For more than 200 years, physicists have wanted to understand why electricity flows through some materials and not others. In some of the first experiments aimed at understanding conductivity, at the start of the 18th century, British autodidact Stephen Gray observed that materials like metals (and some vegetables) conduct electricity, whereas others, like silk or wool, don’t. Decades later, in his Philadelphia experiments, Benjamin Franklin used glass as an insulator and metal as a conductor to study electrical discharges from lightning. In the 20th century, quantum physics provided scientists with new tools to probe the properties of electrons, research that—in the early 21st century—has fueled the discovery and understanding of exotic quantum states of matter.
Read more here.