Stripe fluctuations, carriers, spectroscopies, transport, and BCS–BEC crossover in the high-Tc cuprates

Abstract

Abstract-The quasiparticles of the high-Tc cuprates are found to consist of: polaronlike "stripons" carrying charge, and associated primarily with large-U orbitals in stripe-like inhomogeneities; "quasi-electrons" carrying charge and spin, and associated with hybridized small-U and large-U orbitals; and "svivons" carrying spin and lattice distortion. It is shown that this electronic structure leads to the systematic behavior of spectroscopic and transport properties of the cuprates. High-Tc pairing results from transitions between pair states of stripons and quasi-electrons through the exchange of svivons. The cuprates fall in the regime of crossover between BCS and preformed-pairs Bose-Einstein condensation behaviors.First-principles calculations in the cuprates support an approach based on the existence of both "large-U " and "small-U " orbitals in the vicinity of the Fermi level (E F ). Let us denote the fermion creation operator of a small-U electron in band ν, spin σ (which can be assigned a number ±1), and wave vector k by c † νσ (k). The large-U orbitals in the CuO 2 planes are approached through the "slavefermion" method [1]. A large-U electron in site i and spin σ is then created by d † iσ = e † i s i,−σ , if it is in the "upper-Hubbard-band", and by dif it is in a Zhang-Rice-type "lower-Hubbard-band". Here e i and h i are ("excession" and "holon") fermion operators, and s iσ are ("spinon") boson operators. These auxiliary particles have to satisfy the constraint:Within the "auxiliary space" a chemicalpotential-like Lagrange multiplier is introduced to impose the constraint on the average. Physical observables are calculated as combinations of Green's functions of the auxiliary space. Since the time evolution of Green's functions is determined by the Hamiltonian which obeys the constraint rigorously, it is not expected to be violated as long as the approximations used for these Green's functions are justifiable.The spinon states are diagonalized by applying the Bogoliubov transformation [2]:The Bose operators ζ † σ (k) create spinon states of "bare" energies ǫ ζ (k) which have a V-shape zero minimum at k = k 0 . Bose condensation results in antiferromagnetic (AF) order at wave vector

A Theory for the High-T_c Cuprates: Anomalous Normal-State and Spectroscopic Properties, Phase Diagram, and Pairing

“…The T dependence of the band center approximately corresponds to that of the effective QE chemical potential µ − λ (see Eq. ( 9)); thus [34], this T dependence scales with k B T , if the band is not half filled and its width in not larger than ∼k B T , and it is weaker, otherwise.…”

“…Theoretical studies [43][44][45], based on Hamiltonians like H d in Eq. ( 1), predict that the interplay between the effects of electron hopping and AF exchange is likely to drive the formation of stripe-like inhomogeneities (studied in previous works by the author [34,35]). Thus the physics of the cuprates is consistent with Q m points which correspond to the wave vectors of the striped structures.…”

“…The present auxiliary-particles approach [16] then becomes the "slave-fermion" method, applied in previous works by the author [33][34][35]. This approach is different from homogeneous RVB models [12,14,15] which are also based on auxiliary particles, but generally within the "slave-boson" method, where the fermions are spincarrying "spinons" and the bosons are charge-carrying "holons".…”

“…ℑΣ q (k, ω − i0 + ) is obtained by expressing (ω − i0 + ∓ ω λ (q) − ω q ) −1 in F T (q, ω q , ω − i0 + ), in Eqs. (34,48), as [39,40] πiδ((ω ∓ ω λ (q) − ω q ); such an expression could not be applied to obtain ℑΦ q (k, ω − i0 + ), because of the exp (iφ q k−q (ω q )) phase factors in the rhs of Eq. ( 48), but it could still be applied to obtain a term i Φq (k, ω−i0 + ) in Φ q (k, ω − i0 + ).…”