North Carolina Central University
Title: "EXCITONS, PLASMONS, AND EXCITONIC COMPLEXES IN QUASI-1D SEMICONDUCTORS FROM THEORETICAL PERSPECTIVE"
Rapid progress in the fabrication techniques of advanced low-dimensional nanomaterials opens up new opportunities and challenges to develop new materials by theoretically addressing fundamental physical phenomena at the nanoscale. Theoretical understanding of processes such as absorption, emission, scattering, charge relaxation, dissociation of correlated electron-hole pairs, near-field effects, etc. in systems of reduced dimensionality is important both for the correct interpretation of experimental data and for the development of new improved functionality nanomaterials. In this talk, I will briefly review the latest experiments [1-4] and enlarge on the recent theoretical efforts to develop a physical understanding of quasi-1D semiconductor nanostructures, particularly carbon nanotubes (CNs), -- efforts which have uncovered their intriguing optical attributes lending themselves to new attractive device applications. For instance, low-energy collective interband plasmon excitations that arise in single wall CNs due to the circumferential quantization of electron motion, can be used to tailor their optical and transport properties [5-7]. There is an interesting possibility for Bose-Einstein condensation of excitons that originates from their strong coupling to interband plasmons in single- and double-walled carbon nanotubes [8,9]. Excitonic complexes (trions and biexcitons) in quasi-1D semiconductors exhibit a crossover behavior whereby trions, being more stable than biexcitons in strongly confined quasi-1D nanostructures [10,11], become less stable than biexcitons as the transverse size of the nanostructure increases -- quite a general effect to observe through comparative measurements on semiconducting CNs of increasing diameter . These new findings open up new horizons for a variety of new applications of quasi-1D nano-structures, primarily carbon nanotubes, such as controlled electromagnetic absorption, enhanced light scattering and tunable highly coherent polarized light emission, to mention a few, to enrich the broad areas of contemporary nanoplasmonics, near-field optics, and spinoptronics research.
This research is supported by the US Department of Energy (DE-SC0007117) and the US National Science Foundation (ECCS-1306871).
 A.Graf, et al., Nature Communications 7, 13078 (2016)
 F.Pyatkov, et al., Nature Photonics 10, 420 (2016)
 X.He, et al., Nature Nanotechnology 11, 633 (2016)
 X.Ma, et al., Nature Nanotechnology 10, 671 (2015)
 I.V.Bondarev, L.M.Woods, and K.Tatur, Phys. Rev. B 80, 085407 (2009)
 I.V.Bondarev, Optics Express 23, 3971 (2015); Phys. Rev. B 85, 035448 (2012)
 M.F.Gelin and I.V.Bondarev, Phys. Rev. B 93, 115422 (2016)
 I.V.Bondarev and A.Popescu, MRS Advances, DOI: 10.1557/adv.2017.435
 I.V.Bondarev and A.V.Meliksetyan, Phys. Rev. B 89, 045414 (2014)
 B.Yuma, et al., Phys. Rev. B 87, 205412 (2013)
 L.Colombier, et al., Phys. Rev. Lett. 109, 197402 (2013)
 I.V.Bondarev, Phys. Rev. B 90, 245430 (2014); Phys. Rev. B 83, 153409 (2011)
*Refreshments will be served before the colloquium*
Biography: Dr. Igor V. Bondarev is tenured Professor of Physics in the Department of Mathematics and Physics at North Carolina Central University, Durham, North Carolina. Dr. Bondarev earned his MS (1989, Physics, with Honors) and PhD (1994, Theoretical Physics) degrees from the Belarusian State University in Minsk, Belarus. He earned his DSc degree (2001, Theoretical Solid State Physics) from the National Academy of Sciences of the Republic of Belarus in Minsk. (Doctor of Science in Physics and Mathematics is the Habilitation Degree awarded to less than one per cent of active former Soviet Union scientists having PhD.) In 1989-2005, Dr. Bondarev worked in the Theoretical Physics Lab of the Institute for Nuclear Problems at the Belarusian State University (last occupied position - Principal Research Associate/Group Leader). At the same time, as a visiting Professor he performed his research in Germany, France, Belgium, Italy, Poland, and Japan, supported by DAAD (Germany), OSTC (Belgium), JSPS (Japan), and other highly competitive visiting professorship fellowships. Dr. Bondarev has authored and co-authored over 180 research articles, including one US patent and five book chapters in collective monographs published by Nova Science, Taylor & Francis, CRC Press and American Scientific, USA. He presented his research at over 30 invited seminars and over 130 international conferences and symposia in Europe, China, Japan, Mexico, USA, and Canada. Dr. Bondarev is the recipient of the Presidential Young Investigator Award (Belarus, 1999-2001), NCCU College of Science & Technology Outstanding Faculty Research Award (2007, 2012), NCCU Faculty Senate Award for Scholarly Achievements (2007), NCCU Office of Sponsored Research Award for Technology Innovations (2012), and Research Grant Awards from the US National Science Foundation, the US Department of Energy, and the US Army Research Office. His current research interests are focused on the optoelectronic and sensory properties of semiconductor and carbon nanostructures, exciton/plasmon/polariton effects, efficient solar energy conversion with nanomaterials and nanobiophotonics.