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 J3: CMP-QM: Topology, Domains, and Ferroelectrics |
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Chair: S-W Cheong, Rutgers University Room: 240, Campus Center, NJIT |
Saturday, November 4, 2017 4:15PM - 4:51PM |
J3.00001: Topological Vortex Domains in Quantum Materials Invited Speaker: Sang-Wook Cheong Engineering of domains and domain walls is quintessential for technological exploitation of numerous functional materials. However, it has only recently realized that the configuration of these domains/domain walls can have non-trivial topology. We will discuss a new topological classification scheme of domain/domain boundary configurations with Ising-type or two-dimensional order parameters: $Z_{m}$\texttimes $Z_{n}$ domains ($m$ directional variants and $n$ translational antiphases) and Z$_{l}$ vortices (where $l$ number of domains and that of domain boundaries merge). This classification, with the concept of topological protection and topological charge conservation, has been applied to a wide range of materials such as (hybrid) improper ferroelectrics, chiral ferromagnets, and magnetic superconductors. We will also discuss the emergent physical properties at domain walls, distinct from those of domains. The presented topological consideration provides a basis in understanding the formation, kinetics, manipulation and property optimization of domains/domain walls in quantum materials. [Preview Abstract] |
Saturday, November 4, 2017 4:51PM - 5:27PM |
J3.00002: Domain walls in hybrid improper ferroelectric Ca$_3$Ti$_2$O$_7$ Invited Speaker: Elizabeth Nowadnick Coupling or competition between spin, charge, orbital, and structural order parameters can lead to novel properties and functionality in materials. For example, ferroelectrics that allow a coupling between the polarization and another order parameter can enable electric-field control of non-polar order parameters. This talk will focus on a recently discovered type of ferroelectricity (‘hybrid improper’ ferroelectricity) in the Ruddlesden-Popper compound Ca$_3$Ti$_2$O$_7$ , where the polarization is induced via a trilinear coupling to two octahedral rotation distortions of different symmetry. This octahedral rotation-polarization coupling also leads to a complex structure of coupled domain walls. Using a combination of group theoretic analysis and density functional theory calculations, I will present scenarios for domain wall structures in Ca$_3$Ti$_2$O$_7$ and related materials. [Preview Abstract] |
Saturday, November 4, 2017 5:27PM - 5:39PM |
J3.00003: Topological structural defects and a spin-liquid phase in TbInO$_3$ Jae-Wook Kim, X. Wang, F.-T. Huang, Y. Wang, X. Fang, X. Luo, Y. Li, S. Mori, D. Kwok, Vivien Zapf, Sang-Wook Cheong Geometrical frustration can create highly degenerate ground states, complex spin configurations, or exotic ground states. One example is the spin-liquid, where magnetic ordering is suppressed even at zero temperature by quantum fluctuations and may host novel properties such as spinon excitations, majorana edge states, etc. Here, we report an intriguing coexistence of ferroelectric domains and spin-liquid in hexagonal TbInO$_3$. Geometric ferroelectricity is realized by displacement of Tb$^{3+}$ ions and show topological defects with $Z_2$ $\times$ $Z_3$ domains. At low temperatures, magnetic susceptibility indicates strong in-plane anisotropy without any hysteresis under applied magnetic field. Furthermore, we find no evidence of long range order in specific heat measurement down to temperatures as low as 150 mK suggesting that TbInO$_3$ a spin liquid. Concurrence of topological structural defects and spin-liquid phase in this system provides a unique basis to study intriguing edge states from frustrated magnetism. [Preview Abstract] |
Saturday, November 4, 2017 5:39PM - 6:15PM |
J3.00004: Quantum anomalous Hall and antiferroelectric topological insulators Invited Speaker: David Vanderbilt In this talk I will briefly review two predictions of novel topological states. First I will present the results of a computational study of heavy adatoms chemisorbed on ferromagnetic CrSiTe$_3$ and CrGeTe$_3$ surfaces as part of a search for quantum anomalous Hall (QAH) insulators. Surprisingly, we find QAH states that emerge for La and Lu adatoms on single CrSi(Ge)Te$_3$ layers in which time-reversal symmetry is broken directly in the orbital sector. These ``flux states'' are observed only when using hybrid functionals, suggesting that intersite Coulomb interactions may be responsible. Second, I will discuss our recent work in which we identify a class of potential ``antiferroelectric topological insulators,'' defined as materials in which either the zero-field nonpolar or high-field polar states are topological. By investigating orthorhombic members of an $ABC$ family of compounds, we predict several representative examples including ones for which only one of these two states is topological, so that an electric field can potentially be used to switch between trivial and topological phases. We also investigate the ability of epitaxial strain and hydrostatic pressure to tune the topological order and the band gap of these $ABC$ compounds. [Preview Abstract] |
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