Type Spin Orbit Research Articles

Mimicing the Kane-Mele type spin orbit interaction by spin-flexual phonon coupling in graphene devices

Mimicing the Kane-Mele type spin orbit interaction by spin-flexual phonon coupling in graphene devices

Photoprotected spin Hall effect on graphene with substrate induced Rashba spin–orbit coupling

We propose an experimental realization of the spin Hall effect in graphene by illuminating a graphene sheet on top of a substrate with circularly polarized monochromatic light. The substrate induces a controllable Rashba type spin–orbit coupling which breaks the spin-degeneracy of the Dirac cones but it is gapless. The circularly polarized light induces a gap in the spectrum and turns graphene into a Floquet topological insulator with spin dependent edge states. By analyzing the high and intermediate frequency regimes, we find that in both parameter limits, the spin-Chern number can be tuned by the effective coupling strength of the charge particles to the radiation field and determine the condition for the photoinduced topological phase transition.

Spin Filtering Magnetoresistance in Double‐Well Resonant Structures

A new type of spin filtering mechanism is proposed and experimental evidence for the function of filtering is presented. The mechanism utilizes both Rashba and Dresselhaus type spin–orbit interactions. The present device has an advantage that spin‐polarized electrons can be injected not only into lateral transport devices but also into vertical transport devices like resonant tunneling diodes. Such applicability to vertical type devices also provides possibility to gain robustness to the temperatures.

Weyl type spin–orbit coupled ferromagnetic Bose–Einstein condensates under rotation

We investigate the ground state of ferromagnetic Bose–Einstein condensates with Weyl type spin–orbit coupling and rotation. When the spin–orbit coupling is strong, the ground state of the system exhibits square lattice phase for the non-rotation case, while two half-skyrmion chains can occur, which is perpendicular to each other, for the rotation case. For the weak spin–orbit coupling case, half-skyrmion displays the symmetrical arrangement around Mermin–Ho vortex at the center of condensates as the rotation frequency is increased. Moreover, the effects of spin-independent and spin-dependent interactions on the ground state are also studied.

Effect of Rashba Spin–Orbit Interaction on the Stability of Spin-Vortex-Induced Loop Current in Hole-Doped Cuprate Superconductors: A Scenario for the Appearance of Magnetic Field Enhanced Charge Order and Fermi Surface Reconstruction

Rashba type spin–orbit interaction is included in the model Hamiltonian for the spin-vortex-induced loop current (SVILC) mechanism of superconductivity for hole doped cuprate superconductors and it...

Effect of Rashba type spin–orbit interaction on the electronic spectrum of graphene in the presence of a hydrogenic impurity

The effect of Rashba spin–orbit interaction on the electronic spectrum of gapped graphene with a hydrogenic impurity in the presence of topological defects is analyzed analytically. Degenerate perturbation theory is used to investigate the dependence of electronic spectrum of gapped graphene on the strengths of impurity and Rashba spin–orbit coupling. The results show that, as the strength of Rashba spin–orbit coupling increases, pseudo-Zeeman splitting of energy levels induced by topological defects is enhanced. Therefore, it is possible to tune this pseudo-Zeeman splitting through the strength of Rashba spin–orbit coupling and of the strength of hydrogenic impurity.

Weak localization of bismuth cluster-decorated graphene and its spin\u2013orbit interaction

Weak-localization (WL) measurements were performed in a Bi cluster-decorated graphene sheet. The charge concentration was kept constant, and the amplitude of the conductance correction was suppressed after the Bi-cluster deposition. Detailed WL data were obtained while the gate and temperature were changed. Using E. McCann’s formula, the spin-relaxation time was extracted, which was found to increase with the elastic scattering time. This is attributed to the Elliott–Yafet spin relaxation and Kane–Mele type spin–orbit coupling (SOC). The SOC strength was enhanced to 2.64 meV as a result of the first deposition. The coverage effect is discussed according to the measurement after the second deposition.

Symmetry reduction and boundary modes for Fe chains on an s-wave superconductor

We investigate the superconducting phases and boundary modes for a quasi-1D system formed by up to three Fe chains on an s-wave superconductor, motivated by a recent experiment. While the Rashba type spin–orbit coupling together with a magnetic ordering is necessary to drive the system to be of nontrivial topology, we show that the onsite spin–orbit term, inter-chain diagonal hopping couplings, and magnetic disorders in the Fe chains are crucial in determining the symmetry classes of superconducting phases, which can be topologically trivial or nontrivial in different parameter regimes. In general multiple low-energy Andreev bound states, as well as a single Majorana zero mode if the phase is topological, are obtained in the ends of Fe chains. The nontrivial symmetry reduction mechanism is uncovered to provide an understanding of the present results, and may explain the zero-bias peak observed in the experiment. The present study can be applied to generic multiple-chain system.

Possible polaron formation of zigzag graphene nano-ribbon in the presence of Rashba spin–orbit coupling

In this article we study the role of Rashba spin–orbit coupling and electron–phonon interaction on the electronic structure of zigzag graphene nanoribbon with different width. The total Hamiltonian of nanoribbon is written in the tight binding form and the electron–electron interaction is modeled in the Hubbard term. We used a unitary transformation to reach an effective Hamiltonian for nano ribbon in the presence of electron–phonon interaction. Our results show that small Rashba spin orbit coupling annihilates the anti-ferromagnetic phase in the zigzag edges of ribbon and the electron–phonon interaction yields small polaron formation in graphene nano ribbon. Furthermore, Rashba type spin–orbit coupling increases (decreases) the polaron formation energy for up (down) spin state.

Weakly damped acoustic plasmon mode in transition metal dichalcogenides with Zeeman splitting

We analyze the effect of a strong Zeeman field on the spectrum of collective excitations of monolayer transition metal dichalcogenides. The combination of the Dresselhaus type spin orbit coupling and an external Zeeman field result in the lifting of the valley degeneracy in the valence band of these crystals. We show that this lifting of the valley degeneracy manifests in the appearance of an additional plasmon mode with linear in wavenumber dispersion along with the standard square root in wavenumber mode. Despite this novel mode being subject to the Landau damping, it corresponds to a well defined quasiparticle peak in the spectral function of the electron gas.

Spin dependent transport through triangular graphene quantum dot in the presence of Rashba type spin–orbit coupling

Electronic, magnetic and transport properties of a triangle graphene quantum dot have been studied in the presence of Rashba type spin–orbit coupling. The non-interacting part is written in the tight-binding model, and we use the Kene–Mele–Hubbard (KMH) Hamiltonian to describe the electron–electron and the Rashba spin–orbit interaction. While the Hubbard term split the spin up and down states, the Rashba term mixed these states. The competition between these two effects produces an interesting situation in a nano-device. Our results indicate that the magnetization of zigzag edge and spin coherence are decreased due to the Rashba spin–orbit interaction in the triangle graphene quantum dot. It is shown that the reduction of spin coherence is non-negligible even in the case of weak Rashba spin–orbit interaction.

Efficacy and safety of perindopril arginine + amlodipine in hypertension

Electronic, magnetic and transport properties of a triangle graphene quantum dot have been studied in the presence of Rashba type spin–orbit coupling. The non-interacting part is written in the tight-binding model, and we use the Kene–Mele–Hubbard (KMH) Hamiltonian to describe the electron–electron and the Rashba spin–orbit interaction. While the Hubbard term split the spin up and down states, the Rashba term mixed these states. The competition between these two effects produces an interesting situation in a nano-device. Our results indicate that the magnetization of zigzag edge and spin coherence are decreased due to the Rashba spin–orbit interaction in the triangle graphene quantum dot. It is shown that the reduction of spin coherence is non-negligible even in the case of weak Rashba spin–orbit interaction.

Spin-dependent thermoelectric properties of a Kondo-correlated quantum dot with Rashba spin–orbit coupling

Thermoelectric transport phenomena in a single-level quantum dot coupled to ferromagnetic leads are considered theoretically in the Kondo regime. The dot is described by the Anderson model with Rashba type spin–orbit interactions. The finite-U mean field slave boson technique is used to describe transport characteristics, such as the heat conductance, thermopower and thermoelectric efficiency (figure of merit). The role of quantum interference effects in the thermoelectric parameters is also analyzed.

Pseudo-Spin–Orbit Coupling in Graphene within Hydrogenic Impurity Context

In graphene, we report the first theoretical demonstration of how the intrinsic spin orbit interaction can be deduced from the theory and how it can be controlled by tuning a uniform magnetic field, and/or by changing the strength of a long range Coulomb like impurity (adatom), as well as gap parameter. In the impurity context, we find that intrinsic spin-orbit interaction energy may be enhanced by increasing the strength of magnetic field and/or by decreasing the band gap mass term. Additionally, it may be strongly enhanced by increasing the impurity strength. Furthermore, from the proposal of Kane and Mele [Phys. Rev. Lett. 95, 226801 (2005)], it was discussed that the pristine graphene has a quantized spin Hall effect regime where the Rashba type spin orbit interaction term is smaller than that of intrinsic one. Our analysis suggest the nonexistence of such a regime in the ground state of flat graphene.

Superconductivity with Rashba spin–orbit coupling and magnetic field

Two-dimensional electron systems at oxide interfaces are often influenced by a Rashba type spin–orbit coupling, which is tunable by a transverse electric field. Ferromagnetism near the interface can simultaneously induce strong local magnetic fields. This combination of spin–orbit coupling and magnetism leads to asymmetric two-sheeted Fermi surfaces, on which either intra- or inter-band pairing is favored. The superconducting order parameters are derived within a microscopic pairing model realizing both the Bardeen–Cooper–Schrieffer superconductor with inter-band pairing and a mixed parity state with finite-momentum intra-band pairing. We present a phase diagram for the superconducting groundstates and analyze the density of states, the spectra, and the momentum distribution functions of the different phases. The results are discussed in the context of superconductivity and ferromagnetism at LaAlO3–SrTiO3 interfaces and superconductors with broken inversion symmetry.

Magnetic impurity affected by spin-orbit coupling: Behavior near a topological phase transition

We investigate the effect of spin-orbit coupling on the behavior of a magnetic impurity at the edge of a zigzag graphene ribbon by means of quantum Monte Carlo simulations. A peculiar interplay of Kane-Mele type spin-orbit and impurity-host coupling is found to greatly affect properties for the local moment. The local characters of the impurity are mainly dominated by the local density of states at the edge, such as double occupancy, magnetic moment, and spin susceptibilities. The special helical nature of the topological insulator on the boundary is found to affect nonlocal quantities, such as the two-particle and spin-spin correlation functions linking electrons on the impurity with those in the conduction band; in particular, due to the spin-orbit coupling, the symmetry of the spin rotation in the Kondo cloud around the impurity is partly broken.

Nitrogen doping of CVD multiwalled carbon nanotubes: Observation of a large g-factor shift

Nitrogen doped multi-walled carbon nanotubes (N-CNTs) and undoped multi-walled carbon nanotubes (MWCNTs) were synthesized by a chemical vapour deposition (CVD) floating catalyst method. The N-CNTs were synthesized by the decomposition of a ferrocene/N-source/toluene (N-source = triethylamine, dimethylamine, acetonitrile) mixture at 900 °C. The undoped MWCNTs were synthesized using a ferrocene–toluene mixture without a nitrogen source under similar reaction conditions. The structure of the N-CNTs and MWCNTs was ascertained using HRTEM, SEM and Raman spectroscopy. Systematic ESR measurements of the carbon products produced, in the temperature range of 293–400 K showed line widths that were in general very large ∼ kOe. Most importantly, a large g-factor shift in samples of N-CNTs from that of the free electron g-factor was observed. Further, the shift increased with increasing temperature. The large g shift has been analysed in terms of Elliott-Wagoner and Bottleneck models. The temperature dependence of the g shift in the N-CNT samples rules out the Elliott-Wagoner type spin–orbit coupling scenario. The large g shift and temperature dependence can be qualitatively explained in terms of the Bottleneck model.

Ginzburg-Landau theory of noncentrosymmetric superconductors

The data of temperature dependent superfluid density $n_s(T)$ in Li$_2$Pd$_3$B and Li$_2$Pt$_3$B [Yuan {\it et al.}, \phrl97, 017006 (2006)] show that a sudden change of the slope of $n_s (T)$ occur at slightly lower than the critical temperature. Motivated by this observation, we microscopically derive the Ginzburg-Landau (GL) equations for noncentrosymmetric superconductors with Rashba type spin orbit interaction. Cooper pairing is assumed to occur between electrons only in the same spin split band and pair scattering is allowed to occur between two spin split bands. The GL theory of such a system predicts two transition temperatures, the higher of which is the conventional critical temperature $T_c$ while the lower one $T^*$ corresponds to the cross-over from a mixed singlet-triplet phase at lower temperatures to only spin-singlet or spin-triplet (depending on the sign of the interband scattering potential) phase at higher temperatures. As a consequence, $n_s (T)$ shows a kink at this cross-over temperature. We attribute the temperature at which sudden change of slope occurs in the observed $n_s (T)$ to the temperature $T^*$. This may also be associated with the observed kink in the penetration depth data of CePt$_3$Si. We have also estimated critical field near critical temperature.

Charge transport in normal metal/ [formula omitted]-wave superconductor junctions with Rashba type spin–orbit coupling

We study charge transport in normal metal/ s + p -wave superconductor (S+P) junctions with Rashba type spin–orbit coupling (RSOC). Applying the Blonder–Tinkham–Klapwijk theory, we calculate a bias ( V ) dependence of tunneling conductance, changing the strength of RSOC and Δ p / Δ s . Here Δ s ( p ) is the absolute value of pair potential of S(P) component. For Δ p < Δ s , a gap structure appears ranging from eV = 0 to eV = | Δ s - Δ p | , and a coherent peak appears at eV = | Δ s + Δ p | . For Δ p > Δ s , a zero bias conductance peak (ZBCP) is formed, a dip structure appears at | Δ s - Δ p | , and a weak coherent peak appears at eV = | Δ s + Δ p | . For large RSOC, a weak peak appears at eV = | Δ s - Δ p | because of RSOC. The bias dependence of conductance depends on the ratio Δ p / Δ s and changes qualitatively at Δ p / Δ s = 1 . For Δ p > Δ s , | Δ s - Δ p | can be estimated from a width of ZBCP. For Δ s > Δ p , Δ s and Δ p can be estimated from the gap structure and the coherent peak. Thus, the magnitude of gaps can be determined from the experiment of scanning tunneling spectroscopy.