Two-dimensional Metallic Behavior Research Articles

Two-dimensional metallic behavior at polar MgO/BaTiO3 (110) interfaces**Project supported by the National Basic Research Program of China (Grant No. 2013CB632506), the National Natural Science Foundation of China (Grant Nos. 11374186, 51231007, 51202132, and 51102153), and the Independent Innovation Foundation of Shandong University, China (Grant No. 2012TS027).

The first-principles calculations are employed to investigate the electrical properties of polar MgO/BaTiO3 (110) interfaces. Both n-type and p-type polar interfaces show a two-dimensional metallic behavior. For the n-type polar interface, the interface Ti 3d electrons are the origin of the metallic and magnetic properties. Varying the thickness of BaTiO3 may induce an insulator–metal transition, and the critical thickness is 4 unit cells. For the p-type polar interface, holes preferentially occupy the interface O 2py state, resulting in a conducting interface. The unbalance of the spin splitting of the O 2p states in the interface MgO layer leads to a magnetic moment of about 0.25μ B per O atom at the interface. These results further demonstrate that other polar interfaces, besides LaAlO3/SrTiO3, can show a two-dimensional metallic behavior. It is helpful to fully understand the role of polar discontinuity on the properties of the interface, which widens the field of polar-nonpolar interfaces.

Digital magnetic heterostructures based on Si and Fe

This paper reports on the results of ab initio calculations of the electronic and magnetic properties of Si digital heterostructures doped with a Fe monolayer of the substitutional or interstitial type. It has been revealed that, after the structural relaxation, heterostructures of both types exhibit a two-dimensional metallic behavior and a ferromagnetic ordering in the range of Si spacer thicknesses up to 19 atomic layers. The magnetization and spin polarization at the Fermi level for the heterostructures with an Fe monolayer of the substitutional type are two times higher than those for the system with an Fe monolayer of the interstitial type.

Anisotropy in the magnetization and resistivity of the metallic triangular-lattice magnet PdCrO2

We report results of our magnetization and resistivity measurements using single crystals of the conductive antiferromagnet PdCrO2 with a layered structure, consisting of alternating stacks of a triangular lattice of Pd1+ and of Cr3+ along the c axis. We confirmed that the magnetic susceptibility is nearly isotropic above TN but becomes slightly anisotropic below TN (χab > χc). These results, combined with previously known facts, indicate that PdCrO2 is a Heisenberg spin system, and the spins lie in a plane containing the c axis below TN (an "easy-axis type" 120° structure). We also found that the resistivity exhibits a highly two-dimensional metallic behavior in the whole measured temperature range with an anisotropy ratio ρc/ρab ≥ 150. Interestingly, despite such a strongly anisotropic conductivity, the inter-Pd-layer hopping and the intra-Pd-layer conductivity are both affected by the localized Cr spins in comparable magnitude. The present results make PdCrO2 a promising candidate for the emergence of the unconventional anomalous Hall effect.

Similarities and differences in two-dimensional metallicity induced by temperature and a parallel magnetic field: Effect of screening

We compare the effects of temperature and parallel magnetic field on the two-dimensional metallic behavior within the unified model of temperature and field dependent effective disorder arising from the screened charged impurity scattering. We find, consistent with experimental observations, that the temperature and field dependence of resistivity should be qualitatively similar in $n\text{\ensuremath{-}}\mathrm{Si}$ MOSFETs and different in $n$-type GaAs two-dimensional (2D) systems, with the $p$-type 2D GaAs system being somewhat intermediate. Based on our calculated results we critically comment on the expected similarities and differences between temperature and field dependent carrier transport properties in various dilute 2D semiconductor systems.

Two-Dimensional Metallic ClO 4 Salt of a Novel Dihydrothiophene-Extended Donar, BO-HBDTT, with Relatively Narrow Band Width

A new dihydrothiophene-extended BEDO-TTF (BO) type donor, BO-HBDTT, was synthesized by a convenient method and gave metallic ClO 4 , BF 4 , and PF 6 salts. Of these the ClO 4 salt with β′′ type donor arrangement showed two-dimensional metallic behavior and relatively narrow band width.

Anisotropy of interchain interaction in polymeric (SN) x crystals

The technique of polarized reflection microspectroscopy was used to study anisotropy of polymeric sulfur nitride (SN) x in plasma edge region. The spectra taken from different faces of single crystals indicate the presence of strong anisotropy of interchain interaction due to orientation of the π-electron orbitals and suggest two-dimensional metallic behavior of the π-electron system in (SN) x .