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 C02: Spin-Orbit Coupling: 4D/5D Materials |
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Chair: Wei Tain, Oak Ridge National Lab Room: Holiday Inn Knoxville Downtown Cumberland |
Thursday, November 8, 2018 2:00PM - 2:30PM |
C02.00001: Unconventional metallic phases from doped spin-orbit assisted Mott insulators Invited Speaker: Chetan Dhital The oxides of 4d and 5d transition metals show unique electronic/magnetic behavior due to the interplay between electronic correlation and the spin-orbit coupling as they are comparable to each other. Ruddlesden-Popper iridates [Srn+1IrnO3n+1] are such showing large variation in electronic behaviors depending upon value of n. The first two members (n=1 and n=2) i.e. Sr2IrO4 and Sr3Ir2O7 host Jeff=1/2 Mott insulating state. It is natural to ask how such insulting states evolve with chemical doping and associated disorder. I will present the evolution of electronic/magnetic properties from insulator to unconventional metal in Sr3(Ir1-xRux)2O7 and (Sr1-xLax)3Ir2O7 along with their electronic/magnetic phase diagrams. |
Thursday, November 8, 2018 2:30PM - 3:00PM |
C02.00002: Magnetic ground states of spin-orbit coupled 5d iridates and the electric control of the physics properties Invited Speaker: Feng Ye The unique competition between spin-orbit interactions (SOI) and Coulomb correlation (U) in 5d elements and their compounds drives unusual physical behaviors such as jeff=1/2 Mott insulating state. Due to the entanglement of spin and orbital degrees of freedom, the form of magnetic interactions depends closely on the underlying lattice geometry. In the case of a 180◦ Ir-O-Ir bond, the Hamiltonian is governed by an isotropic Heisenberg term plus a weak dipolar-like anisotropy term due to Hund’s coupling, while for a 90◦ bond the anisotropic term due to the off-diagonal hopping matrix results in a quantum analog of the compass model. The strong SOI limit assumes local cubic symmetry of the IrO6 octahedra, which is rare in real materials. I will talk about the magnetic ground states of the square-lattice Sr2IrO4, honeycomb-lattice Na2IrO3, and the triangle lattice Ca2Sr2IrO6. Our latest work of controlling the physical properties using electric current will also be discussed. |
Thursday, November 8, 2018 3:00PM - 3:30PM |
C02.00003: Magnetic excitations in alpha-RuCl3 - a honeycomb-lattice quantum magnet with strong spin-orbit coupling - as a function of external magnetic field Invited Speaker: Christian Balz It is known that strong spin-orbit coupling entangles the spin and orbital spaces, and leads to a rich variety of the low energy Hamiltonians. This gives way to ‘‘engineer’’ in such Mott insulators for example the exactly solvable spin model by Alexei Kitaev. The insulating magnetic material alpha-RuCl3 is comprised of van der Waals coupled honeycomb layers in which the Ru3+(4d5) ions are in the low spin state and form a honeycomb lattice. A strong cubic crystal field combined with spin-orbit coupling leads to a Kramer’s doublet, nearly perfect J=1/2 ground state thus satisfying the conditions necessary for producing the above mentioned Kitaev couplings in the low energy Hamiltonian. Here, I will present neutron scattering investigations of the magnetic excitations and present how they drastically change under the application of an external magnetic field. We observe that, when a magnetic field of approximately 7.5 T is applied in the honeycomb plane, a transition from zigzag magnetic order to a disordered state, believed to be a quantum spin liquid, takes place. This is reflected in the magnetic excitation spectrum as a disappearance of spin waves and a strengthening of a scattering continuum centered on the 2D gamma point that is interpreted as a signature of fractionalized excitations. Published measurements by Kasahara et al (Nature 559, 227 (2018)) of the thermal Hall effect suggest a possible topological transition at an even higher field. We have performed new high-resolution measurements of the excitations at fields spanning these two transitions. At the highest fields the broad scattering continuum is altered, and the response is seen to be dominated by a sharp peak at the lower bound, providing a strong indication that a new phase has been entered. The implications of these observations will be discussed in detail. |
Thursday, November 8, 2018 3:30PM - 4:00PM |
C02.00004: Spectroscopic investigation of CDW phase transitions 2H-NbSe2, 2H-TaS2 and 1T-TiSe2 Invited Speaker: Utpal Chatterjee Layered transition-metal dichalcogenides (TMDs) are well-known for their rich phase diagrams, which encompass diverse quantum states including metals, semiconductors, Mott insulators, superconductors, and charge density waves (CDWs). For instance, 2H-NbSe2, 2H-TaS2and 1T-TiSe2are canonical TMD CDW systems—2H-NbSe2 and 2H-TaS2host incommensurate CDW order, while 1T-TiSe2 hosts a commensurate one. There is a coexistence/competition of CDW and superconductivity 2H-NbSe2and 2H-TaS2. This is, however, not the case for pristine 1T-TiSe2. Nevertheless, subtle interplay of superconductivity and CDW order appears in each of these materials strain is applied to foreign atoms are introduced in these compounds. Quite generally, the phase diagrams of 2H-NbSe2, 2H-TaS2and 1T-TiSe2 at the presence of strain or chemical intercalation reminisce those of High temperature superconductors and heavy fermion compounds. A critical step towards characterizing these phase diagrams is to first unveil the mechanism of the CDW transition in the parent compounds, which remain an intriguing puzzle despite decades of research. It is almost universally accepted that conventional Fermi surface nesting theory doesn’t apply to the CDW instability of these systems. In the context of alternative models for CDW orders in these systems, we will present our experimental data which combine Angle Resolved Photoemission Spectroscopy, Scanning Tunneling Microscopy , X-ray diffraction and transport measurements. We will also explore the distinctive impacts of disorder and change in carrier concentration of commensurate and incommensurate CDW systems. |
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