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.
April – June 2020
Qiang Li (Brookhaven National Lab): Light-Driven Raman Coherence as a Nonthermal Route to Ultrafast Topology Switching in a Dirac Semimetal: https://journals.aps.org/prx/pdf/10.1103/PhysRevX.10.021013.
BNL/Ames Lab joint PR: https://www.bnl.gov/newsroom/news.php?a=117158
Chris Homes (Brookhaven National Lab): Optical conductivity of the type-II Weyl semimetal TaIrTe4 https://arxiv.org/abs/2004.00147
Host: Mengkun Liu
Title: Electrons, Phonons, and their interactions
Abstract: This talk is NOT a “journal club” discussion of a development in progress. Instead, it is a tutorial. To make partial amends for this lapse, I will emphasize my view of the evolving boundary between well-understood aspects and confusions that still need analysis. Landau gave us permission to think of “quasiparticles” as “real”. To understand the low energy properties of matter, we are supposed to analyze the quasiparticle distribution function. The boundary between fully understood quasiparticle theory and more complicated realities has always been fuzzy, and changes in time. Quasiparticle ideas help guide thinking in areas such as amorphous solids and strongly correlated systems (i.e.”bad metals”) where quasiparticles are obscure at best. In Mengkun’s memorable words, this is a “cruel discussion about the dying research fields”, and why sometimes they refuse to die.
Title: Flexoelectricity in 2D materials
Abstract: Flexoelectricity refers to the generation of electrical polarization in a material with the application of a strain gradient. It is a universal effect in all insulating materials regardless of symmetry and iconicity; however since the magnitude of the effect depends on the size of the strain gradient, it is most relevant in nanostructures where significant strains may be relaxed over relatively short distances. In particular two-dimensional layered materials are interesting in the context of flexoelectricity since interesting strain states may be applied. In this talk I will introduce how we can understand the flexoelectric effect from an atomistic perspective, and, via the example of BN, how this effect manifests itself in 2D materials.
Host: Cyrus Dreyer
Unlocking the secrets of growth and switching in ferroelectric multilayers using synchrotron x-ray diffraction
Powerful new capabilities at the NSLS-II synchrotron at Brookhaven National Laboratory have enabled us to perform a series of in-situ experiments that have allowed us to unlock important secrets about the growth and switching processes in ferroelectric multilayers. In one set of experiments, at 4-ID, the In-Situ and Resonant scattering beamline (ISR), we perform x-ray diffraction during growth of sputtered ferroelectric multilayers and reveal that not only is the polarization intricately linked to crystal structure, also plays an important role in the growth process, influencing growth rates, relaxation mechanisms, electrical properties and domain structures. In a complementary set of experiments on the 11-ID, Coherent Hard X-Ray scattering (CHX) beamline, the high coherent flux at this beamline allows us to perform X-Ray Photon Correlation Spectroscopy measurements that monitor correlations between ferroelectric domain configurations as they are influenced by temperature and electric field stimuli. This method gives us an unprecedented view of the nanoscale arrangement of domains as a statistical ensemble as they are driven through thermal relaxation or switching events. Taken together, and combined with the extensive complimentary characterization we perform in our laboratory these experiments provide an unprecedented end-to-end window on to how strain, polarization and domain structure evolve into the complex configurations that generate much of the interest in these exciting materials.
Quantum Coherence and Dynamics Controlled by Light:
From Higgs Bosons to Chiral Fermions
Department of Physics & Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, IA 50011, USA
Revolutionary properties of quantum materials are often manifestations of coherence and entanglement, e.g. it exists between the Cooper pairs in high-temperature superconductors (SCs); it protects chiral charge transport from disorder scattering in topological states of matter (TSM). The recent development of ultrafast and terahertz (THz) spectroscopy tools facilitates discovering and understanding driven coherent systems involving SCs and TSM controllable by light. In this talk, I will discuss strategic advantages, with help of some recent examples, of implementing this approach to probe and control many-body quantum phases and collective modes by light-driven coherence, e.g., light-induced gapless superconductivity and high harmonics generation , forbidden Anderson pseudo-spin precessions , hidden gapless quantum fluid , hybrid Higgs modes , spin exciton modes , phonon-controlled topology switching [6, 7] and chiral charge pumping …. We argue that the light-driven coherence and sub-cycle dynamic symmetry breaking demonstrated in these work revealed represent universal principles for emergent materials discovery and light-matter quantum control for quantum information science.
 X. Yang, et al., Nature Photonics. 13, 707 (2019)
 C. Vaswani et al., Phys. Rev. Lett. arXiv:1912.01676 (2020)
 X. Yang, et al., Nature Materials. 17, 586 (2018).
 C. Vaswani, et al., submitted (2020)
 X. Yang, et al., Phys. Rev. Lett. 121, 267001 (2018)
 C. Vaswani, et al., Phys Rev X 10, 021013 (2020).
 X. Yang, et al., npj Quantum Materials 5, 13 (2020).
 L. Luo et al., submitted (2020)