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Register a new userThe role of potassium orbitals in the metallic behavior of K3picene
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Detailed electronic structure calculations of picene clusters doped by potassium modeling the crystalline K3picene structure show that while two electrons are completely transferred from potassium atoms to the LUMO of pristine picene, the third one remains closely attached to both material components. Multiconfigurational analysis is necessary to show that many structures of almost degenerate total energies compete to define the cluster ground state. Our results prove that the 4s orbital of potassium should be included in any interaction model describing the material. We propose a quarter filled two orbital model as the most simple model capable of describing the electronic structure of K-intercalated picene. Precise solutions obtained by a development of Lanczos method show low energy electronic excitations involving orbitals located at different positions. Consequently, metallic transport is possible in spite of the clear dominance of interaction over hopping.
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We report magnetic behavior of two intermetallics-based kagome lattices, Tb3Ru4Al12 and Er3Ru4Al12, crystallizing in the Gd3Ru4Al12-type hexagonal crystal structure, by measurements in the range 1.8-300 K with bulk experimental techniques (ac and dc magnetization, heat-capacity and magnetoresistance). The main finding is that the Tb compound, known to order antiferromagnetically below (T_N=) 22 K, shows glassy characteristics at lower temperatures (<15K), thus characterizing this compound as a re-entrant spin-glass. The data reveal that glassy phase is quite complex and is of a cluster type. Since the glassy behavior was not seen for the Gd analogue in the past literature, this finding for the Tb compound emphasizes that this kagome family could provide an opportunity to explore the role of higher order (such as quadrupole) in bringing out magnetic frustration. Additional findings reported here for this compound are: (i) The temperature dependence of magnetic susceptibility and electrical resistivity in the range 12 - 20 K are found to be hysteretic leading to a magnetic phase in this temperature range, mimicking disorder-induced first-order magnetic phase-transition. (ii) Features attributable to an interesting magnetic phase co-existence phenomenon in the magnetoresistance in zero field, after cycling across metamagnetic transition fields, are observed. With respect to the Er compound, we do not find any evidence for long-range magnetic ordering down to 2 K, but this appears to be on the verge of magnetic order at 2 K.
A previously unreported Pb-based perovskite PbMoO$_3$ is obtained by high-pressure and high-temperature synthesis. This material crystallizes in the $Pmbar{3}m$ cubic structure at room temperature, making it distinct from typical Pb-based perovskite oxides with a structural distortion. PbMoO$_3$ exhibits a metallic behavior down to 0.1 K with an unusual $T$-sub linear dependence of the electrical resistivity. Moreover, a large specific heat is observed at low temperatures accompanied by a peak in $C_P/T^3$ around 10 K, in marked contrast to the isostructural metallic system SrMoO$_3$. These transport and thermal properties for PbMoO$_3$, taking into account anomalously large Pb atomic displacements detected through diffraction experiments, are attributed to a low-energy vibrational mode, associated with incoherent off-centering of lone pair Pb$^{2+}$ cations. We discuss the unusual behavior of the electrical resistivity in terms of a polaron-like conduction, mediated by the strong coupling between conduction electrons and optical phonons of the local low-energy vibrational mode.
Magnetotransport measurements performed on several well-characterized highly oriented pyrolitic graphite and single crystalline Kish graphite samples reveal a reentrant metallic behavior in the basal-plane resistance at high magnetic fields, when only the lowest Landau levels are occupied. The results suggest that the quantum Hall effect and Landau-level-quantization-induced superconducting correlations are relevant to understand the metallic-like state(s) in graphite in the quantum limit.
We calculate Raman response functions on the Fermi surface in metallic cuprates.
I study the structural and magnetic instabilities in LaNiO$_3$ using density functional theory calculations. From the non-spin-polarized structural relaxations, I find that several structures with different Glazer tilts lie close in energy. The $Pnma$ structure is marginally favored compared to the $Roverline{3}c$ structure in my calculations, suggesting the presence of finite-temperature structural fluctuations and a possible proximity to a structural quantum critical point. In the spin-polarized relaxations, both structures exhibit the $uparrow!!0!!downarrow!!0$ antiferromagnetic ordering with a rock-salt arrangement of the octahedral breathing distortions. The energy gain due to the breathing distortions is larger than that due to the antiferromagnetic ordering. These phases are semimetallic with small three-dimensional Fermi pockets, which is largely consistent with the recent observation of the coexistence of antiferromagnetism and metallicity in LaNiO$_3$ single crystals by Li textit{et al.} [arXiv:1705.02589].
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