3:35pm March 28, 2018 1130 Mechanical Engineering 111 Church Street SE, Minneapolis, MN 55455

Solid-State Thermal-To-Electrical Energy Conversion Joseph Heremans Ohio Eminent Scholar and Professor; Mechanical and Aerospace Engineering Department – Ohio State University

Mechanical Engineering Department Seminar

Because over 90% of the energy humanity uses originates from thermal energy, the efficiency of thermal to electrical energy is critical. Most efficient thermodynamic engine cycles (Rankine, Bray-ton…) involve fluids or gases. Thermoelectric conversion, based on the thermodynamics of conduc-tion electrons, is an all-solid-state technology that therefore doesn’t wear out, requires no mainte-nance and has a very high specific power. Unfortunately, thermoelectric conversion is expensive to implement and has a low efficiency compared to vapor or gas-based heat cycles, especially at power levels above 1 kW. This talk will analyze why, and will suggest a range of fundamentally new re-search directions that address those problems. The fundamental problem is that electrons have few degrees of freedom that can be thermally excited, and therefore have a low entropy compared to liq-uids and gases. The talk will describe various ways to address that, first by harnessing the spin de-gree of freedom (spin-caloritronics). More recently, we study the effect of the topological electron properties on thermoelectric transport. Technologically the most relevant one is the possibility of switching on topologically protected currents with an external magnetic field, potentially producing all-solid-state thermal switches.

Bio: Heremans is an Ohio Eminent Scholar and Professor in the Mechanical and Aerospace Engi-neering Department at the Ohio State University, with appointments in the Materials Science and Engineering Department and the Department of Physics. He is a member of the National Academy of Engineering, and a fellow of AAAS and the American Physical Society. He joined OSU after a 21-year career in the automotive industry at the General Motors Research Laboratories, where he was the section manager for Semiconductor Physics, and at the Delphi Research Laboratories. His re-search interests focus on energy conservation and recovery, and lie at the intersection between ex-perimental condensed matter physics and thermodynamics. In the last decade, he worked on the transport of heat, charge, and magnetization in solids. For example, some articles pertaining to the talk above include: Nature Materials 9 898 (2010); Nature 487 210 (2012); Nature Nanotechnolo-gy 8 471 (2013); Nature Materials 14, 601 (2015); Nature Communications, 7, 13714 (2016); Nature Reviews Materials 2 17049 (2017).