There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Redox‐Based Resistive Switching Memories – Nanoionic Mechanisms, Prospects, and Challenges

Polarity discontinuities at the interfaces between different crystalline materials (heterointerfaces) can lead to nontrivial local atomic and electronic structure, owing to the presence of dangling bonds and incomplete atomic coordinations. These discontinuities often arise in naturally layered oxide structures, such as the superconducting copper oxides and ferroelectric titanates, as well as in artificial thin film oxide heterostructures such as manganite tunnel junctions. If polarity discontinuities can be atomically controlled, unusual charge states that are inaccessible in bulk materials could be realized. Here we have examined a model interface between two insulating perovskite oxides--LaAlO3 and SrTiO3--in which we control the termination layer at the interface on an atomic scale. In the simple ionic limit, this interface presents an extra half electron or hole per two-dimensional unit cell, depending on the structure of the interface. The hole-doped interface is found to be insulating, whereas the electron-doped interface is conducting, with extremely high carrier mobility exceeding 10,000 cm2 V(-1) s(-1). At low temperature, dramatic magnetoresistance oscillations periodic with the inverse magnetic field are observed, indicating quantum transport. These results present a broad opportunity to tailor low-dimensional charge states by atomically engineered oxide heteroepitaxy.

A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface

Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

/pdf/prospects-of-colloidal-nanocrystals-for-electronic-and-3dxpyhl3r7.pdf

Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Plasmons in strongly correlated systems are attracting considerable attention due to their unconventional behavior caused by electronic correlation effects. Recently, flat plasmons with nearly dispersionless frequency-wave vector relations have drawn significant interest because of their intriguing physical origin and promising applications. However, these flat plasmons exist primarily in low-dimensional materials with limited wave vector magnitudes (q < ~0.7 Å-1). Here, we show that long-lived flat plasmons can propagate up to ~1.2 Å-1 in α-Ti2O3, a strongly correlated three-dimensional Mott-insulator, with an ultra-small energy fluctuation (<40 meV). The strong correlation effect renormalizes the electronic bands near Fermi level with a small bandwidth, which is responsible for the flat plasmons in α-Ti2O3. Moreover, these flat plasmons are not affected by Landau damping over a wide range of wave vectors (q < ~1.2 Å-1) due to symmetry constrains on the electron wavefunctions. Our work provides a strategy for exploring flat plasmons in strongly correlated systems, which in turn may give rise to novel plasmonic devices in which flat and long-lived plasmons are desirable. 

/pdf/ultra-flat-and-long-lived-plasmons-in-a-strongly-correlated-3ba71k7x.pdf

Ultra-flat and long-lived plasmons in a strongly correlated oxide

Epitaxial magnetite (Fe3O4) thin films have been grown on MgO(001) substrates by pulsed laser deposition. The films have characteristics of the “Verwey transition”: the electric conductivity decreases by about one order of magnitude and the magnetization curve shows anomaly at the transition temperature, i.e. about 125 K. Effects of annealing the Fe3O4 thin films at various oxygen partial pressures have also been investigated. Phase identification was made using XRD techniques and infrared reflectivity measurements. The surface morphologies were studied by SEM and AFM. Under an oxidizing atmosphere, the Fe3O4 phase is transformed mainly into α-Fe2O3, and this transformation is accompanied by development of needle-like structures along directions of MgO substrate. It is also found that electrical and magnetic properties of the iron oxide films are changed significantly by the annealing process.

Properties of Iron Oxide Films Grown by Pulsed Laser Deposition

Magnetic behavior of the high Tc composite compound of Y1Ba2Cu3O7-δ in the superconducting phase

Using La0.5Sr0.5CoO3 bottom electrode layers, Bi4Ti3O12 thin films were grown on LaAlO3(001), Al2O3(0001), and Si(001) substrates. Crystalline orientation of the Bi4Ti3O12 thin films was examined by x-ray diffraction techniques. The cross-sectional microstructures of Bi4Ti3O12/La0.5Sr0.5CoO3 heterostructures are investigated. It is found that the crystalline orientation and the microstructure affect leakage current behavior of the Bi4Ti3O12 layers.

Structural and Leakage Current Behavior of Bi4Ti3O12 Thin Films on La0–5Sr0–5jCoO3 Bottom Electrodes Grown by Pulsed Laser Deposition

We measured the temperature ( T -) dependent optical conductivity spectra σ ( ω ) of Y 2 Ru 2 O 7 (insulating), Tl 2 Ru 2 O 7 (metal–insulator transition) and Bi 2 Ru 2 O 7 (metallic). σ ( ω ) of Y 2 Ru 2 O 7 show absorption peaks around 1.7 and 3.2 eV, which are nearly T -independent. σ ( ω ) of Bi 2 Ru 2 O 7 are also nearly T -independent, but have a Drude-like peak in the far-infrared (IR) region. On the other hand, σ ( ω ) of Tl 2 Ru 2 O 7 have a very strong mid-IR peak, and its spectral weight is strongly T -dependent. Its T dependence through the metal–insulator transition is quite similar to the doping dependence of doped transition metal oxides, but there is no external dopant in Tl 2 Ru 2 O 7 . Therefore, these phenomena of Tl 2 Ru 2 O 7 can be interpreted in terms of T -dependent self-doping effects; namely, the electronic structures near the Fermi level change due to the self-doping for the Ru 4d state in the presence of an easily polarizable Tl ion.

Tae Won Noh

Papers

Ultra-flat and long-lived plasmons in a strongly correlated oxide

Properties of Iron Oxide Films Grown by Pulsed Laser Deposition

Magnetic behavior of the high Tc composite compound of Y1Ba2Cu3O7-δ in the superconducting phase

Structural and Leakage Current Behavior of Bi4Ti3O12 Thin Films on La0–5Sr0–5jCoO3 Bottom Electrodes Grown by Pulsed Laser Deposition

Optical investigation of A2Ru2O7 (A=Y, Tl, and Bi): temperature dependent self-doping effects