Pressure-induced transitions from ordered intermetallic phases to substitutional alloys to semi-ordered phases were studied in a series of bismuth tellurides. Using angle-dispersive x-ray diffraction, the compounds Bi4Te5, BiTe, and Bi2Te were observed to form alloys with the disordered body-centered cubic (bcc) crystal structure upon compression to above 14--19 GPa at room temperature. The BiTe and Bi2Te alloys and the previously discovered high-pressure alloys of Bi2Te3 and Bi4Te3 were all found to show atomic ordering after gentle annealing at very moderate temperatures of ~100°C. Upon annealing, BiTe transforms from the bcc to the B2 (CsCl) crystal structure type, and the other phases adopt semi-disordered variants thereof, featuring substitutional disorder on one of the two crystallographic sites. The transition pressures and atomic volumes of the alloy phases show systematic variations across the Bi_mTe_n series including the end members Bi and Te. First-principles calculations were performed to characterize the electronic structure and chemical bonding properties of B2-type BiTe and to identify the driving forces of the ordering transition. The calculated Fermi surface of B2-type BiTe has an intricate structure and is predicted to undergo three topological changes between 20 and 60 GPa.
We report results of micro-Raman spectroscopy investigation of the "graphene-like" mechanically exfoliated single-crystal bismuth telluride films with the thickness ranging from a few-nm-range to bulk limit. It is found that the optical phonon mode A1u, which is not-Raman active in bulk bismuth telluride crystals, appears in the atomically-thin films due to crystal-symmetry breaking. The intensity ratios of the out-of-plane A1u and A1g modes to the in-plane Eg mode grow with decreasing film thickness. The evolution of Raman signatures with the film thickness can be used for identification of b…
Epitaxial films of bismuth telluride topological insulators have received increasing attention due to potential applications in spintronic and quantum computation. One of the most important properties of epitaxial films is the presence of interface defects due to lateral lattice mismatch since electrically active defects can drastically compromise device performance. By describing hybrid reflections in hexagonal bismuth telluride films on cubic substrates, in-plane lattice mismatches were characterized with accuracy at least 20 times better than using other X-ray diffraction methods, providing…
Topological insulator surface properties are strongly correlated to structural properties, requiring high-resolution techniques capable of probing both surface and bulk structures at once. In this work, high flux of synchrotron source, recursive equations for fast X-ray dynamical diffraction simulation, and genetic algorithm for data fitting are combined to reveal the detailed structure of bismuth telluride epitaxic films with thickness ranging from 8 to 168 nm. It includes stacking sequences, thickness and composition of layers in model structures, interface coherence, surface termination and…
In the supporting information file for article Dynamics of Defects in van der Waals Epitaxy of Bismuth Telluride Topological Insulators(J. Phys. Chem. C 2019, 123, 24818-24825, doi: 10.1021/acs.jpcc.9b05377), several topics on X-ray diffraction analysis of thin films were developed or revisited. A simple equation to determine lateral lattice coherence lengths in thin films stands as the main development (section S4 - Lateral lattice coherence length in thin films), while X-ray dynamical diffraction simulation in monochromator crystals stands as an interesting overview on how the ratio between …
We report on graphene-like exfoliation of the large-area crystalline films and ribbons of bismuth telluride with the thicknesses of a few atoms. It is demonstrated that bismuth telluride, the most important material for thermoelectric industry, can be mechanically separated into its building blocks -[Te-Bi-Te-Bi-Te]- atomic five-folds with the thickness of ~1 nm and even further - to subunits with smaller thicknesses. The atomically-thin crystals can be structured into suspended crystalline ribbons providing quantum confinement in two dimensions. The quasi two-dimensional (2-D) crystals of bis…
First-principles approach is demonstrated to calculate the work function of Bi2Te3. The reference potential and the vacuum energy levels are extracted from the Bi2Te3 (0001) surface structure using the reference potential method based on the density functional theory. The one-shot GOWO many-body perturbation theory is used to place the bulk band edge energies with respect to the reference level and the vacuum energy. At last, the work function of 5.301 - 5.131 eV is predicted for Bi2Te3 (0001) surface and compared to various elements.
Bismuth telluride have regained significant attention as a prototype of topological insulator. Thin films of high quality have been investigated as a basic platform for novel spintronic devices. Low mobility of bismuth and high desorption coefficient of telluride compose a scenario where growth parameters have drastic effects on structural and electronic properties of the films. Recently [J. Phys. Chem. C 2019, 123, 24818-24825], a detailed investigation has been performed on the dynamics of defects in epitaxial films of this material, revealing the impact of film/substrate lattice misfit on t…
Tetradymite-structured chalcogenides such as bismuth telluride Bi_{2}Te_{3} are of significant interest for thermoelectric energy conversion and as topological insulators. Dislocations play a critical role during synthesis and processing of such materials and can strongly affect their functional properties. The dislocations between quintuple layers present special interest since their core structure is controlled by the van der Waals interactions between the layers. In this work, using atomic-resolution electron microscopy, we resolve the basal dislocation core structure in Bi_{2}Te_{3}, quant…
We have coupled electron microscopy and energy dispersive spectroscopy experiments with \textit{ab-initio} modeling to study the solubility and diffusion of Au in Bi$_2$Te$_3$. We found that thermal annealing of Au films results in Au concentrations in Bi$_2$Te$_3$ above the previously reported solubility limit. The time scale of Au diffusion into Bi$_2$Te$_3$ is also much greater than expected. To explain our observations, we calculate defect formation energies and diffusion barriers within DFT. We identify an interstitial mechanism consistent with the previously observed low solubility and (…
Decreasing thermal conductivity of a thermoelectric material is always a prerequisite for its potential application. Using first-principle calculations, we examine the magnetism induced change in lattice thermal transport in bismuth telluride. The source of magnetic moment, Cr in the doped system, weakly magnetizes the coordinated Te atoms to make the latter's phonon softer than that in the pure compound. Though the transition metal dopants do not participate directly in the heat conduction process, the anharmonicity induced by them favor in reducing the lattice thermal conductivity. Large anh…
We use a magnetothermal resistance method to measure the lattice thermal conductivity of a single crystal of Bi$_2$Te$_3$ from 5 to 60 K. We apply a large transverse magnetic field to suppress the electronic thermal conduction while measuring thermal conductivity and electrical resistivity. The lattice thermal conductivity is then calculated by extrapolating the thermal conductivity versus electrical conductivity curve to a zero electrical conductivity value. Our results show that the measured phonon thermal conductivity follows the $e^{(Δ_{min}/T)}$ temperature dependence and the Lorenz ratio…
Hetero-epitaxial films based on bismuth telluride with excess of Te were grown by hat wall technique at the surface of the mica (muscovite). Galvanomagnetic properties of the thin films were measured, and quantum oscillations of the magnetoresistance were found at the temperatures below 10 K in the magnetic field from 6 to 14 T. From analysis of magnetoresistance oscillations the main surface state parameters of the films were determined. Expementally obtained Landau level index shift and its temperature dependence are consistent with Berry phase specific for topological Dirac surface states. …
We study the electrical transport properties of ensembles of bismuth telluride (Bi2Te3) nanoplates grown by solution based chemical synthesis. Devices consisting of Bi2Te3 nanoplates are fabricated by surface treatment after dropping the solution on the structured gold plates and the temperature dependence of resistance shows a nonmetallic behavior. Symmetric tunneling behavior in I-V was observed in both our experimental results and theoretical calculation of surface conductance based on a simple Hamiltonian, which excludes carrier-carrier interactions. Here, we present two devices: one showi…
Morphology of the interlayer van der Waals surface and differential tunneling conductance in p-Bi2-xSbxTe3-ySey solid solutions were studied by scanning tunneling microscopy and spectroscopy in dependence on compositions. Topological characteristics of the Dirac fermion surface states were determined. It is shown that the thermoelectric power factor and the material parameter enhance with the shift of the Dirac point to the top of the valence band with increasing of atomic substitution in these thermoelectrics. Correlation between topological characteristics, power factor and material paramete…
Metallic Bi2Te3 crystalline sheets with the room-temperature resistivity of above 10 mΩ cm were prepared and their magnetoresistive transport was measured in a field of up to 9 Tesla. The Shubnikov de Haas oscillations were identified from the secondly-derived magnetoresistance curves. While changing the angle between the field and normal axis of the sheets, we find that the oscillation periods present a cosine dependence on the angle. This indicates a two-dimensional transport due to the surface state. The work reveals a resolvable surface contribution to the overall conduction even in a meta…
We adopted and extended an efficient Grüneisen formalism to study the phonon anharmonicity and linear thermal expansion coefficients (TECs) of trigonal bismuth selenide (Bi$_2$Se$_3$) and antimony telluride (Sb$_2$Te$_3$). Anharmonicity of the systems is studied via extensive calculation of Grüneisen parameters that exploit symmetry-preserving deformations. Consistent with experimental findings, a large anisotropy between the TECs in the $a$ and $c$ directions is found. The larger anharmonicity inherent in Sb$_2$Te$_3$, as compared to Bi$_2$Se$_3$ is offset by the volumetric effect, resulting …
In topological n-type thermoelectrics based on $Bi_{2}Te_{3}$ with atomic substitutions Bi $\rightarrow$ In, Te $\rightarrow$ Se, S, the morphology and the surface states of Dirac fermions on the interlayer (0001) surface of van der Waals were studied by scanning tunneling microscopy and spectroscopy (STM/STS) techniques. By the STM method, the dark and light spots on the surface were found, which intensities depend on the composition and thermoelectric properties of solid solutions. The observed surface morphology features in the solid solutions are explained by distortions of surface electro…
We report on "graphene-like" mechanical exfoliation of single-crystal Bi2Te3 films and thermoelectric characterization of the stacks of such films. Thermal conductivity of the resulting "pseudo-superlattices" was measured by the "hot disk" and "laser flash" techniques. The room-temperature in-plane (cross-plane) thermal conductivity of the stacks decreases by a factor of ~2.4 (3.5) as compared to bulk. The thermal conductivity reduction with preserved electrical properties leads to strong increase in the thermoelectric figure of merit. It is suggested that the film thinning to few-quintuples a…
We performed density functional calculations for ultra-thin bismuth surface alloys: surface alloys of bismuth and face-centered cubic metals Bi/$M$(111)-$(\sqrt{3}\times\sqrt{3})R30°$ ($M$=Cu, Ag, Au, Ni, Co, and Fe). Our calculated Rashba parameters for the Bi/Ag are consistent with the previous experimental and theoretical results. We predicted a trend in the Rashba coefficients $α_R$ of bands around the Fermi energy for noble metals as follows: Bi/Ag > Bi/Cu > Bi/Au. As for the transition metals, there is a trend in $α_R$: Bi/Ni > Bi/Co > Bi/Fe. Our finding may lead to design efficient spin…
Bismuth chalcogenides Bi$_2$Se$_3$ and Bi$_2$Te$_3$ are semiconductors, which can be both thermoelectric materials (TE) and topological insulators (TI). Lattice defects arising from vacancies, impurities, or dopants in these materials are important in that they provide the charge carriers in TE applications and compromise the performance of these materials as TIs. We present the first solid-state nuclear magnetic resonance (NMR) study of the $^{77}$Se and $^{125}$Te NMR resonances in polycrystalline powders of Bi$_2$Se$_3$ and Bi$_2$Te$_3$, respectively. The spin-lattice ($T_1$) relaxation is …
A polycrystalline sample of the high-entropy-alloy-type telluride AgInSnPbBiTe5 was synthesized using high-pressure synthesis. Superconductivity with a transition temperature (Tc) of 2.6 K was observed in AgInSnPbBiTe5. Elemental and structural analyses revealed that five metals are mixed in a metal site of an NaCl-type structure. Since AgInSnPbBiTe5 has a cation site (Ag, In, Sn, Pb, and Bi) and an anion site (Te), this is the first example of a high-entropy-alloy (HEA) pseudo-binary superconductor.
High-entropy-alloy-type tellurides M-Te, which contain five different metals of M = Ag, In, Cd, Sn, Sb, Pb, and Bi, were synthesized using high pressure synthesis. Structural characterization revealed that all the obtained samples have a cubic NaCl-type structure. Six samples, namely AgCdSnSbPbTe5, AgInSnSbPbTe5, AgCdInSnSbTe5, AgCdSnPbBiTe5, AgCdInPbBiTe5, and AgCdInSnBiTe5 showed superconductivity. The highest transition temperature (Tc) among those samples was 1.4 K for AgInSnSbPbTe5. A sample of AgCdInSbPbTe5 showed a semiconductor-like transport behavior. From the relationship between Tc …
Since 2017, epitaxial graphene has been the base material for the US national standard for resistance. A future avenue of research within electrical metrology is to remove the need for strong magnetic fields, as is currently the case for devices exhibiting the quantum Hall effect. The quantum Hall effect is just one of many research endeavours that revolve around recent quantum physical phenomena like composite fermions, charge density waves, and topological properties [1-2]. New materials, like magnetically doped topological insulators (MTIs), offer access to the quantum anomalous Hall effect…
Thermoelectric (TE) materials research plays a vital role in heat-to-electrical energy conversion and refrigeration applications. Bismuth-antimony (Bi-Sb) alloy is a promising material for thermoelectric cooling. Herein, a high figure of merit, ZT, near 0.6 at cryogenic temperatures (100-150K) has been achieved in melt-spun n-type Bi85Sb15 bulk samples consisting of micron-size grains. The achieved ZT is nearly 50 percents higher than polycrystalline averaged single crystal ZT of ~0.4, and it is also significantly higher than ZT of less than ~0.3 measured below 150K in Bi-Te alloys commonly us…
We have systematically investigated the optical properties of the InP1-xBix ternary alloys with 0<x<2.46%, using high resolution polarized Raman scattering measurement. Both InP-like and InBi-like optical vibration modes (LO) were identified in all the samples, suggesting most of the Bi-atoms are incorporated into the lattice sites to substitute P-atoms. And the intensity of the InBi-like Raman modes increase exponentially as Bi-content increasing. Linearly red-shift of the InP-like longitudinal optical vibration modes was observed to be 1.1 cm-1 of percent Bi, while that of the InP-like optic…
Spin-split Rashba bands have been exploited to efficiently control the spin degree of freedom of moving electrons, which possesses a great potential in frontier applications of designing spintronic devices and processing spin-based information. Given that intrinsic breaking of inversion symmetry and sizeable spin-orbit interaction, two-dimensional (2D) surface alloys formed by heavy metal elements exhibit a pronounced Rashba-type spin splitting of the surface states. Here, we have revealed the essential role of atomic orbital symmetry in the hexagonally warped Rashba spin-split surface state o…
Decoding Thermal Stability: In situ Insights into Phase Controlled Phosphine-free Colloidal Bi-Te Nanosheets
University of Rostock（罗斯托克大学）；Pidstryhach Institute for applied problems of mechanics and mathematics of NAS of Ukraine（乌克兰国家科学院普季里哈赫应用力学与数学研究所）；Center for Interdisciplinary Electron Microscopy (ELMI-MV), Department “Life, Light & Matter”, University of Rostock（罗斯托克大学生·光·物质学院跨学科电子显微镜中心）
Half Heusler (HH) thermoelectric alloys provide a wide platform to choose materials with non-toxic and earth abundant elements. This article presents an ab-initio theoretical evaluation of electrical and thermal transport properties of three Bismuth-based most promising thermoelectric alloys, selected out of 54 stable HH compounds. These are brand new compounds which are recently proposed to be stable (Nature Chem. 7, 308 (2015)) and may have interesting properties. The calculated band structure of the three compounds, namely HfRhBi, ZrIrBi and ZrRhBi, served as a hint for their promising ther…
We present x-ray reflectivity measurements from the free surface of a liquid gallium-bismuth alloy (Ga-Bi) in the temperature range close to the bulk monotectic temperature $T_{mono} = 222$C. Our measurements indicate a continuous formation of a thick wetting film at the free surface of the binary system driven by the first order transition in the bulk at the monotectic point. We show that the behavior observed is that of a complete wetting at a tetra point of solid-liquid-liquid-vapor coexistance.
The addition of dilute concentrations of bismuth (Bi) into GaAs to form GaBiAs alloys results in a large reduction of the band gap energy Eg accompanied by a significant increase of the spin-orbit-splitting energy (delta_SO), leading to an Eg < delta_SO regime for ~10% Bi composition which is technologically relevant for the design of highly efficient photonic devices. The quaternary alloy GaBiNAs offers further flexibility for band gap tuning, because both nitrogen and bismuth can independently induce band gap reduction. This work reports sp3s* tight binding and 14-band k.p models for the stu…
We demonstrate that a giant spin Hall effect (SHE) can be induced by introducing a small amount of Bi impurities in Cu. Our analysis based on a new 3-dimensional finite element treatment of spin transport shows that the sign of the SHE induced by the Bi impurities is negative and its spin Hall (SH) angle amounts to -0.24. Such a negative large SH angle in CuBi alloys can be explained by applying the resonant scattering model proposed by Fert and Levy [Phys. Rev. Lett. 106, 157208 (2011)] to 6p impurities.
High-entropy-alloy-type (HEA-type) compound superconductors have been drawing much attention as a new class of exotic superconductors with local structural inhomogeneity. NaCl-type (Ag,In,Sn,Pb,Bi)Te is a typical HEA-type superconductor, but the carrier doping mechanism had been unclear. In this study, we synthesized (Ag,In,Sn,Pb,Bi)Te with various In concentration using high-pressure synthesis: the studied system is (AgSnPbBi)(1-x)/4InxTe (x = 0-0.4). Single-phase samples were obtained for x = 0-0.3. A semiconductor-like temperature dependence of resistivity was observed for x = 0, while supe…
High-entropy-alloy (HEA) superconductors are a new class of disordered superconductors. In this study, we investigate the robustness of superconducting states in HEA-type metal telluride (MTe; M = Ag, In, Sn, Pb, Bi) under high pressure. PbTe exhibits a structural transition from a NaCl-type to an orthorhombic Pnma structure at low pressures, and further transitions to a CsCl-type structure at high pressures. When the superconductivity of the CsCl-type PbTe is observed, it is found that its superconducting transition temperature (Tc) decreases with pressure. However, in the HEA-type AgInSnPbBi…
Hall effects are investigated for three-dimensional Dirac electrons as a model of bismuth alloys. It is found that there is unconventional contributions to the Hall conductivity $σ_{xy}$ generated by the interband effects of a magnetic field. This phenomena is remarkable near the band-edge. The Hall coefficient exhibits two unexpected properties; a sharp peak at around the band-edges, and a drastic sign change in the band gap region. Implications of the present results to bismuth alloys are discussed.
Gallium oxide (Ga2O3) is a wide-band-gap semiconductor promising for UV sensors and high power transistor applications, with Baliga's figure of merit that far exceeds those of GaN and SiC, second only to diamond. Engineering its band structure through alloying will broaden its range of applications. Using hybrid density functional calculations we study the effects on adding Bi to Ga2O3. While in III-V semiconductors, such as GaAs and InAs, Bi tend to substitute on the pnictide site, we find that in Ga2O3, Bi prefers to substitute on the Ga site, resulting in dilute (Ga_{1-x}Bi_{x})2O3 alloys w…
We investigated six heavy element bismuth-based 18-VEC half-Heusler alloys CoTiBi, CoZrBi, CoHfBi, FeVBi, FeNbBi, and FeTaBi by first principles approach, in search of better thermoelectric prospects. The motivation is driven by expected lower thermal conductivity and the recent discovery of CoZrBi-based materials. Significantly, our calculated power factor values of all the systems show an increment of $\sim$40\% in comparison to the reported \textit{p}-type CoTiSb. We propose that doping at Bi-site, on account of electronic features, will be helpful in achieving the proposed power factor val…
Bismuth has been the key element in the discovery and development of topological insulator materials. Previous theoretical studies indicated that Bi is topologically trivial and it can transform into the topological phase by alloying with Sb. However, recent high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements strongly suggested a topological band structure in pure Bi. To address this issue, we study the band structure of Bi and Sb films by ARPES and first-principles calculations. By tuning tight binding parameters, we show that Bi quantum films in topologically trivi…
We report magnetoresistive properties of direct and indirect band gap Bismuth-Antimony (Bi-Sb) alloys. Band gap increases with magnetic field. Large positive magnetoresistance (MR) approaching to 400 % is observed. Low field MR experiences quadratic growth and at high field it follows a nearly linear behavior without sign of saturation. Carrier mobility extracted from low field MR data, depicts remarkable high value. Correlation between MR and mobility is revealed. We demonstrate that the strong nearly linear MR at high field can be well understood by classical method, co-build by Parish and L…
Dilute bismuth (Bi) III-V alloys have recently attracted great attention, due to their properties of band-gap reduction and spin-orbit splitting. The incorporation of Bi into antimonide based III-V semiconductors is very attractive for the development of new optoelectronic devices working in the mid-infrared range (2-5 $μ$m). However, due to its large size, Bi does not readily incorporate into III-V alloys and the epitaxy of III-V dilute bismides is thus very challenging. This book chapter presents the most recent developments in the epitaxy and characterization of GaSbBi alloys and heterostru…
We have investigated the Weyl semimetal (WSM) phases in bismuth antimony ($\rm Bi$$_{1-x}$$\rm Sb$$_{x}$) alloys by the combination of atomic composition and arrangement. Via first principles calculations, we have found two WSM states with the Sb concentration of $x=0.5$ and $x=0.83$ with specific inversion symmetry broken elemental arrangement. The Weyl points are close to the Fermi level in both of these two WSM states. Therefore, it has a good opportunity to obtain Weyl points in Bi-Sb alloy. The WSM phase provides a reasonable explanation for the current transport study of BiSb alloy with …
Spin-Hall conductivity (SHC) of fully relativistic (4x4 matrix) Dirac electrons is studied based on the Kubo formula aiming at possible application to bismuth and bismuth-antimony alloys. It is found that there are two distinct contributions to SHC, one only from the states near the Fermi energy and the other from all the occupied states. The latter remains even in the insulating state, i.e., when the chemical potential lies in the band-gap, and turns to have the same dependences on the chemical potential as the orbital susceptibility (diamagnetism), a surprising fact. These results are applie…
Prediction and characterization of crystal structures of alloys are a key problem in materials research. Using high-throughput ab initio calculations we explore the low-temperature phase diagrams for the following systems: {Bi-In, Bi-Mg, Bi-Sb, In-Mg, In-Sb, and Mg-Sb}. For the experimentally observed phases in these systems we provide information about their stability at low temperatures. Keywords: Binary Alloys, Ab initio, Intermetallics, Transition Metals, Structure Prediction, Phase Stability, Magnesium, Indium, Bismuth, Antimony.
Bismuth has recently attracted interest in connection with Na-ion battery anodes due to its high volumetric capacity. It reacts with Na to form Na$_3$Bi which is a prototypical Dirac semimetal with a nontrivial electronic structure. Density-functional-theory based first-principles calculations are playing a key role in understanding the fascinating electronic structure of Na$_3$Bi and other topological materials. In particular, the strongly-constrained-and-appropriately-normed (SCAN) meta-generalized-gradient-approximation (meta-GGA) has shown significant improvement over the widely used gener…
The electronic structure of Pb$_{1-x}$Sn$_{x}$Te is studied by using the relativistic Korringa-Kohn-Rostoker Green function method in the framework of density functional theory. For all concentrations $x$, Pb$_{1-x}$Sn$_{x}$Te is a direct semiconductor with a narrow band gap. In contrast to pure lead telluride, tin telluride shows an inverted band characteristic close to the Fermi energy. It will be shown that this particular property can be tuned, first, by alloying PbTe and SnTe and, second, by applying hydrostatic pressure or uniaxial strain. Furthermore, the magnitude of strain needed to s…
Incorporation of bismuth (Bi) in dilute quantities in (In)GaAs has been shown to lead to unique electronic properties that can in principle be exploited for the design of high efficiency telecomm lasers. This motivates the development of simple models of the electronic structure of these dilute bismide alloys, which can be used to evaluate their potential as a candidate material system for optical applications. Here, we begin by using detailed calculations based on an $sp^{3}s^{*}$ tight-binding model of (In)GaBi$_{x}$As$_{1-x}$ to verify the presence of a valence band-anticrossing interaction…
Spintronics is the fast growing field that will play a key role in optimizing power consumption, memory, and processing capabilities of nanoelectronic devices. Heusler alloys are potential candidates for application in spintronics due to their room temperature (RT) half-metallicity, high Curie temperature, low lattice mismatch with most substrates, and strong control on electronic density of states at Fermi level. In this work, we investigate the effect of {substitutional doping and disorder} on the half-metallicity, phase stability, and magnetism of Heusler alloys using density functional the…
Recently, new states of matter like superconducting or topological quantum states were found in transition metal dichalcogenides (TMDs) and manifested themselves in a series of exotic physical behaviors. Such phenomena have been demonstrated to exist in a series of transition metal tellurides including MoTe2, WTe2 and alloyed MoxW1-xTe2. However, the behaviors in the alloy system have been rarely addressed due to their difficulty in obtaining atomic layers with controlled composition, albeit the alloy offers a great platform to tune the quantum states. Here, we report a facile CVD method to sy…
A 125Te NMR study of bismuth telluride nanoparticles as function of particle size revealed that the spin-lattice relaxation is enhanced below 33 nm, accompanied by a transition of NMR spectra from single to bimodal regime. The satellite peak features a negative Knight shift and higher relaxivity, consistent with core polarization from p-band carriers. Whereas nanocrystals follow a Korringa law in the range 140-420K, micrometer particles do so only below 200K. The results reveal increased metallicity of these nanoscale topological insulators in the limit of higher surface-to-volume ratios.
The motivation of this work is our recent observation of the robustness of superconductivity in a High-entropy (HE) superconductor Ag0.2In0.2Sn0.2Pb0.2Bi0.2Te (CsCl-type) to external pressure. The superconducting transition temperature (Tc) of Ag0.2In0.2Sn0.2Pb0.2Bi0.2Te is almost constant with pressure, described as robustness of superconductivity to pressure, whereas the PbTe with zero configurational entropy of mixing exhibits a clear decrease in Tc with pressure. Here, we investigated the atomic displacement parameters (Uiso), the atomic-vibration characteristics, and the electronic states…
We present an x-ray reflectivity study of wetting at the free surface of the binary liquid metal gallium-bismuth (Ga-Bi) in the region where the bulk phase separates into Bi-rich and Ga-rich liquid phases. The measurements reveal the evolution of the microscopic structure of wetting films of the Bi-rich, low-surface-tension phase along different paths in the bulk phase diagram. A balance between the surface potential preferring the Bi-rich phase and the gravitational potential which favors the Ga-rich phase at the surface pins the interface of the two demixed liquid metallic phases close to th…
Materials may behave in non-expected ways when subject to unexpected conditions. For example, when Bi was turned into an amorphous phase (\textit{a}-Bi) unexpectedly it became a superconductor at temperatures below $10$ K. We provided an explanation as to why \textit{a}-Bi superconducts and the crystalline (\textit{c}-Bi) had not been found to do so: we computer calculated their electronic properties and found that \textit{a}-Bi has a larger electron density of states, eDoS, at the Fermi surface than \textit{c}-Bi and this explained the phenomenon. We even predicted an upper limit for the supe…
