Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session X36: Novel f- and d-electron Materials: Skutterudites and PnictidesInvited
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Sponsoring Units: DCMP Chair: Subhasish Mandal, Rutgers University, New Brunswick Room: BCEC 205C |
Friday, March 8, 2019 8:00AM - 8:36AM |
X36.00001: Overview of Experimental Results on Filled Skutterudites with Pt-Ge framework Invited Speaker: Roman Gumeniuk Filled skutterudites are compounds with the body-centred (space group Im-3, a = 9 Å) crystal structure and total chemical formula MT4X12 (structure type LaFe4P12), where M = alkaline, alkali-earth, rare-earth or actinide metal, T is a transition metal of Fe-subgroup and X is a pnictogen-atom. Their structural arrangement belongs to the group of the so-called cage-compounds, where positively charged filler-atoms (i.e. M-component) are situated inside large voids formed by a covalently bonded atomic framework (i.e. T4X12). Such a combination of different types of chemical bonding together with vibrational dynamics of the filler results in numerous exciting physical phenomena (e.g. superconductivity, heavy fermion and Kondo behaviours, charge-density wave, thermoelectric properties etc.). In the past decade we succeed in the preparation and study of the physical properties of filled skutterudites with the new Pt-Ge framework and total formula MPt4Ge12 (M = Sr, Ba, La, Ce, Pr, Nd, Eu, Sm). {Sr, Ba, La, Pr}Pt4Ge12 are superconductors with high transition temperatures (i.e. up to ∼8 K). The complete characterization of their properties, which included μSR and penetration depth measurements, revealed LaPt4Ge12 to be a multi-gap superconductor, while the PrPt4Ge12 is an unconventional superconductor with nodes in the energy gap. CePt4Ge12 is found to be a system at the very border between typical intermediate valence and true Kondo lattice behaviour. SmPt4Ge12 is a high-pressure phase with the moderate heavy fermion behaviour. Filled skutterudites {Nd, Eu}Pt4Ge12 show Curie-Weiss paramagnetism in the temperature range 10-400 K and complicated magnetic structures with multiple orderings below 2 K. |
Friday, March 8, 2019 8:36AM - 9:12AM |
X36.00002: Dynamical Mean Field Theory and the Iron Pnictides and Chalcogenides Invited Speaker: Gabriel Kotliar Dynamical mean field theory (DMFT) in its combination with realistic electronic structure methods, now enables the computation of physical properties of materials starting from first principles. It also gives unexpected insights into the physics of strongly correlated systems. |
Friday, March 8, 2019 9:12AM - 9:48AM |
X36.00003: Comprehensive Study of Electronic Structure of Rare-Earth (R) Filled Skuttterudites, RPt4Ge12 Invited Speaker: Khandker F. Quader Materials whose properties are influenced by presence of f-electrons are of current interest. Experiments on rare-earth filled skutterudites demonstrate an intriguing array of thermodynamic, transport and superconducting properties, and bring to fore theoretical challenges posed by f-electron systems. First principle calculations, such as density functional theory (DFT), sparse in the skutterudites, can provide valuable information about electronic structures that can be compared with experiments, and utilized in further theory development. The talk will discuss a comprehensive electronic structure study on a series of rare earth filled skutterudites, RPt4Ge12 (R= La, Ce, Pr), aimed at shedding light on aspects that may be useful for understanding some of their properties: consequences of progressive increase of f-electrons in the series; role of correlation “U” between the f-electrons and its importance relative to spin-orbit coupling; the nature and variation of 3D Fermi surfaces with the number of f-electrons and “U”. The calculated Fermi surfaces may be relevant to the currently debated issue of multi-band versus single-band superconductivity; the density of states (DOS) and bands can be compared with resonant photoemission spectroscopy and specific heat measurements, and provide estimates of effective masses; the pseudogaps in DOS may be useful for understanding possible thermoelectric applications. These DFT calculations were cross-checked with VASP and Wien2K programs, and done for different exchange functionals; hence may serve as benchmark calculations for these materials. |
Friday, March 8, 2019 9:48AM - 10:24AM |
X36.00004: Predictive powers of the DFT+DMFT method for electronic and structural properties Invited Speaker: Gheorghe Lucian Pascut Correlated materials are known to give rise to interesting physical properties such as superconductivity, colossal magnetoresistance, metal to insulator transitions, orbital and charge ordering, etc. In this talk I will present theoretical results for d- and f-systems, obtained with a method based on a combination of density functional theory (DFT) and dynamical mean field theory (DMFT). Due to recent development of forces for structural relaxations in DFT+DMFT method, we are now able to gain further insight into the couplings between electronic and structural degrees of freedom in the vicinity of a Mott transition, thus giving us predictive power for the electronic and structural properties of the correlated materials. Applying this method to AMnO3 (A=Bi,La) oxides, we find unusual electronic states with orbital selectivity, such as Site- and Orbital-Selective Mott state or Orbital-Selective Mott state. I will describe the electronic properties of such states and I will argue that: (1) these switchable novel states are a consequence of a highly sensitive interplay of the lattice with the electronic degrees of freedom of the correlated d-electrons and sp-electrons of the A ions; (2) based on the new understating of these electronic states we can explain the resonant x-ray scattering measurements, which till now could not be explained by other theoretical models. In addition, by comparing the DFT+DMFT structural relaxations at finite temperatures with the experimental crystal structures, we show that DFT+DMFT can capture the fine structural distortions induced by these unusual electronic states much better than DFT, thus confirming the predictive power of the DFT+DMFT method. I will end my talk discussing theoretical correlated electronic structure of filled skutterudites RPt4Ge12 (R=Ce,Pr) and comparison with experimental photoemission spectroscopy data. |
Friday, March 8, 2019 10:24AM - 11:00AM |
X36.00005: Soft-modes and electronic topological transitions in p- and d-electron materials Invited Speaker: Michael Widom The Fermi surface of a metal can be altered through the application of isotropic pressure, symmetry-breaking anisotropic strains, or chemical substitution. Changes in Fermi surface topology, such as the opening of a gap, or the creation or disappearance of a pocket, are known as Lifshitz transitions, and can dramatically influence the electronic, magnetic and mechanical properties of a material. This talk will focus on two examples of such transitions: the Burgers distortion that transforms body centered cubic metals to hexagonal close packed is driven by a Jahn-Teller-Peierls transition associated with a pseudogap in dxy orbitals created by symmetry breaking; the collapse transitions in tetragonal AFe2As2 pnictides (A = Ca, Sr, Ba) are driven by the disappearance of a pz electron pocket upon the application of pressure. These collapse transitions are contrasted with the discontinuous tetragonal to orthorhombic transition in CaFe2As2, which is thermodynamic rather than mechanical in character. Both the Burgers distortion and the collapse transition are connected with soft mode behaviors. |
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