Odd-parity superconductivity in UPt3 and UNi2Al3-NMR studies

We will report the present status of experimental results on heavy-fermion superconductors UPt3 and UNi2Al3. The NMR studies of UPt3 revealed that no reduction in the Pt-195 Knight shift below T, was observed for high-field C-phase. At low fields, the respective Knight shifts for the magnetic field parallel to b- and c-axis decrease at H < 5 kOe and H < 2.3 kOe below T-c, whereas the shift for c-axis does not change across Tc down to the lowest field of H similar to 1.764 kOe. This unconventional behavior in Knight shift which depends on magnetic-field strength and crystal orientation cannot be explained in terms of any even-parity Cooper pairing state, but provides evidence for the odd-parity one being realized in UPt3. In UNi2Al3, Al-27 Knight shift dose not change across T, giving evidence for the odd-parity one as well. This is in marked contrast to the even-parity d-wave superconductivity in UPd2Al3. In order to gain further insight into the odd-parity Cooper pairing state, we remark on the quasi-particle spill susceptibility in the heavy-fermion state. (C) 2004 Elsevier B.V. All rights reserved.