Biased doped silicene as a way to tune electronic conduction

Y. G. Pogorelov and V. M. Loktev

Phys. Rev. B 93, 045117 – Published 15 January 2016

Abstract

Restructuring of the electronic spectrum in a buckled silicene monolayer under some applied voltage between its two sublattices and in the presence of certain impurity atoms is considered. Special attention is given to formation of localized impurity levels within the band gap and to their collectivization at finite impurity concentration. It is shown that a qualitative restructuring of the quasiparticle spectrum within the initial band gap and then specific metal-insulator phase transitions are possible for such disordered system and can be effectively controlled by variation of the electric field bias at a given impurity perturbation potential and concentration. Since these effects are expected at low impurity concentrations but at not too low temperatures, they can be promising for practical applications in nanoelectronic devices.

Received 17 September 2015
Revised 22 November 2015

DOI:https://doi.org/10.1103/PhysRevB.93.045117

Authors & Affiliations

Y. G. Pogorelov¹ and V. M. Loktev^2,3

¹IFIMUP-IN, Departamento de Física, Universidade do Porto, Portugal
²Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, Kyiv, Ukraine
³National Technical University of Ukraine “Kyiv Polytechnic Institute”, Kyiv, Ukraine

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Vol. 93, Iss. 4 — 15 January 2016

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Images

Figure 1
Crystalline structure of a buckled silicene plane where silicon atoms are up- or down-shifted by $d_{z} / 2$ from the initial hexagonal plane (red lines). The dashed line delimits a unit cell at the position $n$ with two nonequivalent sites, of A type (clear) and B type (dark); blue arrows indicate three vectors $δ$ between nearest-neighbor Si atoms.
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Figure 2
Spectrum restructuring in silicene with Lifshitz impurities at the choice of their parameters $U = - Λ$ and $c = 0.01$ as a function of the bias $V$ . Insets show the particular dispersion laws as a function of the momentum variable $ξ$ at (a) weak ( $V = 0.004 Λ$ ), (b) medium ( $V = 0.11 Λ$ ), and (c) strong ( $V = 0.23 Λ$ ) bias. Black lines mark the edges of conduction and valence bands (dashed in absence and solid in presence of impurities). Blue areas present filled bandlike states and golden filled localized states, limited from above by the Fermi level (green dashed line); red dashed lines mark the concentration broadening of impurity level. Vertical dashed lines indicate the critical bias levels: $V_{dec}$ for the band decomposition (orange), $V_{M}$ for the Mott (blue), and $V_{A}$ for the Anderson (purple) phase transitions.
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Figure 3
Anderson impurity at an interstitial position in silicene lattice.
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Figure 4
Silicene dispersion laws near their splitting by the impurity level $ɛ_{imp}$ (red dashed line) show an in-plane anisotropy. Inset resolves them for particular directions: (1) for $ɛ_{+} (ξ, π)$ , (2) for $ɛ_{+} (ξ, 0)$ , (3) for $ɛ_{-} (ξ, 0)$ , (4) for $- (ξ, π / 2)$ , (5) for $ɛ_{-} (ξ, π)$ . The impurity parameters are chosen as $ɛ_{imp} = 0.1 Λ, \tilde{c} = 0.005$ , and the bias $V = 0.4 ɛ_{imp}$ . The arrows indicate the splitting range near the impurity level $ɛ_{imp}$ .
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Figure 5
Dispersion curves for silicene with Anderson impurities at the choice of their parameters as in Fig. 4. At growing bias $V$ , the bottom of the conduction band moves towards the impurity level $ɛ_{imp}$ . MIT occurs at $V_{M} \approx 0.84 ɛ_{imp}$ [in between panels (a) and (b)] and the Anderson transition at $V_{A} \approx 2 ɛ_{imp}$ [in between panels (c) and (d)].
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Figure 6
Phase diagrams of electronic states in biased doped silicene in the variables “impurity concentration–electric bias” for two models of impurity perturbation. The blue areas correspond to metallic phases, separated by the Mott MIT lines $V_{M}$ (dark blue) from insulating phases (white areas); Anderson transitions (collapse of impurity band) are shown by the red lines; dashed lines indicate decoupling of the impurity band from the main band, $V_{dec}$ (in the Lifshitz model), or complete filling of all the states up to the impurity level $ɛ_{imp}$ (in the Anderson model).
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