Ramp reversal memory in bulk crystals of 1T-TaS2

TL;DR

This paper reports the discovery of ramp reversal memory in bulk 1T-TaS2 crystals, demonstrating that RRM is a more general phenomenon than previously observed in thin film oxides, with distinct characteristics and larger magnitude.

Contribution

The study provides the first evidence of RRM in bulk 1T-TaS2 crystals, expanding the understanding of RRM beyond thin film oxides and highlighting its potential universality.

Findings

RRM observed in bulk 1T-TaS2 crystals near 190 K

RRM occurs when reversing from cooling to heating, unlike previous systems

The RRM magnitude in TaS2 is nearly ten times larger than in oxides

Abstract

The ramp reversal memory (RRM) is a non-volatile memory effect previously observed in correlated oxides exhibiting temperature-driven metal-insulator transitions (MITs). In essence, when a system displaying RRM is heated to a specific temperature within the MIT regime - where metallic and insulating domains coexist - and then cooled by reversing the temperature ramp, the resistance increases in the subsequent heating cycle. Crucially, this increase occurs only in the vicinity of the reversal temperature, indicating that the system 'remembers' this temperature. However, this memory is erased in the next heating loop. While such an effect could potentially manifest in various systems, to date, it has only been reported in thin films of correlated transition metal oxides, including VO2, V2O3, and NdNiO3. In this work, we report the observation of RRM in macroscopic crystals of the layered material 1T-TaS2, which undergoes an MIT near 190 K along charge-density wave transitions. Our findings provide compelling evidence that RRM is a general phenomenon, extending beyond the previously studied oxides. Interestingly, the RRM in TaS2 displays significantly different characteristics: it is observed when reversing from cooling to heating (as opposed to heating to cooling), and its magnitude - representing the 'strength' of the memory - is nearly an order of magnitude larger than in correlated oxides. While we discuss potential mechanisms for the RRM in TaS2, a comprehensive first-principles model is still lacking. We hope that this study will prompt further investigation into the underlying mechanisms of ramp reversal memory, enhancing our understanding of this intriguing phenomenon.