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Topological magnetic semimetals, like Co3Sn2S2 and Co2MnGa, display exotic transport properties, such as large intrinsic anomalous (AHE) due to uncompensated Berry curvature. The highly symmetric XPt3 compounds exhibit anti-crossing gapped nodal lines, a driving mechanism in the intrinsic Berry curvature Hall effects. Uniquely, these compounds contain two sets of gapped nodal lines that harmoniously dominate the Berry curvature in this complex multi band system. We calculate a maximum AHE of 1965 S cm-1 in the CrPt3 by first principles electronic structure. We have grown high-quality CrPt3 thin films with perpendicular magnetic anisotropy by magnetron sputtering and measured a robust AHE of 1750 S cm−1 for different sputtering growth conditions. Additionally, the cubic films display an easy magnetic axis along [111] direction. The facile and scalable fabrication of these materials is prime candidates for integration into topological devices. Topological magnetic semimetals can realise large intrinsic anomalous Hall effects using the characteristics of their electronic band structure and Berry curvature. Here, the authors predict an anomalous Hall effect for cubic CrPt3 using first principle calculations and confirm the results experimentally.

Time-reversal-symmetry-breaking Weyl semimetals (WSMs) have attracted great attention recently because of the interplay between intrinsic magnetism and topologically nontrivial electrons. Here, we present anomalous Hall and planar Hall effect studies on Co3Sn2S2 nanoflakes, a magnetic WSM hosting stacked Kagome lattice. The reduced thickness modifies the magnetic properties of the nanoflake, resulting in a 15-time larger coercive field compared with the bulk, and correspondingly modifies the transport properties. A 22% enhancement of the intrinsic anomalous Hall conductivity (AHC), as compared to bulk material, was observed. A magnetic field-modulated AHC, which may be related to the changing Weyl point separation with magnetic field, was also found. Furthermore, we showed that the PHE in a hard magnetic WSM is a complex interplay between ferromagnetism, orbital magnetoresistance, and chiral anomaly. Our findings pave the way for a further understanding of exotic transport features in the burgeoning field of magnetic topological phases.

The topological Hall effect (THE), induced by the Berry curvature that originates from non-zero scalar spin chirality, is an important feature for mesoscopic topological structures, such as skyrmions. However, the THE might also arise from other microscopic non-coplanar spin structures in the lattice. Thus, the origin of the THE inevitably needs to be determined to fully understand skyrmions and find new host materials. Here, we examine the Hall effect in both, bulk- and micron-sized lamellar samples of MnBi. The sample size affects the temperature and field range in which the THE is detectable. Although a bulk sample exhibits the THE only upon exposure to weak fields in the easy-cone state, in micron-sized lamella the THE exists across a wide temperature range and occurs at fields near saturation. Our results show that both the non-coplanar spin structure in the lattice and topologically non-trivial skyrmion bubbles are responsible for the THE, and that the dominant mechanism depends on the sample size. Hence, the magnetic phase diagram for MnBi is size-dependent. Our study provides an example in which the THE is simultaneously induced by two mechanisms, and builds a bridge between mesoscopic and microscopic magnetic structures. © 2022. This work was financially supported by an Advanced Grant from the European Research Council (No. 742068 ) “TOPMAT,” the European Union's Horizon 2020 research and innovation programme (No. 824123 ) “SKYTOP,” the European Union's Horizon 2020 research and innovation programme (No. 766566 ) “ASPIN,” the Deutsche Forschungsgemeinschaft (Project-ID 258499086) “SFB 1143,” the Deutsche Forschungsgemeinschaft (Project-IDs FE 633/30-1, RE 1164/6-1 and LU 2261/2-1) “SPP Skyrmionics,” the DFG through the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter ct.qmat (EXC 2147, Project-ID 39085490). I.S. is grateful to Deutsche Forschungsgemeinschaft for supporting this work through project SO 1623/2-1. D.W. has received funding from the European Research Council (ERC) under the Horizon 2020 research and innovation program of the European Union (grant agreement number 715620 ).

Skyrmionics materials hold the potential for future information technologies, such as racetrack memories. Key to that advancement are skyrmionics systems that exhibit high tunability and scalability, with stored information being easy to read and write by means of all-electrical techniques. Topological magnetic excitations, such as skyrmions and antiskyrmions give rise to a characteristic topological Hall effect (THE) in electrical transport. However, an unambiguous transport signature of antiskyrmions, in both thin films and bulk samples has been challenging to date. Here we apply magnetosensitive microscopy combined with electrical transport to directly detect the emergence of antiskyrmions in crystalline microstructures of Mn1.4PtSn at room temperature. We reveal the THE of antiskyrmions and demonstrate its tunability by means of finite sizes, field orientation, and temperature. Our atomistic simulations and experimental anisotropy studies demonstrate the link between antiskyrmions and a complex magnetism that consists of competing ferro- and antiferromagnetic as well as chiral exchange interactions.

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., 4 figures, 1 table

Itinerant ferromagnets constitute an important class of materials wherein spin-polarization can affect the electric transport properties in nontrivial ways. One such phenomenon is anomalous Hall effect which depends on the details of the band structure such as the amount of band crossings in the valence band of the ferromagnet. Here, we have found extraordinary anomalous Hall effect in an itinerant ferromagnetic metal LaCrSb3. The rather two-dimensional nature of the magnetic subunit imparts large anisotropic anomalous Hall conductivity of 1250 S/cm at 2K. Our investigations suggest that a strong Berry curvature by abundant momentum-space crossings and narrow energy-gap openings are the primary sources of the anomalous Hall conductivity. An important observation is the existence of quasi-dispersionless bands in LaCrSb3 which is now known to increase the anomalous Hall conductivity. After introducing f-electrons, anomalous Hall conductivity experiences more than two-fold increase and reaches 2900 S/cm in NdCrSb3., Comment: 9 pages, 4 figures, and supplementary

A large non-saturating magnetoresistance has been observed in several nonmagnetic topological Weyl semi-metals with high mobility of charge carriers at the Fermi energy. However, ferromagnetic systems rarely display a large magnetoresistance because of localized electrons in heavy d bands with a low Fermi velocity. Here, we report a large linear non-saturating magnetoresistance and high mobility in ferromagnetic MnBi. MnBi, unlike conventional ferromagnets, exhibits a large linear non-saturating magnetoresistance of 5000% under a pulsed field of 70 T. The electrons and holes’ mobilities are both 5000 cm2V−1s−1 at 2 K, which are one of the highest for ferromagnetic materials. These phenomena are due to the spin-polarised Bi 6p band’s sharp dispersion with a small effective mass. Our study provides an approach to achieve high mobility in ferromagnetic systems with a high Curie temperature, which is advantageous for topological spintronics., Ferromagnetic systems rarely display a large or non-saturating magnetoresistance, due to the low Fermi velocity of the predominant charge carrier. Here, the authors show that MnBi, a ferromagnet, bucks this trend, showing both large and non-saturating magnetoresistance, and high charge carrier motilities.

Skyrmionic materials hold the potential for future information technologies, such as racetrack memories. Key to that advancement are systems that exhibit high tunability and scalability, with stored information being easy to read and write by means of all-electrical techniques. Topological magnetic excitations such as skyrmions and antiskyrmions, give rise to a characteristic topological Hall effect. However, the electrical detection of antiskyrmions, in both thin films and bulk samples has been challenging to date. Here, we apply magneto-optical microscopy combined with electrical transport to explore the antiskyrmion phase as it emerges in crystalline mesoscale structures of the Heusler magnet Mn$_{1.4}$PtSn. We reveal the Hall signature of antiskyrmions in line with our theoretical model, comprising anomalous and topological components. We examine its dependence on the vertical device thickness, field orientation, and temperature. Our atomistic simulations and experimental anisotropy studies demonstrate the link between antiskyrmions and a complex magnetism that consists of competing ferromagnetic, antiferromagnetic, and chiral exchange interactions, not captured by micromagnetic simulations., Comment: 30 pages, 4 figures, Supplementary Information with additional 22 pages and 16 figures

Time-reversal-symmetry-breaking Weyl semimetals (WSMs) have attracted great attention recently because of the interplay between intrinsic magnetism and topologically nontrivial electrons. Here, we present anomalous Hall and planar Hall effect studies on Co3Sn2S2 nanoflakes, a magnetic WSM hosting stacked Kagome lattice. The reduced thickness modifies the magnetic properties of the nanoflake, resulting in a 15-time larger coercive field compared with the bulk, and correspondingly modifies the transport properties. A 22% enhancement of the intrinsic anomalous Hall conductivity (AHC), as compared to bulk material, was observed. A magnetic field-modulated AHC, which may be related to the changing Weyl point separation with magnetic field, was also found. Furthermore, we showed that the PHE in a hard magnetic WSM is a complex interplay between ferromagnetism, orbital magnetoresistance, and chiral anomaly. Our findings pave the way for a further understanding of exotic transport features in the burgeoning field of magnetic topological phases.

Tetragonal Mn-based Heusler compounds feature rich exchange interactions and exotic topological magnetic textures, such as antiskyrmions, complimented by the chiral-type Hall effects. This makes the material class interesting for device applications. We report the relation of the magnetic exchange interactions to the thickness and Mn concentration of Mn$_{x}$PtSn films, grown by magnetron sputtering. The competition of the magnetic exchange interactions determines the finite temperature magnetic texture and thereby the chiral-type Hall effects in external magnetic fields. We investigate the magnetic and transport properties as a function of magnetic field and temperature. We focus on the anomalous and chiral-type Hall effects and the behavior of the dc-magnetization, in relation to chiral spin textures. We further determine the stable crystal phase for a relative Mn concentration between 1.5 and 1.85 in the $I\overline{4}2d$ structure. We observe a spin-reorientation transition in all compounds studied, which is due to the competition of exchange interactions on different Mn sublattices. We discuss our results in terms of exchange interactions and compare them with theoretical atomistic spin calculations., 13 pages, 6 figures

The quantum anomalous Hall effect (QAHE) and magnetic Weyl semimetals (WSMs) are topological states induced by intrinsic magnetic moments and spin-orbit coupling. Their similarity suggests the possibility of achieving the QAHE by dimensional confinement of a magnetic WSM along one direction. In this paper, we investigate the emergence of the QAHE in the two-dimensional (2D) limit of magnetic WSMs due to finite-size effects in thin films and step edges. We demonstrate the feasibility of this approach with effective models and real materials. To this end, we have chosen the layered magnetic WSM ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$, which features a large anomalous Hall conductivity and anomalous Hall angle in its three-dimensional bulk as our material candidate. In the 2D limit of ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$, two QAHE states exist depending on the stoichiometry of the 2D layer. One is a semimetal with a Chern number of 6, and the other is an insulator with a Chern number of 3. The latter has a band gap of 0.05 eV, which is much larger than that in magnetically doped topological insulators. Our findings naturally explain the existence of chiral states in step edges of bulk ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ which have been reported in a recent experiment at $T=4\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and present a realistic avenue to realize QAH states in thin films of magnetic WSMs.

Various ${\mathrm{Co}}_{2}$-based Heusler compounds are predicted to be half-metallic ferromagnets with Weyl points. These systems with lack of time inversion symmetry possess a momentum space Berry curvature that can introduce exotic transport properties. The present study, on epitaxially grown ${\mathrm{Co}}_{2}\mathrm{TiSn}$ films, is an approach to understand and explore this possibility. The theoretical investigation shows that the Berry curvature is significant for the total anomalous Hall effect in experimentally grown ${\mathrm{Co}}_{2}\mathrm{TiSn}$ films. The deviation between the theory and experiment is due to the influence of side jump and skew scattering mechanisms. From a theoretical point of view, the intrinsic contribution to the anomalous Hall effect originates from partially gaped nodal lines due to the symmetry reduction induced by the lack of time reversal symmetry. Furthermore, from hard x-ray photoelectron spectroscopy measurements, we establish an electronic structure in the film that is comparable to the theoretical density of states calculations. These results provide intuitive insight into Heusler spintronics rooted in topological electronic structure.

The topological Hall effect (THE) is one of the key signatures of topologically nontrivial magnetic spin textures, wherein electrons feel an additional transverse voltage to the applied current. The magnitude of THE is often small compared to the anomalous Hall effect. Here, we find a large THE of $0.9\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$ that is of the same order of the anomalous Hall effect in the single-crystalline antiskyrmion-hosting Heusler compound ${\mathrm{Mn}}_{1.4}\mathrm{PtSn}$, a noncentrosymmetric tetragonal compound. The THE is highly anisotropic and survives in the whole temperature range where the spin structure is noncoplanar (170 K). The THE is zero above the spin reorientation transition temperature of 170 K, where the magnetization will have a collinear and ferromagnetic alignment. The large value of the THE entails a significant contribution from the momentum-space Berry curvature along with real-space Berry curvature, which has never been observed earlier.

The presence of nontrivial magnetic topology can give rise to nonvanishing scalar spin chirality and consequently a topological Hall or Nernst effect. In turn, topological transport signals can serve as indicators for topological spin structures. This is particularly important in thin films or nanopatterned materials where the spin structure is not readily accessible. Conventionally, the topological response is determined by combining magnetotransport data with an independent magnetometry experiment. This approach is prone to introduce measurement artifacts. In this study, we report the observation of large topological Hall and Nernst effects in micropatterned thin films of Mn

Topological magnetic semimetals promise large Berry curvature through the distribution of the topological Weyl nodes or nodal lines and further novel physics with exotic transport phenomena. We present a systematic study of the structural and magnetotransport properties of Co$_2$MnGa films from thin (20 nm) to bulk like behavior (80 nm), in order to understand the underlying mechanisms and the role on the topology. The magnetron sputtered Co$_2$MnGa films are $L$$2_{\mathrm {1}}$-ordered showing very good heteroepitaxy and a strain-induced tetragonal distortion. The anomalous Hall conductivity was found to be maximum at a value of 1138 S/cm, with a corresponding anomalous Hall angle of 13 %, which is comparatively larger than topologically trivial metals. There is a good agreement between the theoretical calculations and the Hall conductivity observed for the 80 nm film, which suggest that the effect is intrinsic. Thus, the Co$_2$MnGa compound manifests as a promising material towards topologically-driven spintronic applications., 7 pages, 5 figures, 1 table

Spin chirality in metallic materials with non-coplanar magnetic order can give rise to a Berry phase induced topological Hall effect. Here, we report the observation of a large topological Hall effect in high-quality films of Mn$_{1.5}$PtSn that were grown by means of magnetron sputtering on MgO(001). The topological Hall resistivity is present up to $\mu_{0}H \approx 4~$T below the spin reorientation transition temperature, $T_{s}=185$~K. We find, that the maximum topological Hall resistivity is of comparable magnitude as the anomalous Hall resistivity. Owing to the size, the topological Hall effect is directly evident prior to the customarily performed subtraction of magnetometry data. Further, we underline the robustness of the topological Hall effect in Mn\textsubscript{2-x}PtSn by extracting the effect for multiple stoichiometries (x~=~0.5, 0.25, 0.1) and film thicknesses (t = 104, 52, 35~nm) with maximum topological Hall resistivities between $0.76~\mu\Omega$cm and $1.55~\mu\Omega$cm at 150~K., Comment: 6 pages, 5 figures

Very recently, the half-metallic compound Co3Sn2S2 was proposed to be a magnetic Weyl semimetal (WSM) with Weyl points only 60 meV above the Fermi level E-F. Owing to the low charge carrier density and large Berry curvature induced, Co3Sn2S2 possesses both a large anomalous Hall conductivity and a large anomalous Hall angle, which provide strong evidence for the existence of Weyl points in Co3Sn2S2. In this work, we theoretically study the surface topological feature of Co3Sn2S2 and its counterpart Co3Sn2Se2. By cleaving the sample at the weak Sn-S/Se bonds, one can achieve two different surfaces terminated with Sn and S/Se atoms, respectively. The resulting Fermi-arc-related states can range from the energy of the Weyl points to E-F - 0.1 eV in the Sn-terminated surface. Therefore, it should be possible to observe the Fermi arcs in angle-resolved photoemission spectroscopy (ARPES) measurements. Furthermore, in order to simulate quasiparticle interference in scanning tunneling microscopy (STM) measurements, we also calculate the joint density of states for both terminals. This work should be helpful for a comprehensive understanding of the topological properties of these two magnetic WSMs and further ARPES and STM measurements.

Epitaxial films of the B20-structure compound Fe1−yCoyGe were grown by molecular beam epitaxy on Si (111) substrates. The magnetization varied smoothly from the bulklike values of one Bohr magneton per Fe atom for FeGe to zero for nonmagnetic CoGe. The chiral lattice structure leads to a Dzyaloshinskii-Moriya interaction (DMI), and the films' helical magnetic ground state was confirmed using polarized neutron reflectometry measurements. The pitch of the spin helix, measured by this method, varies with Co content y and diverges at y∼0.45. This indicates a zero crossing of the DMI, which we reproduced in calculations using first-principles methods. We also measured the longitudinal and Hall resistivity of our films as a function of magnetic field, temperature, and Co content y. The Hall resistivity is expected to contain contributions from the ordinary, anomalous, and topological Hall effects. Both the anomalous and topological Hall resistivities show peaks around y∼0.5. Our first-principles calculations show a peak in the topological Hall constant at this value of y, related to the strong spin polarization predicted for intermediate values of y. Our calculations predict half-metallicity for y=0.6, consistent with the experimentally observed linear magnetoresistance at this composition, and potentially related to the other unusual transport properties for intermediate value of y. While it is possible to reconcile theory with experiment for the various Hall effects for FeGe, the large topological Hall resistivities for y∼0.5 are much larger than expected when the very small emergent fields associated with the divergence in the DMI are taken into account.

We predict a large anomalous Nernst effect in the inverse Heusler compensated ferrimagnets ${\mathrm{Ti}}_{2}\mathrm{Mn}X$ ($X=\mathrm{Al}$, Ga, and In) with vanishing net magnetic moments. Though the net magnetic moment is zero, the Weyl points in these systems lead to a large anomalous Nernst conductivity (ANC) due to the lack of a global time-reversal symmetry operation that inverts the sign of the Berry curvature. In comparison to the noncollinear antiferromagnets ${\mathrm{Mn}}_{3}\mathrm{Sn}$ and ${\mathrm{Mn}}_{3}\mathrm{Ge}$, the high ANC stems almost entirely from the Weyl points in this class of compounds, and thus it is topologically protected. This work shows a large ANC with zero net magnetic moments in collinear systems, which is helpful for a comprehensive understanding of the thermoelectric effect in zero-moment magnetic materials and its further applications.

The presence of non-trivial magnetic topology can give rise to non-vanishing scalar spin chirality and consequently a topological Hall or Nernst effect. In turn, topological transport signals can serve as indicators for topological spin structures. This is particularly important in thin films or nanopatterned materials where the spin structure is not readily accessible. Conventionally, the topological response is determined by combining magnetotransport data with an independent magnetometry experiment. This approach is prone to introduce measurement artifacts. In this study, we report the observation of large topological Hall and Nernst effects in micropatterned thin films of Mn$_{1.8}$PtSn below the spin reorientation temperature $T_\mathrm{SR} \approx 190$K. The magnitude of the topological Hall effect $\rho_\mathrm{xy}^\mathrm{T} = 8$ n$\Omega$m is close to the value reported in bulk Mn$_2$PtSn, and the topological Nernst effect $S_\mathrm{xy}^\mathrm{T} = 115$ nV K$^{-1}$ measured in the same microstructure has a similar magnitude as reported for bulk MnGe ($S_\mathrm{xy}^\mathrm{T} \sim 150$ nV K$^{-1}$), the only other material where a topological Nernst was reported. We use our data as a model system to introduce a topological quantity, which allows to detect the presence of topological transport effects without the need for independent magnetometry data. Our approach thus enables the study of topological transport also in nano-patterned materials without detrimental magnetization related limitations., Comment: 8 pages, 3 figures

Ab initio electronic structure calculations were carried out for bulk cadmium telluride (CdTe) and the unreconstructed CdTe polar (111) Cd-terminated and ( $$ \bar{1}\bar{1}\bar{1} $$ ) Te-terminated surfaces. The hybrid functional for the exchange and correlation potential improves the overall description of the electronic structure of bulk CdTe, by lowering Cd 4d states and hence reducing the Cd 4d–Te 5p hybridization. The Cd–Te interlayer distance of the Cd-terminated surface exhibits a dramatic contraction in contrast with the expansion of the Te-terminated surface, and the surface relaxations decrease as the slab thickness increases. The underlying mechanism of the convergence of the electrostatic potential energy, work function, and electric dipole moment of the polar surfaces as a function of slab thickness is surface electron rearrangement leading to charge transfer from the Te- to the Cd-terminated surfaces. The surface electric polarization induces an internal electric field in the slab, which in turn tilts the bands of the slab double layers, thus rendering the surface layers metallic. The electric field decreases with increasing slab thickness due to convergence of the difference of electrostatic potentials between the Cd- and Te-terminated surfaces.

We carry out density functional theory calculations which demonstrate that the electron dynamics in the Skyrmion phase of Fe-rich Mn_{1-x}Fe_{x}Ge alloys is governed by Berry phase physics. We observe that the magnitude of the Dzyaloshinskii-Moriya interaction directly related to the mixed space-momentum Berry phases, changes sign and magnitude with concentration x in direct correlation with the data of Shibata et al. [Nat. Nanotechnol. 8, 723 (2013)]. The computed anomalous and topological Hall effects in FeGe are also in good agreement with available experiments. We further develop a simple tight-binding model able to explain these findings. Finally, we show that the adiabatic Berry phase picture is violated in the Mn-rich limit of the alloys.

Materials that crystalize in diamond-related lattices, with Si and GaAs as their prime examples, are at the foundation of modern electronics. Simultaneously, the two atomic sites in the unit cell of these crystals form inversion partners which gives rise to relativistic non-equilibrium spin phenomena highly relevant for magnetic memories and other spintronic devices. When the inversion-partner sites are occupied by the same atomic species, electrical current can generate local spin polarization with the same magnitude and opposite sign on the two inversion-partner sites. In CuMnAs, which shares this specific crystal symmetry of the Si lattice, the effect led to the demonstration of electrical switching in an antiferromagnetic memory at room temperature. When the inversion-partner sites are occupied by different atoms, a non-zero global spin-polarization is generated by the applied current which can switch a ferro-magnet, as reported at low temperatures in the diluted magnetic semiconductor (Ga,Mn)As. Here we demonstrate the effect of the global current-induced spin polarization in a counterpart crystal-symmetry material NiMnSb which is a member of the broad family of magnetic Heusler compounds. It is an ordered high-temperature ferromagnetic metal whose other favorable characteristics include high spin-polarization and low damping of magnetization dynamics. Our experiments are performed on strained single-crystal epilayers of NiMnSb grown on InGaAs. By performing all-electrical ferromagnetic resonance measurements in microbars patterned along different crystal axes we detect room-temperature spin-orbit torques generated by effective fields of the Dresselhaus symmetry. The measured magnitude and symmetry of the current-induced torques are consistent with our relativistic density-functional theory calculations.

We demonstrate that biological molecules such as Watson-Crick DNA base pairs can behave as biological Aviram-Ratner electrical rectifiers because of the spatial separation and weak hydrogen bonding between the nucleobases. We have performed a parallel computational implementation of the ab-initio non-equilibrium Green's function (NEGF) theory to determine the electrical response of graphene---base-pair---graphene junctions. The results show an asymmetric (rectifying) current-voltage response for the Cytosine-Guanine base pair adsorbed on a graphene nanogap. In sharp contrast we find a symmetric response for the Thymine-Adenine case. We propose applying the asymmetry of the current-voltage response as a sensing criterion to the technological challenge of rapid DNA sequencing via graphene nanogaps.

The anomalous Hall effect soars when Dirac quasiparticles meet frustrated magnetism., The anomalous Hall effect (AHE) is one of the most fundamental phenomena in physics. In the highly conductive regime, ferromagnetic metals have been the focus of past research. Here, we report a giant extrinsic AHE in KV3Sb5, an exfoliable, highly conductive semimetal with Dirac quasiparticles and a vanadium Kagome net. Even without report of long range magnetic order, the anomalous Hall conductivity reaches 15,507 Ω−1 cm−1 with an anomalous Hall ratio of ≈ 1.8%; an order of magnitude larger than Fe. Defying theoretical expectations, KV3Sb5 shows enhanced skew scattering that scales quadratically, not linearly, with the longitudinal conductivity, possibly arising from the combination of highly conductive Dirac quasiparticles with a frustrated magnetic sublattice. This allows the possibility of reaching an anomalous Hall angle of 90° in metals. This observation raises fundamental questions about AHEs and opens new frontiers for AHE and spin Hall effect exploration, particularly in metallic frustrated magnets.