A thin film of soap on your hand conforms to the shape of your palm, but clench your fingers and the tension changes unevenly. A monolayer of molybdenum disulfide on a graphite substrate behaves in a similar way. Scientists cooled the sample from room temperature down to liquid helium temperature and tracked the electrons using spectroscopy — a technique that reveals how particles move inside a material.
At room temperature, the substrate's influence on the electrons is described by a simple model: the charge is evenly "spread" over the entire surface. But under strong cooling, the picture becomes more complex: subtler effects come into play, and the shift in energy levels begins to depend on the direction of electron motion. This is similar to how spacetime curvature affects light rays traveling in different directions differently.
This discovery is important for future electronics: transistors made from two-dimensional materials will operate at different temperatures, and their characteristics need to be predictable. Now it is clear that simple models are not always sufficient — sometimes one must account for the "whims" of the quantum world.
A monolayer of molybdenum disulfide is a sheet just three atoms thick, yet it is stronger than steel and could serve as the basis for flexible electronics.