Pb Monolayer Research Articles

Strain-modulated intercalated phases of Pb monolayer with dual periodicity in SiC(0001)-graphene interface

Intercalation of metal atoms at the SiC(0001)-graphene (Gr) interface can provide confined 2D metal layers with interesting electronic properties. The intercalated Pb monolayer (ML) has shown the coexistence of the Gr(10 × 10)-moiré and a stripe phase, which still lacks understanding. Using density functional theory calculation and thermal annealing with ab initio molecular dynamics as motivated by experiment, we have studied the formation energy of Gr/Pb/SiC(0001) for different Pb coverages. Near the coverage of a Pb(111)-like ML mimicking the (10 × 10)-moiré, we find a slightly more stable stripe structure, where one half of the structure has compressive strain with Pb occupying the Si-top sites and the other half has tensile strain with Pb off the Si-top sites. This stripe structure along the Gr zigzag direction has a periodicity of 2.3 nm across the [1 2¯ 10] direction agreeing with the previous observations using scanning tunneling microscopy. Analysis with electron density difference and density of states show the tensile region has a more metallic character than the compressive region, while both are dominated by charge transfer from Pb ML to SiC(0001). The small energy difference between the stripe and Pb(111)-like structures means the two phases are almost degenerate and can coexist, which explains the experimental observations.

Lifshitz Transition in a Single-Atom-Thick GdxYb1-xPb3 Kagome Compound on Si(111).

Lanthanide (Ln) elements Gd and Yb alloyed with a Pb monolayer on the Si(111) substrate form LnPb3 compounds having the same crystal structure. They comprise a single-atom-thick Pb layer arranged in a slightly distorted kagome lattice with Ln atoms filling the hexagonal voids. They have similar electronic band structures except for the Fermi level position, which varies between the divalent Yb- and trivalent Gd-containing compounds by ∼0.47 eV. The ability to create a 2D solid solution with the unified continuous Pb layer and hexagonal voids randomly filled with either Gd or Yb atoms allows precise control of the Fermi level position. Small alteration of the Fermi level triggers drastic changes in the Fermi surface topology due to the Lifshitz transition, hence in the physical properties. In particular, the sheet resistance of the GdxYb1-xPb3/Si(111) system can be controllably varied over an order of magnitude range.

Large-Area Intercalated Two-Dimensional Pb/Graphene Heterostructure as a Platform for Generating Spin-Orbit Torque.

A scalable platform to synthesize ultrathin heavy metals may enable high-efficiency charge-to-spin conversion for next-generation spintronics. Here, we report the synthesis of air-stable, epitaxially registered monolayer Pb underneath graphene on SiC (0001) by confinement heteroepitaxy (CHet). Diffraction, spectroscopy, and microscopy reveal that CHet-based Pb intercalation predominantly exhibits a mottled hexagonal superstructure due to an ordered network of Frenkel-Kontorova-like domain walls. The system's air stability enables ex situ spin torque ferromagnetic resonance (ST-FMR) measurements that demonstrate charge-to-spin conversion in graphene/Pb/ferromagnet heterostructures with a 1.5× increase in the effective field ratio compared to control samples.

Enhancing Electrocatalytic Synthesis of Glycine with CuPb1ML Electrode Synthesized via Pb UPD

AbstractIn the field of reductive organic electrosynthesis, the hydrogen evolution reaction (HER) is considered a parasitic reaction that lowers the Faradaic efficiency of the synthesis. Metals with a high overpotential for HER are often used to prevent this. However, this limits the catalytic materials that can be used in these reactions. To expand upon the scope of available electrocatalysts, we prepared a CuPb electrode via underpotential deposition (UPD). We thereby created an electrocatalyst with a single monolayer of Pb, CuPb1ML, in which Pb weight loading is only 415 ng cm−2, yet its properties could still effectively inhibit HER. The CuPb1ML electrode was used in the electrosynthesis of glycine from oxalic acid and hydroxylamine. This reaction served as a model for a C−N bond forming reaction in acidic aqueous media. The CuPb1ML electrode was compared against a pure Pb and Cu metal electrode. The CuPb1ML electrode showed a Faradaic efficiency for glycine production of 57 %, which was 9‐fold higher than Cu and rivaled the Pb electrode. The catalytic activity of CuPb1ML was 211 μmol h−1 cm−2, which is higher than both Cu and Pb. The mechanism of the electroreduction was then studied via in situ Fourier Transform Infra‐Red (FTIR) spectroscopy. These results hinted to an evolution of the electrocatalyst during the electrolysis reaction, which was then studied via Scanning Electron Microscopy (SEM) and X‐Ray Photoelectron spectroscopy (XPS). We found that the Pb monolayer restructured during catalysis, forming microparticles that were active in the reaction based on the listed experiments. Pb alloying into the lattice, which can occur during UPD, also lowered the HER, further facilitating glycine synthesis. Thus, our research also shows how Pb UPD impacts the catalytic properties of a metal both through monolayer deposition as well as surface alloying.

(Invited) Electroless Cu, Pb and Ag Monolayer Deposition – Generality of an Electroless Monolayer Deposition Phenomenon

Recent progress in fuel cell catalysis has been enabled in great part by facile methods for catalyst monolayer synthesis based on surface limited redox replacement (SLRR) of underpotentially deposited (UPD) monolayers. Although this approach has been very effective, it has shown a limited applications in majority of heterogeneous gas phase catalysis problems where substrates are oxide based materials with very limited conductivity. In this talk we point out a new possibility for catalyst monolayer synthesis via SLRR on metal surfaces which are not part of a broadly conductive substrates such as metal nanoparticles imbedded in various oxide or zeolite supports. This is enabled by discovery of an electroless (E-less) Pb, Cu and Ag monolayer deposition phenomenon. Fundamentals of the E-less monolayer deposition are reviewed, and new data illustrating Cu and Ag monolayer deposition are presented. The focus is on emphasizing generality of the E-less monolayer deposition phenomenon, its self-termination and surface selectivity towards substrates at which Cu, Ag and Pb form UPD monolayer. Examples of the thin films and catalyst monolayer deposition via SLRR of E-less Cu, Ag and Pb monolayer are presented under the auspices of a newly developed two-step electroless atomic layer deposition protocol (E-less ALD)1.1) Electroless Pb Monolayer Deposition – Prelude for Further Advances in Catalyst Monolayer Synthesis via Surface Limited Redox Replacement Reaction”, K. Ahmadi, N. Dole, D. Wu, T. Salavati‐Fard, L. C. Grabow, F. C. Robles Hernandez, and S. R. Brankovic, ACS Catalysis, 11, 4650 (2021).

The Effect of Halide Adsorption on Pb Underpotential Deposition on Au

In many systems with a large lattice mismatch, the formation of surface alloys during deposition has been reported and theoretically predicted.1 Pb monolayer deposition on Au is one such system that has been studied extensively in the past in the UHV and electrochemical environment as the underpotential deposition.2-4 Pb UPD on Au(111) in perchlorate solution has been a model UPD system studied by many surface techniques.2-6 In particular, the in-situ surface stress and the in-situ STM studies5,6 have demonstrated changes associated with the surface alloying at the partial Pb coverage. Our recent electrochemical study showed the effect of extended polarisation and potential cycling on the surface alloying in this system.7 This talk will present further work on this system by examining the effect of Cl- and Br- adsorption on Pb UPD and surface alloying.The formation of the UPD monolayer in the presence of halides is often accompanied by competitive adsorption, changes in the kinetics and energetics of deposition, and the co-adsorption that could stabilise and create new stages/phases of growth. In contrast to many other model UPD systems, the effect of halide adsorption in this system has not been explored much. To our knowledge, there are only a few studies reported so far. The in situ X-ray studies of Pb UPD on Au in the presence of Cl- and Br- by Wang et al. 8 suggested the formation of a series of ordered structures referred to as metal-halide hybrid structures. However, their model analysis did not include surface-alloying as a possible origin of the observed ordered structures.The effect of Cl- and Br- adsorption on Pb UPD was studied by gradually increasing the concentrations of ions (from 5μM-10mM) in the perchlorate solution. The results as illustrated in the Figure below show that both Cl- and Br - compete with Pb UPD causing some of the characteristic peaks to shift towards more negative potentials. The cyclic voltammetry in Cl- reveals the similar stages of the Pb UPD formation as those observed in perchlorate. The most significant differences have been observed in Br- solutions. For bromide concentration above 50 μM pronounced surface reconstruction-type peaks were observed suggesting ordered structures that could include both Br and Au. The difference in the electrochemical behaviour between the perchlorate and halide containing solutions are also visible in the chronoamlerometric current transients in the UPD region. Besides the fundamental interest in understanding halide effects on this UPD system, the interest was in the surface alloy (Pt-Au) formation during polarisation experiments. The comparison with the results of surface alloying in the perchlorate solutions will be presented and discussed. References F. Besenbacher, L. P. Nielsen, and P. T. Sprunger, The Chemical Physics of Solid Surfaces, D. A. King, D. P. Woodruff, Eds. Elsevier 8, 207-257 (1997).E. Herrero, L. J. Buller, and H. D. Abruña, Chemical Reviews, 101 (7), 1897-1930 (2001).A. Hamelin, J. Electroanal. Chem,165(1-2), 167-180, (1984).O. A. Oviedo, L. Reinaudi, S. G. Garcia, and E. P. M. Leiva, Underpotential Deposition. From Fundamentals and Theory to Applications at the Nanoscale, Springer (2016).J. Nutariya, J. Velleuer, W. Schwarzacher, and N. Vasiljevic, ECS Transactions, 28 (25), 15-25 (2010).J. W. Shin, U. Bertocci, and G. R. Stafford, J. Phys. Chem. C, 114 (17), 7926-7932 (2010).A.Szczepanska and N. Vasiljevic J. Electrochem. Soc .169, 112509 (2022).J.X. Wang, I.K. Robinson, J.E. DeVilbiss, R.R. Adzic, J. Phys. Chem. B, 104 (33), 7951-7959, (2000). Figure 1

Two-dimensional MSi2N4 (M = Ge, Sn, and Pb) monolayers: promising new materials for optoelectronic applications

The recent growth of two-dimensional (2D) layered crystals of MoSi2N4 and WSi2N4 has sparked significant interest due to their outstanding properties and potential applications. This development has paved the way for a new and large family of 2D materials with a general formula of MA 2 Z 4. In this regard, motivated by this exciting family, we propose two structural phases (1T- and 1H-) of MSi2N4 (M = Ge, Sn, and Pb) monolayers and investigate their structural, vibrational, mechanical, electronic and optical properties by using first-principles methods. The two phases have similar cohesive energies, while the 1T structures are found to be more energetically favorable than their 1H counterparts. The analysis of phonon spectra and ab initio molecular dynamics simulations indicate that all the suggested monolayers, except for 1H-GeSi2N4, are dynamically and thermally stable even at elevated temperatures. The elastic stability and mechanical properties of the proposed crystals are examined by calculating their elastic constants (C ij ), in-plane stiffness (), Poisson’s ratio (ν), and ultimate tensile strain (UTS). Remarkably, the considered systems exhibit prominent mechanical features such as substantial in-plane stiffness and high UTS. The calculated electronic band structures reveal that both the 1T- and 1H-MSi2N4 nanosheets are wide-band-gap semiconductors and their energy band gaps span from visible to ultraviolet region of the optical spectrum, suitable for high-performance nanoelectronic device applications. Lastly, the analysis of optical properties shows that the designed systems have isotropic optical spectra, and depending on the type of the system, robust absorption of ultraviolet and visible light (particularly in 1H-PbSi2N4 monolayer) is predicted. Our study not only introduces new members to the family of 2D MA 2 Z 4 crystals but also unveils their intriguing physical properties and suggests them as promising candidates for diverse nanomechanical and optoelectronic applications.

Green Synthesis of Magnetite Nanoparticles Mediated Fumaria officinalis L. Plant as Sustainable and Renewable Adsorbing Materials

Magnetite nanoparticles (Fe3O4) have been utilized to mediate Fumaria officinalis L., a plant known for its rich source of various phytogredients such as diterpenes, nor-diterpenoids, tri-terpenoids, flavonoids, and phenolic acids. These natural compounds act as capping, reducing, and stabilizing agents, offering an affordable and safer approach to synthesize nanoparticles in line with sustainable and eco-friendly concepts, such as green nanoparticles. The cost-effective synthesized nanoparticles were employed to adsorb Pb(II) from an aqueous solution. For investigating the surface characteristics of the adsorbent, a range of techniques were employed, including Field Emission Scanning Electron Microscope (FE-SEM), Fourier Transform Infrared Spectroscopy, and X-ray Diffraction. Fourier Transform Infrared (FT-IR) spectroscopy was specifically applied to discern the functional groups present within the compounds. To optimize the adsorption process and achieve the best removal efficiency (R%), several parameters, including pH, initial concentration, temperature, and contact time, were optimized using the Response Surface Methodology (RSM). The experimental results indicated that the Langmuir isotherm provided a well-fitted model, suggesting a monolayer of Pb(II) capping on the surface of magnetite nanoparticles, with a maximum adsorption capacity of 147.1 mg/g. Moreover, the kinetic findings demonstrated a strong alignment with the pseudo-second-order model. The computed (qe) and observed outcomes associated with the pseudo-second-order kinetic model exhibited a commendable concurrence, underscoring the model’s remarkable precision in forecasting the adsorption mechanism of Pb(II) within the examined parameters. The antioxidant activity and green nanocomposite properties were determined using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and standard analytical methods. The phytochemical profile exhibited a total phenolic content of 596 ± 0.001 mg GAE/g dry weight and a total flavonoid content of 18.25 ± 0.001 mg QE/g dry weight. The DPPH radical’s inhibition showed potent antioxidant activity at various concentrations (44.74, 73.86, 119.791, and 120.16% at 200, 400, 600, and 800 μg/mL, respectively), demonstrating the potential of the plant as a natural capping and reducing agent during the green process of nanoparticle formation.

Two-Dimensional Pb Square Nets from Bulk (RO)nPb (R = Rare Earth Metals, n = 1,2).

All two-dimensional (2D) materials of group IV elements from Si to Pb are stabilized by carrier doping and interface bonding from substrates except graphene which can be free-standing. The involvement of strong hybrid of bonds, adsorption of exotic atomic species, and the high concentration of crystalline defects are often unavoidable, complicating the measurement of the intrinsic properties. In this work, we report the discovery of seven kinds of hitherto unreported bulk compounds (RO)nPb (R = rare earth metals, n = 1,2), which consist of quasi-2D Pb square nets that are spatially and electronically detached from the [RO]δ+ blocking layers. The band structures of these compounds near Fermi levels are relatively clean and dominantly contributed by Pb, resembling the electron-doped free-standing Pb monolayer. The R2O2Pb compounds are metallic at ambient pressure and become superconductors under high pressures with much enhanced critical fields. In particular, Gd2O2Pb (9.1 μB/Gd) exhibits an interesting bulk response of lattice distortion in conjunction with the emergence of superconductivity and magnetic anomalies at a critical pressure of 10 GPa. Our findings reveal the unexpected facets of 2D Pb sheets that are considerably different from their bulk counterparts and provide an alternative route for exploring 2D properties in bulk materials.

On the Electrochemically Active Surface Area Determination of Electrodeposited Porous Cu 3D Nanostructures

Porous 3D Cu layers with the following average parameters: thickness ~35 µm, pore density ~4.0 × 106 cm−2, and pore sizes ~25 µm were electrodeposited from an acidic sulphate electrolyte, and the suitability of different electrochemically active surface area determination methods for characterising these electrodes was assessed. Structural characterisation of the samples was conducted using SEM and an optical profiler, while electrochemical measurements were performed using cyclic voltammetry and electrochemical impedance spectroscopy. The evaluation of electrochemically active surface area involved the underpotential deposition of Tl and Pb monolayers as well as double-layer capacitance measurements. The results obtained indicate that both methods yield similar results for non-porous Cu electrodes. However, for Cu 3D nanostructures, the evaluation mode significantly influences the results. Double-layer capacitance measurements show significantly higher values for the electrochemically active surface area compared to the underpotential deposition (UPD) technique. The complex spatial structure of the Cu 3D layer hinders the formation of a continuous monolayer during the UPD process, which is the principal reason for the observed differences.

Domain Boundary Formation Within an Intercalated Pb Monolayer Featuring Charge‐Neutral Epitaxial Graphene

AbstractThe synthesis of new graphene‐based quantum materials by intercalation is an auspicious approach. However, an accompanying proximity coupling depends crucially on the structural details of the new heterostructure. It is studied in detail the Pb monolayer structure after intercalation into the graphene buffer layer on the SiC(0001) interface by means of photoelectron spectroscopy, x‐ray standing waves, and scanning tunneling microscopy. A coherent fraction close to unity proves the formation of a flat Pb monolayer on the SiC surface. An interlayer distance of 3.67 Å to the suspended graphene underlines the formation of a truly van der Waals heterostructure. The 2D Pb layer reveals a quasi ten‐fold periodicity due to the formation of a grain boundary network, ensuring the saturation of the Si surface bonds. Moreover, the densely‐packed Pb layer also efficiently minimizes the doping influence by the SiC substrate, both from the surface dangling bonds and the SiC surface polarization, giving rise to charge‐neutral monolayer graphene. The observation of a long‐ranged () reconstruction on the graphene lattice at tunneling conditions close to Fermi energy is most likely a result of a nesting condition to be perfectly fulfilled.

Enhanced Superconductivity and Rashba Effect in a Buckled Plumbene-Au Kagome Superstructure.

Plumbene, with a structure similar to graphene, is expected to possess a strong spin-orbit coupling and thus enhances its superconducting critical temperature (Tc ). In this work, a buckled plumbene-Au Kagome superstructure grown by depositing Au on Pb(111) is investigated. The superconducting gap monitored by temperature-dependent scanning tunneling microscopy/spectroscopy shows that the buckled plumbene-Au Kagome superstructure not only has an enhanced Tc with respect to that of a monolayer Pb but also possesses a higher value than what owned by a bulk Pb substrate. By combining angle-resolved photoemission spectroscopy with density functional theory, the monolayer Au-intercalated low-buckled plumbene sandwiched between the top Au Kagome layer and the bottom Pb(111) substrate is confirmed and the electron-phonon coupling-enhanced superconductivity is revealed. This work demonstrates that a buckled plumbene-Au Kagome superstructure can enhance superconducting Tc and Rashba effect, effectively triggering the novel properties of a plumbene.

The Submonolayer Structure of Ni(111)–(√3 × √3)R30–Pb: Atomic Relaxation and Vibrational Properties

The results of a theoretical study of the structural and dynamical parameters of surface phases (adsorption phase and surface alloy phase) formed upon the adsorption of 0.33 Pb monolayer on the Ni(111) plane surface are discussed. Calculations were performed using interatomic potentials obtained within the framework of the embedded atom method. The stability of the surface phases was analyzed on the basis of data on the equilibrium atomic configuration, phonon spectra, local density of phonon states, and polarization of localized vibration modes. It is shown that the Pb–Ni surface alloy has the highest dynamic stability among the two possible surface phases.

Thermodynamics and kinetics of Pb intercalation under graphene on SiC(0001)

SiC-supported graphene intercalated by a two-dimensional Pb monolayer can provide an appealing platform for spintronic applications. Such a monolayer structure is thermodynamically ultrastable, as observed in recent experiments. However, important fundamentals such as the structure of intercalated phases, locations of intercalated atoms, thermodynamic preference for intercalation, and intercalation pathways for this system have not yet been understood conclusively. In this work, extensive density functional theory calculations are performed to assess Pb intercalation thermodynamics and kinetics under graphene on SiC(0001). We find that intercalation of isolated Pb atoms is strongly disfavored over adsorption on top of graphene. However, intercalation of complete Pb layers in the gallery between SiC and graphene buffer layer is strongly favored over supported Pb monolayers and moderately favored over formation of supported large three-dimensional Pb islands. We also find that initiation of intercalation either by individual Pb atoms directly penetrating graphene or by hopping under a static graphene step edge is energetically prohibitive at experimental temperatures. Consequently, more complex intercalation pathways are operative and further analyzed. We demonstrated that once an intercalated Pb monolayer forms around a graphene step edge, a facile Pb mass transport by Pb vacancy-mediated diffusion can be triggered for continued growth of the intercalated monolayer.

The Adsorption of Pb(II) Using Silica Gel Synthesized from Chemical Bottle Waste: Optimization Using Box-Behnken Design

The adsorption of Pb(II) on silica gel synthesized from chemical glass bottle waste has been studied. The effect of independent variables (adsorbent dose, initial concentration of Pb(II), contact time, and pH) on the Pb(II) removal from water was evaluated and optimized using the Response Surface Methodology (RSM). Under optimized conditions (adsorbent dose: 20 mg; contact time: 30 min; initial Pb(II) concentration: 120 mg. L−1 ; and pH: 8), the removal of Pb(II) was 99.77%. The adsorption equilibrium data obtained from the batch experiment were investigated using different isotherm models. The Langmuir isotherm model fits the experimental data. This shows that the surface of the silica gel synthesized from chemical bottles waste was covered by a Pb(II) monolayer. XRF analysis showed that the synthesized silica gel had a SiO2 content of 75.63%. Amorphous silica was observed from XRD analysis. SEM-EDX characterization showed that Pb was adsorbed on the silica gel surface. SEM analysis showed that silica gel has irregular particles with a surface area of 297.08 m2 .g−1 with a pore radius of 15.74 nm calculated from BET analysis.

The thermoelectric properties of XTe (X = Ge, Sn and Pb) monolayers from first-principles calculations

Thermoelectric (TE) materials are increasingly attracting the attention of researchers as new energy materials that are capable of converting thermal energy into electrical energy. In this work, combining first-principles calculations and the Boltzmann transport equation, the TE related properties of XTe (X = Ge, Sn and Pb) monolayers have been thoroughly studied. The calculated results show that XTe monolayers are indirect band gap semiconductors, and they possess small effective masses which lead to large carrier mobilities and high electrical conductivities. Except for p-type PbTe, the other XTe monolayers share extremely high PF, thanks to the high Seebeck coefficients and large electrical conductivity. Furthermore, owing to the low phonon group velocity and strong anharmonicity, the lattice thermal conductivities of SnTe and PbTe are quite low. At 500 K, the optimum figure of merit (ZT) values are calculated to be 1.26, 2.61 and 5.91 for GeTe, SnTe and PbTe respectively. The obtained ZT values of the XTe monolayers are larger than these of their bulk counterparts. These results qualify XTe monolayers as promising candidates for building outstanding TE devices.

Surface Alloying During Pb Underpotential Deposition on Au(111)

The surface alloying during Pb underpotential deposition (UPD) on Au(111) films was studied using electrochemical techniques. This UPD system has been known for its unusual stress behavior associated with surface alloying during epitaxial monolayer (ML) formation. The characteristic cyclic voltammetry of Pb UPD on Au(111) exhibits an anodic peak at the most positive potentials that does not have a symmetric cathodic counterpart. The peak can be associated with the surface structural changes due to the Pb dealloying from the top substrate layer. Two electrochemical approaches were used to study the surface transformations: i) extended polarization (up to 60 min) at high Pb coverage of 0.85 ML, and ii) repeated cycling 1150 times between the potentials corresponding to 0.25 ML and 1 ML Pb coverages. In both approaches, it was observed that with the increased time of polarization or number of potential cycles, the prominent UPD peaks gradually reduced in magnitude, became broader and lost their original double-peaks structure. At the same time, the dealloying (the most anodic) peak shifted positive about 0.1 V and increased in magnitude. Quantitative analysis of the changes estimated the coverage of Pb alloying with a surface of 0.28–0.30 ML.

Two-dimensional hourglass Weyl nodal loop in monolayer Pb(ClO2)2 and Sr(ClO2)2

The hourglass fermions in solid-state materials have been attracting significant interest recently. However, realistic two-dimensional (2D) materials with hourglass-shaped band structures are still very scarce. Here, through the first-principles calculations, we identify the monolayer Pb(ClO2)2 and Sr(ClO2)2 materials as the new realistic materials platform to realize 2D hourglass Weyl nodal loop. We show that these monolayer materials possess an hourglass Weyl nodal loop circling around the Γ point and Weyl nodal line on the Brillouin zone (BZ) boundary in the absence of spin–orbit coupling (SOC). Through the symmetry analysis, we demonstrate that the hourglass Weyl nodal loop and Weyl nodal line are protected by the nonsymmorphic symmetries, and are robust under the biaxial strains. When we include the SOC, a tiny gap will be opened in the hourglass nodal loop and nodal line, and the nodal line can be transformed into the spin-orbit Dirac points. Our results provide a new realistic material platform for studying the intriguing physics associated with the 2D hourglass Weyl nodal loop and spin-orbit Dirac points.

Contact of the intrinsic magnetic topological insulator Mn(Bi,Sb)2Te4 with a superconducting Pb film

Intrinsic magnetic topological insulators (MTIs), such as an ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ family, have proved to be an essential platform for the study of various quantum effects and can be used for a range of applications from information storage and dissipationless spin and charge transfer to quantum computers. The latter requires the creation of Majorana fermions, which are expected to emerge when a superconductor is contacted with an MTI surface. Therefore the study of the features arising at the interface between the MTI and the superconductor is of great interest. For this purpose in this paper, the gradual growth of the elemental superconductor (Pb) film on the surface of $\mathrm{Mn}{({\mathrm{Bi}}_{0.7}{\mathrm{Sb}}_{0.3})}_{2}{\mathrm{Te}}_{4}$, which has a Dirac point near the Fermi level, was experimentally investigated by ARPES and XPS methods. We observed that the shape of the Dirac cone state remains almost unchanged up to coverage of $\ensuremath{\sim}1.5$ Pb monolayers, thus remaining topological properties of the material. It was shown that Pb atoms deposition results in surface modification. They detached upper Te atoms and form TePb alloy on the surface. Moreover, Pb deposition leads to disorder of Te, Bi(Sb) layers closest to the surface. As a result, the localization of the Dirac cone state shifts towards the bulk. All these features should be taken into account in the implementation of a topological superconducting state based on the Pb/Mn(Bi,${\mathrm{Sb})}_{2}{\mathrm{Te}}_{4}$ systems.

Topological Lifshitz transition in Weyl semimetal NbP decorated with heavy elements

Studies of the Fermi surface modification after $\mathit{in}\phantom{\rule{0.16em}{0ex}}\mathit{situ}$ covering NbP semimetal with heavy elements Pb and Nb ultrathin layers were performed by means of angle-resolved photoemission spectroscopy (ARPES). First, the electronic structure was investigated for pristine single crystals with two possible terminations (P and Nb) of the (0 0 1) surface. The nature of the electronic states of these two cleaving planes is different: the P-terminated surface shows spoon and bow tie-shaped surface states, whereas these shapes are not present in the Nb-terminated surface. ARPES studies show that even one monolayer (ML) of Pb causes topological Lifshitz transition (TLT) in P-terminated NbP where the surface Fermi arcs (SFAs) teleport to another pair of Weyl points connecting two adjacent Brillouin zones. Depositing one ML of Pb modifies the Fermi surface along with a shift in the Fermi energy. On the other hand, the deposition of approximately 0.8 ML of Nb modifies the electronic structure of P-terminated NbP, pushing the system on the verge of TLT but not yet fully transformed. Regardless of the dramatic surface evolution, SFAs remain connected to topologically protected Weyl points. Additionally, we studied the Nb-terminated NbP covered with 1.9 ML of Pb with only altered trivial surface states caused by an ordinary Lifshitz transition.