Nucleation and Growth Bottleneck in the Conductivity Recovery Dynamics of Nickelate Ultrathin Films

Abstract

We investigate THz conductivity dynamics in NdNiO 3 and EuNiO 3 ultrathin films (15 unit cells, u.c., ∼5.7 nm thick) following a photoinduced thermal quench into the metallic state and reveal a clear contrast between firstand second-order dynamics. While in EuNiO 3 the conductivity recovers exponentially, in NdNiO 3 the recovery is nonexponential and slower than a simple thermal model. Crucially, it is consistent with first-order dynamics and well-described by a 2d Avrami model, with supercooling leading to metastable phase coexistence on the nano-to mesoscopic scale. This novel observation is a fundamentally dynamic manifestation of the first-order character of the insulator-to-metal transition, which the nanoscale thickness of our films and their fast cooling rate enable us to detect. The large transients seen in our films are promising for fast electronic (and magnetic) switching applications.

PERSPECTIVE: Emergent phases in rare earth nickelate heterostructures

“…al. investigated the THz conductivity dynamics in NdNiO 3 following an optical thermal pump from the insulating ground state into a metastable metallic phase [122]. The application of the THz probe revealed a remarkable contrast between the first (in NdNiO 3 ) and second (in EuNiO 3 ) order dynamics.…”

Photoinduced structural recovery dynamics of rare-earth nickelate thin films

“…In this article, we have utilized time-resolved x-ray diffraction (tr-XRD) to study the photoinduced structural recovery dynamics of tensile strained NNO and SNO thin films. While extensive work has been performed on understanding excitation pathways from the insulating to the metallic state [16,[21][22][23][24][25][26][27][28][29], only a few studies have focused on the recovery pathways from the metallic to insulating state in nickelates [15]. Our tr-XRD experiments for NNO revealed a strong laser fluence dependence for structural recovery, indicating the presence of nonthermal pathways at higher fluence.…”

“…Recently, it has been shown that the photoinduced IMT in rare-earth nickelates (RNiO 3 where R = Nd, Pr, Sm, Eu, etc.) can be driven at subpicosecond timescales with a laser fluence nearly an order of magnitude smaller than the widely studied vanadate system [15,16]. Additionally, the IMT can be tuned to near room temperature via substrate strain [6], substrate symmetry [17], or by choice of rare-earth cation [18], making rare-earth nickelates excellent candidates for ultrafast manipulation.…”

Perspective—Emergent Phases in Rare Earth Nickelate Heterostructure

“…In an another experiment, Abreu et al investigated the THz conductivity dynamics in NdNiO 3 following an optical thermal pump from the insulating ground state into a metastable metallic phase. 122 The application of the THz probe revealed a remarkable contrast between the first (in NdNiO 3 ) and second (in EuNiO 3 ) order dynamics. These early experiments clearly demonstrate the importance of pump-probe experiments to investigate nickelates in the time domain and shed light on controversial or unsolved questions in the equilibrium.…”