Electric Current Noise In Mesoscopic Organic Semiconductors Induced By Nuclear Spin Fluctuations

We demonstrate that the nuclear spin fluctuations lead to the electric current noise in mesoscopic samples of organic semiconductors, which show the pronounced magnetoresistance in weak magnetic fields. For the bipolaron and electron-hole mechanisms of organic magnetoresistance, the current noise spectrum consists of the high-frequency peak related to the nuclear spin precession in the Knight field of the charge carriers and the low-frequency peak related to the nuclear spin relaxation. The shape of the spectrum depends on the external magnetic and radio frequency fields, which allows one to prove the role of the nuclei in the magnetoresistance experimentally.