CM Seminar: John Sous – University of California San Diego
Title: Principles for phonon-driven energy solutions in functional electronic materials

Abstract: Functional electronic materials are compounds in which correlations amongst electrons and between electrons and ionic vibrations (phonons) give rise to promising new functionalities poised to revolutionize energy conversion, storage and sustainability. In this talk, I will present principles – that extend the textbook understanding of electron-phonon coupling –  for the design of phonon-driven pathways to electronic materials with energy capabilities, thereby opening a door to new advancements in the materials and energy sciences. I will discuss three examples: 1. Energy conversion in so-called polaronic crystals such as the organic oligo-acene molecules, where I will show that the concept of a polaron becomes very quickly ill-defined as temperature increases from zero, implying that energy absorption and conversion cannot be understood in terms of quasiparticle transport, with ramifications to emerging solar cell technologies. 2. Energy storage in nanoscale materials whose phonons are initially excited by a light pulse, where I will show that the excited phonons relax by releasing their excess energy into the electrons, reshaping their correlations to form novel excited-state non-equilibrium phases such as the light-induced conversion of metals into disordered insulators and (near) superconductors which appear to be immune to thermalization on long timescales, thus serving as new mediums for protected energy storage and utilization. 3. Energy sustainability from vibrationally coupled electrons in multiorbital electronic materials, where I will show that phonons mediate superfluidity of light-mass, small-size bipolarons with a critical transition temperature Tc whose value vastly surpasses widely assumed empirical upper bounds and which I am currently investigating in a number of emerging materials such as the newly synthesized organic terphenyl-based compounds, SrTiO3, LiTi2O4, as well as twisted bilayer graphene moire heterostructures. I will conclude by providing an overview of my future plans.

Speaker Bio: John Sous is an Assistant Professor at the University of California, San Diego (UCSD).  Prior to that he was a Gordon & Betty Moore Postdoctoral Fellow at Stanford University (2022 – 2023), before which he was a Materials Research Science and Engineering Center (MRSEC) Postdoctoral Fellow at Columbia University (2019 – 2022). He obtained a Ph.D. in Physics from the University of British Columbia (UBC) in 2019 and a M.Sc. in Chemical Physics from the University of Waterloo in 2013. His research focuses on the study of materials in which quantum correlations act to stabilize novel electronic states of matter with functionalities which can be useful in applied research, such as energy applications.