Metals have been in use since the Bronze age and are some of the best understood materials in nature. The electrical resistance of many metals is caused by electrons scattering off of one another, which textbooks tell us is characterized by a scattering rate t-1 µ (kBT)2/ħEF, T being the temperature and EF the Fermi energy. The resistivity varies widely across different families of metals, which have widely varying EF.
First seen in the late 1980’s, the strange metal phenomenon has been found in a variety of materials, ranging from Fe- and Cu-based high temperature superconductors to organic molecular crystals to twisted bilayer graphene. The defining property of strange metals a universal scattering rate, t-1 µ kBT/ħ, that depends only on fundamental constants, and is seemingly independent of any parameters specific to the material.
In this talk I will give a general introduction to the strange metal problem focusing on old (now largely forgotten) conjectures about the density fluctuation spectrum in these materials. I will present new, unpublished, inelastic electron scattering experiments on the strange metal Bi2Sr2CaCu2O8+x demonstrating that this material exhibits scale invariance, signifying the existence of a universal phase. I will show, further, that these fluctuations exhibit conformal symmetry, meaning the system behaves as an emergent, zero-dimensional system that lives on a surface of radius 1/T in imaginary time. I will express hope that a wise theorist might help understand what all this means.