Distinctive Features of Metal-Insulator Transitions, Multiscale Phase Separation, and Related Effects in Hole-Doped Cuprates

We study the distinctive features of the metal-insulator transitions, multiscale phase separation, and evolution of coexisting insulating and metallic/superconducting phases in hole-doped cuprates. We show how these interrelated phenomena and related effects manifest themselves in a wide doping range from the lightly doped to optimally doped regime in these systems, where the localized and mobile hole carriers reside in hole-poor (insulating) and hole-rich (metallic or superconducting) regions. We argue that small hole-rich regions (i.e. narrow nanoscale metallic islands or stripes) can persist in the insulating phase of the lightly doped cuprates, while the competing insulating, metallic, and superconducting phases would coexist in the under-doped cuprates. When the doping level is increased further, the hole-poor regions (or insulating zones) gradually narrow from macroscale to nanoscale insulating stripes and disappear in the optimally doped cuprates. We demonstrate clearly that the metal-insulator transitions and the coexisting insulating and metallic/superconducting phases are manifested in the suppression of superconductivity in underdoped cuprates and in the different temperature-dependent behaviors of the magnetic susceptibility and c-axis resistivity of lightly to optimally doped cuprates.

SINGLE-PARTICLE SPECTRAL WEIGHT IN THE ANTIFERROMAGNETIC STRIPE PHASE

Recent angle-resolved photoemission (ARPES) studies of the La2-xSrxCuO4 (LSCO) compound provide a new piece of information on the evolution of the electronic structure in cuprate systems with doping. Our aim is to analyze that evolution by means of the spin polaron approach based on the string picture. We study the motion of a single mobile hole in the stripe phase of a doped antiferromagnet. Holes within the stripes are taken to be static, undoped antiferromagnetic domains between hole stripes are assumed to have an alternating staggered magnetization, as it has been suggested by neutron scattering experiments. The system is described by the t-t′-t′′-J model with realistic parameters and we compute the single particle spectral density. In this paper we concentrate on the filling level 1/12. Theoretical spectra and results of measurements performed at that hole concentration show reasonable agreement. In both cases we observe, along the direction (0,0)→(π,0), "splitting" of the spectrum and formation of new low energy states around (π,0). This splitting is also observed in the direction (0,π)→ (π,π). The spectra along the direction (π,0)→ (π,π) are much broader. That hinders us in assignment of any band for some range of k points in that direction. Finally, the spectra along the direction (0,0)→ (π,π) are very broad and it is also practically impossible to distinguish any sharp band.

Transport and Electronic Properties of Y0.4Pr0.6Ba2-ySryCu3O7-δ (y=0,1.0)

We report measurements of the resistivity, thermoelectric power and Hall carrier number on Y0.4Pr0.6Ba 2-y Sr y Cu3O7-δ (y=0, 1.0) polycrystalline samples. The Sr-free compound exhibits semiconducting behavior, while the Sr-doped sample is superconducting at 18 K with a possible pseudo-gap structure at 255 K. Results of the thermoelectric power and Hall measurements revealed that the revival of superconductivity by the Sr substitution is due to the increase of mobile hole-concentration. We present a band picture of Pr4 f– O 2p hybridization to elucidate the variation of the transport properties.