18 research outputs found
Metal-insulator transition and electrically-driven memristive characteristics of SmNiO3 thin films
The correlated oxide SmNiO3 (SNO) exhibits an insulator to metal transition
(MIT) at 130 {\deg}C in bulk form. We report on synthesis and electron
transport in SNO films deposited on LaAlO3 (LAO) and Si single crystals. X-ray
diffraction studies show that compressively strained single-phase SNO grows
epitaxially on LAO while on Si, mixed oxide phases are observed. MIT is
observed in resistance-temperature measurements in films grown on both
substrates, with charge transport in-plane for LAO/SNO films and out-of-plane
for Si/SNO films. Electrically-driven memristive behavior is realized in
LAO/SNO films, suggesting that SNO may be relevant for neuromorphic devices
Conductivity noise study of the insulator-metal transition and phase co-existence in epitaxial samarium nickelate thin films
Interaction between the lattice and the orbital degrees of freedom not only
makes rare-earth nickelates unusually "bad metal", but also introduces a
temperature driven insulator-metal phase transition. Here we investigate this
insulator-metal phase transition in thin films of using the
slow time dependent fluctuations (noise) in resistivity. The normalized
magnitude of noise is found to be extremely large, being nearly eight orders of
magnitude higher than thin films of common disordered metallic systems, and
indicates electrical conduction via classical percolation in a spatially
inhomogeneous medium. The higher order statistics of the fluctuations indicate
a strong non-Gaussian component of noise close to the transition, attributing
the inhomogeneity to co-existence of the metallic and insulating phases. Our
experiment offers a new insight on the impact of lattice-orbital coupling on
the microscopic mechanism of electron transport in the rare-earth nickelates.Comment: 5 pages, 4 figure
Universal logic with encoded spin qubits in silicon
Qubits encoded in a decoherence-free subsystem and realized in
exchange-coupled silicon quantum dots are promising candidates for
fault-tolerant quantum computing. Benefits of this approach include excellent
coherence, low control crosstalk, and configurable insensitivity to certain
error sources. Key difficulties are that encoded entangling gates require a
large number of control pulses and high-yielding quantum dot arrays. Here we
show a device made using the single-layer etch-defined gate electrode
architecture that achieves both the required functional yield needed for full
control and the coherence necessary for thousands of calibrated exchange pulses
to be applied. We measure an average two-qubit Clifford fidelity of with randomized benchmarking. We also use interleaved randomized
benchmarking to demonstrate the controlled-NOT gate with
fidelity, SWAP with fidelity, and a specialized entangling
gate that limits spreading of leakage with fidelity
Origins of bad-metal conductivity and the insulator–metal transition in the rare-earth nickelates
For most metals, increasing temperature (T) or disorder hastens electron scattering. The electronic conductivity (σ) decreases as T rises because electrons are more rapidly scattered by lattice vibrations. The value of σ decreases as disorder increases because electrons are more rapidly scattered by imperfections in the material. This is the scattering rate hypothesis, which has guided our understanding of metal conductivity for over a century. However, for so-called bad metals with very low σ this hypothesis predicts scattering rates so high as to conflict with Heisenberga's uncertainty principle. Bad-metal conductivity has remained a puzzle since its initial discovery in the 1980s in high-temperature superconductors. Here we introduce the rare-earth nickelates (RNiO₃, R = rare-earth) as a class of bad metals. We study SmNiO₃ thin films using infrared spectroscopy while varying T and disorder. We show that the interaction between lattice distortions and Ni-O covalence explains bad-metal conductivity and the insulator-metal transition. This interaction shifts spectral weight over the large energy scale established by the Ni-O orbital interaction, thus enabling very low σ without violating the uncertainty principle.United States. Army Research Office (Grant W911-NF-09-1-0398)National Science Foundation (U.S.) (Grant DMR-0952794)National Science Foundation (U.S.) (Grant DMR-1206519
Conductivity noise study of the insulator-metal transition and phase coexistence in epitaxial samarium nickelate thin films
Commensurate growth and diminishing substrate influence in a multilayer film of a tris(thieno)hexaazatriphenylene derivative on Au(111) studied by scanning tunneling microscopy
© 2008 The American Physical SocietyThe electronic version of this article is the complete one and can be found online at: http://link.aps.org/doi/10.1103/PhysRevB.77.085433DOI: 10.1103/PhysRevB.77.085433Layer-by-layer growth of the electron-transport material tris 2,5-bis 3,5-bis-trifluoromethyl-phenyl -thieno
3,4-b,h,n -1,4,5,8,9,12-hexaazatriphenylene THAP on Au 111 is probed by scanning tunneling microscopy
STM . A relative of discotic liquid crystalline molecules, THAP is shown to grow in commensurate
ordered planes from the first to fourth monolayers. The four monolayers all show a concordant ordered
structure in which the molecules arrange parallel to the substrate in a hexagonal close-packed lattice with a
herringbone pattern defined by alternating rows of molecules with antiparallel orientation. The unit cell is
rectangular with two molecules per cell and is nearly equivalent for each layer. The spatial broadening of the
local density of states due to the metallic substrate is appreciably diminished in upper layers, as expected and
as evidenced by the localization of states seen in STM. There is good agreement between the highest occupied
molecular orbital obtained in density functional theory calculations for a single molecule and STM images of
the upper layers, in accord with the localized nature of electronic states on molecules under minimal substrate
influence