A sharp peak of the zero-temperature penetration depth at optimal composition in BaFe2(As(1-x)P(x))2.
In a superconductor, the ratio of the carrier density, n, to its effective mass, m*, is a fundamental property directly reflecting the length scale of the superfluid flow, the London penetration depth, λ(L). In two-dimensional systems, this ratio n/m* (~1/λ(L)(2)) determines the effective Fermi temperature, T(F). We report a sharp peak in the x-dependence of λ(L) at zero temperature in clean samples of BaFe(2)(As(1)(-x)P(x))(2) at the optimum composition x = 0.30, where the superconducting transition temperature T(c) reaches a maximum of 30 kelvin. This structure may arise from quantum fluctuations associated with a quantum critical point. The ratio of T(c)/T(F) at x = 0.30 is enhanced, implying a possible crossover toward the Bose-Einstein condensate limit driven by quantum criticality.
Department of Physics, Kyoto University, Kyoto, Japan.
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K
Hashimoto
K
K
Cho
T
T
Shibauchi
S
S
Kasahara
Y
Y
Mizukami
R
R
Katsumata
Y
Y
Tsuruhara
T
T
Terashima
H
H
Ikeda
M A
MA
Tanatar
H
H
Kitano
N
N
Salovich
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Giannetta
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P
Walmsley
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A
Carrington
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R
Prozorov
Y
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Matsuda