Relaxation-free athermal states in VO2 for thermal-breach memory

Thermally induced martensitic phase transitions are broadly divided into two classes—isothermal and athermal. While the isothermal transformations correspond to the diffusive nucleation-and-growth phenomenon associated with the first-order phase transitions, the athermal transformations are characterized by absence of diffusion. Here, the phase evolution at fixed temperature is arrested. The phase transformation in real martensites of course only approximates the two extreme scenarios. It has been recently argued [Mukhuti et al., Phys. Rev. Lett. 134, 076901 (2025)] that this athermal character combined with the return point memory property of the hysteresis loops opens up the possibility of the use of such athermal martensites as thermal-breach memory where a small and reversible temperature perturbation can be inferred from the irreversible phase evolution of the material. In this Letter, we examine the possibility of the use of vanadium dioxide (VO2) films, which show a hysteretic metal–insulator transition above room temperature for such applications. We find that the metastable states show a temporal evolution of less than 2% at constant temperature over a period of 15 h and during this period a thermal perturbation of 1 K experienced by the sample in a suitably prepared metastable state can be inferred from irreversible change in its resistance. Apart from usage in thermal analogs of logic units in neuromorphic computational devices, the highly sensitive and stable behavior of these athermal states of VO2 establishes the viability of thermal-breach memory near room temperature.