We explore the electrical transport and magneto-conductance in quasi two-dimensional strongly correlated ultrathin films of LaNiO$_{3}$ (LNO) to investigate the effect of hetero-epitaxial strain on electron-electron and electron-lattice interactions from the low to intermediate temperature range (2K$sim$170K). The fully epitaxial 10 unit cell thick films spanning tensile strain up to $sim4%$ are used to investigate effects of enhanced carrier localization driven by a combination of weak localization and electron-electron interactions at low temperatures. The magneto-conductance data shows the importance of the increased contribution of weak localization to low temperature quantum corrections. The obtained results demonstrate that with increasing tensile strain and reduced temperature the quantum confined LNO system gradually evolves from the Mott into the Mott-Anderson regime.
We report $beta$-detected NMR of ion-implanted $^{8}$Li in a single crystal and thin film of the strongly correlated metal LaNiO$_{3}$. In both samples, spin-lattice relaxation measurements reveal two distinct local metallic environments, as is evide
nt from $T$-linear Korringa $1/T_{1}$ below 200 K with slopes comparable to other metals. A small, approximately temperature independent Knight shift of $sim 74$ ppm is observed, yielding a normalized Korringa product characteristic of substantial antiferromagnetic correlations, but, we find no evidence for a magnetic transition from 4 to 310 K. Two distinct, equally abundant $^{8}$Li sites is inconsistent with the widely accepted rhombohedral structure of LaNiO$_{3}$, but cannot be simply explained by either of the common alternative orthorhombic or monoclinic distortions.
The kagome lattice is a fruitful source of novel physical states of matter, including the quantum spin liquid and Dirac fermions. Here we report a structural, thermodynamic, and transport study of the two-dimensional kagome metal-organic frameworks N
i_3(HIB)v2 and Cu_3(HIB)_2 (HIB = hexaiminobenzene). Magnetization measurements yield Curie constants of 1.12 and 0.352 emu K mol f.u.-1 Oe-1 respectively, close to the values expected for ideal S=1 and S=1/2 moments. Weiss temperatures of -20.3 K and -6.52 K, respectively, indicate moderate to weak magnetic interactions. Electrical transport measurements reveal that both materials are semiconducting, with gaps of Eg = 22.2 and 103 meV, respectively. Specific heat measurements reveal a large T-linear contribution of {gamma} = 148(4) mJ mol-f.u.-1 K-2 in Ni_3(HIB)_2 with only a gradual upturn below T ~ 5 K and no evidence of a phase transition to an ordered state down to T = 0.1 K. Cu_3(HIB)_2 also lacks evidence of a phase transition above T = 0.1 K, with a substantial, field-dependent, magnetic contribution below T ~ 5 K. Despite being superficially in agreement with expectations of magnetic frustration and spin liquid physics, we are able to explain these observations as arising due to known stacking disorder in these materials. Our results further state the art of kagome lattice physics, especially in the rarely explored regime of semiconducting but not metallic behavior.
Although the isotope effect in superconducting materials is well-documented, changes in the magnetic properties of antiferromagnets due to isotopic substitution are seldom discussed and remain poorly understood. This is perhaps surprising given the p
ossible link between the quasi-two-dimensional (Q2D) antiferromagnetic and superconducting phases of the layered cuprates. Here we report the experimental observation of shifts in the N{e}el temperature and critical magnetic fields ($Delta T_{rm N}/T_{rm N}approx 4%$; $Delta B_{rm c}/B_{rm c}approx 4%$) in a Q2D organic molecular antiferromagnets on substitution of hydrogen for deuterium. These compounds are characterized by strong hydrogen bonds through which the dominant superexchange is mediated. We evaluate how the in-plane and inter-plane exchange energies evolve as the hydrogens on different ligands are substituted, and suggest a possible mechanism for this effect in terms of the relative exchange efficiency of hydrogen and deuterium bonds.
Experimental evidence for the possible universality classes of the metal-insulator transition (MIT) in two dimensions (2D) is discussed. Sufficiently strong disorder, in particular, changes the nature of the transition. Comprehensive studies of the c
harge dynamics are also reviewed, describing evidence that the MIT in a 2D electron system in silicon should be viewed as the melting of the Coulomb glass. Comparisons are made to recent results on novel 2D materials and quasi-2D strongly correlated systems, such as cuprates.
Experimental results on the metal-insulator transition and related phenomena in strongly interacting two-dimensional electron systems are discussed. Special attention is given to recent results for the strongly enhanced spin susceptibility, effective
mass, and thermopower in low-disordered silicon MOSFETs.
E.J. Moon
,B.A. Gray
,M. Kareev
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(2011)
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"Strain dependent transport properties of the quasi two-dimensional correlated metal, LaNiO$_{3}$"
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Eun Ju Moon
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