Seong Jang, Geon-Hyoung Park, Kenji Watanabe
et al.
The observation of Josephson current in the quantum Hall regime has attracted considerable attention, revealing the coexistence of two seemingly incompatible phases: the quantum Hall and superconducting states. However, the mechanism underlying the Josephson current remains unclear because of the observed h/2e magnetic interference period and the lack of precisely quantized Hall plateaus. To address this issue, we investigate the edge dependence of the Josephson current in graphene Josephson junctions operating in the quantum Hall regime. By systematically comparing devices with native, etched, edge-free, and gate-defined edges, we demonstrate that the Josephson current is confined to the physical edges and is highly sensitive to specific edge configurations. Our findings provide direct evidence that counter-propagating quantum Hall edge states mediate Andreev bound states, enabling Josephson coupling. These results clarify the underlying mechanism of Josephson current in the quantum Hall regime and offer new strategies for engineering superconducting hybrid devices.
Current induced spin torque is essential and crucial in spintronics. In this work, we systematically investigate the spin torque in transition metal(TM)/ferromagnet(FM) bilayers by using first-principles calculations and taking into account the phonon scattering at room temperature. To examine the spin and orbital Hall contribution, the studied transition metals include 5d heavy metals Pt, W, Au as well as 3d light metals Ti, V, Cr, Cu etc. We found that in TM/CoFe bilayers with typical 3d and 5d transition metals, the spin torque on CoFe mainly originates from spin Hall mechanism with the magnitude and sign of damping like torque efficiency consistent with the spin Hall conductivity. In TM/Ni bilayers, the spin torque is contributed by three mechanisms including spin and orbital Hall current in TM, as well as self-torque in Ni. The orbital Hall contribution in TM is accompanied by noteworthy opposite self spin torque in Ni, which leads to inapparent torque efficiency in Ti/Ni and V/Ni bilayers. For TM(5d heavy metal)/Ni bilayers, the spin torque induced by orbital Hall and self-torque in Ni nearly cancel each other, which makes the spin torque on Ni still align with that of the spin Hall effect in TM. Our work reveals much less efficient contribution of orbital Hall than spin Hall effect on the spin torque in transition metal/ferromagnet bilayers.
Justin Schirmann, Peru d'Ornellas, Charles Stahl
et al.
In non-interacting systems, disorder can drive a trivial phase into a topological one. However little is known how to construct a fractional quantum Hall ground-state, a paradigmatic topologically ordered state, that exists both in crystalline and disordered lattices and is qualitatively different to known topological phases. Here, we propose a general method for building such a phase. This is done by coupling quantum wires placed aperiodically in real-space, where the spatial positioning allows us to tune the inter-wire couplings. We call the emergent phase the Fractonic Fractional Quantum Hall Effect as it displays a rich interplay of fractional quantum Hall physics with fractonic constraints, formed by coupling differently-fractionalised wires into a globally gapped phase. The ground state has an exponential degeneracy in system size, a signature of the emergence of fractons. It displays a rich phenomenology of excitations, which can either behave like anyons confined to move in one dimension (lineons), multiples of which can then hop between two wires (s-lineons) or be free to travel across the system (C-anyons), depending on the multiplicity. Both the ground state degeneracy and mutual statistics are directly determined by the real-space positions of the wires, which can be disordered. Our method provides an analytically solvable pathway to non-crystalline fractional quantum Hall effects and fractonic theories in two-dimensions, examples of which were lacking.
We introduce a novel platform for realizing interaction-induced Hall crystals with diverse Chern numbers $C$. This platform consists of a two-dimensional semiconductor or graphene subjected to an out-of-plane magnetic field and a one-dimensional modulation, which can be realized by moiré or dielectric engineering. We show that interactions drive the system to spontaneously break the residual translational symmetry, resulting in Hall crystals with various $C$ (including $|C|>1$). Remarkably, these phases persist across continuous ranges of filling and magnetic field, and the global phase diagram can be understood in a unified manner.
Nonlinear Hall effects have been previously investigated in non-centrosymmetric systems for electronic systems. However, they only exist in metallic systems and are not compatible with ferroelectrics since these latter are insulators, hence limiting their applications. On the other hand, ferroelectrics naturally break inversion symmetry and can induce a non-zero Berry curvature. Here, we show that a non-volatile electric-field control of heat current can be realized in ferroelectrics through the nonlinear phonon Hall effects. More precisely, based on Boltzmann equation under the relaxation-time approximation, we derive the equation for nonlinear phonon Hall effects, and further show that the behaviors of nonlinear phonon (Boson) Hall effects are very different from nonlinear Hall effects for electrons (Fermion). Our work provides a route for electric-field control of thermal Hall current in ferroelectrics.
Cells were lysed in 1% Triton X 100 lysis buffer with protease and phosphatase inhibitors. Cell lysates were electrophoresed with NuPage™ Bis-Tris protein gels. Proteins were transferred to a PVDF membrane, blocked in 10% milk and treated with primary and secondary antibodies in 5% milk. Antibody binding was detected using the GE Healthcare Amersham™ electro-chemi-luminescence (ECL)™ Prime Western Blotting Detection Reagent.
S. H. Sajjadi, A. R. Khorshidvand, M. Jabbari
et al.
AbstractIn this paper, a new brittle fracture criterion was developed to predict the fracture in sharp V‐shaped notches. This criterion, by defining a quantity called “V‐shaped notch effective stress,” takes into account the effect of the shear stress in addition to the tangential stress. The initial crack criterion, which lays the foundation for developing this criterion, has yielded remarkable results for a broad spectrum of brittle materials in the entire range of mixed‐mode I/II loading conditions. This development helps to employ a novel criterion for V‐shaped notches with the capability of being used in the entire range of mixed‐mode I/II loading conditions. The outcomes of the two other valid criteria and multiple experimental results were compared with the developed criterion results to validate it. The developed criterion's predicted results revealed a strong correlation with experimental results, particularly in conditions where mode II loading was predominant.
Spin Hall effect, an electric generation of spin current, allows for efficient control of magnetization. Recent theory revealed that orbital Hall effect creates orbital current, which can be much larger than spin Hall-induced spin current. However, orbital current cannot directly exert a torque on a ferromagnet, requiring a conversion process from orbital current to spin current. Here, we report two effective methods of the conversion through spin-orbit coupling engineering, which allows us to unambiguously demonstrate orbital-current-induced spin torque, or orbital Hall torque. We find that orbital Hall torque is greatly enhanced by introducing either a rare-earth ferromagnet Gd or a Pt interfacial layer with strong spin-orbit coupling in Cr/ferromagnet structures, indicating that the orbital current generated in Cr is efficiently converted into spin current in the Gd or Pt layer. Furthermore, we show that the orbital Hall torque can facilitate the reduction of switching current of perpendicular magnetization in spin-orbit-torque-based spintronic devices.
Magnetotransport and magnetism of epitaxial SmTiO3/EuTiO3 heterostructures grown by molecular beam epitaxy are investigated. It is shown that the polar discontinuity at the interface introduces ~ 3.9x10^14 cm^-2 carriers into the EuTiO3. The itinerant carriers exhibit two distinct contributions to the spontaneous Hall effect. The anomalous Hall effect appears despite a very small magnetization, indicating a non-collinear spin structure and the second contribution resembles a topological Hall effect. Qualitative differences exist in the temperature dependence of both Hall effects when compared to uniformly doped EuTiO3. In particular, the topological Hall effect contribution appears at higher temperatures and the anomalous Hall effect shows a sign change with temperature. The results suggest that interfaces can be used to tune topological phenomena in itinerant magnetic systems.
We report the synthesis and magneto-transport measurements on the single crystal of Dirac semimetal PdTe$_2$. The de Haas-van Alphen oscillations with multiple frequencies have been clearly observed, from which the small effective masses and nontrivial Berry phase are extracted, implying the possible existence of the Dirac fermions in PdTe$_2$. The planar Hall effect and anisotropic longitudinal resistivity originating from the chiral anomaly and nontrivial Berry phase are observed, providing strong evidence for the nontrivial properties in PdTe$_2$. With the increase of temperature up to 150 K, planar Hall effect still remains. The possible origin of mismatch between experimental results and theoretical predictions is also discussed.
Une enquête réalisée auprès de jeunes LGBTI (lesbiennes, gays, bisexuels, transgenres, intersexués) a permis de recueillir 18 histoires de vie. On constate que, pour advenir à une identité assumée, ces adolescents et jeunes adultes passent par trois mondes différents, faits de leurs rapports, à la fois, à la réalité et aux imaginaires individuels ou collectifs. Le premier monde est constitué par leurs environnements immédiats, ceux qui ne sont pas choisis mais subis : famille, classe sociale, territoire, éducation, culture, religion. Le second monde est un monde de changements, révélé par les remaniements pubertaires : les interactions avec les pairs, le corps, les affects et la sexualité, le vécu de la différence. Le troisième monde est un monde d’engagement et d’affirmation de soi : les stratégies d’existence, les rites de passage, la découverte des mondes et cultures LGBTI, les projets.
We develop a theoretical formula of spin Hall torque in the presence of two ferromagnets. While the direction of the conventional spin Hall torque always points to the in-plane direction, the present system enables to manipulate the torque direction acting on one magnetization by changing the direction of another magnetization. Based on the diffusion equation of the spin accumulation and the Landauer formula, we derive analytical formula of the spin Hall torque. The present model provides a solution to switch a perpendicular ferromagnet deterministically at zero field using the spin Hall effect.
We suggest a theory for a deformable and sliding charge density wave (CDW) in the Hall bar geometry for the quantum limit when the carriers in remnant small pockets are concentrated at lowest Landau levels (LL) forming a fractionally ($ν<1$) filled quantum Hall state. The gigantic polarizability of the CDW allows for a strong redistribution of electronic densities up to a complete charge segregation when all carriers occupy, with the maximum filling, a fraction $ν$ of the chain length - thus forming the integer quantum Hall state, while leaving the fraction $(1-ν)$ of the chain length unoccupied. The electric field in charged regions easily exceeds the pinning threshold of the CDW, then the depinning propagates into the nominally pinned central region via sharp domain walls. Resulting picture is that of compensated collective and normal pulsing counter-currents driven by the Hall voltage. This scenario is illustrated by numerical modeling for nonstationary distributions of the current and the electric field. This picture can interpret experiments in mesa-junctions showing depinning by the Hall voltage and the generation of voltage-controlled high frequency oscillations (Yu.I. Latyshev, P. Monceau, A.A. Sinchenko, et al, presented at ECRYS-2011, unpublished).
Muamer Kadic, Robert Schittny, Tiemo Bückmann
et al.
In 2009, Briane and Milton proved mathematically the existence of three-dimensional isotropic metamaterials with a classical Hall coefficient which is negative with respect to that of all of the metamaterial constituents. Here, we significantly simplify their blueprint towards an architecture composed of only a single constituent material in vacuum/air, which can be seen as a special type of porosity. We show that the sign of the Hall voltage is determined by a separation parameter between adjacent tori. This qualitative behavior is robust even for only a small number of metamaterial unit cells. The combination of simplification and robustness brings experimental verifications of this striking sign-inversion into reach.
A finite-temperature effective free energy of the boundary of a quantized thermal Hall system is derived microscopically from the bulk two-dimensional Dirac fermion coupled with a gravitational field. In two spatial dimensions, the thermal Hall conductivity of fully gapped insulators and superconductors is quantized and given by the bulk Chern number, in analogy to the quantized electric Hall conductivity in quantum Hall systems. From the perspective of effective action functionals, two distinct types of the field theory have been proposed to describe the quantized thermal Hall effect. One of these, known as the gravitational Chern-Simons action, is a kind of topological field theory, and the other is a phenomenological theory relevant to the Středa formula. In order to solve this problem, we derive microscopically an effective theory that accounts for the quantized thermal Hall effect. In this paper, the two-dimensional Dirac fermion under a static background gravitational field is considered in equilibrium at a finite temperature, from which an effective boundary free energy functional of the gravitational field is derived. This boundary theory is shown to explain the quantized thermal Hall conductivity and thermal Hall current in the bulk by assuming the Lorentz symmetry. The bulk effective theory is consistently determined via the boundary effective theory
Spin-orbit coupling in ferromagnets gives rise to the anomalous Hall effect and the anisotropic magnetoresistance, both of which can be used to create spin-transfer torques in a similar manner as the spin Hall effect. In this paper we show how these effects can be used to reliably switch perpendicularly magnetized layers and to move domain walls. A drift-diffusion treatment of the anomalous Hall effect and the anisotropic magnetoresistance describes the spin currents that flow in directions perpendicular to the electric field. In systems with two ferromagnetic layers separated by a spacer layer, an in-plane electric field cause spin currents to be injected from one layer into the other, creating spin transfer torques. Unlike the related spin Hall effect in non-magnetic materials, the anomalous Hall effect and the anisotropic magnetoresistance allow control of the orientation of the injected spins, and hence torques, by changing the direction of the magnetization in the injecting layer. The torques on one layer show a rich angular dependence as a function of the orientation of the magnetization in the other layer. The control of the torques afforded by changing the orientation of the magnetization in a fixed layer makes it possible to reliably switch a perpendicularly magnetized free layer. Our calculated critical current densities for a representative CoFe/Cu/FePt structure show that the switching can be efficient for appropriate material choices. Similarly, control of the magnetization direction can drive domain wall motion, as shown for NiFe/Cu/NiFe structures.
Christian Herschbach, Dmitry V. Fedorov, Martin Gradhand
et al.
We predict spin Hall angles up to 80% for ultrathin noble metal films with substitutional Bi impurities. The colossal spin Hall effect is caused by enhancement of the spin Hall conductivity in reduced sample dimension and a strong reduction of the charge conductivity by resonant impurity scattering. These findings can be exploited to create materials with high efficiency of charge to spin current conversion by strain engineering.
As current flows through a Pt/Co/Pt trilayer, spin Hall effect induced by charge current in the Pt layer leads to spin accumulation at the Co/Pt interfaces. Our experiment and calculation show an indication of the effect of spin accumulation at the Co/Pt interfaces on anomalous Hall coefficient in the Pt/Co/Pt sandwich, which depends on the Pt layer thickness and spin diffusion length in Pt layer. The ratio of the longitudinal current in the Pt cap layer due to anomalous Hall effect to the injected transverse current in the Co layer increases with the Pt cap layer thickness.
Strongly correlated fractional quantum Hall liquids support fractional excitations, which can be understood in terms of adiabatic flux insertion arguments. A second route to fractionalization is through the coupling of weakly interacting electrons to topologically nontrivial backgrounds such as in polyacetylene. Here we demonstrate that electronic fractionalization combining features of both these mechanisms occurs in noncoplanar itinerant magnetic systems, where integer quantum Hall physics arises from the coupling of electrons to the magnetic background. The topologically stable magnetic vortices in such systems carry fractional (in general irrational) electronic quantum numbers and exhibit Abelian anyonic statistics. We analyze the properties of these topological defects by mapping the distortions of the magnetic texture onto effective non-Abelian vector potentials. We support our analytical results with extensive numerical calculations.
We analyze the Landau level (LL) structure and spin Hall effect in a MoS2 trilayer. Due to orbital asymmetry, the low-energy Dirac fermions become heavily massive and the LL energies grow linearly with $B$, rather than with $\sqrt{B}$. Spin-orbital couplings break spin and valley degenerate LL's into two time reversal invariant groups, with LL crossing effects present in the valence bands. We find a field-dependent unconventional Hall plateau sequence $ν=...$ $-2M-6$, $-2M-4$, $-2M-2$, $-2M-1$, ..., -5, -3, -1, 0, 2, 4 .... In a p-n junction, spin-resolved fractionally quantized conductance appears in two-terminal measurements with a controllable spin-polarized current that can be probed at the interface. We also show the tunability of zero-field spin Hall conductivity.