Effect Of Magnetic Impurities Research Articles

Enhancing Emission via Radiative Lifetime Manipulation in Ultrathin InGaN/GaN Quantum Wells: The Effects of Simultaneous Electric and Magnetic Fields, Thickness, and Impurity.

Ultra-thin quantum wells, with their unique charge confinement effects, are essential in enhancing the electronic and optical properties crucial for optoelectronic device optimization. This study focuses on theoretical investigations into radiative recombination lifetimes in nanostructures, specifically addressing both intra-subband (ISB: e-e) and band-to-band (BTB: e-hh) transitions within InGaN/GaN quantum wells (QWs). Our research unveils that the radiative lifetimes in ISB and BTB transitions are significantly influenced by external excitation, particularly in thin-layered QWs with strong confinement effects. In the case of ISB transitions (e-e), the recombination lifetimes span a range from 0.1 to 4.7 ns, indicating relatively longer durations. On the other hand, BTB transitions (e-hh) exhibit quicker lifetimes, falling within the range of 0.01 to 1 ns, indicating comparatively faster recombination processes. However, it is crucial to note that the thickness of the quantum well layer exerts a substantial influence on the radiative lifetime, whereas the presence of impurities has a comparatively minor impact on these recombination lifetimes. This research advances our understanding of transition lifetimes in quantum well systems, promising enhancements across optoelectronic applications, including laser diodes and advanced technologies in detection, sensing, and telecommunications.

Effect of Gd magnetic impurities on the superconducting properties of highly disordered molybdenum nitride microstrips

Effect of Gd magnetic impurities on the superconducting properties of highly disordered molybdenum nitride microstrips

Anomalous Hall effect from a non-Hermitian viewpoint

Non-Hermitian descriptions often model open or driven systems away from the equilibrium. Nonetheless, in equilibrium electronic systems, a non-Hermitian nature of an effective Hamiltonian manifests itself as unconventional observables such as a bulk Fermi arc and skin effects. We theoretically reveal that spin-dependent quasiparticle lifetimes, which signify the non-Hermiticity of an effective model in the equilibrium, induce the anomalous Hall effect, namely the Hall effect without an external magnetic field. We first examine the effect of nonmagnetic and magnetic impurities and obtain a non-Hermitian effective model. Then, we calculate the Kubo formula from the microscopic model to ascertain a non-Hermitian interpretation of the longitudinal and Hall conductivities. Our results elucidate the vital role of the non-Hermitian equilibrium nature in the quantum transport phenomena.

Tunable correlation effects of magnetic impurities by cubic Rashba spin-orbit coupling

We theoretically study the influence of the $k$-cubic Rashba spin-orbit coupling (SOC) on the correlation effects of magnetic impurities by combining the variational method and the Hirsch-Fye quantum Monte Carlo (HFQMC) simulations. Markedly different from the normal $k$-linear Rashba SOC, even a small cubic Rashba term can greatly alter the band structure and induce a Van Hove singularity in a wide range of energy; thus, the single impurity local moment becomes largely tunable. The cubic Rashba SOC adopted in this paper breaks the rotational symmetry, but the host material is still invariant under the operations ${\mathcal{R}}^{z}(\ensuremath{\pi}), {\mathcal{IR}}^{z}(\ensuremath{\pi}/2), {\mathcal{M}}_{xz}, {\mathcal{M}}_{yz}$, where ${\mathcal{R}}^{z}(\ensuremath{\theta})$ is the rotation of angle $\ensuremath{\theta}$ about the $z$ axis, $\mathcal{I}$ is the inversion operator, and ${\mathcal{M}}_{xz}$ (${\mathcal{M}}_{yz}$) is the mirror reflection about the $x\text{\ensuremath{-}}z$ ($y\text{\ensuremath{-}}z$) principal plane. Saliently, various components of spin-spin correlation between the single magnetic impurity and the conduction electrons show three- or sixfold rotational symmetry. This unique feature is due to the triple winding of the spins with a $2\ensuremath{\pi}$ rotation of $\mathbf{k}$, which is a hallmark of the cubic Rashba effect, and can possibly be an identifier to distinguish the cubic Rashba SOC from the normal $k$-linear Rashba term in experiments. Although the cubic Rashba term drastically alters the electronic properties of the host, we find that the spatial decay rate of the spin-spin correlation function remains essentially unchanged. Moreover, the carrier-mediated Ruderman-Kittel-Kasuya-Yosida interactions between two magnetic impurities show twisted features, the ferromagnetic diagonal terms dominate when two magnetic impurities are very close, but the off-diagonal terms become important at long distances.

Emergent quantum transport due to quenched magnetic impurity scattering by antiferromagnetic proximity in SrCuO2/SrIrO3

Through an antiferromagnetic proximity effect, we demonstrate the evidence for quenched magnetic impurity scattering in a spin-orbit-coupled semimetal ${\mathrm{SrIrO}}_{3}$ proximitized with an antiferromagnetic ${\mathrm{SrCuO}}_{2}$ layer from quantum interference originated magnetoconductance study. Two distinct observations, i.e., (i) enhanced effective phase coherence length (${l}_{\ensuremath{\phi}}$) and (ii) emergence of chiral-anomaly-induced topological response in longitudinal magnetoconductance ($\stackrel{P\vec}{B}||\stackrel{P\vec}{E}$), signify that the magnetic impurity scattering is suppressed in the ${\mathrm{SrCuO}}_{2}/{\mathrm{SrIrO}}_{3}$ bilayer. The quenching of magnetic impurity scattering is discussed in the framework of the antiferromagnetic proximity effect, which is originated from spin Andreev reflection at the ${\mathrm{SrCuO}}_{2}/{\mathrm{SrIrO}}_{3}$ interface. This work unfolds a practical means to circumvent the detrimental effect of unintended magnetic impurity scattering and preserve quantum phenomena in complex materials.

Effect of Magnetic Impurities on the Physical Properties of Cd3As2-Based Composites in Wide Temperature and Pressure Ranges

Effect of Magnetic Impurities on the Physical Properties of Cd3As2-Based Composites in Wide Temperature and Pressure Ranges

Single magnetic impurity effects in graphene based superconductors

The magnetic impurity effects and the existence of bound states (i.e. Yu-Shiba-Rusinov states) in superconductors have been a topic of great interest. Recently, the existence of Yu-Shiba-Rusinov states in graphene-based superconducting materials has been successfully observed in the laboratory. In this work, an effective Hamiltonian in real space is established to describe the superconducting state of graphene materials by considering a single magnetic impurity. Thus the Bogoliubov-de Gennes (BdG) equation is constructed and the self-consistency calculations of the superconducting order parameter are conducted. On this basis, the effects of magnetic impurities on graphene-like superconductors are investigated theoretically. The numerical results show that the Yu-Shiba-Rusinov state can only appear in the symmetry of the superconducting pair of the traditional <i>s</i>-wave coupling. The position and strength of the bound state are related to the magnetic moment of the impurity, showing a notable electron-hole asymmetry. There are no bound states in the energy gap for other pairing symmetries. This theoretical calculation not only provides a reasonable explanation for experimental phenomena, but also demonstrates that the heterojunction system composed of graphene and traditional superconductors has an <i>s</i>-wave superconducting pairing induced by the proximity effect in the graphene layer.

Effect of Fe Magnetic Impurity to the Crystal Structure and Magnetic Properties of Eu 1.83+y Ce 0.17−y Cu 1−y Fe y O 4+α−δ

In the overdoped regime of superconductors, both electron- and hole-doped superconductors exhibit intriguing phenomena like the Quantum Critical Point. Other phenomena, such as cooper-pair breaking and stripe pinning, can be observed by eliminating superconductivity by the addition of impurities. In this study, we investigate the crystal structure and magnetic properties of electron-doped superconducting cuprates of Eu2-x+y Ce x-y Cui1-y Fe y O4+α-δ in the overdoped regime of x = 0.17 for Ce doping with y = 0.005, 0.01 and 0.03 for Fe impurity. The material has a tetragonal T’ structure that matches the ECCO crystal structure, according to the XRD analysis of the crystal structure. The addition of magnetic impurity has no effect on the structure but does decrease the lattice parameter. SQUID was used to measure the magnetic susceptibility at low temperatures between 2 K and 30 K. The spin-glass was observed at y = 0.03, due to the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction as shown in a hole-doped system. Due to the significant contribution from the magnetic moment of the Fe ion, the addition of Fe concentrations increases the effective magnetic moment. The conduction layer’s spin correlation of Cu is dramatically disrupted by the addition of Fe, resulting in the breakage of the copper-pair and the elimination of superconductivity.

Effect of Magnetic Impurities on Superconductivity in LaH10.

Polyhydrides are a novel class of superconducting materials with extremely high critical parameters, which is very promising for sensor applications. On the other hand, a complete experimental study of the best so far known superconductor, lanthanum superhydride LaH10 , encounters a serious complication because of the large upper critical magnetic field HC2 (0), exceeding 120-160T. It is found that partial replacement of La atoms by magnetic Nd atoms results in significant suppression of superconductivity in LaH10 : each at% of Nd causes a decrease in TC by 10-11K, helping to control the critical parameters of this compound. Strong pulsed magnetic fields up to 68T are used to study the Hall effect, magnetoresistance, and the magnetic phase diagram of ternary metal polyhydrides for the first time. Surprisingly, (La,Nd)H10 demonstrates completely linear HC2 (T)∝|T -TC |, which calls into question the applicability of the Werthamer-Helfand-Hohenberg model for polyhydrides. The suppression of superconductivity in LaH10 by magnetic Nd atoms and the robustness of TC with respect to nonmagnetic impurities (e.g., Y, Al, C) under Anderson's theorem gives new experimental evidence of the isotropic (s-wave) character of conventional electron-phonon pairing in lanthanum decahydride.

Effect of magnetic impurity scattering on transport in topological insulators

Charge transport in topological insulators is primarily characterised by so-called topologically projected helical edge states, where charge carriers are correlated in spin and momentum. In principle, dissipation-less current can be carried by these edge states as backscattering from impurities and defects is suppressed as long as time-reversal symmetry is not broken. However, applied magnetic fields or underlying nuclear spin-defects in the substrate can break this time reversal symmetry. In particular, magnetic impurities lead to back-scattering by spin-flip processes. We have investigated the effects of point-wise magnetic impurities on the transport properties of helical edge states in the BHZ model using the Non-Equilibrium Green's Function formalism and compared the results to a semi-analytic approach. Using these techniques we study the influence of impurity strength and spin impurity polarization. We observe a secondary effect of defect-defect interaction that depends on the underlying material parameters which introduces a non-monotonic response of the conductance to defect density. This in turn suggests a qualitative difference in magneto-transport signatures in the dilute and high density spin impurity limits.

Perpendicularly Polarized Spin Hall Effects Induced by Spin-Dependent Scattering in Ferromagnetic Metals

Spin currents in ferromagnets afford diverse functionalities. We evaluate the extrinsic spin Hall effects of magnetic impurity scattering in ferromagnetic metals. We show that spin-dependent scattering can provide a high spin current polarized perpendicularly to the magnetization direction and is a dominant mechanism in the moderate-conductivity regime. We find that the superposition of the spin-conserve and spin-flip channels causes the spin currents. These findings suggest that optimizing alloy composition is an effective strategy to control the spin Hall effect.

Unveiling the hybridization between the Cr-impurity-mediated flat band and the Rashba-split state of the α-Au/Si(111) surface.

Adsorption of foreign atoms onto 2D materials can either lead to ordinary electron doping or the emergence of new electronic effects including topology, superconductivity, and quantum anomalous Hall and Kondo states. We have investigated the effect of Cr doping on the electronic structure of the α-Au/Si(111)- surface and its adsorbate-modified family. It has been found that below a critical coverage of ∼0.05 monolayer, Cr adatoms penetrate beneath the Au and topmost Si layers and induce the occupied resonance flat band in the electronic spectrum as revealed by angle-resolved photoelectron spectroscopy. Further deposition of Cr leads to the growth of the 3D islands spoiling the surface homogeneity. Using density functional theory calculations, we have disclosed the effects of Cr doping on the electronic band structure and revealed the nature of hybridization between the Cr-induced magnetic-split band and the Au-induced Rashba-split surface state. We believe that the synthesized 2D phases and electronic effects produced by magnetic atom doping in the ultimate two-dimensional limit will stimulate further investigations related to the highly correlated phases and will find practical applications in nanoelectronic devices.

Electron scattering by magnetic impurity in Weyl semimetals

Weyl semimetals are prominent examples of topologically protected quantum matter. These materials are the three-dimensional counterparts of graphene and great efforts are being devoted to achieve a thorough understanding of their fundamental physics. In this work, we aim at contributing to this end by discussing the effect of a single magnetic impurity in Weyl semimetals as a first step towards considering a larger number of point-like impurities. We find that resonances appear in the local density of states (LDOS) with a Friedel-like behaviour, oscillating as a function of distance. By studying the spin-resolved LDOS, we can observe non-trivial and anisotropic spin textures where the spin components perpendicular to the spin of the impurity wind around the latter, until the spin becomes completely parallel to the impurity right at the impurity’s location. Friedel oscillations also play a relevant role in the form of the spin textures, forming an oscillatory pattern. We believe our results can pave the way to further studies which consider the presence of a large number of random magnetic impurities.

The Effect of Partial Substitution of Non-Magnetic Impurity Zn on the Magnetic Moments of Eu<sub>1.88</sub>Ce<sub>0.12</sub>Cu<sub>1-y</sub>Zn<sub>y</sub>O<sub>4+α-δ</sub>

Structure and magnetic properties of electron-doped superconducting cuprates have been investigated in order to study the effect of magnetic impurity to its physical properties. Here, we reported structure and magnetic properties of Eu1.88Ce0.12Cu1-yZnyO4+α-δ (ECCZO) with y = 0 and 0.03. The properties of ECCZO have been studied from X-ray diffraction data and temperature dependence of magnetic susceptibility data, to elucidate the effect of partial substitution of non-magnetic impurity Zn for Cu to its structure, Tc and the value of magnetic moments per unit volume extracted from susceptibility data in normal state. Magnetic-susceptibility measurements were carried out down to 2 K on-field cooling at 5 Oe for Eu1.88Ce0.12Cu1-yZnyO4+a-d with y = 0 and 0.03. For ECCZO sample with y = 0 and d = 0.0669 indicated the change of magnetic behavior from paramagnetic to diamagnetic below 12 K which is addressed to the Tc onset of this samples. Diamagnetic behavior is observed starting from about 12 K. Above 12 K, all samples show paramagnetic behavior with the values of the magnetic moment in every volume unit increased with increasing Zn.

Spin Symmetry Breaking: Superparamagnetic and Spin Glass-Like Behavior Observed in Rod-Like Liquid Crystalline Organic Compounds Contacting Nitroxide Radical Spins

Liquid crystalline (LC) organic radicals were expected to show a novel non-linear magnetic response to external magnetic and electric fields due to their coherent collective molecular motion. We have found that a series of chiral and achiral all-organic LC radicals having one or two five-membered cyclic nitroxide radical (PROXYL) units in the core position and, thereby, with a negative dielectric anisotropy exhibit spin glass (SG)-like superparamagnetic features, such as a magnetic hysteresis (referred to as ‘positive magneto-LC effect’), and thermal and impurity effects during a heating and cooling cycle in weak magnetic fields. Furthermore, for the first time, a nonlinear magneto-electric (ME) effect has been detected with respect to one of the LC radicals showing a ferroelectric (chiral Smectic C) phase. The mechanism of the positive magneto-LC effect is proposed and discussed by comparison of our experimental results with the well-known magnetic properties of SG materials and on the basis of the experimental results of a nonlinear ME effect. A recent theoretical study by means of molecular dynamic simulation and density functional theory calculations suggesting the high possibility of conservation of the memory of spin-spin interactions between magnetic moments owing to the ceaseless molecular contacts in the LC and isotropic states is briefly mentioned as well.

Metallic islands in the Kondo insulator SmB6

The authors study the effects of magnetic impurities in a Kondo insulator and demonstrate that the Kondo insulating state is destroyed locally around impurities.

Magnetic and thermodynamic properties of GaAs quantum dot confined by parabolic-inverse square plus gaussian potential

The effects of magnetic field, temperature, potential parameters and impurity on the magnetic and thermodynamic properties of GaAs quantum dot confined by the parabolic-inverse square plus Gaussian potential are investigated. The Hamiltonian of the system is solved within the effective-mass approach and energy levels are obtained. The results show that temperature, magnetic field, potential parameters and impurity have a great influence on the magnetic and thermodynamic properties of the structure.

Magnetic impurities in thin films and 2D Ising superconductors

In the theory of dilute magnetic impurities in superconductors, the effect of all impurity spin-components is expressed via a single magnetic scattering rate Γm. In a more realistic setting, magnetic impurities are anisotropic. In this case, the spatial randomness of three spin-components of impurities gives rise to generally different scattering rates Γi (i=1,2,3). We explore the effects of anisotropic magnetic impurities on the in-plane critical field in 2D superconductors. We discuss singlet, triplet, and parity-mixed order parameters allowed in systems without the inversion center. Also, the addition of a small amount of magnetic impurities may cause singlet to triplet crossovers. In all cases, different components of impurity spin affect the magnetic field—temperature phase diagram differently. We show that anisotropy of the magnetic impurities can serve as a probe of unconventional triplet or parity-mixed superconductivity.

Robust Gapless Surface State against Surface Magnetic Impurities on (Bi_{0.5}Sb_{0.5})_{2}Te_{3} Evidenced by InSitu Magnetotransport Measurements.

Despite extensive experimental and theoretical efforts, the important issue of the effects of surface magnetic impurities on the topological surface state of a topological insulator (TI) remains unresolved. We elucidate the effects of Cr impurities on epitaxial thin films of (Bi_{0.5}Sb_{0.5})_{2}Te_{3}: Cr adatoms are incrementally deposited onto the TI held in ultrahigh vacuum at low temperatures, and insitu magnetoconductivity and Hall effect measurements are performed at each increment with electrostatic gating. In the experimentally identified surface transport regime, the measured minimum electron density shows a nonmonotonic evolution with the Cr density (n_{Cr}): it first increases and then decreases with n_{Cr}. This unusual behavior is ascribed to the dual roles of the Cr as ionized impurities and electron donors, having competing effects of enhancing and decreasing the electronic inhomogeneities in the surface state at low and high n_{Cr}, respectively. The magnetoconductivity is obtained for different n_{Cr} on one and the same sample, which yields clear evidence that the weak antilocalization effect persists and the surface state remains gapless up to the highest n_{Cr}, contrary to the expectation that the deposited Cr should break the time-reversal symmetry and induce a gap opening at the Dirac point.

Effect of Magnetic Impurities on Superfluid ^{3}He.

It is known that both magnetic and nonmagnetic impurities suppress unconventional superconductivity. Here we compare their effect on the paradigm unconventional superconductor, superfluid ^{3}He, using highly dilute silica aerogel. Switching magnetic to nonmagnetic scattering in the same physical system is achieved by coating the aerogel surface with ^{4}He. We find a marginal influence on the transition temperature itself. However, we have discovered that the A phase, which breaks time reversal symmetry, is strongly influenced, while the isotropic B phase is unchanged. Importantly, this occurs only if the impurities are anisotropically distributed on a global scale.