Topological phase in a dx2−y2+(p+ip)d_{x^2-y^2}+(p+ip) superconductor in presence of spin-density-wave

We consider a mean-field Hamiltonian for a $d_{x^2-y^2}+(p+ip)$ superconductor(SC) in presence of spin-density-wave(SDW) order. This is due to the fact that the non-commutativity of any two orders produces the third one. The energy spectrum of such a Hamiltonian is shown to be gapped and it yields a topological phase in addition to the conventional one. A phase diagram characterizing different topological phases is construted. The Chern numbers and hence the nature of the topological phases are determined. The edge state spectrum and the possibility of whether the vortex state harbouring the zero modes are discussed.Comment: 5 pages, 3 figure

Effective Charge and Spin Hamiltonian for the Quarter-Filled Ladder Compound α′\alpha'-NaV2_2O5_5

An effective intra- and inter-ladder charge-spin hamiltonian for the quarter-filled ladder compound $\alpha'$-NaV$_2$O$_5$ has been derived by using the standard canonical transformation method. In the derivation, it is clear that a finite inter-site Coulomb repulsion is needed to get a meaningful result otherwise the perturbation becomes ill-defined. Various limiting cases depending on the values of the model parameters have been analyzed in detail and the effective exchange couplings are estimated. We find that the effective intra-ladder exchange may become ferromagnetic for the case of zig-zag charge ordering in a purely electronic model. We estimate the magnitude of the effective inter-rung Coulomb repulsion in a ladder and find it to be about one-order of magnitude too small in order to stabilize charge-ordering.Comment: Eur. Phys. J. B (submitted

A Generalized Ginzburg-Landau Approach to Second Harmonic Generation

We develop a generalized Ginzburg-Landau theory for second harmonic generation (SHG) in magnets by expanding the free energy in terms of the order parameter in the magnetic phase and the susceptibility tensor in the corresponding high-temperature phase. The non-zero components of the SHG susceptibility in the ordered phase are derived from the symmetries of the susceptibility tensor in the high-temperature phase and the symmetry of the order parameter. In this derivation, the dependence of the SHG susceptibility on the order parameter follows naturally, and therefore its nonreciprocal optical properties. We examine this phenomenology for the magnetoelectric compound Cr$_2$O$_3$ as well as for the ferroelectromagnet YMnO$_3$.Comment: European Journal of Physics B (accepted

Is Li2_2Pd3_3B a self-doped hole superconductor ?

We propose that the electrons responsible for superconductivity in Li2Pd3B come from the palladium 4d-electrons. So, its electronic properties are likely to be dominated by strong electronic correlations. The basic unit in this material are Pd$_6$B octahedra which share vertices to form a 3-dimensional network. Due to the highly distorted nature of the Pd$_6$B octahedron, one far stretched Pd atom per octahedra becomes almost inactive for electronic conduction. Thus, the material escapes the fate of becoming a half- filled insulating Mott antiferromagnet by hiding extra charges at these inactive Pd sites and becomes a self-doped correlated metal. We propose a 3-dimensional single band t-J model which could be the correct minimal model for this material.Comment: 4 pages Revtex, 2 figures included in the text, some typos corrected, some text and references adde

Hidden Quantum Critical Point in a Ferromagnetic Superconductor

We consider a coexistence phase of both Ferromagnetism and superconductivity and solve the self-consistent mean-field equations at zero temperature. The superconducting gap is shown to vanish at the Stoner point whereas the magnetization doesn't. This indicates that the para-Ferro quantum critical point becomes a hidden critical point. The effective mass in such a phase gets enhanced whereas the spin wave stiffness is reduced as compared to the pure FM phase. The spin wave stiffness remains finite even at the para-Ferro quantum critical point.Comment: 4 pages, Phys. Rev. B (Rapid) accepte

Formation of local moment near a static vacancy in the one-dimensional large-

The effect of non-magnetic impurities in the one-dimensional large-U Hubbard model has been studied. For a single non-magnetic scatterer, it is shown that a bound state is obtained which is due to the singular behaviour of the T-matrix. It has been argued that the bound state which yields a δ-function density of states might correspond to local moment in the system giving rise to Curie-like contribution to the susceptibility. The spatial dependence of the impurity state wave function is shown to follow an algebraic decay. Its possible relevance to some recently discovered one-dimensional antiferromagnets has been discussed

Chiral magnetic effect and Maxwell–Chern–Simons electrodynamics in Weyl semimetals

The Weyl semimetal, due to a non-zero energy difference in the pair of Weyl nodes, shows chiral magnetic effect (CME). This leads to a flow of dissipationless electric current along an applied magnetic field. Such a chiral magnetic effect in Weyl semimetals has been studied using the laws of classical electrodynamics. It has been shown that the CME in such a semimetal changes the properties namely, frequency-dependent skin depth, capacitive transport, plasma frequency, etc., in an unconventional way as compared to the conventional metals. In the low-frequency regime, the properties are controlled by a natural length scale due to CME called the chiral magnetic length. Furthermore, unlike the conventional metals, the plasma frequency in this case is shown to be strongly magnetic field-dependent. Since the plasma frequency lies below the optical frequency, the Weyl semimetals will look transparent. Such new and novel observations might help in exploiting these class of materials in potential applications which would completely change the future technology

Chiral magnetic effect in Weyl semimetals and negative refraction

The role of the chiral magnetic effect (CME) in Weyl semimetals is considered within the framework of classical electrodynamics. The dispersion relation of electromagnetic waves is studied using their helical polarization. It has been shown that the refractive index in this class of materials becomes negative in the frequency range below the plasma frequency. The CME (a signature of chiral anomaly/ axial anomaly) which is due to the application of parallel electric and magnetic fields in Weyl semimetals thus opens up a new way of realizing negative refractive index (NRI). The relevance of the present work to negative refraction through chiral route where cross polarization (magnetization) induced by magnetic fields (electric fields) occurs in chiral materials is discussed. This novel phenomenon of negative refraction in Weyl semimetals might help in exploiting this class of materials in potential applications