Quantum Oscillations and Intense Magnetic Field Tuning of the Charge Order in Na 0.5 CoO 2

1. Quantum Oscillations and Intense Magnetic Field Tuning of the Charge Order in Na0.5CoO2 Layered cobalt oxide materials generate considerable fundamental and practical interest. For example, LixCoO2 is an important cathode material for lithium batteries used in laptop computers. The replacement of lithium by sodium to form NaxCoO2 leads to a series of new compounds displaying a fascinating array of phases (right), from superconductor (for x ~ 0.3) to insulator (for x = 0.5) to metals with a huge thermopower in the metallic state (near x = 0.5) that might one day out-perform highly- doped semiconductors now used for thermoelectric power conversion. Spin- density wave metal The in-plane resistivity of a Na 0.5CoO2 single crystal as a function of the in-plane field magnetic field B. The phase diagram of NaxCoO2 (from M.L. Foo, et al., Phys. Rev. Lett. 92, 247001 (2004). Recent high-magnetic-field research using the National High Magnetic Field Laboratory to study the charge ordered insulating state of Na0.5CoO2(left) has revealed that the role played by the Na ions is not restricted to passively providing charge carriers to the CoO2 layers, but also forms complex ordered patterns that profoundly effect the electronic response of NaxCoO2 L. Balicas, et al.,Physical Review Letters94, 236402 (2005)