Dimensional Crossover and Topological Phase Transition in Dirac Semimetal Na<sub>3</sub>Bi Films

Xia, Hui-Nan; Yang, Li; Cai, Min; Qin, Le; Zou, Nianlong; Peng, Lang; Duan, Wenhui; Xu, Yong; Zhang, Wenhao; Fu, Ying-Shuang

doi:10.1021/acsnano.9b04933

Cited by 28 publications

(46 citation statements)

References 57 publications

(131 reference statements)

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“…A topologically non‐trivial scenario was subsequently predicted by Xia et al. [ 72 ] for films with thickness up to seven ML; for thicker films interlayer coupling is expected to induce a further s–p band inversion and a transition to a topologically trivial state. Figure 5d shows the size of the bulk bandgap reported by Xia et al.…”

Section: D Confinementmentioning

confidence: 81%

“…In this regard, a post‐growth anneal in pure Na overflux has been demonstrated to be effective in “curing” the surface by mitigating the presence of vacancies. [ 72 ]…”

Section: Experimental Results In Thin‐film Na3bimentioning

confidence: 99%

“…Thin films of Na 3 Bi were first explored in bilayer graphene on SiC [ 70–72 ] and Si(111) 7 × 7 [ 67–70 ] as they are ultraflat, possess similar threefold rotational symmetry, and had been used in the past to grow ultrathin films of other topological insulators. [ 92–96 ] Zhang et al.…”

Section: Experimental Results In Thin‐film Na3bimentioning

confidence: 99%

“…[ 69 ] Several works showing large‐area STM scans of Na 3 Bi, like the one in Figure a, often reported the formation of atomically flat terraces with lateral extent of hundreds of nanometers, [ 66,69,71,74,98,99 ] sometimes of very different thicknesses. [ 72 ] The appearance of screw lines and hexagonal domains has been observed on all substrates, [ 67,71 ] while from atomic resolution images (inset of Figure 2a) a lattice constant of 5.45Å can be measured. [ 67,68,73 ]…”

Section: Experimental Results In Thin‐film Na3bimentioning

confidence: 99%

“…These values for the Fermi velocity, confirming the anisotropy of the dispersion, are in good agreement with several other reports on Na 3 Bi bulk and thin films obtained by a variety of experimental techniques and substrates. [ 47,56,72,73,77,100 ]…”

Section: Experimental Results In Thin‐film Na3bimentioning

confidence: 99%

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Progress in Epitaxial Thin‐Film Na₃Bi as a Topological Electronic Material

et al. 2021

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Trisodium bismuthide (Na3Bi) is the first experimentally verified topological Dirac semimetal, and is a 3D analogue of graphene hosting relativistic Dirac fermions. Its unconventional momentum–energy relationship is interesting from a fundamental perspective, yielding exciting physical properties such as chiral charge carriers, the chiral anomaly, and weak anti‐localization. It also shows promise for realizing topological electronic devices such as topological transistors. Herein, an overview of the substantial progress achieved in the last few years on Na3Bi is presented, with a focus on technologically relevant large‐area thin films synthesized via molecular beam epitaxy. Key theoretical aspects underpinning the unique electronic properties of Na3Bi are introduced. Next, the growth process on different substrates is reviewed. Spectroscopic and microscopic features are illustrated, and an analysis of semiclassical and quantum transport phenomena in different doping regimes is provided. The emergent properties arising from confinement in two dimensions, including thickness‐dependent and electric‐field‐driven topological phase transitions, are addressed, with an outlook toward current challenges and expected future progress.

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Section: D Confinementmentioning

confidence: 81%

“…In this regard, a post‐growth anneal in pure Na overflux has been demonstrated to be effective in “curing” the surface by mitigating the presence of vacancies. [ 72 ]…”

Section: Experimental Results In Thin‐film Na3bimentioning

confidence: 99%

Section: Experimental Results In Thin‐film Na3bimentioning

confidence: 99%

Section: Experimental Results In Thin‐film Na3bimentioning

confidence: 99%

Section: Experimental Results In Thin‐film Na3bimentioning

confidence: 99%

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Progress in Epitaxial Thin‐Film Na₃Bi as a Topological Electronic Material

et al. 2021

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2D Weyl‐Semimetal States Achieved by a Thickness‐Dependent Crossover and Topological Phase Transition in Bi_0.96Sb_0.04 Thin Films

Jang,

Salawu,

Kim

et al. 2023

Adv Funct Materials

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Despite theoretical expectations for 2D Weyl semimetals (WSMs), realizing stable 2D topological semimetal states experimentally is currently a great challenge. Here, 2D WSM states achieved by a thickness‐dependent topological phase transition from 3D Dirac semimetal to 2D WSM in molecular‐beam‐epitaxy‐grown Bi0.96Sb0.04 thin films are reported. 2D weak anti‐localization (WAL) and chiral anomaly arise in the Bi0.96Sb0.04 films for thicknesses below ≈10 nm, supporting 2D Weyl semimetallic transport in the films. This is particularly evident from magnetoresistance (MR) measurements which show cusp structures at around B = 0, indicating WAL, and negative MR, typical of chiral anomaly, only for layers with thicknesses below ≈10 nm. The temperature dependencies of the dephasing length for various thicknesses are consistent with those of the MR. Analysis based on second harmonic generation, terahertz emission, Seebeck/Hall effects, Raman scattering, X‐ray diffraction, and X‐ray photoemission demonstrates that the Dirac‐ to Weyl‐semimetal phase transition for films thinner than ≈10 nm is induced by inversion‐symmetry breaking due to the lattice‐mismatch strain between the Bi0.96Sb0.04 film and substrate. The realization of 2D WSMs is particularly significant for applications in high‐speed electronics, spintronics, and quantum computations due to their high mobility, chiral spin, and topologically‐protected quantum qubits.

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Atomic Visualization and Switching of Ferroelectric Order in β‐In₂Se₃ Films at the Single Layer Limit

et al. 2021

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BiFeO 3 ). [8,9] The polarization instability with depolarization field in ultrathin ferroelectrics thus critically limit their applications in nanoelectronics. [10] With the help of strong anisotropy and lower free carrier density, 2D vdW materials and heterostructures may overcome these obstacles, as demonstrated in CuInP 2 S 6 , [11] WTe 2 , [12] MoTe 2 . [13] and SnSe. [14] 2D ferroelectricity has been established as an advantageous property that inspires broad applications in high-density capacitors, piezoelectric sensors, and field effect transistors. [15] As a typical representative of III-VI semiconductor, a branch of In 2 Se 3 -based vdW family has been theoretically predicted [16] and experimentally verified [17][18][19] to host intrinsic room-temperature ferroelectricity down to the 2D limit, where reversible spontaneous electric polarization is expected in both out-of-plane and in-plane orientations. For the polymorphic structure of bulk In 2 Se 3 , there exist about five stable phases at ambient pressure: α-, β-, γ-, δ-, and κ-In 2 Se 3 , among which only the α and β phases can be stabilized in nature as vdW materials that are easily exfoliated or synthetized into thin films. [20] Within a primitive unit cell (UC), both αand β-In 2 Se 3 are constituted of bonded quintuple layer (QL) in a sequence of Se-In-Se-In-Se, but vertically stack in different orders. While α-In 2 Se 3 has a zincblende crystal structure and possesses outof-plane ferroelectricity with dipole locking in both bulk and nanoflake forms, [18,19,21,22] there is still no consensus on the precise alignments of the atomic layers in β-In 2 Se 3 . [23][24][25] Theoretically speaking, the pristine β-In 2 Se 3 is arranged in a facecentered cubic (fcc) order with a metastable nature, and can easily evolve into an unsymmetric fcc′ structure (β′-In 2 Se 3 ) by slightly shifting the central Se layer in horizontal direction away from the ideal fcc positions, [16] as compared in Figure 1a,b. The total energy of β′-In 2 Se 3 is only 0.057 eV per UC higher than α-In 2 Se 3 , however, its ferroelectricity is much more complex, partially due to its structural ambiguity and environmentdependent phase transition among variant metastable states. [16] Robust ferroelectricity has been experimentally confirmed in both αand β′-In 2 Se 3 down to the single layer limit and can survive at room temperature. [23,26] However, very recent optical and electron microscopy measurements argue that β′-In 2 Se 3 is in an in-plane anti-ferroelectric order that is featured by anisotropic nanostriped surface morphology. [24] Moreover, a 2D ferroelectrics have received wide interest due to the remarkable quantum states of emerging physics at reduced dimensionality, associated with their exotic properties in high-performance and nonvolatile functional devices. Here, by combing molecular beam epitaxy synthesis and scanning tunneling microscopy characterization, two metastable phases of layered In 2 Se 3 films: β′and β*-In 2 Se 3 are reported, which develop different types of in...

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Dimensional Crossover and Topological Phase Transition in Dirac Semimetal Na₃Bi Films

Cited by 28 publications

References 57 publications

Progress in Epitaxial Thin‐Film Na₃Bi as a Topological Electronic Material

Progress in Epitaxial Thin‐Film Na₃Bi as a Topological Electronic Material

2D Weyl‐Semimetal States Achieved by a Thickness‐Dependent Crossover and Topological Phase Transition in Bi_0.96Sb_0.04 Thin Films

Atomic Visualization and Switching of Ferroelectric Order in β‐In₂Se₃ Films at the Single Layer Limit

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Dimensional Crossover and Topological Phase Transition in Dirac Semimetal Na3Bi Films

Cited by 28 publications

References 57 publications

Progress in Epitaxial Thin‐Film Na3Bi as a Topological Electronic Material

Progress in Epitaxial Thin‐Film Na3Bi as a Topological Electronic Material

2D Weyl‐Semimetal States Achieved by a Thickness‐Dependent Crossover and Topological Phase Transition in Bi0.96Sb0.04 Thin Films

Atomic Visualization and Switching of Ferroelectric Order in β‐In2Se3 Films at the Single Layer Limit

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Product

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Dimensional Crossover and Topological Phase Transition in Dirac Semimetal Na₃Bi Films

Progress in Epitaxial Thin‐Film Na₃Bi as a Topological Electronic Material

Progress in Epitaxial Thin‐Film Na₃Bi as a Topological Electronic Material

2D Weyl‐Semimetal States Achieved by a Thickness‐Dependent Crossover and Topological Phase Transition in Bi_0.96Sb_0.04 Thin Films

Atomic Visualization and Switching of Ferroelectric Order in β‐In₂Se₃ Films at the Single Layer Limit