Zero Magnetic Field Research Articles

Disordering Induced Second Magnetization Peak Effect and the Vortex Pinning Mechanism in V0.0007NbSe2 Single Crystal

The consequences of the random pinning in the presence of weak disorder are studied systematically based on the appearance of the second magnetization peak (SMP) and peak effect in the magnetic measurement. Here, we have observed the system dependency of the SMP effect. We have analysed the dc magnetization curves and the associated vortex pinning mechanisms of V0.0007NbSe2 single crystal at different temperatures and magnetic fields to estimate its pinning strengths in the external magnetic field H oriented parallel to the crystallographic ab plane. The characteristics of critical current density result in the presence of weak collective pinning near zero-magnetic field and the large bundle collective pinning along with SMP effect at the intermediate magnetic fields. The field dependence characteristics of the pinning force density highlights the presence of Bean-Livingstone’s zero-field peak with the presence of intermediate peak and high-field peak effect phenomena. The temperature dependence of the critical current density shows the dominating nature of δl pinning in the intermediate fields region. The vortex phase diagram of V0.0007NbSe2 is drawn showing different vortex phases at altered temperatures and magnetic fields. Thus, this study depicts the SMP effect and the diverse pinning characteristics in the quasi-two-dimensional superconductor associated with the external defects.

Magnetization of Paramagnetic Ions by Phase-Modulated Microwave Pulses in a Zero Magnetic Field

The effect of magnetization formation for paramagnetic ions with spin S = 1 in a solid under a zero magnetic field by pulsed manipulations with electron spins has been theoretically predicted. To this end, it is suggested to use crossed microwave pulses with different initial phases or finite pulses. Resonance cases where the microwave pulse frequency coincides with the frequency of level splitting in a zero field are described. It is shown that this effect is similar to the alignment–orientation transition, which is observed in optical experiments.

Molecular States of Composite Fermions in Self-Organized InP/GaInP Quantum Dots in Zero Magnetic Field

The size and positions of regions of line localization and the magnetic-field (0–10 T) dependence of the low-temperature (10 K) photoluminescence spectra of single InP/GaInP quantum dots with a number of electrons of N = 5–7 and a Wigner–Seitz radius of ~2.5 are determined using a near-field scanning optical microscope. The formation of composite fermion molecules with a size coinciding with that of localization regions and bond lengths of ~30 and 50 nm, respectively, at a Landau-level filling factor from 1/2 to 2/7 in zero magnetic field is established. At N = 6, the pairing and rearrangement of composite fermions under photoexcitation are found, which offers opportunities for the use of InP/GaInP quantum dots to create a magnetic-field-free topological quantum gate.

Superconductivity and weak anti-localization in GaSb whiskers under strain

Strain influence on the behavior of temperature dependences of resistance was studied in the n-type conductivity GaSb whiskers with tellurium concentration 1.7 1018 сm–3. Analyzing these dependences in the temperature range 4.2–30 K strain inducted metal–insulator transition and partial superconductivity were found in the whiskers. The transverse and longitudinal magnetoresistances for unstrained and strained GaSb whiskers were also studied in ranges of magnetic field 0–3 T and temperature 1.5–60 K. The effects, such as a superconductivity and weak anti-localization were observed for unstrained and strained samples. The upper critical zero magnetic fields for superconductivity suppression were obtained in the whiskers. Strain was shown to decrease the superconductivity in GaSb samples. The strain induced splitting of degenerate level on two components with opposite and parallel spins was found in the n-type conductivity GaSb whiskers due to weak localization and anti-localization effects, respectively.

On the Molecular Mechanisms of the Effect of a Zero Magnetic Field on the Production of Reactive Oxygen Species in Inactivated Neutrophils

Abstract—It is shown that the lower intensity of 2,7-dichlorodihydrofluorescein oxidation processes in inactivated neutrophils exposed to hypomagnetic field (the residual static magnetic field 20 nT) is not related to calcium-mediated mechanisms as shown by the absence of the effect of cell-permeant Ca2+ chelators, such as 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester), on the intensity of the process. This decrease is hardly likely to be caused by effects of a hypomagnetic field on phosphorylation of NADPH-oxidase components, because addition of the protein kinase C inhibitor Ro 31-6233 decreases the fluorescence intensity of intracellular dichlorodihydrofluorescein little, if at all. Addition of phospholipase C inhibitor U73122 causes a negligible decrease in ROS production in the control and experiment, almost equally. Different concentrations of apocynin increase ROS production in nonactivated neutrophils and this effect is approximately two times lower under hypomagnetic conditions. The decrease in ROS production is more pronounced in cells treated with a hypomagnetic field with the presence of rotenone, indicating that the mitochondrial electron-transport chain is involved in the mechanism of the effect of hypomagnetism.

Design and characterization of zero magnetic field chambers for high efficiency neutron polarization transport

Several methods of polarized neutron scattering call for a zero magnetic field (ZF) region to reduce magnetic field integral aberrations while preserving the neutron polarization. Though the design for large angle neutron scattering has been presented in various places, the design characterization and tuning has not been discussed before. In this report, the tuning procedure will be discussed with both neutron polarization transport method and utilization of fluxgate magnetometers. As a tuning procedure, polarized neutrons are sensitive to any local field distortions along all trajectories within the beam, but the process is slow. With fluxgates, the entire beam region cannot be accessed simultaneously, but very fast and precise measurements can be made in accessible regions of interest. Consequently, we would like to benchmark the usage of fluxgates as a fast tuning probe compared with polarization measurements made with neutrons. Polarization transport results for tuned ZF chambers, up to 2.25 m in length, are presented.

Zero-Magnetic Field Fractional Quantum States.

Since the discovery of the fractional quantum Hall effect in 1982 there has been considerable theoretical discussion on the possibility of fractional quantization of conductance in the absence of Landau levels formed by a quantizing magnetic field. Although various situations have been theoretically envisaged, particularly lattice models in which band flattening resembles Landau levels, the predicted fractions have never been observed. In this Letter, we show that odd and even denominator fractions can be observed, and manipulated, in the absence of a quantizing magnetic field, when a low-density electron system in a GaAs based one-dimensional quantum wire is allowed to relax in the second dimension. It is suggested that such a relaxation results in formation of a zigzag array of electrons with ring paths which establish a cyclic current and a resultant lowering of energy. The behavior has been observed for both symmetric and asymmetric confinement but increasing the asymmetry of the confinement potential, to result in a flattening of confinement, enhances the appearance of new fractional states. We find that an in-plane magnetic field induces new even denominator fractions possibly indicative of electron pairing. The new quantum states described here have implications both for the physics of low dimensional electron systems and also for quantum technologies. This work will enable further development of structures which are designed to electrostatically manipulate the electrons for the formation of particular configurations. In turn, this could result in a designer tailoring of fractional states to amplify particular properties of importance in future quantum computation.

Geometrically Tailored Skyrmions at Zero Magnetic Field in Multilayered Nanostructures

Magnetic skyrmions are chiral spin structures that have recently been observed at room temperature (RT) in multilayer thin films. Their topological stability should enable high scalability in confined geometries - a sought-after attribute for device applications. While umpteen theoretical predictions have been made regarding the phenomenology of sub-100 nm skyrmions confined in dots, in practice their formation in the absence of an external magnetic field and evolution with confinement remain to be established. Here we demonstrate the confinement-induced stabilization of sub-100 nm RT skyrmions at zero field (ZF) in Ir/Fe(x)/Co(y)/Pt nanodots over a wide range of magnetic and geometric parameters. The ZF skyrmion size can be as small as ~50 nm, and varies by a factor of 4 with dot size and magnetic parameters. Crucially, skyrmions with varying thermodynamic stability exhibit markedly different confinement phenomenologies. These results establish a comprehensive foundation for skyrmion phenomenology in nanostructures, and provide immediate directions for exploiting their properties in nanoscale devices.

Integer quantum Hall conductivity and longitudinal conductivity in silicene under the electric field and magnetic field

We investigate the integer Hall conductivity and longitudinal conductivity of silicene under the magnetic field, electric field, and exchange field in this paper. We focus not only on the case of low-temperature and δ-function impurities (i.e., independent of the scattering momentum), which only exist the intra-Landau level transition, but also on the case of inter-Landau level transition which also with the non-elastic scattering. The resulting longitudinal conductivity is very different from the intra-Landau level one at low-temperature. The expressions of the Hall conductivity, longitudinal conductivity, valley contributed Hall conductivity, and the spin or valley Hall conductivity are deduced in this paper. We also compute the dynamical polarization under the magnetic field which is an important quantity related to many exciting and novel properties of the two-dimension materials, including the screened Coulomb scattering due to the charged impurities. The polarization function here is also related to the Landau level index under the magnetic field, and shows a step-like feature rather than the logarithmically divergent as which appears in the zero-magnetic field case, and it is also naturally related to the conductivity in silicene. The generalized Laguerre polynomial is used in both the longitudinal conductivity and dynamical polarization function under magnetic field. Our results are also valid for the silicene-like materials like the genmanene, MoS2.

Topological valley transport at the curved boundary of a folded bilayer graphene

The development of valleytronics demands long-range electronic transport with preserved valley index, a degree of freedom similar to electron spin. A promising structure for this end is a topological one-dimensional channel formed in a bilayer graphene, called a domain wall. In these channels, the valley-index defines the propagation direction of the charge carriers, and the chiral edge states are robust over many kinds of disorder. However, the fabrication of domain walls are challenging, requiring the design of complex multi-gate structures or production on rough substrates, showing a limited mean free path. Here, we report on a high-quality domain wall formed at the curved boundary of a folded bilayer graphene. Our experiments reveal long-range ballistic transport at such topological channels with the two-terminal resistance close to the ballistic resistance R = e2/4h at zero-magnetic field and the four-terminal resistance near to zero. At the bulk, we measure a tunable band gap.

Zero Magnetic Field Calibration for Single-Beam Atomic Magnetometers Using Second Harmonics

In this letter, we propose a simple and rapid method for zero field calibration of single elliptically polarized beam atomic magnetometers. This method uses a wobble adjustment that applies a small amplitude and low-frequency (70 Hz) ac magnetic field and sweeps the dc magnetic field. The second harmonic signal reaches its maximum when the dc magnetic field noise is zero. Our single-beam atomic magnetometer operates with elliptically polarized light, which has both circularly and linearly polarized light components. The wavelength of a single beam for a rubidium atom was determined to be 780.206 nm with a power of 2.72 mW.

Multi-frequency ODMR of Nitrogen-Vacancy Color Centers in Diamond Crystals in zero magnetic fields

Techniques of optical detection of magnetic resonance, as applied tothe nitrogen-vacancy center in diamond, provide a tool for controlling both electron and nuclear spins. These techniques generally use a combination of microwave (MW) drive field for electronic spin transitions and radiofrequency (RF) drive field for nuclear spin transitions. They are most effective in strong magnetic fields where levels anticrossing (LAC) occurs; therefore NV spin system dynamics is mostly studied under these conditions. Nevertheless, zero-field LAC can probably also be used for controlling electron and nuclear spin states as well for exciting narrow resonances for metrological application, and these perspectives are not yet properly investigated. Here we present two-quantum resonances appearing in ODMR spectra of NV centers in bulk diamond under multi-frequency (MW+RF) resonance excitation in zero and ultra-low magnetic fields, and discuss their specifics.

Universal holonomic quantum gates over geometric spin qubits with polarised microwaves

A microwave shares a nonintuitive phase called the geometric phase with an interacting electron spin after an elastic scattering. The geometric phase, generally discarded as a global phase, allows universal holonomic gating of an ideal logical qubit, which we call a geometric spin qubit, defined in the degenerate subspace of the triplet spin qutrit. We here experimentally demonstrate nonadiabatic and non-abelian holonomic quantum gates over the geometric spin qubit on an electron or nitrogen nucleus. We manipulate purely the geometric phase with a polarised microwave in a nitrogen-vacancy centre in diamond under a zero-magnetic field at room temperature. We also demonstrate a two-qubit holonomic gate to show universality by manipulating the electron−nucleus entanglement. The universal holonomic gates enable fast and fault-tolerant manipulation for realising quantum repeaters interfacing between universal quantum computers and secure communication networks.

Effect of Magnetic state of Austenite on Martensitic transformation in Fe–Ni Alloys in High and Zero Magnetic Fields

The effect of high pulsed magnetic fields on the martensitic γ → α transformation in Fe–Ni and Fe–Ni–Mn alloys characterized by dual kinetics has been analyzed. It has been shown that the higher the iron content and the lower the martensitic transformation temperature, the more substantial the effect of pulsed magnetic field on the athermal martensitic transformation (MT) in the Fe–Ni alloys. The possibility of athermal martensite nucleation at magnetic inhomogenities of austenite, which is characterized by disordered magnetic moments (antiferromagnetic contribution) within a local area that assumes coherent conjugation at the interface, has been discussed. It has been suggested that athermal MT in Invar Fe–Ni alloys characterized by dual kinetics occurs in a pulsed magnetic field via a first-order magnetic phase transformation.

Cooper-pair splitting in two parallel InAs nanowires

We report on the fabrication and electrical characterization of an InAs double-nanowire (NW) device consisting of two closely placed parallel NWs coupled to a common superconducting electrode on one side and individual normal metal leads on the other. In this new type of device we detect Cooper-pair splitting (CPS) with a sizeable efficiency of correlated currents in both NWs. In contrast to earlier experiments, where CPS was realized in a single NW, demonstrating an intrawire electron pairing mediated by the superconductor (SC), our experiment demonstrates an interwire interaction mediated by the common SC. The latter is the key for the realization of zero-magnetic field Majorana bound states, or Parafermions; in NWs and therefore constitutes a milestone towards topological superconductivity. In addition, we observe transport resonances that occur only in the superconducting state, which we tentatively attribute to Andreev bound states and/or Yu-Shiba resonances that form in the proximitized section of one NW.

Electrical Initialization of Electron and Nuclear Spins in a Single Quantum Dot at Zero Magnetic Field.

The emission of circularly polarized light from a single quantum dot relies on the injection of carriers with well-defined spin polarization. Here we demonstrate single dot electroluminescence (EL) with a circular polarization degree up to 35% at zero applied magnetic field. The injection of spin-polarized electrons is achieved by combining ultrathin CoFeB electrodes on top of a spin-LED device with p-type InGaAs quantum dots in the active region. We measure an Overhauser shift of several microelectronvolts at zero magnetic field for the positively charged exciton (trion X+) EL emission, which changes sign as we reverse the injected electron spin orientation. This is a signature of dynamic polarization of the nuclear spins in the quantum dot induced by the hyperfine interaction with the electrically injected electron spin. This study paves the way for electrical control of nuclear spin polarization in a single quantum dot without any external magnetic field.

Dynamics of a quasiparticle in the α-T3 model: role of pseudospin polarization and transverse magnetic field on zitterbewegung

We consider the α-T3 model which provides a smooth crossover between the honeycomb lattice with pseudospin 1/2 and the dice lattice with pseudospin 1 through the variation of a parameter α. We study the dynamics of a wave packet representing a quasiparticle in the α-T3 model with zero and finite transverse magnetic field. For zero field, it is shown that the wave packet undergoes a transient zitterbewegung (ZB). Various features of ZB depending on the initial pseudospin polarization of the wave packet have been revealed. For an intermediate value of the parameter α i.e. for the resulting ZB consists of two distinct frequencies when the wave packet was located initially in rim site. However, the wave packet exhibits single frequency ZB for and . It is also unveiled that the frequency of ZB corresponding to gets exactly half of that corresponding to the case. On the other hand, when the initial wave packet was in hub site, the ZB consists of only one frequency for all values of α. Using stationary phase approximation, we find analytical expression of velocity average which can be used to extract the associated timescale over which the transient nature of ZB persists. On the contrary, the wave packet undergoes permanent ZB in presence of a transverse magnetic field. Due to the presence of a large number of Landau energy levels, the oscillations in ZB appear to be much more complicated. The oscillation pattern depends significantly on the initial pseudospin polarization of the wave packet. Furthermore, it is revealed that the number of the frequency components involved in ZB depends on the parameter α.

Electric-field-induced extremely large change in resistance in graphene ferromagnets

A colossal magnetoresistance (∼) and an extremely large magnetoresistance (∼) have been previously explored in manganite perovskites and Dirac materials, respectively. However, the requirement of an extremely strong magnetic field (and an extremely low temperature) makes them not applicable for realistic devices. In this work, we propose a device that can generate even larger changes in resistance in a zero-magnetic field and at a high temperature. The device is composed of graphene under two strips of yttrium iron garnet (YIG), where two gate voltages are applied to cancel the heavy charge doping in the YIG-induced half-metallic ferromagnets. By calculations using the Landauer–Büttiker formalism, we demonstrate that, when a proper gate voltage is applied on the free ferromagnet, changes in resistance up to () can be achieved at the liquid helium (nitrogen) temperature and in a zero magnetic field. We attribute such a remarkable effect to a gate-induced full-polarization reversal in the free ferromagnet, which results in a metal-state to insulator-state transition in the device. We also find that the proposed effect can be realized in devices using other magnetic insulators, such as EuO and EuS. Our work should be helpful for developing a realistic switching device that is energy saving and CMOS-technology compatible.

Quantifying phase separation in terms of magnetoresistive hysteresis loops in strongly phase-separated manganite thin films

The present work reports the scaling behaviour of thermomagnetic hysteresis in temperature and magnetic field-dependent resistivity [(ρ–T) and (ρ–H)] measured during cooling/warming and H increasing/decreasing cycles in single crystalline La0.21Pr0.42Ca0.37MnO3 thin films. The zero-magnetic field (H = 0) insulator–metal transition temperature (IMT) measured in warming cycle ( $$T_{{{\text{IM}}}}^{{\text{W}}}$$ ~ 163 K) is higher than that in the cooling cycle ( $$T_{{{\text{IM}}}}^{{\text{C}}}$$ ~ 116 K) and the difference between the two IMTs shrinks as H is increased. The magnetic field dependence of the two IMTs is well fitted by the equation $${T_{{\text{IM}}}}=T_{{{\text{IM}}}}^{0}+\beta {H^\alpha }$$ . Here, $$T_{{{\text{IM}}}}^{0}$$ is the H-independent contribution and the constants, pre-factor $$\beta$$ and exponent $$\alpha$$ determine the H-dependent part of the IMT. The ρ–T loop area diminishes with the increasing H and its scaling with H in the regime which is akin to a magnetic liquid and unstable towards external H (H < 30 kOe) is nicely described by $${A_T}={A_{T0}}{e^{ - {\Gamma}H}}$$ . Here, $${A_{T0}}$$ is the zero-field normalized area and Γ is a constant related to the degree of phase separation. The analysis of the isothermal ρ–H loop area, which increases with H shows a scaling behaviour of the type $$A(H)=a{(H - {H_{{\text{IM}}}})^\eta }$$ . Here, the constant HIM corresponds to the induced AFMI–FMM phase transition and decreases with temperature, while the exponent ‘η’ measures the degree of phase separation.

Invited Review Article: Instrumentation for nuclear magnetic resonance in zero and ultralow magnetic field.

We review experimental techniques in our laboratory for nuclear magnetic resonance (NMR) in zero and ultralow magnetic field (below 0.1 μT) where detection is based on a low-cost, non-cryogenic, spin-exchange relaxation free 87Rb atomic magnetometer. The typical sensitivity is 20-30 fT/Hz1/2 for signal frequencies below 1 kHz and NMR linewidths range from Hz all the way down to tens of mHz. These features enable precision measurements of chemically informative nuclear spin-spin couplings as well as nuclear spin precession in ultralow magnetic fields.