arXiv subjects

D. Schmeltzer

Publications and source records attributed to D. Schmeltzer.

At least 37 records · Page 2Linked to original sources

arXiv2011

A-geometrical approach to Topological Insulators with defects

The study of the propagation of electrons with a varying spinor orientability is performed using the coordinate transformation method. Topological Insulators are characterized by an odd number of changes of the orientability in the Brillouin zone. For defects the change in orientability takes place for closed orbits in real space. Both cases are characterized by nontrivial spin connections. Using this method , we derive the form of the spin connections for topological defects in three dimensional Topological Insulators. On the surface of a Topological Insulator, the presence an edge dislocation gives rise to a spin connection controlled by torsion. We find that electrons propagate along two dimensional regions and confined circular contours. We compute for the edge dislocations the tunneling density of states. The edge dislocations violates parity symmetry resulting in a current measured by the in-plane component of the spin on the surface.

cond-mat.mes-hall↗

arXiv2011

The two dimensional local density of states of a Topological Insulator with an edge dislocation

We investigate the effect of a crystal edge dislocation on the metallic surface of a Topological Insulator. The edge dislocation gives rise to torsion which the electrons experience as a spin connection. As a result the electrons propagate along confined two dimensional regions and circular contours. Due to the edge dislocations the parity symmetry is violated resulting in a current measured by the in-plane component of the spin on the surface. The tunneling density of states for Burger vectors in the $y$ direction is maximal along the $x$ direction. The evidence of the enhanced tunneling density of states can be verified with the help of the scanning tunneling technique.

cond-mat.mes-hall↗

arXiv2011

Dirac's method for constraints - an application to quantum wires,the 0.7 conductance anomaly

We investigate the Hubbard model in the limit $U=\infty$, which is equivalent to the statistical condition of exclusion of double occupancy. We solve this problem using Dirac's method for constraints. The constraints are solved within the Bosonization method. We find that the constraints modify the anomalous commutator. We apply this theory to quantum wires at finite temperatures where the Hubbard interaction is $U=\infty$. We find that the anomalous commutator induced by the constraints gives rise to the 0.7 anomalous conductance.

cond-mat.str-el↗

arXiv2009

A Scaling Approach for Interacting Quantum Wires -a Possible Explanation for the 0.7 Anomalous Conductance

We consider a weakly interacting finite wire with short and long range interactions. The long range interactions enhance the $4k_{F}$ scattering and renormalize the wire to a strongly interacting limit. For large screening lengths, the renormalized charge stiffness Luttinger parameter $K_{eff.}$ decreases to $K_{eff.}< {1/2}$, giving rise to a Wigner crystal at T=0 with an anomalous conductance at finite temperatures. For short screening lengths, the renormalized Luttinger parameter $K_{eff.}$ is restricted to ${1/2}\leq K_{eff.}\leq 1$. As a result, at temperatures larger than the magnetic exchange energy we find an interacting metal which for $K_{eff.}\approx {1/2}$ is equivalent to the Hubbard $U\to\infty$ model, with the anomalous conductance $G\approx\frac{e^2}{h}$ .

cond-mat.mes-hall↗

arXiv2009

The wave functions in the presence of constraints - Persistent Current in Coupled Rings

We present a new method for computing the wave function in the presence of constraints. As an explicit example we compute the wave function for the many electrons problem in coupled metallic rings in the presence of external magnetic fluxes. For equal fluxes and an even number of electrons the constraints enforce a wave function with a vanishing total momentum and a large persistent current and magnetization in contrast to the odd number of electrons where at finite temperatures the current is suppressed. We propose that the even-odd property can be verified by measuring the magnetization as a function of a varying gate voltage coupled to the rings. By reversing the flux in one of the ring the current and magnetization vanish in both rings; this can be used as a non-local control device.

cond-mat.mes-hall↗

arXiv2009

The Marginal Fermi Liquid - An Exact Derivation Based on Dirac's First Class Constraints Method

Dirac's method for constraints is used for solving the problem of exclusion of double occupancy for Correlated Electrons. The constraints are enforced by the pair operator $Q(\vec{x})=ψ_{\downarrow}(\vec{x})ψ_{\uparrow}(\vec{x})$ which annihilates the ground state $|Ψ^0>$. Away from half fillings the operator $Q(\vec{x})$ is replaced by a set of $first$ $class$ Non-Abelian constraints $Q^{(-)}_α(\vec{x})$ restricted to negative energies. The propagator for a single hole away from half fillings is determined by modified measure which is a function of the time duration of the hole propagator. As a result: a) The imaginary part of the self energy - is linear in the frequency. At large hole concentrations a Fermi Liquid self energy is obtained. b) For the Superconducting state the constraints generate an asymmetric spectrum excitations between electrons and holes giving rise to an asymmetry tunneling density of states.

cond-mat.mes-hall↗

arXiv2008

Mechanical and superfluid properties of dislocations in solid He4

Dislocations are shown to be smooth at zero temperature because of the effective Coulomb-type interaction between kinks. Crossover to finite temperature rougnehing is suggested to be a mechanism responsible for the softening of \he4 shear modulus recently observed by Day and Beamish (Nature, {\bf 450}, 853 (2007)). We discuss also that strong suppresion of superfuidity along the dislocation core by thermal kinks can lead to locking in of the mechanical and superfluid responses.

cond-mat.stat-mech↗

arXiv2008

Rectified Voltage Induced by a Microwave Field in a Confined Two-Dimensional Electron Gas with a Mesoscopic Static Vortex

We investigate the effect of a microwave field on a confined two dimensional electron gas which contains an insulating region comparable to the Fermi wavelength. The insulating region causes the electron wave function to vanish in that region. We describe the insulating region as a static vortex, which gives rise to non-commuting kinetic momenta. The two-dimensional electron gas is described as a fluid with a density which obeys the Fermi-Dirac statistics. The presence of the confinement potential gives rise to vanishing kinetic momenta in the vicinity of the classical turning points. As a result, the Cartesian coordinates do not commute. The non-commutativity of coordinates gives rise to a Hall current which, in the presence of a modified Fermi-Surface caused by the microwave field, results in a rectified voltage. The proposed theory may explain the experimental results recently reported by J. Zhang et al.

cond-mat.mes-hall↗

arXiv2007

Persistent Current for a genus g=2 structure

We report the first calculation of persistent current in two coupled rings which form a character ``8'' genus g=2 structure. We obtain an exact solution for the persistent current and investigated the exact solution numerically. For two large coupled rings with equal fluxes, we find that the persistent current in the two coupled rings is equal to that in a single ring. For opposite fluxes the energy has a chaotic structure. For both cases the periodicity is $h/e$. This results are obtained within an extension of Dirac's second class method to fermionic constraints. This theory can be tested in the ballistic regime.

cond-mat.mes-hall↗

arXiv2007

Persistent Current in Two Coupled Rings

We report the solution of the persistent current in two coupled rings in the presence of external magnetic fluxes. We showed that the magnetic fluxes modify the global phase of the electronic wave function for multiple connected geometry formed by the coupled rings. We obtained an exact solution for the persistent current and investigated the exact solution numerically. For two large coupled rings with equal fluxes, we found that the persistent current in the two coupled rings is in fact equal to that in a single ring. This theory explains the experimental results observed in a line of sixteen coupled rings. (Phys. Rev. Lett. 86, 3124 (2001).)

cond-mat.mtrl-sci↗

arXiv2005

The Non-Dissipative Spin-Hall Current

A theory based on the Aharonov -Bohm effect in the momentum space for the Spin-Hall conductivity without a magnetic field is presented. The two dimensional Rashba Hamiltonian is diagonalized in the momentum spinor basis. This spinor is singular at K=0. The representation of the cartesian coordinates in the spinor momentum basis obey non-commutative rules. The non-commuting relations are a result of an effective Aharonov-Bohm vortex at K=0. We find the exact value of $\frac{e}{4π}$ for the Spin-Hall conductivity. The effect of a time reversal scattering potential on the Spin-Hall current causes the current to vanishes for an infinite system.

cond-mat.mes-hall↗

arXiv2005

The Non-Dissipative Spin-Hall Conductivity and The Identification of the Conserved Current

The two dimensional Rashba Hamiltonian is investigated using the momentum representation.One finds that the SU(2) transformation which diagonalizes the Hamiltonian gives rise to non commuting Cartesian coordinates for K=0 and zero otherwise.This result corresponds to the Aharonov -Bohm phase in the momentum space. The Spin -Hall conductivity is given by $\frac{e}{4π}$ which disagree with the result $\frac{e}{8π}$ given in the literature.Using Stokes theorem we find that the Spin -Hall current is carried equally by the up and down electrons on the Fermi surface. We identify the Magnetic current and find that for an electric field with a finite Fourier component in the momentum space a non zero Spin -Hall current is obtained.For the electric field which is constant in space, the orbital magnetic current cancels the spin current. In order to measure the Spin-Hall conductance we propose to apply a magnetic field gradient $ΔH_{2}$ in the $i=2$ direction and to measure a Charge- Hall current $\frac{e}{h}(\frac{g}{2})μ_{B}ΔH_{2}$ in the $i=1$ direction.

cond-mat.str-el↗

arXiv2005

Transport in a spin polarized Luttinger liquid in the presence of a single impurity

The conductance for a single impurity in a one dimensional gas with electron-electron interaction and Zeeman splitting $v_F^\uparrow - v_F^\downarrow = Δ\neq 0$ is considered. We find that for an extented Hubbard model, $ρ_\uparrow^R ρ_\uparrow^L + ρ_\downarrow^R ρ_\downarrow^L$, a Luttinger liquid for spin up and spin down is obtained. As a result the conductances for spin up $G_\uparrow$ and spin down $G_\downarrow$ are not equal. The anisotropy in the conductances $G_\uparrow \neq G_\downarrow$ gives rise to a spin polarized wire.

cond-mat.str-el↗

arXiv2005

Topological spin current

We present an exact derivation for non-commuting coordinates induced by the SU(2) transformation used to diagonalize the spin-orbit hamiltonian in two dimension.As a result an exact non-dissipative Hall current less sensitive to disorder and complementary to the dissipative conductivity is found. We compute the non-dissipative charge and spin-Hall conductance for the spin-orbit problem.We find that the spin-Hall conductance is quantized in units of $\frac{egμ_{B}}{h}$ .In the presence of a Zeeman interaction the charge-Hall conductivity is proportional to the magnetic field. We propose an experiment to test our theory.

cond-mat.mes-hall↗

arXiv2004

Electron transmission through a short interacting wire: 0.7 conductance anomaly

We investigate tunneling through a short interacting wire. We identify two temperature regimes (a) $T_{Kondo}<T\le T^{wire}=\hbar v_F/k_Bd$ ($d$ is the length of the short wire) and (b) $T<T_{Kondo}\ll T^{wire}$. In the first regime the effective (renormalized) electron-electron interaction is smaller than the tunneling matrix element. This is the situation at finite temperature $T$ where the single particle spectrum of the wire is characterized by a multilevel "quantum dot" system with magnetic quantum number S=0 which is higher in energy than the SU(2) spin doublet $S=\pm1/2$. Due to the single particle energy we find that the tunneling electron into the wire must have an opposite spin to the one in the short wire giving rise to a conductance, $G= G_\uparrow+G_\downarrow$, $e^2/h\le G\ll 2e^2/h$. In the second regime, when $T \to0$ we have a situation that the effective (renormalized) electron-electron interaction is larger than the tunneling matrix element. This problem is equivalent to a Kondo problem. We find for $T<T_{Kondo}$ that the conductance is given by $G=2e^2/h$. These results are in agreement with recent experiments where for $T_{Kondo}<T<T^{wire}$ the conductance $G$ obeys $e^2/h\le G\ll 2e^2/h$, and for $T< T_{Kondo}$, $G=2e^2/h$. In both regimes the current is not polarized and the SU(2) symmetry is not broken.

cond-mat.mes-hall↗

arXiv2004

Z_2 Gauge Theory of Electron Fractionalization in the t,t'-J Model

We consider a strongly correlated "t,t'-J" spin model with a positive uniaxial anisotropy. We show that in 2+1 dimensions, this model is equivalent to spin-charge excitations coupled to Z_2 Ising gauge fields and not to a U(1) gauge fields (as in the "t-J" model). As a result a phase of frozen Z_2 gauge fluctuations is possible, giving rise to a spin-charge-separated liquid.

cond-mat.str-el↗

arXiv2004

Persistent spin currents induced by a spatially-dependent magnetic field in a spin-1/2 Heisenberg antiferromagnetic ring

We show that a spatially-dependent magnetic field can induce a persistent spin current in a spin-1/2 Heisenberg antiferromagnetic ring, proportional to the solid angle subtended by the magnetic field on a unit sphere. The result is a direct consequence of Berry "parallel transport" in space. The magnitude of the spin current is determined by the ratio of longitudinal and transverse exchange interactions $J_\parallel/J_\perp$ and by the magnetic field. For large magnetic fields the Zeeman energy strongly renormalizes the Ising term giving rise to a maximum spin current. In the limit of $J_\parallel/J_\perp\ll1$ the amplitude of the current behaves like $1-(J_\parallel/J_\perp)^2$. In the opposite limit $πJ_\perp> J_\parallel>J_\perp$ the amplitude scales as $\sqrt{J_\parallel/ J_\perp}\exp{(-\sqrt{J_\parallel/J_\perp})}$.

cond-mat.mes-hall↗

arXiv2002

Transport through short quantum wires

At temperatures $T < {\hbar v_F}/{K_B d} \equiv T^{wire}$ the collective excitations are negligible and the spectrum of the short wire is dominated by the ''zero modes'' particle excitations. At temperature $ T > T^{wire}$ a spin polarized state controlled by the electron-electron interaction and electron density is identified at short times. As a result the anomaly in the conductance $G > 2 \times 0.5 {e^2}/{h} $ appears. At $T \to 0$ by varying the gate voltage we find that our problem is equivalent to a resonant impurity level. As a result perfect transmission with a conductance $G \simeq \frac{2 e^2}{h}$ is obtained. The model presented here can be used as a spin filter which operate by varying the temperature. Transport through a short quantum wire with electron-electron interaction and length ``$d$'' coupled to Luttinger leads is considered. The short wire model might explain the ``0.7 anomaly'' observed in quantum point contacts.

cond-mat.str-el↗