The increase of electrical conduction (σ-σ0)/σ0 in a pristine (red) and cryocycled (black) single crystal of (TMTSF)2PF6.Thermal cycling relaxes the pinning potential of the crystalline defects and the threashold field becomes smeared between two values indicated by arrows.
Right: Narrow band noise (NBN) for different electric fields. The corresponding d.c. currents are indicated in the noise spectra. Arrows indicate the main peak and harmonics.
More in the article published in magazine Fizika.
Spin-density-wave (SDW) systems, like (TMTSF)2PF6, have two mechanisms of electrical conduction: 1) the single particle conduction of electrons thermally excited to the conduction band above the SDW energy gap and 2) the collective conduction of the SDW condensate. This collective conduction is pinned by the defects and is released at sufficiently high electric fields (voltages). Here we see the sharp threshold field for the onset of this SDW collective conduction. Above the threshold, the whole SDW condensate adds to the electrical conduction. But the presence of defects is the obstacle for the collective conduction. On the right graph we can see the peaks in random (noise) voltage at frequencies that scale with the SDW current density. This narrow band noise (NBN) peaks are the consequence of condensate being pinned by defects in the single crystal of (TMTSF)2PF6.