A combined THz and DC transport method to probe electronic phase-coexistence in complex material systems

The coexistence of multiple phases in complex material systems is a common phenomenon. Consequently, unravelling the underlying mechanisms of phase-transitions in such systems becomes extremely difficult. One powerful approach to tackle this problem is real-time visualization of the growth and evolution of coexisting phases during the phase-transition. Here, we present a method to probe the evolution of electronic phase-coexistence by combining terahertz (THz) transport with DC transport. We demonstrate our novel methodology on rare-earth nickelate films, which exhibit a first-order metal-insulator transition (MIT). As we modulate the insulating/metallic domain sizes in the phase-coexistence region of the films by introducing a controlled amount of disorder, the DC transport measurement continues to detect the MIT. However, the signature of this transition in the THz transport measurement successively weakens and completely disappears above a critical limit of disorder. This disparity occurs due to the high sensitivity of THz radiation to those insulating/metallic domains whose sizes are comparable or greater than the THz probing wavelengths and its insensitivity to other smaller sized domains. Thus, exploiting this property of THz radiation in THz transport measurements, the evolution of electronic phase-coexistence can successfully be probed in a variety of material systems.