Temperature and pressure dependence of the optical gaps in Hf1−xZrxS2

1988 ◽  
Vol 66 (7) ◽  
pp. 633-637 ◽  
Author(s):  
Larbi Roubi ◽  
Cosmo Carlone
Keyword(s):  
Three Dimensional ◽  
Volume Effect ◽  
Electronic Energy ◽  
Coupling Constant ◽  
Indirect Transition ◽  
Three Dimensional Model ◽  
Intrinsic Volume ◽  
Electron Phonon Interaction ◽  
Electron Phonon Coupling ◽  
Layered Crystals

Mixed layered crystals of the type Hf1−xZrxS2, with x = 0.0, 0.1, 0.25, 0.5, 0.75, 0.90, and 1.0, have been grown by the iodine transport method. The direct (at the Γ points) and indirect (Γ to L) transitions have been measured (at T = 290 K) as a function of pressure from 0 to 30 kbar, and (at p = 0 kbar) as a function of the temperature (15–290 K). The phonon frequency assisting the indirect transition is 40 ± 2 MeV. The intrinsic (volume effect) and extrinsic (interaction effect) contributions to the change in electronic energy have been evaluated. We find that the electron–phonon interaction is more aptly described by a quasi-three-dimensional model than a purely two-dimensional one. From the shift of the indirect gap, we find that the electron–phonon coupling constant g varies linearly from 0.54 ± 0.03 (x = 0) to 0.44 ± 0.03 (x = 1.0).

scholarly journals Tracking ultrafast hot-electron diffusion in space and time by ultrafast thermomodulation microscopy

2019 ◽  
Vol 5 (5) ◽  
pp. eaav8965 ◽  
Author(s):  
A. Block ◽  
M. Liebel ◽  
R. Yu ◽  
M. Spector ◽  
Y. Sivan ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Nonequilibrium Dynamics ◽  
Hot Electron ◽  
Temperature Model ◽  
Three Dimensional Model ◽  
Electron Diffusion ◽  
Diffusion Dynamics ◽  
Electron Phonon Coupling ◽  
20 Nm ◽  
Two Temperature

The ultrafast response of metals to light is governed by intriguing nonequilibrium dynamics involving the interplay of excited electrons and phonons. The coupling between them leads to nonlinear diffusion behavior on ultrashort time scales. Here, we use scanning ultrafast thermomodulation microscopy to image the spatiotemporal hot-electron diffusion in thin gold films. By tracking local transient reflectivity with 20-nm spatial precision and 0.25-ps temporal resolution, we reveal two distinct diffusion regimes: an initial rapid diffusion during the first few picoseconds, followed by about 100-fold slower diffusion at longer times. We find a slower initial diffusion than previously predicted for purely electronic diffusion. We develop a comprehensive three-dimensional model based on a two-temperature model and evaluation of the thermo-optical response, taking into account the delaying effect of electron-phonon coupling. Our simulations describe well the observed diffusion dynamics and let us identify the two diffusion regimes as hot-electron and phonon-limited thermal diffusion, respectively.

ELECTRON–PHONON INTERACTION AND ELECTRONIC STRUCTURE OF SMALL METAL CLUSTERS

1996 ◽  
Vol 03 (01) ◽  
pp. 489-492 ◽  
Author(s):  
JIJUN ZHAO ◽  
XIAOSHUANG CHEN ◽  
FENGQI LIU ◽  
GUANGHOU WANG
Keyword(s):  
Electronic Structures ◽  
Metal Clusters ◽  
Energy Levels ◽  
Iteration Process ◽  
Coupling Constant ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Size Dependent ◽  
Electron Phonon Coupling ◽  
Valence Electrons

The Su–Schrieffer–Heeger (SSH) Hamiltonian has been extended to study the electron–phonon interaction and the electronic structures of the alkali-like metal clusters. The eigen-energy levels of s valence electrons are obtained from a Hückel-like Hamiltonian including the correction of the electron–phonon interaction in the hopping integral, which is proportional to the variable of bond length. The self-consistent equations for electrons and phonons are solved adiabatically through an iteration process. The energy-level structures of an octahedral Cu6 cluster are calculated with variable electron–phonon coupling constant λ to investigate the influence of electron–phonon interaction on the lattice distortion and electronic structures of metal clusters. The size-dependent ionization potential for small Cun clusters are calculated and compared with the experimental results.

ELASTIC PROPERTIES OF THE Zn SUBSTITUTED ErBa2Cu3O7-δ SUPERCONDUCTOR

2003 ◽  
Vol 17 (02) ◽  
pp. 75-82
Author(s):  
T. V. CHONG ◽  
R. ABD-SHUKOR
Keyword(s):  
Longitudinal Velocity ◽  
Shear Velocity ◽  
Spin Correlation ◽  
Coupling Constant ◽  
Phonon Coupling ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Electron Phonon Coupling ◽  
Overlap Method ◽  
Pulse Echo

Ultrasonic longitudinal and shear velocity in superconducting ErBa 2( Cu 3-x Zn x) O 7-δ (x = 0, 0.01 and 0.05) have been measured using the pulse-echo-overlap method at frequency 5–10 MHz in the temperature range 80–300 K. Longitudinal velocity hysteresis and elastic anomaly were observed in the x = 0 sample. Similar hysteresis was not observed in the x = 0.01 and 0.05 samples. The characteristic Debye temperature and electron–phonon coupling constant were calculated. The absence of hysteresis for longitudinal velocity in the x = 0.01 and 0.05 samples may be due to the spin correlation at the CuO 2 planes which affects the electron–phonon interaction.

The Estimate of the Electron–Phonon Coupling Constant in the Thin Film

1998 ◽  
Vol 12 (02) ◽  
pp. 177-189 ◽  
Author(s):  
M. Pantić ◽  
Lj. D. Mašković ◽  
B. S. Tošić
Keyword(s):  
Experimental Fact ◽  
Coupling Constant ◽  
Phonon Coupling ◽  
Metallic Films ◽  
Critical Temperatures ◽  
Dominant Form ◽  
Electron Phonon Interaction ◽  
Electron Phonon Coupling ◽  
Surface Electrons ◽  
Bulk Structures

Hamiltonians of electron–phonon interaction for thin metallic films are formulated. This is the basis for the estimate of the superconductivity critical temperature for films and corresponding bulk structures. It is shown that the interaction of surface electrons in the film with bulk phonons could explain the experimental fact that critical temperatures of the films are higher than the corresponding ones in bulk (massive) structures. Since above fact is valid nearly for all pure metallic, one can conclude that the dominant form or the interaction in films is the interaction of surface electrons with bulk phonons.

scholarly journals Superconductivity in LiGa2Ir Heusler type compound with VEC = 16

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Karolina Górnicka ◽  
Gabriel Kuderowicz ◽  
Michał J. Winiarski ◽  
Bartłomiej Wiendlocha ◽  
Tomasz Klimczuk
Keyword(s):  
Heat Capacity ◽  
Solid State Reaction Method ◽  
Lattice Parameter ◽  
Coupling Constant ◽  
X Ray Diffraction ◽  
Electron Phonon Interaction ◽  
Type Ii Superconductor ◽  
Electron Phonon Coupling ◽  
A Minor ◽  
Type Crystal

AbstractPolycrystalline LiGa2Ir has been prepared by a solid state reaction method. A Rietveld refinement of powder x-ray diffraction data confirms a previously reported Heusler-type crystal structure (space group Fm-3m, No. 225) with lattice parameter a = 6.0322(1) Å. The normal and superconducting state properties were studied by magnetic susceptibility, heat capacity, and electrical resistivity techniques. A bulk superconductivity with Tc = 2.94 K was confirmed by detailed heat capacity studies. The measurements indicate that LiGa2Ir is a weak-coupling type-II superconductor ($${\uplambda }$$ λ e–p = 0.57, $${\Delta }$$ Δ C/$${\upgamma }$$ γ Tc = 1.4). Electronic structure, lattice dynamics, and the electron–phonon interaction are studied from first principles calculations. Ir and two Ga atoms equally contribute to the Fermi surface with a minor contribution from Li. The phonon spectrum contains separated high frequency Li modes, which are seen clearly as an Einstein-like contribution in the specific heat. The calculated electron–phonon coupling constant $${\uplambda }$$ λ e–p = 0.68 confirms the electron–phonon mechanism for the superconductivity. LiGa2Ir and recently reported isoelectronic LiGa2Rh are the only two known representatives of the Heusler superconductors with the valence electron count VEC = 16.

CROSSOVER FROM 3D TO 2D IN THE ELECTRONIC STRUCTURE OF MgB2-TYPE SYSTEMS

2002 ◽  
Vol 16 (24) ◽  
pp. 3671-3680
Author(s):  
G. Q. HUANG ◽  
M. LIU ◽  
L. F. CHEN
Keyword(s):  
Electronic Structure ◽  
Phonon Frequency ◽  
Three Dimensional ◽  
Type Systems ◽  
Orbital Method ◽  
Full Potential ◽  
Hole Density ◽  
Coupling Constant ◽  
Phonon Coupling ◽  
Electron Phonon Coupling

Using the Stuttgart Full-potential Linearized Muffin-tin Orbital method, we study a crossover of the electronic structure of MgB 2 from three-dimensional (3D) to 2D by artificially increasing the lattice constant along the c-axis. With the inter-layer coupling decreased by increasing c, the density of states (DOS) at E F has a considerable growth; at the same time, the charge transfer from Mg plane to B plane decreases so that the hole density in the B plane increases. As c is increased to 4c0, the electronic structure exhibits 2D characteristic and a van Hove peak in the DOS appears. The E2g phonon frequency at Γ point and the electron–phonon coupling constant λ are estimated by using the frozen phonon method. The calculated results indicate that T c in MgB 2 could be further increased if the inter-layer coupling might be reduced.

scholarly journals Nonadiabatic superconductivity in a Li-intercalated hexagonal boron nitride bilayer

2020 ◽  
Vol 11 ◽  
pp. 1178-1189
Author(s):  
Kamila A Szewczyk ◽  
Izabela A Domagalska ◽  
Artur P Durajski ◽  
Radosław Szczęśniak
Keyword(s):  
Boron Nitride ◽  
Hexagonal Boron Nitride ◽  
Point Of View ◽  
Coupling Constant ◽  
Electron Phonon Interaction ◽  
Vertex Corrections ◽  
Electron Phonon Coupling ◽  
Nonadiabatic Effects ◽  
Debye Frequency ◽  
Very High

When considering a Li-intercalated hexagonal boron nitride bilayer (Li-hBN), the vertex corrections of electron–phonon interaction cannot be omitted. This is evidenced by the very high value of the ratio λωD/εF ≈ 0.46, where λ is the electron–phonon coupling constant, ωD is the Debye frequency, and εF represents the Fermi energy. Due to nonadiabatic effects, the phonon–induced superconducting state in Li-hBN is characterized by much lower values of the critical temperature (T LOVC C ∈ {19.1, 15.5, 11.8} K, for μ* ∈ {0.1, 0.14, 0.2}, respectively) than would result from calculations not taking this effect into account (T ME C∈ {31.9, 26.9, 21} K). From the technological point of view, the low value of T C limits the possible applications of Li-hBN. The calculations were carried out under the classic Migdal–Eliashberg formalism (ME) and the Eliashberg theory with lowest-order vertex corrections (LOVC). We show that the vertex corrections of higher order (λ3) lower the value of T LOVC C by a few percent.

LARGE POLARON IN AN ANHARMONIC CRYSTAL LATTICE

2009 ◽  
Vol 23 (01) ◽  
pp. 19-38 ◽  
Author(s):  
ADIL-GERAI KUSSOW
Keyword(s):  
Large Radius ◽  
Coupling Constant ◽  
Phonon Coupling ◽  
Anharmonic Crystal ◽  
Electron Phonon Interaction ◽  
Anharmonic Lattice ◽  
Longitudinal Phonon ◽  
Electron Phonon Coupling ◽  
Comparison Of The Results ◽  
Perovskite Type

Extending the Frohlich polaron problem to an anharmonic lattice, the author studies a polaronic state with a large radius of the wave function. The appropriate anharmonic part of the electron–phonon interaction Hamiltonian is derived, based on the methods of quantum field theory. Then, with the help of the perturbation theory, the anharmonic correction to the electron–phonon coupling constant is straightforwardly calculated. The estimate of this correction shows that the anharmonicity can considerably increase the e–ph coupling constant if the longitudinal phonon frequency is lower than ~10 meV. Several materials, molecular crystals α-sexithiophene (α-6T), α, ω dihexylsexithiophene (H-6T), and perovskite-type oxides, in which the anharmonic polaronic effects should be pronounced, are discussed. A comparison of the results with other anharmonic models of a polaronic state is drawn.

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