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

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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 10¹5cm-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.