The magnetotransport properties of disordered ferromagnetic kagome layers are investigated numerically. We show that a large domain-wall magnetoresistance or negative magnetoresistance can be realized in kagome layered materials (e.g. Fe$_3$Sn$_2$, Co$_3$Sn$_2$S$_2$, and Mn$_3$Sn), which show the quantum anomalous Hall effect. The kagome layers show a strong magnetic anisotropy and a large magnetoresistance depending on their magnetic texture. These domain-wall magnetoresistances are expected to be robust against disorder and observed irrespective of the domain-wall thickness, in contrast to conventional domain-wall magnetoresistance in ferromagnetic metals.
Magnetic nanoarray with special geometries exhibits nontrivial collective behaviors similar to those observed in the spin ice materials. Here we present a novel circuit model to describe the complex magnetotransport phenomena in artificial kagome spin ice. In this picture, the system can be viewed as a resistor network driven by voltage sources that are located at vertices of the honeycomb array. The differential voltages across different terminals of these sources are related to the ice-rules that govern the local magnetization ordering. The circuit model relates the transverse Hall voltage o…
A tight-binding model with randomly fluctuating atomic positions is studied to discuss the effect of strong disorder in graphene. We employ a strong-disorder expansion for the transport quantities and find a diffusive behavior, where the conductivity is decreasing with increasing disorder. Surprisingly, the magnetic field drops out of the transport quantities in leading order of this expansion. This signals a strong suppression of magnetotransport effects for sufficiently strong disorder. This result is consistent with recent experimental observations by Morozov {\it et al.}
In this numerical study we investigate the influence and interplay of disorder, spin-orbit coupling and magnetic field on the edge-transport in HgTe/CdTe quantum wells in the framework of coherent elastic scattering. We show that the edge states remain unaffected by the combined effect of moderate disorder and a weak magnetic field at realistic spin-orbit coupling strengths. Agreement with the experimentally observed linear magnetic field dependence for the conductance of long samples is obtained when considering the existence of charge puddles.
We study magnetotransport in a disordered Weyl semimetal taking into account localization effects exactly. In the vicinity of a Weyl node, a single chiral Landau level coexists with a number of conventional non-chiral levels. Disorder scattering mixes these topologically different modes leading to peculiar localization effects. We derive the average conductance as well as the full distribution function of transmission probabilities along the field direction. Remarkably, we find that localization of the non-chiral modes is greatly enhanced in a strong magnetic field with the typical localizatio…
The unexpected "0.7" plateau of conductance quantisation is usually observed for ballistic one-dimensional devices. In this work we study a quasi-ballistic quantum wire, for which the disorder induced backscattering reduces the conductance quantisation steps. We find that the transmission probability resonances coexist with the anomalous plateau. The studies of these resonances as a function of the in-plane magnetic field and electron density point to the presence of spin polarisation at low carrier concentrations and constitute a method for the determination of the effective g-factor suitable…
Complex electronic topography and magnetotransport in an in-plane ferromagnetic kagome metal
University of Central Florida（中佛罗里达大学）；Hiroshima University（广岛大学）；The University of Tennessee（田纳西大学）；Northeastern University（东北大学）；S. N. Bose National Centre for Basic Sciences（S.N.玻色基础科学国家中心）
We discuss theoretically how electrons confined to two dimensions in a delta-doped heterostructure can arrange themselves in a droplet-like spatial distribution due to disorder and screening effects when their density is low. We apply this droplet picture to magnetotransport and derive the expected dependence on electron density of several quantities relevant to this transport, in the regimes of weak and moderate magnetic fields. We find good qualitative and quantitative agreement between our calculations and recent experiments on delta-doped heterostructures.
Antiferromagnets (AFMs) with zero net magnetization are proposed as active elements in future spintronic devices. Depending on the critical thickness of the AFM thin films and the measurement temperature, bimetallic Mn-based alloys and transition metal oxide-based AFMs can host various coexisting ordered, disordered, and frustrated AFM phases. Such coexisting phases in the exchange coupled ferromagnetic (FM)/AFM-based heterostructures can result in unusual magnetic and magnetotransport phenomena. Here, we integrate chemically disordered AFM IrMn3 thin films with coexisting AFM phases into comp…
We report on magnetotransport measurements performed on a large metallic two-dimensional $\mathcal{T}_{3}$ network. Superimposed on the conventional Altshuler-Aronov-Spivak (AAS) oscillations of period $h/2e$, we observe clear $h/e$ oscillations in magnetic fields up to $8 T$. Different interpretations of this phenomenon are proposed.
Magnetic fields are often used for characterizing transport in nanoscale materials. Recent magnetotransport experiments have demonstrated that ballistic transport is possible in graphene antidot lattices (GALs). These experiments have inspired the present theoretical study of GALs in a perpendicular magnetic field. We calculate magnetotransport through graphene antidot barriers (GABs), which are finite rows of antidots arranged periodically in a pristine graphene sheet, using a tight-binding model and the Landauer-Büttiker formula. We show that GABs behave as ideal Dirac mass barriers for anti…
We consider the effect of a magnetic field $B$ on the transport of neutral composite particles, excitons, in weakly disordered 2D systems. In the case of classical transport, when the interference of different paths is neglected, the magnetic field suppresses exciton transport, and the static diffusion constant $D(B)$ monotonically drops with $B$. When quantum-mechanical corrections due to weak localization are taken into account, $D(B)$ becomes a nonmonotonic function of $B$. In weak magnetic fields, where the magnetic length is much larger than the exciton Bohr radius, $l_B >> a_B$, a positi…
We have studied the magnetotransport of conical and disk-shaped nanocarbon particles in magnetic fields $\left|B\right|\leq9\:\mathrm{T}$ at temperatures $2\leq T\leq300\:\mathrm{K}$ to characterize electron scattering in a three dimensional disordered material of multilayered quasi 2D and 3D carbon nanoparticles. The microstructure of the particles was modified by graphitization at temperatures $1600^{\circ}\mathrm{C}$ and $2700^{\circ}\mathrm{C}$. We find clear correlations between the microstructure as seen in transmission electron microscopy and the magnetotransport properties of the parti…
We report a theoretical low-field magnetotransport study unveiling the effect of pseudospin in realistic models of weakly disordered graphene-based materials. Using an efficient Kubo computational method, and simulating the effect of charges trapped in the oxide, different magnetoconductance fingerprints are numerically obtained in system sizes as large as 0.3 micronmeter squared, containing tens of millions of carbon atoms. In two-dimensional graphene, a strong valley mixing is found to irreparably yield a positive magnetoconductance (weak localization), whereas crossovers from positive to a …
We present the magnetoresistance (MR) of highly doped monolayer graphene layers grown by chemical vapor deposition on 6H-SiC. The magnetotransport studies are performed on a large temperature range, from $T$ = 1.7 K up to room temperature. The MR exhibits a maximum in the temperature range $120-240$ K. The maximum is observed at intermediate magnetic fields ($B=2-6$ T), in between the weak localization and the Shubnikov-de Haas regimes. It results from the competition of two mechanisms. First, the low field magnetoresistance increases continuously with $T$ and has a purely classical origin. Th…
We have investigated the magnetic and magnetotransport properties of Ba$_2$FeMoO$_6$ thin films produced by pulsed laser deposition from optimized bulk material. The films are comprised of grains of crystalline Ba$_2$FeMoO$_6$ with a disordered grain boundary region that lowers the net saturation magnetization of the film and prevents full magnetic alignment below a Curie temperature $T_C$$\sim$305 K. Magnetotransport measurements point to the Ba$_2$FeMoO$_6$ grains retaining the high spin polarization of a half-metal up to $T_C$, while the grain boundaries greatly reduce the spin polarization…
Magnetotransport measurements in combination with molecular dynamics (MD) simulations on two-dimensional disordered Lorentz gases in the classical regime are reported. In quantitative agreement between experiment and simulation, the magnetoconductivity displays a pronounced peak as a function of perpendicular magnetic field $B$ which cannot be explained in the framework of existing kinetic theories. We show that this peak is linked to the onset of a directed motion of the electrons along the contour of the disordered obstacle matrix when the cyclotron radius becomes smaller than the size of th…
The two dimensional kagome spin lattice structure of Mn atoms in the family of Mn$_3$X non-collinear antiferromagnets are providing substantial excitement in the exploration of Berry curvature physics and the associated non-trivial magnetotransport responses. Much of these studies are performed in the hexagonal systems, mainly Mn$_3$Sn and Mn$_3$Ge, with the kagome planes having their normal along the [001] direction. In this manuscript, we report our study in the cubic Mn$_3$Pt thin films with their kagome planes normal to the [111] crystal axis. Our studies reveal a hole conduction dominant …
Charge density waves are thought to be common in two-dimensional electron systems in quantizing magnetic fields. Such phases are formed by the quasiparticles of the topmost occupied Landau level when it is partially filled. One class of charge density wave phases can be described as electron solids. In weak magnetic fields (at high Landau levels) solids with many particles per unit cell - bubble phases - predominate. In strong magnetic fields (at the lowest Landau level) only crystals with one particle per unit cell - Wigner crystals - can form. Experimental identification of these phases is f…
We investigate experimentally magnetic frustration effects in thermally active artificial kagome spin ice. Starting from a paramagnetic state, the system is cooled down below the Curie temperature of the constituent material. The resulting magnetic configurations show that our arrays are locally brought into the so-called spin ice 2 phase, predicted by at-equilibrium Monte Carlo simulations and characterized by a magnetic charge crystal embedded in a disordered kagome spin lattice. However, by studying our arrays on a larger scale, we find unambiguous signature of an out-of-equilibrium physics…
We propose a flexible numerical framework for extracting the energy spectra and photon transfer dynamics of a unit kagome cell with disordered cavity-cavity couplings under realistic experimental conditions. A projected-entangled pair state (PEPS) ansatz to the many-photon wavefunction allows to gain a detailed understanding of the effects of undesirable disorder in fabricating well-controlled and scalable photonic quantum simulators. The correlation functions associated with the propagation of two-photon excitations reveal intriguing interference patterns peculiar to the kagome geometry and p…
Internodal dynamics of quasiparticles in Weyl semimetals manifest themselves in hydrodynamic, transport and thermodynamic phenomena and are essential for potential valleytronic applications of these systems. In an external magnetic field, coherent quasiparticle tunnelling between the nodes modifies the quasiparticle dispersion and, in particular, opens gaps in the dispersion of quasiparticles at the zeroth Landau level. We study magnetotransport in a Weyl semimetal taking into account mechanisms of quasiparticle scattering both affected by such gaps and independent of them. We compute the long…
We investigate the universal properties of quantum transport in graphene nanowires that engender subtle universal conductance fluctuations. We present results for three of the main microscopic models that describe the sublattice of graphene and generate, as we shall show, all the chiral universal symmetries. The results are robust and demonstrate the widely sought sign of chirality even in the regime of many open channels. The fingerprints paves the way to distinguish systems with sublattice symmetry such as topological insulators from ordinary ones by an order of magnitude. The experimental r…
The magnetotransport properties of disordered ferromagnetic Weyl semimetals are investigated numerically. We found an extraordinarily stable and huge magnetoresistance effect in domain walls of Weyl semimetals. This effect originates from the helicity mismatch of Weyl fermions and is a specific property of Weyl semimetals. Although conventional magnetoresistance effects are strongly suppressed in domain walls where local magnetization varies gradually, the helicity-protected magnetoresistance in Weyl semimetals maintains almost $100\%$ of the magnetoresistance ratio for any kind of thick domai…
We study theoretically magnetoresistance (MR) of graphene with different types of disorder. For short-range disorder, the key parameter determining magnetotransport properties---a product of the cyclotron frequency and scattering time---depends in graphene not only on magnetic field $H$ but also on the electron energy $\varepsilon$. As a result, a strong, square-root in $H$, MR arises already within the Drude-Boltzmann approach. The MR is particularly pronounced near the Dirac point. Furthermore, for the same reason, "quantum" (separated Landau levels) and "classical" (overlapping Landau level…
We present a general quantum kinetic theory of low-field magnetotransport in weakly disordered crystals that accounts fully for the interplay between electric-field induced interband coherence, Bloch-state scattering, and an external magnetic field. The quantum kinetic equation we derive for the Bloch-state density matrix naturally incorporates the momentum-space Berry phase effects whose influence on Bloch-state wavepacket dynamics is normally incorporated into transport theory in an ad hoc manner. The Berry phase correction to the momentum-space density of states in the presence of an extern…
The topological Hall effect is used extensively to study chiral spin textures in various materials. However, the factors controlling its magnitude in technologically-relevant thin films remain uncertain. Using variable temperature magnetotransport and real-space magnetic imaging in a series of Ir/Fe/Co/Pt heterostructures, here we report that the chiral spin fluctuations at the phase boundary between isolated skyrmions and a disordered skyrmion lattice result in a power-law enhancement of the topological Hall resistivity by up to three orders of magnitude. Our work reveals the dominant role of…
