CENTER FOR QUANTUM MATERIALS AND CONDENSED MATTER PHYSICS SEMINARS

 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 name.lastname@stonybrook.edu)

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.

The lectures in this series will attract a broad audience of physicists from SBU and BNL,
and SBU graduate students.
Apr
10
Fri
Igor Zaliznyak (BNL) — ZOOM SEMINAR
Apr 10 @ 1:30 pm – 2:30 pm

Title: Negative thermal expansion and entropic elasticity in ScF3 type empty perovskites

While most solids expand when heated, some materials show the opposite behavior: negative thermal expansion (NTE). NTE is common in polymers and biomolecules, where it stems from the entropic elasticity of an ideal, freely-jointed chain. The origin of NTE in solids had been widely believed to be different, with phonon anharmonicity and specific lattice vibrations that preserve geometry of the coordination polyhedra – rigid unit motions (RUMs) – as leading contenders for explaining NTE. Our neutron scattering study of a simple cubic NTE material, ScF3, overturns this consensus [1]. We observe that the correlation in the positions of the neighboring fluorine atoms rapidly fades on warming, indicating an uncorrelated thermal motion, which is only constrained by the rigid Sc-F bonds. These experimental findings lead us to a quantitative, quasi-harmonic theory of NTE in terms of entropic elasticity of a Coulomb floppy network crystal, which is applicable to a broad range of open framework solids featuring floppy network architecture [2]. The theory is in remarkable agreement with experimental results in ScF3, accurately describing NTE, phonon frequencies, entropic compressibility, and structural phase transition governed by entropic stabilization of criticality. We thus find that NTE in a family of insulating ceramics stems from the same simple and intuitive physics of entropic elasticity of an under-constrained floppy network that has long been appreciated in soft matter and polymer science, but broadly missed by the “hard” condensed matter community. Our results reveal the formidable universality of the NTE phenomenon across soft and hard matter [1,2].

[1] D. Wendt, et al., Sci. Adv. 5: eaay2748. (2019).
[2] A. V. Tkachenko, I. A. Zaliznyak. arXiv:1908.11643 (2019).

Host: Sasha Abanov

Apr
17
Fri
JOURNAL CLUB: Yuan Fang, Sahal Kaushik, and Evan Phillip (Stony Brook University)
Apr 17 @ 10:00 am – 11:00 am

We will have three student APS-style talks:

1) Yuan Fang: Higher-order topological insulators in antiperovskites https://arxiv.org/abs/2002.02969

2) Sahal Kaushik: Chiral terahertz wave emission from the Weyl semimetal TaAs: https://www.nature.com/articles/s41467-020-14463-1

3) Evan Phillip: Chiral magnetic photocurrent in Dirac and Weyl semimetals: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.99.075150

Host: Mengkun Liu

Link to slides; link to video

Apr
24
Fri
JOURNAL CLUB: Qiang Li and Chris Homes (Brookhaven National Lab)
Apr 24 @ 10:00 am – 11:00 am

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

Link to video:
Link to slides:
May
1
Fri
JOURNAL CLUB: Dr. Yinming Shao (Columbia University) and Prof. Xu Du (Stony Brook University)
May 1 @ 10:00 am – 11:00 am
Yinming Shao: Electronic correlations in nodal-line semimetals
Xu Du will talk about his recent work on QH antidot and on-going work on superlattice potential.
May
8
Fri
JOURNAL CLUB: Phil Allen (SBU)
May 8 @ 10:00 am – 11:00 am

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.

Links to slides and video

 

May
15
Fri
JOURNAL CLUB: Cyrus Dreyer (SBU)
May 15 @ 10:00 am – 11:00 am

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.

Links: video and slides

May
22
Fri
Dr. Manuel Zingl (Flatiron Institute)
May 22 @ 1:30 pm – 2:30 pm
Recent theoretical and experimental insights on the normal state properties of Sr2RuO4
The fascinating physics of strongly-correlated materials is often governed by the interplay of several factors of various strength. These are, for example, the bare band width, the Coulomb interaction, the Hund’s coupling, spin-orbit coupling, and band structure details like van Hove singularities. In this talk, I will discuss recent experimental and theoretical insights on Sr2RuO4 which reveal how these factors interplay and shape the properties of this exemplar quantum material. Additionally, I will show that in Sr2RuO4 the self-energies extracted directly from high-resolution photoemission data strongly support the notion of dominantly momentum-independent self-energies; an assumption made within the dynamical mean-field theory (DMFT). This result is of fundamental importance as the combination of ab-initio electronic structure theory and DMFT has become a powerful tool to model, explain, and predict the properties of strongly-correlated materials in a qualitative and quantitative way.

Host: Cyrus Dreyer

May
29
Fri
Ken Burch (Boston College)
May 29 @ 10:00 am – 11:00 am
Probing Nontrivial Topology with Nonlinear Optics and 2D Heterostructures
Abstract: A key challenge in condensed matter is measuring the non-trivial topology responsible for novel phases. In this talk I will outline our recent efforts to reveal non-trivial topology with nonlinear optics and tunneling spectroscopy. First I will focus on our efforts to use nonlinear optics to measure the Berry connection in the Weyl semimetal TaAs. Specifically using new FIB fabricated mesoscopic devices we have succeeded in measuring photocurrents at room temperature associated with the electron chirality and Berry curvature. I will briefly touch on how these experiments offer hope for using Weyl semimetals for power generation and optical detection. In the second half I will discuss recent development in the study of FeTeSe, and in particular our 2D atomic heterostructures that reveal evidence for the unique higher order, superconducting topological state.
Links to slides and talk
Host: Mengkun
Jun
5
Fri
JOURNAL CLUB: Matt Dawber (SBU)
Jun 5 @ 10:00 am – 11:00 am

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.

Jun
12
Fri
JOURNAL CLUB: Dr. Kevin Cremin (UCSD) and Jeremy Lee-Hand (SBU)
Jun 12 @ 1:30 pm – 2:30 pm
Two talks!
1:30 pm -2:00 pm: Kevin Cremin (postdoc in Richard Averitt’s group at UCSD)
“Photo-enhanced metastable c-axis electrodynamics in stripe-ordered cuprate La_{1.885}Ba_{0.115}CuO_4″
The emergence of superconductivity in high-temperature cuprates arises out of a rich landscape of competing order. For example, stripe order can hoard the electrons needed to form Cooper pairs and establish superconductivity. Intriguingly, the complex interactions of such intertwined orders can be manipulated with light, where nonequilibrium dynamics alter the primacy of one order over another. Following photoexcitation of La2−xBaxCuO4 (x = 0.115) with near-infrared pulses, we observe a long-lived state that exhibits enhanced superconducting correlations well above the equilibrium superconducting transition temperature. Our analysis reveals that this metastable phase arises from a collapse of stripe order, providing an important demonstration of light-directed control in quantum materials.
2:00 pm -2:30 pm: Jeremy Lee-Hand (Ph.D. student in Cyrus Dreyer’s group)
First-principles study of molybdinate perovskite oxides
Perovskite oxides have a characteristic ABO3 structure that is able to accommodate a large number of different cations in the A and B locations. A relatively recently fabricated class of perovskites, are the molybdinates with B = Mo. We use first-principles calculations based on density-functional theory (DFT) plus Hubbard U to investigate the family of perovskite molybdenates: SrMoO3, PbMoO3, and LaMoO3 in order to determine their ground-state atomic and magnetic structures. We determine the dependence with the choice of U and interpret the ground-state structures in terms of unstable phonon modes.