Ultrafast Nanoimaging of the Photoinduced Phase Transition Dynamics in VO2.
Many phase transitions in correlated matter exhibit spatial inhomogeneities with expected yet unexplored effects on the associated ultrafast dynamics. Here we demonstrate the combination of ultrafast nondegenerate pump-probe spectroscopy with far from equilibrium excitation, and scattering scanning near-field optical microscopy (s-SNOM) for ultrafast nanoimaging. In a femtosecond near-field near-IR (NIR) pump and mid-IR (MIR) probe study, we investigate the photoinduced insulator-to-metal (IMT) transition in nominally homogeneous VO2 microcrystals. With pump fluences as high as 5 mJ/cm(2), we can reach three distinct excitation regimes. We observe a spatial heterogeneity on ∼50-100 nm length scales in the fluence-dependent IMT dynamics ranging from <100 fs to ∼1 ps. These results suggest a high sensitivity of the IMT with respect to small local variations in strain, doping, or defects that are difficult to discern microscopically. We provide a perspective with the distinct requirements and considerations of ultrafast spatiotemporal nanoimaging of phase transitions in quantum materials.
Department of Physics, Department of Chemistry, and JILA, University of Colorado , Boulder, Colorado 80309, United States.
Sven A
SA
Dönges
Department of Physics, Department of Chemistry, and JILA, University of Colorado , Boulder, Colorado 80309, United States.
Omar
O
Khatib
Department of Physics, Department of Chemistry, and JILA, University of Colorado , Boulder, Colorado 80309, United States.
Brian T
BT
O'Callahan
Department of Chemistry, University of North Carolina , Chapel Hill, North Carolina 27514, United States.
Joanna M
JM
Atkin
Department of Physics, University of Washington , Seattle, Washington 98195, United States.
Jae Hyung
JH
Park
Department of Physics, University of Washington , Seattle, Washington 98195, United States.
David
D
Cobden
Department of Physics, Department of Chemistry, and JILA, University of Colorado , Boulder, Colorado 80309, United States.
Markus B
MB
Raschke
Nano-imaging; phase transition; s-SNOM; ultrafast spectroscopy; vanadium dioxide