Biography:

Nicholas Curro received his PhD in 1998 from the University of Illinois at Urbana-Champaign, and did his Postdoctoral studies at Los Alamos National Laboratory. He then transitioned to a permanent staff member at Los Alamos for several years before joining the faculty at UC Davis in 2008. He has published over 100 papers on NMR studies of the physics of correlated electron systems.

Abstract:

Correlated electron materials exhibit a rich spectrum of unusual ordered states at low temperature, including magnetism, superconductivity, and other exotic ground states. Often the ground state can be tuned by an external parameter such as pressure or field, and in some cases there exists a quantum phase transition that gives rise to a breakdown of conventional Fermi liquid theory in the disordered phase at high temperature. Nuclear Magnetic Resonance (NMR) is an ideal probe these materials because the nuclei offer a window into the microscopic electronic degrees of freedom via the hyperfine coupling. Furthermore, NMR can be performed under a broad range of extreme pressures, fields and temperatures, and is a microscopic in situ probe that does not perturb the electrons. Several examples of the power of this technique to study the phenomena of superconductivity, heavy fermion behavior, and inhomogeneous magnetism will be discussed.

Biography:

Abstract:

In this work the cooperative N2- effect is considered, that is the radiation whose power is ~ N2, where N is the number of emitters which in this case is equal to the number of nonlinear coupled oscillators which model the electrons in a bunch. We consider two different models: in first case the predicted effect is the result of combining two others, namely Gunn-effect in GaAs and undulator-like radiation which can be produced by means of microstructure with grating (microundulator). In the second case, suggested effect is in a sense similar to Dicke superradiance, however it is not the spontaneous phase coherence arising in the ensemble of two-level atoms interacting via the emitted electromagnetic field, but rather, the result of interplay of another two effects. The first one is the ’pumping wave’ acting on the electrons and which is the result of undulator field, while the second is the backward effect of radiation which is produced by electrons moving within such microundulator. As a result, the specific phase coherence (’synchronization’) develops in the ensemble of emitters and they start to generate as a single oscillating charge Ne, while the power of emitted radiation becomes ~N2. It is very probable, that the effect can be used for the developing of a new semiconductor-based room temperature source of the GHz and THz-radiation.

Biography:

Myung Joon (MJ) Han received B.S and Ph.D degree from Seoul National University in 2001 and 2007, respectively. Before coming back to Korea in 2012, he spent his postdoc period in UC Davis, Columbia University, and Argonne National Lab. He is now an assistant professor in Department of Physics, KAIST.

Abstract:

Recently Sr2IrO4 has attracted considerable attention due to the intriguing interplay between spin and orbital degrees of freedom, and its manifestation in the material characteristics. Along this line I will present our recent progress on the iridium oxide and other related compounds based on 4d-/-5d- transition metals. The first example is Rh-doped iridate, Sr2Ir1-xRhxO4, for which the doping dependent metal-insulator transition (MIT) has been reported experimentally and the controversial discussion developed regarding the origin of this transition [1]. We tried to suggest a new picture for understanding the MIT. The second is the artificially-structured iridate superlattice, SrIrO3/SrTiO3. The electronic structure change caused by the interface and the strain was examined in detail and compared with the optical spectra [2]. Finally, I will introduce a fairly different family of compounds, GaT4X8 (T=Nb, Mo, Ta, and X=Se,Te). Interesting similarities with Sr2IrO4 suggests a new possibility for the novel ground states in this series of compounds.

Biography:

A F Isakovic graduated from University of Minnesota in 2003,with thesis on spin transport, after which he joined Cornell University as a Postdoc, studying mesoscopic transport in charge and spin density wave materials. In 2006, he moved to Brookhaven National Laboratory, where his main focus was development of nanofocusing X-rayoptics. He joined Khalifa University, a start-up research university in Abu Dhabi in 2010, where he founded Group for Spintronics, Nanophotonics and Complex Systems, and where he serves as a coordinator for Core Nanocharacterization Facilities.

Abstract:

Minimal energy electronic systems (MEES) have attracted significant attention in recent years due to the variety of fundamental and practical problems arising with the scale down of the components on a chip, broadly addressed via Moore’s law. The MEES design constraint is necessitated, among other processes,by the increase in the release of heat as the size of the active components decreases, which leads to the need to decrease the operating currents, for example. Regardless of the type of device (magnetic memory, electronic switch etc.), nanoelectronic and mesoscopic device physicists are confronted by the number of parameters that need to be optimized in order to minimize the energy (power) expenditure of the device without sacrificing the overall performance. Such problems often involve a number of parameters that make it intractable for nanofabrication and nanotechnology practitioners to cover in a short time scale, which forces the use of an extensive experimentation search combined with an educated guess. In this contribution, we show how a biologically motivated computing technique, such as Particle Swarm Optimization (PSO), can be used to speed up the process of optimal selection of the values of geometric (size) and physical parameters. Specifically, in two examples, we show how critical current needed to perform the switching operation of magnetic tunnel junction (MTJ) and thermoelectric emission current from an anowire could be optimized. A comparison of a computational output with nano-/mesodevice (MTJ or nanowire diodes) literature data shows a good agreement.

Biography:

Leonardo Degiorgi was awarded the title of Professor at ETH Zurich in 2005. He is Coordinator (Delegierter), Department of Physics, and he is head of the Optical Spectroscopy Group at the Laboratory for Solid State Physics. Magneto-optical investigation of strongly correlated systems and of novel materials with peculiar ground states is the main topic of his research activity.

Abstract:

We collect optical reflectivity data as a function of temperature across the structural tetragonal-to-orthorhombic phase transition at TS on Ba(Fe1−xCox)2As2 for x = 0, 2.5% and 4.5%, with uniaxial and in-situ tunable applied pressure in order to detwin the sample and to exert on it an external symmetry breaking field. At T < TS, we discover a remarkable optical anisotropy as a function of the applied pressure at energies far away from the Fermi level and very much reminiscent of a hysteretic-like behavior. Such an anisotropy turns into a reversible linear pressure dependence at T≥TS. Moreover, the optical anisotropy gets progressively depleted with increasing Cocontent in the underdoped regime, consistent with the doping dependence of the orthorhombicity but contrary to the non-monotonic behavior observed for the dc anisotropy. Our findings bear testimony for an important anisotropy of the electronic structure and thus underscore an electronic polarization upon (pressure) inducing and entering the nematic phase.

Biography:

Fengyuan Yang received his PhD in 2001 from The Johns Hopkins University. He is now an Associate Professor in the Department of Physics at The Ohio State University. He is the Chair of the Users Committee of the NanoSystems Laboratory (NSL) and the Associate Director of the Institute for Materials Research (IMR) at The Ohio State University. He has published more than 85 papers in peer-reviewed journals.

Abstract:

Spintronics relies on the generation, transmission, manipulation, and detection of spin current mediated by itinerant charges or magnetic excitations. Ferromagnetic resonance (FMR) spin pumping is a powerful technique in understanding pure spin current. Building on the high-quality Y3Fe5O12 (YIG) films grown by our sputtering technique and the large inverse spin Hall Effect (ISHE) signals enabled by these films, we have characterized spin currents in several classes of materials with different magnetic structures, including: Nonmagnetic (NM) metals, ferromagnetic (FM) metals, nonmagnetic insulators, and antiferromagnetic (AF) insulators. The spin Hall angles determined for a series of 3d, 4d, and 5d NM metals show that both atomic number and d-electron count play important roles in spin Hall physics. By inserting an insulating spacer of various materials between YIG and Pt, we are able to probe the mechanism of spin pumping and the spin propagation. Using several NM insulating spacers, we observed exponential decay of the ISHE voltages in YIG/spacer/Pt trilayers, demonstrating dominant role of exchange coupling in spin pumping. Strikingly, we achieved robust spin transport from YIG to Pt across AF insulators, which initially enhances the ISHE signals and can transmit spin currents up to 100 nm thickness, demonstrating highly efficient spin transport through an AF insulator carried by magnetic excitations.

Biography:

Dr. Lokendra Kumar has completed his Ph.D. at the age of 26 years from C.C.S. University, Meerut, India and postdoctoral studies from CSIR-National Physical Laboratory, New Delhi, India. He is the Assistant Professor of Physics, University of Allahabad (Govt. of India) where his work focuses on the physics of molecular materials and devices. Presently, he is working as a Raman fellow visiting scholar at the School of Electrical and Computer Engineering, Purdue University, USA on the stability issues of organic solar cell technology. He has published more than 40 papers in reputed journals and proceedings. He is serving as a reviewer of several journals

Abstract:

Organic semiconductors (OSCs) offer several potential advantages for the fabrication of low cost ‘Plastic Electronics’ such as Organic Light Emitting Diodes (OLEDs), Organic Photovoltaics (OPVs) and transistors. As Van der Waal’s solids, OSCs form disordered films that results in a large number of defects with in the energy band gap (Eg) which lead the overall photo-physics and performance of devices. Single layer, bilayer and bulk heterojuction (BHJ) OPVs architectures have been studied extensively, but the mechanisms by which these processes improve the devices remain subjects of ongoing debate. Therefore, the understanding of photo-physics is still an important point and needs more discussion. This talk includes, the defect induced optoelectronic properties and exciton physics of organic semiconductors (OSCs) for OPVs. In addition to improved power conversion efficiency, OPVs also need to be sufficiently stable in order to be commercially viable. Ambient atmosphere dependent photovoltaic parameters of OPVs shall be discussed1. Recently, we studied ZnPc/PTCDA bilayer devices2 and the role of nanostructuring of ZnPC surface on photovoltaic properties. It has been observed that nanostructured ZnPc surface in ZnPc/PTCDA bilayer devices shows a considerable improvement in short circuit current density (Jsc) and power conversion efficiency.

Biography:

Ido Kaminer is a Graduate of the Technion Excellence Program, receiving his Bachelor in both Electrical Engineering and Physics. He was granted the Knesset (Israeli Parliament) Award for outstanding undergraduate student achievements in 2007. He has completed his PhD degree in the Physics Department. In his dissertation, he discovered new classes of accelerating beams in nonlinear optics and electromagnetism, for which he received the 2012 Israel Physical Society Prize and the 2014 APS Award for Outstanding Doctoral Dissertation in Laser Science. He is currently a Marie Curie fellow at MIT working in the group of Prof. Marin Soljačić.

Abstract:

The past two decades showed a growing interest in shaping the spatial profile of optical beams by imprinting them with a phase singularity that gives them discrete values of orbital angular momentum. Recently this idea has led to shaping the quantum wavepacket of free electrons, imprinting them with orbital angular momentum and with other intriguing structures. The author show that by shaping wavepackets of relativistic free electrons, fundamental relativistic effects such as length contraction and time dilation can be engineered, leading to the exciting possibility of extending the lifetime of decaying particles. When interacting with matter, the author show how specially designed electron wavepackets create a new kind of ÄŒerenkov radiation, significantly deviating from the conventional ÄŒerenkov Effect. Some of these effects remain even in the classical limit, without requiring a special design of the wavepacket, proving that the well-established ÄŒerenkov Effect contains new phenomena arising directly from the quantum nature of the charged particles. Finally, the author discusses novel phenomena that occur when electrons interact with photons in novel nanophotonic structures. These interactions can lead to novel physical phenomena such as new types of radiation, coherent x-ray sources, and improved detectors for high-energy physics experiments.

Biography:

Hideo Kaiju received his PhD from Keio University in 2005. During the Doctoral course, he worked as a Research Fellow of the Japan Society for the Promotion of Science (JSPS). He worked as a Research Associate from 2004-2007 and an Assistant Professor from 2007-2013 in Research Institute for Electronic Science (RIES) at Hokkaido University. From 2009-2013, he also worked as a Precursory Research for Embryonic Science and Technology (PRESTO) Researcher of Japan Science and Technology Agency (JST). From 2013 to the present, he worked as an Associate Professor in RIES at Hokkaido University. He has published more than 45 papers, including original and review articles. He also received academic awards, including Keio Engineering Society Award in 2000, Applied Physics and Physico-Infomatics Award in 2002, Matsumoto-Hadori Award in 2007, and MRS Best Poster Presentation Award and MSJ Young Scientist Award in 2014.

Abstract:

Recently, we have proposed a new method for the fabrication of nanoscale junctions utilizing thin-film edges. In this method, the edges of two metal thin films are crossed, and molecules, metal-oxide, etc. are sandwiched between their two edges. The junction area is determined by the film thickness, in other words 10 nm thick films could produce 10×10 nm2 nanoscale junctions. This method offers a way to overcome the feature size limit of conventional optical lithography. Moreover, novel spintronics devices, such as large magnetoresistance devices and spin-filter devices, could be created when magnetic materials are used as metal thin films. In this presentation, we report the detail fabrication technique for nanoscale junctions and discuss the structural and electrical characteristics in various nanoscale junctions. The results include the observation of ohmic characteristics in Ni/Ni devices, nanoscale tunneling phenomena in Ni/NiO/Ni devices, and the ballistic regime of nanoscale molecules in Ni/P3HT:PCBM/Ni devices. Moreover, we report ongoing spintronics devices utilizing stray magnetic fields as a new type of spin-filter device. This device consists of inorganic complexes or quantum dots (QDs) sandwiched between two crossed edges of magnetic thin films. In this structure, a high magnetic field could be locally generated in the inorganic complexes or QDs due to the contributions of the stray field from both edges of the magnetic thin films. Since a large magnetic field produces a large Zeeman effect, energy splitting of the inorganic complexes or QDs can be enhanced. Therefore, a large spin-filter effect can be expected. In this talk, we will focus on the structural and magnetic properties in our proposed nanoscale spintronics devices.

Biography:

KK has completed his Ph.D from TU Berlin working a the Hahn-Meitner Institut, Berlin. He joined the Institute for Solid State Physics of the University of Tokyo as an assistant professor and became a professor in 1997. He was the Director General of the QuBS Directorate at the JAEA until 2014 and now serves as a Senior Consultant in the QuBS Center, JAEA.

Abstract:

The recent development of neutron scattering techniques, especially polarized neutron scattering utilization, will be reported with examples from the recent investigations on mutiferroic materials. The recent discovery of the spin-driven ferroelectricity triggered intense exploration of new multiferroic materials and research of the novel magneto-electric effect in condensed matter. In studying these advanced functional materials, one is permanently confronted with complex spin configurations, for example, non-collinear, incommensurate magnetic structure such as helimagnetic or cycloidal spin structure as a result of frustrated magnetic interactions. Since the giant functional responses in these materials are direct consequences of these complex magnetic structures breaking the inversion symmetry, the detailed knowledge of the spin structure is mandatory to understand the essence of these advanced magnetic functional materials. More recently an electric-dipole-active magnetic excitation, often termed as electromagnon, has been observed in these multiferroic materials. The polarized neutron technique, in addition to the conventional unpolarized neutron scattering, can greatly contribute to obtain deep insight into these complex spin structures and excitations. The examples include investigations on ferroelectricity induced by a proper screw-type helical spin ordering in Ga-doped CuFeO2 and electromagnon in the Y-type hexaferrite Ba2Mg2Fe12O22 with transverse conical spin structure. These investigations were performed in collaboration with S. Wakimoto and M. Takeda, Quantum Beam Science Center, Japan Atomic Energy Agency, Japan; T. Nakajima, T. Arima, Y. Taguchi, Y. Tokunaga, Y. Kaneko and Y. Tokura, Center for Emergent Matter Science, RIKEN, Japan, N. Terada and H. Kitazawa, National Institute for Materials Science, Japan; S. Mitsuda, Dep. of Physics, Tokyo University of Science, Japan; S. Ishiwata, Department of Applied Physics, University of Tokyo, Japan; D. Okuyama, IMRAM, Tohoku University, Japan ; M. Matsuda and J. Fernandez-Baca, Quantum Condensed Matter Division, Oak Ridge National Laboratory, USA.

Biography:

Abstract:

The 1H spin-lattice and spin-spin relaxation time as well as high data point density 1H–31P cross-polarization kinetics (static and upon MAS) measurements have been carried out for calcium hydroxyapatite containing amorphous phosphate phase (ACP-CaHA) and nano-structured hydroxyapatite (CaHA). The chosen setting of the sampling frequency of 5×104 s–1 allowed to reveal all spin interactions having the dipolar splitting b£25 kHz that in the case of 1H–31P interaction means the structures with the internuclear distances r³0.125 nm could be resolved. The advanced processing of CP MAS kinetic data has been developed introducing the variable cut-off distribution of the dipolar coupling. This procedure allows to describe the oscillatory kinetics and CP curves in nano-structured materials over a wide range of contact time and to determine the characteristic size profile and composition of the spin clusters. The characteristic size of 31P–(1H)n spin nano-cluster being within 0.3¸0.5 nm has been determined for nano-structured CaHA. The 1H spin-lattice and spin-spin relaxation time measurements revealed the fast spin motion takes place in ACP-CaHA. The effect of MAS rate on the 31P signal shape confirms that the correlation time of this motion gets into the time scale of microseconds or even nanoseconds. Such fast dynamics can be attributed to the rotational diffusion of adsorbed water molecules. The magnitude of the inhomogeneous anisotropic broadening of 1220±20 Hz determined for nano-structured sample is very close to 1185 Hz that corresponds to the maximum of Gauss distribution of dipolar 1H–31P coupling obtained using 31P–1H CP MAS kinetics. The dynamics of this interactions runs in the time scale of microseconds and it is much slower that in ACP-CaHA.

Biography:

N Foy is actually completing his PhD thesis dedicated to the theoretical, numerical and experimental studies of the contact between metallic bodies under severe mechanical compression, paying a special attention to their applications to railway transport (power supply-train propulsion).

Abstract:

Many industrial applications, such as power transfer systems for train propulsion or mechanical contact between solid surfaces, involve multi-contact interfaces (MCI). This challenging field has attracted the attention of many researchers and engineers attempting to build a complete and coherent description of such interfaces. This field offers a natural framework for complexity studies since MCI involve both tribological, mechanical and physical processes intimately intricated at different scales. Through the strong coupling between different classes of properties, that complexity is also the main obstacle towards a comprehensive understanding of the Physics of MCIs. In accordance with the common trends in the field, we propose a theoretical approach to the electrical transport through metallic MCIs, treated as a discrete collection of a large but finite number of contacting asperities (mechanical spots due to surface roughness), and taking into account its natural coupling with thermal transfer. A first one-spot model is derived, leading to the temperature (current) dependence of the constriction resistance of individual spots. We predict a critical current depending on the spot size and thermal conductivities of the metal pieces and controlling the transition to a highly resistive state of the interface. Extension of the model to a many spots interface is briefly discussed. The results are finally confronted with experimental data regarding a two-bead system revealing a very good agreement with the model. Implications of the model on the mechanism of the so-called Branly effect are also discussed along with the likely influence of tunneling between the contacting solids.