Columbia University Alumni: Physics Duo Finds Magic in Two Dimensions
Molybdenite, even to the trained eye, looks almost identical to graphite — a lustrous, silvery crystal. It acts similarly too, sloughing off flakes in a way that would make for a good pencil filling. But to an electron, the two grids of atoms form different worlds. The distinction first entered the scientific record 244 years ago. Carl Scheele, a Swedish chemist renowned for his discovery of oxygen, plunged each mineral into assorted acids and watched the lurid clouds of gas that billowed forth. Scheele, who eventually paid for this approach with his life, dying of suspected heavy metal poisoning at 43, concluded that molybdenite was a new substance. Describing it in a letter to the Royal Swedish Academy of Science in 1778, he wrote, “I refer here not to the commonly known graphite that one can acquire from the apothecary. This transition metal seems to be unknown.”
With its tendency to flake into powdery fragments, molybdenite became a popular lubricant in the 20th century. It helped skis glide farther through the snow and smoothed the exit of bullets from rifle barrels in Vietnam.
Today, that same flakiness is fueling a physics revolution.
The breakthroughs started with graphite and Scotch tape. Researchers discovered by chance in 2004 that they could use tape to peel off flakes of graphite just one atom thick. These crystalline sheets, each a flat array of carbon atoms, had astonishing properties that were radically different from those of the three-dimensional crystals they came from. Graphene (as its discoverers dubbed it) was a whole new category of substance — a 2D material. Its discovery transformed condensed matter physics, the branch of physics that seeks to understand the many forms and behaviors of matter. Nearly half of all physicists are condensed matter physicists; it’s the subfield that brought us computer chips, lasers, LED bulbs, MRI machines, solar panels, and all manner of modern technological marvels. After graphene’s discovery, thousands of condensed matter physicists started studying the new material, hoping it would undergird future technologies.
Graphene’s discoverers received the Nobel Prize in Physics in 2010. That same year, two young physicists at Columbia University, Jie Shan and Kin Fai Mak, saw signs that flakes of molybdenite might be even more magical than graphene. The lesser-known mineral has properties that make it tough to study — too tough for many labs — but it captivated Shan and Mak. The tenacious duo devoted nearly a decade to wrangling 2D molybdenite (or molybdenum disulfide, as the lab-grown version of the crystal is called) and a family of closely related 2D crystals.
This article was originally published in QuantaMagazine. Read the full article here.