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 H3: CMP-QM: Ferroelectrics and other Novel Materials / NSF |
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Chair: Premala Chandra, Rutgers University Room: 215, Campus Center, NJIT |
Saturday, November 4, 2017 2:00PM - 2:12PM |
H3.00001: Current-density implementation for calculating flexoelectric coefficients Cyrus E. Dreyer, Massimiliano Stengel, David Vanderbilt The flexoelectric (FxE) effect, where polarization is induced by a strain gradient, is universal in all insulators. As devices shrink to the micro and nano scale, large strain gradients can occur, and therefore the FxE effect can play a significant role in their electrical and mechanical properties; also, the FxE effect can be exploited for novel device design paradigms such as piezoelectric ``meta-materials'' constructed from nonpiezoelectric constituents, or mechanical switching of ferroelectric polarization. One of the crucial limitations to understanding and exploiting the FxE effect is the lack of an efficient first-principles methodology to calculate all of the components of the bulk FxE tensor; the transverse and shear components in particular are problematic. In this work we develop such a methodology based on density functional theory to calculate the full bulk, clamped-ion FxE tensor from a single unit cell by calculating the current-density response to the adiabatic displacement of atoms from a long wavelength acoustic phonon. We benchmark our methodology on simple systems of isolated nobel gas atoms, and apply it to calculate the clamped-ion flexoelectric constants for a variety of technologically important cubic materials. [Preview Abstract] |
Saturday, November 4, 2017 2:12PM - 2:24PM |
H3.00002: Modulation doping in LaNiO$_3$/SrIrO$_3$ superlattices from first principles Michele Kotiuga, Heung-Sik Kim, David Vanderbilt, Karin M. Rabe Doping is commonly used to tune and optimize material properties such as conductivity and optical properties. Doping at extremely high concentrations, at the level of an electron per formula unit, can stabilize novel phases. Here we study lanthanum nickelate (LaNiO$_3$)/strontium iridate (SrIrO$_3$) superlattices using the first-principles density functional theory (DFT) +U method, focusing on the 1/1 superlattice. For this superlattice we find that there is a complete modulation doping in which one electron per formula unit is transferred from the SrIrO$_3$ layers to the LaNiO$_3$ layers, converting all nickels from Ni$^{3+}$ to Ni$^{2+}$ in the electron-doped LaNiO$_3$ layers and and all iridiums from Ir$^{4+}$ to Ir$^{5+}$ in the hole-doped SrIrO$_3$ layers. We will present results on the low energy structures and orbital occupations as well as the electronic and magnetic structures. [Preview Abstract] |
Saturday, November 4, 2017 2:24PM - 2:36PM |
H3.00003: Cluster dynamical mean-field theory study on deficient spinel chalcogenide GaV$_{\mathrm{4}}$S$_{\mathrm{8}}$ Heung Sik Kim, Kristjan Haule, David Vanderbilt Here I will present my current research progress about a deficient~spinel compound GaV$_{\mathrm{4}}$S$_{\mathrm{8}}$ (GVS) using a cluster dynamical mean-field (DMFT) approach. GVS has been of growing interest recently because of its multiferroicity below T$_{\mathrm{C}}$\textasciitilde 13K. It has an additional structural transition around T$_{\mathrm{f}}$ \textasciitilde 70K, lowering the symmetry of the high-temperature cubic phase to a rhombohedral structure as it is cooled. Across the two structural transitions GVS remains insulating with the gap size estimated to be \textasciitilde 0.3 eV, and the insulating nature of its high-temperature cubic paramagnetic phase is suspected to be a Mott-type. However, there has not been a systematic study about the Mott-insulating phases of GVS, which should be important to understand the low- temperature ferroelectric and multiferroic phases. Hence we apply a cluster DMFT method to GVS with V$_{\mathrm{4}}$ as our cluster problem, employing a molecular orbital basis set instead of an atomic one. ~Comparing with single-V-site DMFT calculations, we show that intra-cluster correlations are essential in reproducing the Mott-insulating phase of the high-T cubic paramagnetic phase. Correlation effects on the crystal structure of GVS will be also discussed, and especially the role of Hund's coupling in tuning V$_{\mathrm{4}}$-clustering by switching low to high spin states will be shown. [Preview Abstract] |
Saturday, November 4, 2017 2:36PM - 3:12PM |
H3.00004: New Perspectives on Quantum Phase Transitions from Ferroelectrics Invited Speaker: Premala Chandra The quest for universality at continuous quantum phase transitions suggests that quantum criticality should be studied in a variety of settings. Displacive quantum paraelectrics have been proposed as simple quantum critical systems as they have few degrees of freedom, propagating (phonon) dynamics and they reside at their marginal dimension where both scaling and generalized Langevin random field theories apply (up to unobservable logarithmic corrections). I will present characterization of temperature-dependent measurable quantities in the vicinity of displacive ferroelectric quantum critical points, indicating good agreement between theory and experiment. I will end with open questions for future research on this area that include unusual forms of superconductivity in doped quantum paraelectrics. [Preview Abstract] |
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