Mahmoud Lababidi | George Mason University (original) (raw)

Papers by Mahmoud Lababidi

Research paper thumbnail of Order parameter and triplet correlations near a superconductor-topological insulator interface

At the interface between a 3D topological band insulator and an s- wave superconductor forms a re... more At the interface between a 3D topological band insulator and an s- wave superconductor forms a remarkable 2D superconductor that can host Majorana fermions at vortex cores. Going beyond the original work of Fu and Kane [Phys. Rev. Lett. 100, 096407 (2008)], we present a microscopic theory for the proximity effect near the TI-S interface. We compute the superconducting order parameter as a function of the distance away from the interface by self-consistently solving the Bogoliubov-de Gennes equation. We discuss the suppression of the order parameter by the topological insulator. Moreover, we show that triplet superconducting correlations of px±ipy orbital symmetry are induced near the interface by the spin-orbit coupling inside the topological insulator.

Research paper thumbnail of Spin active scattering at the interface between a metal and a topological insulator

We present theoretical results for the spin-active scattering and local spectrum at the interface... more We present theoretical results for the spin-active scattering and local spectrum at the interface between a metal and a three-dimensional topological band insulator. We show that there exists a critical incident angle at which complete (100%) spin flip reflection occurs and the spin rotation angle jumps by π. We discuss the origin of this phenomena, and systematically study the dependence of spin-flip and spin-conserving scattering amplitudes on the interface transparency and metal Fermi surface parameters. The interface spectrum contains a well-defined Dirac cone in the tunneling limit, and smoothly evolves into a continuum of metal induced gap states for good contacts. We also investigate the complex band structure of Bi2Se3.

Research paper thumbnail of Microscopic simulation of superconductor/topological insulator proximity structures

Physical Review B, 2011

We present microscopic, self-consistent calculations of the superconducting order parameter and p... more We present microscopic, self-consistent calculations of the superconducting order parameter and pairing correlations near the interface of an sss-wave superconductor and a three-dimensional topological insulator with spin-orbit coupling. We discuss the suppression of the order parameter by the topological insulator and show that the equal-time pair correlation functions in the triplet channel, induced by spin-flip scattering at the interface, are of pxpmipyp_x\pm i p_ypxpmipy symmetry. We verify that the spectrum at sub-gap energies is well described by the Fu-Kane model. The sub-gap modes are viewed as interface states with spectral weight penetrating well into the superconductor. We extract the phenomenological parameters of the Fu-Kane model from microscopic calculations, and find they are strongly renormalized from the bulk material parameters. This is consistent with previous results of Stanescu et al for a lattice model using perturbation theory in the tunneling limit.

Research paper thumbnail of Mott scattering at the interface between a metal and a topological insulator

Physical Review B, 2010

We compute the spin-active scattering matrix and the local spectrum at the interface between a me... more We compute the spin-active scattering matrix and the local spectrum at the interface between a metal and a three-dimensional topological band insulator. We show that there exists a critical incident angle at which complete (100%) spin flip reflection occurs and the spin rotation angle jumps by pi\pipi. We discuss the origin of this phenomena, and systematically study the dependence of spin-flip and spin-conserving scattering amplitudes on the interface transparency and metal Fermi surface parameters. The interface spectrum contains a well-defined Dirac cone in the tunneling limit, and smoothly evolves into a continuum of metal induced gap states for good contacts. We also investigate the complex band structure of Bi$_2$Se$_3$.

Research paper thumbnail of Robustness of single-qubit geometric gate against systematic error

Physical Review A, 2011

Universal single-qubit gates are constructed from a basic Bloch rotation operator realized throug... more Universal single-qubit gates are constructed from a basic Bloch rotation operator realized through nonadiabatic Abelian geometric phase. The driving Hamiltonian in a generic two-level model is parameterized using controllable physical variables. The fidelity of the basic geometric rotation operator is investigated in the presence of systematic error in control parameters, such as the driving pulse area and frequency detuning. Compared to a conventional dynamic rotation, the geometric rotation shows improved fidelity.

Research paper thumbnail of Order parameter and triplet correlations near a superconductor-topological insulator interface

At the interface between a 3D topological band insulator and an s- wave superconductor forms a re... more At the interface between a 3D topological band insulator and an s- wave superconductor forms a remarkable 2D superconductor that can host Majorana fermions at vortex cores. Going beyond the original work of Fu and Kane [Phys. Rev. Lett. 100, 096407 (2008)], we present a microscopic theory for the proximity effect near the TI-S interface. We compute the superconducting order parameter as a function of the distance away from the interface by self-consistently solving the Bogoliubov-de Gennes equation. We discuss the suppression of the order parameter by the topological insulator. Moreover, we show that triplet superconducting correlations of px±ipy orbital symmetry are induced near the interface by the spin-orbit coupling inside the topological insulator.

Research paper thumbnail of Spin active scattering at the interface between a metal and a topological insulator

We present theoretical results for the spin-active scattering and local spectrum at the interface... more We present theoretical results for the spin-active scattering and local spectrum at the interface between a metal and a three-dimensional topological band insulator. We show that there exists a critical incident angle at which complete (100%) spin flip reflection occurs and the spin rotation angle jumps by π. We discuss the origin of this phenomena, and systematically study the dependence of spin-flip and spin-conserving scattering amplitudes on the interface transparency and metal Fermi surface parameters. The interface spectrum contains a well-defined Dirac cone in the tunneling limit, and smoothly evolves into a continuum of metal induced gap states for good contacts. We also investigate the complex band structure of Bi2Se3.

Research paper thumbnail of Microscopic simulation of superconductor/topological insulator proximity structures

Physical Review B, 2011

We present microscopic, self-consistent calculations of the superconducting order parameter and p... more We present microscopic, self-consistent calculations of the superconducting order parameter and pairing correlations near the interface of an sss-wave superconductor and a three-dimensional topological insulator with spin-orbit coupling. We discuss the suppression of the order parameter by the topological insulator and show that the equal-time pair correlation functions in the triplet channel, induced by spin-flip scattering at the interface, are of pxpmipyp_x\pm i p_ypxpmipy symmetry. We verify that the spectrum at sub-gap energies is well described by the Fu-Kane model. The sub-gap modes are viewed as interface states with spectral weight penetrating well into the superconductor. We extract the phenomenological parameters of the Fu-Kane model from microscopic calculations, and find they are strongly renormalized from the bulk material parameters. This is consistent with previous results of Stanescu et al for a lattice model using perturbation theory in the tunneling limit.

Research paper thumbnail of Mott scattering at the interface between a metal and a topological insulator

Physical Review B, 2010

We compute the spin-active scattering matrix and the local spectrum at the interface between a me... more We compute the spin-active scattering matrix and the local spectrum at the interface between a metal and a three-dimensional topological band insulator. We show that there exists a critical incident angle at which complete (100%) spin flip reflection occurs and the spin rotation angle jumps by pi\pipi. We discuss the origin of this phenomena, and systematically study the dependence of spin-flip and spin-conserving scattering amplitudes on the interface transparency and metal Fermi surface parameters. The interface spectrum contains a well-defined Dirac cone in the tunneling limit, and smoothly evolves into a continuum of metal induced gap states for good contacts. We also investigate the complex band structure of Bi$_2$Se$_3$.

Research paper thumbnail of Robustness of single-qubit geometric gate against systematic error

Physical Review A, 2011

Universal single-qubit gates are constructed from a basic Bloch rotation operator realized throug... more Universal single-qubit gates are constructed from a basic Bloch rotation operator realized through nonadiabatic Abelian geometric phase. The driving Hamiltonian in a generic two-level model is parameterized using controllable physical variables. The fidelity of the basic geometric rotation operator is investigated in the presence of systematic error in control parameters, such as the driving pulse area and frequency detuning. Compared to a conventional dynamic rotation, the geometric rotation shows improved fidelity.