Charge puddles in a completely compensated topological insulator

Rischau, Carl Willem; Giannini, E.; Beek, C. J. van der

doi:10.1088/1367-2630/18/7/073024

Cited by 12 publications

(18 citation statements)

References 41 publications

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“…In the last line we uses that in the asymptotic regime, n 0 ∼ 1/∆ 3 , see Eq. (7). This formula misses logarithmic corrections to n 0 which give, however only subleading terms beyond the precision of Eq.…”

Section: Screening By Metallic Surface Statesmentioning

confidence: 97%

“…As discussed in the introduction, Efros and Shklovskii [16] estimated the length scale triggering puddle formation (for a different geometry) from the condition σ(L z ) ∼ ∆, leading to a length scale proportional to ∆ 2 as discussed in Eq. (7). We will need in the following a more quantitative version of this argument.…”

Section: Screening By Metallic Surface Statesmentioning

confidence: 99%

“…In graphene it has been shown both theoretically and experimentally that puddles are necessary to understand most transport experiments close to charge neutrality [2][3][4][5]. Recently, they have been observed for the first time in the bulk of a three-dimensional topological insulator [6,7]. These materials, from the class of the Bi 2−x Sb x Te 3−y Se y compounds [8], are almost perfectly compensated semiconductors with a band gap of order 250 − 300 meV almost 2 orders of magnitude larger than the typical Coulomb energy E c of neighboring dopants [6].…”

Section: Introductionmentioning

confidence: 99%

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Length scale of puddle formation in compensation-doped semiconductors and topological insulators

et al. 2017

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Section: Screening By Metallic Surface Statesmentioning

confidence: 97%

Section: Screening By Metallic Surface Statesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Length scale of puddle formation in compensation-doped semiconductors and topological insulators

et al. 2017

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“…Puddles partially screen the large fluctuations of the Coulomb potential, and they "evaporate" with increasing temperature due to the additional screening contribution of thermally activated carriers [15]. For * grueninger@ph2.uni-koeln.de bulk transport, puddles are assumed to explain the small activation energy observed in the resistivity [12], the coexistence of electron-type and hole-type carriers in compensated samples [16], and the gigantic negative magnetoresistance observed in TlBi 0.15 Sb 0.85 Te 2 [17]. However, the smoking gun for bulk puddles is a Drude-like feature in the optical conductivity which is suppressed on a temperature scale k B T = E C given by the Coulomb interaction between neighboring dopants [15].…”

Section: Introductionmentioning

confidence: 99%

Charge puddles in the bulk and on the surface of the topological insulator BiSbTeSe2 studied by scanning tunneling microscopy and optical spectroscopy

et al. 2017

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The topological insulator BiSbTeSe2 corresponds to a compensated semiconductor in which strong Coulomb disorder gives rise to the formation of charge puddles, i.e., local accumulations of charge carriers, both in the bulk and on the surface. Bulk puddles are formed if the fluctuations of the Coulomb potential are as large as half of the band gap. The gapless surface, in contrast, is sensitive to small fluctuations but the potential is strongly suppressed due to the additional screening channel provided by metallic surface carriers. To study the quantitative relationship between the properties of bulk puddles and surface puddles, we performed infrared transmittance measurements as well as scanning tunneling microscopy measurements on the same sample of BiSbTeSe2, which is close to perfect compensation. At 5.5 K, we find surface potential fluctuations occurring on a length scale rs = 40 − 50 nm with amplitude Γ = 8 − 14 meV which is much smaller than in the bulk, where optical measurements detect the formation of bulk puddles. In this nominally undoped compound, the value of Γ is smaller than expected for pure screening by surface carriers, and we argue that this arises most likely from a cooperative effect of bulk screening and surface screening. arXiv:1708.09166v1 [cond-mat.mes-hall]

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“…In BiSbTeSe 2 , E C /k B = 30 − 60 K was observed [6,8]. Also, puddles can explain the coexistence of electron-type and hole-type carriers in compensated samples [9] and the small activation energy observed in dc resistivity data [5]. Intriguingly, puddles are further found to be responsible for the surprising effect of gigantic negative magnetoresistance reported for TlBi 0.15 Sb 0.85 Te 2 [10].…”

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confidence: 99%

Large positive magnetoconductivity at microwave frequencies in the compensated topological insulator BiSbTeSe2

et al. 2019

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The bulk electronic properties of compensated topological insulators are strongly affected by the self-organized formation of charge puddles at low temperature, but their response in the microwave frequency range is little studied. We employed broadband impedance spectroscopy up to 5 GHz to address the ac transport properties of well-compensated BiSbTeSe2, where charge puddles are known to form as metallic entities embedded in an insulating host. It turns out that the average puddle size sets the characteristic frequency νc in the GHz range, across which the insulating dc behavior is separated from a metal-like high-frequency response of delocalized carriers within the puddles. This νc is found to be controlled by a magnetic field, giving rise to a large positive magneto-conductivity observable only in the GHz range. This curious phenomenon is driven by the Zeeman energy which affects the local band filling in the disordered potential landscape to enhance the puddle size.One of the most prominent features of topological insulators is the spin-momentum locking in the surface states [1], which is particularly useful for spintronic applications [2]. To efficiently utilize the spin-momentum-locked surface states in applications, one should get rid of the residual bulk conduction, and this has been achieved by carefully compensating residual donors by residual acceptors through composition tuning in the Bi x Sb 2−x Te y Se 3−y compound [1,3,4]. Although such compensated topological insulators show reasonably high bulk insulation in dc, it has been elucidated that their transport properties are not only determined by the topologically protected surface states but also by the presence of charge puddles in the bulk [5], particularly at finite frequencies up to the infrared range [6]. This is because the Coulomb disorder of the randomly distributed charged donors and acceptors gives rise to potential fluctuations which grow as √ R in a volume of size R 3 [5, 7]; this inevitably leads to the self-organized formation of charge puddles on a mesoscopic length scale L at low temperatures. On this length scale, portions of a sample contain delocalized charge carriers which give rise to a Drude-like contribution to the optical conductivity σ (ν) above the Thouless cut-off frequency 2πν c = D/L 2 [6]. This cut-off is given by the time scale needed to diffuse through a puddle with the diffusion constant D. Using a simple scaling argument [5,7], L ≈ 100 − 500 nm is expected on the basis of infrared data [6]. This corresponds to ν c in the GHz range.Since the current-day information technology operates in the GHz range, understanding the microwave response of topological-insulator materials would be of crucial importance for their future applications in spintronics; nevertheless, the role of puddles in the transport properties in the GHz range has not yet been studied. This work is conceived to address this lack of understanding. At low temperature, the Drude-like puddle contribution to σ (ν) and its discrepancy with the dc conducti...

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Charge puddles in a completely compensated topological insulator

Cited by 12 publications

References 41 publications

Length scale of puddle formation in compensation-doped semiconductors and topological insulators

Length scale of puddle formation in compensation-doped semiconductors and topological insulators

Charge puddles in the bulk and on the surface of the topological insulator BiSbTeSe2 studied by scanning tunneling microscopy and optical spectroscopy

Large positive magnetoconductivity at microwave frequencies in the compensated topological insulator BiSbTeSe2

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