Electronic phase diagram of a hole-doped two-leg ladder system,

¹ Department of Superconductivity, The University of Tokyo 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan
² Institute for Solid State Physics, University of Tokyo Kashiwanoha, Kashiwa-shi, Chiba 277-8581, Japan
³ College of Humanities and Sciences, Nihon University 3-25-40 Sakurajosui, Setagaya-ku, Tokyo 156-8550, Japan

Received: 13 September 2001
Accepted: 6 March 2002

Abstract

We have investigated the evolution of the electronic state of hole-doped two-leg ladder compounds, SrCa_xCu₂₄O₄₁ with Ca content x (x = 0–12) and hydrostatic pressure P (P ≤ 8 GPa) by measuring anisotropic resistivity on single crystals. An insulator-to-metal transition occurs by applying P ~ 6.5 GPa for Sr₁₄Cu₂₄O₄₁ which is activation-type insulating at low P. The compounds with 8 show an insulating behavior at all P, though the doped hole density is fairly high (0.07–0.17 holes/Cu). On the other hand, the compounds with 10 become a superconductor by applying pressure P = 3–5 GPa. From these results, we constructed an x-P phase diagram.