Quasiparticle states and quantum interference induced by magnetic impurities on a two-dimensional topological superconductor

We theoretically study the effect of localized magnetic impurities on two-dimensional topological superconductor (TSC). We show that the local density of states (LDOS) can be tuned by the effective exchange field m, the chemical potential μ of TSC, and the distance Δr as well as the relative spin angle α between two impurities. The changes in Δr between two impurities alter the interference and result in significant modifications to the bonding and antibonding states. Furthermore, the bound-state spin LDOS induced by single and double magnetic impurity scattering, the quantum corrals and the quantum mirages are also discussed. Finally, we briefly compare the impurities in TSC with those in topological insulators.     

Tail states in a superconductor with magnetic impurities

A field theoretic approach is developed to investigate the profile and spectrum of subgap states in a superconductor subject to a weak magnetic impurity potential. Such states are found to be associated with spatially inhomogeneous instanton configurations of the action.     

Persistent current induced by magnetic impurities

We calculate the average persistent current in a normal conducting, mesoscopic ring in the diffusive regime. In the presence of magnetic impurities, a contribution to the persistent current is identified, which is related to fluctuations in the electron spin density. Assuming a spin-flip scattering rate which is comparable to the Thouless energy E _c and low temperature, this new contribution to the persistent current is of the order I ～ E _c ² (kTφ₀), which is considerably larger than the persistent current induced by the electron-electron interaction.     

Spin-triplet superconductivity induced by off-site Coulomb interaction in a triangular lattice

In order to study how superconductivity emerges when the charge fluctuation coexists with the spin fluctuation in a triangular lattice, we obtain a phase diagram against the nearest-neighbor Coulomb repulsion V and band filling n on the extended Hubbard model using the fluctuation exchange (FLEX) approximation. We find that a charge density wave (CDW) phase exists in the region where the value of V is large, and the f-wave spin-triplet pairing mediated by a strong charge fluctuation is dominant near the CDW phase.     

A superconductor with 4-fermion attraction weakly perturbed by magnetic impurities

A superconductor with 4-fermion attraction, considered by Maćkowiak and Tarasewicz is modified by adding to the Hamiltonian a long-range magnetic interaction V between conduction fermions and localized distinguishable spin 1/2 magnetic impurities. V has the form of a reduced s-d interaction. An upper and lower bound to the system’s free energy density f(H, β) is derived and the two bounds are shown to coalesce in the thermodynamic limit. The resulting mean-field equations for the gap Δ and a parameter y, characterizing the impurity subsystem are solved and the solution minimizing f is found for various values of magnetic coupling constant g and impurity concentration. The phase diagrams of the system are depicted with five distinct phases: the normal phase, unperturbed superconducting phase, perturbed superconducting phase with nonzero gap in the excitation spectrum, perturbed gapless superconducting phase and impurity phase with completely suppressed superconductivity.     

Decoherence induced by magnetic impurities in a quantum hall system

Scattering by magnetic impurities is known to destroy coherence of electron motion in metals and semiconductors. We investigate the decoherence introduced in a single act of electron scattering by a magnetic impurity in a quantum Hall system. For this, we introduce a fictitious nonunitary scattering matrix for electrons that reproduces the exactly calculated scattering probabilities. The strength of decoherence is identified by the deviation of eigenvalues of the product from unity. Using the fictitious scattering matrix, we estimate the width of the metallic region at the quantum Hall effect inter-plateau transition and its dependence on the exchange coupling strength and the degree of polarization of magnetic impurities.     

On the theory of impurities in a lattice of magnetic ions: Crystalline field effects

We present a formalism for treating the problem of impurities in a lattice of magnetic rare earth ions. Latter are subject to a crystalline field and special attention is paid to non-Kramers ions in a singlet ground state. Our calculations are restricted to the paramagnetic regime. We derive the conditions for magnetic localized modes to occur and discuss the appearance of local magnetic instabilities. It is shown that the impurity effects are especially large if the system is close to a magnetic phase transition. Furthermore we compute the influence of impurities on the magnetic transition temperature. For the case of vacancies or nonmagnetic impurities the dependence of the Curie temperature on impurity concentration is derived. It is demonstrated that small amounts of impurities can often completely suppress magnetic ordering.     

Octupolar order in the multiple spin exchange model on a triangular lattice

We show how a gapless spin liquid with hidden octupolar order arises in an applied magnetic field, in a model applicable to thin films of 3He with competing ferromagnetic and antiferromagnetic (cyclic) exchange interactions. Evidence is also presented for nematic--i.e., quadrupolar--correlations bordering on ferromagnetism in the absence of a magnetic field.     

Homogeneous NMR line shift induced by magnetic doping in a superconductor

It is shown theoretically that a uniform conduction electron spin polarization, induced by magnetic doping, arises in a superconducting state. Measurements of the corresponding Knight shift enable one to determine the sign of the s-f exchange constant.     

Free energy of a strong-coupling superconductor with magnetic impurities in Shiba-Rusinov approximation

We evaluate numerically the free energy of a strong-coupling superconductor with paramagnetic impurities in the model of Shiba and Rusinov. Our work is based on a recent formula for the free energy given by Yamamoto and Nagi. This formula is based on the same fundamental expression as used by Schossmann and Schachinger but without their simplfying approximations. Our results are numerically quite different from the previous ones. It is still concluded, however, that the thermodynamic critical field is very sensitive to the model chosen to describe the scattering.     

Symmetry breaking induced by a magnetic field in a quasi-two-dimensional d-wave superconductor

A model of quasi-two-dimensional d-wave superconductor, with strong nesting properties of the Fermi surface is considered. The orbital effect of a moderate magnetic field applied perpendicularly to the conducting planes is studied in the mean field approximation. It is shown that the field can induce a time reversal symmetry breaking SDW order coexisting with the superconducting order and can open a gap over the whole Fermi surface. The anomalies recently observed in the heat conductivity in might be ascribed to this effect. Received 7 May 1999 and Received in final form 13 August 1999     

Tunable striped-patterns by lattice anisotropy and magnetic impurities in d-wave superconductors

The pattern transition induced by lattice anisotropy (LA) and magnetic impurities is computationally observed in near-optimally doped d-wave superconductors (DSCs). For the single impurity case, a transition from the checkerboard to stripe pattern can be induced by a very weak LA. For the two-impurity case, an orientation transition from the longitudinal stripe into transverse pattern is observed when the LA ratio reaches some critical value. At the critical point, the structures around impurities can restore checkerboard patterns. These results indicate that the formation of stripes in DSCs might induced by various effects, and could be tunable experimentally.     

Laplacian roughening on a triangular lattice

Monte Carlo simulation of the laplacian roughening model on a triangular lattice indicates that the model has a single first-order phase transition.     

双色场中钾原子的量子干涉现象

采用多态展开方法,对里德堡钾原子与双色场相互作用时诱发的量子干涉效应进行了研究计算,讨论和分析了布居数跃迁过程中的干涉相长及相消的原因.     

Transition temperature of a superconductor containing magnetic impurities in the spin fluctuation limit

Renormalization group techniques are used to calculate the transition temperature of a BCS-Superconductor containing magnetic impurities described by the symmetric one orbital Anderson model for small U/πΓ. The suppression of superconductivity is related to the static spin fluctuation susceptibility. Superconductivity is quenched above a critical impurity concentration c_cr = λ?²πΓ/[U_effχ(0)].     

Quantum brownian motion on a triangular lattice and c=2 boundary conformal field theory

We study a single particle diffusing on a triangular lattice and interacting with a heat bath, using boundary conformal field theory (CFT) and exact integrability techniques. We derive a correspondence between the phase diagram of this problem and that recently obtained for the 2-dimensional 3-state Potts model with a boundary. Exact results are obtained on phases with intermediate mobilities. These correspond to nontrivial boundary states in a conformal field theory with 2 free bosons which we explicitly construct for the first time. These conformally invariant boundary conditions are not simply products of Dirichlet and Neumann ones and unlike those trivial boundary conditions, are not invariant under a Heisenberg algebra.