Research Categories

Spintronics

NameResearch Interests
Assoc Prof Dong ZhiliDr. Dong has more than twenty years experience in transmission electron microscopy and X-ray diffraction of materials. His research interests include open-framework materials, nanostructured functional materials, advanced coatings and materials synthesis.
Assoc Prof Fan WeijunHis research interests include semiconductor band structure calculations by using effective mass theory, the first-principles method and empirical pseudopotential method (EPM); Compound semiconductor material growth, characterizations and device fabrications; Si photonics; Spintronics.
Prof Lew Wen SiangDr Lew's areas of expertise are spintronic devices, nanoscale magnetism, and bio magnetic sensors.
Asst Prof Liew Chi Hin TimothySpin Dynamics of Excitonic Systems : Excitons are bound hydrogen-like states of electrons and holes, typically appearing in semiconductor quantum wells. Their electric dipole moment allows them to couple to light, particularly in semiconductor microcavities, and if this coupling is strong enough it can lead to hybrid states of excitons and light known as exciton-polaritons. Being hybrid states, exciton-polaritons inherit a mix of electronic and optical properties, including strong nonlinearities, sensitivity to electric/magnetic fields, long coherence times, fast picosecond scale dynamics. Theoretically, excitons and exciton-polaritons are also interesting for their rich spin dynamics, which gives rise to the optical spin Hall effect, spin-to-orbital angular momentum conversion; and spinor vortex dynamics. Optical Circuits : The nonlinearity of exciton-polaritons implies their application as optical circuit elements. While exciton-polariton systems are highly lossy, they admit a mechanism of signal propagation that mimics the signal propagation of biological neurons where losses are fully compensated by amplification. Recently a complete theoretical framework of polariton based circuits has been developed , accounting fully for disorder and finite lifetime. Mechanisms of hybrid electro-optic circuits can be based on incoherently excited polariton transistors or alternative mechanisms of bistability. Quantum Optics in Weakly Nonlinear Systems : To generate quantum effects from an optical system one typically requires nonlinearity stronger than the system decay rate. For example, the well known photon blockade effect requires the interaction energy between two photons to exceed the linewidth. Unfortunately, most photonic systems (e.g., microcavities or photonic crystals) have short photon lifetimes. Recent research moves to circumvent this problem by making use of quantum interferences or mechanisms of amplifying a weak nonlinearity. Bosonic Quantum Cascade Lasers : A variety of semiconductor nanophotonic systems have been considered for the emission of terahertz radiation, where one typically aims to convert an optical photon into a terahertz photon. While terahertz sources have several practical applications, this process is highly inefficient as the terahertz photon carries only a small fraction of the initial energy. To overcome this problem, the concept of a bosonic quantum cascade laser has been introduced , making use of multiple terahertz emitting transitions in an exciton trap. Unlike fermionic quantum cascade lasers, the efficiency is greatly increased by bosonic final state stimulation (achieving quantum efficiency above unity) while the system size is on the micron scale. Topological Photonic/Exciton Systems : The field of topology has proven how macroscopic properties of physical systems can result in exotic features at the boundaries between topologically distinct materials. Following earlier ideas from electronic topological insulators and photonics, the theory of topological polaritons and topological indirect excitons was recently introduce. In these systems, density currents propagating in chiral edge states are protected from scattering with disorder, which is a clear advantage for exciton based optical circuits. Optical Neural Networks : Neural networks exploit massive interconnectivity to become highly efficient at certain tasks, such as classification, and pattern recognition. While biological neurons may operate individually on millisecond time scales, their simultaneous connection to several thousands of other neurons allows a parallelization of tasks far beyond the capabilities of complementary metal-oxide-semiconductor logic. Naturally, this observation has motivated research into optical neural networks. Open Positions: PhD and Postdoc Positions are available (http://www.spms.ntu.edu.sg/pap/Home/Faculty/TimothyLiew.html).
Asst Prof Marco BattiatoIn the past, Marco Battiato developed the model of superdiffusive spin transport as a mechanism of the ultrafast demagnetisation, prediction which was experimentally confirmed. He has worked since then on several topics that stemmed from the discovery of the ultrafast spin transport: 1) ultrafast spin injection, 2) triggering of ultrafast demagnetisation via injection of excited unpolarised carriers, 3) ultrafast increase of the magnetisation, 4) generation of THz emission via injection of ultrashort spin current pulses in high SO coupling materials, and 5) injection of ultrashort spin current pulses from ferromagnetic metals into semiconductors. He is currently interested in a wide range of phenomena that arise from the complex interplay of strongly out-of-equilibrium electronic populations in real band-structures, out-of-equilibrium transport in multilayers, and formation of THz electromagnetic fields. He is developing a massively parallel solver for the full Boltzmann-Maxwell system for real space transport in ab-initio band-structures, using the most general (without close to equilibrium approximations) expression of the collision operator for strongly out-of-equilibrium thermalisation dynamics. He is applying the method to: - Thermalisation of laser excited carriers in topological insulators; - Ultrafast spin transport in metallic multilayers and metal-semiconductor junctions; - THz emission after laser excitation of multilayers; - Ultrafast dynamics triggered by THz excitation. Finally one of his main goals is the construction of all the building blocks of ultrafast THz spintronics using the sub-picosecond spin current pulses as vector of information.
Prof Raju V. RamanujanNanomaterials are the focus of research work in Ramanujan?s group, especially magnetic and thermoelectric nanomaterials for energy, bioengineering, information storage and defense applications. Processing, characterization and property measurements are carried out in his group (presently 8 graduate students and 3 Research Fellows). Recent PhD theses include: Characterization and processing of cobalt based magnetic nanomaterials (Li Huafang),Microstructural evolution and processing of melt spun and mechanically alloyed Fe-Ni-B-Mo nanomagnetic materials (Du Siwei), Alloying effects on nanostructure formation in iron based soft magnetic materials (Yanrong Zhang) and Directed self assembly of patterned magnetic nanostructures (A. Srivastava). A strong emphasis is placed on electron microscopy and phase transformations are used as an important tool to tailor the microstructure. A bioengineering project, in collaboration with SingHealth, aims to develop magnetic nanoparticles for human liver cancer treatment. Synthesis of magnetic nanoparticles, coating these particles with a suitable polymer and cancer drug, followed by in-vitro and in-vivo testing of the coated particles is being carried out. MRI imaging is being used as an investigative tool in this work. Microelectronic reliability issues, e.g., stress-induced diffusive voiding in microelectronic materials are being studied. Magnetocaloric materials for energy applications, patterned nanostructures for ultra high density data storage media, giant energy product exchange coupled magnetic nanomaterials and nanomaterials for artificial muscles, targeted drug delivery and gene delivery are topics of ongoing research.
Assoc Prof S. N. PiramanayagamThe research interests of A/Prof S.N. Piramanayagam lies in the interdisciplinary areas of condensed matter physics, materials science and electronics. In particular, his research aims to solve problems related to magnetism and electronics and to provide technological solutions. His research interests can be divided into the the following sub-categories: • Magnetic Nanostructures (for memory, energy and biological applications) • Neuromorphic Computing • Spintronics Materials Students who wish to work in his group can contact him at prem@ntu.edu.sg
Prof Shen ZexiangRaman spectroscopy and microscopy Graphene and graphene composite materials for electric energy storage - Li & Na ion batteries, supercapacitors flexible battery for bendable electronics Nano Science and Nano Technology Plasmonics Optical and electronic properties of 2D materials Optical study of perovskite materials Ultra low wavenember Raman spectroscopy High pressure study Theoretical simulation of graphene, 2D materials, and perovskites Industrial collaborators: Johnson Matthey, UK Elbit Systems, Israel Thales, France Akzo Nobel, Netherlands Globalfoundries Wintech Nano
Prof Sum Tze ChienMy research focuses on investigating light matter interactions; energy and charge transfer mechanisms; and probing carrier and quasi-particle dynamics in a broad range of emergent nanoscale light emitting and light harvesting systems using Femtosecond time-resolved spectroscopy. These can be categorized under two main research themes: (1) light emitters/lasing and (2) photovoltaics. I have also established a 3rd category: (3) Aspirational Areas to explore new ideas and concepts away from my two core research themes. Specifically, I seek to address the following three questions in these systems: (a) Where did the energy go? That is the interplay of carrier/quasi-particle dynamics between the host energy levels, defect energy levels and the dopant energy levels. (b) What are the underlying photo-physics and light-matter interactions that give this system its unique characteristics? That is the various processes such as carrier-carrier scattering, carrier-phonon scattering, radiative recombination and auger recombination etc. (c) How can these properties/technologies be improved for practical applications? That is how the knowledge gained be used for the development of novel optoelectronic devices; nanolasers; and photovoltaic devices. Today, my group tackles a broad spectrum of research problems in emergent materials (such as halide perovskites, 2D materials etc) ranging from novel photophysics, solar cells, LEDs, lasing, spin phenomena, hot-carrier phenomena and nonlinear properties. (1) Light Emitters/Lasing: We seek to understand the interplay of carrier/quasi-particle dynamics between the host energy levels, defect energy levels and the dopant energy levels and the factors affecting amplified spontaneous emission or lasing in these II-VI nanostructures such as ZnO nanowires, CdS nanowires and even the mixed dimension CdSe dot/ CdS nanorod heterostructures and organic-inorganic halide perovskites. (2) Photovoltaics: Ultrafast optical spectroscopy allows us to trace the fate of the carriers and quasi-particles in photovoltaic devices from genesis to the end with timescales spanning over ten orders of magnitude. Correlated with electrical characterization techniques, new insights into the mechanisms of charge generation, transfer, trapping, recombination and transport in novel PV materials can be gained through these studies. (3) Aspirational Areas: Presently, we live in a highly competitive era of rapid technological changes and shortened innovation cycles, where a keen sense and nimbleness to seek out opportunities is key to sustaining economic growth and our quality of life. These aspirational areas on 2-D Materials, novel nonlinear optical properties and spin phenomena allow us to explore new ideas and concepts apart from our core research.
Assoc Prof Tang Xiaohong. Compound semiconductors and photonic devices. . Metal organic vapor phase epitaxy. . Nanophotonics and nanoelectronics: materials, physics and devices. . Heterogeneous epitaxy growth of compound semiconductors on silicon substrate. . Semiconductor quantum dot, nanowire photonics and electronics.