Translacijski invarijantna dijagramska teorija smetnje za polarone

The structure of the translationally-invariant diagrammatic perturbation theory for one polaron is examined on the 1D discrete lattice described by the Holstein Hamiltonian. The latter is characterized by the electron hopping t, the phonon frequency ω0 and the electron-phonon coupling g. It is shown that the polaron localization (and translation) properties are contained in the electron propagator of one electron, intermittently added to the lattice, and/or in the phonon correlation function with one electron permanently present in the lattice. The order by order analysis in g/ω0 shows that the expansion of the irreducible electron self-energy corresponds to the expansion of the phonon correlation function, rather than of the irreducible phonon self-energy. The range of polaronic correlations is determined in this way. For small t/ω0 and already to the second order g/ω0 small, the electron-lattice correlation becomes very short ranged, i.e. the polaron is already localized to one site, although the overall translational symmetry remains unbroken. For large t/ω0, the second order result is meaningful up to large g/ω0 ≈ (t/ω0) 1 4 , where it becomes degenerate with the results for the large adiabatic Holstein polaron. This suggests that the translationally invariant perturbation theory crosses then over smoothly, without symmetry breaking, into the adiabatic, continuous quantum limit, as rigorously demonstrated in the companion paper. Thus the quantum theory of the large adiabatic Holstein polaron provides a simple, instructive example of the quantum crossover which replaces the behavior in the quantum critical point.Istraživali smo strukturu translacijski invarijantne dijagramske perturbacijske teorije jednog polarona na 1D diskretnoj rešetki opisanoj Holsteinovim hamiltonijanom. Taj je hamiltonijan karakteriziran elektronskim preskokom t, fononskom frekvencijom ω0, i elektron-fononskim vezanjem g. Pokazali smo da su lokalizacijska (i translacijska) svojstva polarona sadržana u propagatoru jednog elektrona, privremeno dodanog rešetki, i/ili u fononskoj korelacijskoj funkciji s jednim elektronom stalno prisutnim u rešetki. Analiza po potencijama od g/ω0 pokazuje da razvoj elektronske ireducibilne vlastite energije odgovara razvoju fononske korelacijske funkcije, a ne razvoju fononske ireducibilne vlastite energije. Na taj je način određen doseg polaronskih korelacija. Za mali t/ω0, već u drugom redu po g/ω0 elektronreetka korelacija postaje vrlo kratkodosena, odnosno polaron je lokaliziran na jedno čvorište rešetke, iako opća translacijska simetrija ostaje sačuvana. Za veliki t/ω0 rezultat računa u drugom redu ostaje primjenjiv do velikih g/ω0 ≈ (t/ω0) 1/4 , gdje postaje degeneriran s rezultatom za veliki, adijabatski Holsteinov polaron. To naznačuje da translacijski invarijantna perturbacijska teorija tada prelazi glatko, bez loma simetrije, u adijabatsku kontinuiranu kvantnu granicu, što e biti rigorozno dokazano u članku-pratitelju. Kvantna teorija velikog adijabatskog Holsteinovog polarona, dakle, predstavlja jednostavan i poučan primjer kvantnog križanja koje zamjenjuje ponašanje u kvantnoj kritičnoj točki

Dynamic structure factor of a one-dimensional Peierls system

The Newtonian dynamics of a one-dimensional system with a complex order parameter and an anharmonic potential energy of the Landau type is examined in a wide temperature range using numerical Monte Carlo–molecular dynamics simulations. Results are discussed with an emphasis on the incommensurate Peierls systems. Dispersive-mode behavior found previously in the quartic region near TMF can be followed to lower temperatures where the frequency of the phonon mode decreases and the damping increases. Below 0.4TMF the dynamic structure factor is characterized by the overdamped mode down to 0.3TMF, when the separation between the phase and the amplitude mode becomes effective. The relation between the different regimes in S(k,ω) and the pseudogap in the electronic spectrum is also briefly discussed

Comment on “Strain and High Temperature Superconductivity: Unexpected Results from Direct Electronic Structure Measurements in Thin Films”

Comment on “Strain and High Temperature Superconductivity: Unexpected Results from Direct Electronic Structure Measurements in Thin Films”

Recalculation of 4kF correlations in one-dimensional systems

The 4kF response function is recalculated for the one-dimensional electron system in the presence of the umklapp matrix element g3. It is shown that the 1/ω2-4γc singularity is replaced by a finite value below the energy gap set by g3

Optička svojstva u modelu s više vrpci - pristup pomoću jednadžbi gibanja

The electrodynamic features of the multiband model are examined using the transverse equation of motion approach in order to give the explanation of several longstanding problems. It turns out that the exact summation of the most singular terms in powers of 1/ωn leads to the total optical conductivity which, in the zerofrequency limit, reduces to the results of the Boltzmann equation, both for the metallic and semiconducting two-band regime. The detailed calculations have been carried out for the quasi-one-dimensional (Q1D) two-band model corresponding to the imperfect charge-density-wave (CDW) nesting. It is also shown that the results of the present treatment of the impurity-scattering processes for the DC conductivity of the ordered CDW state are in agreement with the experimental observation. Finally, the DC and optical conductivity are calculated numerically for a few typical Q1D cases.Primjenom formalizma jednadžbi gibanja razmatrali smo elektrodinamička svojstva modela s više vrpci u cilju rješavanja nekoliko starih problema. Pokazuje se da egzaktno zbrajanje najsingularnijih doprinosa u potencijama od 1/ωn vodi do ukupne optičke vodljivosti koja se u statičkoj granici podudara s rezultatima Boltzmannovih jednadžbi, u obje granice modela s dvije vrpce, metalnoj i poluvodičkoj. Načinili smo precizne račune za kvazi-jednodimenzijski (K1D) model dvije vrpce koji odgovara slučaju s neidelnim ugnježđenjem tipa val-gustoće naboja (VGN). Također se pokazuje da izloženi opis procesa raspršenja na nečistoćama daje istosmjernu vodljivost uređenog VGN stanja koja je u skladu s eksperimentalnim opažanjem. Na koncu, daju se numerički rezultati istosmjerne i optičke vodljivosti za nekoliko karakterističnih K1D primjera

Optička svojstva u modelu s više vrpci - pristup pomoću jednadžbi gibanja

The electrodynamic features of the multiband model are examined using the transverse equation of motion approach in order to give the explanation of several longstanding problems. It turns out that the exact summation of the most singular terms in powers of 1/ωn leads to the total optical conductivity which, in the zerofrequency limit, reduces to the results of the Boltzmann equation, both for the metallic and semiconducting two-band regime. The detailed calculations have been carried out for the quasi-one-dimensional (Q1D) two-band model corresponding to the imperfect charge-density-wave (CDW) nesting. It is also shown that the results of the present treatment of the impurity-scattering processes for the DC conductivity of the ordered CDW state are in agreement with the experimental observation. Finally, the DC and optical conductivity are calculated numerically for a few typical Q1D cases.Primjenom formalizma jednadžbi gibanja razmatrali smo elektrodinamička svojstva modela s više vrpci u cilju rješavanja nekoliko starih problema. Pokazuje se da egzaktno zbrajanje najsingularnijih doprinosa u potencijama od 1/ωn vodi do ukupne optičke vodljivosti koja se u statičkoj granici podudara s rezultatima Boltzmannovih jednadžbi, u obje granice modela s dvije vrpce, metalnoj i poluvodičkoj. Načinili smo precizne račune za kvazi-jednodimenzijski (K1D) model dvije vrpce koji odgovara slučaju s neidelnim ugnježđenjem tipa val-gustoće naboja (VGN). Također se pokazuje da izloženi opis procesa raspršenja na nečistoćama daje istosmjernu vodljivost uređenog VGN stanja koja je u skladu s eksperimentalnim opažanjem. Na koncu, daju se numerički rezultati istosmjerne i optičke vodljivosti za nekoliko karakterističnih K1D primjera