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Condensed Matter Seminar

CANCELLED. Sebastian Deffner, University of Maryland Baltimore County
Speaker: CANCELLED. Sebastian Deffner, University of Maryland Baltimore County Title: TBA Abstract: Host: Ar. Abanov

19 Jan 2018, 4:00PM | MIST M102
Hosted By: Ar. Abanov


Brian La Cour, UT Austin
Speaker: Brian La Cour, UT Austin Title: Quantum Emulation Abstract: The breakdown of Moore's law, coupled with an ever increasing demand for computational power, impel us to seek new paradigms in computing and information processing. The peculiar physics of quantum systems has the potential to solve computational problems in new and more powerful ways. In what ways are quantum computers distinctly different from classical computers? In this talk I will describe a particular approach we have developed for emulating a gate-based quantum computer using only analog electronics. Such a device is capable of exhibiting many of the important features traditionally thought to be uniquely quantum, such as superposition and entanglement, yet is entirely classical in nature. By representing a quantum state by the frequency content of an analog signal, one achieves an inherent "quantum parallelism" that can provide for greater computational efficiency. Finally, I will discuss some new work that uses models of stochastic classical systems to bring us even closer to the quantum world. Host: Helmut Katzgraber

26 Jan 2018, 4:00PM | MIST M102
Hosted By: Helmut Katzgraber


Jing Xia, University of California, Irvine
Speaker: Jing Xia, University of California, Irvine Title: Studying 2D magnetism and superconductivity with a Sagnac MOKE microscope Abstract: In this talk, I will discuss our recent results on 2D magnetism and superconductivity using a scanning Sagnac MOKE microscope, which is based on a Sagnac interferometer technique first developed at Stanford [1], and has achieved unprecedented nanoradian level Kerr and Fraday sensitivity even at DC. In exfoliated Cr2Ge2Te6 (CGT) atomic layers, we report [1] the discovery of intrinsic ferromagnetism in 2D van der Walls crystals, defying the well-known Mermin-Wagner theorem. Unlike 3D magnetism, the ferromagnetic order in this 2D system is stabilized by magnetic anisotropy from the CGT structure, which is not present in graphene. As a result, changing the magnetic anisotropy with a small external magnetic field was found to strongly enhance the Curie temperature, which is a feature unique to 2D magnetism. An emerging alternative route for developing new multifunctional perovskite is by modification of the oxygen octahedral structure. We demonstrate [2] the control of structural oxygen octahedral rotation in ultrathin perovskite SrRuO3 films by the deposition of a SrTiO3 capping layer, which can be patterned to achieve local control. We show an increase in the Curie temperature of SrRuO3 due to the suppression octahedral rotations revealed by the synchrotron x-ray diffraction. In epitaxial Bi/Ni bilayer samples, we report [3] the observation of 2D superconductivity that spontaneously breaks time-reversal symmetry (TRS). Because of strong spin-orbit interaction and lack of inversion symmetry in a Bi/Ni bilayer, superconducting pairing cannot be classified as singlet or triplet. We propose a theoretical model where magnetic fluctuations in Ni induce the superconducting pairing of the dxy ± idx2+y2 orbital symmetry between the electrons in Bi. In this model, the order parameter has a nonzero phase winding number around the Fermi surface, thus making it a rare example of a 2D topological superconductor. We will also discuss a more recent result of realizing a spin-polirized 2D electron gas between two non-magnetic insulators. 1. “Discovery of intrinsic ferromagnetism in 2D van der Waals crystals”, Nature, 546, 265-269 (2017). 2. “Localized Control of Curie Temperature in Perovskite Oxide Film by Capping-layer-induced Octahedral Distortion”, Phys. Rev. Lett. , 119, 177203 (2017). 3. “Time-Reversal-Symmetry-Breaking Superconductivity in Epitaxial Bismuth/Nickel Bilayers”, Science Advances, 3, 3, e1602579 (2017). Host: Ar. Abanov

2 Feb 2018, 4:00PM | MIST M102
Hosted By: Ar. Abanov


Chandra Varma, UC Riverside
Speaker: Chandra Varma, UC Riverside Title: Quantum Critical Fluctuations Leading to Marginal Fermi-Liquids Abstract: Models for metallic anti-ferromagnets map to the dissipative XY model as do XY ferromagnets, the superconductor-insulator transition, and the model for loop-current order in Cuprates. The spectral function of the quantum-critical fluctuations for this model in 2D for a range of parameters is determined by topological defects - warps and 2D vortices; it is a separable function of space and time, with a 1/τ dependence at criticality. The marginal fermi-liquid properties for the fermions follow from coupling to such fluctuations. Host: Ar. Abanov

9 Feb 2018, 10:00AM | MIST M102
Hosted By: Ar. Abanov


Cristian Cernov, TAMU
Speaker: Cristian Cernov, TAMU Title: A New Technoogical Paradigm: Blockchain. Abstract: Blockchains are immutable digital ledger systems implemented without a central repository and usually without a central trusted authority. This talk will provide a comprehensive technical overview of blockchain technology. This talk is designed for audiences with little or no knowledge of blockchains and the discussion is abstracted to provide a conceptual understanding. The purpose of this talk is to address the following questions: -How does a blockchain work? -How can a blockchain be appropriately and usefully applied to technological problems? -How are blockchains currently being implemented? -What are some constraints to their viability? The core ideology behind blockchain emerged in 1991 at Bell Communications Research, Inc. when Stuart Haber and W. Scott Stornetta [1] proposed computationally practical procedures for digitally signing documents in a way that prevents users from feasibly changing the collection of data. The advent of the first blockchain came in 2008 when it was implemented by Satoshi Nakamoto [2] as a public ledger for all network transactions on a virtual currency called bitcoin. Blockchain implementation allowed bitcoin to become the first virtual currency that fixed the famous double-spending flaw without the use of a central repository/authority. This innovation landscape comprises only a decade of work by groups of world-class cryptographers, mathematicians, and computer scientists. Already, international currency transfers utilizing blockchain has gone from hours to minutes, as opposed to the current system, which can take days and has a lower degree of reliability. Virtual currencies are only the tip of the iceberg when it comes to blockchain implementation. Other applications are already in development including: delivery drones and self-driving cars, which will use blockchain to pay for services like repairs and charging stations; documenting provenance to increase transparency in academia and change the funding model of journal publishers; food traceability and RFID-based supply chain economics; and even voting. [1] Haber, Stuart; Stornetta, W. Scott (January 1991). “How to time-stamp a digital document”. Journal of Cryptology. 3 (2): 99-111. doi:10.1007/bf00196791. [2] Nakamoto, S., “Bitcoin: A Peer-to-Peer Electronic Cash System,” 2008. https://bitcoin.org/bitcoin.pdf Host: Ar. Abanov

16 Feb 2018, 4:00PM | MIST M102
Hosted By: Ar. Abanov


Arkady Shekhter, NHMFL
Speaker: Arkady Shekhter, NHMFL Title: Scale-invariant transport in high-temperature superconductors Abstract: Although multiple measurements indicate quantum critical origin of the phase diagram of high-temperature superconductors, the physics of the anomalous transport behavior in the "strange metal" state near critical doping and the very nature of its charge carriers are still in flux. Our high-magnetic-filed measurements of resistivity in LSCO cuprates near critical doping (x=0.20) reveal linear-in-field resistivity observed at very high magnetic fields and a characteristic temperature-field competition at lower fields. Such scale-invariant behavior of magnetoresistance suggests non-quasiparticle transport in the strange metal state. Hall measurements in the same field and temperature range further support this conclusion. Host: A. Finkelstein

23 Feb 2018, 4:00PM | MIST M102
Hosted By: A. Finkelstein


Rahul Mahajan Nandkishore, UC Boulder
Speaker: Rahul Mahajan Nandkishore, UC Boulder Title: Fractons Abstract: In recent years a new class of quantum phases of matter have been (theoretically) discovered. These are the `fracton’ phases and they support a phenomenology unlike anything we have seen before. In this talk I will introduce the basic properties of fracton phases, and how they may be understood. I will also survey some of the rich dynamic and thermodynamic behaviors supported by fracton phases, and discuss some of the (many) important open questions. Host: Ar. Abanov

2 Mar 2018, 4:00PM | MIST M102
Hosted By: Ar. Abanov


APS March meeting, Los Angeles, CA
Speaker: APS March meeting, Los Angeles, CA Title: Abstract: Host:

9 Mar 2018, 4:00PM | MIST M102


Spring Break
Speaker: Spring Break Title: Abstract: Host:

16 Mar 2018, 4:00PM | MIST M102


CANCELED. Ania Bleszynski Jayich, UCSB
Speaker: CANCELED. Ania Bleszynski Jayich, UCSB Title: Quantum sensing and imaging with diamond spins Abstract: The nitrogen vacancy (NV) center in diamond is an atomic-scale defect in diamond that is highly sensitive to a wide variety of fields: magnetic, electric, thermal, and strain. A versatile quantum sensor, the NV center holds particular promise for nanometer-scale imaging. Here I discuss an NV-based imaging platform where we have incorporated an NV center into a scanning probe microscope and used it to image a variety of condensed matter systems, including vortices in superconductors and skyrmions, nanoscale topological spin textures, in thin film magnetic multilayers. I also discuss recent experiments that utilize the NV center’s sensitivity to fluctuating magnetic fields to image conductivity with nanoscale spatial resolution. A grand challenge to improving the spatial resolution and magnetic sensitivity of the NV is mitigating surface-induced quantum decoherence, which I will discuss in the second part of this talk. Decoherence at interfaces is a universal problem that affects many quantum technologies, but the microscopic origins are as yet unclear. Our studies guide the ongoing development of quantum control and diamond surface preparation techniques, pushing towards the ultimate goal of NV-based single nuclear spin imaging. Host: Ar. Abanov

23 Mar 2018, 4:00PM | MIST M102
Hosted By: Ar. Abanov


Good Friday
Speaker: Good Friday Title: Abstract: Host:

30 Mar 2018, 4:00PM | MIST M108


Marco Nardelli, University of North Texas
Speaker: Marco Nardelli, University of North Texas Title: High-throughput materials discovery and development: breakthroughs and challenges in the mapping of the materials genome. Abstract: High-Throughput Quantum-Mechanics computation of materials properties by ab initio methods has become the foundation of an effective approach to materials design, discovery and characterization. This data driven approach to materials science currently presents the most promising path to the development of advanced technological materials that could solve or mitigate important social and economic challenges of the 21st century. In particular, the rapid proliferation of computational data on materials properties presents the possibility to complement and extend materials property databases where the experimental data is lacking and difficult to obtain. Enhanced repositories such as AFLOW open novel opportunities for structure discovery and optimization, including uncovering of unsuspected compounds, metastable structures and correlations between various properties. The practical realization of these opportunities depends almostexclusively on the the design of efficient algorithms for electronic structure simulations of realistic material systems beyond the limitations of the current standard theories. In this talk, I will review recent progress in theoretical and computational tools, and in particular, discuss the development and validation of novel functionals within Density Functional Theory and of local basis representations for effective ab-initio tight-binding schemes. Host: Joseph Ross

13 Apr 2018, 4:00PM | MIST M102
Hosted By: Joseph Ross


Group meeting
Speaker: Group meeting Title: Abstract: Host:

20 Apr 2018, 4:00PM | MIST M102


Michael Levin, University of Chicago
Speaker: Michael Levin, University of Chicago Title: Criteria for protected edge modes in interacting topological phases Abstract: Some 2D quantum many-body systems with a bulk energy gap have the property that they support gapless edge modes which are extremely robust. These modes cannot be gapped out or localized by general classes of interactions or disorder at the edge: they are "protected" by the structure of the bulk phase. A basic problem is how to predict, for general interacting systems, when such edge modes are present or absent. In this talk, I will discuss this problem for some simple classes of topological phases. Host: Ar. Abanov

27 Apr 2018, 4:00PM | MIST M102
Hosted By: Ar. Abanov


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