Differential

Differential negative resistance fascinates me, and I recently read about a supposed "true" negative resistance device. The experiments showed IV curves with straight negative slopes that crossed the origin. At first I thought I had stumbled upon a neat home-brewable device for simple two-port amplification experiments, but things just didn't look right. The schematics indicated the device had four ports, and they were measuring voltage on one set and current on the other, which is wrong as there is significant semiconductor material between the voltage ports and the current ports in the form of carbon fiber. The origin of the work, a university website, looks fairly legit:
http://www.wings.buffalo.edu/academic/department/eng/mae/cmrl/Apparent%20negative%20electrical%20resistance%20in%20carbon%20fiber%20composites.pdf
 So I paid more attention, hoping that this could be a useful device for homebrew electronics, but the more I thought about it the more this thing seemed to be, at best, a peculiar inverter-attenuator. Any negative slope in the IV curve can be used to amplify, sometimes fairly linearly. But, this device has no possible way of developing gain, and furthermore if the bias or physical pressure on the device is carefully adjusted the "resistance" thus measured by their methods appears to cross through zero! Is this thing a room temperature superconductor? I'm pretty damn certain it's not. The authors, despite supposed scientific expertise, have made a freshman error in their methods. What they are measuring is NOT a resistance.