NEWS: During the spring 2020 semester, the Long Island Condensed Matter Social Distancing Journal Club will replace most seminars.
Journal Club events will be posted on this calendar and take place via Zoom. To join the mailing list and get the link, email Mengkun Liu (first email@example.com)
The CQM Distinguished Lecture series has been established in the Fall of 2015 to bring to Stony Brook University the renown experts in the physics of quantum matter.
September – November 2019
Title: Structure Inference from X-ray Absorption Spectroscopy: Pilot Projects for Operando Experimentation
host: Phil Allen
abstract: X-ray Absorption Near Edge Structure (XANES) is well-adapted for in situ and operando experiments. It is both atomically specific and it encodes local structure of the surrounding atoms. Due to multiple scattering effects, inferring that structure from the spectra can be complex. In the Center for Functional Nanomaterials, we are pursuing several prototype projects with collaborating groups to explore approaches to solve this inverse problem and pursue nanomaterials research enabled by these methods. We seek to go beyond the empirical fingerprint method, particularly to broaden applicability to structural motifs that emerge in studies of new or nanostructured materials. Our over-arching approach is two-fold: exploit theory for direct computation of XANES spectra for a pertinent database of material structures to support and train data analysis techniques; develop and validate these techniques through comparison to experiments. Following a brief introduction of operando experimental techniques and the role of X-ray absorption spectroscopy, I will describe a series of pilot projects [1-3] that illustrate different aspects of structure inference, including the training of artificial neural network models.
Work performed in part at the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.
 J. Timoshenko, et al., J. Phys. Chem. Lett. 8, 5091 (2017).
 M. R. Carbone, et al., Phys. Rev. Mater. 3, 033604 (2019).
 D. Yan, et al., Nano Lett. 19, 3457, (2019).
Brief Biography: Mark S. Hybertsen holds a BA in Physics from Reed College in Portland, OR (1980) and a PhD in Physics from The University of California, Berkeley (1986) where his thesis research was directed to many-body perturbation theory and the GW approach. Dr. Hybertsen joined Bell Laboratories in 1986, pursuing a variety of research projects in the theory of the electronic properties of materials. He supervised the Device and Materials Physics Group in the Semiconductor Photonics Research Department for four years. From 2003 to 2006, Dr. Hybertsen was a Senior Research Scientist in the Department of Applied Physics and Applied Mathematics at Columbia University in New York, where he has also been an Adjunct Professor in the Department of Electrical Engineering. In 2006, Dr. Hybertsen joined the new Center for Functional Nanomaterials at Brookhaven National Laboratory. He is a Senior Scientist, leading the Theory and Computation Group. He has also had adjunct research appointments at Columbia University. Dr. Hybertsen is a fellow of the American Physical Society and a member of the IEEE and the American Chemical Society.
Title: First observations of topological phonons in crystalline materials
Host: Jen Cano
Condensed matter systems have now become a fertile ground to discover emerging topological quasiparticles with symmetry protected modes. While many studies have focused on fermionic excitations, the same conceptual framework can also be applied to bosons yielding new types of topological states. This idea has, for example, been applied to great effect in macroscopic waveguides. Motivated by the application of these ideas to naturally occurring crystal lattices, we used inelastic x-ray scattering to make the first observation of topological phonons . We demonstrate that new classes of topological crossing can be accessed in this way, such as “Double Weyl” crossings in FeSi and parity-time symmetry protected helical nodal lines in MoB2. Phonon band structures thus provide compelling new playgrounds for exploring topological properties and I will discuss how they differ from the well-studied electronic band structures from this perspective. I will end by speculating how this might be useful in the future.
H. Miao, T. T. Zhang, L. Wang, D. Meyers, A. H. Said Y. L. Wang, Y. G. Shi, H. M. Weng, Z. Fang, and M. P. M. Dean, Phys. Rev. Lett. 121, 035302 (2018)
 T. T. Zhang, H. Miao, Q. Wang, J. Q. Lin, Y. Cao, G. Fabbris, A. H. Said, X. Liu, H. C. Lei, Z. Fang, H. M. Weng, and M. P. M. Dean, submitted (2019)
Title: Synchrotron Multi-Dimensional & Multi-Modal Study of Functional Materials
Host — Phil Allen
Abstract: Multi-modal and multi-dimensional characterization at synchrotrons can provide unprecedented information for complex, heterogeneous materials system. A multi-modal approach combines multiple synchrotron techniques to gain complementary information. Furthermore, with imaging techniques specifically, multi-dimensional imaging includes techniques such as tomography, spectroscopic microscopy, or in situ/operando imaging. These capabilities are particularly powerful when used to study complex structures with morphological and chemical heterogeneity. This talk will address the applications in nano-/meso-porous and bicontinuous metals, energy storage and conversion materials, and molten salts research. Broader impacts regarding cultural heritage and environmentally friendly anti-corrosion surface treatment will also be briefly discussed
host: Jin Wang
Mechanistic Basis of Spindle Size Control and Scaling
The size and morphology of intracellular structures such as the nucleus, Golgi apparatus, and mitotic spindle dramatically vary between different cell types, yet the mechanisms that regulate the size of these structures are not understood. Interestingly, the size of most intracellular structures scales with cell size, i.e., larger cells tend to have a larger nucleus and spindle. So far, many models have been proposed to explain such scaling behavior, but rigorous testing of these models inside the cells is challenging, and often not feasible. To overcome this challenge, we combined the statistical framework of quantitative genetics, with cell biology and biophysics to develop a general methodology to quantitatively examine different models of spindle size control and scaling for the first mitotic spindle in C. elegans. We developed a high-throughput microscopy platform to measure the size and dynamics of the spindle for ~200 genotyped recombinant inbred lines, which are created by the random crossing of two genetically distinct C. elegans wild isolates. We observed quantitative variations for all attributes of spindle size and dynamics, as well as cell size, across these lines. We used these variations to discriminate between different models of spindle size regulation and scaling, and we proposed a new model based on the effect of cortical forces on spindle elongation. To further examine our model, we used laser ablation technique to selectively cut different populations of microtubules and compared the results with predictions of the model. The combination of quantitative genetics with cell biology and biophysics provides a systematic and unbiased method to study mechanisms that contribute to size regulation of intracellular structure and also will give us a deeper understanding of the evolution of these structures.
Two-dimensional isotropic fluids can possess an anomalous part of the viscous stress tensor known as odd or Hall viscosity. This peculiar viscosity does not lead to any dissipation in the fluid. Examples of fluids with odd viscosity include rotating superfluids, plasmas in magnetic fields, quantum Hall fluids, and chiral active fluids. I will describe some manifestations of the odd viscosity. In particular, I will focus on surface waves propagating along the boundaries of such fluids. I will also present a variational principle and the corresponding Hamiltonian structure for fluid dynamics with odd viscosity.
Title: Heat conduction in defective and complex crystals: phonon scattering and beyond
* Material Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
* Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
The flow of heat through materials is a topic of scientific interest and technological importance in fields of microelectronics, power generation, heat management, and thermoelectrics. For example, advancement in microelectronic technologies (e.g. microprocessors, and high-power electronics) demands ever more efficient removal of the heat generated in these devices. In contrast, technologies such as thermal barrier coatings and thermoelectric materials are designed to stop the flow of heat. In simple, defect-free crystals the thermal conductivity is generally well understood. However, in materials containing defects and/or in those with very complex crystal structures there is a lack of basic understanding which inhibits technological progress.
In this presentation, I will highlight several experimental and theoretical results which aim to establish a fundamental understanding of heat transport in defective materials. First, I will discuss several studies related to heat conduction across interfaces. Secondly, I will demonstrate in several material systems how defects can soften a materials lattice which reduces the phonon group velocity and thus decreases thermal conductivity. Lastly, the transition from crystalline-like to amorphous-like thermal conduction is investigated by studying the lattice dynamics of crystals with very complex crystal structures both computationally and experimentally. Through this analysis emerges a description of phonon transport which is divided between two channels. One is the standard phonon-gas transport mechanism and the other we term the diffuson-channel since it is mathematically the same mechanism in which ‘diffusons’ were defined.
Title: Optical Control of Chiral Charge Pumping in a Topological Weyl Semimetal
host: Dima Kharzeev
host: Laszlo Mihaly
1. Lee, M. M. et al.,Science 338, 643-647 (2012).
2. see reports of the Gaetzel and Hagfeldt groups
3. Horvath et al., Nano Letters 14, 6761, (2015)
4.Spina et al., (2016) Scientific Reports, 6, 1
5.Spina et al., (2015) Small, 11, 4823 ; Spina et al., Nanoscale, 2016, 8, 4888
6.Nafradi et al., J. Phys. Chem. C 2015, 119, 25204
host: Phil Allen
title: Carrier lifetime effects on thermoelectric efficiency
Recent developments in electronic structure algorithms based on the Wannier function interpolation of electronic wave functions have enabled accurate first-principles calculations of electron-phonon interactions and intrinsic carrier lifetimes in the relaxation time approximation. This has supplied the final missing piece of the puzzle for predicting the thermoelectric figure of merit zT=s S2 T/k, where the conductivity s, the Seebeck coefficient S, and the total thermal conductivity k now can all be obtained from the density-functional theory (DFT). This opens up exciting possibilities for theoretically understanding and reliably predicting new materials with high values of zT. We will review several examples from our recent work, including a Li-intercalated analogue of lead telluride (Li2TlBi), an intermetallic compound with unexpectedly high value of S (CoSi), and a theoretically predicted full Heusler compound with ultrahigh zT (Ba2BiAu). General factors for high thermoelectric power factors in these compounds include energy dependence of carrier lifetimes for high S, high degeneracy of carrier pockets at the Fermi level, weak electron-phonon scattering for high mobility, and concomitantly low Lorentz numbers for low electronic thermal conductivity.
Title: Emergent Phenomena at the Interface of Complex Oxides
Host: Cyrus Dreyer
Progress in epitaxial growth of complex oxides have led to heterostructures with exquisite physical phenomena, such as the formation of a high-density two-dimensional electron gas (2DEG) at the interface between two normally insulating materials—e.g. SrTiO3/LaAlO3. Superconductivity and magnetic ordering have been demonstrated in these systems, sparking the interest in novel device applications. The formation of a 2DEG at the interface between SrTiO3 and Mott insulators, such as GdTiO3, has also been demonstrated, with electron densities that are over an order of magnitude higher than those realized with conventional semiconductors. Charge transport in these systems exhibit intriguing behavior, varying drastically from metal to insulator depending on the thickness of the building-block layers. Intensive research efforts in the last decade have raised questions regarding the origin of the excess charge, the mechanisms that determine the density of the 2DEG, and fundamental properties of the 2DEG. In this presentation, we will discuss how computer simulations can provide insights into the origin and nature of the 2DEG. Based on results of first-principles calculations we will discuss electron correlation effects and how the electronic structure of these heterostructures can be drastically altered, turning from metallic into insulating, through charge localization in ultrathin layers. Finally, we will address the interplay between orbital, charge, and spin in the manipulation of the magnetic ordering observed in some of these heterostructures.