Quantum transport through 3D Dirac materials

Bismuth and its alloys provide a paradigm to realize three dimensional materials whose low-energy effective theory is given by Dirac equation in 3+1 dimensions. We study the quantum transport properties of three dimensional Dirac materials within the framework of Landauer-B\"uttiker formalism. Charge carriers in normal metal satisfying the Schr\"odinger equation, can be split into four-component with appropriate matching conditions at the boundary with the three dimensional Dirac material (3DDM). We calculate the conductance and the Fano factor of an interface separating 3DDM from a normal metal, as well as the conductance through a slab of 3DDM. Under certain circumstances the 3DDM appears transparent to electrons hitting the 3DDM. We find that electrons hitting the metal-3DDM interface from metallic side can enter 3DDM in a reversed spin state as soon as their angle of incidence deviates from the the direction perpendicular to interface. However the presence of a second interface completely cancels this effect.Comment: compile with the .bbl file include

Stable local moments of vacancies and hollow-site impurities in graphene

Taking into account the possibility of a p-wave hybridization function $V(\vec k)$ of ad-atom with Dirac electrons in graphene -- which arises for vacancies and hollow-site impurities -- we study the nature of magnetic moment formation within the single impurity Anderson model (SIAM). Compared to the s-wave hybridization function, we find that the local moments formed within the Hartree mean field are robust against the change in the parameters of the model. Further we investigate the stability of the local moments with respect to quantum fluctuations by going beyond the Hartree approximation. We find that for parameter regimes where local moments formed by top-site ad-atoms are completely washed out by quantum fluctuations, those formed by vacancies (or hollow-site impurities) survive the quantum fluctuations captured by post-Hartree approximation. Hence vacancies and hollow-site ad-atoms are suitable candidates to produce stable local moments.Comment: 7 page, 6 figure

Dynamical Mean Field Theory equations on nearly real frequency axis

The Iterated Perturbation Theory (IPT) equations of the Dynamical Mean Field Theory (DMFT) for the half-filled Hubbard model, are solved on nearly real frequencies at various values of the Hubbard parameters $U$, to investigate the nature of metal-insulator transition (MIT) at finite temperatures. This method avoids the instabilities associated with the infamous Pad\'e analytic continuation and reveals fine structures across the MIT at finite temperatures, which {\em can not be captured} by conventional methods for solving DMFT equations on Matsubara frequencies. Our method suggests that at finite temperatures, there is an abrupt decrease in the height of the quasi-particle (Kondo) peak at a critical value of $U_c$, to a non-zero but small bump which gradually suppresses as one moves deeper into the {\em bad} insulator regime. In contrast to Vollhardt and coworkers [J. Phys. Soc. Jpn. {\bf 74} (2005) 136], down to $T=0.01$ of the half-bandwidth we find no $T^*$ separating bad insulator from a true Mott insulator.Comment: revisions corresponding to adding a new Fig.

Reply to "Comment on Anderson Transition in Disordered Graphene"

We show that the very small numeric effects discussed in the comment by Schleede et al (arXiv:1005.0497) is not the source of mobility edge predicted in graphene in our letter [Eur. Phys. Lett., 87 (2009) 37002].Comment: two pages, two figure

Neutral Triplet Collective Mode in Doped Graphene

Particle-hole continuum in Dirac sea of graphene has a unique window underneath, which provides a unique opportunity for emergence of a pole in the susceptibility of the {\em triplet} particle-hole channel in the entire Brillouin zone (BZ). Here we use random phase approximation (RPA) to study such collective mode at zero temperature, in a single layer of doped graphene. We find that due to the chiral nature of one-particle states, in undoped graphene, the wave function overlap factors do not lead to qualitative differences, while in doped graphene they will kill small momentum part of the branch of magnetic excitations by pushing it to touch the lower part of the continuum. The pole corresponding to magnetic excitations survives for for larger momenta in the BZ.Comment: major revision

Localized magnetic states in three dimensional Dirac solids

Formation of localized magnetic states in a metallic host is a classic problem ofcondensed matter physics formalized by P. W. Anderson within the so called single impurity Anderson model (SIAM). The general picture in a host of a simple one-band metal is that a large Hubbard $U$ in the impurity orbital is pre-requisite for the formation of localized magnetic states. In recent years three dimensional (3D) Dirac solids have emerged the hallmark of which is strong spin-orbit interaction. In this work we show that such a strong spin-orbit interaction allows to form localized magnetic states even with small values of Hubbard $U$. This opens up the fascinating possibility of forming magnetic states with $s$ or $p$ orbital impurities -- different from traditional paradigms of $d$ or $f$ orbital based magnetic moments

Effects of coating rate on morphology of copper surfaces

We have used standard fractal analysis and Markov approach to obtain further insights on roughness and multifractality of different surfaces. The effect of coating rates on generating topographic rough surfaces in copper thin films with same thickness has been studied using atomic force microscopy technique (AFM). Our results show that by increasing the coating rates, correlation length (grain sizes) and Markov length are decreased and roughness exponent is decreased and our surfaces become more multifractal. Indeed, by decreasing the coating rate, the relaxation time of embedding the particles is increased

Spin Hall effect originated from fractal surface

Spin hall effect (SHE) in thin films is inherited by surface roughness. Although roughness effect on SHE has been studied in thin films, but roughness is not only parameter in rough surfaces. Our results show that how other statistical parameters of rough surface play important role in SHE. In this paper we investigate theoretically the effects of correlated surface roughness in the SHE with self affine fractal surface in non-heavy metallic thin films in the frame work of the Born approximation. The surface roughness is described by the k-correlation model and is characterized by the roughness exponent H (0 <= H <= 1), the in plane correlation length kesi and the rms roughness amplitude delta. We show that the spin Hall angle can increase by one order of magnitude when H decreasing from H = 1 to H = 0. We also demonstrate the SHE for surface roughness with distribution function of the Gaussian profile is mainly contributed by the side jump scattering while for that with a non-Gaussian profile, both side jump and skew scattering are present. our achievements demonstrate the important role of roughness texture profile for SHE in non-heavy metals.Comment: 15 pages,7 figure

Assessment of petrophysical quantities inspired by joint multifractal approach

In this paper joint multifractal random walk approach is carried out to analyze some petrophysical quantities for characterizing the petroleum reservoir. These quantities include Gamma emission (GR), sonic transient time (DT) and Neutron porosity (NPHI) which are collected from four wells of a reservoir. To quantify mutual interaction of petrophysical quantities, joint multifractal random walk is implemented. This approach is based on the mutual multiplicative cascade notion in the multifractal formalism and in this approach $L_0$ represents a benchmark to describe the nature of cross-correlation between two series. The analysis of the petrophysical quantities revealed that GR for all wells has strongly multifractal nature due to the considerable abundance of large fluctuations in various scales. The variance of probability distribution function, $\lambda_{\ell}^2$, at scale $\ell$ and its intercept determine the multifractal properties of the data sets sourced by probability density function. The value of $\lambda_0 ^2$ for NPHI data set is less than GR's, however, DT shows a nearly monofractal behavior, namely $\lambda_0 ^2\rightarrow 0$, so we find that $\lambda_0^2({\rm GR})>\lambda_0^2({\rm NPHI})\gg\lambda_0^2({\rm DT})$. While, the value of Hurst exponents can not discriminate between series GR, NPHI and DT. Joint analysis of the petrophysical quantities for considered wells demonstrates that $L_0$ has negative value for GR-NPHI confirming that finding shaly layers is in competition with finding porous medium while it takes positive value for GR-DT determining that continuum medium can be detectable by evaluating the statistical properties of GR and its cross-correlation to DT signal.Comment: 13 pages, 5 figures and 3 table

Analytical expression for wave scattering from exponential height correlated rough surfaces

Wave scattering from rough surfaces in addition the inverse scattering is an interesting approach to obtain the surface topography properties in various fields. Analytical expression in wave scattering from some known rough surfaces, not only help us to understand the scattering phenomena, but also would prove adequate to be a criterion to measure the information for empirical rough surfaces. For a rough surface with an exponential height correlation function, we derive an analytical expression for the diffused part and expanded it in two asymptotic regimes. We consider one surface as slightly rough and the other as very rough based on the framework of the Kirchhoff theory. In the end, we have measured the role of various Hurst exponents and correlation lengths on scattering intensity in self-affine surfaces. We have shown that by increasing the Hurst exponent from H=0 to H=1, the diffuse scattering decreases with the scattering angle.Comment: 13 pages, 4 figure