For the first time, scientists have observed a collection of particles, also known as a quasiparticle, that's massless when moving one direction but has mass in the other direction. The quasiparticle, called a semi-Dirac fermion, was first theorized 16 years ago, but was only recently spotted inside a crystal of semi-metal material called ZrSiS. The observation of the quasiparticle opens the door to future advances in a range of emerging technologies from batteries to sensors, according to researchers at Penn State.
The important thing here is that this is about a quasi particle, something that behaves sort of like a particle but is not (like a hole in the electron distribution), in a 2D crystal lattice. This only happens because the lattice is not isotropic, you see a different pattern depending in the direction you look, so having properties change with direction is not totally unexpected. We already have materials with anisotropic thermal conductivity for example.
This won’t happen in vacuum as vacuum is isotropic.
The important thing here is that this is about a quasi particle, something that behaves sort of like a particle but is not (like a hole in the electron distribution), in a 2D crystal lattice. This only happens because the lattice is not isotropic, you see a different pattern depending in the direction you look, so having properties change with direction is not totally unexpected. We already have materials with anisotropic thermal conductivity for example.
This won’t happen in vacuum as vacuum is isotropic.