Bulletin of the American Physical Society
Mid-Atlantic Section Fall Meeting 2020
Volume 65, Number 20
Friday–Sunday, December 4–6, 2020; Virtual
Session G04: Quantum Magnetism II & Supercond. |
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Chair: Junjie Yang, NJIT |
Saturday, December 5, 2020 4:15PM - 4:51PM |
G04.00001: Magnetism and quantum transport in the kagome lattices of semi-metallic Mn3X Invited Speaker: Collin Broholm Lamellar insulating materials with magnetic ions on the kagome lattice of corner-sharing triangles have attracted much attention over the years because of the geometrical frustration and the consequent lack of magnetic ordering at low temperatures. Now it turns out that the non-collinear antiferromagnetic ordering induced by the longer range and inter-kagome-layer interactions of a semi-metal can have interesting effects on quantum transport. Specifically, the AB stacked kagome layers of Mn3X form an anti-chiral co-planar magnetic order that gives rise to strong anomalous Hall and Nernst effects at room temperature linked to Weyl points in the electronic band structure[1]. I shall describe an experimental study of the magnetic order and excitations in Mn3Ge[2]. While a phenomenological spin Hamiltonian including exchange interactions, Dzyaloshinskii-Moriya interactions, and single-ion crystal field terms can describe aspects of the Mn-based magnetism, spin-wave damping, and the extended range of magnetic interactions indicate the strong interactions with conduction electrons that underly its quantum transport anomalies. The talk will illustrate the constructive interplay between the pursuit of a fundamental understanding of electrons in solids and the discovery of materials with novel properties for technological applications. [1] ``Large anomalous Hall effect in a non-collinear antiferromagnet at room temperature,''~S. Nakatsuji, N. Kiyohara and T. Higo,~Nature~\textbf{527}~(2016)~212-215. [2] ``Antichiral spin order its Goldstone modes and their hybridization with phonons in the topological semimetal Mn$_{\mathrm{3}}$Ge,''\textbf{~}Y. Chen, J. Gaudet, S. Dasgupta, G. G. Marcus, J. Lin, T. Chen, T. Tomita, M. Ikhlas, Y. Zhao, W. C. Chen, M. B. Stone, O. Tchernyshyov, S. Nakatsuji, C. Broholm,~Phys. Rev. B~\textbf{102}, 054403, (2020). [Preview Abstract] |
Saturday, December 5, 2020 4:51PM - 5:27PM |
G04.00002: Resonant Inelastic X-ray Scattering (RIXS) to Probe Spin Dynamics in Magnonic Materials Invited Speaker: Valentina Bisogni h $-abstract-$\backslash $pardSpin excitations in quantum materials provide a revolutionary alternative for devices with improved performances and energy-efficiency, as they permit the transfer of information without any movement of charge, thus eliminating the dominant source of energy dissipation. Understanding how to manipulate such spin excitations would provide a foundation for the next generation of energy-efficient electronic devices. $\backslash $In this talk, I will present recent results achieved by Resonant Inelastic X-ray Scattering on spin excitations in magnetic thin films of decreasing thickness [1]. Our study demonstrates that confinement is responsible for decreasing the spin excitation energy and increasing their lifetime: we thus propose that the film thickness can be used as a knob to tune the effective refractive for spin excitations in magnetic media used in future magnonic devices.$\backslash $pard1] J. Pelliciari, S. Lee, K. Gilmore, J. Li, Y. Gu, A. Barbour, I. Jarrige, C. H. Ahn, F. J. Walker, V. Bisogni; arXiv: 2010.08745, Accepted in Nature Materials.$\backslash $pard-/abstract-$\backslash $\tex [Preview Abstract] |
Saturday, December 5, 2020 5:27PM - 5:39PM |
G04.00003: $\mathbb{Z}_2$ Topologically Obstructed Superconducting Order Canon Sun, Yi Li We propose a class of topological superconductivity in which the pairing order is $\mathbb{Z}_2$ topologically obstructed in a time-reversal invariant system in three dimensions. When two Fermi surfaces are related by time-reversal and mirror symmetries, such as those in a $\mathbb{Z}_2$ Dirac semimetal, the inter-Fermi-surface pairing in the weak-coupling regime inherits the band topological obstruction. As a result, the pairing order cannot be well-defined over the entire Fermi surface and forms a time-reversal invariant generalization of U($1$) monopole harmonic pairing. A tight-binding model of the $\mathbb{Z}_2$ topologically obstructed superconductor is constructed based on a doped $\mathbb{Z}_2$ Dirac semimetal and exhibits nodal gap function. At an open boundary, the system exhibits a time-reversal pair of topologically protected surface states. [Preview Abstract] |
Saturday, December 5, 2020 5:39PM - 5:51PM |
G04.00004: Coupling of fully symmetric As phonon to magnetism in iron based superconductors shangfei wu, weilu zhang, Li Li, huibo cao, Athena Sefat, Hsiang-Hsi kung, Hong Ding, Pierre Richard, Girsh Blumberg Raman coupling to the fully symmetric As phonon $A_g$(As) in iron based superconductors is forbidden for the XY scattering geometry with cross-polarized light along the Fe-As directions in the tetragonal phase, whereas it becomes allowed in the orthorhombic phase: The emerging mode’s intensity indicates the lattice orthorhombicity, which is expected to be small. However, in the orthorhombic phase of several families of parent compounds of Fe-based superconductors (BaFe$_2$As$_2$, NaFeAs, FeSe, and LaFeAsO) [1], as well as in the gold doped compounds Ba(Fe$_{1−x}$Au$_x$)$_2$As$_2$ [2], we find that the $A_g$(As) phonon intensity is significantly enhanced when the magnetic order sets in below the Neel temperature $T_N$. The $A_g$(As) phonon also shows an asymmetric line shape below $T_N$ and an anomalous linewidth broadening upon Au doping. By the Fano model analysis, we conclude the temperature dependence of light coupling amplitude to the $A_g$(As) phonon follows the evolution of the magnetic order parameter. We propose that the intensity enhancement of the $A_g$(As) phonon is due to electronic anisotropy induced by the collinear spin density wave order. [1]Phys.Rev.Research 2, 033140 (2020) [2]Phys.Rev B 102, 014501 (2020) [Preview Abstract] |
Saturday, December 5, 2020 5:51PM - 6:03PM |
G04.00005: Determining the Two Energy Gaps of Assymetrical all-MgB$_{\mathrm{2\thinspace }}$Thin Film Josephson Junctions Roberto Ramos, Joseph Lambert, Masahito Sakoda, Michio Naito We have previously reported high-resolution tunneling spectroscopy measurements of substructure within the two superconducting energy gaps of Magnesium diboride (MgB ). The samples used consisted of 1-gap/2-gap heterojunctions, where the counter-electrode is a conventional single-gap superconductor (Pb or Sn). Here, we report similar measurements of 2-gap/2-gap all-MgB Josephson junctions. The crystal orientations of the two MgB films are mostly c-axis parallel to the tunneling direction, with very small contribution from the larger $\sigma $ gap. Due to differences in growth conditions, we find that the two MgB electrodes have different T 's and gap values. We represent this physical system using a modified tunneling model where each electrode is represented as a weighted sum of two BCS densities of states. We report results of this ongoing analysis that focuses on (1) a transition from SIS to NIS behavior as temperature increases past the lower Tc electrode, and (2) the presence of multiple quasiparticle peaks due to the sums and differences in pairwise combinations of disparate $\pi $ and $\sigma $ gap values within each electrode. [Preview Abstract] |
Saturday, December 5, 2020 6:03PM - 6:15PM |
G04.00006: Electrostatic effects and topological superconductivity in semiconductor-superconductor-magnetic insulator hybrid wires Benjamin Woods We investigate the impact of electrostatics on the proximity effect between a magnetic insulator and a semiconductor wire in semiconductor-superconductor-magnetic insulator hybrid structures. By performing self-consistent Schrodinger-Poisson calculations using an effective model of the hybrid system, we find that large effective Zeeman fields consistent with the emergence of topological superconductivity emerge within a large parameter window in wires with overlapping layers of magnetic insulator and superconductor, but not in non-overlapping structures. We show that this behavior is essentially the result of electrostatic effects determining the amplitude of the low-energy wave functions near the semiconductor-magnetic insulator interface. [Preview Abstract] |
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