Ming-Chul Oh

Abstract Magic-angle twisted bilayer graphene exhibits a variety of electronic states, including correlated insulators1–3, superconductors2–4 and topological phases3, 5, 6. Understanding the microscopic mechanisms responsible for these phases requires determination of the interplay between electron–electron interactions and quantum degeneracy (the latter is due to spin and valley degrees of freedom). Signatures of strong electron–electron correlations have been observed at partial fillings of th

Abstract The unusual properties of superconductivity in magic-angle twisted bilayer graphene (MATBG) have sparked considerable research interest 1–13 . However, despite the dedication of intensive experimental efforts and the proposal of several possible pairing mechanisms 14–24 , the origin of its superconductivity remains elusive. Here, by utilizing angle-resolved photoemission spectroscopy with micrometre spatial resolution, we reveal flat-band replicas in superconducting MATBG, where MATBG i

We analytically compute the scanning tunneling microscopy (STM) signatures of integer-filled correlated ground states of the magic angle twisted bilayer graphene (TBG) narrow bands. After experimentally validating the strong-coupling approach at ±4 electrons/moiré unit cell, we consider the spatial features of the STM signal for 14 different many-body correlated states and assess the possibility of Kekulé distortion (KD) emerging at the graphene lattice scale. Remarkably, we find that coupling t

The number of isolated Mn2+ ions and Mn2+ clusters in ZnS:Mn powder and thin films has been studied using Mn2+ spectra measured at room temperature with an X-band electron-paramagnetic-resonance spectrometer. While the concentration of the isolated Mn2+ ions decreases with increasing Mn concentration, the concentration of the clusters increases. At low Mn concentration, the Mn2+ ion substitutes for the Zn ion in ZnS:Mn in the cubic phase. At high Mn concentrations, where the ZnS powder has a dom

Amorphous thin films were deposited by radio‐frequency magnetron sputtering at the substrate temperatures of 100, 200, and 300°C, respectively. The electrical properties of thin films were investigated as a function of substrate temperature and film thickness. The leakage current of the films was in the order of to for an applied field of 1 MV/cm. The charge storage capacitances were 7.7 (100°C), 7.9 (200°C), and . Most of the electrical analyses were performed with the data obtained for the thi

The dielectric reliability for polycrystalline and multilayered BaTiO3 thin films has been evaluated using time-zero and time-dependent dielectric breakdown techniques. The histogram of dielectric breakdown for multilayered BaTiO3 thin films showed a typical Weibull distribution in contrast to a random distribution when compared with polycrystalline BaTiO3 thin films. The measurement resulted in that the 400 nm-thick multilayered BaTiO3 thin film sustained about 105 hour-long operation at 1 MV/c

Defects in wide bandgap materials have emerged as promising candidates for solid-state quantum optical technologies. Electrical excitation of single emitters may lead to scalable on-chip devices and therefore is highly sought after. However, most wide bandgap materials are not amenable to efficient doping, posing challenges for electrical excitation and on-chip integration. Here, we demonstrate narrowband electroluminescence from visible and near-infrared color centers in hexagonal boron nitride

We observed a decrease of the number of effective emission centers Mn2+ in the aged ZnS:Mn electroluminescence (EL) devices compared to the fresh EL devices using the electron-paramagnetic-resonance technique. Such phenomena can take place during the operation of the EL device, since the isolated Mn can easily diffuse into another site and forming cluster. Another possible explanation is that Mn2+ changes into Mn1+ or Mn3+ by transferring the electronic charge of the isolated Mn2+ to the neighbo

We have studied the enhancement of electron emission by diamond-like carbon (DLC) coating on Mo field emitter arrays by a layer-by-layer technique using plasma enhanced chemical vapor deposition. The turn-on voltage was lowered from 55 V to 30 V by 20 nm DLC coating and maximum emission current was increased from 166 /spl mu/A to 831 /spl mu/A. Also the gate voltage required to get the anode current of 0.1 (/spl mu/A/emitter) decreases from 77 V to 48 V. Furthermore, the emission current from DL

Abstract Helmet continuous positive applied pressure is a form of noninvasive ventilation (NIV) that has been used to provide respiratory support to COVID-19 patients. Helmet NIV is low-cost, readily available, provides viral filters between the patient and clinician, and may reduce the need for invasive ventilation. Its widespread adoption has been limited, however, by the lack of a respiratory monitoring system needed to address known safety vulnerabilities and to monitor patients. To address