Perpendicular Magnetic Field Research Articles

Third-order nonlinear Hall effect in a quantum Hall system.

In two-dimensional systems, perpendicular magnetic fields can induce a bulk band gap and chiral edge states, which gives rise to the quantum Hall effect. The quantum Hall effect is characterized by zero longitudinal resistance (Rxx) and Hall resistance (Rxy) plateaus quantized to h/(υe2) in the linear response regime, where υ is the Landau level filling factor, e is the elementary charge and h is Planck's constant. Here we explore the nonlinear response of monolayer graphene when tuned to a quantum Hall state. We observe a third-order Hall effect that exhibits a nonzero voltage plateau scaling cubically with the probe current. By contrast, the third-order longitudinal voltage remains zero. The magnitude of the third-order response is insensitive to variations in magnetic field (down to ~5 T) and in temperature (up to ~60 K). Moreover, the third-order response emerges in graphene devices with a variety of geometries, different substrates and stacking configurations. We term the effect third-order nonlinear response of the quantum Hall state and propose that electron-electron interaction between the quantum Hall edge states is the origin of the nonlinear response of the quantum Hall state.

Implementation of Logic Function and Memristive Behavior in Synthetic Antiferromagnet with Strong Immunity to Perpendicular Magnetic Field Interference

Spintronic devices with heavy metal/ferromagnet structures have shown potential applications for in‐memory computing. However, the sensitivity of ferromagnet to external magnetic field raises a challenge for the practical applications of these devices. The usage of synthetic antiferromagnet (SAF) can effectively address this issue due to its good magnetic field immunity. This work demonstrates the implementation of all 16 types of Boolean logic functions via controlling the magnetization states of the SAF layer by using current pulses, and also the stable multistate storage under the interference of perpendicular magnetic field in these devices. The SAF devices also exhibit synaptic plasticity under the stimulation of current pulses. The artificial neural network constructed based on the SAF device can perform handwritten digit recognition tasks with an accuracy rate of 90%. These results showcase the viability and superiority of the SAF device in building logic‐in‐memory architecture for its strong immunity to magnetic field interference.

Isotropic Quantum Griffiths Singularity in Nd_{0.8}Sr_{0.2}NiO_{2} Infinite-Layer Superconducting Thin Films.

This work reports on the emergence of quantum Griffiths singularity (QGS) associated with the magnetic field induced superconductor-metal transition (SMT) in unconventional Nd_{0.8}Sr_{0.2}NiO_{2} infinite layer superconducting thin films. The system manifests isotropic SMT features under both in-plane and perpendicular magnetic fields. Importantly, after scaling analysis of the isothermal magnetoresistance curves, the obtained effective dynamic critical exponents demonstrate divergent behavior when approaching the zero-temperature critical point B_{c}^{*}, identifying the QGS characteristics. Moreover, the quantum fluctuation associated with the QGS can quantitatively explain the upturn of the upper critical field around zero temperature for both the in-plane and perpendicular magnetic fields in the phase boundary of SMT. These properties indicate that the QGS in the Nd_{0.8}Sr_{0.2}NiO_{2} superconducting thin film is isotropic. Moreover, a higher magnetic field gives rise to a metallic state with the resistance-temperature relation R(T) exhibiting lnT dependence among the 2-10K range and T^{2} dependence of resistance below 1.5K, which is significant evidence of Kondo scattering. The interplay between isotropic QGS and Kondo scattering in the unconventional Nd_{0.8}Sr_{0.2}NiO_{2} superconductor can illustrate the important role of rare region in QGS and help to uncover the exotic superconductivity mechanism in this system.

Effects of axial electric and transverse magnetic fields on a rotating electro-osmotic flow in micro-parallel plates

This paper explores the combined influence of an axial electric field and a perpendicular magnetic field imposed on rotating micro-parallel plates immersed in an electrolyte solution. A specialized computer program was developed to solve the velocity as well as the EDL potential fields using the finite difference method, employing the Debye-Hückel (DH) approximation to linearization the EDL potential. The study examines the influence of various non-dimensional parameters, including rotational speed (ω), Hartmann number (Ha), Debye-Hückel parameter (κ), and the non-dimensional parameter ‘S’, on axial, and transverse velocities, wall shear stress, and net flow rate. Results demonstrate that, both velocity components decrease with increased rotational speed and Hartmann number, while the net flow rate increases with the Debye-Hückel parameter for both rotating and non-rotating systems. The impact of these parameters on shear stress was also analyzed. Analysis of Ekmann spirals in the velocity plane revealed closed spirals at a higher rotational speed and open spirals at lower speeds, with spiral size reducing as rotational speed increases.

Autonomous dynamics of two-dimensional insulating domain with superclimbing edges

Superclimbing dynamics is the signature feature of transverse quantum fluids describing wide superfluid one-dimensional interfaces and/or edges with negligible Peierls barrier. Using Lagrangian formalism, we show how the essence of the superclimb phenomenon—dynamic conjugation of the fields of the superfluid phase and geometric shape—clearly manifests itself via characteristic modes of autonomous motion of the insulating domain (“droplet”) with superclimbing edges. In the translation invariant case and in the absence of supercurrent along the edge, the droplet demonstrates ballistic motion with the velocity-dependent shape and zero bulk currents. In an isotropic trapping potential, the droplet features a doubly degenerate sloshing mode. The period of the ground-state evolution of the superfluid phase (dictating the frequency of the AC Josephson effect) is sensitive to the geometry of the droplet. The supercurrent along the edge dramatically changes the droplet dynamics: The motion acquires features resembling that of a two-dimensional charged particle interacting with a perpendicular magnetic field. In a linear external potential (uniform force field), the state with a supercurrent demonstrates a spectacular gyroscopic effect—uniform motion in the perpendicular to the force direction. Published by the American Physical Society 2024

Three-dimensional quantum Griffiths singularity in bulk iron-pnictide superconductors

ABSTRACT The quantum Griffiths singularity (QGS) is a phenomenon driven by quenched disorders that break conventional scaling invariance and result in a divergent dynamic critical exponent during quantum phase transitions (QPT). While this phenomenon has been well-documented in low-dimensional conventional superconductors and in three-dimensional (3D) magnetic metal systems, its presence in 3D superconducting systems and in unconventional high-temperature superconductors (high-Tc SCs) remains unclear. In this study, we report the observation of robust QGS in the superconductor-metal transition (SMT) of both quasi-2D and 3D anisotropic unconventional high-Tc superconductor CaFe1-xNixAsF (x <5%) bulk single crystals, where the QGS states persist to up to 5.3 K. A comprehensive quantum phase diagram is established that delineates the 3D anisotropic QGS of SMT induced by perpendicular and parallel magnetic fields. Our findings reveal the universality of QGS in 3D superconducting systems and unconventional high-Tc SCs, thereby substantially expanding the range of applicability of QGS.

Confinement of Dirac fermions in gapped graphene

We explore the electronic transport characteristics of gapped graphene subjected to a perpendicular magnetic field and scalar potential barriers. Employing the Dirac–Weyl Hamiltonian and the transfer-matrix method, we calculate the transmission and conductance of the system. Our investigation delves into the impact of the energy, the gap energy parameter (Δ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta $$\\end{document}) and the magnetic flux parameters, including the number of magnetic barriers (N), the magnetic field strength (B) and the width of the magnetic barriers. We demonstrate that manipulating energy and total magnetic flux parameters allow precise control over the range of incident angle variation. Moreover, adjusting the tunable parameter Δ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta $$\\end{document} effectively confines quasiparticles within the magnetic system under study. Notably, an increase in N results in a strong wave vector filtering effect. The resonance effects and the peaks in the transmission and conductance versus Δ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta $$\\end{document} are observed for N>1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$N>1$$\\end{document}. The tunability of the system’s transport properties, capable of being toggled on or off, is demonstrated by adjusting Δ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta $$\\end{document} and B. As Δ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta $$\\end{document} or B increases, we observe suppression of the transmission and conductance beyond critical parameter values.

Influence of electron–phonon interaction on linear and nonlinear magneto-optical absorption properties in monolayer transition metal dichalcogenides

In this study, we investigate the linear and non-linear magneto-optical properties of TMDC monolayer semiconductors MX2 (M = Mo/W, X = S/Se) in a perpendicular magnetic field by evaluating the magneto-optical absorption coefficients (MOACs) and the refractive index changes (RICs) subject to the influence of electron–phonon interaction (EPI). Our results are achieved by considering the influence of electron couplings with acoustic (AC) and optical (OP) phonons via the absorption (AB) and emission (EM) mechanisms. When compared to the neglected EPI case, the intensity of the linear MOAC and RIC increases about 2.6–4 times and 5.3–10.5 times, respectively. The absorption peaks exhibit the blue-shifts, with the largest blue-shift observed for the OP-EM phonon scatterings, followed by the AC phonons and the smallest for the OP-AB phonon scatterings. Meanwhile, the greatest contribution to MOAC and RIC comes from the OP-AB phonons, which is followed by that of the AC phonons and the OP-EM phonons, respectively. The MoX2 group is more significantly affected by the scattering mechanism compared to the WX2 one. Although the OP-EM phonons contribution for the MoX2 group is much smaller than that of the other two interaction mechanisms, it nevertheless produces a very noticeable blue-shift. Meanwhile, for the WX2 group, all three mechanisms erect comparable results. The biggest (smallest) value of the linear MOAC and RIC are both founded in MoSe2 (MoS2). Notably, the absolute values of the non-linear MOAC and RIC terms increase by tens to hundreds of times, leading to the total MOAC terms being negative, contrary to when EPI is not taken into account, while the characteristics of the non-linear RIC curves also undergo considerable changes. Among the four TMDC materials, MoX2 is more significantly affected by the EPI effect than WX2.

Optical manipulation of the charge-density-wave state in RbV3Sb5.

Broken time-reversal symmetry in the absence of spin order indicates the presence of unusual phases such as orbital magnetism and loop currents1-4. The recently discovered kagome superconductors AV3Sb5 (where A is K, Rb or Cs)5,6 display an exotic charge-density-wave (CDW) state andhave emerged as astrong candidate for materialshosting a loop currentphase. The idea that the CDW breaks time-reversal symmetry7-14 is, however, being intensely debated due to conflicting experimental data15-17. Here we use laser-coupled scanning tunnelling microscopy to study RbV3Sb5. By applying linearly polarized light along high-symmetry directions, we show that the relative intensities of the CDW peaks can be reversibly switched, implying a substantial electro-striction response, indicative of strong nonlinear electron-phonon coupling. A similar CDW intensity switching is observed with perpendicular magnetic fields, which implies an unusual piezo-magnetic response that, in turn, requires time-reversal symmetry breaking. We show that the simplest CDW that satisfies these constraints is an out-of-phase combination of bond charge order and loop currents that we dub a congruent CDW flux phase. Our laser scanning tunnelling microscopy data open the door to the possibility of dynamic optical control of complex quantum phenomenon in correlated materials.

Controlling the orbital Hall effect in gapped bilayer graphene in the terahertz regime

We study the orbital Hall effect (OHE) in the AC regime using bilayer graphene (BLG) as a prototypical material platform. While the unbiased BLG has gapless electronic spectra, applying a perpendicular electric field creates an energy band gap that can be continuously tuned from zero to high values. By exploiting this flexibility, we demonstrate the ability to control the behavior of AC orbital Hall conductivity. Particularly, we demonstrate that the orbital Hall conductivity at the neutrality point changes its signal at a critical frequency, the value of which is proportional to the perpendicular electric field. For BLG with narrow band gaps, the active frequency region for the AC OHE may extend to a few terahertz, which is experimentally accessible with current technologies. We also consider the introduction of a perpendicular magnetic field in the weak-coupling regime using first-order perturbation theory to illustrate how the breaking of time-reversal symmetry enables the emergence of the AC charge Hall effect in the charge-doped situation and modifies the AC orbital Hall conductivity. Our calculations suggest that BLG with narrow band gaps is a practical candidate for investigating time-dependent orbital angular momentum transport. Published by the American Physical Society 2024

Superconducting Diode Effect in a Constricted Nanowire

AbstractDue to isotropic superconducting properties and the lack of breaking of inversion symmetry for conventional s‐wave superconductors, a nonreciprocal superconducting diode effect is absent. Recently, a series of superconducting structures, including superconducting superlattice, and quantum‐material‐based superconducting Josephson junction, have exhibited a superconducting diode effect in terms of polarity‐dependent critical current. However, due to complex structures, these composite systems are not able to construct large‐scale integrated superconducting circuits. Here, it is demonstrated that the minimal superconducting electric component‐superconducting nanowire‐based diode with a nonreciprocal transport effect under a perpendicular magnetic field, in which the superconducting to normal metallic phase transition relies on the polarity and amplitude of the bias current. These nanowire diodes can be reliably operated near at all temperatures below the critical temperature, and the rectification efficiency at 2 K can be more than 24%. Moreover, the superconducting nanowire diode is able to rectify both square wave and sine wave signals. Combining the superconducting nanowire‐based diodes and transistors, superconducting nanowires hold the possibility to construct novel low‐dissipation superconducting integrated circuits.

The enhancement of low-temperature excitation of magnons via interlayer exchange coupling in perpendicularly magnetized [Co/Pd] multilayers

In this study, we analyze the correlation between magnetization and magnetoresistance of perpendicularly anisotropic [Co/Pd] multilayered films with different thicknesses of Pd layers tPd = 0.6–2.0 nm in a wide range of temperatures, T = 4–300 K. We revealed that electron scattering by magnons makes a significant contribution to the magnetoresistance of the multilayers regardless of the layer thickness. Contrary to expectations, the effect of magnon magnetoresistance (MMR) increases with decreasing temperature below T = 50 K in the films with tPd = 0.8 and 1.0 nm. The revealed low-temperature MMR increase, which is most pronounced in the [Co0.5/Pd1.0] multilayers, is associated with the enhanced magnon excitation due to antiferromagnetic exchange coupling between the Co layers. The latter ensures an atypical shape of the magnetization curves of the [Co0.5/Pd1.0] multilayers at low temperatures in a perpendicular magnetic field, which combine a quadratic hysteresis loop of a perpendicularly anisotropic ferromagnet and an anomalous magnetization drop resulting from a violation of the ordering of magnetic moments and their amplified oscillations initiated by the interlayer exchange coupling.

In-plane gate induced transition asymmetry of spin-resolved Landau levels in InAs-based quantum wells

The crossover from quasi-two- to quasi-one-dimensional electron transport subject to transverse electric fields and perpendicular magnetic fields is studied in the diffusive to quasi-ballistic and zero-field to quantum Hall regime. In-plane gates and Hall-bars have been fabricated from an InGaAs/InAlAs/InAs quantum well hosting a 2DEG with a carrier density of about 6.8 × 1011 cm−2, a mobility of 1.8 × 105 cm2/Vs, and an effective mass of 0.042me after illumination. Magnetotransport measurements at temperatures down to 50 mK and fields up to 12 T yield a high effective Landé factor of g*=16, enabling the resolution of spin-split subbands at magnetic fields of 2.5 T. In the quantum Hall regime, electrostatic control of an effective constriction width enables steering of the reflection and transmission of edge channels, allowing a separation of fully spin-polarized edge channels at filling factors ν = 1 und ν = 2. A change in the orientation of a transverse in-plane electric field in the constriction shifts the transition between Zeeman-split quantum Hall plateaus by ΔB ≈ 0.1 T and is consistent with an effective magnetic field of Beff ≈ 0.13 T by spin-dependent backscattering, indicating a change in the spin-split density of states.

Temperature dependence of the properties of stochastic magnetic tunnel junction with perpendicular magnetization

Stochastic magnetic tunnel junctions (s-MTJs) are attracting attention as key elements for spintronics-based probabilistic (p-) computers. The performance of p-computers is governed by the time-domain and the time-averaged response of single s-MTJs varying with temperature. Here we present results of the time-domain (rf) voltage and time-averaged (dc) resistance R of s-MTJs with perpendicular magnetization as functions of perpendicular magnetic fields H z and temperatures T = 20 °C–130 °C. We observe that both relaxation time (time-domain response) and the slope of the R – Hz curve (time-averaged response) decrease with increasing temperature. We discuss the physics underlying these results including the thermally induced spatially non-uniform collective spin dynamics.

The guiding center role in defining the eigenstates of an electron in the fractional quantum Hall effect regime: ladder operators approach

The quantum problem of a two-dimensional electron in a uniform perpendicular magnetic field is considered. Using the formalism of ladder operators, the electron eigenfunctions are derived for all quantum numbers n and m, where n denotes the Landau level and m the eigenvalue of the angular momentum L z , with m taking all possible eigenvalues. We note that existing one-electron orbitals, in most of the known literature on the fractional quantum Hall effect (FQHE), correspond to a restricted range of possible eigenvalues m, some are missing. Similarly detailed calculations using ladder operator techniques show that for a state ∣n, m〉, the quantum number (n − m) represents a precise physical quantity, that is the distance from the origin to the center of the electron orbit. This finding allowed us to obtain, for this known quantum problem, a new set of basis states for which both quantum numbers have a physical meaning namely n and (n − m).

Topological superconductivity induced by spin-orbit coupling, perpendicular magnetic field, and superlattice potential

Topological superconductivity induced by spin-orbit coupling, perpendicular magnetic field, and superlattice potential

Characterizing an effective magnetic field during asymmetric creep motion of Dzyaloshinskii domain walls

Understanding the role of Landau Lifshitz Gilbert dynamics in describing magnetic domain wall (DW) motion in the creep regime is complicated by the presence of static pinning, but has regained interest due to recently observed directional growth in thin films with significant interfacial Dzyaloshinskii–Moriya interaction. Here, we delve into this directional domain growth behaviour in Pt/Co/Ni-based multi-layers under the influence of combined longitudinal and perpendicular magnetic fields via magneto-optical Kerr effect microscopy. Observations, including the onset field, μ0Honset , where the growth direction reverses by 180 degrees, align with the transient steady-state model predictions. By systematically varying the applied perpendicular magnetic field, we estimate the strength of an effective perpendicular field that acts on the DW during creep movement, which was expectedly found to be much smaller than the applied external field itself. This work further adds to the complexity of asymmetric domain expansion in the creep regime, but also highlights the range of magnetic information that can be extracted from careful analysis of this behavior.

Tunable quantized spin Hall effect of light in graphene

The spin Hall effect of light is an appealing toolset for metrology that holds incredible potential for precision measurements due to its high sensitivity to the refractive index and nanostructure physical parameters. Here, we theoretically examine the quantized spin Hall effect of light on the surface of a monolayer graphene–substrate system subjected to an external perpendicular magnetic field. We discuss the impact of Landau levels induced by the external magnetic field B and the photon energy on magneto-optical conductivities and Fresnel reflection coefficients. We find that the spin-dependent splittings in graphene exhibit quantized characteristics due to the Landau levels quantization of the magneto-optical conductivities and Fresnel’s reflection coefficients near the Brewster angle. Moreover, the spin-dependent shifts are quantized and show oscillatory behavior with changes in the magnetic field and the photon energy. Our results manifest that the quantized photonic spin-dependent separations are sensitive to variations in the incidence angle, magnetic field, and incident photonic energies. The quantized spin-dependent splitting opens a promising route to find the quantized Hall conductivity and discrete Landau levels in the monolayer graphene by a direct optical weak measurement.

The impact of motion on onboard MRI-guided pencil beam scanned proton therapy treatments

Objective. Online magnetic resonance imaging (MRI) guidance could be especially beneficial for pencil beam scanned (PBS) proton therapy of tumours affected by respiratory motion. For the first time to our knowledge, we investigate the dosimetric impact of respiratory motion on MRI-guided proton therapy compared to the scenario without magnetic field. Approach. A previously developed analytical proton dose calculation algorithm accounting for perpendicular magnetic fields was extended to enable 4D dose calculations. For two geometrical phantoms and three liver and two lung patient cases, static treatment plans were optimised with and without magnetic field (0, 0.5 and 1.5 T). Furthermore, plans were optimised using gantry angle corrections (0.5 T +5° and 1.5 T +15°) to reproduce similar beam trajectories compared to the 0 T reference plans. The effect of motion was then considered using 4D dose calculations without any motion mitigation and simulating 8-times volumetric rescanning, with motion for the patient cases provided by 4DCT(MRI) data sets. Each 4D dose calculation was performed for different starting phases and the CTV dose coverage V 95% and homogeneity D 5%–D 95% were analysed. Main results. For the geometrical phantoms with rigid motion perpendicular to the beam and parallel to the magnetic field, a comparable dosimetric effect was observed independent of the magnetic field. Also for the five 4DCT(MRI) cases, the influence of motion was comparable for all magnetic field strengths with and without gantry angle correction. On average, the motion-induced decrease in CTV V 95% from the static plan was 17.0% and 18.9% for 1.5 T and 0.5 T, respectively, and 19.9% without magnetic field. Significance. For the first time, this study investigates the combined impact of magnetic fields and respiratory motion on MR-guided proton therapy. The comparable dosimetric effects irrespective of magnetic field strength indicate that the effects of motion for future MR-guided proton therapy may not be worse than for conventional PBS proton therapy.

Magnetic field dependence of critical currents of cross-type Josephson junctions with inhomogeneous critical current density under oblique magnetic fields

Abstract Studies of the magnetic interference of sandwich-type Josephson junctions in which perpendicular or oblique magnetic fields are applied to the junction plane have received less attention than those where the applied magnetic fields are parallel. Recently, it has been theoretically demonstrated that a variety of magnetic interferences of the critical currents appear when oblique magnetic fields are applied to a cross-type junction with homogeneous critical current density. We theoretically investigated the effect of the inhomogeneous critical current density in the junction plane, and found that more complicated magnetic interferences appeared. We considered the distribution of the current density flowing through the junction plane to explore the cause of these complex magnetic interferences.