Onset of a Boson mode at the superconducting critical point of underdoped YBa2Cu3Oy.
The thermal conductivity kappa of underdoped YBa2Cu3Oy was measured in the T-->0 limit as a function of hole concentration p across the superconducting critical point at pSC identical with 5.0%. The evolution of bosonic and fermionic contributions to kappa was tracked as the doping level evolved continuously in each of our samples. For p< or =pSC, we observe a T3 component in kappa which we attribute to the boson excitations of a phase with long-range spin or charge order. Fermionic transport, observed as a T-linear term in kappa which persists unaltered through pSC, violates the Wiedemann-Franz law, since the electrical resistivity varies as log(1/T) and grows with decreasing p.
Doiron-Leyraud
Nicolas
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Département de physique and RQMP, Université de Sherbrooke, Sherbrooke, Canada.
Sutherland
Mike
M
Li
S Y
SY
Taillefer
Louis
L
Liang
Ruixing
R
Bonn
D A
DA
Hardy
W N
WN