Nai Phuan Ong
Eugene Higgins Professor of Physics. Ong is an experimentalist in condensed matter physics with broad interests in topological insulators, Dirac/Weyl semimetals, high-temperature superconductivity, vortex liquid states, quantum spin liquids and 2D chalcogenides. Ong was co-discoverer (in 1976) of sliding charge-density-wave (CDW) conduction in the linear-chain metal NbSe3 (with Pierre Monceau of CNRS, Grenoble). In this unusual phenomenon, the electrons "condense" into a monolithic CDW condensate that is accompanied by a weak, periodic distortion of the lattice. When an electric field is applied, the condensate is able to move (slide). When sliding, the CDW condensate emits a weak voltage oscillation with a frequency proportional to the sliding velocity. In the period 1986--2008, Ong's research focused on high-temperature superconductivity based on cuprates. His group produced some of the earliest evidence (from the Hall effect) that the superconducting phase in cuprates derives from introducing hole carriers into the parent Mott insulator state. They demonstrated that the charge transport properties in the normal state (above the critical temperature Tc) are anomalous compared with ordinary metals. Ong shared the Kamerlingh Onnes Prize with Uchida and Takagi (Univ. Tokyo) for these findings. Ong's group used the Nernst effect and torque magnetometry to show that, at temperatures well above Tc, the electrons remain Cooper paired, but the collective wave function fluctuates strongly in phase due to continual nucleation and annihilation of vortices and antivortices. In this unusual "vortex liquid" state, the Nernst effect signal is extraordinarily large, while the sample exhibits a large diamagnetism up to 100 Kelvin above Tc. These findings, initially puzzling, have been recently confirmed by several independent spectroscopy and scattering experiments, and now seems widely accepted by the community. Starting in 2007, Ong's group investigated the new class of materials called topological insulators predicted by Kane, Fu and Mele (U Penn) and by Zhang and Qi (Stanford). The electronic wave functions in these materials exhibit a topological "winding" property, which protects surface Dirac states. Ong and long-time collaborator Robert Cava published the first transport evidence for the predicted surface Dirac states using quantum oscillations in a tilted magnetic field. A different category of topological materials are the Dirac/Weyl semimetals which feature protected bulk 3D Dirac states. A long-standing prediction (1983) is that 3D Dirac states should exhibit the chiral anomaly as an enhancement in the electrical conduction in an intense magnetic field. The chiral anomaly is the first of a series of anomalies investigated in QED, QCD and gravity. Ong, Cava and students reported (2015) the observation of the chiral anomaly as a prominent signal in the longitudinal magnetoresistance in Na3Bi and the half-Heusler GdPtBi. A current direction in the group is employing the thermal Hall conductivity arising purely from spin excitations to investigate quantum spin liquids.
1982 Alfred P. Sloan fellowship (1982-1984)
1989 Fellow of the American Physical Society
2006 H. Kamerlingh Onnes Prize for pioneering and seminal transport experiments which illuminated the unconventional nature of the metallic state of high temperature superconducting cuprates (with H. Takagi and S. Uchida) http://www.m2s-dresden.de/frs_default.htm
2006 Elected to the American Academy of Arts and Sciences
http://www.amacad.org/news/classsec2006.aspx
2010 Elected Fellow of the American Association for the Advancement of Sciences. http://www.aaas.org/publications/annual_report/2010/aaas_ann_rpt_10_p24_fellows.pdf
2012 Served on board of reviewing Editors, Science Magazine, Jan. 2012 – Feb. 2014
2012 Elected to the U.S. National Academy of Sciences
http://www.nasonline.org/news-andmultimedia/news/2012_05_01_NAS_Election.html
2014 Awardee in Experimental Investigators in Quantum Materials (EPiQS) program, Gordon and Betty Moore Foundation
http://www.moore.org/programs/science/emergent-phenomena-in-quantum-systems