Effect Of In-plane Magnetic Field Research Articles

The superconducting FFLO state induced by orbital effect of in-plane magnetic field

The superconducting FFLO state induced by orbital effect of in-plane magnetic field

Unconventional superconductivity with preformed pairs in twisted bilayer graphene

We present a theory of superconductivity in magic-angle twisted bilayer graphene and analyze the superconducting phase diagram in presence of the magnetic field. Namely, we consider a model of a granular array hosting localized states, which are hybridized via the delocalized fermions in the inter-grain regions. We study a strong coupling situation when the interactions lead to an incoherent state with preformed Cooper pairs inside the grains. The Andreev scattering among different grains manifests itself through the global phase-coherent superconducting state at lower temperatures. We demonstrate that a new phase transition between the preformed Cooper pairing state and the Larkin-Ovchinnikov-Fulde-Ferrell state might be induced by the spin pair-breaking effect of in-plane magnetic field. The upper critical magnetic field is shown to be enhanced in the strong coupling case.

Quantum nonlinear planar Hall effect in bilayer graphene: An orbital effect of a steady in-plane magnetic field

We study the quantum nonlinear planar Hall effect in bilayer graphene under a steady in-plane magnetic field. When time-reversal symmetry is broken by the magnetic field, a charge current occurs in the second-order response to an external electric field as a result of the Berry curvature dipole in momentum space. We show that a nonlinear planar Hall effect originating from the anomalous velocity is caused by an orbital effect of an in-plane magnetic field on electrons in bilayer graphene in the complete absence of spin-orbit coupling. Taking into account the symmetry analysis, we derive the dominant dependence of the Berry curvature dipole moment on the magnetic field components. Moreover, we illustrate how to control and modulate the Berry curvature dipole with an external planar magnetic field, gate voltage, and Fermi energy.

In plane magnetic field and intense laser field effects on second harmonic generation of asymmetric AlGaAs/GaAs double quantum well

The optical properties for nano-structured semiconductor systems are of great importance nowadays, due to its possible implementation for the design of efficient optoelectronic devices. It is also well known that external fields can modify the electronic structure, and induce changes the optical properties as well. In particular the asymmetric double quantum well structures are of paramount importance because its wide range on possible configurations and also because are experimentally feasible and well controlled, particularly AlxGa1-xAs/GaAs heterostructures. In this work we report a systematic study on second harmonic generation (SHG) for an asymmetric AlxGa1-xAs/GaAs double quantum well as a function of non-resonant intense laser field and in-plane magnetic field effect. We analyze the energy level behavior as well as the dipole matrix elements as a function of the above mentioned factors that are important for the SHG. We report a particular configuration that optimize the SHG peak, with and without intense laser field effect, as well as magnetic fields, that also tune the SHG.

Magnetic Field Resilience of Three-Dimensional Transmons with Thin-Film Al/AlOx/Al Josephson Junctions Approaching 1 T

Magnetic-field-resilient superconducting circuits enable sensing applications and hybrid quantum computing architectures involving spin or topological qubits and electromechanical elements, as well as studying flux noise and quasiparticle loss. We investigate the effect of in-plane magnetic fields up to 1 T on the spectrum and coherence times of thin-film three-dimensional aluminum transmons. Using a copper cavity, unaffected by strong magnetic fields, we can probe solely the effect of magnetic fields on the transmons. We present data on a single-junction and a superconducting-quantum-interference-device (SQUID) transmon that are cooled down in the same cavity. As expected, the transmon frequencies decrease with increasing field, due to suppression of the superconducting gap and a geometric Fraunhofer-like contribution. Nevertheless, the thin-film transmons show strong magnetic field resilience: both transmons display microsecond coherence up to at least 0.65 T, and ${T}_{1}$ remains above $1\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\text{s}$ over the entire measurable range. SQUID spectroscopy is feasible up to 1 T, the limit of our magnet. We conclude that thin-film aluminum Josephson junctions are suitable hardware for superconducting circuits in the high-magnetic-field regime.

Electronic and optical properties of eccentric quantum ring under parallel magnetic field

Using the effective mass approximation, within the plane wave expansion, the effect of in-plane magnetic field on the electronic states and the intersubband optical absorption in a two-dimensional GaAs eccentric quantum ring are studied. The obtained results show that an applied magnetic field, eccentricity and the light polarization direction provide efficient tools to tune the peaks positions and intensities in the optical absorption coefficients. In addition some allowed optical transitions with strong intensity which occurs only in eccentric QRs under an x oriented magnetic field can be considered as footprint of eccentricity. It is also found that, for y-polarization of the light incident, the effect of eccentricity on the optical absorption spectra is preserved in the presence of magnetic field, whereas, its effect vanish at large magnetic field in the case of x-polarization.

Helical magnetic order and Fermi surface nesting in noncentrosymmetric ScFeGe

An investigation of the structural, magnetic, thermodynamic, and charge transport properties of noncentrosymmetric hexagonal ScFeGe reveals it to be an anisotropic metal with a transition to a weak itinerant incommensurate helimagnetic state below TN=36 K. Neutron diffraction measurements discovered a temperature and field independent helical wave vector k = (0 0 0.193) with magnetic moments of 0.53 μB per Fe confined to the ab plane. Density functional theory calculations are consistent with these measurements and find several bands that cross the Fermi level along the c axis with a nearly degenerate set of flat bands just above the Fermi energy. The anisotropy found in the electrical transport is reflected in the calculated Fermi surface, which consists of several warped flat sheets along the c axis with two regions of significant nesting, one of which has a wave vector that closely matches that found in the neutron diffraction. The electronic structure calculations, along with a strong anomaly in the c -axis conductivity at TN, signal a Fermi surface driven magnetic transition, similar to that found in spin density wave materials. Magnetic fields applied in the ab plane result in a metamagnetic transition with a threshold field of ≈6.7 T along with a sharp, strongly temperature dependent discontinuity and a change in sign of the magnetoresistance for in-plane currents. Thus, ScFeGe is an ideal system to investigate the effect of in-plane magnetic fields on a helimagnet with a c -axis propagation vector, where the relative strength of the magnetic interactions and anisotropies determine the topology and magnetic structure.6 MoreReceived 18 September 2020Revised 9 December 2020Accepted 11 January 2021DOI:https://doi.org/10.1103/PhysRevB.103.014443©2021 American Physical SocietyPhysics Subject Headings (PhySH)Physical SystemsNoncentrosymmetric materialsNoncollinear magnetsTechniquesDensity functional calculationsMagnetization measurementsNeutron diffractionResistivity measurementsCondensed Matter & Materials Physics

Orbital effects of a strong in-plane magnetic field on a gate-defined quantum dot

We theoretically investigate the orbital effects of an in-plane magnetic field on the spectrum of a quantum dot embedded in a two-dimensional electron gas (2DEG). We derive an effective two-dimensional Hamiltonian where these effects enter in proportion to the flux penetrating the 2DEG. We quantify the latter in detail for harmonic, triangular, and square potential of the heterostructure. We show how the orbital effects allow one to extract a wealth of information, for example, on the heterostructure interface, the quantum dot size and orientation, and the spin-orbit fields. We illustrate the formalism by extracting this information from recent measured data [L.~C.~Camenzind, et al., arXiv:1804.00162; Nat. Commun. 9, 3454 (2018)].

Coupled effect of in-plane magnetic field and size effect on vibration properties of the completely free double-layered nanoplate system

The coupled effects of an in-plane magnetic field and the size effect on free vibration of a completely free magnetically affected orthotropic double-layered nanoplate system (DLNS) embedded in elastic media are examined by a Hamiltonian-based method combined with Eringen's nonlocal elasticity theory. The Lorentz magnetic force exerted on the DLNS is derived based on Maxwell's equations and Lorentz's formula. By introducing a full-state vector as the primary unknown, the classical governing equation is converted into its Hamiltonian form so that exact solutions of the DLNS are obtained by symplectic expansion and a superposition of boundaries. Analytical frequency equation and vibration mode functions are obtained simultaneously. Numerical results illustrate that, by changing the magnetic parameter, the natural frequencies of the DLNS show two opposite variation trends with increasing nonlocal parameter; and the vibration modes are re-arranged. These findings demonstrate that applying an in-plane magnetic field is an efficient way to control the natural frequencies and vibration modes of such magnetically affected DLNS.

Dirac semimetal thin films in in-plane magnetic fields.

In this work we study the effects of in-plane magnetic fields on thin films of the Dirac Semimetal (DSM) Na3Bi where one of the in-plane directions is perpendicular to the k-separation between the two Weyl nodes that exist for each spin orientation. We show numerically that the states localized near the surfaces of these thin films are related to the Fermi arc states in semi-infinite slabs. Due to the anisotropy between the two in-plane directions, the application of a magnetic field along these directions have differing effects. A field parallel to the k space separation between the Weyl nodes leads to a broadening of the surface state band and the formation of an energy plateau, while a perpendicular field shifts the energy where the hole and particle bands meet upwards, and sharpens the tips of the bands. We illustrate the effects of these changes to the dispersion relation by studying the transmission from a source segment without a magnetic field to a drain segment with a field, with the field and interface at various in-plane directions.

Effect of in-plane magnetic field and applied strain in quantum spin Hall systems: Application to InAs/GaSb quantum wells

Motivated by the recent discovery of quantized spin Hall effect in InAs/GaSb quantum wells\cite{du2013}$^,$\cite{xu2014}, we theoretically study the effects of in-plane magnetic field and strain effect to the quantization of charge conductance by using Landauer-Butikker formalism. Our theory predicts a robustness of the conductance quantization against the magnetic field up to a very high field of 20 tesla. We use a disordered hopping term to model the strain and show that the strain may help the quantization of the conductance. Relevance to the experiments will be discussed.

In-plane magnetic field effect on switching voltage and thermal stability in electric-field-controlled perpendicular magnetic tunnel junctions

The effect of in-plane magnetic field on switching voltage (Vsw) and thermal stability factor (Δ) are investigated in electric-field-controlled perpendicular magnetic tunnel junctions (p-MTJs). Dwell time measurements are used to determine the voltage dependence of the energy barrier height for various in-plane magnetic fields (Hin), and gain insight into the Hin dependent energy landscape. We find that both Vsw and Δ decrease with increasing Hin, with a dominant linear dependence. The results are reproduced by calculations based on a macrospin model while accounting for the modified magnetization configuration in the presence of an external magnetic field.

Evidence for a new symmetry breaking mechanism reorienting quantum Hall nematics

We report on the effect of in-plane magnetic field $B_\parallel$ on stripe phases in higher ($N=2,3$) Landau levels of a high-mobility 2D electron gas. In accord with previous studies, we find that a modest $B_\parallel$ applied parallel to the native stripes aligns them perpendicular to it. However, upon further increase of $B_\parallel$, stripes are reoriented back to their native direction. Remarkably, applying $B_\parallel$ perpendicular to the native stripes also aligns stripes parallel to it. Thus, regardless of the initial orientation of stripes with respect to $B_\parallel$, stripes are ultimately aligned \emph{parallel} to $B_\parallel$. These findings provide evidence for a $B_\parallel$-induced symmetry breaking mechanism which challenge current understanding of the role of $B_\parallel$ and should be taken into account when determining the strength of the native symmetry breaking potential. Finally, our results might indicate nontrivial coupling between the native and external symmetry breaking fields, which has not yet been theoretically considered.

Spin–orbit interaction effects on the optical properties of quantum wires under the influence of in-plane magnetic fields

In this work, we studied the effects of in-plane magnetic field and Rashba spin–orbit interaction on the intersubband optical absorption coefficients and changes in refractive index for transitions between the first two lower-lying electronic levels of quantum wire represented by a parabolic confining potential. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism and iterative scheme. Optical properties are investigated as a function of quantum wire radius, strength and orientation of magnetic field, strength of Rashba spin–orbit interaction and photon energies. Numerical results reveal that the optical absorption coefficients and refractive index changes are strongly affected and thus can be controlled by these parameters.

Phase diagram and collective modes in Rashba spin–orbit coupled BEC: Effect of in-plane magnetic field**Project supported by the National Natural Science Foundation of China (Grant No. 10774088).

We studied the system of pure Rashba spin–orbit coupled Bose gas with an in-plane magnetic field. Based on the mean field theory, we obtained the zero temperature phase diagram of the system which exhibits three phases, plane wave (PW) phase, striped wave (SW) phase, and zero momentum (ZM) phase. It was shown that with a growing in-plane field, both SW and ZM phases will eventually turn into the PW phase. Furthermore, we adopted the Bogoliubov theory to study the excitation spectrum as well as the sound speed.

Transport in a quantum spin Hall bar: Effect of in-plane magnetic field

We demonstrate theoretically that edge transport in quantum spin Hall bar can be controlled by in-plane magnetic fields. The in-plane magnetic field couples the opposite spin orientation helical edge states at the opposite edges, and induces the gaps in the energy spectrum. The hybridized electron wave functions ψ↑(x,ky) of the edge states can be destroyed with increasing the in-plane magnetic fields. When the Fermi surface is located within this energy gap induced by the in-plane magnetic field, one can expect that the conductance of the edge states becomes e2/h. By tuning the magnetic field and Fermi energy, the edge channels can be transited from opaque to transparent. This switching behavior offers us an efficient way to control the topological edge state transport.

Photogalvanic current in a parabolic well

We study the in-plane stationary photocurrent in a parabolic potential well. The well has vertical asymmetry due to inhomogeneous distribution of scatterers. The electric field of light has both vertical and in-plane components. The photogalvanic effect originates from the periodic oscillation of electrons in a vertical direction caused by the normal component of the alternating electric field with simultaneous in-plane acceleration/deceleration by the in-plane component of electric field. The problem is considered in classical approximation assuming inhomogeneously-distributed friction. Photocurrent has a resonance character. Resonance occurs at light frequencies close to a characteristic well frequency. The effect of in-plane magnetic field is also studied.

Resonance in-plane magnetic field effect as a means to reveal the Fulde-Ferrell-Larkin-Ovchinnikov state in layered superconductors

The vector potential of a parallel magnetic field produces a modulation of the interlayer coupling between adjacent superconducting layers. In some cases the period of this modulation can coincide with the period of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) modulation of the superconducting order parameter. Such a resonance condition results in cusps on the temperature and in-plane angular dependencies of the upper critical field Hc2. This effect can open up a possibility to unambiguously evidence a spatially modulated superconducting phase in layered conductors. Remarkably, the proposed signature of the FFLO state is directly based on the main feature of the FFLO state, the spatial modulations of the order parameter.

Effect of in-plane magnetic field on spin polarization in the presence of the Dresselhaus spin–orbit effect

In this paper, we theoretically study the effect of the in-plane magnetic field on spin polarization in the presence of the Dresselhaus spin–orbit effect. It is shown that the large spin polarization can be achieved in such a nanostructure due to the effects of both the Dresselhaus spin–orbit term and the in-plane magnetic field, but the latter plays a main role in the tunneling process. It is also shown that with the increase of in-plane magnetic field, the degree of spin splitting obviously becomes larger.

The role of optical rectification in the generation of terahertz radiation from GaBiAs

We report on a detailed study of the emission of terahertz-frequency electromagnetic radiation from layers of GaBiyAs1−y (0≤y<0.04) grown by molecular beam epitaxy on (311)B and (001) GaAs substrates. We measure two orthogonally polarized components of the terahertz radiation emitted under excitation by ultrashort near-infrared laser pulses in both transmission and reflection geometries as a function of the crystal rotation about its surface normal as well as the effect of in-plane magnetic field and pump fluence on the terahertz emission. We conclude that the principal mechanism for terahertz generation is via optical rectification rather than transient currents.