dependent modifications in the Coulomb interaction and the hopping. Furthermore, we find an enhanced fraction of monolayers in the doped system. Our work demonstrates how the combination of time-resolved spectroscopy and advanced theoretical modeling provides insights into the physics of correlated transition metal dichalcogenides.

cond-mat.str-el↗
arXiv2025

Orbital-selective band modifications in a charge-ordered kagome metal LuNb$_6$Sn$_6$

The origin of the charge order in kagome lattice materials has attracted great interest due to the unique electronic structure features connected to kagome networks and the interplay between electron and lattice degrees of freedom. Recently, compounds with composition $Ln$Nb$_6$Sn$_6$ ($Ln$ = Ce-Nd, Sm, Gd-Tm, Lu, Y) appear as a new family of kagome metals, structurally analogous to $R$V$_6$Sn$_6$ ($R$ = Sc, Y, or rare earth) systems. Among them, LuNb$_6$Sn$_6$ emerges as a novel material hosting charge density wave (CDW) with a $\sqrt{3}$ $\times$ $\sqrt{3}$ $\times$ $3$ wave vector, akin to that in ScV$_6$Sn$_6$. Here, we employ high-resolution angle-resolved photoemission spectroscopy, scanning tunneling microscopy, and density functional theory calculations to systematically investigate the electronic properties of LuNb$_6$Sn$_6$. Our observation reveals the characteristic band structures of the "166" kagome system. A charge instability driven by Fermi surface nesting is decisively ruled out through an analysis of the interactions between van Hove singularities. Across the CDW transition, we observe orbital-selective band modifications, with noticeable evolutions of Lu 5$d$ and Sn 5$p$ electrons, while Nb 4$d$ electrons exhibit minimal change, suggesting that the Lu and Sn sites other than the Nb kagome lattice play a key role in the formation of CDW. Our findings substantiate a universal lattice-driven CDW mechanism rather than a charge-instability-driven one in the "166" kagome compounds, making it a distinct material class compared to other charge-ordered kagome systems, such as $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) and FeGe.

cond-mat.str-el↗
arXiv2025

Concurrent Multifractality and Anomalous Hall Response in the Nodal Line Semimetal Fe$_3$GeTe$_2$ Near Localization

Topological states of matter exhibit unique protection against scattering by disorder. Different topological classes exhibit distinct forms and degrees of protection. Here, we investigate the response of the ferromagnetic nodal line semimetal Fe$_3$GeTe$_2$ to disorder and electronic interactions. By combining global magneto-transport with atomic-scale scanning tunneling spectroscopy we find a simultaneous onset of diverse phenomena below a common temperature scale of about 15 K: A crossover from metallic to insulating temperature dependence of the longitudinal resistivity, saturation of the anomalous Hall conductivity to its maximal value, formation of a sharp zero-bias dip in the tunneling density of state, and emergence of multi-fractal structure of the electronic wavefunction peaking at the Fermi energy. These concurrent observations reflect the emergence of a novel energy scale possibly related to the opening of a gap in the nodal line band of Fe$_3$GeTe$_2$. Our study provides overarching insight into the role of disorder, electronic interactions and Berry curvature in setting the micro- and macro-scale responses of topological semimetals.

cond-mat.str-el↗
arXiv2024

Pressure-induced superconductivity in monoclinic RhBi$_2$

RhBi$_2$ is a polymorphic system that exhibits two distinct phases. RhBi$_2$ in the triclinic phase has been identified as a weak topological insulator with a van Hove singularity point close to the Fermi energy. Thus, triclinic RhBi$_2$ is expected to exhibit exotic quantum properties under strain or pressure. In this study, we report on the emergence of superconductivity in the monoclinic RhBi$_2$ under external pressures. The electrical resistivity behavior of the monoclinic RhBi$_2$ single crystal is studied at a wide range of applied external pressures up to 40 GPa. We observe a pressure-induced superconductivity with a dome-shaped dependence of the critical temperature on pressure at pressures above 10 GPa. A maximum critical temperature ($T_\mathrm{c}$) value of $T_\mathrm{c}$ = 5.1 K is reached at the pressure of 16.1 GPa. Furthermore, we performed detailed ab initio calculations to understand the electronic band structures of monoclinic RhBi$_2$ under varying pressures. The combination of topology and pressure-induced superconductivity in the RhBi$_2$ polymorphic system may provide us with a new promising material platform to investigate topological superconductivity.

cond-mat.supr-con↗
arXiv2024

Superconductivity in ternary pyrite-type compound IrBi$_{1-x}$Te$_{1+x}$ ($x \approx 0.2$) at ambient and high pressure

We report superconductivity in the ternary compound IrBi$_{0.8}$Te$_{1.2}$ with critical temperature 1.7 K. The replacement of Bi by Te leads to the metallic conductivity in contrast to the semiconducting parent compound IrBiTe. The superconductivity can be further enhanced by application of external pressure. $T_c$ demonstrates dome-shaped dependence on pressure with a maximum value of 2.6 K at 26.5 GPa. Pressure effects on electronic properties and lattice dynamic of IrBi$_{0.8}$Te$_{1.2}$ were studied by pressure dependent electrical resistivity, Hall effect and Raman spectroscopy measurements.

cond-mat.supr-con↗
arXiv2024

Striped magnetization plateau and chirality-reversible anomalous Hall effect in a magnetic kagome metal

Kagome materials with magnetic frustration in two-dimensional networks are known for their exotic properties, such as the anomalous Hall effect (AHE) with non-collinear spin textures. However, the effects of one-dimensional (1D) spin chains within these networks are less understood. Here, we report a distinctive AHE in the bilayer-distorted kagome material GdTi$_3$Bi$_4$, featuring 1D Gd zigzag spin chains, a one-third magnetization plateau, and two successive metamagnetic transitions. At these metamagnetic transitions, Hall resistivity shows abrupt jumps linked to the formation of stripe domain walls, while within the plateau, the absence of detectable domain walls suggests possible presence of skyrmion phase. Reducing the sample size to a few microns reveals additional Hall resistivity spikes, indicating domain wall skew scattering contributions. Magnetic atomistic spin dynamics simulations reveal that the magnetic textures at these transitions have reverse chirality, explaining the evolution of AHE and domain walls with fields. These results underscore the potential of magnetic and crystal symmetry interplay, and magnetic field-engineered spin chirality, for controlling domain walls and tuning transverse properties, advancing spintronic applications.

cond-mat.str-el↗
arXiv2024

Spectroscopic origin of giant anomalous Hall effect in an interwoven magnetic kagome metal

The discovery of a giant anomalous Hall effect (AHE) and its novel mechanism holds significant promise for advancing both fundamental research and practical applications. Magnetic kagome lattice materials are uniquely suited for studying the AHE due to their interplay between electronic structure, topology, and magnetism. However, the geometric frustration inherent in kagome lattices often limits the configuration and tunability of magnetic order. Here, we present a new design strategy for kagome-lattice materials with emergent magnetism, exemplified by the magnetic kagome metal TbTi$_3$Bi$_4$, which features interwoven magnetic Tb zigzag chains and non-magnetic Ti kagome bilayers. This material exhibits a record-high anomalous Hall conductivity (AHC) of 10$^5$ $\Omega^{-1}$ cm$^{-1}$. Spectroscopy measurements reveal a large band folding gap observed via angle-resolved photoemission spectroscopy, coexisting spin-density-wave (SDW) order detected through spin-polarized scanning tunneling spectroscopy, and a spiral magnetic order with large magnetic moments identified by neutron diffraction. These findings highlight a strong electron-magnetic coupling between itinerant charges and ordered magnetic moments, offering a spectroscopic explanation for the giant AHC in TbTi$_3$Bi$_4$. This work establishes a pathway for innovative material design strategies, unlocking new possibilities for future exploration and applications in quantum and spintronic technologies.

cond-mat.str-el↗
arXiv2022

Magnetic phase crossover in strongly correlated EuMn2P2

Strong electron correlations underlie a plethora of electronic and magnetic components and devices and are often used to identify and probe novel ground states in quantum materials. Herein we report a magnetic phase crossover in EuMn2P2, an insulator which shows Eu antiferromagnetism at TN=17K, but no phase transition attributed to Mn magnetism. The absence of a Mn magnetic phase transition contrasts with the formation of long-range Mn order at T=130K in isoelectronic EuMn2Sb2 and EuMn2As2. Temperature-dependent specific heat and 31P NMR measurements provide evidence for the development of Mn magnetic correlations from T=250-100 K. Density functional theory calculations demonstrate an unusual sensitivity of the band structure to the details of the imposed Mn and Eu magnetic order, with antiferromagnetic Mn order required to recapitulate an insulating state. Our results imply a picture in which long range Mn magnetic order is suppressed by chemical pressure, but that magnetic correlations persist, narrowing bands and producing an insulating state.

cond-mat.str-el↗
arXiv2022

Bonding and Electronic Nature of the Anionic Framework in LaPd$_3$S$_4$

Double Dirac materials are a topological phase of matter in which a non-symmorphic symmetry enforces greater electronic degeneracy than normally expected up to eightfold. The cubic palladium bronzes NaPd$_3$O$_4$ and LaPd$_3$S$_4$ are built of Pd$_3$X$_4$ (X = O, S) anionic frameworks that are ionically bonded to A cations (A = Na, La). These materials were recently identified computationally as harboring eightfold fermions. Here we report the preparation of single crystals and electronic properties of LaPd$_3$S$_4$. Measurements down to T = 0.45 K and in magnetic fields up to $μ$0H = 65 T are consistent with normal Fermi liquid physics of a Dirac metal in the presence of dilute magnetic impurities. This interpretation is further confirmed by analysis of specific heat, magnetization measurements and comparison to density functional theory (DFT) calculations. Through a bonding analysis of the DFT electronic structure of NaPd$_3$O$_4$ and LaPd$_3$S$_4$, we identify the origin of the stability of the anionic Pd$_3$X$_4$ framework at higher electron counts for X = S than X = O, and propose chemical tuning strategies to enable shifting the 8-fold fermion points to the Fermi level.

cond-mat.mtrl-sci↗
arXiv2022

New Buckled Honeycomb Lattice Compound Sr3CaOs2O9 Exhibiting Antiferromagnetism above Room Temperature

Synthesis, crystal structure and magnetic properties of a new 2:1 ordered triple perovskite Sr3CaOs2O9 are reported. The compound crystallizes in P21/c space group and features a unique buckled honeycomb lattice of osmium. It exhibits long-range antiferromagnetic ordering with a high Neel temperature of 385 K as confirmed by susceptibility, heat capacity and neutron diffraction measurements and is electrically insulating. This compound is also the first example of a 2:1 ordered osmate perovskite. Theoretical investigations indicate that Sr3CaOs2O9 features a sizeable antiferromagnetic exchange between the puckered planes resulting in a high TN. The magnetic properties of the known compound Sr3CaRu2O9 are elucidated in comparison. It shows antiferromagnetic order below TN = 200 K.

cond-mat.mtrl-sci↗
arXiv2021

Anomalous thermoelectric effects and quantum oscillations in the kagome metal CsV$_3$Sb$_5$

The kagome metal compounds $A$V$_3$Sb$_5$ ($A$ = K, Rb, and Cs) feature a wealth of phenomena including nontrivial band topology, charge density wave (CDW), and superconductivity. One intriguing property is the time-reversal symmetry breaking in the CDW state without local moments, which leads to anomalous transport responses. Here, we report the investigation of magneto-thermoelectric effects on high-quality CsV$_3$Sb$_5$ single crystals. A large anomalous Nernst effect is observed at temperatures below 30 K. Multiple Fermi surfaces with small effective masses are revealed by quantum oscillations in Nernst and Seebeck signals under high magnetic field. Furthermore, we find an unknown frequency, and attribute it to the magnetic breakdown across two smaller Fermi surfaces. A gap around 20 meV can be resolved from the breakdown threshold field, which we propose to be introduced by the CDW. These results shed new light on the CDW-related phenomena, particularly in $A$V$_3$Sb$_5$ compounds.

cond-mat.mtrl-sci↗
arXiv2021

Large topological Hall effect in an easy-cone ferromagnet (Cr0.9B0.1)Te

The Berry phase understanding of electronic properties has attracted special interest in condensed matter physics, leading to phenomena such as the anomalous Hall effect and the topological Hall effect. A non-vanishing Berry phase, induced in momentum space by the band structure or in real space by a non-coplanar spin structure, is the origin of both effects. Here, we report a sign conversion of the anomalous Hall effect and a large topological Hall effect in (Cr0.9B0.1)Te single crystals. The spin reorientation from an easy-axis structure at high temperature to an easy-cone structure below 140 K leads to conversion of the Berry curvature, which influences both, anomalous and topological, Hall effects in the presence of an applied magnetic field and current. We compare and summarize the topological Hall effect in four categories with different mechanisms and have a discussion into the possible artificial fake effect of topological Hall effect in polycrystalline samples, which provides a deep understanding of the relation between spin structure and Hall properties.

cond-mat.mtrl-sci↗
arXiv2021

Large anomalous Hall effect in the kagome ferromagnet LiMn$_6$Sn$_6$

Kagome magnets are believed to have numerous exotic physical properties due to the possible interplay between lattice geometry, electron correlation and band topology. Here, we report the large anomalous Hall effect in the kagome ferromagnet LiMn$_6$Sn$_6$, which has a Curie temperature of 382 K and easy plane along with the kagome lattice. At low temperatures, unsaturated positive magnetoresistance and opposite signs of ordinary Hall coefficient for $ρ_{xz}$ and $ρ_{yx}$ indicate the coexistence of electrons and holes in the system. A large intrinsic anomalous Hall conductivity of 380 $Ω^{-1}$ cm$^{-1}$, or 0.44 $e^2/h$ per Mn layer, is observed in $σ_{xy}^A$. This value is significantly larger than those in other $R$Mn$_6$Sn$_6$ ($R$ = rare earth elements) kagome compounds. Band structure calculations show several band crossings, including a spin-polarized Dirac point at the K point, close to the Fermi energy. The calculated intrinsic Hall conductivity agrees well with the experimental value, and shows a maximum peak near the Fermi energy. We attribute the large anomalous Hall effect in LiMn$_6$Sn$_6$ to the band crossings closely located near the Fermi energy.

cond-mat.mtrl-sci↗
arXiv2021

Crystal Growth of a New 8H Perovskite Sr8Os6.3O24 Exhibiting High TC Ferromagnetism

Single crystals of a new twinned hexagonal perovskite compound Sr8Os6.3O24 have been synthesized, and structural and magnetic properties have been determined. The compound crystallizes in a hexagonal cell with lattice parameters a = 9.6988(3) Å and c = 18.1657(5) Å. The structure is an eight-layered hexagonal B-site deficient perovskite with the layer sequence (ccch)2 and represents the first example of a hexagonal structure among 5d oxides adopting a twin option. The sample shows spontaneous ferromagnetic magnetization below 430 K with a small saturation moment of 0.11 μB/Os ion. This is the highest Curie temperature (TC) reported for any bulk perovskite containing only 5d ions at the B site.

cond-mat.mtrl-sci↗