Magnetic Field Parallel Research Articles

Anisotropic spin dynamics in semiconductor narrow wires from the interplay between spin-orbit interaction and planar magnetic field

The anisotropic spin dynamics in wires based on a [001]-oriented semiconductor quantum well were investigated to determine the effect of applying an in-plane magnetic field both parallel to and perpendicular to the spin-orbit magnetic field, and the interaction between them. In one-dimensional spin motion where the wire width is less than the spin-precession length, it is known that the global spin precession is essentially determined by the spin-orbit induced precession along the wire direction. In this study, our objective is to investigate the nature of anisotropic spin dynamics in such narrow semiconductor wires along various crystal orientations. We proposed an analytic expression for the anisotropic spin-relaxation rates and the Larmor-precession frequencies for the arbitrary magnetic field orientation based on a theoretical understanding of the spin dynamics in the narrow wire structure. This expression describes the interaction between the spin-orbit field and all orientations of the in-plane magnetic field. We experimentally investigated the spin dynamics for lithographically defined 800-nm-width wires oriented along the $[\overline{1}10]$, [100], and [110] crystal orientations using a [001] GaAs/AlGaAs quantum well. Time-resolved Kerr rotation microscopy measurements indicated that the spin-relaxation time was the longest for the in-plane magnetic field perpendicular to the spin-orbit field, whereas the parallel configuration was found to be the shortest among all the directions. The precession frequency was found to have the opposite symmetry. These relations are well explained by the theoretical considerations developed in this work. Because the Rashba and Dresselhaus spin-orbit fields are mutually orthogonal in the [100] crystal orientation, it is possible to evaluate both spin-orbit coefficients from the precession anisotropy. These findings suggest that it is possible to control the spin state in narrow wires approaching the one-dimensional state and evaluate the spin-orbit coefficient. This has the potential to provide a greater understanding of quantum and topological information in semiconductor one-dimensional wires.

Hydrogen Lyman β, γ, and Balmer β Spectral Lines in Strong Uniform Magnetic and Electric Fields

Abstract This paper reports computational results on hydrogen Lyman β, γ, and Balmer β spectral lines in the presence of parallel magnetic and electric fields. A two-dimensional B-spline approach is adopted in the current calculations. This approach was originally developed to treat high-lying states but was found to be also effective for low-lying states. Wavelengths and oscillator strengths are presented for a total of 31 transitions in magnetic and electric fields with field strengths ranging, respectively, from 23.5 to 2350 MG and from 0 to 108 V m−1. These spectral data are compared to available results from other theoretical methods, and good agreement is clearly visible. Our calculations show that in the scope of field strengths we are concerned with, Lyman β and γ spectral lines lie in the ultraviolet region, while the Balmer β lines lie in the ultraviolet and visible-light regions. Furthermore, Zeeman spectral lines related to atomic states in the n = 4 manifold may be blue- or redshifted by a strong electric field, dependent on the transitions as well as on magnetic field strengths. Atomic spectral data of the 31 transitions listed are applicable for modeling discrete spectra of magnetic white dwarfs when a strong electric field exists in the hydrogen-dominated atmospheres of these celestial objects.

Spin effect on the low-temperature resistivity maximum in a strongly interacting 2D electron system

The increase in the resistivity with decreasing temperature followed by a drop by more than one order of magnitude is observed on the metallic side near the zero-magnetic-field metal-insulator transition in a strongly interacting two-dimensional electron system in ultra-clean SiGe/Si/SiGe quantum wells. We find that the temperature T_{text {max}}, at which the resistivity exhibits a maximum, is close to the renormalized Fermi temperature. However, rather than increasing along with the Fermi temperature, the value T_{text {max}} decreases appreciably for spinless electrons in spin-polarizing (parallel) magnetic fields. The observed behaviour of T_{text {max}} cannot be described by existing theories. The results indicate the spin-related origin of the effect.

Inhomogeneous superconducting states in two weakly linked superconducting ultrathin films

A sufficiently large parallel magnetic field will generate staggered supercurrent loops and superfluid density wave in two weakly linked superconducting (SC) ultrathin films, resulting in an inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The SC order parameter of such an FFLO state is characterized by Bloch wave functions, called the "Bloch SC state". The staggered supercurrent loops form an array of Josephson vortex-antivortex pairs, instead of the usual Josephson vortex lattice. Enclosing a unit cell of the array, the London's fluxoid is quantized as $\Phi^{\prime}=\Phi_0=hc/2e$, while the net orbital magnetization caused by the staggered supercurrent is zero. Meanwhile, a small parallel magnetic field gives rise to an Fulde-Ferrell (FF) state that has uniform superfluid density. The phase transition between the Bloch SC state and the FF state belongs to the universality class of two-dimensional commensurate-incommensurate transitions. An analytical solution in terms of Jacobian elliptic functions is found to be an excellent approximation to the Bloch SC order parameter.

Linear magnetoresistance induced by mobility fluctuations in iodine-intercalated tungsten ditelluride

We report a systematic study of the magnetoresistance, Hall effect, and the electronic structure in an iodine-intercalated tungsten ditelluride (${\mathrm{WTe}}_{2}\mathrm{I}$) single crystal, which crystallizes in a centrosymmetric structure. ${\mathrm{WTe}}_{2}\mathrm{I}$ presents significant anisotropic magnetotransport behavior with the magnetic field rotated in the $xz$ and $yz$ planes and violation of the Kohler's rule. Unexpectedly, nonsaturating linear magnetoresistance (LMR) was observed under the magnetic field parallel to the $z$ axis and the current along the $x$ axis. The analysis of the Hall effect reveals that the carrier mobility in ${\mathrm{WTe}}_{2}\mathrm{I}$ is notably lower than that of ${\mathrm{WTe}}_{2}$ and meets the picture of the Parrish and Littlewood model, suggesting that the LMR is likely caused by disorder effects. First-principles calculations show that the electronic structure undergoes a topological phase transition from a Weyl state to a Dirac state due to iodine intercalation. This finding provides a platform to search for physical phenomena related to ${\mathrm{WTe}}_{2}$ and study the topological phase transition.

Quantum versus classical nature of the low-temperature magnetic phase transition in TbAl3(BO3)4

Specific heat, $C_B$, of a TbAl$_3$(BO$_3$)$_4$ crystal was studied for 50 mK $<T<$ 300 K, with emphasis on $T<1$ K, where a phase transition was found at $T_c =0.68$ K. Nuclear, non-phonon ($C_m$), and lattice contributions to $C_B$ were separated. Lowering of $T_c$ with ncrease of magnetic field parallel to the easy magnetization axis, $B_{||}$, was found. It was established that $C_m$ and a Gr\"uneisen ratio depend on $B_{||}$ and $T$ in a way characteristic of systems, in which a classical transition is driven by quantum fluctuations, QF, to a quantum critical point at $T=0$, by tuning a control parameter ($B_{||}$). The $B_{||} - T$ phase diagram was constructed and the dynamical critical exponent $0.82 \le z \le 0.96$ was assessed. Nature of the transition was not established explicitly. Magnetization studies point at the ferromagnetic ordering of Tb$^{3+}$ magnetic moments, however, lowering of $T_c$ with increase in $B_{||}$ is opposite to the classical behavior. Hence, a dominant role of QF was supposed.

Chiral Triplet Quasi-Two-Dimensional Superconductor in a Parallel Magnetic Field

We calculate the parallel upper critical magnetic field {{H}_{parallel }}(0) for an in-plane isotropic quasi-two-dimensional chiral triplet superconductor at zero temperature, T = 0. In particular, the ratio {{H}_{parallel }}(0){text{/}}left( {{text{|}}dH_{parallel }^{{GL}}{text{/}}dT{{{text{|}}}_{{T = {{T}_{c}}}}}{{T}_{c}}} right) = 0.815 is defined, where {text{|}}dH_{parallel }^{{GL}}{text{/}}dT{{{text{|}}}_{{T = {{T}_{c}}}}} is the so-called Ginzburg–Landau slope of the upper critical magnetic field, Tc is a superconducting transition temperature at H = 0. We show that the theoretically obtained above mentioned value strongly contradicts to the experimentally measured ones in a candidate for a chiral triplet superconductivity Sr2RuO4, which provides one more argument against the chiral triplet scenario of superconductivity in this compound. Our results may be useful for establishing chiral triplet superconductivity in other quasi-two-dimensional candidates for this phenomenon.

Single-sideband microwave-to-optical conversion in high-Q ferrimagnetic microspheres

Coherent conversion of microwave and optical photons can significantly expand the capabilities of information processing and communications systems. Here, we experimentally demonstrate the microwave-to-optical frequency conversion in a magneto-optical whispering gallery mode microcavity. By applying a magnetic field parallel to the microsphere equator, the intracavity optical field will be modulated when the magnon is excited by the microwave drive, leading to a microwave-to-optical conversion via the magnetic Stokes and anti-Stokes scattering processes. The observed single-sideband conversion phenomenon indicates a nontrivial optical photon–magnon interaction mechanism derived from the magnon that induced both the frequency shift and modulated coupling rate of optical modes. In addition, we demonstrate the single-sideband frequency conversion with an ultrawide tuning range up to 2.5 GHz, showing its great potential in microwave-to-optical conversion.

Numerical study of PbTe-Pb hybrid nanowires for engineering Majorana zero modes

Epitaxial semiconductor-superconductor (SM-SC) hybrid nanowires are potential candidates for implementing Majorana qubits. Recent experimental and theoretical works show that charged impurities in SM remain a major problem in all existing hybrid nanowires, in which the SM is either InAs or InSb while the SC is mainly Al. Here, we theoretically validate the recently proposed PbTe-Pb hybrid nanowire as a potential candidate for Majorana devices. By studying the electrostatic and electronic properties of PbTe nanowires, we demonstrate that the huge dielectric constant of PbTe endows itself a high tolerance of charged impurity, which is a potential advantage over InAs and InSb nanowires. Moreover, we find that the effective axial Land\'e $g$ factor and Rashba spin-orbit coupling strength of PbTe nanowires are comparable to those of InAs nanowires. The conceivable merits of using Pb as the SC are (i) Pb has a larger superconducting gap, higher critical temperature, and higher parallel critical magnetic field than those of Al; (ii) a superconducting gap comparable with those of InAs-Al and InSb-Al can be induced in PbTe-Pb even by a weak coupling between Pb and PbTe, which simultaneously relieves the adverse renormalization and induced disorder effects on SM from SC; and (iii) Pb film can be grown on PbTe with a thin buffer CdTe layer in between, solving the lattice mismatch problem as an important source of disorder. In the presence of a parallel magnetic field, we show that the typical BdG energy spectrum and tunneling spectroscopy of PbTe-Pb resemble those of InAs and InSb based hybrid nanowires exposed to a tilting magnetic field, as a result of the highly anisotropic Land\'e $g$ factors of PbTe nanowires. The calculated topological phase diagrams of PbTe-Pb indicate that the multivalley character of PbTe makes it easier than InAs and InSb to access topological superconducting phases. Our results could facilitate the experimental realization of PbTe-Pb hybrid nanowires and inspire further theoretical works.

Nonlinear Meissner effect in Nb3Sn coplanar resonators

We investigated the nonlinear Meissner effect (NLME) in ${\mathrm{Nb}}_{3}\mathrm{Sn}$ thin-film coplanar resonators by measuring the resonance frequency as a function of a parallel magnetic field at different temperatures. We used low rf power probing in films thinner than the London penetration depth $\ensuremath{\lambda}(B)$ to significantly increase the field onset of vortex penetration and measure the NLME under equilibrium conditions. Contrary to the conventional quadratic increase of $\ensuremath{\lambda}(B)$ with $B$ expected in $s$-wave superconductors, we observed a nearly linear increase of the penetration depth with $B$. We concluded that this behavior of $\ensuremath{\lambda}(B)$ is due to weak linked grain boundaries in our polycrystalline ${\mathrm{Nb}}_{3}\mathrm{Sn}$ films, which can mimic the NLME expected in a clean $d$-wave superconductor.

Vortex shaking study with use of linear voltage–current law

Experiments show that the application of an AC magnetic field parallel to a thin superconductor tape can reduce the magnetization caused by screening currents. A theory has been developed by Sakamoto and Brandt stating that a DC electric field is generated during the application of the AC magnetic field and leads to the decay of the screening currents through the homogenization of the current density within the tape. The DC electrical field has the same direction as the current lines and is linear with the current density magnitude. First, we perform numerical simulations via a finite difference method in MATLAB to compute the effects of such a DC electrical field and its linear law and compare it with the widely used power law on two different cases an infinitely long thin tape and a single tape solenoid. We then study the effects of vortex-shaking computed with both laws on a coil made of several turns.

Anomalous magnetic interference of cross-type Josephson junctions exposed to oblique magnetic fields

Gauge-invariant phase difference and critical currents of cross-type Josephson junctions with thin and narrow superconducting strips exposed to three-dimensional magnetic fields are theoretically investigated. When a sandwich-type Josephson junction in the xy plane is exposed to parallel magnetic fields H x and H y , the phase difference linearly depends on the spatial coordinates, x and y, and the critical currents exhibit the standard Fraunhofer-type magnetic interference. The perpendicular field H z , on the other hand, nonlinearly modulates the distribution of the phase difference and the critical currents as the functions of the oblique field exhibit anomalous magnetic interference. We obtain simple analytical expressions for critical currents of small cross-type junctions by neglecting the effects of self-field and trapped vortices. The resulting dc critical currents show anomalous and diverse interference patterns depending on the parallel and perpendicular magnetic fields.

Effects of the packing factor on magnetic anisotropy in a 3x3 array of square hollow Ni nanopillars

A study about the magnetic anisotropy in a 3x3 array, constituted by square nickel nanometric pillars (NPs), is present. The NPs geometry was defined by wide D = 30 nm and length L = 120 nm. The center to center NPs distance a = 35, 40, 50 and 80 nm, were chosen to create variations in magnetic anisotropy, originated by the hard dipolar interactions. A concentric central cavity was included, within the variables in the study, with lateral dimension of d = 0, 10 and 20 nm. The data was generated through micromagnetic simulation by using a ferromagnetic resonance (FMR) standard problem. The OOMMF package was used by applying an external magnetic field in parallel and perpendicular directions, relative to the pillars symmetry axis. The anisotropy field (HA) was obtained by the typical FMR uniaxial model. The HA values decrease with the center to center NPs distance for all cavity size. Based on previous reported studies in nanowires, the volumetric NPs packing (P) was related to HA. Thus, an empirical dependence of HA was proposed to describe the linear decrease with P. Even with the geometric characteristics of array it was evident, by the calculations with perpendicular field, that the simplified uniaxial model is no longer appropriate. Therefore, an analysis using the model composing two anisotropy constants (K1 and K2) was included. This proposal and the traditional uniaxial model are not suitable as the distance between the pillars decreases.

Magnetic order and magnetic properties of the oxygen deficient SmBaMn2O5 layered perovskite

Magnetism in SmBaMn2O5 was investigated on a single crystal by magnetic and neutron diffraction measurements. This is an oxygen deficient perovskite with a layered ordering of Sm and Ba cations. Mn atoms are coordinated with five oxygens forming a square pyramid and they are ordered in a checkerboard pattern of expanded-compressed pyramids in the ab-plane. The neutron diffraction study revealed a ferrimagnetic ordering of Mn moments below TN=134 K. Macroscopic measurements reveal a very anisotropic behavior. Measurements with the external magnetic field parallel (M||c) and perpendicular (M⊥c) to the c-axis confirm that this is the easy axis above 10 K. Below this temperature, the Sm sublattice begins to polarize and the magnetization M||c decreases while M⊥c experiences a huge increase. This indicates that Sm moments begin to order around 10 K in the ab-plane with a minor component on the c-axis that opposes the overall magnetization from Mn sublattices.

Andreev Interference in the Surface Accumulation Layer of Half-Shell InAsSb/Al Hybrid Nanowires.

Understanding the spatial distribution of charge carriers in III-V nanowires proximity coupled to superconductors is important for the design and interpretation of experiments based on hybrid quantum devices. In this letter, the gate-dependent surface accumulation layer of half-shell InAsSb/Al nanowires is studied by means of Andreev interference in a parallel magnetic field. Both uniform hybrid nanowires and devices featuring a short Josephson junction fabricated by shadow lithography, exhibit periodic modulation of the switching current. The period corresponds to a flux quantum through the nanowire diameter and is consistent with Andreev bound states occupying a cylindrical surface accumulation layer. The spatial distribution is tunable by a gate potential as expected from electrostatic models.

The NANOGrav 12.5 yr Data Set: Polarimetry and Faraday Rotation Measures from Observations of Millisecond Pulsars with the Green Bank Telescope

Abstract In this work, we present polarization profiles for 23 millisecond pulsars observed at 820 and 1500 MHz with the Green Bank Telescope as part of the NANOGrav pulsar timing array. We calibrate the data using Mueller matrix solutions calculated from observations of PSRs B1929+10 and J1022+1001. We discuss the polarization profiles, which can be used to constrain pulsar emission geometry, and present both the first published radio polarization profiles for nine pulsars and the discovery of very low-intensity average profile components (“microcomponents”) in four pulsars. We obtain the Faraday rotation measures for each pulsar and use them to calculate the Galactic magnetic field parallel to the line of sight for different lines of sight through the interstellar medium. We fit for linear and sinusoidal trends in time in the dispersion measure and Galactic magnetic field and detect magnetic field variations with a period of 1 yr in some pulsars, but overall find that the variations in these parameters are more consistent with a stochastic origin.

Effect of surfactants on the stability, rheological properties, and thermal conductivity of Fe3O4 nanofluids

Stability is the major factor that enables the application of nanofluids in energy conversion systems. Excellent rheological and thermal conductivity is the key for nanofluids to be an ideal heat transfer medium. In this work, we investigated the stability of Fe3O4 nanofluids by four characterization techniques, mainly from the viewpoint of surfactant type and mass ratio, and systematically studied its rheological and thermal conductivity properties by different experimental methods and analyzed the behavior of magnetic fluid thermal anisotropy by mathematical methods. The experimental results show that the surfactant Tetramethylammonium hydroxide (TMAH) has the best stability effect and can keep the Fe3O4 nanofluids more than 120 h. And the best ratio is when the mass ratio of Fe3O4 to TMAH is 1:4. The surfactant Polyvinylpyrrolidone (PVP) has the greatest effect on nanofluids viscosity. The increase in TMAH mass leads to a Newtonian fluid behavior of the nanofluids at low temperatures and low shear rates, besides shifting its shear thinning towards the high temperature region. However, from the curve relationship between the shear rate and shear stress, the Fe3O4 nanofluids belongs to the expansion fluid among non-Newtonian fluids. The surfactant Sodium dodecyl sulfate (SDS) have the greatest effect on the thermal conductivity of Fe3O4 nanofluids. Theoretical calculations show that as the concentration increases, the rate of heat transfer in the direction of the parallel magnetic field is significantly greater than in the direction of the perpendicular magnetic field, while the rate of heat transfer in the absence of a magnetic field is somewhere in between.

Magnetic field tailoring effects on ion beam properties in cylindrical Hall thrusters

The magnetic field is the most important element in designing a Hall thruster and improving thruster performance because it directly influences the behavior of electrons in the discharge channel. In this work, magnetic field tailoring, parallel magnetic fields to the thruster channel wall, has been attempted in a cylindrical Hall thruster, and the resultant ion beam properties are studied. The magnetic field tailored cylindrical Hall thruster demonstrated much higher ion current and propellant efficiencies than the conventional cylindrical Hall thruster, with an identical mass flow rate. A large fraction of multiply charged ions (&amp;gt;65%) was observed and reduced beam emission was demonstrated near the channel wall. Further, the channel wall is solely coated without erosion even at the end of the channel. Hence, tailoring of the magnetic field in cylindrical Hall thrusters could significantly enhance the potential of Hall thrusters in space applications owing to their higher propellant efficiency and reduced wall interaction.

Effects of variable magnetic field on particle fouling properties of magnetic nanofluids in a novel thermal exchanger system

Magnetic nanofluids, as a new type of heat transfer media, propose a possible way to achieve low energy consumption and carbon neutrality, which has attracted a lot of attention in the heat transfer field. To comprehensively discuss the feasibility of magnetic nanofluids application in heat exchange systems, this paper conducted an experimental study of the particle fouling properties based on Fe3O4–H2O-AG magnetic nanofluids. The effects of variables including Reynolds number, magnetic field form, and magnetic flux density B on the fouling properties were analyzed. The anti-fouling rate η was introduced to evaluate the anti-fouling properties. The results showed that high Reynolds number (Rf (Re = 9000) = 2.83 × 10−6 m2 W K−1), constant parallel magnetic field with high magnetic flux density (Rf (B = 18mT) = 3.86 × 10−6 m2 W K−1), and corrugated tube with twisted turbulator (Rf (with turbulator) = 3.74 × 10−6 m2 W K−1) demonstrated less fouling thermal resistance Rf. Meanwhile, constant parallel magnetic field with high magnetic flux density also exhibited better anti-fouling properties (η(B = 18mT) = 1.35), which indicated that the parallel magnetic field has a positive effect on preventing the deposition of magnetic nanoparticles.

Generalized phenomenological model for the magnetic field penetration and magnetization hysteresis loops of a type-II superconductor

A generalized phenomenological model for the critical state of type-II superconductors with magnetic field parallel to the superconducting plate is proposed. This model considers the global magnetization including both the equilibrium magnetization from surface screening current and the non-equilibrium magnetization from bulk pinning in a self-consistent way. Our model can be used to simulate the magnetization-hysteresis-loops (MHLs) and flux penetrating process of different type-II superconductors, from low- to high-kappa values. Here we take an optimally doped Ba0.6K0.4Fe2As2 single crystal as a testing example. The model can fit the data quite well and several important parameters can be extracted from the fitting. Thus, the model can be extended to a general case for studying the magnetization and flux penetration in other type-II superconductors.