Zeeman Magnetic Field Research Articles

Excitonic correlations in the system of gated metallic wires with the applied Zeeman magnetic field

We have studied the electron–electron interactions in the system composed of two metallic one-dimensional point contact and zero-sized wires, in the applied electric field and exposed to the influence of the external Zeeman magnetic field. The interactions between the electrons within wires have been taken into account within the usual Hubbard model. We have considered different limits of particle-filling on the atomic lattice site positions. We show the existence of the excitonic pairing in this one-dimensional system in different limits of the electron–electron interactions, magnetic field, and temperature. We demonstrate that the usual Hubbard-U interaction leads to strong electron localization, which enhances the local antiferromagnetic order in the system.

Magnetic impurity states of a Fermi system in a local magnetic field

The ultracold atomic Fermi gas provides a flexible and controllable experimental platform for exploring magnetic impurity states. In this study, we theoretically examine the magnetic impurity states in a Fermi system with spin-1/2 and spin-3/2 under a local magnetic field. Firstly, the spin-1/2 impurity system contains three types of magnetic solutions. One type magnetic solution with higher energy can be regarded as the result of induced magnetization of a trivial solution, while the other two types magnetic solutions with lower energy can be understood as the results of Zeeman splitting of nontrivial solutions with double degeneracy. Notably, the magnetic solution corresponding to the spin state parallel to the Zeeman magnetic field is always the most stable in terms of the energy. Secondly, we extend the idea of studying spin-1/2 impurity to spin-3/2 impurity, where the half-filled state of impurity atoms is calculated. We found that four types of magnetic solutions at zero magnetic field were split into four, six, four, and twelve new magnetic solutions in the presence of a Zeeman magnetic field, respectively. We obtained that the magnetic solution corresponding to the spin state parallel to the magnetic field is the most stable, and its energy is lower than that of the corresponding magnetic solution at zero magnetic field. Therefore, the introduction of a local magnetic field is beneficial for the formation of magnetic impurity states. Finally, the calculated data illustrate that the Anderson impurity model we adopt exhibits invariance under the combined transformations of spin-flip and particle–hole.

Probing dark matter axions using the hyperfine structure splitting of hydrogen atoms

QCD axions can be a substantial part of dark matter if their mass ma∼10−5 eV. Since the axions were created by the misalignment mechanism, their local energy spectrum density is large. Consequently, the axion-induced atomic transition rate is enhanced if the atomic energy gap matches the axion mass. The hyperfine splitting between the spin 0 singlet ground state and the spin 1 triplet state of hydrogen is 0.59×10−5 eV, which is close to the preferred mass of dark matter axions. With an energy gap adjustment by applying a weak Zeeman magnetic field, dark matter axions can induce atomic hydrogen transitions. Furthermore, because the total spins of the hydrogen triplet and singlet differ, the axion-induced transitions are detectable by a Stern–Gerlach apparatus or a sensitive magnetic field detector. A potential realization of the proposed scheme can be similar to existing hydrogen masers.

Spin-singlet topological superconductivity in the attractive Rashba-Hubbard model

Fully gapped, spin-singlet superconductors with antisymmetric spin-orbit coupling in a Zeeman magnetic field provide a promising route to realize superconducting states with non-Abelian topological order and therefore fault-tolerant quantum computation. Here we use a quantum Monte Carlo dynamical cluster approximation to study the superconducting properties of a doped two-dimensional attractive Hubbard model with Rashba spin-orbit coupling in a Zeeman magnetic field. We generally find that the Rashba coupling has a beneficial effect towards $s$-wave superconductivity. In the presence of a finite Zeeman field, when superconductivity is suppressed by Pauli pair breaking, the Rashba coupling counteracts the spin imbalance created by the Zeeman field by mixing the spins, and thus restores superconductivity at finite temperatures. We show that this favorable effect of the spin-orbit coupling is traced to a spin-flip driven enhancement of the amplitude for the propagation of a pair of electrons in time-reversed states. Moreover, by inspecting the Fermi surface of the interacting model, we show that for sufficiently large Rashba coupling and Zeeman field, the superconducting state is expected to be topologically nontrivial.

Electronic density of states of a U(1) quantum spin liquid with spinon Fermi surface. II. Zeeman magnetic field effects

This work studies the Zeeman magnetic field effect on a quantum spin liquid with a spinon Fermi surface. In the absence of gauge binding, the quantum spin liquid electronic density of states exhibits no Zeeman shift in the threshold energy. As the gauge binding increases, the band edge resonance peaks exhibit a reduced Zeeman shift and eventually have the Zeeman shift direction reversed for a sufficiently large gauge binding. The authors further suggest to use such anomalous Zeeman response to identify the gapless quantum spin liquid phase.

Tunable valley characteristics of WSe2 and WSe2/VSe2 heterostructure

Information technology can be improved by using the magnetic proximity effect to control two-dimensional valleytronics. Ferrovalley materials attract wide attention because of spontaneous valley polarization and magnetism. Here, the first-principles density functional theory has been used to examine the valley characteristics of monolayer WSe2 caused by the ferrovalley VSe2 substrate. The results demonstrate that monolayer WSe2 experiences the largest spin and absolute valley splitting at energies of 466 and 8.223 meV, respectively. With the k•p model, the effective Zeeman magnetic field of 73.36 T was found for the most stable configuration. More intriguingly, due to the ferrovalley nature of VSe2 substrates, just one valley state at the K' point exhibits a single valley-dependent optical transition in WSe2/VSe2 heterostructure. Additionally, the strain is applied to modify the spin-valley splitting. With the in-plane strain effect, the sign-reversible with the reversed spin state is obtained in biaxial strain, and a fascinating type-I to type-III band alignment transition occurs in the WSe2/VSe2, which intensifies the valley splitting. In vertical strain, the pure spin-valley polarization of the WSe2/VSe2 heterostructure can be observed. Ferrovalley substrates provide new opportunities for valleytronics applications.

Magnetically-controlled spin filter and spin-polarized oscillations in a four-quantum-dot system

Spin polarization through a four-quantum-dot system is theoretically studied by considering the effects of Zeeman magnetic field, extrinsic Rashba spin–orbit interaction and external magnetic field. We analyze how the resonance and anti-resonance bands are formed by means of the mathematical formula. By adjusting the external magnetic field, the spin polarization can be converted between −100% and 100%, which suggests a physical scheme of an effective magnetically-controlled spin filter. The combined effect of external magnetic field and extrinsic Rashba spin–orbit interaction leads to spin-polarized oscillations. The introduction of the Zeeman magnetic field makes the system easier to be applied as a spin filter. This study provides theoretical insights into the realization of quantum computing, quantum information transmission and development of nanoscale quantum devices.

Migdal-Eliashberg theory as a classical spin chain

We formulate the Migdal-Eliashberg theory of electron-phonon interactions in terms of classical spins by mapping the free energy to a Heisenberg spin chain in a Zeeman magnetic field. Spin components are energy-integrated normal and anomalous Green's functions and sites of the chain are fermionic Matsubara frequencies. The Zeeman field grows linearly with the spin coordinate and competes with ferromagnetic spin-spin interaction that falls off as the square of the inverse distance. The spin-chain representation makes a range of previously unknown properties plain to see. In particular, infinitely many new solutions of the Eliashberg equations both in the normal and superconducting states emerge at strong coupling. These saddle points of the free-energy functional correspond to spin flips. We argue that they are also fixed points of kinetic equations and play an essential role in far from equilibrium dynamics of strongly coupled superconductors. Up to an overall phase, the frequency-dependent gap function that minimizes the free energy must be non-negative. There are strong parallels between our Eliashberg spins and Anderson pseudospins, though the two sets of spins never coincide.

Spin polarization transport through a four InAs quantum dots system irradiated by terahertz light field

We design a four InAs quantum dot system in which two leads are irradiated by terahertz light fields. The average current through the system is obtained by means of non-equilibrium Green's function theory. Typical photon-assisted tunneling is observed in the current energy spectrum. 100% polarization can be achieved by adjusting the intensity of Zeeman magnetic field or the amplitude of terahertz light field. As the frequency of terahertz light field is invariant, a zero current can be obtained by adjusting the amplitude of the terahertz light field, indicating an optically controlled quantum switch device. The spin polarization can be converted between 0 and 1 by tuning the energy level of quantum dots, suggesting a physical scheme of a polarization pulse device. Moreover, the system can be constructed as a terahertz detector due to the oscillation properties of spin polarization. The present work sheds lights onto the design of quantum computing and spin-dependent quantum devices.

Influence of Rashba spin-orbit coupling on Josephson effect in triplet superconductor/two-dimensional semiconductor/triplet superconductor junctions

We study theoretically Josephson effect in a planar ballistic junction between two triplet superconductors with p-wave orbital symmetries and separated by a two-dimensional (2D) semiconductor channel with strong Rashba spin–orbit coupling. In triplet superconductors, three types of orbital symmetries are considered. We use Bogoliubov–de Gennes formalism to describe quasiparticle propagations through the junction and the supercurrents are calculated in terms of Andreev reflection coefficients. The features of the variation of the supercurrents with the change of the strength of Rashba spin–orbit coupling are investigated in some detail. It is found that for the three types of orbital symmetries considered, both the magnitudes of supercurrent and the current-phase relations can be manipulated effectively by tuning the strength of Rashba spin–orbit coupling. The interplay of Rashba spin–orbit coupling and Zeeman magnetic field on supercurrent is also investigated in some detail.

Photon-assisted spin transport characteristics of A-B interferometer embedded with three quantum dots

We design an A-B interferometer with a “single quantum dot atom” embedded in the upper arm and a “double quantum dot molecule” embedded in the lower arm. The transmission coefficient and average current characteristics are studied as the time-dependent external field is introduced. When the interdot coupling strength is weak, the change of Rashba spin orbit coupling strength has a strong influence on the spin transmission coefficient. When the interdot coupling strength and Rashba spin orbit coupling strength take appropriate values, the spin up and spin down transmission coefficients completely coincide, and a resonance band emerges at the Fermi level. The spin polarization can be close to +1 or −1 by adjusting the Zeeman magnetic field, the interdot coupling strength, and the gate voltage. In the presence of photon assistance, the spin polarization changes periodically in a certain proportion, so as to realize the spin-polarized transport with controllable time-dependent external field. These findings provide a theoretical basis for the spin polarized function of A-B interferometer.

Large valley polarization in a novel two-dimensional semiconductor H-ZrX2 (X = Cl, Br, I)

Inspired by the new progress in the research field of two-dimensional valleytronics materials, we propose a new class of transition metal halides, i.e. H-ZrX2 (X = Cl, Br, I), and investigated their valleytronics properties under the first-principles calculations. It harbors the spin-valley coupling at K and K′ points in the top of valence band, in which the valley spin splitting of ZrI2 can reach up to 115 meV. By carrying out the strain engineering, the valley spin splitting and Berry curvature can be effectively tuned. The long-sought valley polarization reaches up to 108 meV by doping Cr atom, which corresponds to the large Zeeman magnetic field of 778 T. Furthermore, the valley polarization in ZrX2 can be lineally adjusted or flipped by manipulating the magnetization orientation of the doped magnetic atoms. All the results demonstrate the well-founded application prospects of single-layer ZrX2, which can be considered as great candidate for the development of valleytronics and spintronics.

Tunable spin-valley splitting and magnetic anisotropy of two-dimensional 2H-VS2/h-VN heterostructure

Valleytronics is proposed to explore a new approach for information storage using valley degrees of freedom. In this work, the electronic structure, spin-valley splitting and magnetic anisotropy (MA) of two-dimensional (2D) 2H-VS2/h-VN magnetic van der Waals (vdW) heterostructure are investigated systematically by first-principles calculations. The results show that the considerable spin splitting of 364.7 meV and 543.7 meV are observed at the K and K' valleys, respectively, generating an intrinsic valley splitting of 68.9 meV in the valence band for the 2H-VS2/h-VN heterostructure, which corresponds to an effective Zeeman magnetic field of 774 T based on the k·p model. The valley splitting of 2H-VS2 is well preserved in the heterostructure and can be further adjusted by altering stacking patterns, in-plane strain and interfacial distance due to the interfacial orbital hybridization. Compared with the pristine 2H-VS2 monolayer, the 2H-VS2 of heterostructure still exhibits the in-plane MA, which mainly originates from the positive contribution of the matrix element difference between the V dxy and dx2-y2 orbitals. With the increase of strain from −2% to 3%, the orientation of easy magnetization axis is transformed from in-plane to out of plane. These results suggest that the 2H-VS2/h-VN heterostructure is a potential candidate in further valleytronics and spintronics.

Topological superconductivity in quasicrystals

We propose realization of non-Abelian topological superconductivity in two-dimensional quasicrystals by the same mechanism as in crystalline counterparts. Specifically, we study a two-dimensional electron gas in Penrose and Ammann-Beenker quasicrystals with Rashba spin-orbit coupling, perpendicular Zeeman magnetic field, and conventional $s$-wave superconductivity. We find that topological superconductivity with broken time-reversal symmetry is realized in both Penrose and Ammann-Beenker quasicrystals at low filling, where the Bott index is unity. The topological nature of this phase is confirmed by the existence of a zero-energy surface bound state and the chiral propagation of a wave packet projected onto the midgap bound state along the surfaces. Furthermore, we confirm the existence of a single Majorana zero mode each in a vortex at the center of the system and along the surfaces, signifying the non-Abelian character of the system when the Bott index is unity.

Chiral splitting of Kondo peak in triangular triple quantum dot

New characteristics of the Kondo effect, arising from spin chirality induced by the Berry phase in the equilibrium state, are investigated. The analysis is based on the hierarchical equations of motion (HEOM) approach in a triangular triple quantum-dot (TTQD) structure. In the absence of magnetic field, TTQD has four-fold degenerate chiral ground states with degenerate spin chirality. When a perpendicular magnetic field is applied, the chiral interaction is induced by the magnetic flux threading through TTQD and the four-fold degenerate states split into two chiral state pairs. The chiral excited states manifest as chiral splitting of the Kondo peak in the spectral function. The theoretical analysis is confirmed by the numerical computations. Furthermore, under a Zeeman magnetic field B, the chiral Kondo peak splits into four peaks, owing to the splitting of spin freedom. The influence of spin chirality on the Kondo effect signifies an important role of the phase factor. This work provides insight into the quantum transport of strongly correlated electronic systems.

Controllable enormous valley splitting in Janus WSSe on CrN monolayer

Manipulation of valley polarization in low-dimensional systems is desirable for future applications in information process and storage. Here, we design two-dimensional WSSe/CrN van der Waals heterostructures and control the valley degree of freedom based on the first-principles calculations. Combining the internal electric field and magnetic proximity effect, the interfacial interaction and the valley splitting are efficiently modulated in the system. Intrinsic enormous valley splitting of 103 meV and 144 meV are generated in S- and Se-terminated WSSe/CrN heterostructures, which corresponds to the effective Zeeman magnetic field of 1280 and 1574 T, respectively. A prominent anomalous Hall conductivity at K valley is induced by time-reversal symmetry breaking and sizable Berry curvature. Furthermore, valley splitting can be manipulated continually by the in-plane strain and interlayer distance. The largest valley splitting of 272 (240) meV and the effective Zeeman magnetic field of 2560 (2275) T are achieved for S (Se)-terminated WSSe/CrN heterostructures, respectively, under the compressive interlayer distance. It is found that the changes of induced spin charges around S and W atom are responsible for the modulated valley splitting. This work opens new vistas for the design of valleytronic devices.

Coherence Protection of Electron Spin in Earth-Field Range by All-Optical Dynamic Decoupling

In recent years, unshielded atomic systems have been attracting researchers' attention, in which decoherence is one of the major problems, especially for high precision measurements. The nonlinear Zeeman effect and magnetic field gradient are the main decoherence sources of atomic electron spin in Earth-field range. Here, we propose a method to cancel out the two dominant broadening effects simultaneously by an all-optical dynamic decoupling approach based on Raman scattering in the 87Rb Zeeman sublevels. By adjusting the parameters of the Raman lasers, we realize spin control along an arbitrary direction. We analyze the state evolution of atomic spin under the Raman light control sequence in detail. The results show that both the nonlinear Zeeman effect and magnetic field gradient can be significantly suppressed.

Zeeman coupling and Dzyaloshinskii-Moriya interaction driven by electric current vorticity

The Dzyaloshinskii-Moriya interaction, i.e., antisymmetric exchange interaction, combined with a Zeeman magnetic field gives rise to various magnetic states such as chiral, helical, and skyrmionic states. This interaction conventionally originates from spin-orbit coupling and thus needs somewhat heavy elements. In contrast, we here show a Dzyaloshinskii-Moriya interaction which is driven by electric current vorticity. We also find that the vorticity acts on localized spins as a Zeeman field, which may explain a recent experiment on current-driven magnetic skyrmion creation and annihilation without an external magnetic field in a device with a notch structure in FeGe. theory explains the control of skyrmion creation and annihilation by current direction and opens different possibilities for studies of magnetic textures by using structural settings.

Electrojet Estimates From Mesospheric Magnetic Field Measurements

AbstractThe auroral electrojet is traditionally measured remotely with magnetometers on ground or in low Earth orbit (LEO). The sparse distribution of measurements, combined with a vertical distance of some 100 km to ground and typically >300 km to LEO satellites, means that smaller scale sizes can't be detected. Because of this, our understanding of the spatiotemporal characteristics of the electrojet is incomplete. Recent advances in measurement technology give hope of overcoming these limitations by multi‐point remote detections of the magnetic field in the mesosphere, very close to the electrojet. We present a prediction of the magnitude of these disturbances, inferred from the spatiotemporal characteristics of magnetic field‐aligned currents. We also discuss how Zeeman magnetic field sensors (Yee et al., 2021) onboard the Electrojet Zeeman Imaging Explorer satellites will be used to essentially image the equivalent current at unprecedented spatial resolution. The electrojet imaging is demonstrated by combining carefully simulated measurements with a spherical elementary current representation using a novel inversion scheme.

Modeling multiorbital effects in Sr2IrO4 under strain and a Zeeman field

We present a comprehensive study of a three-orbital lattice model suitable for the layered iridate Sr2IrO4. Our analysis includes various on-site interactions (including Hubbard and Hund's) as well as compressive strain, and a Zeeman magnetic field. We use a self-consistent mean field approach with multiple order parameters to characterize the resulting phases. While in some parameter regimes the compound is well described by an effective J=1/2 model, in other regimes the full multiorbital description is needed. As a function of the compressive strain, we uncover two quantum phase transitions: first a continuous metal-insulator transition, and subsequently a first order magnetic melting of the antiferromagnetic order. Crucially, bands of both J=1/2 and J=3/2 nature play important roles in these transitions. Our results qualitatively agree with experiments of Sr2IrO4 under strain induced by a substrate, and motivate the study of higher strains.