Characterization of structure and superconducting properties of low-temperature phase of Pb-Bi alloy films

Tian, Mingyang; Wang, Jufeng; Du, Hongjian; Chuan-Xu, Ma; Wang, Bing

doi:10.7498/aps.70.20210482

Cited by 4 publications

(4 citation statements)

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“…15,41,44 The growth morphology is clearly contrasted from the formation of Pb−Bi alloy films through the codeposition of Pb and Bi. 46,47 This clearly indicates that the extra islands are Bi islands in a distinct monolayer structure from that of the α-Bi films reported previously.…”

Section: Square-lattice Bismuth Monolayer On Pb Filmssupporting

confidence: 59%

“…The height profile of one representative island is shown in Figure d, where one can measure the diameter of the 1 ML (2 ML) island as 16 nm (3 nm) and the layer height as ∼3.2 Å for both layers. The monolayer height is distinct from that of Pb islands and half of those of most α-Bi films reported, which correspond to the puckered structure. ,, The growth morphology is clearly contrasted from the formation of Pb–Bi alloy films through the codeposition of Pb and Bi. , This clearly indicates that the extra islands are Bi islands in a distinct monolayer structure from that of the α-Bi films reported previously.…”

Section: Resultsmentioning

confidence: 58%

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Realizing a Superconducting Square-Lattice Bismuth Monolayer

Jin

Yeom

2023

ACS Nano

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Interplay of crystal symmetry, strong spin−orbit coupling (SOC), and many-body interactions in low-dimensional materials provides a fertile ground for the discovery of unconventional electronic and magnetic properties and versatile functionalities. Two-dimensional (2D) allotropes of group 15 elements are appealing due to their structures and controllability over symmetries and topology under strong SOC. Here, we report the heteroepitaxial growth of a proximityinduced superconducting 2D square-lattice bismuth monolayer on superconducting Pb films. The square lattice of monolayer bismuth films in a C 4 symmetry together with a stripey moireś tructure is clearly resolved by our scanning tunneling microscopy, and its atomic structure is revealed by density functional theory (DFT) calculations. A Rashba-type spin-split Dirac band is predicted by DFT calculations to exist at the Fermi level and becomes superconducting through the proximity effect from the Pb substrate. We suggest the possibility of a topological superconducting state in this system with magnetic dopants/field. This work introduces an intriguing material platform with 2D Dirac bands, strong SOC, topological superconductivity, and the moirésuperstructure.

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Section: Square-lattice Bismuth Monolayer On Pb Filmssupporting

confidence: 59%

Section: Resultsmentioning

confidence: 58%

Realizing a Superconducting Square-Lattice Bismuth Monolayer

Jin

Yeom

2023

ACS Nano

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“…不同元素配比的铅铋(Pb-Bi)合金相的超导转变温度和临界磁场性质都被大量研究 [14−16] , 包括合金相图中的稳定e相, 即Pb 7 Bi 3 [17] . 通常情况下, 低温制备的铅铋合金结构不同于e相 [18,19] , 但其具体的结构信息和电子学性质仍缺乏深入研究. 我们之前的工作报道了低温稳定的Pb 1-x Bi x (x ≈ 0.1)合金相 [20] , 确定了合金结构是部分铅被 dI/dV谱超导能隙的拟合采用如下公式 [21] :…”

Section: 引言unclassified

Structural and superconducting properties of low-temperature ultrathin PbBi<sub>3</sub> films

王巨丰¹,

田明阳²,

杜宏健³

et al. 2022

Acta Phys. Sin.

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Bismuth (Bi), as the stable heaviest element in the periodic table of elements, has strong spin-orbit coupling, which has attracted a lot attention as the parent material of various known topological insulators. Previous calculations predicted that Bi(111) with a thickness of less than eight bilayers and the ultrathin black-phosphorus-like Bi(110) films were single-element two-dimensional (2D) topological insulators. However, it is generally believed that these crystalline bismuth phases are either non-superconductive or with quite low transition temperature (0.5 mK). Since lead (Pb) is a good superconducting elementary material and there is a relatively small radius difference between the Bi and Pb atoms, they can be mixed to form superconducting alloys with any ratios, according to the Hume-Rothery rule. One may thus expect to form crystalline Bi based superconductors by Pb substitution, which might host intriguing topological superconductivities. While our previous work has demonstrated a low-temperature stable Pb1-xBix (x~0.1) alloy phase in which Pb in the Pb(111) structure is partially replaced by Bi, the Bi crystalline structure-based phases of the superconducting alloys still lack in-depth research. Here, we report a new low-temperature phase of Pb-Bi alloy thin films, namely PbBi3, on the Si(111)-(7×7) substrate, by co-depositing Pb and Bi at a low temperature of about 100 K followed by an annealing treatment of 200 K for 2 h. Using low-temperature scanning tunneling microscopy and spectroscopy (STM/STS), we in situ characterize the surface structure and superconducting properties of the Pb-Bi alloy films with a nominal thickness of about 4.8 nm. Two spatially separated phases with quasi-tetragonal structures are observed in the surface of the Pb-Bi alloy films, which can be identified as the pure Bi(110) phase and the PbBi3 phase, based on their distinct atomic structures, step heights and STS spectra. The PbBi3 film has a base structure similar to Bi(110), where about 25% of the Bi atoms are replaced by Pb, and the surface shows a root2×root2R45° reconstructed structure. The superconducting behavior of the PbBi3 phase is characterized by the STS spectra. The superconducting transition temperature is about 6.13 K, determined by the variable-temperature measurements. The corresponding ratio of 2Delta(0)/kBTc is about 4.62 with the superconducting gap Delta(0)=1.22 meV at 0 K, suggesting that PbBi3 is a strong coupling superconductor. By measuring the magnetic field dependent superconducting coherence lengths, we obtain that the upper critical field is larger than 0.92 T. We further investigate the superconducting proximity effect in the normal metal-superconductor (N-S) heterojunctions consisting of the non-superconducting Bi(110) and the superconducting PbBi3 domains. The N-S heterojunctions with both in-plane and step-like configurations are measured, which suggest that the atomic connection and the area of the quasi-2D Josephson junctions and the external magnetic field can affect the lateral superconducting penetration lengths. We also observe the zero-bias conductance peaks (ZBCPs) in the superconducting gap of the PbBi3 surfaces in some cases at zero magnetic field. By measuring dI/dV spectra at variable temperatures and by adopting a superconducting Nb tip, we identify that the ZBCPs are originated from the superconductor-insulator-superconductor (S-I-S) junction formed between a superconducting tip and the sample, Nevertheless, the Bi(110)-based PbBi3 phase may provide a possible platform to explore the intriguing topological superconducting behaviors by further examining the behaviors at the vortexes under magnetic fields, or in the vicinity of the potentially topological superconducting Bi(110) islands by considering the proximity effect.

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“…Recently it was found that PbBi compound of atomic thickness grown on silicon surface was found to demonstrate one-dimensional metallic spin-polarized electron states (Mihalyuk et al, 2021) a promising quantum effect relevant for spintronic applications. Remarkably that Pb-Bi films with a nominal thickness of about 4.8 nm grown on silicon demonstrate a superconducting transition at 6.13 K (Tian et al, 2021;Wang et al, 2022). In this regard there is an interest for engineering Pb and Bi containing materials on other semiconducting surfaces.…”

Section: Introductionmentioning

confidence: 99%

Insights Into the Electronic Properties of PbBi Atomic Layers on Ge(111) and Si(111) Surfaces

et al. 2022

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Co-adsorption of Pb and Bi onto Si(111) and Ge(111) surfaces has been found to result in formation of atomic-layer PbBi compounds having similar structures. These are two co-existing crystalline PbBi phases with 23×23 and 2 × 2 periodicities. Using density functional theory calculations, we found that these two phases present insulating and highly anisotropic metallic systems, respectively. However, electronic structure of the metallic 2 × 2-PbBi phase on Ge(111) appears qualitatively different from that on the Si(111). We investigated electronic properties of the PbBi compound considering the effects induced by the different supporting substrates, namely Si(111) and Ge(111). As a part of comparative study, we made the chemical-bonding analysis and examined a free-standing PbBi layer inspecting the dependence of its spectral characteristics on the compressive/tensile strain. We believe that the present findings will play an important role in the development of new electronic devices fabricated in the ultimate two-dimensional limit.

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Characterization of structure and superconducting properties of low-temperature phase of Pb-Bi alloy films

Cited by 4 publications

References 38 publications

Realizing a Superconducting Square-Lattice Bismuth Monolayer

Realizing a Superconducting Square-Lattice Bismuth Monolayer

Structural and superconducting properties of low-temperature ultrathin PbBi<sub>3</sub> films

Insights Into the Electronic Properties of PbBi Atomic Layers on Ge(111) and Si(111) Surfaces

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