Electron transport in condensed matter. A novel approach using quantum chemical methods

2016

J Supercond Nov Magn

Self Cite

Simulation of the resistivity in the normal state of doped La 2−x Sr x CuO 4 has been performed using a hopping model based on Marcus theory. The results are in substantial agreement with experimental results. At oxidative doping, Cu(III) sites are formed and electron mobility possible due to hopping: Cu(III)Cu(II) → Cu(II)Cu(III) (one-electron exchange). In the underdoped, non-metallic region, the resistivity (ρ) decreases from almost insulation at T = 0 to a minimum at about T = 100 K. ρ then increases more than linearly with T (∼ T 3/2 ) in the region 100 < T < 500 K. A photo-induced metal-metal (MM) charge transfer transition at 2 eV 2Cu(II) + hν → Cu(I) + Cu(III) is responsible for the strong absorption in the visible spectrum of La 2 CuO 4 . The down-shift of spectral density with doping (x) in La 2−x Sr x CuO 4 depends on the appearance of Cu(III) sites which makes optical as well as thermal one-electron exchange transitions possible with lower energy. Disproportionation occurs spontaneously for x > 0.06, opening up for electron pair formation. Configuration interaction between two-electron states of low chemical potential, but strong vibrational coupling, gives rise to the superconductor and pseudogaps. Data from photo-induced conductivity and absorption spectra are used in the simulation, which gives results in good agreement with experiments. Possible explanations for Raman and MIR absorption suggest themselves.

Section: Discussionmentioning

confidence: 99%

Section: Electron Transfer Between Sitesmentioning

confidence: 99%

See 1 more Smart Citation

Conductivity in Cuprates Arises from Two Different Sources: One-Electron Exchange and Disproportionation

2016

J Supercond Nov Magn

Self Cite

“…In chemical physics, this is done using the Jortner model [3]. The logarithm of the conductivity tends to linearly decrease as a function of 1 / T [4]. The Jortner model includes "nuclear tunnelling" which means a slower decrease than linear for low temperatures [3].…”

Section: Resistivity For T →0mentioning

confidence: 99%

“…A better alternative would be to use the free energy models of Marcus or Jortner for electron transfer or electron pair transfer [1][2][3] and derive an expression for resistivity based on electron transfer (ET) rates. Such an approach involves a calculation of the probability for site-to-site transfer, based on spectroscopic information or quantum chemical calculation [4,5].…”

Section: Introductionmentioning

confidence: 99%

Resistivity in Cuprates and the Pseudogap

2016

J Supercond Nov Magn

Self Cite

The temperature dependence of resistivity (ρ) in the normal state of La 2−x Sr x CuO 4 is calculated from electron transfer (ET) rates. The minimum at about 100 K for doping levels less than 6 % is characteristic for all cuprates. The resistivity depends on ET between Cu(III) and Cu(II) sites. For T < 300 K, the resistivity is proportional to T 3/2 . The more than linear increase of ρ for T >100 K depends on increased kinetic energy in a Landau avoided crossing. The agreement with experimental data is convincing. The behaviour for T → 0 can be explained as nuclear tunnelling. For T > 400 K, ρ bends down, presumably because the pseudogap is overcome at a higher kinetic energy.

Conductivity in polyacetylene. II. Ab initio and tight-binding calculations of soliton structure and reorganization energy in ordered and disordered structures

Rodríguez‐Monge

1996

Int. J. Quantum Chem.

Self Cite

Alkali-doped polyacetylene is considered as an electron-transfer system. To estimate the reorganization energy due to bond-length changes when electrons are added or subtracted, we applied the (U)MP2 and CASSCF methods to small systems of the type H(CH), H. The simple tight-binding (Hiickel) model with bond-length-dependent resonance integrals has been applied to the same and larger polyenes. The bond lengths are obtained via the bond orders for the various oxidation states. The results agree very well with the ab initio results and experiments for small polyenes. Odd-N and even-N systems behave differently. In odd-N systems, a structural "soliton" exists in the neutral molecule. An electron can be added or removed without bond-length change. In even-N chains, with perfect bond alternation in the neutral molecule, the bond length changes when an electron is accepted occur over about 20 carbon atoms. The reorganization energy tends to a constant value (0.22 eV) as the chain length is increased. Soliton structure is studied as a function of out-of-plane torsional defects and it is found that an additional electron is localized primarily on a segment with an odd number of carbon atoms. In the presence of positively charged ions, electrons are attracted toward this charge and positive solitons formed at some distance from the perturbing ion. 0 1996