Imaginary Part Of Self-energy Research Articles

Exploring temperature dependent electron–electron interaction of rocksalt SnS and SnSe within Matsubara-time domain

Both experimental and theoretical studies show non-trivial topological behaviour in native rocksalt phase for SnS and SnSe and categorize these materials in topological crystalline insulators. Here, the detailed electronic structures studies of SnS and SnSe in the rocksalt phase are carried out using many-body GW based theory and density functional theory both for ground states and temperature dependent excited states. The estimated values of fundamental direct bandgaps around L-point using G 0 W 0 (mBJ) are ∼0.27 (∼0.13) eV and ∼0.37 (∼0.17) eV for SnS and SnSe, respectively. The strength of hybridization between Sn 5p and S 3p (Se 4p) orbitals for SnS (SnSe) shows strong k-dependence. The behaviour of (ω), which is the averaged value of diagonal matrix elements of fully screened Coulomb interaction, suggests to use full-GW method for exploring the excited states because the correlation effects within these two materials are relatively weak. The temperature dependent electronic structure calculations for SnS and SnSe provide linearly decreasing behaviour of bandgaps with rise in temperatures. The existence of collective excitation of quasiparticles in form of plasmon is predicted for these compounds, where the estimated values of plasmon frequency are ∼9.5 eV and ∼9.3 eV for SnS and SnSe, respectively. The imaginary part of self-energy and mass renormalization factor (Z k (ω)) due to electron–electron interaction (EEI) are also calculated along W–L–Γ direction for both the materials, where the estimated ranges of Z k (ω) are 0.70 to 0.79 and 0.71 to 0.78 for SnS and SnSe, respectively, along this k-direction. The present comparative study reveals that the behaviour of temperature dependent EEI for SnS and SnSe are the almost same and EEI is important for high temperature transport properties.

Electron-Phonon Coupling on the Surface of the Topological InsulatorBi2Se3Determined from Surface-Phonon Dispersion Measurements

In this Letter, we report measurements of the coupling between Dirac fermion quasiparticles (DFQs) and phonons on the (001) surface of the strong topological insulator Bi2Se3. While most contemporary investigations of this coupling have involved examining the temperature dependence of the DFQ self-energy via angle-resolved photoemission spectroscopy measurements, we employ inelastic helium-atom scattering to explore, for the first time, this coupling from the phonon perspective. Using a Hilbert transform, we are able to obtain the imaginary part of the phonon self-energy associated with a dispersive surface-phonon branch identified in our previous work [Phys. Rev. Lett. 107, 186102 (2011)] as having strong interactions with the DFQs. From this imaginary part of the self-energy we obtain a branch-specific electron-phonon coupling constant of 0.43, which is stronger than the values reported from the angle-resolved photoemission spectroscopy measurements.

High-energy supersymmetry at finite temperature

We study the leading thermal corrections to various observables in the high-energy limit in supersymmetric theories and observe that they preserve supersymmetry. Our findings generalize previous observations on the equality of asymptotic thermal masses in weakly coupled plasmas. We observe supersymmetry in the leading thermal effects for both the real and imaginary parts of self-energies, on the light cone and away from it, in both weakly and strongly interacting theories. All observed supersymmetry violations are found to be suppressed by more than two powers of the (large) energy.

Pions at finite temperature.

The properties of pions in hot hadronic matter are analyzed with an effective chiral Lagrangian which includes vector and axial-vector mesons. To obtain the dispersion relation and the absorptive properties of the pions in hot matter, the real and imaginary parts of the pion self-energy are calculated to one-loop order. The dispersion relation is very similar to that of free pions even at $T\ensuremath{\sim}160$ MeV. The mean free path is estimated from the imaginary part of the self-energy. The mass is obtained from the pole position of the propagator and from the screening limit of the pion self-energy. Even though the deviation of the mass at finite temperature is small, both masses decrease as $T$ increases. Pions remain massless in the chiral limit at finite temperature. Possible mixing of the pions with the ${A}_{1}$ mesons at finite temperature is discussed.

Transversality of the resummed thermal gluon self-energy

The perturbative Ward identities obeyed by the effective vertices and propagators for thermal quantum chromodynamics (QCD) have recently been used to prove to order g2T the on-shell transversality of the imaginary part of the (resummed) gluon self-energy in all linear gauges. Here the same result is derived for both the real and imaginary parts of the self-energy using the nonperturbative gauge-fixing identities obeyed by the generating functional for QCD.