Absence of equilibrium edge currents in theoretical models of topological insulators

Chen, Wei

doi:10.1103/physrevb.101.195120

Cited by 18 publications

(13 citation statements)

References 57 publications

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“…Having obtained I eq ij for a given system, the change in magnetic field ∆B(r) can be calculated using the Biot-Savart law, as discussed in Ref. [24]. Experiments can follow the reverse path, for instance, use SQUIDs to measure ∆B(r) [20] and infer the local equilibrium current.…”

Section: B Local Currents In Quantum Hall Systems: Numerical Resultsmentioning

confidence: 99%

“…The computation of the equilibrium currents is more involved, since it requires an energy integration of T α iσ,jσ over all occupied states. A recent paper [24] has shown that the spin equilibrium currents vanish for Fermi energies at the Dirac point for the BHZ model, a feature that could simplify the integration in Eq. (21).…”

Section: B Numerical Resultsmentioning

confidence: 99%

“…We conclude by stressing that, like in the IQH regime, the local equilibrium spin currents I s,eq ii cannot be detected by nonequilibrium transport experiments. Yet, one can envisage strategies to indirectly measure equilibrium currents, for instance, I s,eq ii carries a magnetic moment that gives origin to an electric dipolar field [24], which can in principle be measured.…”

Section: B Numerical Resultsmentioning

confidence: 99%

“…The situation is less clear for QSH systems. Equilibrium currents in topological insulators have been studied for massless [23,24] as well as for massive Dirac electrons [25]. Interestingly, these works overlook the literature on spin currents in the spin Hall regime.…”

Section: Introductionmentioning

confidence: 99%

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Local equilibrium charge and spin currents in two-dimensional topological systems

Lima,

Lewenkopf

2021

Preprint

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We study the equilibrium and nonequilibrium electronic transport properties of multiprobe topological systems using a combination of the Landauer-Büttiker approach and nonequilibrium Green's functions techniques. We obtain general expressions for both nonequilibrium and equilibrium local electronic currents that, by suitable projections, allow one to compute charge, spin, valley, and orbital currents. We show that external magnetic fields give rise to equilibrium charge currents in mesoscopic system and study the latter in the quantum Hall regime. Likewise, a spin-orbit interaction leads to local equilibrium spin currents, that we analyze in the quantum spin Hall regime.

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Section: B Local Currents In Quantum Hall Systems: Numerical Resultsmentioning

confidence: 99%

Section: B Numerical Resultsmentioning

confidence: 99%

Section: B Numerical Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Local equilibrium charge and spin currents in two-dimensional topological systems

Lima,

Lewenkopf

2021

Preprint

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“…However, it is shown recently that the above naive picture of equilibrium surface spin current has a serious flaw, namely it does not take into account the contribution from the valence bands. 44 For the cubic lattice model of an isolated TI, i.e., the i ∈ T I terms in Eq. ( 7), the surface spin current produced by the surface states is in fact canceled out exactly by the contribution from the valence bands, rendering no net surface spin current.…”

Section: Persistent Spin Currentmentioning

confidence: 99%

Spin torque and persistent currents caused by percolation of topological surface states

Chen

2020

Preprint

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The topological insulator/ferromagnetic metal (TI/FMM) bilayer thin films emerged as promising topological surface state-based spintronic devices, most notably in their efficiency of current-induced spin torque. Using a cubic lattice model, we reveal that the surface state Dirac cone of the TI can gradually merge into or be highly intertwined with the FMM bulk bands, and the surface states percolate into the FMM and eventually hybridize with the quantum well states therein. The magnetization can distort the spin-momentum locking of the surface states and yield an asymmetric band structure, which causes a laminar flow of room temperature persistent charge current. Moreover, the proximity to the FMM also promotes a persistent laminar spin current. Through a linear response theory, we elaborate that both the surface state and the FMM bulk bands contribute to the current-induced spin torque, and their real wave functions render the spin torque predominantly field-like, with a magnitude highly influenced by the degree of the percolation of the surface states. On the other hand, impurities can change the spin polarization expected from the Edelstein effect and generate a damping-like torque, and produce a torque even when the magnetization points in-plane and orthogonal to the current direction.

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Optical absorption measurement of spin Berry curvature and spin Chern marker

Chen¹

2023

J. Phys.: Condens. Matter

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In two-dimensional time-reversal symmetric topological insulators described by Dirac models, the Z2 topological invariant can be described by the spin Chern number. We present a linear response theory for the spin Berry curvature that integrates to the spin Chern number, and introduce its spectral function that can be measured at finite temperature by momentum- and spin-resolved circular dichroism, which may be achieved by pump-probe type of experiments using spin- and time-resolved ARPES. As a result, the sign of the Pfaffian of the Z2 invariant can be directly measured. A spin Chern number spectral function is further introduced from the optical spin current response, and is shown to be measurable from the spin-resolved opacity of two-dimensional materials under circularly polarized light, pointing to an optical measurement of the Z2 invariant and a frequency sum rule. The spin Chern number expressed in real space is known to yield a spin Chern marker, and we propose that it may be measurable from spin-resolved local heating rate caused by circularly polarized light. A nonlocal spin Chern marker is further proposed to characterize the quantum criticality near topological phase transitions, and is shown to be equivalent to an overlap between spin-selected Wannier states.

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Absence of equilibrium edge currents in theoretical models of topological insulators

Cited by 18 publications

References 57 publications

Local equilibrium charge and spin currents in two-dimensional topological systems

Local equilibrium charge and spin currents in two-dimensional topological systems

Spin torque and persistent currents caused by percolation of topological surface states

Optical absorption measurement of spin Berry curvature and spin Chern marker

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