Electron-phonon Coupling Constant Research Articles

Evaluation of Constants of Electron–Phonon Coupling between Gas Molecules and Graphene

The adsorption of CO, NO, NO2, Н2О, and NH3 molecules on ideal graphene and graphene doped with aluminum is analyzed using simple models. The constants of electron–phonon coupling are evaluated with the Lennard-Jones 6–12 potential for ideal graphene and the 2–4 potential for doped graphene. It is demonstrated that the dimensionless electron–phonon-coupling constant for ideal graphene is ζ ≫ 1, while ζ ~ 1 corresponds to graphene doped with aluminum. Ways to use both types of graphene as a resistive gas sensor are discussed.

A superconducting battery material: Lithium gold boride (LiAu3B)

The superconducting and potential cathode material properties of ternary boride of LiAu3B have been investigated by density functional first principles. The Li-concentration effects on the actual electronic and structural properties, namely the properties of LixAu9B3 (x = 0, 1, 2) sub-systems are studied. It is remarkably shown that the existence of Li-atoms has no considerable effect on the structural properties of Au-B skeleton in LiAu3B. Then, it can be offered as a potential cathode material for Li-ion batteries with the very small volume deviation of 0.42%, and the suitable average open circuit voltage of ∼1.30 V. Furthermore, the vibrational and superconducting properties such as electron-phonon coupling constant (λ) and critical temperature (Tc) of LiAu3B are studied. The calculated results suggest that LiAu3B should be a superconductor with Tc ∼5.8 K, also.

Investigate the electrical and thermal properties of the low temperature resistant silver nanowire fabricated by two-beam laser technique

A two-beam laser fabrication technique is introduced to fabricate the single silver nanowire (AgNW) on polyethylene terephthalate (PET) substrate. The resistivity of the AgNW is (1.31 ± 0.05) × 10−7 Ω·m, which is about 8 times of the bulk silver resistivity (1.65 × 10−8 Ω·m). The AgNW electrical resistance is measured in temperature range of 10–300 K and fitted with the Bloch-Grüneisen formula. The fitting results show that the residue resistance is 153 Ω, the Debye temperature is 210 K and the electron-phonon coupling constant is (5.72 ± 0.24) × 10−8 Ω·m. Due to the surface scattering, the Debye temperature and the electron-phonon coupling constant are lower than those of bulk silver, and the residue resistance is bigger than that of bulk silver. Thermal conductivity of the single AgNW is calculated in the corresponding temperature range, which is the biggest at the temperature approaching the Debye temperature. The AgNW on PET substrate is the low temperature resistance material and is able to be operated stably at such a low temperature of 10 K.

Оценки констант электрон-фононной связи молекул газа с графеном

AbstractThe adsorption of CO, NO, NO_2, Н_2О, and NH_3 molecules on ideal graphene and graphene doped with aluminum is analyzed using simple models. The constants of electron–phonon coupling are evaluated with the Lennard-Jones 6–12 potential for ideal graphene and the 2–4 potential for doped graphene. It is demonstrated that the dimensionless electron–phonon-coupling constant for ideal graphene is ζ ≫ 1, while ζ ~ 1 corresponds to graphene doped with aluminum. Ways to use both types of graphene as a resistive gas sensor are discussed.

Electron-Phonon Coupling Constant of Metallic Overlayers from Specular He Atom Scattering.

He atom scattering has been shown to be a sensitive probe of electron-phonon interaction properties at surfaces. Here it is shown that measurements of the thermal attenuation of the specular He atom diffraction peak (the Debye-Waller effect) can determine the electron-phonon coupling constant, λ, for ultrathin films of metal overlayers on various close-packed metal substrates. Values of λ obtained for single and multiple monolayers of alkali metals, and for Pb layers on Cu(111), extrapolated to large thicknesses, agree favorably with known bulk values. This demonstrates that He atom scattering can measure the electron-phonon coupling strength as a function of film thickness on a layer-by-layer basis.

Estimation of electron temperature in heated metallic nanoparticle

A method is proposed for determining the temperature of hot electrons in a metallic nanoparticle embedded in a dielectric matrix under ultrashort laser pulses irradiation. The amplitude and power of the longitudinal spherical acoustic oscillations as functions of density and elastic properties of the medium, the laser pulse duration, the electron temperature, radii of particles, and the electron-phonon coupling constant are obtained. The efficiency of the electron energy transfer from heated noble nanoparticles to a surrounding environment is estimated for different electron temperatures.

Influences of temperature on asymmetric quantum dot qubit in Coulombic impunity potential

Using the variational method of the Pekar-type, we study the influences of the temperature on the asymmetric quantum dot (QD) qubit in the Coulombic impunity potential. Then we derive the numerical results and formulate the derivative relationships of the electron probability density and the electron oscillation period in the superposition state of the ground state and the first-excited state with the electron–phonon coupling constant, the Coulombic impurity potential, the transverse and longitudinal confinement strengths at different temperatures, respectively.

Ab initio calculation of thermal boundary resistance at the interface of metals with GeTe, In $$_3$$ 3 SbTe $$_2$$ 2 and In $$_2$$ 2 GeTe $$_3$$ 3 phase change compounds

First principles calculations of phonon dispersion relations have been performed to estimate the phononic contribution to the thermal boundary resistance at the interfaces between GeTe, In $$_3$$ SbTe $$_2$$ and In $$_2$$ GeTe $$_3$$ phase change compounds and metals (Al, Pt and TiN). The diffuse mismatch model has been used. The electron–phonon coupling constants provide an estimate of the electron–phonon contribution to the thermal boundary resistance. The electron–phonon and phononic contributions to the thermal boundary resistance turn out to be comparable and they have to be both included for a reliable estimate of the thermal conductance at the interface with phase change compounds.

On the critical temperature discontinuity at the theoretical bcc-fcc phase transition in compressed selenium and tellurium superconductors

Recent hydrides-driven advent in the high-pressure phonon-mediated superconductivity motivates research on chemical elements which compound with hydrogen. It is desired that such elements should allow chemical pre-compression of hydrogen to assure the induction of the superconducting phase with the high transition temperature (TC). Herein, we present detailed theoretical insight into the properties of the superconducting state induced under pressure (p) in two of such component elements, namely selenium (Se) and tellurium (Te) at GPa and GPa, respectively. The assumed external pressure conditions allow us to conduct our analysis just above previously theoretically predicted bcc-fcc structural phase transition of Se and Te, and identify the possible associated discontinuity effect of the critical temperature. In particular, our numerical analysis is conducted within Migdal-Eliashberg formalism, due to the confirmed electron–phonon pairing mechanism and relatively high electron–phonon coupling constant in the materials of interest. We predict that TC values in Se and Te equal 8.13 K and 5.96 K, respectively, and mark the highest critical temperature values for these elements within the postulated fcc phase. Additionally, we supplement these results by the estimated maximum values of the superconducting energy band gap and the effective mass of electrons. We predict that all these parameters can be used as a guidelines for experimental observation of the critical temperature discontinuity and the corresponding bcc-fcc phase transition in Se and Te superconductors. Moreover, we show that the thermodynamics of superconducting phase in both elements may exhibit deviations from the conventional estimates of the Bardeen–Cooper–Schrieffer theory, and suggest existence of the strong-coupling and retardation effects. Finally, we note that our results can be also instructive for future screening of chemical elements for applications in superconducting hydrides.

Luminescence and phonon sideband analysis of Eu3+ doped alkali fluoroborate glasses for red emission applications

Trivalent europium (Eu3+) doped alkali fluoroborate glasses (KBZFB) with molar composition 10K2O + 10BaO + 10ZnF2+(70 − x)B2O3 + xEu2O3 (x = 0.1, 1.0, 2 and 2.5 mol%) have been prepared by melt quenching technique. The structural aspects were explored through XRD, FTIR and Raman analyses. The spectroscopic properties were investigated using optical absorption, photoluminescence and decay curve analyses. Under 393 nm excitation, Eu3+ doped KBZFB glasses give intense red emission (612 nm) of Eu3+ ions corresponding to 5D0→7F2 transition. Judd–Ofelt theory has been employed to evaluate the phenomological intensity parameters. Radiative properties like radiative transition probabilities (A), radiative life time (τR) and branching ratios (βR) were also calculated. Phonon sidebands were observed in the excitation spectra on the high energy side of the pure electronic transition 7F0 → 5D2. The phonon energy (ℏω) and the electron–phonon coupling constant (g) were derived from the phonon sideband spectra. The luminescence decay was analyzed and the lifetime of the samples has been estimated. The experimental lifetime is compared with theoretical value and better quantum efficiency is obtained. The emission intensities were characterized using CIE chromaticity diagram and the prepared glasses offer pure intense red emission which is useful for various photonic applications.

Temperature effects on bound polaron in triangular quantum dot qubit subjected to an electromagnetic field

In this work, the variational method of the Pekar type is used to theoretically study the temperature effects on the bound polaron in the triangular quantum dot (QD) qubit subjected to an electromagnetic field. We analyze and discuss in detail the numerical results and show that the relationships of the ground and first excited state energies, the electron probability density and the electron oscillation period in the superposition state of the ground state and the first-excited state with the temperature, the cyclotron frequency, the electron-phonon coupling constant, the electric field strength, the confinement strength and the Coulomb impurity potential, respectively.

Ultrafast optical spectroscopy of high-temperature superconductors

The mechanism of high-temperature superconductivity is still an unsolved mystery in physics, and it is the ″pearl in the crown″ of condensed matter physics. Among the numerous optical methods investigating superconductors, ultrafast spectroscopy is one of the most exquisite methods and the most powerful control means. It can interact with superconductors in all the charge, lattice, spin and orbital degrees of freedom. It can probe the excited state of superconductors. It can uniquely realize investigations of the ultrafast processes of quasiparticles, the coherence control of lattices, electron-phonon coupling strength, and the interface superconductivity. Here we briefly review the ultrafast optical spectroscopy (especially the ultrafast dynamics) investigations of high temperature superconductors, with concrete examples. Particularly, we demonstrate the unique virtues of this experimental method in the observation and realization of quasiparticle excited states, bosonic coherent states, laser-induced superconductivity, and interface superconductivity. We give the prospect of this area at the end. The complexity, profundity and serendipity of superconductivity quite much root in its bridging between both fermions and bosons in the condensed matters—a solid universe. Ultrafast spectroscopy can probe both the electrons and bosonic collective elementary excitations, thus making it feasible for revealing the superconducting mechanism. The time-resolved measurements provide direct evidences of the superconducting Bose-Einstein condensate and clues to distinguish it from the pseudogaps, charge density waves, spin density waves, etc. Delicate ultrafast spectroscopy investigations can also yield testifying information on the gap symmetry, including whether there is a nodal line in the system. The electron-phonon coupling constant can be obtained by directly observing the quasiparticle relaxation, which usually occurs at picosecond scales and marks the rate of energy transferring among carriers and phonons—a direct reflection of electron-coupling strength. The unique way of generating and detection coherent phonons in a solid adds another way of looking into the lattice behavior in a superconductor—if it is phonon glue, which mode plays the major role? The aforementioned methods have been used to study all the cuprates, iron-based superconductors, and interface single-layer superconductors. Furthermore, ultrafast laser pulse can act as a natural controlling tool. It is known photo-doping can be more efficient than chemical doping in some situations, but more dramatically, ultrafast light pulses can induce superconducting phenomenon in a non-superconducting system with even room temperature T c. Since the superconducting feature occurs and evolves in picoseconds, this transient superconductivity can only be observed using ultrafast spectroscopy. This excited state superconductivity is a concrete example of the importance of excited state in superconductivity investigation. The accessibility for ultrafast spectroscopy to excited states (non-equilibrium quantum states) making it an exceptionally feasible experimental means among the all in such investigations. Currently, ultrafast spectroscopy is extending to the THz and mid-IR range to resonantly probe the narrow gaps or phonon excitation, to the X-ray range (RIXS) to achieve momentum-resolved information of bosonic excitations, to adding angle-resolved photoemission spectroscopy to access the momentum-resolved electronic features, to adding Transmission Electron Microscopy (TEM), Scanning Tunnel Microscope (STM) or Scanning Nearfield Optical Microscope (SNOM) for spatially-resolved properties, etc. We foresee that ultrafast spectroscopy of superconductors is going to be mature area in 30 years. During this period, it is going to proceed in a foreseeable way marked by the aforementioned science problems and physics techniques, and in an un-foreseeable way marked by novel exciting results.

First-principles study of mechanical, thermodynamic, transport and superconducting properties of Sr3SnO

We have performed a comprehensive set of first-principles calculations to study mechanical, thermal, transport and superconducting properties of Sr3SnO, an antiperovskite Dirac-metal oxide. Sr3SnO cubic crystal is found to be elastically stable, anisotropic and brittle in nature. The Debye temperature and bulk modulus are found to decrease with increasing temperature but increase with increasing pressure. However, the specific heats are found to increase due to the increase of temperature. The Gaspari and Gyorffy formalism within the rigid muffin tin approximation is used to calculate the electron phonon coupling constant and hence transition temperature (Tc). The density of states is dominated by Sr-4d and Sn-5p electrons near the Fermi level and the mixing of Sr-4d and Sn-5p causes the topological superconductivity in Sr3SnO. The calculated Tc (8.38 K) is reasonably close to the experimental value (∼5 K).

A Comprehensive Investigation of Superconductor KBi2 via First-Principles Calculations

The electronic properties, lattice vibration, and electron-phonon interaction properties of KBi2 are studied systematically by first-principles calculations. The agreement of calculated Debye temperature, electron-phonon coupling constant, and transition temperature with latest experiments validates the reliability of our work. Our results provide evidence that the superconducting transition of KBi2 originates from isotropical coupling of all phonon modes according to isotropical Migdal-Eliashberg theory.

Structural phase transition, electronic and superconducting properties of ScBi and YBi

The structural, electronic, lattice dynamic and superconducting properties of ScBi and YBi compounds are investigated using density functional theory. The calculated values of structural phase transition pressure from NaCl-type (B1) to CsCl-type (B2) phase and ground state properties such as lattice constant (a0), bulk modulus (B) and its pressure derivative (B׳) are compared with the available theoretical data. The electronic and bonding properties are discussed in terms of band structure, density of states and charge density difference plots. The phonon dispersion curves and phonon density of states are also discussed for both the compounds and calculated for the first time for ScBi compound. The phonon frequencies are positive at ambient and high pressure throughout the Brillouin zone in rock-salt structure revealing the stability in that phase. Eliashberg spectral function, electron-phonon coupling constant and superconducting transition temperature of ScBi and YBi are discussed in detail. The values of Tc are 0.97K for ScBi and 1.29K for YBi at ambient pressure.

Temperature Dependence of Electron–Phonon Interactions in Gold Films Rationalized by Time-Domain Ab Initio Analysis

The nonequilibrium dynamics of excited electrons in metals is probed by ultrafast laser measurements. Using a real-time Kohn–Sham time-dependent density functional theory and nonadiabatic molecular dynamics, we report direct modeling of such experiments, rationalizing the observed temperature dependence. Focusing on thin gold films, we analyze the effect of temperature on film structure, electronic state densities, nonadiabatic electron–phonon coupling, elastic electron–phonon scattering times, and electron–phonon relaxation rates. The effective electron–phonon coupling constants calculated at different temperatures are in good agreement with the values deduced from experiments and an alternative theory. A temperature increase accelerates both inelastic and elastic electron–phonon scattering and allows a larger number of higher-frequency phonon modes to couple to the electronic subsystem. The inelastic electron–phonon coupling is largest between nearest states, indicating that carrier relaxation involves ...

Study of superconducting phase in cubic anti-perovskite Cr3RhN

The paper characterizes the thermodynamic properties of the phonon-induced superconducting state in Cr3RhN compound. Due to the high value of the electron-phonon coupling constant (λ ∼ 1), the calculations have been conducted in the framework of the Eliashberg formalism. It has been shown that the critical temperature (TC) is relatively high and it changes in the range from 14.24 K to 21.55 K, for the values of the Coulomb pseudopotential (μ⋆) from 0.3 to 0.1. Due to the significant strong-coupling and the retardation effects, the values of the order parameter (Δ), the thermodynamic critical field (HC), and the specific heat of the superconducting state (CS), highly deviate from the values predicted by the BCS model. In particular, RΔ=2Δ(0)kBTC∈{4.06,3.94,3.86},RH=TCCN(TC)HC2(0)∈{0.147,0.156,0.158}, and RC=ΔC(TC)CN(TC)∈{2.13,1.89,1.82}, respectively for μ⋆ ∈ {0.1, 0.2, 0.3}. The BCS model predicts RΔBCS=3.53,RHBCS=0.168, and RCBCS=1.43.

Efficient method to calculate the electron–phonon coupling constant and superconducting transition temperature

We show an efficient way to compute the electron–phonon coupling constant, λ, and the superconducting transition temperature, Tc from first-principles calculations. This approach gives rapid convergence of Tc with respect to the size of the k-point mesh, and is seamlessly connected to the formulation used in large molecular systems such as alkali fullerides where momentum dependence can be neglected. Since the phonon and electron–phonon calculations are time consuming particularly in complicated systems, the present approach will strongly reduce the computational cost, which facilitates high-throughput superconducting material design.

Proximity-induced superconductivity in all-silicon superconductor /normal-metal junctions

We have realised laser-doped all-silicon superconducting (S)/ normal metal (N) bilayers of tunable thickness and dopant concentration. We observed a strong reduction of the bilayers critical temperature when increasing the normal metal thickness, a signature of the highly transparent S/N interface associated to the epitaxial sharp laser doping profile. We extracted the interface resistance by fitting with the linearised Usadel equations, demonstrating a reduction of one order of magnitude from previous superconductor/doped Si interfaces. In this well controlled crystalline system we exploited the low resistance S/N interfaces to elaborate all-silicon lateral SNS Josephson junctions with long range proximity effect. Their dc transport properties, such as the critical and retrapping currents, could be well understood in the diffusive regime. Furthermore, this work lead to the estimation of important parameters in ultra-doped superconducting Si, such as the Fermi velocity, the coherence length, or the electron-phonon coupling constant, fundamental to conceive an all-silicon superconducting electronics.

Elastic, electronic, lattice dynamical properties and electron-phonon interaction in the ternary superconductors Sr(GaGe) and Sr(GaSi) at high pressure

We report the results of an ab−initio study of electronic, and detailed lattice dynamical properties of superconducting materials, Sr(GaGe) and Sr(GaSi) under high pressure. The phonon dispersion curves along the high-symmetry directions and phonon frequencies parameters at the Brillouin zone center are computed by using density functional perturbation theory while the elastic constants are calculated in metric-tensor formulation. The Vickers hardness belonging to the compounds is also evaluated clearly. Moreover the band structures, partial densities of states and Fermi surface topologies are discussed in detail. At the same time we advance in-depth understanding of the relationship between the properties determined and superconducting characteristic. The transition temperatures for the compounds have been detected. We find the values of electron-phonon coupling constant as 0.99 and 0.92 for Sr(GaSi) and Sr(GaGe), respectively.