Bulletin of the American Physical Society
2017 Annual Meeting of the APS Mid-Atlantic Section
Volume 62, Number 19
Friday–Sunday, November 3–5, 2017; Newark, New Jersey
Session E2: CMP-QM: Topological Insulators and Semimetals I |
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Chair: Peter Armitage, Johns Hopkins University Room: Ballroom B, Campus Center, NJIT |
Saturday, November 4, 2017 10:00AM - 10:36AM |
E2.00001: Ballistic surface plasmons in high mobility Dirac liquid of graphene Invited Speaker: Dmitri Basov Optical spectroscopies are an invaluable resource for exploring new physic of new quantum materials. Surface plasmon polaritons and other forms of hybrid light-matter polaritons provide new opportunities for advancing this line of inquiry. In particular, polaritonic images obtained with modern nano-infrared tools grant us access into regions of the dispersion relations of various excitations beyond what is attainable with conventional optics. I will discuss this emerging direction of research with two examples from graphene physics: $i)$ ultrafast dynamics of hot photo-excited electrons [2]; and \textit{ii)} ballistic electronic transport at low temperatures [3].$\backslash $pard$\backslash $pard$\backslash $pard[1] D.N. Basov, M.M. Fogler and F. J. Garcia de Abajo ``\textit{Polaritons in van der Waals materials}'', Science 354, 195 (2016).$\backslash $[2] G. X. Ni, L. Wang, M. D. Goldflam, M. Wagner, Z. Fei, A. S. McLeod, M. K. Liu, F.Keilmann, B. \"{O}zyilmaz, A. H. Castro Neto, J. Hone, M. M. Fogler and D. N. Basov \textit{Nature Photonics} \textbf{10}, 244 (2016)$\backslash $[3] G. X. Ni, A. S. McLeod, L. Xiong et al. [in preparation]. [Preview Abstract] |
Saturday, November 4, 2017 10:36AM - 11:12AM |
E2.00002: Zero-energy vortices in two-dimensional Dirac semimetals Invited Speaker: Mikhail Portnoi Contrary to a widespread belief, full electrostatic confinement is possible for Dirac-Weyl fermions with linear dispersion in gapless 2D systems such as graphene, surface states on the surface of topological insulators and gapless HgTe quantum wells. The confinement is possible precisely at the Dirac point where the particles pseudospin is ill-defined, and these bound states must possess non-zero angular momentum (vorticity). Formation of fully-confined zero-energy vortices provides an alternative explanation for various STM experiments in graphene. We also show that a pair of two-dimensional massless Dirac-Weyl fermions can form a bound state independently on the sign of the inter-particle interaction potential, as long as this potential decays at large distances faster than Kepler's inverse distance law. The coupling occurs only at the Dirac point, when the charge carriers lose their chirality. These two-particle states must have a non-zero internal angular momentum, meaning that they only exist as stationary vortices. This leads to the emergence of a new type of energetically-favourable quasiparticles: double-charged zero-energy vortices. Their bosonic nature allows condensation and gives rise to Majorana physics without invoking a superconductor. The presence of dark-matter-like silent immobile vortices explains a range of poorly understood experiments in gated graphene structures at low doping. [Preview Abstract] |
Saturday, November 4, 2017 11:12AM - 11:24AM |
E2.00003: Giant dielectric anomaly and low frequency transport in a 3D quadratic band touching system: the \textit{Luttinger} semimetal Pr$_2$Ir$_2$O$_7$ Bing Cheng, Takumi Ohtsuki, Dipanjan Chaudhuri, Satoru Nakatsuji, Mikk Lippmaa, Peter Armitage Zero-gap semimetals with linearly crossing bands such as Dirac and Weyl semimetals are the focus of much recent work in condensed matter physics. Although they host diverse and fascinating phenomena, their physics can be understood in terms of weakly interacting electrons. In contrast, it was pointed out more than 40 years ago by Abrikosov that quadratic band touchings generically lead to strongly interacting phases and potentially even richer physics. We have performed a terahertz spectroscopic study of thin films of the conducting pyrochlore Pr$_2$Ir$_2$O$_7$, which has been predicted to host a quadratic band touching. We observe a strongly temperature dependent dielectric constant that reaches an abnormally large value of $ \tilde{\varepsilon }/\epsilon_0 \sim 180$ at the lowest temperature. These features can be understood by considering it as a slightly doped strongly interacting \textit{quadratic} band touching system. In such systems, the dielectric constant can be regarded as a measure of the size of interactions, which puts our material in the strongly interacting regime where the scale of the electron-hole interactions is two orders of magnitude larger than the scale of the kinetic energy. Despite this, the inelastic scattering rate exhibits a $T^2$ dependence b [Preview Abstract] |
Saturday, November 4, 2017 11:24AM - 12:00PM |
E2.00004: The quantized magnetoelectric effect 3D topological insulator Invited Speaker: N. Peter Armitage Topological insulators have been proposed to be best characterized as bulk magnetoelectric materials that show response functions quantized in terms of fundamental physical constants. Here we lower the chemical potential of three-dimensional (3D) Bi$_2$Se$_3$ films to $\sim$30 meV above the Dirac point, and probe their low-energy electrodynamic response in the presence of magnetic fields with high-precision time-domain terahertz polarimetry. For fields higher than 5 T, we observed quantized Faraday and Kerr rotations, whereas the DC transport is still semi-classical. A non-trivial Berry phase offset to these values gives evidence for axion electrodynamics and the quantized topological magnetoelectric effect. This is the quantized response that establishes topological insulators as a unique state of matter. Among other things, the time structure used in these measurements allows a direct measure of the fine structure constant based on a topological invariant of a solid-state system. [Preview Abstract] |
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