Pressure dependence of the superconducting transition and electron correlations in Na_xCoO_2 \cdot 1.3H_2O

Abstract

We report T_c and ^{59}Co nuclear quadrupole resonance (NQR) measurements on the cobalt oxide superconductor Na_{x}CoO_{2}\cdot 1.3H_{2}O (T_c=4.8 K) under hydrostatic pressure (P) up to 2.36 GPa. T_c decreases with increasing pressure at an average rate of -0.49\pm0.09 K/GPa. At low pressures P\leq0.49 GPa, the decrease of T_c is accompanied by a weakening of the spin correlations at a finite wave vector and a reduction of the density of states (DOS) at the Fermi level. At high pressures above 1.93 GPa, however, the decrease of T_c is mainly due to a reduction of the DOS. These results indicate that the electronic/magnetic state of Co is primarily responsible for the superconductivity. The spin-lattice relaxation rate 1/T_1 at P=0.49 GPa shows a T^3 variation below T_c down to T\sim 0.12T_c, which provides compelling evidence for the presence of line nodes in the superconducting gap function.

published on 19, Sept. 2007 on Phys. Rev. B

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• Detection of an Unconventional Superconducting Phase in the Vicinity of the Strong First-Order Magnetic Transition in CrAs Using ^75As-Nuclear Quadrupole Resonance
• Pressure-induced unconventional superconductivity near a quantum critical point in CaFe2As2
• Measurement of electron correlations in LixCoO2 (x=0.0 - 0.35) using 59Co nuclear magnetic resonance and nuclear quadrupole resonance techniques
• Hydration-induced anisotropic spin fluctuations in Na_{x}CoO_{2}\cdot1.3H_{2}O superconductor