Crossover of the three-dimensional topological insulator Bi2Se3 to the two-dimensional limit

Zhang, Yi; He, Ke; Chang, Cui Zu; Song, Can-Li; Wang, Li Li; Chen, Xi; Jia, Jin; Fang, Zhong; Dai, Xi; Shan, Wen-Yu; Shen, Shun-Qing; Niu, Qian; Qi, Xiao Liang; Zhang, Shou Cheng; Cun, Xu; Xue, Qi Kun

doi:10.1038/nphys1689

Cited by 1,310 publications

(984 citation statements)

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“…In a 3QL Bi 2 Se 3 film, a hybridized gap is expected to open at the Dirac point due to the coupling of top and bottom surface states [18], which has been observed in ARPES measurements [6]. Evidence of a gap opening can be seen in the spectra in Fig.…”

Section: (B))mentioning

confidence: 54%

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Scanning tunneling microscopy of gate tunable topological insulator Bi2Se3thin films

Zhang

Levy

et al. 2013

Phys. Rev. B

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Electrical field control of the carrier density of topological insulators (TI) has greatly expanded the possible practical use of these materials. However, the combination of low temperature local probe studies and a gate tunable TI device remains challenging. We have overcome this limitation by scanning tunneling microscopy and spectroscopy measurements on in-situ molecular beam epitaxy growth of Bi 2 Se 3 films on SrTiO 3 substrates with pre-patterned electrodes. Using this gating method, we are able to shift the Fermi level of the top surface states by ≈250 meV on a 3 nm thick Bi 2 Se 3 device. We report field effect studies of the surface state dispersion, band gap, and electronic structure at the Fermi level.

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Section: (B))mentioning

confidence: 54%

“…Angle resolved photoemission (ARPES) [3][4][5][6] and scanning tunneling microscopy (STM) [7][8][9][10] have confirmed the existence of these surface states in various compounds. These protected surface states are helical Dirac fermions which are predicted to host many striking quantum phenomena [1,2].…”

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confidence: 99%

Scanning tunneling microscopy of gate tunable topological insulator Bi2Se3thin films

Zhang

Levy

et al. 2013

Phys. Rev. B

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“…Moreover, we find rather large spin-splitting (~180 meV) at the valence band maximum (VBM) of the monolayer Figure 1b shows the reflection high-energy electron diffraction (RHEED) pattern of our substrate of epitaxial bilayer graphene-terminated 6H-SiC(0001) 22 . The similar layered structure and chemically inert surface of graphene make it a perfect substrate for van der Waals epitaxial growth of two-dimensional layered materials 21,23,24 . We have successfully grown high-quality singlecrystal MoSe 2 films of large size (~5 mm× 2 mm), from monolayer up to 8 ML, with layer-by-layer control of thickness, by delicate control of the growth conditions.…”

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confidence: 99%

Direct observation of the transition from indirect to direct bandgap in atomically thin epitaxial MoSe2

et al. 2013

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The layered transition metal dichalcogenides (TMDs) MX 2 (M = Mo, W; X = S, Se, Te), a class of graphene-like two-dimensional materials, have attracted significant interest because they demonstrate quantum confinement at the single-layer limit 13 . As with graphene, these layered materials can be easily exfoliated mechanically to provide monolayers 3-7,14-16 and assume a hexagonal honeycomb structure in which the M and X atoms are located at alternating corners of the hexagons. However, unlike graphene, which has a gapless Dirac cone band structure, MX 2 has a rather large bandgap, making these materials more versatile as candidates for thin, flexible device applications and useful for a variety of other applications including lubrication 16 , catalysis 17 , transistors 18 and lithium-ion batteries 19 . Most interestingly, an indirect to direct bandgap transition in the monolayer limit has been predicted theoretically and supported experimentally by optical measurements [3][4][5]9,12 . Because of the direct bandgap, monolayer MX 2 is favourable for optoelectronic applications5 and field-effect transistors 15,16,18 . Furthermore, both the conduction and valence bands have two energy degenerate valleys at corners of the first Brillouin zone, making it viable to optically control the charge carriers in these valleys and suggesting the possibility of valley-based electronic and optoelectronic applications 3,6-8 .Despite these exciting developments, direct experimental verification of the novel band structure at the monolayer limit remains lacking. Furthermore, for many applications, it is vital to manufacture high-quality epitaxial films with controllable methods such as chemical vapour deposition (CVD) or molecular beam epitaxy (MBE) 20,21 .

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“…On the other hand, the part of the nanoribbon with only 1 QL shows little signal in both MIM-C and MIM-R channels, implying very high local R s > 10 MΩ/square. Indeed, we have studied multiple Bi 2 Se 3 nanoribbons with 1 or 2 QLs and measured negligible conductivity by MIM.Recent theoretical calculations and ARPES measurements have addressed the 3D to 2D crossover of ultrathin topological insulators 17,18 . For Bi 2 Se 3 down to 1 and 2 QLs, large energy gaps open up in both the bulk and the surface states, whereas for 3QLs and above, the surface gap starts to diminish.…”

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confidence: 99%

“…Recent theoretical calculations and ARPES measurements have addressed the 3D to 2D crossover of ultrathin topological insulators 17,18 . For Bi 2 Se 3 down to 1 and 2 QLs, large energy gaps open up in both the bulk and the surface states, whereas for 3QLs and above, the surface gap starts to diminish.…”

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confidence: 99%

Ultrathin Topological Insulator Bi₂Se₃ Nanoribbons Exfoliated by Atomic Force Microscopy

Hong¹,

Kundhikanjana²,

Judy³

et al. 2010

Nano Lett.

168

141

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Ultra-thin topological insulator nanostructures, in which coupling between top and bottom surface states takes place, are of great intellectual and practical importance. Due to the weak Van der Waals interaction between adjacent quintuple layers (QLs), the layered bismuth selenide (Bi 2 Se 3 ), a single Dirac-cone topological insulator with a large bulk gap, can be exfoliated down to a few QLs. In this paper, we report the first controlled mechanical exfoliation of Bi 2 Se 3 nanoribbons (> 50 QLs) by an atomic force microscope (AFM) tip down to a single QL. Microwave impedance microscopy is employed to map out the local conductivity of such ultra-thin nanoribbons, showing drastic difference in sheet resistance between 1~2 QLs and 4~5 QLs. Transport measurement carried out on an exfoliated (≤5 QLs) Bi 2 Se 3 device shows nonmetallic temperature dependence of resistance, in sharp contrast to the metallic behavior seen in thick (>50 QLs) ribbons. These AFM-exfoliated thin nanoribbons afford interesting candidates for studying the transition from quantum spin Hall surface to edge states.Keywords: Topological insulator, Bismuth selenide, Nanoribbon, Mechanical exfoliation, Atomic force microscopy The metallic surface states of 3D topological insulators 1-7 are protected from disorder effects such as crystal defects and non-magnetic impurities, promising realization of dissipationless electron transport in the absence of high magnetic fields 8 . After the initial discovery of the 2D quantum spin Hall effect (QSHE) in HgTe quantum wells 7,9 , three binary compounds -Bi 2 Se 3 , Bi 2 Te 3 , and Sb 2 Te 3 were predicted and later confi rmed by angle-resolved photoemission spectroscopy (ARPES) as 3D topological insulators 10-13 . In particular, Bi 2 Se 3 has been studied due to the relatively large bulk band gap (~0.3 eV) and the simple band structure near the Dirac point. 12-17 Many exotic physical phenomena are predicted to emerge in low dimensional nanostructures of Bi 2 Se 3 . 18,19 For example, ultra-thin Bi 2 Se 3 down to a few (≤5) nanometers is expected to exhibit topologically non-trivial edge states, which serves as a new platform for the 2D QSHE 18 .In addition, tuning of the chemical potential becomes easier than thick Bi 2 Se 3 due to the suppression of bulk contribution. Fortunately, such ultra-thin Bi 2 Se 3 can be naturally obtained due to its layered rhombohedral crystal structure; two Bi and three Se atomic sheets are covalently bonded to form one quintuple layer (QL, ~1 nm thick) (Figure 1b), where adjacent QLs are coupled by relatively weak van der Waals interaction. Such anisotropic bonding structure implies that similar to the case of graphene, 20 low dimensional crystals of Bi 2 Se 3 can be generated by mechanical exfoliation, which has been achieved by several groups [21][22][23] . However, the obtained flakes are usually irregular in shape and the yield of obtaining ultra-thin flakes is low: the typical reported flakes (~10 nm) are still thick compared with the 2D limit where strong coupling betwe...

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Crossover of the three-dimensional topological insulator Bi2Se3 to the two-dimensional limit

Cited by 1,310 publications

References 32 publications

Scanning tunneling microscopy of gate tunable topological insulator Bi2Se3thin films

Scanning tunneling microscopy of gate tunable topological insulator Bi2Se3thin films

Direct observation of the transition from indirect to direct bandgap in atomically thin epitaxial MoSe2

Ultrathin Topological Insulator Bi₂Se₃ Nanoribbons Exfoliated by Atomic Force Microscopy

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Crossover of the three-dimensional topological insulator Bi2Se3 to the two-dimensional limit

Cited by 1,310 publications

References 32 publications

Scanning tunneling microscopy of gate tunable topological insulator Bi2Se3thin films

Scanning tunneling microscopy of gate tunable topological insulator Bi2Se3thin films

Direct observation of the transition from indirect to direct bandgap in atomically thin epitaxial MoSe2

Ultrathin Topological Insulator Bi2Se3 Nanoribbons Exfoliated by Atomic Force Microscopy

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Ultrathin Topological Insulator Bi₂Se₃ Nanoribbons Exfoliated by Atomic Force Microscopy