Effective Theory of Floquet Topological Transitions

Kundu, Arijit; Fertig, H. A.; Seradjeh, Babak

doi:10.1103/physrevlett.113.236803

Cited by 205 publications

(153 citation statements)

References 37 publications

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“…In a milestone paper, Haldane envisioned that breaking either or both of these symmetries would open a gap at the Dirac points in graphene, allowing one to tune between a trivial insulator and a Chern insulator 9 . While equilibrium band gap engineering has become a major theme since the first synthesis of monolayer graphene, it was only recently proposed that circularly polarized, high-frequency laser light could turn trivial equilibrium bands into topological nonequilibrium Floquet bands [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] , coined Floquet topological insulator (FTI).…”

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confidence: 99%

Theory of Floquet band formation and local pseudospin textures in pump-probe photoemission of graphene

et al. 2015

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Ultrafast materials science promises optical control of physical properties of solids. Continuous-wave circularly polarized laser driving was predicted to induce a light-matter coupled state with an energy gap and a quantum Hall effect, coined Floquet topological insulator. Whereas the envisioned Floquet topological insulator requires high-frequency pumping to obtain well-separated Floquet bands, a follow-up question regards the creation of Floquet-like states in graphene with realistic low-frequency laser pulses. Here we predict that short optical pulses attainable in experiments can lead to local spectral gaps and novel pseudospin textures in graphene. Pump-probe photoemission spectroscopy can track these states by measuring sizeable energy gaps and Floquet band formation on femtosecond time scales. Analysing band crossings and pseudospin textures near the Dirac points, we identify new states with optically induced nontrivial changes of sublattice mixing that leads to Berry curvature corrections of electrical transport and magnetization.

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confidence: 99%

Theory of Floquet band formation and local pseudospin textures in pump-probe photoemission of graphene

et al. 2015

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“…Most of these are induced by external driving. For example, a Floquet topological insulator may arise when graphene is irradiated by circularly polarized light [1, 3,4,6,7]. However, a topological Floquet phase can also be created in an isolated system such as a BCS superfluid following an instantaneous quench of the interaction strength [8][9][10].…”

Section: A Idea and Overview Of Resultsmentioning

confidence: 99%

“…Much of the previous work focused on the connection between the band structure and topological properties [2,5], but did not take into account the distribution function which might be essential to determine experimental observables. The problem of irradiated graphene has been considered mainly in the Landauer-Büttiker formalism, wherein the mode occupation is fixed by ideal leads [3,4,6,7]. Even in that simplified setting, however, the relationship between the topology and Floquet edge states to measured transport coefficients is complicated, and the latter are not generically quantized [4,6,7].…”

Section: A Idea and Overview Of Resultsmentioning

confidence: 99%

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Spectroscopic probes of isolated nonequilibrium quantum matter: Quantum quenches, Floquet states, and distribution functions

Liao

Foster

2015

Phys. Rev. A

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We investigate radio-frequency (rf) spectroscopy, metal-to-superconductor tunneling, and angle-resolved photoemission spectroscopy (ARPES) as probes of isolated out-of-equilibrium quantum systems, and examine the crucial role played by the nonequilibrium distribution function. As an example, we focus on the induced topological time-periodic (Floquet) phase in a two-dimensional p + ip superfluid, following an instantaneous quench of the coupling strength. The post-quench Cooper pairs occupy a linear combination of "ground" and "excited" Floquet states, with coefficients determined by the distribution function. While the Floquet band structure exhibits a single avoided crossing relative to the equilibrium case, the distribution function shows a population inversion of the Floquet bands at low energies. For a realization in ultracold atoms, these two features compensate, producing a bulk average rf signal that is well captured by a quasiequilibrium approximation. In particular, the rf spectrum shows a robust gap. The single crossing occurs because the quench-induced Floquet phase belongs to a particular class of soliton dynamics for the BCS equation. The population inversion is a consequence of this, and ensures the conservation of the pseudospin winding number. As a comparison, we compute the rf signal when only the lower Floquet band is occupied; in this case, the gap disappears for strong quenches. The tunneling signal in a solid-state realization is ignorant of the distribution function, and can show wildly different behaviors. We also examine rf, tunneling, and ARPES for weak quenches, such that the resulting topological steady state is characterized by a constant nonequilibrium order parameter. In a system with a boundary, tunneling reveals the Majorana edge states. However, the local rf signal due to the edge states is suppressed by a factor of the inverse system size, and is spatially deconfined throughout the bulk of the sample.

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“…In fact FTIs are extremely rich, showing a variety of topological phases as the amplitude, frequency, and polarization of the periodic drive is varied [17][18][19][20] .…”

Section: Introductionmentioning

confidence: 99%

Occupation probabilities and current densities of bulk and edge states of a Floquet topological insulator

Dehghani

Mitra

2016

Phys. Rev. B

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Results are presented for the occupation probabilities and current densities of bulk and edge states of half-filled graphene in a cylindrical geometry, and irradiated by a circularly polarized laser. It is assumed that the system is closed, and that the laser has been switched on as a quench. Laser parameters corresponding to some representative topological phases are studied: one where the Chern number of the Floquet bands equals the number of chiral edge modes, a second where anomalous edge states appear in the Floquet Brillouin zone boundaries, and a third where the Chern number is zero, yet topological edge states appear at the center and boundaries of the Floquet Brillouin zone. Qualitative differences are found for the high frequency off-resonant and low frequency on-resonant laser with edge states arising due to resonant processes occupied with a high effective temperature, whereas edge states arising due to off-resonant processes occupied with a low effective temperature. For an ideal half-filled system where only one of the bands in the Floquet Brillouin zone is occupied and the other empty, particle-hole and inversion symmetry of the Floquet Hamiltonian implies zero current density. However the laser switch-on protocol breaks the inversion symmetry, resulting in a net cylindrical sheet of current density at steady-state. Due to the underlying chirality of the system, this current density profile is associated with a net charge imbalance between the top and bottom of the cylinders.

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Effective Theory of Floquet Topological Transitions

Cited by 205 publications

References 37 publications

Theory of Floquet band formation and local pseudospin textures in pump-probe photoemission of graphene

Theory of Floquet band formation and local pseudospin textures in pump-probe photoemission of graphene

Spectroscopic probes of isolated nonequilibrium quantum matter: Quantum quenches, Floquet states, and distribution functions

Occupation probabilities and current densities of bulk and edge states of a Floquet topological insulator

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