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D. Schmeltzer

Publications and source records attributed to D. Schmeltzer.

At least 19 recordsLinked to original sources
arXiv2019

Two body interactions induces the axion-phason field in Weyl semimetals

Following our results that the two-body interaction can induce a space and time dependent topological axion term $ \frac{e^2}{2π\hbar}θ(z,t)(\vec{E}\cdot\vec{B})$, we show that by applying this theory to a Weyl semimetal with two nodes in a magnetic field a one-dimensional sliding charge density wave (CDW) in agreement with the recent experimental finding of J. Gooth et al. [Nature, https://doi.org/10.1038/s41586-019-1630-4 (2019)]. We show that the theory is equivalent to a time and space dependent of the topological angle which represents the phason.

cond-mat.other↗
arXiv2019

Thermal conductance of an Edge mode

Thermoelectric conductance of an edge mode is investigated. The edge modes of a $2D $ and $3D$ two band model with parabolic dispersion is considered. For the the one dimensional non interacting fermions the thermal conductivity computed agrees with the result known from $Bosonization$ computations. In the presence of a magnetic field, backscattering is allowed and controls the value of the thermal conductivity. The thermal conductivity is obtained from the continuity equation of thermal current energy conservation. The thermal conductivity is computed introducing the $Scattering$ matrix for particles and anti-particles. At finite temperatures the backscattering is allowed, the electric conductance, the thermoelectric conductance and the thermal conductance decrease with the increase of the magnetic field. At finite temperatures, weak localization effects are small and can be ignored. We confirm the experimental results in a magnetic field for a $3D$ Topological Insulator. An experimental set-up was proposed to test our theory.

cond-mat.mes-hall↗
arXiv2019

Superconductivity in Graphene Induced by the Rotated Layer

Recent discoveries in graphene bilayers revealed that when one of the layers is rotated, superconductivity emerges. We provide an explanation for this phenomenon . We find that due to the layer rotations, the spinors are modified in such way that a repulsive interaction, becomes attractive in certain directions. This result is obtained following a sequence of steps: when layer $2$ is rotated by an angle $θ$ ,this rotation is equivalent to a rotation of an angle $-θ$ of the linear momentum .Due to the discreet lattice, in layer $1$, the Fourier transform conserves the linear momentum $modulo$ the hexagonal reciprocal lattice vector . In layer $2$, due to the rotation, the linear momentum is conserved $modulo$ the $Moire$ reciprocal lattice vector . Periodicity is achieved at the $magical $ angles obtained from the condition of commensuration of the two lattices. We find that the rotations transform the spinors around the nodal points, such that a repulsive interaction becomes attractive, giving rise to superconductivity.

cond-mat.mes-hall↗
arXiv2018

Thermal conductance of zero modes on the surface boundary of a Weyl semimetal

Thermoelectric conductance of Dirac materials and in particular zero modes reveals the effect of topology .Weyl semimetals with a boundary at z = 0 give rise to chiral zero modes with- out backscattering resulting in a significant contribution to thermal conductivity. By doping the surface with paramagnetic impurities backscattering is allowed, and the thermal conductivity is controlled by the decrease of the transmission function |t|^{2} < 1. We attach a thermal reservoir at the edge of the sample and study the thermal and electrical conductance. For the ballistic and mesoscopic situations, quantum uctuations causes oscillations of the thermal and electric conduc- tance. The thermoelectric conductance varies periodically with the voltage bias. We compare the thermal conductance with and without impurity scattering and observe the effects of topology. An experimental set-up is proposed to test this theory. 1Thermoelectric conductance of Dirac materials and in particular zero modes reveals the effect of topology .Weyl semimetals with a boundary at z = 0 give rise to chiral zero modes with- out backscattering resulting in a significant contribution to thermal conductivity. By doping the surface with paramagnetic impurities backscattering is allowed, and the thermal conductivity is controlled by the decrease of the transmission function |t|^{2} < 1 . We attach a thermal reservoir at the edge of the sample and study the thermal and electrical conductance. For the ballistic and mesoscopic situations, quantum uctuations causes oscillations of the thermal and electric conduc- tance. The thermoelectric conductance varies periodically with the voltage bias. We compare the thermal conductance with and without impurity scattering and observe the effects of topology. An experimental set-up is proposed to test this theory.

cond-mat.mes-hall↗
arXiv2018

The $S$-matrix for surface boundary states: an application to photoemission for Weyl semimetals

We present a new theory of photoemission for Weyl semimetals. We derive this theory using a model with a boundary surface at $z=0$. Due to the boundary, the self adjoint condition needs to be verified in order to ensure physical solutions. The solutions are given by two chiral zero modes which propagate on the boundary. Due to the Coulomb interaction, the chiral boundary model is in the same universality class as interacting graphene. The interactions cause a temperature dependence of the velocity and and life time. \noindent Using the principle of minimal coupling, we identify the electron-photon Hamiltonian. The photoemission intensity is computed using the $S$-matrix formalism. The $S$-matrix is derived using the initial photon state, the final state of a photoelectron and a hole in the valence band. The photoemission reveals the final valence band dispersion $ \hbar v(\pm k_{y}-k_{0})+\hbarΩ$ after absorbing a photon of frequency $ Ω$ ($k_{0}$ represents the shift in the momentum due to the crystal potential). The momentum in the $z$ direction is not conserved, and is integrated out. As a result, the scattering matrix is a function of the parallel momentum . We observe two dimensional contours, representing the $^{"}$Fermi arcs $^{"}$, which for opposite spin polarization have opposite curvature. This theory is in agreement with previous experimental observations.

cond-mat.mes-hall↗
arXiv2016

Topological Insulators,Weyl Semimetals and Topological Superconductors A Transport View

The electronic bands are classified according to their topology. We compute the connection and curvature for the electronic bands and show that the physical properties are determined by topological invariants which are equivalent to the existence of the zero modes. We apply this method to the Topological Insulators and Topogical Superconductors.

cond-mat.mes-hall↗
arXiv2016

Weyl semimetals with a boundary at $z=0$ a photoemission study

We consider a Weyl semimetal with two nodes and derive the scattering Hamiltonian in the presence of a boundary at $z=0$. We compute the photoemission spectrum and demonstrate the presence of the Fermi arcs which connect the two nodes. In the presence of an electric field parallel to the scattering surface we observe the one dimensional chiral anomaly.

cond-mat.mes-hall↗
arXiv2016

Proposal for the detection of Majorana Fermions in Topological Superconductors

One of the goals of modern spectroscopy is to invent techniques which detect neutral excitations that have been theoretically proposed. For superconductors, two point transport measurements detect the Andreev crossed reflection which confirms the existence of the Majorana fermions. Similar information can be obtained from a measurement using two piezoelectric transducers. One transducer measures the stress tensor response from the strain field generated by the second transducer. The ratio between the stress response and strain velocity determines the dissipative response. We will show that the dissipative stress response can be used for a Topological Superconductor. We will investigate a Topological Superconductor in a magnetic field, an Abrikosov vortex lattice with Majorana dispersive fermions is formed which is used to compute the dissipative stress response and identify the Majorana fermions and quasi-particles.

cond-mat.mes-hall↗
arXiv2015

Fractional Topological Insulators- A Bosonization Approach

A metallic disk with strong spin orbit interaction is investigated . The finite disk geometry introduces a confining potential. Due to the strong spin-orbit interaction and confining potential the metal disk is described by an effective one dimensional with a harmonic potential. The harmonic potential gives rise to classical turning points. As a result open boundary conditions must be used. We Bosonize the model and obtain chiral Bosons for each spin on the edge of the disk. When the filling fraction is reduced to $ν=\frac{k_{F}}{k_{so}}=\frac{1}{3}$ the electron- electron interactions are studied using the Jordan Wigner phase for composite fermions which gives rise to a Luttinger liquid. When the metallic disk is in the proximity with a superconductor a Fractional Topological Insulators is obtained. An experimental realization is proposed. We show that by tunning the chemical potential we control the classical turning points for which a Fractional Topological Insulator is realized.

cond-mat.str-el↗
arXiv2015

Topological insulators and superconductors -a curved space a prroach

The method of the space dependent basis is applied to study electronic spinors in a crystal. The crystal in the momentum space is described by the Brillouine zone which might contains obstructions or degeneracies for which requires different gauges for different regions. The electronic bands are classified according to their topology. The connection and curvature determines the physical properties which are clasified according to the topological invariants. We apply this method to the Topological Insulators, Topological Superconductors, Persistent Currents in coupled rings and photoemission for a curved crystal-face boundary

cond-mat.mes-hall↗
arXiv2015

The Andreev crossed reflection -a Majorana path integral approach

We investigate the effect of the Majorana Fermions which are formed at the boundary of a p-wave superconductor. When the Majorana overlapping energy is finite we construct the scattering matrix $\mathbf{S}$ by maping the Majorana zero mode to Fermions for which coherent states are defined and a path integral is obtained . The path integral is used to compute the scattering matrix in terms of the electrons in the leads . This method is suitable for computing the conductivity. We investigate a chiral Majorana Hamiltonian and show that in the absence of vortices the conductivity vanish. We compute the conductivity for p wave superconductor coupled to two metallic leads we show that when the overlapping energy between the two Majorana fermions is finite the Andreev Crossed reflection conductance is finite.

cond-mat.supr-con↗
arXiv2015

A green's function approach for surface state photoelectrons in topological insulators

The topology of the surface electronic states is detected with photoemission. We explain the photoemission from the topological surface state . This is done by identifying the effective coupling between surface electrons-photons and vacuum electrons. The effective electron photon coupling is given by $eτ^2$ where $τ$ is the dimensionless tunneling amplitude of the zero mode surface states to tunnel into the vacuum. We compute the polarization and intensity of the emitted photoelectrons. We introduce a model which takes in account the Dirac Hamiltonian for the surface electron to photons coupling and the tunneling of the zero mode into the vacuum. Within the Green's function formalism we obtain exact results for the emitted Photoelectrons to second order in the laser field. The number of the emitted photoelectrons is sensitive to the laser coherent state intensity, the polarization is sensitive to the surface topology of the electronic states and the incoming photon polarization. The calculation is performed for the helical, Zeeman and warping case allowing to study spin textures.

cond-mat.mes-hall↗
arXiv2015

Probing Topological Superconductors with Sound Waves

A new method is introduced for probing Topological Superconductors. The integration of the superconding fermions generates a topological $\mathbf{Chern-Simons}$ sound action . Dislocations induce Majorana zero modes inside the sample, resulting in a new Hamiltonian which couple the Majorana modes, the electron field and the non-Abelian strain field sound. This Hamiltonian is used to compute the anomalous sound absorption. The Topological superconductor absorbs sound below the superconducting gap due to the transition between the quasi particles and the Majorana fermions. The sound waves offers a new tool for detecting Majorana fermions.

cond-mat.supr-con↗
arXiv2013

Propagation of Phonon in a Curved Space Induced by Strain Fields Instantons

We show that for a \textbf{multiple-connected} space the low energy strain fields excitations are given by instantons. Dirac fermions with a chiral mass and a pairing field propagates effectively in a multiple conected space. When the elastic strain field response is probed one finds that it is given by the \textbf{Pointriagin} characteristic. As a result the space time metric is modified. Applying an external stress field we observe that the phonon path bends in the transverse direction to the initial direction.

cond-mat.other↗
arXiv2013

Interference and transport properties of conductions electrons on the surface of a topological insulator

The surface conductivity for conduction electrons with a fixed chirality in a topological insulator with impurities scattering is considered. The surface excitations are described by the Weyl Hamiltonian. For a finite chemical potential one projects out the hole band and one obtains a single electronic band with a fixed chirality. One obtains a model of spinless electrons which experience a half vortex when they return to the origin. As a result the conductivity is equivalent to a spinless problem with correlated noise which gives rise to anti-localization. We compute conductivity as a function of frequency and compare our results with the $Raman$ shift measurement for $Bi_{2}Se_{3}$.

cond-mat.mes-hall↗
arXiv2013

Optical conductivity for the surface of a Topological Insulator

The optical conductivity for the surface excitations for a Topological Insulator as a function of the chemical potential and disorder is considered. Due to the time reversal symmetry the chiral metallic surface states are protected against disorder. This allow to use the averaged single particle Green's function to compute the optical conductivity. We compute the conductivity in the limit of a finite disorder. We find that the conductivity as a function of the chemical potential $μ$ and frequency $Ω$ is given by the universal value $σ(Ω>2μ)= \frac{e^2 π}{8h}$. For frequencies $Ω< μ$ and elastic mean free path $l_{el}=vτ$ which obey $k_{F}l>1$ we obtain the conductivity is given by $σ(Ω<2|μ|)=\frac{e^2}{2h}\frac{k_{F}l_{el}}{(Ωτ)^2+1}$. In the limit of zero disorder we find $σ(μ\neq0,Ω, k_{F}l\rightarrow \infty)=\frac{e^2 π}{2h}|μ|δ(Ω)$.

cond-mat.mes-hall↗
arXiv2011

The $p_{x}+ip_{y}$ Chiral Superconductor wire weakly coupled to two metallic rings pierced by an external flux

We consider a p-wave superconductor wire coupled to two metallic rings. confined to a one-dimensional wire. At the two interface between the the wire and the metallic rings the pairing order parameter vanishes, as result two zero modes Majorana fermion appear. The two metallic rings are pierced by external magnetic fluxes. The special features of the Majorana Fermions can be deduced from the correlation between the currents in the two rings.

cond-mat.supr-con↗