Strange metals and Planckian dissipation

7 problems

• Why T-linear resistivity persists across the overdoped cuprate range

  Open

  A zero-temperature phase transition should affect a metal most strongly at a single value of the tuning parameter, yet in overdoped cuprates a part of the resistance stays linear in temperature over a wide range of doping.

• Why Hall angle and resistivity follow different temperature laws

  Contested

  In cuprates the resistance grows linearly with temperature while the Hall angle, the deflection of current by a magnetic field, behaves as if a second scattering rate grows as temperature squared.

• Is the Planckian scattering rate universal, and is it a bound?

  Contested

  Data in several materials suggest the electron scattering rate equals temperature times a fixed combination of Boltzmann's and Planck's constants; it is unknown whether this is a true limit.

• Origin of quadrature scaling of strange-metal magnetoresistance

  Open

  In some strange metals the resistance in a magnetic field depends only on a combined measure of temperature and field, growing linearly with field without saturating.

• Do strange metals carry current in electron-like quasiparticles?

  Contested

  Shot noise, the current fluctuation caused by charge arriving in discrete packets, reveals whether current is carried by electron-like particles; in one strange metal the noise was far smaller than expected.

• Does spatially random Yukawa coupling explain strange-metal transport quantitatively?

  Open

  A recent theory proposes that electrons scattering off critical fluctuations whose coupling strength varies randomly in space give resistance linear in temperature; it needs quantitative tests against data.

• Microscopic origin of T-linear resistivity in strange metals

  Open

  Ordinary metals show resistance growing as temperature squared at low temperature, but strange metals show resistance growing linearly in temperature down to the lowest temperatures reached.