Polaron-Plasmon Superconductivity in Strontium Titanate

Alex Edelman and Peter Littlewood August 28, 2017 Disintertwining Order

Keimer et al, Nature 518 (2015) Disintertwining Order

Lin et al, PRL 112 Kedem et al, 1602.00437 Battle Plan

1. STO is weird: a skimpy introduction 2. Digression: phonons and how electrons talk to them 3. Collective behavior of the electron-phonon fluid 4. Results: photoemission 5. Results: Superconductivity Structure

Müller, PRB (1979) 105K: cubic to tetragonal

37K: quantum paraelectric Gervais, PRB (1993) Superconductivity with peculiarities

Thiemann et al, 1703.0471

Swartz et al, 1608.05621 Lin, PRX 3(2013) Strong electron-phonon coupling Swartz et al, 1608.05621

5 ) -2 cm

-1 (S V (S

2 0 dv / i 2 d

-5

0.1 0.2 0.3 0.4 V (V)

Wang, Nature Materials (2016) Battle Plan

1/q

Longitudinal

Optical:

Transverse

Acoustic Phonons in detail

Static dielectric constant

Optical dielectric constant

TO phonon LO phonon The Electron-Phonon Coupling

Rock salt: The Model

Parameters of the theory:

rs = Ekin/ECoul Ω/EF γ aB

-1 kF Battle Plan

ω Plasmons:

Plasmon, high density (low rs)

Phonon, Ω

Electron-Hole Continuum

k Plasmon, low density (high rs) Some quick formal developments The Players: Coupled Phonons and Plasmons The Players: Coupled Phonons and Plasmons Battle Plan

Im Σ A(k=0, ω)

ω ω

~ α Density (screening)-driven crossover

Higher electron density Anti-adiabatic to adiabatic crossover

Lower phonon energy An imitation of STO Battle Plan

Coulomb repulsion

Coupling Completeness of strength screening Attraction Superconductivity: Results

decreasing ΩLO ΩTO

Approximations worsen Approximations worsen Punchlines and Speculation

• Superconductivity can be unconventional with conventional ingredients: phonons and electrons can produce novel collective behavior • Proximity to the critical point enters as a parametric influence on the coupling constants only • STO is more than your favorite substrate