Interfaces of two dimensional (2D) van der Waals (vdW) crystals constitute the most versatile material platforms for the exploration of new physical phenomena, particularly emergent quantum phases. Here we apply femtosecond pump-probe spectroscopy/microscopy to develop a time-domain view of quantum phases at 2D vdW interfaces of semiconducting, ferro/antiferro-magnetic, and ferroelectric materials. For transitional metal dichalcogenide (TMDC) moiré interfaces, we show the robustness of correlated electron phases and their coupling to phonons. In the layered magnetic semiconductors, we discover the coupling between interlayer electronic hybridization to magnetic order and, as a result, the strong coupling of excitons to coherent magnons. In the layered ferroelectric semiconductors, we discover the strong coupling of across-gap electronic excitation to the ferroelectric order. These time-domain views reveal not only the nature of the quantum phases, but also prospects of controlling these quantum phases by light.
Xiaoyang Zhu is the Howard Family Professor of Nanoscience at Columbia University. He received a BS degree from Fudan University in 1984 and a PhD from the University of Texas at Austin in 1989. After postdoctoral research with Gerhard Ertl at the Fritz-Haber-Institute, he joined the faculty at Southern Illinois University as an Assistant Professor in 1993. In 1997, he moved to the University of Minnesota as a tenured Associate Professor, later a Full Professor, and a Merck endowed professor. In 2009, he returned to the University of Texas at Austin as the Vauquelin Regents Professor and Served as directors of the DOE Energy Frontier Research Center (EFRC) and the Center for Materials Chemistry. In 2013, he moved to Columbia University. His honors include a Dreyfus New Faculty Award, a Cottrell Scholar Award, a Friedrich Wilhelm Bessel Award, an APS Fellowship, a Vannevar Bush Faculty Fellowship from DOD, an Ahmed Zewail Award from the American Chemical Society, and an Earle K. Plyler Prize from the American Physical Society. His research interests include quantum materials, photophysics, and ultrafast dynamics.