Superconductor-insulator transition in space charge doped one unit cell Bi<sub>2.1</sub>Sr<sub>1.9</sub>CaCu<sub>2</sub>O<sub>8+x</sub>.

Wang, Fang; Biscaras, Johan; Erb, Andreas; Shukla, Abhay · Nat Commun · 2021

basic_science · Level V

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Abstract

The superconductor-insulator transition in two dimensions is a prototype continuous quantum phase transition at absolute zero, driven by a parameter other than temperature. Here we reveal this transition in one unit-cell Bi<sub>2.1</sub>Sr<sub>1.9</sub>CaCu<sub>2</sub>O<sub>8+x</sub> by space charge doping, a field effect electrostatic doping technique. We determine the related critical parameters and develop a reliable way to estimate doping in the nonsuperconducting region, a crucial and central problem in these materials. Finite-size scaling analysis yields a critical doping of 0.057 holes/Cu, a critical resistance of ~6.85 kΩ and a scaling exponent product νz ~ 1.57. These results, together with earlier work in other materials, provide a coherent picture of the superconductor-insulator transition and its bosonic nature in the underdoped regime of emerging superconductivity in high critical temperature superconductors.