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Condensed Matter Seminar

Martin Mourigal, Georgia Tech
Speaker: Martin Mourigal, Georgia Tech Title: Anomalous spin dynamics in triangular quantum magnets. Abstract: The spin-1/2 triangular-lattice antiferromagnet is a central model in frustrated quantum magnetism: it is the first two-dimensional magnet proposed to host a SU(2) symmetric resonating valence-bond ground-state and its fractionalized magnetic excitations. Although it is now accepted that the model, at least in its simplest Heisenberg form, orders magnetically, it remains intimately associated with the concepts of quantum spin-liquid and exotic magnetic excitations. In the last few years, advances in materials discovery, crystal growth, neutron spectroscopy and theory have fueled a lively triangular-lattice antiferromagnet “renaissance”. In this talk, I will describe recent neutron scattering investigations on two realizations of this model: the transition metal compound Ba3CoSb2O9 and the rare-earth system YbMgGaO4. Experimental results elucidate the role of quantum fluctuations, spin-orbit coupling, chemical disorder, and non-linear effects in generating anomalous spin dynamics in these materials. This project is supported by the NSF under grant DMR-1750186. Host: Ar. Abanov

18 Jan 2019, 4:00PM | MIST M102
Hosted By: Ar. Abanov

Speaker: Workshop Title: Next Generation Xenon-based Dark Matter and Neutrino Detection. Abstract: Host: L. Strigari

1 Feb 2019, 4:00PM | MIST M102
Hosted By: L. Strigari

Ania Bleszynski Jayich, UCSB
Speaker: Ania Bleszynski Jayich, UCSB Title: The NV center in diamond: a versatile quantum technology. Abstract: The nitrogen vacancy (NV) center in diamond is an atomic-scale defect that exhibits remarkably coherent quantum properties in a uniquely accessible way: over a wide range of temperatures (1K-300K) and in ambient and high vacuum conditions. By incorporating the NV center into a scanning probe microscope geometry, we have demonstrated a powerful tool for imaging nanoscale magnetism in condensed matter systems [1]. Here I discuss two novel functionalities of the NV center afforded by its unique nature as a quantum sensor. I present NV-based conductivity imaging on the nanoscale in a quantitative and noninvasive way [2]. We also extend recently developed NV sensing techniques to simultaneously probe both the nanoscale structure and fluctuation dynamics of skyrmions in a thin-film system. [1] M. Pelliccione et al, Nature Nanotehcnology 11, 700 (2016) [2] Ariyaratne et al, Nature Communications 9, 2406 (2018) Host: Ar. Abanov

8 Feb 2019, 4:00PM | MIST M102
Hosted By: Ar. Abanov

Michael Pretko, UC Boulder
Speaker: Michael Pretko, UC Boulder Title: Fractons, Elasticity, and Tensor Gauge Theories. Abstract: A fracton is a new type of emergent quasiparticle which cannot move by itself, yet is able to form mobile bound states. These exotic quasiparticles were first encountered in certain exactly solvable spin models. More recently, it has been demonstrated that fractons are concretely realized as the lattice defects of ordinary two-dimensional crystals. In this talk, I will first develop the theoretical framework for fractons in terms of tensor gauge theories, which have unusual conservation laws leading to the immobility of fractons. I will then discuss the physical realizations of fractons, focusing on the example of elasticity theory. Finally, I will discuss the phenomenology of fracton systems and some of the experimental signatures which can be used to diagnose the presence of these unusual new particles. Host: Ar. Abanov

22 Feb 2019, 4:00PM | MIST M102
Hosted By: Ar. Abanov

Shenglong Xu, University of Maryland, College Park
Speaker: Shenglong Xu, University of Maryland, College Park Title: Quantum information dynamics in many-body systems Abstract: In this talk, I will discuss new perspectives on many-body dynamics based on quantum information. Under unitary time evolution, information about a single spin gradually spreads out in space, and an effective light cone naturally emerges as an intrinsic property of the time evolution operator. Based on this picture, I will present a low-cost tensor network method that can accurately capture the shape of the causal light cone for generic 1D systems of hundreds of spins, a regime that was previously beyond reach. Using the method, we identify a new dynamical phase, characterized by a power-law-like causal light cone. Signatures of this new phase have already been observed in recent ultracold atom experiments on interacting quasi-periodic systems. Host: Ar. Abanov

1 Mar 2019, 4:00PM | MIST M102
Hosted By: Ar. Abanov

APS March meeting,
Speaker: APS March meeting, Title: Abstract: Host: APS

8 Mar 2019, 4:00PM | Boston, MA
Hosted By: APS

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

15 Mar 2019, 4:00PM | MIST M102

Gregory David Fuchs, Cornell
Speaker: Gregory David Fuchs, Cornell Title: A new kind of magnetic microscope: using ultrafast heat pulses to image spin-orbit torques and dynamics in ferromagnetic and antiferromagnetic devices. Abstract: Understanding new magnetic phenomena to enable emerging memory, logic, and oscillator technologies is aided by magnetic imaging techniques that possess simultaneous picosecond temporal resolution and 10 – 100 nm spatial resolution. Conventionally, this combination is available only at facility-based research centers using e.g., pulsed x-ray dichroism techniques. Likewise, many of the most exciting magnetic material systems, including ultrathin ferromagnetic or antiferromagnetic insulators coupled to layers that produce spin-orbit interactions, are difficult to image with any method. To address these challenges in an accessible way, we have developed a table-top spatiotemporal magnetic microscope based on nanoscale, picosecond thermal pulses. Our method takes advantage of magneto-thermal interactions that couple heat flow to spin transport, including the anomalous Nernst effect [1] and the longitudinal spin Seebeck effect [2]. Using focused light as a picosecond heating source, we demonstrate that these imaging modalities have time resolution on the order of 10 ps and sensitivities to magnetization angle of 0.1‑0.3°/ for ferromagnetic metals and insulators. In combination with phase-sensitive microwave current imaging, phase-sensitive ferromagnetic resonance imaging [3] enables direct imaging of the gigahertz-frequency magnetic driving torque vector, which is valuable for understanding spin-orbit interactions [4]. We also demonstrate magneto-thermal imaging of Neel order in FeRh [5] (an antiferromagnetic metal) and NiO [6] (an antiferromagnetic insulator), offering an accessible method to study spin-orbit torque switching of antiferromagnetic devices. Finally, I will describe how the resolution of time-resolved magnetic imaging with heat can be improved to greatly exceed the optical diffraction limit, both theoretically [6] and experimentally. We demonstrate scanning a sharp gold tip illuminated by picosecond laser pulses as the basis of a nanoscale spatiotemporal magnetic microscope. [1] J. M. Bartell, D. H. Ngai, Z. Leng, and G. D. Fuchs, Nat. Commun. 6, 8460 (2015). [2] J. M. Bartell, C. L. Jermain, S. V. Aradhya, J. T. Brangham, F. Yang, D. C. Ralph, and G. D. Fuchs, Phys. Rev. Appl. 7, 044004 (2017). [3] F. Guo, J. M. Bartell, D. H. Ngai, and G. D. Fuchs, Phys. Rev. Appl. 4, 044004 (2015). [4] F. Guo, J. M. Bartell, and G. D. Fuchs, Phys. Rev. B 93, 144415 (2016). [5] I. Gray, G. M. Stiehl, A. B. Mei, D. Schlom, J. T. Heron, D. C. Ralph, and G. D. Fuchs, in prep. (2019). [6] I. Gray, T. Moriyama, N. Sivadas, G. M. Stiehl, J. T. Heron, R. Need, B. J. Kirby, D. H. Low, K. C. Nowack, D. G. Schlom, D. C. Ralph, T. Ono, and G. D. Fuchs, arXiv:1810.03997 (2018). [7] J. C. Karsch, J. M. Bartell, and G. D. Fuchs, APL Photonics 2, 086103 (2017). Host: Ar. Abanov

22 Mar 2019, 4:00PM | MIST M102
Hosted By: Ar. Abanov

Ilya Krivorotov, UC Irvine
Speaker: Ilya Krivorotov, UC Irvine Title: Spin transfer and magnon condensation in magnetic heterostructures Abstract: Transfer of spin angular momentum across the interface between a ferromagnetic (FM) and a non-magnetic (NM) materials can drive magnetization reversal and induce non-equilibrium condensation of magnons. In this talk, I will discuss two recently discovered mechanisms for generating pure spin currents across the FM/NM interface. One mechanism is spin Seebeck effect arising from a temperature gradient across the interface. The other mechanism relies on spin-orbit scattering in the FM [1] and is closely related to anisotropic magneto-resistance. We experimentally demonstrate that both mechanisms can give rise to high spin current densities leading to condensation of magnons into a macroscopic phase-coherent state [1, 2]. 1. C. Safranski, et al., Nature Nanotechnology 14, 27 (2019) 2. C. Safranski et al., Nature Communications 8, 117 (2017) Host: Ar. Abanov

29 Mar 2019, 4:00PM | MIST M102
Hosted By: Ar. Abanov

Judy Cha, Yale
Speaker: Judy Cha, Yale Title: Controlling topological nanomaterials and superconductors Abstract: The last decade has witnessed an explosion of new condensed matter: topological materials whose band structure belongs to non-trivial topology. This leads to the emergence of topological surface or edge states in these materials, which can be harnessed for next generation electronics. In particular, a network of one-dimensional (1D) topological superconductors would enable fault-tolerant quantum computations based on Majorana bound states that can be supported, manipulated, and braided at the junctions of the nanowires. To this end, synthesis of topological nanomaterials, particularly in the nanowire form, of high crystalline quality that preserves the desired topological transport properties is essential. I will discuss synthesis and transport measurements of tin telluride, a topological crystalline insulator, into nanostructures. Doping tin telluride nanowires with indium induces superconductivity, meeting the necessary ingredients for 1D topological superconductivity. Current challenges in realizing topological superconducting nanowires based on tin telluride will also be addressed. Host: Ar. Abanov

12 Apr 2019, 4:00PM | MIST M102
Hosted By: Ar. Abanov

Shixiong Zhang, Indiana University Bloomington
Speaker: Shixiong Zhang, Indiana University Bloomington Title: Controlled Synthesis and Emergent Properties of Spin-Orbit Coupled Materials Abstract: Spin-orbit coupling (SOC) is a relativistic interaction between a particle’s spin and its motion. In most of the solid state physics textbooks, SOC is considered only a small perturbation to the electronic band structures of solid materials. The recent discovery of topological insulators, however, has manifested a key role of SOC in driving topologically non-trivial states. Since the interaction increases as the fourth power of the atomic number, topological electronic states are often realized in materials that are composed of heavy atoms. In this talk, I will discuss our recent work on two classes of such “heavy materials”, namely metal chalcogenides and pyrochlore iridates that host exotic states driven by strong SOC. For the chalcogenides, I will present the controlled synthesis and growth mechanism of one-dimensional nanowires and their enhanced thermoelectric properties which may be associated with the non- trivial surface states. For the pyrochlore iridates, I will focus on the synthesis of bulk crystals and pulsed laser deposition of thin films. I will further discuss their unusual magnetic and electrical properties arising from the interplay of SOC, electron correlation, and geometrical frustration. Host: D. Naugle

19 Apr 2019, 4:00PM | MIST M102
Hosted By: D. Naugle

Gabor Csathy, Purdue
Speaker: Gabor Csathy, Purdue Title: Pairing and Nematicity in the Two-dimensional Electron Gas Abstract: The competition of paired and nematic ground states occurring in strongly correlated systems, such as high Tc superconductors and transition metal dicalchogenides, remains poorly understood. Paired and nematic states are also known to exist in the two-dimensional electron gas. However, these phases form in different areas of the phase space and, therefore, a phase transition between them was not possible. In this talk I will discuss the observation of a pressure-driven direct phase transition between a paired fractional quantum Hall state and a nematic phase in the electron gas. The role of the pressure driving the transition and special properties of this phase transition will be discussed. Host: Ar. Abanov

26 Apr 2019, 4:00PM | MIST M102
Hosted By: Ar. Abanov

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