Faculty Research Interests

Stacks of intrinsic Josephson junctions (IJJs) in extremely anisotropic high-temperature superconductors such as Bi₂Sr₂CaCu₂O₈ are a promising compact solid-state source of coherent radiation in the ‘terahertz gap’ range. At present, no such sources exist in the range from approximately 0.5 THz to 1.3 terahertz, and this region is of particular interest for many applications in science, medicine, and high-bandwidth communications, as well as in security and defense. In order to generate technologically useful levels of power from these stacks, it is necessary to obtain efficient phase-synchronized emission from the largest possible number of individual Josephson junctions. Following this approach, I have recently increased the coherent power output from this type of device to 0.6 milliwatts at 0.51 THz, which is approximately the power level required for practical real-time imaging applications.

High temperature superconductors which contain stacked IJJs – namely the bismuth- and thallium-based cuprate compounds – offer a further unique property: they are expected to allow the propagation of Josephson Plasma Waves. Theorists predict that the copper-oxide planes of these HTS cuprates act as natural superconducting waveguides which can channel energy through the structures of these crystals at microwave and terahertz frequencies. My experiments in Bi₂Sr₂CaCu₂O₈ provide strong indirect evidence of this phenomenon. The efficient propagation and non-linearity of Josephson Plasma Waves offers the possibility of novel devices for THz frequency signal processing, such as ridge waveguides, mixers, and modulators/demodulators. Such devices would be extremely valuable for ultra-high bandwidth telecommunications for both wired and wireless applications.

Realizing the full technological potential of complex oxide materials such as these will require advances in thin film growth technology beyond what is presently available, and I am currently developing techniques for growth of thin films with the quality of a single crystal.

We probe our environment and communicate with one another with classical waves. Because of wave-particle duality, studies of classical waves also serve as models of electronic transport, involving quantum mechanical electron waves in the solid state. The goal of our studies of microwave and optical propagation is to provide a universal description of wave propagation in random systems and to apply the understanding gained to imaging and communications. We explore the diversity of propagation phenomena in ensembles of sample realizations which reflect the openness, scattering strength, internal reflection, dissipation or gain, and topology of the system. The work in the lab has demonstrated Anderson localization, the statistics of transport in space and time, including short-, long- and infinite-range intensity correlation in space and frequency; crossovers between ballistic, diffusive and localized wave transport, acousto-optic tomography, band-edge lasing, the photon localization laser, correlation of non-orthogonal modes in open media, and robust transport of edge states in photonic topological insulators, which emulate the spin and valley degrees of freedom in condensed matter. Research in the lab contributed to the formation of Chiral Phonics, Inc. (https://www.chiralphotonics.com/), which develops and produces microfabricated optical fiber-based components and assemblies for applications in coupling and sensing.

The microwave laboratory was started together with Dr. Narciso Garcia.

Prof. Deych research is currently focused on properties and applications of optical Whispering Gallery Modes. These modes arise when light is confined within an axially symmetric optical resonator. Examples of such resonators are dielectric spheres or toroids. Light propagating along an equator of such a structure almost tangentially to its surface is prevented from escaping from the resonator due to total internal reflection: the light is trapped (or confined) inside the resonator. The similar phenomenon also occurs with sound waves and can be observed in a number of historically famous buildings such as St. Paul’s Cathedral in London or Grand Central station in New York City: if one whispers something into the wall of a circular gallery, the sound of the whisper will propagate along the circumference of the wall and can be heard by someone standing by the wall at the diametrically opposite point. Hence, the name: Whispering Gallery Modes (WGM).

These special excitations of light have very special properties and are extremely useful for various applications. Prof. Deych’s research interests lie in application of these modes in biosensing, where the goal is to develop a sensor capable of detecting viruses or other biological objects. The unique ability of WGMs to detect small particles and even single molecules results from two important characteristics of these modes. First, they produce extremely narrow lines in the spectrum of light scattered from the resonators. As a result, even very small shifts of these lines can be spectrally resolved. Second, the field of these modes is concentrated in the vicinity of the resonator’s surface, where it is strongly enhanced. This enhancement of the field amplifies effects of smallest changes in the environment, such as adsorption of a virus to the surface of the resonator, resulting in observable shifts of the spectral lines.  

Another aspect of the Whispering Gallery Modes studied by Prof. Deych and his students is concerned with mechanical action of light. It has been well known for a long time that light can produce mechanical forces on polarizable dielectrics. Prof. Deych’s research showed that confining light within WGM resonators significantly changes these forces and give them new unexpected characteristics. Prof. Deych studies how these changes can be exploited for optical manipulation of small objects and optical cooling. 

 A separate direction of Prof. Deych’s research is concerned with optical properties of  Bragg Multiple Quantum Wells. These are periodic structures consisting of very thin (about 10 nm) layers of one semiconductor (wells) separated by wider (about 100 nm) layers of other semiconductors (barriers). When the period of such a structure is made equal to the half wavelength of light emitted by excitons confined inside wells, the structure is called Bragg structure, because the light emitted by the structure is in the resonance (called Bragg resonance) with the period of the structure. Prof. Deych and his QC colleague, Prof. Lisyansky, developed a theoretical description of optical properties of these structures. Main predictions of this theory have been observed experimentally by another QC faculty member, Prof. Menon in collaboration with Prof. Oktyabrsky of SUNY College of Nanoscale Science and Engineering. The results of this work have been published in Nature Photonics.  

I applly methods of statistical physics to solve problems in biophysics – with the focus on intracellular transport, population dynamics, and collective biological dynamics.

Statistical properties of cargo transport in biological cells.  Cells are complex systems in which multiple functions take place simultaneously.  Production, transport, and delivery of cargo between different organelles is an important part of the proper cell function.  Cargo is transported by special molecules called molecular motors that walk on cytoskeletal filaments.  The morphologies of these filaments can take on many forms, with varying degree of disorder.  In addition, cells are noisy environments, so motors tend to fall off the filaments, diffuse in the cytoplasm and rejoin other filaments.  Because of all the disorder and noise, questions concerning transport of cargo (time for delivery, time for getting stuck in local traffic jams, etc.) are naturally statistical.  This work intersects the subject of stochastic transport in disorderly environments, since microtubule morphologies tend to be disordered (possibly with applicaitons with bio-inspired materials).   Finally – organelles interact with each other by exchanging material.  This is called interactome.  It is of great interest to understand how the disturbance of this network affects transport functionality of the cell.  

If you’re a student interested in using physics and math to understand biological world, please inquire.  I have many projects of various levels of difficulty and abstraction – starting from simple “exercises” that can lead to results quickly, to in-depth projects that would form PhD thesis.
 

Collective dynamics of swarmalators.  I also study collective dynamics of a specific type of active particles called “swarmalators”,  with relevance to biological systems.  Swarmalators have an internal cycle (represented by a periodic variable), and these cycles can synchronize with each other – that is, oscillators that swarm.  The motion of each particle depends on the level of synchronization with other particles, and synchronization depends on the physical proximity of particles to each other.  This double-feedback produces complex collective states.  The goal is to understand collective behavior of swarmalators and connect with applications. Swarmalators have been implemented in condensed matter physics and in robotics.  There’s also a strong evidence that some animals – such as Japanese tree frogs and some microorganisms (sperm cells and some bacteria) may act as swarmalators.  Recently, colleagues and I studied the role of time delay in swarmalators, and found the existence of delay-induced phase phase transitions.  

If you’re a new student and find this intruiguing, there are many tantalizing projects that are waiting to be addressed: connection of swarmalation with glass physics and frustration (we have some exciting results); dynamics of externally-forced swarmalators; applications to molecular robotics; using microtubules and molecular motors to form active swarms; nanorobots in complex environments.  Swarmalators are also a good test-bed for the study of nonequilibrium fluctuations.  

Science and technology at nanoscale have numerous opportunities both for fundamental research and new applications. Quantum dots, nanocrystals, nanowires, and nanorods are among the most important building blocks of nano-photonic devices. Therefore, the understanding of underlying fundamental physical phenomena in such structures is very important for future progress. We are interested in fundamental properties of wide bad gap nanostructured materials, particularly those with type-II band alignment, with potential application in photo-detection, quantum information, and biomedical field. Type-II heterostructures have several substantial advantages over type-I systems in that that they suppress non-radiative Auger recombination, and their emission can be controlled by external means such as intensity of excitation, electric and magnetic fields. We particularly focused on properties of epitaxial ZnTe/ZnSe quantum dot multilayers and related alloys, type-II colloidal core-shell nanoparticles, and II-VI nanowires.

In the ZnTe-ZnSe systems holes are strongly confined within ZnTe-rich quantum dots, whereas electrons locate in ZnSe barriers, and only weakly attracted to holes via the Coulomb interaction, forming the spatially indirect (type-II) excitons. It is important that QDs in this system coexist with Te_n isoelectronic centers, and a smooth transition between these two different species is indicated by experimental results. Therefore, QDs here are formed by continuing enlargement of Te_n/Se isoelectronic centers. In magnetic field this system exhibits one of the most interesting quantum phenomena – so-called optical Aharonov-Bohm Effect, for which we observed photoluminescence intensity as well as energy oscillations within the same sample, experimentally, for the first time. The samples are grown by Prof. M. C. Tamargo’s group of The City College. Other similar systems, for instance ZnTe/ZnCdSe multilayers of submonolayer type-II QDs, can be used as intermediate band material in QD-based intermediate-band solar cells; such solar cells can have efficiency as high as 63% under full solar concentration. We are interested in both material properties and application of this material system.

In addition to epitaxial quantum dots we, currently, are working on several aspects of optical properties of colloidal ZnO nanostructures, including core-shell systems. We have shown that quantum size effects can be achieved in ZnO nanorods, and we continue to investigate the role of dielectric confinement on ZnO nanorods optical properties, as it is important for 1-D systems. We investigate also the role of morphology on the optical properties of ZnO nanostrutures, including origin of the green band. Recently, we began growing ZnO nanowires using in-house built CVD system.

We are also working in application of type-II structures for high sensitivity biological detectors. This work is in collaboration with Prof. Mourokh and Prof. H. Matsui of Hunter College. The pathogen diagnostics is constrained by a variety of challeneges that compromise essential elements of detection. Our approach uses unique optical properties of type-II colloidal fluorescent quantum dots.

Recent discoveries in quantum nanoplasmonics have raised high hopes for the future development of ultrafast and super small optoelectronic devices. Nanoplasmonic applications utilize plasmons – oscillations of free electrons in metals – to achieve high concentration of the electromagnetic energy at a subwavelength volume. One of the most striking developments in nanoplasmonics has been a theoretical prediction and experimental implementation of the SPASER (Surface Plasmon Amplification by Stimulated Emission of Radiation). Similar to a laser that radiate coherent photons, the spaser generates stimulated emission of coherent surface plasmons in resonating metallic nanoparticles. 

In order to be able to use spasers, one must understand their behavior in the external electromagnetic field. Since the spaser is a nonlinear system, its interaction with the external field is very nontrivial. Currently, investigating different aspects of physics of spasers is one of my main areas of interest. This include synchronization of spasers with an external electromagnetic wave, collective behavior of systems of spasers, a possibility of loss compensation by spasers, and creating new types of spasers such as the channel and magneto-optical spasers. I am also interested in studying the light propagation and localization in resonant photonic crystals, optics of magneto-photonic crystals, as well as the general theory of localization.

Prof. Murokh has established a vigorous research program addressing charge and energy transfer at the nanoscale both in conventional semiconductor nanostructures and especially in living organisms. The main object of these studies, living organisms at the nanoscale, can be viewed as molecular complexes, whose dynamics is often controlled by the transfer of single charges or single-photon absorption events. In many senses, it is similar to the principles of operation of semiconductor nanostructures and elements of molecular electronics. In the interdisciplinary research of Prof. Murokh, combining biological, physical, material, and engineering sciences, this similarity is explored. The goals are (i) to shed light on the processes occurring in biological systems, (ii) to enable mimicking these processes in physical systems, which are easier to control and to access experimentally, and (iii) to facilitate building electronic and photonic devices combining with the machinery of life. These studies are based on his recent works in conventional nanoelelctronics performed in collaboration with various experimentalists, such as Prof. J. Bird (University at Buffalo), Prof. R. Blick (Hamburg University, Germany), Profs. I. Kuskovsky and F. Cadieu (Queens College). Recently, a project concerning heavy-duty capacitors based on organic supramolecules is started in collaboration with Dr. Pavel Lazarev (Capacitors Sciences, Inc., Palo Alto, CA). In another new project with Profs. M. Vittadello (Medgar Evers College of CUNY) and S. Minteer (University of Utah), hybrid structures combining artificial and natural parts in the same nanodevice will be explored.

Dr. Takei’s research focuses on understanding how macroscale, collective behavior of electrons and atoms in matter emerges from the laws of quantum mechanics governing their motion on the microscopic scale. His research activities primarily involve the use analytical tools, supplemented by numerical techniques, to study the transport of mass, charge, spin, and/or heat through various low-dimensional quantum matter, including systems tuned close to thermal and quantum critical points, magnetically ordered systems (e.g., ferromagnets and antiferromagnets), as well as quantum spin systems hosting a myriad of interesting phenomena such as topological order and emergent excitations with fractional quantum numbers and statistics. Of particular interest is in understanding how spin angular momentum can be transported through insulating spin systems, an emerging subfield of condensed matter physics, still largely unexplored but a topic of relevance due to the recent exciting experimental developments that have come out of the field of spintronics.

Research in Dr. Takei’s group maintains a healthy synergy with experiments; they are a driving force for his theoretical efforts, and his goal, in turn, is to stimulate future experiments. Transport properties of different materials are theoretically studied with the machinery of linear-response theory, nonequilibrium quantum field theory, semi-classical dynamics, the renormalization group technique, scaling theories and more. While his ultimate goal is to advance the fundamental understanding of quantum matter via transport studies, an important subset of his work focuses on proposing novel device applications, such as new platforms for classical and quantum computation, based on the theoretical understanding that he develops through his research.