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 M3: CMP-QM: Scattering and Spectroscopy |
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Chair: Trevor Tyson, New Jersey Institute of Technology Room: 215, Campus Center, NJIT |
Sunday, November 5, 2017 10:00AM - 10:36AM |
M3.00001: Magnetic structures and dynamics of multiferroic systems obtained with neutron scattering Invited Speaker: William Ratcliff Multiferroics are materials which possess ferroelectric and magnetic order. For technological applications, we desire that these two order parameters be tightly coupled. Unfortunately, despite years of searching, there has been a paucity of these materials which are both ordered at room temperature, while evincing control of magnetism by an applied voltage. Thus, engineering artificial multiferroics using heterostructuring at the atomic scale is rapidly becoming an attractive alternative. In this work, we combined two crystallographically similar but poor multiferroic materials (LuFeO3 and LuFe2O4) to engineer a new family of ferromagnetic multiferroic heterostructures [1] which exhibit magnetoelectric coupling at room temperature. I will discuss the role of neutron scattering in understanding these materials. [1] J. Mundy, et. al., “Atomically engineered ferroic layers yield a room temperature magnetoelectric multiferroic”, Nature 537, 523 (2016) [Preview Abstract] |
Sunday, November 5, 2017 10:36AM - 11:12AM |
M3.00002: Infrared and THz radiation from relativistic electron beams and applications in condensed matter physics Invited Speaker: G. Lawrence Carr Many spectroscopic methods used in condensed matter physics investigations become throughput limited as the far-infrared range is reached. These include studies of materials at low temperatures, in high magnet fields, or under the extreme pressures available with the diamond anvil cell. Other techniques, such as spectroscopic ellipsometry, are inherently throughput limited due to constraints on angle-of-incidence. Infrared and THz synchrotron radiation from storage ring light sources, such as NSLS-II at Brookhaven, can overcome these limitations. Indeed, the brightness is sufficient for wide-band near-field infrared spectroscopy to be performed with a spatial resolution on the order of 10 nm. This presentation will describe the first infrared beamline, presently under construction at NSLS-II, and the various measurement methods it will enable. Example results from materials physics will be reviewed. Additionally, a proposed second infrared beamline, designed for far-infrared nanospectroscopy of materials, will be described. [Preview Abstract] |
Sunday, November 5, 2017 11:12AM - 11:24AM |
M3.00003: Optical spectroscopy of magnons, electromagnons, phonons, and crystal field excitations in orthoferrites $R$FeO$_{\mathrm{3}}$ T. N. Stanislavchuk, V. A. Martinez, A.A. Sirenko, Y. Janssen, G. L. Carr, Y. Wang, S-W. Cheong Mueller matrix ellipsometry and transmission polarimetry were used at Brookhaven National Lab to study multiferroic orthoferrites $R$FeO$_{\mathrm{3}}$ ($R=$Tb and Dy) in the far-IR range (10 - 2000 cm$^{\mathrm{-1}})$ and low temperatures and magnetic fields up to 10 T. Magnetic properties of $R$FeO$_{\mathrm{3\thinspace }}$are due to interplay of two magnetic subsystems: $R^{\mathrm{3+}}$ and Fe$^{\mathrm{3+}}$. Spectra of magnons, electromagnons, and optical phonons have been investigated and described in terms of the temperature and field dependencies of their frequency, damping, and oscillator strength. Below the magnetic ordering of $R^{\mathrm{3+}}$ spins $T_{\mathrm{N}}(R^{\mathrm{3+}})$, we observed hardening of the magnon frequencies and modification of the magnon selection rules. In TbFeO$_{\mathrm{3}}$ the quasi-AFM magnon gains electric-dipole activity below $T_{\mathrm{N}}$(Tb) and behaves as a hybrid mode. In addition to quasi-AFM and quasi-FM magnons in $R$FeO$_{\mathrm{3}}$, we discovered electromagnons which are electric-dipole active along the $c$-axis. The oscillator strength of electromagnon in DyFeO$_{\mathrm{3}}$ at 20 cm$^{\mathrm{-1\thinspace }}$provides a significant contribution of about 50{\%} to the static magnetodielectric effect. In contrast, the electromagnon in TbFeO$_{\mathrm{3}}$ at 27~cm$^{\mathrm{-1}}$ has a weaker strength and it appears only in a narrow temperature range 2.7 $-$ 3.3 K at $H=$0 and in a narrow range of magnetic fields \quad of \quad 2.4~ -~2.7~T applied along the $b$-axis at $T=$1.5~K. Spectra of the ir-active optical phonons and crystal field excitations were measured for all three orthorhombic axes of $R$FeO$_{\mathrm{3}}$. [Preview Abstract] |
Sunday, November 5, 2017 11:24AM - 11:36AM |
M3.00004: Momentum dependence in K-edge resonant inelastic x-ray scattering and its application to screening dynamics in CE-phase La0.5Sr1.5MnO4 K. H. Ahn, T. F. Seman, X. Liu, J. P. Hill, M. van Veenendaal We present a formula for the calculation of K-edge resonant inelastic x-ray scattering on transition metal compounds, based on a local interaction between the valence shell electrons and the $1s$ core hole. Extending a previous result, we include explicit momentum dependence and a basis with multiple core-hole sites. We apply this formula to a single-layered charge, orbital and spin ordered manganite, La$_{0.5}$Sr$_{1.5}$MnO$_4$, and obtain good agreement with experimental data, in particular with regards to the large variation of the intensity with momentum. We find that the screening in La$_{0.5}$Sr$_{1.5}$MnO$_4$ is highly localized around the core-hole site and demonstrate the potential of K-edge resonant inelastic x-ray scattering as a probe of screening dynamics in materials. [Preview Abstract] |
Sunday, November 5, 2017 11:36AM - 11:48AM |
M3.00005: Temperature-dependent excitonic superfluid plasma frequency evolution in excitonic insulator, Ta$_2$NiSe$_5$ Jungseek Hwang, Yu-Seong Seo, Man Jin Eom, Jun Sung Kim, Chang-Jong Kang, Byung Il MIn We investigate an excitonic insulate, Ta$_{2}$NiSe$_{5}$, using optical spectroscopy. Ta$_{2}$NiSe$_{5}$ has quasi-one dimensional chains along the $a$-axis. We have obtained anisotropic optical properties of a single crystal Ta$_{2}$NiSe$_{5}$ along the $a$- and $c$-axes. The measured $a$- and $c$-axis optical conductivities exhibit large anisotropic electronic and phononic properties. With regard to the $a$-axis optical conductivity, a sharp peak near 3050 cm$^{-1}$ at 9 K, with a well-defined optical gap ($\Delta^{EI} \simeq$ 1800 cm$^{-1}$) and a strong temperature-dependence, is observed. With an increase in temperature, this peak broadens and the optical energy gap closes around $\sim$325 K($T_c^{EI}$). The spectral weight redistribution with respect to the frequency and temperature indicates that the normalized optical energy gap ($\Delta^{EI}(T)/\Delta^{EI}(0)$) is $1-(T/T_c^{EI})^2$. The temperature-dependent superfluid plasma frequency of the excitonic condensation in Ta$_{2}$NiSe$_{5}$ has been determined from measured optical data. [Preview Abstract] |
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