Presence Of In-plane Magnetic Field Research Articles

Weak Localization in p-Type Heterostructures in the Presence of Parallel Magnetic Field

Theory of weak localization is developed for two-dimensional holes in the presence of in-plane magnetic field. The Zeeman splitting even in the hole momentum results in the spin-dependent phase changing the quantum interference. The negative correction to the conductivity is shown to decrease by a factor of two by the in-plane magnetic field. The positive magnetoconductivity in a classically weak perpendicular field caused by the weak localization is calculated for both quadratic and quartic in momentum Zeeman hole splittings. Calculations show that the conductivity corrections are very close to each other in these two cases of low and high hole density.

Enhancement of frequency by tuning in-plane magnetic field in spin-torque oscillator

We show the possibility of high-frequency oscillations in a spin-torque oscillator that consists of an in-plane magnetized free and pinned layers in the presence of in-plane magnetic field by numerically solving the associated Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. We discover that frequency can be tuned significantly by tuning the direction of the in-plane magnetic field. Further, we observe the oscillation frequencies as high as 65 GHz for appropriate in-plane magnetic field angles. We also show the tunability of microwave frequency from ~15 GHz to ~68 GHz by tuning the magnitude of the direct current or the in-plane field angle and from ~35 GHz to ~65 GHz by varying the strength of the in-plane magnetic field. The power is proved to be enhanced by the in-plane field angle and current.

Sign Structure of Thermal Hall Conductivity and Topological Magnons for In-Plane Field Polarized Kitaev Magnets.

The appearance of half-quantized thermal Hall conductivity in α-RuCl_{3} in the presence of in-plane magnetic fields has been taken as a strong evidence for the Kitaev spin liquid. Apart from the quantization, the observed sign structure of the thermal Hall conductivity is also consistent with predictions from the exact solution of the Kitaev honeycomb model. Namely, the thermal Hall conductivity changes sign when the field direction is reversed with respect to the heat current, which is perpendicular to one of the three nearest neighbor bonds on the honeycomb lattice. On the other hand, the thermal Hall conductivity is almost zero when the field is applied along the bond direction. Here, we theoretically demonstrate that such a peculiar sign structure of the thermal Hall conductivity is a generic property of the polarized state in the presence of in-plane magnetic fields. In this case, the thermal Hall effect arises from topological magnons with finite Chern numbers, and the sign structure follows from the symmetries of the momentum space Berry curvature. Using a realistic spin model with bond-dependent interactions, we show that the thermal Hall conductivity can have a magnitude comparable to that observed in the experiments. Hence, the sign structure alone cannot make a strong case for the Kitaev spin liquid. The quantization at very low temperatures, however, will be a decisive test as the magnon contribution vanishes in the zero temperature limit.

Topological properties of Josephson current between two s- and p-wave superconducting nanowires with Majorana fermions

Josephson current between two one-dimensional nanowires with proximity induced either s-wave or p-wave pairing and separated by a narrow dielectric barrier is calculated in the presence of Rashba spin-orbit interaction, in-plane and normal Zeeman magnetic fields. We show that Andreev retro-tunneling is realized by means of two channels. The main contribution to the Josephson current in junction of s- or p-wave superconductors is shown to give Andreev scattering in a conventional particle-hole channel, when an electron-like quasiparticle reflects to a hole-like quasiparticle with opposite spin yielding a current which depends only on the order parameters’ phase differences φ and oscillates with fractional 4π period. Nevertheless Andreev bound state energy in second anomalous particle-hole channel, corresponding to the reflection of an incident electron-like quasiparticle to a hole-like quasiparticle with the same spin orientation, survives only in the presence of the in-plane magnetic field, and oscillates with 4π period not only with φ but also with orientational angle of the in-plane magnetic field θ resulting in a magneto-Josephson effect. In the presence of Rashba spin-orbit coupling (SOC) and normal-to-plane magnetic field h, a forbidden gap is shown to open in the dependence of Andreev bound state energies on the phases φ and θ at several values of SOC strength and magnetic field, where Josephson current seems to vanish. The magnetic fields destroy also the particle-hole symmetry of the mid-gap states around Fermi level.

Josephson current between two p-wave superconducting nanowires in the presence of Rashba spin-orbit interaction and Zeeman magnetic fields

Josephson current between two one-dimensional nanowires with proximity induced p-wave superconducting pairing is calculated in the presence of Rashba spin-orbit interaction, in-plane and normal magnetic fields. We show that Andreev retro-reflection is realized by means of two different channels. The main contribution to the Josephson current gives a scattering in a conventional particle-hole channel, when an electron-like quasiparticle reflects to a hole-like quasiparticle with opposite spin yielding a current which depends only on the order parameters’ phase differences φ and oscillates with 4π period. Second anomalous particle-hole channel, corresponding to the Andreev reflection of an incident electron-like quasiparticle to an hole-like quasiparticle with the same spin orientation, survives only in the presence of the in-plane magnetic field. The contribution of this channel to the Josephson current oscillates with 4π period not only with φ but also with orientational angle of the in-plane magnetic field θ resulting in a magneto-Josephson effect. In the presence of Rashba spin-orbit coupling (SOC) and normal-to-plane magnetic field h, a forbidden gap is shown to open in the dependence of Andreev bound state energies on the phases φ and θ at several values of SOC strength and magnetic field, where Josephson current seems to vanish. We present a detailed theoretical analysis of both DC and AC Josephson effects in such a system showing contributions from these channels and discuss experiments which can test our theory.

Active control of thermomagnetic avalanches in superconducting Nb films with tunable anisotropy

Active triggering and manipulation of ultrafast flux dynamics in superconductors are demonstrated in films of Nb. Controlled amounts of magnetic flux were injected from a point along the edge of a square sample, which at 2.5 K responds by nucleation of a thermomagnetic avalanche. Magneto-optical imaging was used to show that when such films are cooled in the presence of in-plane magnetic fields they become anisotropic, and the morphology of the avalanches changes systematically, both with the direction and magnitude of the field. The images reveal that the avalanching dendrites consistently bend towards the direction perpendicular to that of the in-plane field. The effect increases with the field magnitude, and at 1.5 kOe the triggered avalanche becomes quenched at the nucleation stage. The experimental results are explained based on a theoretical model for thermomagnetic avalanche nucleation in superconducting films, and by assuming that the frozen-in flux generates in-plane anisotropy in the film thermal conductance. The results demonstrate that applying in-plane magnetic fields to film superconductors can be a versatile external tool for controlling their ultrafast flux dynamics.

Structural distortion behind the nematic superconductivity in SrxBi2Se3

An archetypical layered topological insulator Bi2Se3 becomes superconductive upon doping with Sr, Nb or Cu. Superconducting properties of these materials in the presence of in-plane magnetic field demonstrate spontaneous symmetry breaking: 180◦-rotation symmetry of superconductivity versus 120◦-rotation symmetry of the crystal. Such behavior brilliantly confirms nematic topological superconductivity. To what extent this nematicity is due to superconducting pairing in these materials, rather than due to crystal structure distortions? This question remains unanswered, because so far no visible deviations from the 3-fold crystal symmetry were resolved in these materials. To address this question we grow high quality single crystals of SrxBi2Se3, perform detailed x-ray diffraction and magnetotransport studies and reveal that the observed superconducting nematicity direction correlates with the direction of small structural distortions in these samples (∼0.02% elongation in one crystallographic direction). Additional anisotropy comes from orientation of the crystallite axes. 2-fold symmetry of magnetoresistance observed in the most uniform crystals well above the critical temperature demonstrates that these structural distortions are nevertheless strong enough. Our data in combination with strong sample-to-sample variation of the superconductive anisotropy parameter are indicative for significance of the structural factor in the apparent nematic superconductivity in SrxBi2Se3.

Zeeman splitting and spin-orbit interaction in Hg1−xCdxTe inversion layers

We studied the suppression of the weak antilocalization (WAL) effect and the dependence of spin dynamics for a two-dimensional electron gas in the inversion layers of two different Hg1−xCdxTe samples in the presence of in-plane magnetic field . The WAL magnetoconductance is fitted by the Golub model to acquire the variations of phase coherence time with increasing . The effective g-factors in the form of ( is the relative effective mass) at zero magnetic field and high magnetic field are obtained by investigating the electron dephasing with varying and measuring the spin splitting of the Shubnikov-de Hass oscillations, respectively. As the obtained g-factors are in accordance with the reported results, the suppression of the WAL effect can be attributed to the competition between Zeeman splitting and spin-orbit interaction rather than to the microroughness scattering.

Influence of magnetic quantum confined Stark effect on the spin lifetime of indirect excitons

We report on the unusual and counter-intuitive behaviour of spin lifetime of excitons in coupled semiconductor quantum wells (CQWs) in the presence of in-plane magnetic field. Instead of conventional acceleration of spin relaxation due to the Larmor precession of electron and hole spins we observe a strong increase of the spin relaxation time at low magnetic fields followed by saturation and decrease at higher fields. We argue that this non-monotonic spin relaxation dynamics is a fingerprint of the magnetic quantum confined Stark effect. In the presence of electric field along the CQW growth axis, an applied magnetic field efficiently suppresses the exciton spin coherence, due to inhomogeneous broadening of the $g$-factor distribution.

Nondiagonal graphene conductivity in the presence of in-plane magnetic fields

We study the electron/hole transport in puddle-disordered and rough graphene samples which are subject to in-plane magnetic fields. Previous treatments, mostly devoted to regimes where the electron/hole scattering wavelengths are larger than the surface height correlation length, are based on the use of transport equations with appropriate forms for the collision term. We point out in this work, as a counterpoint, that classical Lorentz force effects, which are expected to hold when the Fermi level is far enough away from the charge neutral point, can be heuristically assessed through disordered Boltzmann equations that contain magnetic-field dependent material derivatives, and keep the zero magnetic-field structure of the collision term. It turns out that the electric conductivity tensor gets a peculiar nondiagonal component, induced by the in-plane magnetic field that crosses the rough topography of the graphene sheet, even if the projected random transverse magnetic field vanishes in the mean. Numerical estimates of the transverse conductivities suggest that they are suitable of observation under conditions which are within the reach of up-to-date experimental methods.

Magnetic control of ferroelectric polarization in a self-formed single magnetoelectric domain of multiferroic Ba3NbFe3Si2O14

We have discovered strong magnetoelectric (ME) effects in the single chiral-helical magnetic state of single-crystalline langasite Ba3NbFe3Si2O14 that is crystallographically chiral. The ferroelectric polarization, predominantly aligned along the a axis below the Nèel temperature of ∼27 K, changes in a highly non-linear fashion in the presence of in-plane magnetic fields (H) perpendicular to the a axis (H//b*). This ME effect as well as smaller ME effects in other directions exhibit no poling dependence, suggesting the presence of a self-formed single ME domain. In addition, these ME effects accompany no-measurable hysteresis, which is crucial for many technological applications.

Spin-phonon induced magnetic order in the kagome ice

We study the effects of lattice deformations on the Kagome spin ice, with Ising spins coupled by nearest neighbor exchange and long range dipolar interactions, in the presence of in-plane magnetic fields. We describe the lattice energy according to the Einstein model, where each site distortion is treated independently. Upon integration of lattice degrees of freedom, effective quadratic spin interactions arise. Classical MonteCarlo simulations are performed on the resulting model, retaining up to third neighbor interactions, under different directions of the magnetic field. We find that, as the effect of the deformation is increased, a rich plateau structure appears in the magnetization curves.

Equal coupling strength approach to spin precession effects concerning Rashba and Dresselhaus spin–orbit interactions in the presence of in-plane magnetic fields

The influence of Rashba and Dresselhaus spin–orbit interactions on the electronic properties of quasi one-dimensional systems like InAs quantum wires is discussed in the presence of in-plane magnetic fields. One shows that equal coupling strength conditions are provided specifically by the commutativity of two-dimensional constituents of velocity and current operators. The interesting point is that equal strength spin–orbit couplings one deals with proceed in conjunction with related spin conservations, which amounts to account for selected orientations of the magnetic field. Accordingly, the in-plane magnetic fields should be directed solely along the bisectrices. Other angles may be conceivable, but in this case spin conservations alluded to above are lost. Such results open the way to a consistent derivation of the equal coupling strength limit of the energy, which leads in turn to the derivation of novel spin-precession effects. A related effective gyromagnetic factor has also been established.

Asymmetric kinetics of magnetization reversal of thin exchange-coupled ferromagnetic films

This paper reports on the results of the investigation of the kinetics of magnetization reversal in FeNi-FeMn ferromagnet-antiferromagnet thin hybrid films grown by magnetron sputtering on silicon substrates in the presence of in-plane magnetic field, which provided unidirectional in-plane magnetic anisotropy in the ferromagnetic layer and a single-domain structure of the ferromagnet in the absence of an external magnetic field. The constructed hysteresis loops and magnetization loci have made it possible to reveal the specific features of the magnetization reversal process of an exchange-coupled ferromagnet, to establish new types of asymmetry, and to obtain new proofs for the existence of a spin spring at the ferromagnet-antiferromagnet interface. The visualization of the magnetization reversal process has allowed one to establish a one-to-one correspondence between the macrocharacteristics of the material and the real processes occurring in ferromagnet-antiferromagnet hybrid structures.

Spin-orbit coupling and the electronic properties of quantum wires

We review recent work on the effects of the Rashba spin-orbit interaction on the electronic structure and the conductance of quantum wires. We first discuss the importance of the intersubband coupling induced by the Rashba interaction for the wire subband-energies and spin distributions, especially in the presence of in-plane magnetic fields. We then consider the calculation of the evanescent modes, emphasizing the peculiarities of these states in the presence of spin-orbit coupling. Finally, we discuss the physical effects of a localized Rashba interaction in a quantum wire. We predict in this case the occurrence of Fano resonances in the dependence of the wire conductance with the incident electron energy. The Fano lineshapes manifest themselves more clearly in the spin-resolved transmissions. We obtain exact numerical results within the quantum-transmittingboundary algorithm and also propose a simplified approach (the coupled-channel model) that captures the main ingredients of the effect and allows a more transparent physical interpretation.

Strong anisotropic spin dynamics in narrow n-InGaAs∕AlGaAs (110) quantum wells

Anisotropic spin dynamics of two-dimensional electrons in strained n-InGaAs∕AlGaAs (110) quantum wells (QWs) is investigated by a time-resolved Faraday rotation technique. Strong anisotropy of the relaxation time for the electron spins in parallel (τ‖) and perpendicular (τ⊥) to the QWs is observed (τ⊥∕τ‖∼60) at 150 K as a result of the enhanced D'yakonov–Perel' (DP) spin relaxation mechanism. At 5 K, an anisotropic feature of the spin relaxation time is also observed in the presence of in-plane magnetic field, suggesting that the DP mechanism is effective for low-temperature spin relaxation.

Vortex-chain phases in layered superconductors

Layered superconductors in tilted magnetic field have a very rich spectrum of vortex lattice configurations. In the presence of in-plane magnetic field, a small c-axis field penetrates in the form of isolated vortex chains. The structure of a single chain is mainly determined by the ratio of the London [$\lambda$] and Josephson [$\lambda_{J}$] lengths, $\alpha= \lambda/\lambda_{J}$. At large $\alpha$ the chain is composed of tilted vortices [tilted chains] and at small $\alpha$ it consists of a crossing array of Josephson vortices and pancake stacks [crossing chains]. We studied the chain structures at intermediate $\alpha$'s and found two types of behavior. (I) In the range $0.4 < \alpha < 0.5$ a c-axis field first penetrates in the form of pancake-stack chains located on Josephson vortices. Due to attractive coupling between deformed stacks, their density jumps from zero to a finite value. With further increase of the c-axis field the chain structure smoothly evolves into modulated tilted vortices and then transforms via a second-order phase transition, into the tilted straight vortices. (II) In the range $0.5 < \alpha < 0.65$ a c-axis field first penetrates in the form of kinks creating kinked tilted vortices. With increasing the c-axis field this structure is replaced via a first-order phase transition by the strongly deformed crossing chain. This transition is accompanied by a large jump of pancake density. Further evolution of the chain structure is similar to the higher anisotropy scenario: it smoothly transforms back into the tilted straight vortices.

Spatially Indirect Excitons in GaAs/Al0.35Ga0.65As Double Quantum Wells in the Presence of In-Plane Magnetic Fields

We studied the optical properties of GaAs/Al0.35Ga0.65As asymmetric double quantum wells at T = 4.2 K and in the presence of in-plane magnetic fields up to 20 T. In an electric field F ≳ 45 kV/cm, electrons and holes are respectively confined in the wide and narrow well and form spatially indirect excitons with a binding energy of∼3.5 meV. The photoluminescence (PL) peak shifts diamagnetically by 0.02 meV/T2 and is quenched by fields of ∼5 T, the suppression being stronger at higher biases. The experimental results are well explained by numerical calculations which show that the magnetic field makes the e–h recombination indirect also in k-space. The suppression of the PL cannot be described in the picture of free e–h pairs, but rather scales as the ratio between the magnetic length and the e–h distance; we therefore believe that it is a peculiar manifestation of the exciton binding.

Spatially Indirect Excitons in GaAs/Al0.35Ga0.65As Double Quantum Wells in the Presence of In-Plane Magnetic Fields

Spatially Indirect Excitons in GaAs/Al0.35Ga0.65As Double Quantum Wells in the Presence of In-Plane Magnetic Fields

Behavior of carriers in ?-doped quantum wells under in-plane magnetic fields

Self-consistent electronic structure calculations of δ-doped quantum wells (QW) in the presence of in-plane magnetic fields B up to 20 Tesla are carried out within the frameworks of the effective mass and the local density approximations. QWs composed of two layers of Ga1-xA1xAs, separated by a layer of GaAs with a donor δ-doped sheet in the center, are considered. The width of the GaAs layer was varied from 100 to 400 A. It is shown that the diamagnetic shift increases with the increasing of the GaAs QW width. The magnetic field induces remarkable changes in the energy dispersions of electrons and holes, along an in-plane direction perpendicular to B. The most striking effect occurs in the nature of the band gap of these systems. We found that the valence band displays a double-maximum character instead of a single maximum at the center of the Brillouin zone. © 1996 John Wiley & Sons, Inc.