Bulletin of the American Physical Society
85th Annual Meeting of the APS Southeastern Section
Volume 63, Number 19
Thursday–Saturday, November 8–10, 2018; Holiday Inn at World’s Fair Park, Knoxville, Tennessee
Session E01: Condensed Matter III |
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Chair: Jian Liu, University of Tennessee, Knoxville Room: Holiday Inn Knoxville Downtown Summit |
Friday, November 9, 2018 8:30AM - 8:42AM |
E01.00001: Dynamics epitaxial stabilization of Sr3Ir2O7 phase in thin film synthesis Junyi Yang, Peyton R Nanney, Lin Hao, Kyle R Noordhoek, Han Zhang, Jian Liu Ruddlesden-popper series of Srn+1IrnO3n+1 has been a main focus of 5d strong correlated electron systems where the competition between different electronic interactions of similar energy scales has generated a lot of interesting emergent phenomena. With the increasing effective dimensionality within the Srn+1IrnO3n+1 series, the ground state evolves from an antiferromagnetic insulating state (Sr2IrO4) to a paramagnetic metallic state (SrIrO3). The small charge gap and collinear antiferromagnetic ordering in Sr3Ir2O7 has made itself a unique playground to study exotic physics near the Mott transition critical point. Tuning electronic and magnetic properties in Sr3Ir2O7 single crystal has resulted in many interesting phenomena, while larger response and more flexibility are expected in Sr3Ir2O7 thin films. However, the synthesis window of Sr3Ir2O7 thin films so far has been limited to a small region. In our research, we have studied the thermal dynamic process of the synthesis of Sr3Ir2O7 thin films under different ambient pressures. In addition, we have found that by changing the ambient pressure through gas mixing the synthesis window for Sr3Ir2O7 can be largely enhanced. This provides a more accessible phase space of epitaxial growth to study the correlated physics in Sr3Ir2O7. |
Friday, November 9, 2018 8:42AM - 8:54AM |
E01.00002: Giant magnetic response in layered antiferromagnetic iridate heterostructures Lin Hao, Derek Meyers, Hidemaro Suwa, Junyi Yang, Clayton Frederick, Tamene Dasa, Gilberto Fabbris, Lukas Horak, Dominik Kriegner, Yongseong Choi, Jong-Woo Kim, Daniel Haskel, Philip Ryan, Haixuan Xu, Cristian Batista, Mark P. M. Dean, Jian Liu Layered iridates hosting square lattices have recently gained plenty of interests with potential of unconventional superconductivity leading the charge. The large spin-orbit coupling of the Ir pseudospin half state, on the other hand, may enable a hidden SU(2) symmetry much stronger than that in cuprates. Probing and unveiling this symmetry is however hindered in the bulk material, because of the non-trivial interlayer coupling. Through accurately tailoring the magnetic structure, we exploited this symmetry in heterostructures as composed of perovskite SrIrO3 and SrTiO3 [1]. Upon approaching the 2D limit, the hidden symmetry triggers large magnetic fluctuations and enables an unprecedentedly strong coupling between the antiferromagnetic order and external magnetic field [2]. The ability of materializing the hidden symmetry in artificial structures provides a fruitful playground for pursuing novel phenomena beyond the cuprate physics. [1] L. Hao, et.al, Phys. Rev. Lett. 119, 027204 (2017). [2] L. Hao, et.al, Nat. Phys. 14, 806–810 (2018).
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Friday, November 9, 2018 8:54AM - 9:06AM |
E01.00003: Tunable Mott Variable-Range Hopping in Sr2IrO4 Epitaxial Thin Films by Misfit Strain and Isovalent Doping Maryam Souri, John Connell, Eric Teipel, John Nichols, Jasminka Terzic, Gang Cao, Ambrose Seo The Jeff = 1/2 Mott insulator Sr2IrO4 has attracted attention due to its novel electronic states originating from coexisting strong spin-orbit interaction and electron correlation. The similar magnetic and structural properties of Sr2IrO4 to layered cuprates has led to theoretical predictions of new superconducting states. Indeed, the d-wave gap symmetry has been observed with surface-electron doping. However, no superconducting transport property has been discovered in this compound so far. We report three-dimensional Mott variable-range hopping (3D Mott-VRH) transport of Sr2IrO4 epitaxial thin films, analogous to other transition-metal oxide Mott insulators. However, the characteristic temperature of the 3D Mott-VRH varies under misfit strain or isovalent doping, implying that the density of states near the Fermi energy is reconstructed. Magneto-transport data indicates that the transport mechanism is governed by a disorder induced localization and electron-electron correlations. We will discuss the Mott VRH transport in Sr2IrO4 thin films in comparison with other Mott insulators such as La2CuO4 and LaMnO3.
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Friday, November 9, 2018 9:06AM - 9:18AM |
E01.00004: Intrinsic interfacial van der Waals monolayers and their effect on the high-temperature superconductor FeSe / SrTiO3 Hunter Sims, Donovan N Leonard, Axiel Yael Birenbaum, Zhuozhi Ge, Tom Berlijn, Lian Li, Valentino R Cooper, Matthew F Chisholm, Sokrates T Pantelides It was recently demonstrated that monolayer FeSe on a SrTiO3 substrate is a superconductor with Tc between 60 and 100 K, compared to 8 K in bulk FeSe. This is in contrast to the expected behavior; thinning a superconductor typically reduces Tc. Similar results have been obtained in monolayer FeSe deposited on BaTiO3 and on anatase or rutile TiO2. Here we determine the atomic structure of an interfacial layer and identify a possible role in driving the increase in Tc using a combination of quantum mechanical calculations and scanning transmission electron microscopy. Within our DFT calculations, this interfacial layer hosts long-range magnetic and orbital order not found in the typical TiO2 surface termination nor in previously identified surface reconstructions. |
Friday, November 9, 2018 9:18AM - 9:30AM |
E01.00005: Pairng with an incipient band with enhanced TC from forward scattering phonons. Ken Nakatsukasa, Yan Wang, Steven S. Johnston The discovery of a mono-layer FeSe grown on STO substrate as well as other intercalated layered Fe-based superconductors raised questions regarding the validity of spin fluctuation pairing in these materials. Because theses systems show hole bands several 10 meV below the Fermi-level, it may seem that spin fluctuation exchange is not the primary contributor for the pairing. Here, we utilize fully self-consistent Fluctuation-exchange (FLEX) approximations in a bilayer Hubbard model to demonstrate the superconductivity can still appear from spin fluctuation exchange between an electron pocket and an incipient hole band. The resulting spectral function shows an s-wave superconducting gap opening at the Fermi-level centering at the electron band; at the same time, additional spectral weights appearing what seems to be a mirror of the hole band (mirror band) above the Fermi-level. In addition, the simulation has also considered the intra-orbital, attractive electron-phonon interactions with a strong forward scattering limit. The preliminary result has shown a larger enhancement in TC suggesting that such a type of phonons can coexist with the S± paring that arises from the spin fluctuation pairing. |
Friday, November 9, 2018 9:30AM - 9:42AM |
E01.00006: Charge balance and relaxation effects in the Fe based supercondutors Paolo Vilmercati, Federica Bondino, Alexei Fedorov, Brian C. Sales, David George Mandrus, Norman Mannella Doping this family of compounds with electrons (substitution of Fe for Co) destroys the magnetic order of the parent compound and progressively introduces superconductivity. The extra electrons from Co are possibly inserted in the Fe As plane the one responsible for superconductivity. The evolution of the electronic structure as seen from the atomic point of view is an important piece of information for understanding these compounds. Core level photoemission (XPS) has the capability of catching some aspects of the electron dynamic at the Fermi surface by means of relaxation and screening effects. In my contribution, I will show and discuss a series of core level spectra whose data have been collected at 30 K and with and high resolution (40meV), thus achieving a high detail of information which will show the intricate interplay among different degrees of freedom. |
Friday, November 9, 2018 9:42AM - 9:54AM |
E01.00007: Neutron scattering investigation of the magnetic interactions in the quasi-2D itinerant ferromagnet Fe3-xGeTe2 Stuart Calder, Yaohua Liu, Alexander Kolesnikov, Andrew May Reducing a materials dimensionality to topologically constrained two-dimensional (2D) layers yields phenomena beyond well-established classical behavior. The resultant material properties are of interest for fundamental studies as well as having the potential to drive new functionality in electronic/spintronic devices. Neutron scattering provides a powerful probe of bulk quasi-2D compounds. The quantitative extraction of the spin Hamiltonian from neutron scattering can in turn provide routes to understanding behavior in the bulk down to a single 2D-monolayer and allow the targeting of novel fundamental and applied phenomena. Here we present neutron scattering results on the quasi-2D itinerant ferromagnetic Fe3-xGeTe2, an exfoliable material with weakly connected van der Waals bonded 2D layers. As part of our study we investigate the influence of the high Fe site vacancy of up to 25% which controls the magnetic ordering temperature. By probing the inelastic excitations and elastic diffuse scattering we are able to reveal short range correlations in the 2D-layers associated with the Fe vacancies. Despite the appreciable disorder robust and gapped magnetic excitations are observed. The implications of the neutron data are discussed and models presented. |
Friday, November 9, 2018 9:54AM - 10:06AM |
E01.00008: Proximate orders and spin-triplet superconductivity in the quasi-one-dimensional AxCr3As3 materials Keith M Taddei, Guangzong Xing, Jifeng sun, Qiang Zheng, Athena Sefat, David J Singh, Clarina R dela Cruz Quasi-one-dimensional AxCr3As3 (with A = K, Cs, Rb and x = 1,2) is an intriguing new family of superconductors which exhibit many similar features to the high temperature unconventional superconductor families. Yet in contrast to these systems, no charge or magnetic ordering has been observed which could provide the electronic correlations presumed necessary for an unconventional superconducting pairing mechanism - an absence which defies predictions of first principles models. We report the results of neutron scattering experiments on polycrystalline K2Cr3As3 (Tc~7K) which probed the low temperature dynamics near Tc. Neutron diffraction data evidence a strong response of the nuclear lattice to the onset of superconductivity while inelastic scattering reveals highly dispersive scattering at the wavevector k=(001/2) indicative of short-range magnetic fluctuations. Furthermore, ab initio calculations predict and neutron total scattering confirms a structural instability. These observations suggest that K2Cr3As3 is in close proximity to multiple instabilities - in direct analogy with the iron-based and cuprate superconductors. |
Friday, November 9, 2018 10:06AM - 10:18AM |
E01.00009: Understanding spin excitations of a doped 1D Mott insulator Ekaterina M. Pärschke, Yao Wang, Brian Moritz, Thomas P. Devereaux, Cheng-Chien Chen, Krzysztof Wohlfeld The surprising persistence of collective spin excitations upon doping a 2D Mott insulator has |
Friday, November 9, 2018 10:18AM - 10:30AM |
E01.00010: Study of the origin of magnetic excitations at Γ-point in RIXS measurements on one-dimensional antiferromagnets Umesh Kumar, Steve Johnston We study the momentum-resolved resonant inelastic x-ray scattering (RIXS) cross-section at Cu L3-edge of Sr2CuO3, a one-dimensional antiferromagnet. The RIXS cross-section at this edge consists of spin conserving (ΔS = 0) and spin non-conserving (ΔS = 1) channels for magnetic excitations. A recent work1 has shown the existence of multi-spinons at the Γ-point in the ΔS = 0 channel. The exact nature of these excitations is still an open question due to the complicated RIXS cross-section. Using the ultrafast core-hole lifetime (UCL) expansion, we show that the higher order terms in UCL generate the excitations in the new phase and hence propose a new correlation function for studying these multi-spinons. Our work can open up a possibility to study the nature of these excitations in terms of spinons using Bethe ansatz. Additionally, we show that the scattering geometry can be used to resolve ΔS = 0 and ΔS = 1 components of the excitations in the RIXS spectra. [1] J. Schlappa, et. al., (2018), arXiv:1802.09329. |
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