External Perpendicular Magnetic Field Research Articles

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 Shape Complexity of a Particle in the Circular Quantum Well with Homogeneous Perpendicular Magnetic Field

The shape complexity of a particle confined in the circular quantum well with an external homogeneous perpendicular magnetic field is investigated. First, the Shannon entropy and the averaging electron probability density, as well as the shape complexities in the position and momentum spaces for several quantum states, are computed and discussed. The quantum confinement effect on the shape complexity of this system is extensively explored. Then, the influence of the magnetic field on the shape complexities of the particle confined in the circular quantum well is discussed. It is demonstrated that the shape complexity exhibits scaled invariance under the influence of the magnetic field. However, when the radius of the quantum well is fixed, the shape complexity of the given quantum state changes with the magnetic field strength. Results suggest that the shape complexity of a particle confined in the quantum well can be changed by varying both the strength of the magnetic field and the size of the well. This study has some practical applications in quantum information measurement of the confined particle and can guide future researches for the disorder characteristics of confined particle in semiconductor quantum dots.

Spin and charge persistent currents in a Kane Mele α-T 3 quantum ring

We conduct a thorough study of different persistent currents in a spin-orbit coupled α-T 3 (pseudospin-1) fermionic quantum ring (QR) that smoothly interpolates between graphene (α = 0, pseudospin-1/2) and a dice lattice (α = 1, pseudospin-1) in presence of an external perpendicular magnetic field. In particular, we have considered effects of intrinsic (ISOC) and Rashba spin-orbit couplings (RSOC) that are both inherent to two dimensional quantum structures and yield interesting consequences. The energy levels of the system comprise of the conduction bands, valence bands, and flat bands which show non-monotonic dependencies on the radius, R of the QR, in the sense that, for small R, the energy levels vary as 1/R , while the variation is linear for large R. The dispersion spectra corresponding to zero magnetic field are benchmarked with those for finite fields to enumerate the role played by the spin–orbit coupling terms therein. Further, it is noted that the flat bands demonstrate dispersive behavior, and hence is able to contribute to the transport properties only for finite ISOC. Moreover, RSOC yields spin-split bands, thereby contributing to the spin-resolved currents. The charge and the spin-polarized persistent currents are hence computed in presence of these spin-orbit couplings. The persistent currents in both the charge and spin sectors oscillate as a function of the magnetic field with a period equal to the flux quantum, as they should be; although they now depend upon the spin–orbit coupling parameters. Interestingly, the ISOC distorts the current profiles, owing to the distribution of the flat band caused by it, whereas RSOC alone preserves the flat band and hence a perfect periodicity of the current characteristic is maintained. Further, we have explored the role played by the parameter α in our entire analysis to enable studies while interpolating from graphene to a dice lattice.

Caloric Effect Due to the Aharonov-Bohm Flux in an Antidot.

In this work, we report the caloric effect for an electronic system of the antidot type, modeled by combining a repulsive and attractive potential (parabolic confinement). In this system, we consider the action of a perpendicular external magnetic field and the possibility of having an Aharonov-Bohm flux (AB-flux) generated by a current passing through a solenoid placed inside the forbidden zone for the electron. The energy levels are obtained analytically, and the model is known as the Bogachek and Landman model. We propose to control the caloric response of the system by varying only the AB-flux, finding that, in the absence of an external magnetic field, the maximization of the effect always occurs at the same AB-flux intensity, independently of the temperature, while fixing the external magnetic field at a non-zero value breaks this symmetry and changes the point where the caloric phenomenon is maximized and is different depending on the temperature to which the process is carried. Our calculations indicate that using an effective electron mass of GaAs heterostructures and a trap intensity of the order of 2.896 meV, the modification of the AB-flux achieves a variation in temperature of the order of 1 K. Our analysis suggests that increasing the parabolic confinement twofold increases the effect threefold, while increasing the antidot size generates the reverse effect, i.e., a strong decrease in the caloric phenomenon under study. Due to the great diversity in technological applications that have antidots in electronics, the possibility of controlling their thermal response simply by varying the intensity of the internal current inside the solenoid (i.e., the intensity of AB-flux) can be a platform of interest for experimental studies.

Investigation of electron acceleration in a perpendicularly magnetized plasma wave

Electron acceleration is investigated in a plasma wake generated via the interaction of a high-intensity laser pulse with the plasma in the presence of a perpendicular magnetic field. For this purpose, using the Maxwell equation, the wakefield profile in the perpendicularly magnetized plasma is obtained and then using the magnetized wakefied the electron energy and momentum equations are numerically solved. It turns out that the electron acceleration in a magnetized wake having a different profile than unmagnetized one increases with the perpendicular magnetic field strength so that in presence of a magnetic field with a strong enough amplitude the acceleration goes beyond the resonance regime. The numerical results demonstrate that the electron could be significantly accelerated in a low-amplitude laser-driven wake in presence of an external perpendicular magnetic field which can be superseded the high-amplitude laser-driven wake acceleration regime. Furthermore, we concluded in such systems that the electron acceleration is drastically sensitive to amplitude and initial phase of the wakefield as well as the initial energy of the electron.

Bloch oscillations in moiré flat band systems

Bloch oscillations of wave packets in moiré flat band systems are investigated. We find that the real space trajectories and group velocity of wave packet undergo Bloch oscillations in the moiré flat band. It is shown that the Bloch dynamics is affected significantly by the magnitude and orientation of an applied in-plane electric field. In the presence of both external perpendicular magnetic field and in-plane electric field, confinement and de-confinement of cyclotron orbits occur which strongly depend on the relative strength of the applied fields.

SuperConga: An open-source framework for mesoscopic superconductivity

We present SuperConga, an open-source framework for simulating equilibrium properties of unconventional and ballistic singlet superconductors, confined to two-dimensional (2D) mesoscopic grains in a perpendicular external magnetic field, at arbitrary low temperatures. It aims at being both fast and easy to use, enabling research without access to a computer cluster, and visualization in real-time with OpenGL. The core is written in C++ and CUDA, exploiting the embarrassingly parallel nature of the quasiclassical theory of superconductivity by utilizing the parallel computational power of modern graphics processing units. The framework self-consistently computes both the superconducting order-parameter and the induced vector potential and finds the current density, free energy, induced flux density, local density of states (LDOS), and the magnetic moment. A user-friendly Python frontend is provided, enabling simulation parameters to be defined via intuitive configuration files, or via the command-line interface, without requiring a deep understanding of implementation details. For example, complicated geometries can be created with relative ease. The framework ships with simple tools for analyzing and visualizing the results, including an interactive plotter for spectroscopy. An overview of the theory is presented, as well as examples showcasing the framework's capabilities and ease of use. The framework is free to download from https://gitlab.com/superconga/superconga, which also links to the extensive user manual, containing even more examples, tutorials, and guides. To demonstrate and benchmark SuperConga, we study the magnetostatics, thermodynamics, and spectroscopy of various phenomena. In particular, we study flux quantization in solenoids, vortex physics, surface Andreev bound-states, and a “phase crystal.” We compare our numeric results with analytics and present experimental observables, e.g., the magnetic moment and LDOS, measurable with, for example, scanning probes, STM, and magnetometry.

A criterion for determination of the upper critical fields H-=SUB=-c2-=/SUB=- in YBCO thin films with different ion irradiation doses

Magnetotransport measurements were carried out for YBa2Cu3O7-x (YBCO) thin films in external perpendicular magnetic fields of H. The studies were performed both for the virgin samples and for the irradiated ones. Xenon ions were used as an external irradiation. Thus we studied features of the broadening of superconducting transition in YBCO films (virgin and irradiated). The broadening of superconducting drop was analyzed depending on an external magnetic field H, as well as on an irradiation dose nD. When processing the experimental data R(H,T), we studied a criterion for determination of temperature dependence of the upper critical field Hc2(T). The criterion was analyzed depending on the defect concentration in the film corresponding to a certain value of nD. It was found out that for a virgin sample, Hc2 should be determined by the resistance level R=0.4RN inside the superconducting transition, where RN=R(T=100 K). With a gradual increase in nD, this resistance level decreases. At sufficiently high radiation doses nD>7·1012 cm-2, the Hc2(T) phase transition line should be determined by the level R~0. Keywords: thin films, HTSC, xenon ion irradiation, magnetotransport studies, broadening of the superconducting transition, upper critical field, phase transition line, Tinkham's formula, Abrikosov vortices.

Критерий определения верхних критических полей H-=SUB=-c2-=/SUB=- в тонких пленках YBCO с разной дозой ионного облучения

Magnetotransport measurements were carried out for YBa_2Cu_3O_{7-x} (YBCO) thin films in external perpendicular magnetic fields of H. The studies were performed both for the virgin samples and for the irradiated ones. Xenon ions were used as an external irradiation. Thus we studied features of the broadening of superconducting transition in YBCO films (virgin and irradiated). The broadening of superconducting drop was analyzed depending on an external magnetic field H, as well as on an irradiation dose n_D. When processing the experimental data R(H, T), we studied a criterion for determination of temperature dependence of the upper critical field H_{c2}(T). The criterion was analyzed depending on the defect concentration in the film corresponding to a certain value of n_D. It was found out that for a virgin sample, H_{c2} should be determined by the resistance level R = 0.4R_N inside the superconducting transition, where R_N = R(T = 100 K). With a gradual increase in n_D, this resistance level decreases. At sufficiently high radiation doses n_D > 7·10^{12} cm^{-2}, the H_{c2}(T) phase transition line should be determined by the level R ≈ 0.

Photon and magnetic field controlled electron transport of a multiply-resonant photon-cavity double quantum dot system

We study electron transport through double quantum dots (DQD) coupled to a cavity with a single photon mode. The DQD is connected to two electron reservoirs, and the total system is under an external perpendicular magnetic field. The DQD system exhibits a complex multi-level energy spectrum. By varying the photon energy, several anti-crossings between photon dressed electron states of the DQD-cavity system are found at low strength of the magnetic field. The anti-crossings are identified as multiple Rabi resonances arising from the photon exchange between these states. As the results, a dip in the current is seen caused by the multiple Rabi resonances. By increasing the strength of the external magnetic field, a dislocation of the current dip to a lower photon energy is found and the current dip can be diminished. The interplay of the strength of the magnetic field and the geometry of the states the DQD system can weaken the multiple Rabi resonances in which the exchange of photon between the anti-crossings is decreased. We can therefore confirm that the electron transport behavior in the DQD-cavity system can be controlled by manipulating the external magnetic field and the photon cavity parameters.

Effects of a far-infrared photon cavity field on the magnetization of a square quantum dot array

The orbital and spin magnetization of a cavity-embedded quantum dot array defined in a GaAs heterostructure are calculated within quantum-electrodynamical density-functional theory. To this end, a gradient-based exchange-correlation functional recently employed for atomic systems is adapted to the hosting two-dimensional electron gas submitted to an external perpendicular homogeneous magnetic field. Numerical results reveal the polarizing effects of the cavity photon field on the electron charge distribution and nontrivial changes of the orbital magnetization. We discuss its intertwined dependence on the electron number in each dot, and on the electron-photon coupling strength. In particular, the calculated dispersion of the photon-dressed electron states around the Fermi energy as a function of the electron-photon coupling strength indicates the formation of magnetoplasmon-polaritons in the dots.

Impact of Magnetic Substrate on Dynamic Loss and Magnetization Loss of HTS Coated Conductors

Direct current carrying Type II superconductors present a dc electric field under external perpendicular AC magnetic field, commonly referred to as “dynamic resistance effect”. Two kinds of AC losses occur in this situation: dynamic loss due to the interaction between the DC current and moving fluxons, and magnetization loss due to shielding current caused by the external AC magnetic fields. In general, HTS coated conductors have one substrate layer, which can be non-magnetic (Hastelloy) or magnetic (NiW). In this paper, we present the impacts of the magnetic substrate and their strength of ferromagnetism on dynamic loss and magnetization loss by using a finite-element method model based on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -formulation. This work reveals that the magnetic substrate layer does influence the dynamic loss and magnetization loss of HTS coated conductors. The dynamic loss is reduced by the adjacent magnetic substrate in the low field region and is increase in the high field region. The magnetization loss is reduced significantly by the magnetic substrate. This work will help choose HTS coated conductors with different substrate layers in different applications.

Experimental Determination of the Recovery Time of the Superconducting Properties of the HTS-2G Tape After Removing an External Perpendicular Magnetic Field

Continuous improvement of fuel efficiency and reducing harmful emissions is a trend driven by economic and environmental considerations. It's primarily relevant for transport. Implementation of integrated electric propulsion (IEP), or full electric propulsion (FEP) systems is one of the ways to accomplish this. The power plant works in the rated mode as part of the electric propulsion system. Also, these systems usually include power static converters – rectifiers and inverters. The traditional power switches, based on semiconductor elements, for example, an insulated-gate bipolar transistor (IGBT), have significant heat generation and cannot be placed in the cryogenic zone of fully superconducting systems. Placing of the power static converters (rectifiers and inverters) in a warm zone increases the coolant consumption due to heat inflows into cryogenic zones with superconducting equipment through current leads. Thus, the task of creating power cryogenic switches based on other physical principles is required. This experimental research is dedicated to the determination of the recovery time of the superconducting properties of the HTS-2G tape after removing an external perpendicular magnetic field. That's necessary to estimate the possibility of its use as a superconducting switch (cryotron) for large-scale applications. Moreover, this experimental research methodology is applicable for the estimation of the current-carrying capacity and measures the operation stability in the case of large-scale superconducting devices where HTS-2G tape is in an external alternating magnetic field.

Active Control of Near-Field Radiative Heat Transfer Between InSb and Graphene Multilayered Magneto-Optical Metamaterials

We theoretically investigate the active control of the near-field radiative heat transfer (NFRHT) between two multilayered metamaterials consisting of alternating two kinds of magneto-optical materials, i.e., graphene and InSb. The active control of NFRHT can be realized by applying an external perpendicular magnetic field. We found that, when the chemical potential of graphene μ is 0.05 eV or 0.1 eV, the surface magneto-plasmon polaritons (MPPs) gradually split, and one part moves toward higher frequencies with the increase of the magnetic field. When H = 7 T, the relative thermal magnetoresistance ratio is as high as 82.2% compared with the zero field for μ = 0.05 eV. And most importantly, due to the strong coupling between the MPPs of graphene and the surface modes of InSb, when μ = 0.7 eV, the heat flux reaches 286% compared with the zero field by changing the magnetic field to 1 T. In addition, the effect of the thicknesses of InSb, period number and vacuum gap on heat transfer are also investigated. Through the combined effect of the external magnetic field, the chemical potential of graphene and other factors on the local surface electromagnetic modes, the active control of the NFRHT between two multilayered metamaterials can be realized.

Unified approach to cyclotron and plasmon resonances in a periodic two-dimensional GaAs electron gas hosting the Hofstadter butterfly

We present theoretical calculations for the cyclotron resonance and various magnetoplasmon modes of a Coulomb interacting two-dimensional GaAs electron gas (2DEG) modulated as a lateral superlattice of quantum dots subjected to an external perpendicular constant magnetic field. We use a real-time excitation approach based on the Liouville-von Neumann equation for the density operator, that can go beyond linear response delivering information of all longitudinal and transverse collective modes of interest to the same order. We perform an extensive analysis of the coexisting collective modes due to the lateral confinement and the magnetic field for a different number of electrons in each dot. In the limit of vanishing dot modulation of the 2DEG we find signs of the structure of the Hofstadter butterfly in the excitation spectra.

Quantization of Goos–Hänchen shift in monolayer graphene under partial and total internal reflection conditions

We theoretically investigate the Goos-Hänchen (GH) shifts of a reflected light beam from the dielectric interface containing a monolayer graphene sheet in the presence of an external perpendicular magnetic field. Using Kubo formalism we derive the expressions for the magneto-optical (MO) conductivities. Based on the angular spectrum analysis, we calculate and demonstrate that quantized GH shifts on the surface of graphene monolayer can be tuned by varying the intensity of the applied magnetic field and the beam incidence angle. We show that the GH shifts are quantized due to the Landau level (LL) quantization of the magneto-optical conductivities. In the vicinity of Brewster's angle the GH shift exhibit extreme positive or negative peaks around the magneto-excitation photonic energies in the terahertz regime. We discuss the dependence of the GH shifts on the strength of the magnetic field, the incidence angle, chemical potential, and the impinging frequency of the Gaussian beam. We also discuss the GH shifts for partial reflection (PR) and total internal reflection (TIR) conditions. We find that in the total internal reflection geometry, we have giant angular and spatial GH shifts in the vicinity of the Brewster angle as well as near the critical angle. The MO-modulated GH shift in graphene–substrate system provides a new mechanism to realize photonic devices in the terahertz region.

An external perpendicular magnetic field does not influence survival and DNA damage after proton and carbon ion irradiation in human cancer cells

Background and purposeMagnetic field effects on the radiobiological effectiveness during treatment of magnetic resonance (MRI) guided particle therapy are being debated. This study aims at assessing the influence of a perpendicular magnetic field on the biological effects in two human cancer cell lines irradiated with proton or carbon ions. Methods and materialsIn vitro cell irradiations were performed in water inside a perpendicular magnetic field of 0 and 1T for both protons and carbon ions. Samples were located in the center of a spread-out Bragg peak at 8cm water equivalent depth with a dose averaged linear energy transfer (LETd) of 4.2 or 83.4keV/μm for protons and carbon ions, respectively. Physical dose levels of 0, 0.5, 1, 2, 4 and 6Gy were employed. The irradiation field was shifted and laterally enlarged, to compensate for the beam deflection due to the magnetic field and ensure consistent and homogenous irradiations of the flasks. The human cancer cell lines SKMel (Melanoma) and SW1353 (chondrosarcoma) were selected which represent a high and a low (α/β)x ratio cell type. Cell survival curves were generated applying a linear-quadratic curve fit. DNA damage and DNA damage clearance were assessed via γH2AX foci quantification at 1 and 24h post radiation treatment. ResultsWithout a magnetic field, RBE10 values of 1.04±0.03 (SW1353) and 1.51±0.06 (SKMel) as well as RBE80 values of 0.93±0.15 (SW1353) and 2.28±0.40 (SKMel) were calculated for protons. Carbon treatments yielded RBE10 values of 1.68±0.04 (SW1353) and 2.30±0.07 (SKMel) and RBE80 values of 2.19±0.24 (SW1353) and 4.06±0.33 (SKMel). For a field strength of B=1T, RBE10 values of 1.06±0.03 (SW1353) and 1.47±0.06 (SKMel) resulted from protons, while RBE10 values of 1.70±0.05 (SW1353) and 2.37±0.08 (SKMel) were obtained for carbon ions. RBE80 values were calculated to be 1.06±0.12 (SW1353) and 2.33±0.40 (SKMel) following protons and 2.13±0.25 (SW1353) and 4.29±0.35 (SKMel) following carbon treatments. Substantially increased γH2AX foci per nucleus were found in both cell lines 1h after radiation with both ion species. At the 24h time point only carbon treated samples of both cell lines showed increased γH2AX levels. The presence of the magnetic field did neither influence the survival parameters of either cell line, nor initial DNA damage and DNA damage clearance. ConclusionsApplying a perpendicular magnetic field did not influence the cell survival, DNA repair, nor the biological effectiveness of protons or carbon ions in two human cancer cell lines.

Holographic Abrikosov lattice: Vortex matter from black hole

The $\mathrm{AdS}/\mathrm{CFT}$ correspondence provides a unique way to study the vortex matter phases in superconductors. We solve the dynamical evolution of a superconductor in $2+1$ dimensions at a finite temperature subjected to a magnetic field quench in terms of a gravitational ``hairy black hole'' dual living in an asymptotic ${\mathrm{AdS}}_{4}$ space. We exploit this to determine the nature of the equilibrium states realized at long times after the quench of this two dimensional type II superconductor in a perpendicular external uniform magnetic field ${B}_{0}$. This holographic superconductor exhibits the generic lower (${B}_{c1}(T)$) and upper (${B}_{c2}(T)$) critical fields. For ${B}_{0}&lt;{B}_{c1}(T)$ the magnetic field is completely expelled revealing the Meissner phase, while the superconductivity is destroyed when ${B}_{0}&gt;{B}_{c2}(T)$. Abrikosov lattices appear in the range ${B}_{c1}(T)&lt;{B}_{0}&lt;{B}_{c2}(T)$ that realize various configurations in the form of hexagonal, square and slightly irregular square lattices pending the magnetic field strength and the influence of finite size boundaries. We show this to be consistent with the expectations of Ginzburg-Landau theory where the upper and lower critical fields are associated with the inverse squares of the coherence length and magnetic penetration depth, respectively.

Influence of deformations on the reentrant conductance feature in semiconducting nanowires

Helical states can be measured through the observation of the reentrant behavior, which is a dip in the conductance probed in semiconducting nanowires (NWs) with strong spin-orbit coupling (SOC) under the presence of an external perpendicular magnetic field. We investigate the effects of deformation in the electronic transport in NWs considering the coupling between different transverse modes. Within this approach, we show that the dip in the conductance is affected by the presence of a local constriction in the NW. Moreover, we find that the reentrant feature in the conductance can appear in NWs containing a local expansion of its radius, even in the absence of SOC and magnetic field. This result demonstrates that the reentrant feature can be found within certain conditions that differ from those expected to probe helical states. Therefore, the reentrant feature cannot always be associated with the observation of helical states. Furthermore, we develop a numerical approach to calculate transport properties, which can include the deformation and the coupling among several scattering channels.

Seebeck and Nernst effects in topological insulator: The case of strained HgTe

We theoretically study the thermoelectric transport properties of strained HgTe in the topological insulator phase. We developed a model for the system using a Dirac Hamiltonian including the effect of strain induced by the interface between HgTe and the CdTe substrate. The conductivity tensor was explored assuming the electrons are scattered by charge impurities, while the thermopower tensor was addressed using the Mott relation. Seebeck and Nernst responses exhibit remarkable enhancements in comparison with other two-dimensional Dirac materials, such as graphene, germanane, prosphorene and stanene. The intensity of these thermometric responses, their dependencies with the external perpendicular magnetic field and temperature are also addressed.