Holographic Maps of Quasiparticle Interference
Figure 5: Trial Wannier functions.Topological polarons*
[Reprinted with permission Macmillan Publishers Ltd: Nature Physics © 2016]
The analysis of Fourier-transformed scanning tunnelling microscopy images with subatomic resolution is a common tool for studying the properties of quasiparticle excitations in strongly correlated materials. Although Fourier amplitudes are generally complex valued, earlier analysis primarily focused on their absolute values. Their complex phases were often deemed random, and thus irrelevant, due to the unknown positions of the impurities in the sample.
In an article in Nature Physics*, Prof. Emanuele G. Dalla Torre (former Harvard physics postdoc, currently professor of physics at Bar Ilan University), grad student Yang He, and Prof. Eugene Demler show how to factor out these random phases by analysing overlaps between Fourier amplitudes that differ by reciprocal lattice vectors. The resulting holographic maps provide important and previously unknown information about the electronic structures. When applied to superconducting cuprates, this method solves a long-standing puzzle of the dichotomy between equivalent wavevectors. The authors show that d-wave Wannier functions of the conduction band provide a natural explanation for experimental results that were interpreted as evidence for competing unconventional charge modulations. This work opens a new pathway to identify the nature of electronic states in scanning tunnelling microscopy.
*See Emanuele G. Dalla Torre, Yang He & Eugene Demler, "Holographic maps of quasiparticle interference," Nature Physics (2016), doi:10.1038/nphys3829.