Direct Atomic Observation of Discrete Bond Lengths and Fractional Quantized Conductance in Gold Atomic Chains

Metallic bonds play an important role in the physicochemical properties of metals and alloys. So far, metallic bonds can be stretched within a limited strain range, usually less than 10%, with linear response behaviors while exhibiting good conductivity, but the metallic bond lengths and their impacts on physical properties under high-strain conditions remain elusive. Here, using aberration-corrected high-resolution transmission electron microscopy, we investigate the bond elongation in gold atomic chains under tensile strain up to 46%, while excluding the influence of light elements. When the strain exceeds 12%, the bond lengths exhibit a plateau distribution and stepwise stretching characteristics. The short-long bond alternation tendency, likely corresponding to the dimerized configuration, is directly observed in a strain range of 12-25%. The conductance undergoes a stepwise decrease, transitioning from 1G₀ to 0.13G₀ before eventually dropping to 0. The discrete bond length with fractional quantized conductance holds great significance for understanding the nature of metallic bonds and developing quantum devices.