Showing papers by "Carmine Ortix published in 2018"
TL;DR: In this article, the bulk topological invariant for chiral higher-order topological insulators is defined in terms of symmetric hybrid Wannier functions of the filled bands, and can be readily calculated from the knowledge of the crystalline symmetry labels of the bulk band structure.
Abstract: We provide the bulk topological invariant for chiral higher-order topological insulators in (i) fourfold rotoinversion invariant bulk crystals, and (ii) inversion-symmetric systems with or without an additional threefold rotation symmetry. These states of matter are characterized by a nontrivial ${\mathbb{Z}}_{2}$ index, which we define in terms of symmetric hybrid Wannier functions of the filled bands, and can be readily calculated from the knowledge of the crystalline symmetry labels of the bulk band structure. The topological invariant determines the generic presence or absence of protected chiral gapless one-dimensional modes localized at the hinges between conventional gapped surfaces.
180 citations
TL;DR: In this article, the existence of higher-order topological insulators with protected chiral hinge modes in quasi-two-dimensional systems made out of coupled layers stacked in an inversion-symmetric manner was proved.
Abstract: We prove the existence of higher-order topological insulators with protected chiral hinge modes in quasi-two-dimensional systems made out of coupled layers stacked in an inversion-symmetric manner. In particular, we show that a homogeneous external magnetic field slightly tilted away from the stacking direction drives alternating $p$- and $n$-doped honeycomb sheets into a higher-order topological phase, characterized by a nontrivial three-dimensional ${\mathbb{Z}}_{2}$ invariant. We identify graphene, silicene, and phosphorene multilayers as potential material platforms for the experimental detection of this second-order topological insulating phase.
49 citations
TL;DR: In this article, the authors identify a one-to-one correspondence between the charge localized around a dislocation characterized by a generic Burgers vector and the Berry phase associated with the electronic Bloch waves of two-dimensional crystalline insulators using this correspondence, reveal a link between dislocation charges and the topological invariants of inversion and rotation symmetry-protected insulating phases both in the absence and in the presence of time-reversal symmetry.
Abstract: We identify a one-to-one correspondence between the charge localized around a dislocation characterized by a generic Burgers vector and the Berry phase associated with the electronic Bloch waves of two-dimensional crystalline insulators Using this correspondence, we reveal a link between dislocation charges and the topological invariants of inversion and rotation symmetry-protected insulating phases both in the absence and in the presence of time-reversal symmetry Our findings demonstrate that dislocation charges can be used as generic probes of crystalline topologies
38 citations
TL;DR: In this article, the appearance of topological insulators protected by spatial symmetries is discussed, and three representative, theoretical examples are reviewed in three dimensions (3D) and one dimension (1D).
Abstract: We discuss recent advances in the study of topological insulators protected by spatial symmetries by reviewing three representative, theoretical examples. In three dimensions (3D), these states of matter are generally characterized by the presence of gapless boundary states at surfaces that respect the protecting spatial symmetry. We discuss the appearance of these topological states in both crystals with negligible spin–orbit coupling and a fourfold rotational symmetry, as well as in mirror-symmetric crystals with sizable spin–orbit interaction characterized by the so-called mirror Chern number. Finally, we also discuss similar topological crystalline states in one-dimensional (1D) insulators, such as nanowires or atomic chains, with mirror symmetry. There, the prime physical consequence of the non-trivial topology is the presence of quantized end charges.
17 citations
TL;DR: In this article, a one-dimensional solid-state electronic setup that operates as a topological charge pump in the complete absence of superimposed oscillating local voltages is presented.
Abstract: We propose and analyze theoretically a one-dimensional solid-state electronic setup that operates as a topological charge pump in the complete absence of superimposed oscillating local voltages. The system consists of a semiconducting narrow channel with a strong Rashba spin-orbit interaction patterned in a mesoscale serpentine shape. A rotating planar magnetic field serves as the external ac perturbation, and cooperates with the Rashba spin-orbit interaction, which is modulated by the geometric curvature of the electronic channel to realize the topological pumping protocol, originally introduced by Thouless, in a different fashion. We expect the precise pumping of electric charges in our mesoscopic quantum device to be relevant for quantum metrology purposes.
13 citations
TL;DR: In this article, the transport properties of a quantum spin-Hall insulator with sizable Rashba spin-orbit coupling in a disk geometry are discussed, and the presence of topologically protected helical edge states allows for the control and manipulation of spin polarized currents.
Abstract: We discuss the transport properties of a quantum spin-Hall insulator with sizable Rashba spin-orbit coupling in a disk geometry. The presence of topologically protected helical edge states allows for the control and manipulation of spin polarized currents: When ferromagnetic leads are coupled to the quantum spin-Hall device, the ballistic conductance is modulated by the Rashba strength. Therefore, by tuning the Rashba interaction via an all-electric gating, it is possible to control the spin polarization of injected electrons.
9 citations
01 Jan 2018
TL;DR: In this paper, the theory underlying spin-induced modulations of unpolarized currents in quantum rings subject to the Rashba spin-orbit interaction is presented, and the connection between the conductance modulations and the geometric phase acquired by the spin during transport, as well as pathways to directly control them are discussed.
Abstract: Quantum interference effects in rings provide suitable means to control spins at the mesoscopic scale. In this chapter we present the theory underlying spin-induced modulations of unpolarized currents in quantum rings subject to the Rashba spin-orbit interaction. We discuss explicitly the connection between the conductance modulations and the geometric phase acquired by the spin during transport, as well as pathways to directly control them.
2 citations
Journal Article•
TL;DR: In this paper, the effect of disorder on the weak coupling instabilities of a quadratic band crossing point (QBCP) in two-dimensional Fermi systems was analyzed.
Abstract: We analyze the effect of disorder on the weak-coupling instabilities of a quadratic band crossing point (QBCP) in two-dimensional Fermi systems, which, in the clean limit, display interaction-driven topological insulating phases. In the framework of a renormalization group procedure, which treats fermionic interactions and disorder on the same footing, we test all possible instabilities and identify the corresponding ordered phases in the presence of disorder for both single-valley and two-valley QBCP systems. We find that disorder generally suppresses the critical temperature at which the interaction-driven topologically nontrivial order sets in. Strong disorder can also drive a topological phase transition into a topologically trivial insulating state.
1 citations
Posted Content•
11 Jun 2018
TL;DR: In this article, the existence of higher-order topological insulators in fourfold rotoinversion invariant bulk crystals and inversion-symmetric systems with or without an additional three-fold rotation symmetry was proved.
Abstract: We prove the existence of higher-order topological insulators in: {\it i}) fourfold rotoinversion invariant bulk crystals, and {\it ii}) inversion-symmetric systems with or without an additional three-fold rotation symmetry. These states of matter are characterized by a non-trivial $\mathbb{Z}_2$ topological invariant, which we define in terms of symmetric hybrid Wannier functions of the filled bands, and can be readily calculated from the knowledge of the crystalline symmetry labels of the bulk band structure. The topological invariant determines the generic presence or absence of protected chiral gapless one-dimensional modes localized at the hinges between conventional gapped surfaces.
1 citations
TL;DR: In this paper, the theory underlying spin-induced modulations of unpolarized currents in quantum rings subject to the Rashba spin-orbit interaction is presented, and the connection between the conductance modulations and the geometric phase acquired by the spin during transport, as well as pathways to directly control them are discussed.
Abstract: Quantum interference effects in rings provide suitable means to control spins at the mesoscopic scale. In this chapter we present the theory underlying spin-induced modulations of unpolarized currents in quantum rings subject to the Rashba spin-orbit interaction. We discuss explicitly the connection between the conductance modulations and the geometric phase acquired by the spin during transport, as well as pathways to directly control them.