Quantum critical fluctuations in cobaltate superconductor Nax(H3O)zCoO2 · yH2O

✍ Scribed by Yoshihiko Ihara; Hideo Takeya; Kenji Ishida; Chishiro Michioka; Kazuyoshi Yoshimura; Kazunori Takada; Takayoshi Sasaki; Hiroya Sakurai; Eiji Takayama-Muromachi

• Publisher: Elsevier Science
• Year: 2007
• Tongue: English
• Weight: 138 KB
• Volume: 460-462
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/j.physc.2007.03.064

✦ Synopsis

In cobaltate superconductor Na x (H 3 O) z CoO 2 AE yH 2 O with bilayered hydrate (BLH) structure, Co nuclear magnetic resonance (NMR) measurement was performed to investigate the low-temperature magnetic excitations in magnetic field. The nuclear spin-lattice relaxation rate (1/T 1 ) of Co was measured in the field range of 1.5-14 T parallel to the CoO 2 plane. In the normal state, 1/T 1 T follows the temperature dependence expressed as 1=T 1 T / 1= ffiffiffiffiffiffiffiffiffiffiffi ffi T À h p in all the field range. At the field lower than 10 T, 1/T 1 T continues to increase down to T c and decrease due to superconductivity below T c . T 1 T = Const. behavior is not observed at all above T c . When the field is higher than 10 T, 1/T 1 T does not show clear decrease, but stop increasing below T * . Using T c and T * we determine, a H-T phase diagram is developed. The field dependence of T c at low fields is as small as dT c /dH $ À0.06 K/T. A novel phase characterized by a small kink of 1/T 1 T seems to be present at high-field region above 10 T.