Anomalous nodal many body density of states

The density of states (DOS) is a basic quantity, e.g., for describing free electrons in a solid. The electron DOS says how many electrons the material can accomodate at a certain energy value.

In a strongly correlated electron system such as high temperature superconductors, the equivalent quantity is the many body density of states (MBDOS), $\int d\vec k A(\vec k, \omega)$, where $A$ is the single particle spectral function, measured by ARPES. Even when the DOS is predicted to be finite at the Fermi energy (“band metal”), strong correlation can lead to a vanishing MBDOS (“Mott-Hubbard insulator”).

A very important question that has been very tough to answer so far is “does the Mott insulator physics have a distinctive signature in near the optimally doped high temperature superconductor?”

The nMBDOS anomaly

ARPES is a recognized main tool for studing many body interactions in cuprates. Here at UCSC, we have taken some unique data for the past few years. The unique data that we have obtained at the SSRL and the ALS have led to a discovery of a new anomaly in ARPES. This is a new anomaly, since it is experimentally quite distinct from the two anomalies the filed is familiar with (the low energy dispersion anomaly and the high energy dispersion anomaly; dispersion anomaly = “kink” in common ARPES lingo).

The nMBDOS anomaly, discovered here at UC Santa Cruz, is new and imply that the following two ingredients are ipmortant for the theory of high temperature superconductors: electron-hole asymmetry and k-dependet Dyson self energy.

What does the nMBDOS anomaly mean?

The Mott insulator physics is important for an extended doping range around the optimal doping. It also shows that the phenomenological modification introduced for the simple ECFL model may be important for the superconductivity. For details, please read the manuscript.

Links, students

• The manuscript

• Phenomenological ECFL

• Simple ECFL

• All ARPES data obtained in this paper were obtained by GHG at the SSRL, through many a nights of blissful data-taking, in the past few years.