Correlation of optical conductivity and ARPES spectra of strong-coupling large polarons and its display in cuprates

TL;DR

This paper establishes a universal relationship between optical conductivity and ARPES spectra for strong-coupling large polarons, enabling predictions of spectral features and confirming the presence of such polarons in cuprates.

Contribution

It introduces a universal model linking ARPES and optical conductivity spectra via polaron binding energy, validated by experimental data on cuprates.

Findings

ARPES band maximum is at about 3.2 times the polaron binding energy

Optical conductivity band maximum is at about 4.2 times the binding energy

Underdoped cuprates contain strong-coupling large polarons with binding energies of 0.1-0.2 eV

Abstract

Common approach is used to calculate band due to strong-coupling large polaron (SCLP) photodissociation in ARPES and in optical conductivity (OC) spectra. It is based on using the coherent-states representation for the phonon field in SCLP. The calculated positions of both band maximums are universal functions of one parameter - the SCLP binding energy Ep: ARPES band maximum lies at binding energy about 3.2Ep; the OC band maximum is at the photon energy about 4.2Ep. The half-widths of the bands are mainly determined by Ep and slightly depend on Frohlich electron-phonon coupling constant: for its value 6-8 the ARPES band half-width is 1.7-1.3Ep and the OC band half-width is 2.8-2.2Ep. Using these results one can predict approximate position of ARPES band maximum and half-width from the maximum of mid-IR OC band and vice versa. Comparison of the results with experiments leads to a conclusion that underdoped cuprates contain SCLPs with Ep=0.1-0.2 eV that is in good conformity with the medium parameters in cuprates. The values of the polaron binding energy determined from experimental ARPES and OC spectra of the same material are in good conformity too: the difference between them is within 10 percent.