Figure 1
From: Synchronized charge oscillations in correlated electron systems
Stabilizing a non-hysteretic and reversible phase transition in VO2 and single oscillator dynamics.
(a) Schematic of the circuit used to access the non-hysteretic transition regime in VO2 using the negative feedback generated by the series resistor Rs. (b) Rs modifies the VO2 phase transition dynamics through negative feedback. A non-hysteretic reversible (NHR) transition regime can be accessed using the appropriate Rs (>RC). Electrical load lines for non-hysteretic (1) and hysteretic (2) switching are superimposed. (c) Time domain waveform of the VO2 relaxation oscillator. (Inset) shows the waveform for one oscillation period with the two time constants (τ1 = 0.35 μs and τ2 = 0.65 μs) associated with IMT and MIT. (d) Power (Mean Square Amplitude in dB) spectrum of a single oscillator. The fundamental frequency of the oscillator here is ~1 MHz. (e) Simultaneous measurement of the voltage and scattered x-ray diffraction intensity for an oscillating VO2 device. Based upon the Bragg peaks, the structural phase of VO2 is labeled. (Inset) shows the 
and [002] Bragg peaks of the M1 and rutile phase of VO2, respectively. The dashed line indicates the θ/2θ angle ( = 51.714°) at which this measurement was performed. Details of x-ray diffraction measurement are described in the Supplementary S4. (f) Frequency scaling of the VO2 relaxation oscillator with Rs. The frequency increases as the external Rs is scaled down. The device resistance has also been scaled to further increase the output frequency.
