https://repository.library.northeastern.edu/files/neu:331186/fulltext.pdf

A survey of the Van Hove scenario for high-tc superconductivity with special emphasis on pseudogaps and striped phases

Angle-resolved photoemission spectroscopy (ARPES) has emerged as a leading experimental probe for studying the complex phenomena in quantum materials, a subject of increasing importance The power of this technique stems from the directness and the richness of the momentum-resolved information it can provide, such as band dispersion, Fermi surface topology, and electron self-energy Over the past decade, the significantly improved energy and momentum resolution and carefully matched experiments have turned this technique into a sophisticated tool in characterizing the electronic structure of complex materials This revolution is mostly evident in the study of cuprate high-temperature superconductors More recently, this technique has played a critical role in advancing our understanding of the newly discovered iron-based superconductors and topological insulators In this paper we review some of the recent ARPES results and discuss the future perspective in this rapidly developing field

Angle-Resolved Photoemission Studies of Quantum Materials

An exact diagonalization of the Hamiltonian in the p-d model of a CuO6 cluster was used to obtain dependences on the model parameters of the lowest-energy two-hole terms: the energy difference between the 2p orbitals of planar and apical oxygen Δ(apex)=e(2p)−e[2p(apex)], the crystal field parameter \(\Delta _d = \varepsilon _{3z^2 - r^2 } - \varepsilon _{x^2 - y^2 } \), and the ratio of the distances between the copper atom and the apical and planar oxygen atoms d(apex)/d(pl). In the limit of large d(apex)/d(pl) and Δd, our model is equivalent to the three-band p-d model and, in this case, large singlet-triplet splitting Δe⩾1 eV is also observed. As the parameters decrease, a singlet-triplet crossover is observed. Two mechanisms are identified for stabilization of the triplet term 3B1g(0) as the ground state. It is shown that for realistic values of the parameters, reduction of the p-d model to the three-band model is limited by the low energies of the current excitations because of the presence of the lower excited 3B1g and 1A1g cluster states. Intercluster hopping causes strong mixing of singlet and triplet states far from the G point. The results of the calculations are compared with data obtained by angle-resolved photoelectron emission in Sr2CuO2Cl2.

Low-energy electron spectrum in copper oxides in the multiband p-d model

The Fermi and Bose quasiparticle spectrum in copper oxides is studied in a many-band p-d model taking account of the strong electronic correlations. It is shown that hole-doped systems possess a Bose mode — a spin exciton — which is associated with the singlet-triplet excitation of the two-hole ground-state term of CuO4 clusters. Intercluster hopping leads to fermion-boson interaction with a spin exciton as the intermediate boson. Such a mechanism does not exist for n-type systems.

Spin excitons — a new mechanism of superconducting pairing in copper oxides

We propose a generalization of the conventional theory based on the assumption of the well-isolated Zhang–Rice 1 A 1 g singlet to be a first electron-removal state in insulating copper oxide. The photohole is assumed to be localized on either small (pseudo) Jahn–Teller (PJT) polaron or large non-adiabatic polaron-enclosed one or four to five CuO 4 centers, respectively, with active one-center valent ( 1 A 1g – 1,3 E u ) manifold. In the framework of the cluster model we have performed the model microscopic calculation of the k -dependence of the matrix element effects and photon polarization effects for the angle-resolved photoemission (ARPES) in insulating cuprates like Sr 2 CuO 2 Cl 2 . We show that effects like the “remnant Fermi surface” detected in the ARPES experiment for Ca 2 CuO 2 Cl 2 may be, in fact, the manifestation of the matrix element effects rather than of the original band-structure Fermi surface or strong antiferromagnetic correlations. The measured dispersion-like features in the low-energy part of the ARPES spectra may be the manifestation of the complex momentum-dependent spectral line shape of the large PJT polaron response, in addition to the dispersion effect for the well-isolated Zhang–Rice singlet in antiferro-magnetic matrix.

Large non-adiabatic hole polarons and matrix element effects in the angle-resolved photoemission spectroscopy of dielectric cuprates

Recent angle resolved photoemission (ARPES) measurements for the insulating cuprate Sr2CuO2Cl2 have provided the first experimental data which can be directly compared to the (theoretically) well-studied problem of a single hole propagating in an antiferromagnet. Some discrepancies withthe familiar 2D t— J model were observed. Here we discuss a comparison between the ARPES results and the quasiparticle dispersion of both (i) the extended t— t′— J Hamiltonian and (ii) the three-band Hubbard model.

R. J. Gooding

Papers

Quasiparticle dispersion of Sr2CuO2Cl2