During Fall 2020, seminars will be posted on this calendar and take place via Zoom. To join the mailing list and get the link, email Jennifer Cano (first firstname.lastname@example.org)
The CQM Distinguished Lecture series has been established in the Fall of 2015 to bring to Stony Brook University the renowned experts in the physics of quantum matter.
February – May 2020
“Exploring Quantum Materials with Atomic Qubit Sensor”
We are witnessing a revolution in which quantum phenomena are being harnessed for next-generation technology. In this context, atomic qubits associated with defects in solids, such as nitrogen-vacancy (NV) centers in diamond, provide versatile building blocks for quantum technologies due to their optical addressability, atomic size, and excellent coherence. Among the applications being explored with such platform, quantum sensing technology realized with NV centers has emerged as a powerful probe of quantum materials. Due to its ability to sense magnetic field with high spatial resolution over wide temperature and dynamic range, NV sensors enable the exploration of condensed matter phenomena in parameter space inaccessible to existing probes. In this talk, I will discuss our application of NV quantum sensing technology to study correlated electronic and spin phenomena. We have directly imaged, for the first time, the viscous Poiseuille flow of the Dirac fluid in neutral graphene, a finding that holds implications for other strongly correlated electrons such as those in high-Tc superconductors. Enabled by the NV platform, we have developed new capabilities for probing coherent spin-waves, which can be applied to study novel magnetic materials and spintronic devices, and a technique for characterizing low-dimensional high-Tc cuprates without electrical contacts. Looking forward, I will highlight opportunities for advancing the frontiers of quantum materials and quantum technology enabled by NVs and other solid-state atomic qubits.
Non-volatile quantized states are ideal for the realization of classical Boolean logics. Abrikosov vortex represents the most compact magnetic object in superconductors with the size determined by the London penetration depth ~100 nm. Therefore, it can be utilized for creation of high-density digital cryoelectronics. In this talk we will describe operation of memory cells, in which a single vortex is used as an information bit . The vortex is pinned at a nano-scale trap and is read-out by a nearby Josephson junction [2,3]. Unlike SQUID-based memory cells, such cells have non-degenerate 0 and 1 states, which greatly simplify the device architecture. Furthermore, SQUID-based devices have a problem with increasing write current upon decreasing the SQUID loop size, preventing a straightforward miniaturization. To the contrary, write current for a vortex is determined by the depinning current density and, therefore, scales with the size. All together this allows simple miniaturization down to sub-micron sizes. We demonstrate that vortex memory cells have a high-endurance operation, are characterized by an infinite magnetoresistance, do not require external magnetic field, have a short access time, and a low write energy. Non-volatility and perfect reproducibility are inherent for such devices due to the quantized nature of the vortex. We argue that vortex-based memory can be used in superconducting digital supercomputers.
 T. Golod, A. Iovan, and V. M. Krasnov, Nat. Commun. 6, 8628 (2015).
 T. Golod, A. Rydh, and V. M. Krasnov, Phys. Rev. Lett. 104, 227003 (2010).
 T. Golod, A. Pagliero, and V. M. Krasnov, Phys. Rev. B 100, 174511 (2019).
Acknowledgements: The work was done in collaboration with Taras Golod, Adrian Iovan, Alessandro Pagliero, Olena Kapran and Lise Morlet-Decarnin. The work was supported by the European Union H2020-WIDESPREAD-05-2017-Twinning project SPINTECH under Grant Agreement No. 810144.
Vladimir Krasnov has graduated from Moscow Institute of Physics and Technology in 1990. He completed his PhD in 1995 from the Institute of Solid State Physics, Chernogolovka, Russia and postdoctoral studies from Danish Technical University and Chalmers University of Technology, Sweden. Since 2005 he is professor and head of the Experimental Condensed Matter Physics group at the Department of Physics, Stockholm University.
Supersymmetry method for interacting chaotic and disordered systems: the SYK model
The supersymmetry method was originally developed for studies of quantum phenomena in non-interacting disordered and chaotic systems.
I will report a step forward in this direction and develop the supersymmetry method for the Sachdev-Ye-Kitaev (SYK) model and other similar 0+1 dimensional interacting systems with disorder, where analytical techniques for quenched averaging have so far been based on the replica trick. As a demonstration of how the supersymmetry method works for such interacting systems, I will derive saddle point equations. In the semiclassical limit, the results are in agreement with those found using the replica technique. I will also discuss the formally exact superbosonized representation of the SYK model and argue that it paves the way for the precise calculation of the window of universality in which random matrix theory is applicable to the chaotic SYK system.
Introduction to Topological Insulators and Semimetals
Jennifer Cano (Stony Brook University)
I will first review topological insulators following the RMP by Hasan and Kane . I will then extend the concept of a topological invariant to topological semimetals. Finally, I will describe some of my own work classifying topological semimetals with crystal symmetry [2,3].
 https://arxiv.org/abs/1603.03093 (Science 10.1126/science.aaf5037 (2016))
 https://arxiv.org/abs/1904.12867 (APL Materials 7, 101125 (2019)).
Host: Mengkun Liu
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 . 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 . 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].
 D. Wendt, et al., Sci. Adv. 5: eaay2748. (2019).
 A. V. Tkachenko, I. A. Zaliznyak. arXiv:1908.11643 (2019).
Host: Sasha Abanov
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
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