Our new paper is out, “Three interaction energy scales in the single-layer high-Tc cuprate HgBa2CuO4+δ

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.102.205109

Congratulations to Sudheer, Antonio, Jayita, and all our collaborators!

Summary: Cuprate high-temperature superconductors have the highest transition temperatures (Tc) at ambient conditions, but the microscopic mechanism of superconductivity and other mysterious electronic phases in these materials remains unresolved.  These materials share a common structural unit of a CuO2 plane, and different cuprate compounds differ from one another in the number of nearby CuO2  planes (single-layer vs multiple-layer) and in the chemistry of the layers separating CuO2  planes or blocks of CuO2  planes from one another.

Among single-layer cuprates, the Tc varies between 40K and 100K, but the origin of this difference is not understood.  The mechanism of producing or enhancing superconductivity can be revealed through interactions between electrons (which pair up into Cooper pairs in the superconducting state) and collective excitations of the atomic lattice, spins, etc (which can serve as the ‘pairing glue’); similar statements can be made about other emergent electronic phases.  In cuprate high-temperature superconductors, the electronic properties tend to be different for electrons moving in different directions relative to the atomic bonds in the CuO$_2$  planes, which necessitates a momentum-resolved probe such as angle-resolved photoemission spectroscopy (ARPES). Notably, it is only in the lower-Tc single-layer cuprates that these interactions between electrons and collective excitations have been well-characterized by ARPES.

We present the first comprehensive ARPES study of HgBa2CuO4+δ (Hg1201), a single-layer cuprate which reaches a Tc of 98K.  We identify three different interactions between electrons and collective excitations, which may play a role in enhancing superconductivity and explaining the mysterious electronic phase above Tc called the pseudogap.  This allows us to draw connections to existing studies of cuprates to establish which electronic phenomena are universal and which are materials- or technique-dependent.  Hg1201 has yielded important insights from multiple experimental techniques, and the comprehensive nature of the present ARPES work makes it a starting point for establishing a cohesive multi-technique narrative about this prototype material.