Metastability, Adaptability and Memory in Charge Density Waves
It is one of the most puzzling problems how a complex system changes itself in order to adapt itself to the external environment. Such adaptive responses have been mainly observed in the biological systems (circadian clock, neural networks, immune system and so on) [1,2]. Recently, however, the adaptation of the charge density waves (CDW) to the pulse fields has been discovered by Ido et al. in quasi-one-dimensional conductors, which is called Ido step memory effect . When the identical pulse fields are repeatedly applied to the sample (NbSe3), the CDW adjusts its sliding motion so that the oscillatory current response to the pulse shows a steady response, which has a common regularity regardless of the pulse width. That is, oscillations always cease at a maximum at the pulse end and the sliding displacement of the CDW within the pulse duration is quantized such as an integral multiple of the CDW wavelength. After the system has shown a steady response, further application of pulses induces no further changes in the response. This fact suggests that the CDW has already remembered the applied pulse width.
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