Through the looking glass: optical spectroscopy of electronic correlations
Nimrod Bachar
Department of Quantum Matter Physics, University of Geneva, Switzerland
Many body systems involving strongly interacting electrons exhibit various rich and interesting
physical states, such as Mott insulators, superconductors, heavy Fermions and etc. Optical
properties serve as an important tool to study these correlations and their resulting collective
excitations. In my talk I will briefly review several examples of our experimental observations
regarding: I. Pairing symmetry, energy gap, superfluid stiffness and phase collective modes in
superconducting thin films [1,2,3]. II. Hybridization of localized and conduction energy bands and
their optical plasmons in heavy Fermion systems [4]. III. The interplay between the coherent and
incoherent sectors of the dynamic conductivity of doped Mott insulator systems [5]. I will then
dwell into the latter example and show the in-plane dynamic and static charge conductivity of
electron doped Sr2IrO4 using optical spectroscopy and DC transport measurements. I will
demonstrate the similarity of the optical signature for a pseudo-gap in several systems. Based on
these similarities, and the absence of a correlation between superconductivity and pseudo-gap in the
doped iridate compound I will argue that the pseudo-gap is a signature of the presence of residual
correlations inherited from the insulating anti-ferromagnetic state.
1. U. S. Pracht, N.B. et al., Phys. Rev. B 93, 100503(R) (2016).
2. U. S. Pracht et al., Phys. Rev. B 96, 094514 (2017).
3. N.B. et al., EPL (Europhysics Letters) 104, 67006 (2013).
4. N.B. et al., Phys. Rev. B 94, 235101 (2016).
5. K. Wang, N.B. et al., Phys. Rev. B 98, 045107 (2018).