Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C06: Electronic States in S and Te Chalcogenides |
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Sponsoring Units: DCMP Chair: Rico Schoenemann, National High Magnetic Field Laboratory Room: BCEC 109A |
Monday, March 4, 2019 2:30PM - 2:42PM |
C06.00001: Physical Properties of Low Dimensional Ternary Transition-Metal Sulfides Shermane Benjamin, Alisa Drenner, Mitch Baker, Michael Smith, John J Neumeier Transition-metal sulfides exhibit behaviors such as metal-insulator transitions, superconductivity, and magnetism. They provide an interesting class of compounds for comparison to transition-metal oxides. In this work, polycrystalline SrTa2S5 and BaTa2S5 samples were synthesized. Large (15 x 15 x 0.25 mm3) single crystals of BiNbS3 were grown by chemical vapor deposition. SrTa2S5 and BaTa2S5 superconduct at Tc=2.14 K and 3.2 K, respectively. BiNbS3 shows no signs of superconductivity above ~0.4 K. The magnetic properties, specific heat, electrical resistivity, structural analysis, and compositional analysis will be discussed. The influence of hydrostatic pressure on the electrical resistivity will be presented. |
Monday, March 4, 2019 2:42PM - 2:54PM |
C06.00002: Bulk and topological effects on the optical conductivity of BaNiS2 Ricardo Lobo The BaCo1-xNixS2 system forms a solid solution with an almost Mott like insulating phase when x=0 to a weakly correlated conductor in the Ni end member. This weakly correlated material has a series of interesting topological properties such as a hidden spin polarization due to a Rashba coupling and three dimensional Dirac-like cones close to the Fermi level. Here, I will discuss the temperature dependence of the optical conductivity (σ) of this material. The room temperature real part of σ shows a Drude like peak followed by a linear-in-frequency region. Upon cooling the material there is a spectral weight transfer from about 0.1 eV to 0.3 eV. Interestingly the linear region remains unchanged as a function of temperature. Combining the optical measurements with first principle calculations shows that this spectral weight transfer is a competition between regular carriers and Dirac-like bands. |
Monday, March 4, 2019 2:54PM - 3:06PM |
C06.00003: Photoemission study on a special type of multiferroics: GaV4S8 & GeV4S8 Amol Singh, Jung-Han Li, Yen-Fa Liao, Hsiao-Yu Huang, Yen-Yi Chu, Jing Chang, Ku-Ding Tsuei, Lunyong Zhang, Sang-Wook Cheong, Michel A Van Veenendaal, Di-Jing Huang The lacunar spinels (AV4S8) with A=Ga and Ge, consisting of tetrahedral (AS4)n- and weakly linked cubane (V4S4)n+ are unique in known skyrmions because of a sizable ferroelectric polarization of ~ 1 μC/cm2 and polar crystal structure. Their electronic properties depend on the special degrees of freedom of the basic electronic units of V4S4. These materials are classified as a special class of Mott insulators in which strong electron correlations arise from weak intercluster hybridization. From the viewpoint of ionic formula, average valency of V is 3.25+ in GaV4S8 and 3+ in GeV4S8, yet exact valency of V in these compounds is not known. We conducted hard X-ray photoemission to study the electronic structure of GaV4S8 & GeV4S8 single crystals and to investigate the valency of V in these compounds. The V 2p photoemission spectra are best explained with (V4S4)5+ and (V4S4)6+ for GeV4S8 and GaV4S8 respectively. Further S 2p XPS spectra shows results consistent with the scenario of dynamical Jahn-Teller distortion in the paraelectric phase. |
Monday, March 4, 2019 3:06PM - 3:18PM |
C06.00004: Orbital-Order Driven Ferroelectricity and Dipolar Relaxation Dynamics in Multiferroic GaMo4S8 Korbinian Geirhos, Stephan Krohns, Hiroyuki Nakamura, Takeshi Waki, Yoshikazu Tabata, István Kézsmárki, Peter Lunkenheimer GaMo4S8, a compound of the lacunar spinel family, was recently shown to exhibit non-canonical, orbitally-driven ferroelectricity [1]. Our dielectric spectroscopy measurements on this multiferroic material reveal complex relaxation dynamics, above as well as below its Jahn-Teller transition at TJT= 47 K [2]. Above the Jahn-Teller transition, two types of coupled dipolar-orbital dynamics were found: On the one hand, relaxations within cluster-like regions with short-range polar order, as known from relaxor ferroelectrics. On the other hand, critical fluctuations of only weakly interacting dipoles, resembling the typical dynamics of order-disorder type ferroelectrics. Below TJT, the system is driven into long range ferrolectric order by the onset of orbital order and dipolar dynamics within the ferroelectric domains is observed: The found marked differences to the skyrmion host GaV4S8 seem to be related to the different structural distortions in these systems. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C06.00005: Noise spectroscopy study of metal-insulator transition in CuIr2S4 Dasharath Adhikari, Ahmed Ali, Ali M Alsaqqa, Colin P Kilcoyne, Nobuhiro Matsumoto, Sambandamurthy Ganapathy Single crystals of the CuIr2S4 exhibit a metal-insulator transition (MIT) at a critical temperature (Tc ) ∼ 231 K, accompanied by simultaneous charge ordering and spin dimerization, making it an interesting system to study the interplay of interaction among many degrees of freedom. By employing low-frequency electrical noise spectroscopy, we observe that the power spectral density (PSD) of the resistance fluctuations peaks around Tc likely due to the formation of domains of opposite phase. The ultra-low frequency window of our measurements serves as a tool to measure the increased scattering of charge carriers near Tc, due to nucleation, pinning and/or propagation of domains. The probability density function (PDF) of the fluctuations in the transition region shows a significant deviation from the expected Gaussian behavior further supporting the intermixing of phases near Tc. In addition, an abrupt phase transition with a threshold behavior can also be triggered electrically from the insulating phase. The analysis of the PSD, PDF and 1/f behavior suggests a significant role of the domains in the electrically driven case too. |
Monday, March 4, 2019 3:30PM - 3:42PM |
C06.00006: Anomalous conductivity near percolative metal-insulator transition in monolayer MoS2 Byoung Hee Moon, Jung Jun Bae, Gang Hee Han, Hyun Kim, Homin Choi, Young Hee Lee Conductivity of the insulating phase increases generally upon increasing a drain-source voltage due to the field-enhanced hopping or heating effect. Here, we report the opposite behavior, and anomalous metallic to insulating phase transition driven by a voltage at low voltage regime in monolayer molybdenum disulfide. We ascribe these features to the inhomogeneous state of the system in which the transport is governed by a percolation. At the higher voltage regime, the insulating phase is transformed further to the metallic phase, exhibiting unique multi-phases in this system. In this talk, we discuss these anomalous behaviors and their implications in a metal-insulator transition in two-dimension. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C06.00007: Optical Thermal Measurements of Thermal Diffusivity in 1T-TaS2 Erik Kountz, Jiecheng Zhang, Aharon Kapitulnik Thermal response of electronic materials can detect phase transitions and transport processes. Moreover, micron-scale measurements avoid sample imperfections such as dislocations, grain boundaries, and other defects, and allow for proper averaging on macroscopic samples. We use a photo-thermal microscope for high resolution thermal diffusivity and optical reflectivity measurements. A laser beam is focused at the surface of the targeted sample; the laser power is modulated to create a periodic, point-like heat source. A nearby laser measures the local reflectivity. In this talk we focus on 1T-TaS2, a quasi-2D Mott insulator with various competing charge density wave (CDW) orders and a proposed quantum spin liquid phase at low temperature [1]. We study the nature of the phase transitions through anomalies in differential reflectivity (dR/dT) and the transport behavior though measurements of thermal diffusivity (DQ). In particular, anomalies in dR/dT at the 180K- and 345K- CDW transitions are discussed in terms of the nature of the phase transitions and DQ is discussed in terms of its implications on transport mechanisms. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C06.00008: Real space imaging of tuneable magnetic order in Fe1+xTe with x>0.12 Christopher Trainer, Chi Ming Yim, Peter Wahl
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Monday, March 4, 2019 4:06PM - 4:18PM |
C06.00009: Visualizing uniaxial-strain-manipulation of antiferromagnetic domains in Fe1+yTe using spin-polarized scanning tunneling microscope Joel Friedman, Mariam Kavai, Ioannis Giannakis, Justin Leshen, Pawel Zajdel, Pegor Aynajian The quest to understand correlated electronic systems has pushed the frontiers of experimental measurements towards development of new experimental techniques and methodologies. Here we use a novel home-built uniaxial-strain device integrated into our variable temperature scanning tunneling microscope (STM) that enables one to controllably manipulate in-plane uniaxial strain in the samples and probe their electronic response at the atomic scale. Using STM with spin-polarization techniques, we visualize antiferromagnetic (AFM) domains and their atomic structure in Fe1+yTe, the parent compound of iron-based superconductors, and demonstrate how these domains respond to applied uniaxial-strain. We observe the bi-directional AFM domains in the unstrained sample, with an average domain size of ~ 50-150 nm, to transition into a single unidirectional domain under applied uniaxial-strain. Our findings open a new direction to utilize a valuable tuning parameter in STM as well as other spectroscopic techniques both for tuning the electronic properties as well as inducing symmetry breaking in quantum material systems. |
Monday, March 4, 2019 4:18PM - 4:30PM |
C06.00010: Dimensional crossover in a van der Waals ferromagnet detected by spin correlation driven distortions Alon Ron, Eli Zoghlin, Leon Balents, Stephen Wilson, David Hsieh Magneto-elasticity – the structural deformation of a crystal in response to a change in its magnetic energy – is commonly detected across magnetic long-range ordering (LRO) transitions and yields insight into magnetic ground state energetics. In principle, distortions are also induced by magnetic short-range ordering (SRO), which provide complementary information about short-range correlations and energetics that are essential for understanding how LRO is established. However these distortions are difficult to resolve because the associated atomic displacements are exceedingly small and do not break symmetry. Here we demonstrate high-multipole nonlinear optical polarimetry as a sensitive and mode selective probe of SRO induced distortions using CrSiTe3 as a testbed. This compound is composed of van der Waals bonded sheets of ferromagnetically interacting Heisenberg spins that, in isolation, would be impeded from LRO by the Mermin-Wagner theorem. Our results show that CrSiTe3 evades this law via a two-step crossover from two- to three-dimensional magnetic SRO above its Curie temperature (Tc=31K), manifested through two previously undetected totally symmetric distortions at T2D~110K and T3D~60K, respectively. Such data open new avenues for mechanical control of magnetism. |
Monday, March 4, 2019 4:30PM - 4:42PM |
C06.00011: Thermal Expansion in Ba3Zr2S7 Nathan Koocher, Ryan Klein, Alison Altman, Danna Freedman, James M Rondinelli
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Monday, March 4, 2019 4:42PM - 4:54PM |
C06.00012: Charge density patterns in spin-selectively photoexcited interacting fermions Thomas Koehler, Sebastian Paeckel, Salvatore Manmana We describe the formation of charge-density patterns induced by spin-selective photoexcitations of interacting fermionic systems with an underlying magnetic microstructure. Using tensor-network methods for one-dimensional model systems, we find stable charge-density patterns for a wide range of parameters. We discuss a generic mechanism explaining this effect for systems that possess a periodic modulation of local observables in any dimension. Realizations in pump-probe experiments on materials and by experiments with ultracold gases on optical lattices are proposed. |
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