Doping dependence of the low-energy excitations in superconducting Bi2Sr2CaCu2O8+δ: Evidence for thermal phase fluctuations

G. Lamura; J. Le Cochec; A. Gauzzi; F. Licci; D. Di Castro; A. Bianconi; J. Bok

doi:10.1103/PhysRevB.67.144518

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Doping dependence of the low-energy excitations in superconducting Bi2Sr2CaCu2O8+δ: Evidence for thermal phase fluctuations

G. Lamura, J. Le Cochec, A. Gauzzi, F. Licci, D. Di Castro, A. Bianconi, J. Bok

DOI 10.1103/PhysRevB.67.144518 · Physical Review B

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Abstract

By using a single-coil technique, we study the low-temperature dependence of the in-plane magnetic penetration depth λab in several Bi2Sr2CaCu2O8+δ (BSCCO) single crystals prepared with various doping levels δ ranging from the under- to the overdoped regime. Four samples exhibit a linear dependence of thermally activated low-energy excitations Δλab≡λab(T)−λab(0)∼T. The thermal activation rate ∝∂λab/∂T is minimum, 8 Å/K, at optimum doping, in good quantitative agreement with the d-wave model of superconducting order parameter. The much larger rates, ≳40Å/K, observed in all under- and overdoped samples indicate that, in these samples, another type of low-energy excitations is relevant. These large rates are quantitatively consistent with a model of thermal phase fluctuations suitable for granular superconductors with short coherence length like cuprates. One underdoped sample exhibits a quadratic dependence suggesting an incipient crossover from thermal to quantum fluctuations.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Bi2Sr2CaCu2O8+δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	92	Pressure not reported	onset
Bi2Sr2CaCu2O8+δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	83	Pressure not reported	onset
Bi2Sr2CaCu2O8+δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	74	Pressure not reported	onset
Bi2Sr2CaCu2O8+δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	75	Pressure not reported	onset
Bi2Sr2CaCu2O8+δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	80	Pressure not reported	onset