Thermoelectrics & Topology - E. Cheng
Electrical, thermal, and thermoelectric transport are intrinsically intertwined manifestations of how charge and quasiparticles—such as phonons, magnons, and spin excitations—propagate in solids. Their controlled interconversion underpins key technologies including waste-heat recovery, solid-state cooling, and magnetic-field sensing. At the same time, transport measurements serve as powerful probes of quantum materials, revealing the interplay of electronic structure, spin, orbital degrees of freedom, correlations, and topology.
We pursue high-performance thermoelectric materials along two complementary directions. On the materials side, we explore emerging topological and correlated systems as platforms for unconventional thermoelectric responses, including enhanced longitudinal and transverse effects. On the device side, we employ focused ion beam (FIB) techniques to fabricate micro-scale thermoelectric devices. By engineering microstructures—such as geometry, interfaces, and dimensionality—directly at the device level, we aim to further optimize thermoelectric performance beyond bulk limitations.
A second major focus is quantum and topological materials with unconventional magnetism, including kagome systems and complex antiferromagnets. In addition to material side, we utilize strain as an active tuning parameter to modify crystal symmetry, thereby controlling electronic band structures and magnetic orders. This approach allows us to systematically investigate how symmetry breaking influences transport and collective phenomena, such as the anomalous Hall and anomalous Nernst effects, superconductivity, and strong electronic correlations.
To uncover the microscopic origins of these phenomena, we combine neutron scattering and resonant elastic X-ray scattering (REXS) to determine magnetic structures with angle-resolved photoemission spectroscopy (ARPES) to resolve electronic band dispersions and topology. By integrating these techniques with comprehensive electrical, thermal, and thermoelectric transport measurements, we establish direct links between magnetism, band structure, excitations, and transport responses.
Through this multi-probe and multi-scale approach—spanning crystal growth, strain engineering, micro-device fabrication, spectroscopy, and transport—our research aims to uncover new physical mechanisms and material platforms for next-generation spintronics and thermoelectric technologies.