Mark Stockman: Evangelist for Plasmonics

Mark Stockman was a founding member and evangelist for the plasmonics field for most of his creative life. He never sought recognition, but fame came to him in a different way. He will be dearly remembered by colleagues and friends as one of the most influential and creative contributors to the science of light from our generation. ■ A SHORT BIOGRAPHY OF PROFESSOR MARK STOCKMAN Mark Stockman was born on the 21st of July 1947 in Kharkov, a major cultural, scientific, educational, and industrial center in the mainly Russian-speaking northern Ukraine, a part of the Soviet Union at that point in time. His father, Ilya Stockman, was a mining engineer by training, who fought in World War II and became a highly decorated enlisted officer. After the war, Ilya Stockman embraced an academic career and eventually became a Professor at the Dnepropetrovsk Higher Mining School. He was from a Cantonist family descended from Jewish conscripts to the Russian Imperial army, who were educated in special “canton schools” for future military service. Mark was an avid reader at school, and it was the undergraduate textbook on applied mathematics by Yakov Zeldovich, the famous theoretical physicist, who played a crucial role in the development of the Soviet Union’s nuclear bomb project that turned his attention to physics in a serious way. Following successful participation in the national school physics competition, Mark was accepted into a highly selective institution for gifted children in Kiev known as the Republican Specialized Physics and Mathematics Boarding School. The school was established by the father of Soviet cybernetics Victor Glushkov. Mark left his family in Dnepropetrovsk and moved to Kiev as a boarding student. Upon graduating from the school, he successfully applied to the Physics Department of Kiev State University, aided by his reputation as a top student and links between the school and university academics: for a Jewish boy with no family connections, to enter this prestigious university in the Ukrainian capital was a formidable challenge in the Soviet Union. However, after his second year, feeling uncomfortable at the University in Kiev, Mark decided to leave the blessed city for Novosibirsk State University far away in Siberia where a more cosmopolitan atmosphere prevailed at that time. He studied for a diploma in the Institute of Nuclear Physics where after graduation he became a researcher registered as a Ph.D. student. He defended a dissertation on collective phenomena in nuclei under the supervision of Russian theoretical physicists Spartak Belyaev and Vladimir Zelelevinsky. While a Ph.D. candidate, Mark met and married Branislava Mezger, a junior research scientist in biomedicine, and in 1978 they had a son, Dmitry. After a few years in the Institute of Nuclear Physics, Mark became disillusioned with nuclear physics, where research projects involved large groups and implied very long experimental cycles. He moved to the neighboring Institute of Automation and Electrometry in Novosibirsk to work on the fundamentals of nonlinear optics with Sergey Rautian. He habilitated in 1989 with a D.Sc. dissertation on nonlinear optical phenomena in macromolecules. Around this time, the political regime in the Soviet Union softened and the Iron Curtain was lifted. In 1990, on the invitation of Professor Thomas F. George, Mark was permitted to leave Russia with his family to take a research post at the State University of New York at Buffalo. He later followed Professor George to Washington State University and eventually settled with his family in Atlanta, Georgia, as Professor of Physics at Georgia State University. In 2012, he became the founding director of the Center for Nano Optics at Georgia State. Mark traveled widely, but never returned to Russia. Professor Mark Stockman passed away in his beloved Atlanta, Georgia, U.S.A. on Wednesday, November 11, 2020. To honor Mark, a Virtual Issue organized by ACS Photonics features articles from ACS Photonics, ACS Nano, and Nano Letters authored by friends and colleagues of Mark. Received: February 25, 2021 Accepted: February 25, 2021 Published: March 17, 2021 Editorial pubs.acs.org/journal/apchd5 Published 2021 by American Chemical Society 683 https://dx.doi.org/10.1021/acsphotonics.1c00299 ACS Photonics 2021, 8, 683−698 D ow nl oa de d vi a 69 .1 74 .1 56 .1 62 o n M ar ch 1 7, 2 02 1 at 1 8: 59 :1 8 (U T C ). Se e ht tp s: //p ub s. ac s. or g/ sh ar in gg ui de lin es f or o pt io ns o n ho w to le gi tim at el y sh ar e pu bl is he d ar tic le s. Mark Stockman posing a question to a speaker during a NANOP 2019 conference onNanophotonics. Photo courtesy of PremC. ■ PLASMONIC LENS Javier Aizpurua. Mark Stockman contributed intensely, sharply, and brilliantly to many subfields within nanophotonics. In the era when calculating the plasmonic response of a complex nanostructure was still a challenge, greatly mitigated nowadays by the capabilities of software tools available to solve Maxwell’s equation in almost any architecture, Mark proposed several canonical plasmonic structures that had a strong impact in the further development of plasmonic nanoantennas later on. Among them, Mark and colleagues proposed a canonical plasmonic nanolens made of a self-similar chain of particles with decreasing size, as a particularly efficient field-enhancing nanoantenna. The principle of this lensing effect was based on the concept of cooperative, or cascade, plasmonic enhancement. Within this simple concept, Mark et al. designed a set of plasmonic nanoparticles with gradually reduced size, where each smaller nanoparticle progressively localized the electromagnetic field induced by the immediately larger particle into a more confined space, and thus producing a much larger enhancement than the nanoparticles by themselves. This concept of a cascade plasmonic lens was successfully implemented experimentally by several groups in the community, which proved that the concept could be practically used in surface-enhanced spectroscopy and microscopy. The near-field cascade effect introduced by Mark et al. can be understood as the discrete version of his adiabatic compression of a plasmon traveling along a tapered metallic guide toward its apex. When the plasmon oscillation is constrained into smaller transverse dimensions, the associated local field unavoidably gets enhanced. One can also understand the localization and enhancement of optical fields in atomic protrusions as an extreme case of the cascade effect also occurring at the atomic scale. Metal atoms protruding from a metallic nanostructure can be considered as smaller “polarizable particles” subjected to the local field induced by the larger hosting nanoantenna (particle, tip, gap, etc.), and thus, the original local field at the hosting nanoantenna can be further enhanced and localized around single protruding atoms due to this atomic-scale cascade effect. This type of architecture, recently termed a “picocavity”, has allowed for confining light at atomic dimensions, pushing the limits of nanophotonics into the realm of picophotonics and emphasizing the relevance of the inspirational work by Mark on the plasmonic lens concept. ■ ACTIVE PLASMONICS Harry A. Atwater. Mark Stockman, like the field of plasmonics, was extremely active. No speaker at a photonics conference would go unquestioned or unchallenged whenever Mark was sitting in the front row. But challenging the community was Mark’s way of conveying his infectious love and enthusiasm for photonic science. His penetrating and deep scientific questions were also the ultimate compliments he could pay his colleagues and almost always gave a gift of insight or taught a physics lesson to the recipient. Those who also saw him or joined him on the ski slopes were surprised at how active Mark could be while navigating a black diamond run. For some, the field of plasmonics has always had a dark side, arising from the inherent Ohmic losses of our beloved plasmonic materials, limiting the achievable quality factor or degree of coherence of nanoconfined optical modes. But Mark’s signature achievement of the plasmonic spaser embodies the old adage that one person’s loss is another person’s gain; in the case of the spaser, it is the lossy metal juxtaposed with a gain medium that is the key to making a subwavelength-scale nonradiative stimulated emission source. It was Mark’s genius to see where others did not that this concept was not only interesting, but possible. Mark’s work on active plasmonics and the nanoconfinement of light was tremendously stimulating to me and my research group, who from the beginnings in 2000 shared Mark’s conviction that combining subwavelength confinement with active media opens a myriad of possibilities for nanoscience. In our lab, this led to the first prototype for a subwavelength-scale nanoparticle waveguide, an all-optical plasmonic modulator, a transistor-like modulator for light, plasmonic light trapping in solar cells, and achievement of unity-order modulation of the refractive index under electrical control, which later gave rise to electrically reconfigurable reflectarray metasurfaces, both using lower loss plasmonicmaterials such as conducting oxides and tunable perfect absorbers, as well as phased arrays for beam steering of infrared radiation using actively tunable graphene elements. Mark’s insistence to me over a breakfast in Japan once about the possibility of an infrared spaser composed of graphene active elements inspired me to begin exploring excited state radiative decay processes in graphene under ultrafast optical excitation. This effort, while not yet yielding a spaser, has recently demonstrated ultrabright mid-infrared spontaneous emission by plasmon generation from excited state relaxation in graphene. His work will continue to inspire students and researchers long after his passing. ■ NANOCAVITIES Jeremy J. Baumberg.The energy and stimulat