29Si Nuclear-Spin Decoherence Process Directly Observed by Multiple Spin-Echoes for Pure and Carrier-Less Silicon

We report on the 29Si nuclear spin decoherence time at room temperature for a pure (99.99999%, 7N) and carrier-less (p-type, doping level of 1015 cm-3) silicon in which 29Si nuclei are naturally abundant (4.7%). Despite the experimental difficulties coming from the extremely long spin-lattice relaxation time T1 (of the order of 104 s), we have successfully observed a series of spin-echoes of which the time dependence is characterized by the decoherence time T2. We found that the decoherence process deviates from a single Gaussian or Lorentzian function but is well-reproduced by a bi-exponential function with the shorter T2S=15± 5 ms and the longer T2L=200± 20 ms.