The effect of superstructural ordering on the properties of high-temperature oxide superconductor systems

METAL-INSULATOR TRANSITIONS IN DOPED La-BASED SUPER CONDUCTORS WITH SMALL-RADIUS DOPANTS

“…0.5 0.213 0.5 0.141 0.5 0.098 optimally doped (0.06≤ x ≤0.15) and from the underdoped to heavily overdoped (0.06≤x ≤0.21) regimes in full accordance with the existing experimental results [18][19][20][21].We have shown that the metal-insulator transitions in these cuprate superconductors are induced by the localization of hole carriers near the smallradius dopants and in the regions without such impurities. We have found that the criteria for metal-insulator transitions driven by the hole-impurity-lattice and hole-lattice interactions are quite different.…”

“…This new model predicts much more reliable results for metal-insulator transitions in doped La-based cuprates than other existing results predicted by the single-carrier cuprate superconductor model. We have argued that none of the previously proposed theoretical models considering only one type of localized charge carriers in doped cuprates, are capable of accounting for the full body of experimental data [6,9,[18][19][20][21] and the metal-insulator transitions observed in a wide doping range from the lightly doped to heavily doped regime in a La-based cuprates with small-radius dopants. The scientific significance of our obtained results is that the metalinsulator transitions in La-based cuprate compounds occur not only in underdoped regime in accordance with experimental results [18] but also in the two distinct doping ranges, namely, from the underdoped to…”

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

“…Thus, we see that, in LSCO, the metal-insulator transitions and multiscale (from nanoscale to macroscale) phase separation into carrier-rich metallic (at > 1 and > 2 ) regions and carrier-poor insulating (at < 2 and < 1 ) regions may occur in the doping interval from ≃ 0.042 (lightly doped region) to 0.131 (underdoped region including also the "magic doping = 1/8"), while such metalinsulator transitions and phase separation in YBCO would occur in the doping interval from ≃ 0.021 to ≃ 0.125. These results are in reasonable agreement with the experimental data on the metal-to-insulator crossover and the stripe formation in lightly doped and underdoped cuprates [18,24,25,61,62].…”

“…Our results indicate that the first metallic phases appear in the lightly doped cuprates at > 0.02 in the form of narrow stripes (Fig. 1, b) in accordance with the experimental findings [18,67]. It follows that the insulator-to-metal transition and the nanoscale phase separation in the lightly doped cuprates ( ≃ 0.02-0.05) occur only on a local scale (in small carrier-rich regions).…”

“…Recent micro X-ray diffraction studies have provided the best evidence of the multiscale phase separation from nanoscale to microscale stripes [16]. There are also indications for the coexistence of insulating and metallic/superconducting phases in highc cuprates [17][18][19] and for the manifestations of these coexisting phases in the normal and superconducting properties of lightly doped, underdoped, and optimally doped cuprates [19][20][21]. Ap-parently, the evolution of the insulating and metallic/superconducting phases in these materials are manifested in the temperature dependences of their magnetic susceptibility [22] and resistivity [23], as well as in the suppression of superconductivity (i.e.…”