Room temperature electrically tunable terahertz Faraday effect

Shuvaev, A.; Pimenov, A.; Astakhov, G. V.; Mühlbauer, Mathias; Brüne, C.; Buhmann, H.; Molenkamp, L. W.

doi:10.1063/1.4811496

Cited by 39 publications

(34 citation statements)

References 25 publications

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“…This unique property allows to observe of the quantum Hall effect 18 and Shubnikov-de Haas oscillations 24 in strained HgTe film and, thus to analyse surface state transport in TIs. Furthermore, the negligible contribution from bulk carriers opens a way to study Dirac fermions in 3D TI by cyclotron resonance measured via transmission or Faraday effect [39][40][41] and, as we show below, terahertz (THz) radiation induced photocurrents. Here, we report on the observation of cyclotron resonance assisted photocurrents, excited in surface states of strained HgTe films.…”

Section: Pacs Numbersmentioning

confidence: 99%

Cyclotron-resonance-assisted photocurrents in surface states of a three-dimensional topological insulator based on a strained high-mobility HgTe film

et al. 2015

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We report on the observation of cyclotron resonance induced photocurrents, excited by continuous wave terahertz radiation, in a 3D topological insulator (TI) based on an 80 nm strained HgTe film. The analysis of the photocurrent formation is supported by complimentary measurements of magneto-transport and radiation transmission. We demonstrate that the photocurrent is generated in the topologically protected surface states. Studying the resonance response in a gated sample we examined the behavior of the photocurrent, which enables us to extract the mobility and the cyclotron mass as a function of the Fermi energy. For high gate voltages we also detected cyclotron resonance (CR) of bulk carriers, with a mass about two times larger than that obtained for the surface states. The origin of the CR assisted photocurrent is discussed in terms of asymmetric scattering of TI surface carriers in the momentum space. Furthermore, we show that studying the photocurrent in gated samples provides a sensitive method to probe the effective masses and the mobility of 2D Dirac surface states, when the Fermi level lies in the bulk energy gap or even in the conduction band.

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Section: Pacs Numbersmentioning

confidence: 99%

Cyclotron-resonance-assisted photocurrents in surface states of a three-dimensional topological insulator based on a strained high-mobility HgTe film

et al. 2015

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“…Among the representatives of the latter group, the HgTe-based crystalline structures have attracted particular attention, because they allow one to fabricate two-and three-dimensional topological insulators [7][8][9][10][11][12][13][14][15][16]. In this very system, one can obtain Dirac-like, inverted, and normal energy dispersions without changing the material [7,8,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. Thus, investigating various electronic properties in HgTe-based quantum wells with different thicknesses one can address similarities and differences in phenomena excited for different types of electron energy spectra.…”

Section: Introductionmentioning

confidence: 99%

Quantum oscillations of photocurrents in HgTe quantum wells with Dirac and parabolic dispersions

et al. 2014

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We report on the observation of magneto-oscillations of terahertz radiation induced photocurrent in HgTe/HgCdTe quantum wells of different widths, which are characterized by a Dirac-like, inverted, and normal parabolic band structure. The photocurrent data are accompanied by measurements of photoresistance (photoconductivity), radiation transmission, as well as magnetotransport. We develop a microscopic model of a cyclotron-resonance assisted photogalvanic effect, which describes main experimental findings. We demonstrate that the quantum oscillations of the photocurrent are caused by the crossing of Fermi level by Landau levels resulting in the oscillations of spin polarization and electron mobilities in spin subbands. Theory explains a photocurrent direction reversal with the variation of magnetic field observed in experiment. We describe the photoconductivity oscillations related with the thermal suppression of the Shubnikov-de Haas effect.

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“…We note that in high magnetic fields far above the cyclotron resonance [35], classical Faraday rotation and ellipticity are expected to fade out as θ ∼ 1/B, η ∼ 1/B 2 . Remarkably, in Fig.…”

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“…The DC data correspond well to the universal value of the Faraday rotation θ = α. Indeed, in the limit of small absorption by thin film [35] we may write: θ ∼ t c /t p ∼ t c ∼ Z 0 /2R xy , which leads to θ = α for R xy = h/e 2 . Direct correspondence between quantum Hall effect and quantized Faraday rotation is well known in ordinary 2D electron gases [38].…”

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Universal Faraday Rotation in HgTe Wells with Critical Thickness

et al. 2016

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The universal value of Faraday rotation angle close to the fine structure constant (α ≈ 1/137) is experimentally observed in thin HgTe quantum wells with thickness on the border between trivial insulating and the topologically non-trivial Dirac phases. The quantized value of the Faraday angle remains robust in the broad range of magnetic fields and gate voltages. Dynamic Hall conductivity of the hole-like carriers extracted from the analysis of the transmission data shows theoretically predicted universal value of σxy = e 2 /h consistent with the doubly degenerate Dirac state. On shifting the Fermi level by the gate voltage the effective sign of the charge carriers changes from positive (holes) to negative (electrons). The electron-like part of the dynamic response does not show quantum plateaus and is well described within the classical Drude model. PACS numbers:The strong spin-orbit coupling and an inverted band structure in mercury telluride makes this material to a nearly universal tool to probe novel physical effects with the film thickness being a tuning parameter [1,2]. If the thickness of HgTe wells is below critical, d < d c ≈ 6.3 nm, the sequence of the conduction and valence bands is conventional and a trivial insulating state is realized. For thicker films and in the bulk mercury telluride the inversion of valence and conduction bands leads to topologically non-trivial surface states [3,4]. This state is characterised by the locking of the electron spin and the electron momentum and they are topologically protected against non-magnetic impurity scattering.If the thickness of HgTe well is equal to critical, the gap between valence and conduction bands disappears and a two-dimensional (2D) electron gas is formed with Dirac cone dispersion [1,2]. Close to the center of the Dirac cone the electron spin is not a good quantum number, but has to be replaced by pseudo-spin or helicity [3,5]. Due to the particle-hole symmetry of these states, the quantum Hall effect becomes shifted by a half-integer and takes the form σ xy = γ(n+1/2)e 2 /h. In well-investigated case of graphene [6,7] the states are fourfold degenerate, i.e. γ = 4, as two Dirac cones are present in the Brillouin zone which are both doubly spin-degenerate.Magneto-optics in the terahertz range has been proven to be an effective tool to investigate two-dimensional conducting states in several quantum systems, like graphene [8-10], Bi 2 Se 3 [11][12][13][14], and HgTe [15][16][17][18][19][20][21][22]. Magneto-optical spectroscopy has the advantages of being contact-free and of directly accessing the effective mass m c via the cyclotron resonance Ω c = eB/m c . Here B is the external magnetic field.In the dynamical regime the unusual character of the quantum Hall effect in systems with Dirac cones can be shown [23][24][25][26] to lead to a universal values of the Faraday and Kerr rotation with θ F = α ∼ 1/137 and θ K = π/2, respectively. Such predictions have been recently confirmed experimentally in graphene [9], where the Faraday angle is additio...

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Room temperature electrically tunable terahertz Faraday effect

Cited by 39 publications

References 25 publications

Cyclotron-resonance-assisted photocurrents in surface states of a three-dimensional topological insulator based on a strained high-mobility HgTe film

Cyclotron-resonance-assisted photocurrents in surface states of a three-dimensional topological insulator based on a strained high-mobility HgTe film

Quantum oscillations of photocurrents in HgTe quantum wells with Dirac and parabolic dispersions

Universal Faraday Rotation in HgTe Wells with Critical Thickness

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