Flexible ultrafast spintronic terahertz emitter with exceptional working temperature range.

Spintronic terahertz (THz) emitters (TEs) leverage the spin degree of freedom. To address the growing demand for flexible TEs, we demonstrate a soft spintronic ultrafast TE based on a NiFe/SrRuO3/SrTiO3/mica(substrate) heterostructure. It emits picosecond 0-4 THz waves under near-infrared laser excitation, driven by the inverse spin Hall effect. Bendable samples with largely tunable curvatures (-2 cm-1≤ κ ≤ 2 cm-1) are achieved, by which a maximum 82% enhancement in the THz field strength is observed. We attribute it to tensile strain-induced large spin-orbit torque in SrRuO3. Significantly, we demonstrate an 80-500 K working temperature range for this all-inorganic flexible device, enabling applications under unprecedented extreme conditions (e.g., on the Moon's surface or at the poles). Our work ushers in the dawn of extreme-temperature-environment, all-inorganic, wearable, and broadband ultrafast THz devices, which uncovers an unexplored area for the application of ultrafast THz photonics.