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"Chu, M.-W."
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Hidden lattice instabilities as origin of the conductive interface between insulating LaAlO3 and SrTiO3
The metallic interface between insulating LaAlO
3
and SrTiO
3
opens up the field of oxide electronics. With more than a decade of researches on this heterostructure, the origin of the interfacial conductivity, however, remains unsettled. Here we resolve this long-standing puzzle by atomic-scale observation of electron-gas formation for screening hidden lattice instabilities, rejuvenated near the interface by epitaxial strain. Using atomic-resolution imaging and electron spectroscopy, the generally accepted notions of polar catastrophe and cation intermixing for the metallic interface are discounted. Instead, the conductivity onset at the critical thickness of 4-unit cell LaAlO
3
on SrTiO
3
substrate is accompanied with head-to-head ferroelectric-like polarizations across the interface due to strain-rejuvenated ferroelectric-like instabilities in the materials. The divergent depolarization fields of the head-to-head polarizations cast the interface into an electron reservoir, forming screening electron gas in SrTiO
3
with LaAlO
3
hosting complementary localized holes. The ferroelectric-like polarizations and electron–hole juxtaposition reveal the cooperative nature of metallic LaAlO
3
/SrTiO
3
.
The origin of interfacial conductivity between two insulating oxides, LaAlO
3
and SrTiO
3
, remains elusive despite a long time research. Here, Lee
et al
. report atomic-scale observation of electron-gas formation for screening hidden ferroelectric-like lattice instabilities, discounting the role of polar catastrophe and cation intermixing.
Journal Article
Positive Psychology Interventions in Practice
\"This book presents recent advancements in positive psychology, specifically its application across broad areas of current interest. Chapters include submissions from various international authors in the field and cover discussion and presentation of relevant research, theories, and applications. The volume covers topics such as CBT, Psychotherapy, Coaching, Workplaces, Aging, Education, Leadership, Emotion, Interventions, Measurement, Technology, Design, Health, Relationships, Experiences, Communities. With the growing interest in the applications of positive psychology across diverse fields within psychology and beyond, this book will make a worthwhile contribution to the field. It will also fill the current need for a volume that highlights specifically the various recent advancements in positive psychology into diverse fields and as such will be of benefit to a wide range of professionals, including psychologists, educators, clinicians, therapists, and many others.\" -- Publisher's website.
Book
Observation of half-quantum flux in the unconventional superconductor β-Bi₂Pd
Magnetic flux quantization is one of the defining properties of a superconductor. We report the observation of half-integer magnetic flux quantization in mesoscopic rings of superconducting β-Bi₂Pd thin films. The half-quantum fluxoid manifests itself as a π phase shift in the quantum oscillation of the superconducting critical temperature. This result verifies unconventional superconductivity of β-Bi₂Pd and is consistent with a spin-triplet pairing symmetry. Our findings may have implications for flux quantum bits in the context of quantum computing.
Journal Article
Atomic-scale observation of spontaneous hole doping and concomitant lattice instabilities in strained nickelate films
Thin oxide films are of vast opportunities for modern electronics and can facilitate emergent phenomena by factors absent in the bulk counterparts, such as the ubiquitous epitaxial strain and interfacial charge doping. Here, we demonstrate the twisting of intended bulk-metallic phases in 10-unit-cell LaNiO 3 , PrNiO 3 , and NdNiO 3 films on (001)-oriented SrTiO 3 into distinct charge-lattice entangled states by epitaxial strains. Using atomically-resolved electron microscopy and spectroscopy, the interfacial electron doping into SrTiO 3 in the conventional context of band alignments are discounted. Instead, spontaneously doped holes that are localized and at the order of 10 13 cm −2 are atomically unraveled across all three heterointerfaces and associated with strain mitigations by the accompanied atomic intermixing with various ionic radii. The epitaxial strains also lead to condensations of monoclinic- C 2/ c lattice instabilities, which are hidden to the bulk phase diagram. The group-theoretical analysis of characteristic transition pathways unveils the strain resurrection of the hidden C 2/ c symmetry. While this strain-induced monoclinic phase in LaNiO 3 remains metallic at room temperature, those in PrNiO 3 and NdNiO 3 turn out to be insulating. Such strain-induced monoclinic lattice instabilities and parasitic localized holes go beyond the classical elastic deformations of films upon epitaxial strains and hint on plausible hidden orders in versatile oxide heterostructures with unexpected properties, of which the exploration is only at the infancy and full of potentials.
Journal Article
Midlife Body Mass Index Trajectory and Risk of Frailty 8 Years Later in Taiwan
Few studies have focused on weight change and frailty, especially in Asia. This research aimed to evaluate midlife body mass index (BMI) trajectory and assess its relationship with frailty 8 years later in Taiwan.
A prospective cohort study.
Data were retrieved from the Taiwan Longitudinal Study on Aging conducted from 1999 to 2007. The analysis was restricted to respondents aged between 50 to 69 years old, who were not frail in 1999 and were alive in 2007 (n=1609).
Frailty was defined using the Fried criteria. The group-based model of trajectory was used to estimate BMI trajectories among elderly participants. Logistic regression analysis was used to examine the association between BMI change and frailty.
Four trajectory classes were identified and each remained stable during the 8-year follow-up. There were 316 participants (20.3%) in the low-normal weight group (baseline BMI=20.38 kg/m2), 737 participants (44.7%) in the high-normal weight group (baseline BMI=23.22 kg/m2), 449 participants (28.4%) in the overweight group (baseline BMI=26.24 kg/m2), and 107 participants (6.6%) in the obesity group (baseline BMI=30.65 kg/m2). After adjustment for confounding factors, the low-normal weight group and obesity group were associated with increased frailty compared with the high-normal weight group.
Our results showed that the BMI trajectories of midlife individuals tended to be constant and those in both the low-normal weight group and obesity group had an increased risk of developing frailty in later life. Therefore, an optimal weight-targeting strategy should be considered for Asian elderly individuals.
Journal Article
Condensation of two-dimensional oxide-interfacial charges into one-dimensional electron chains by the misfit-dislocation strain field
The success of semiconductor technology is largely ascribed to controlled impacts of strains and defects on the two-dimensional interfacial charges. Interfacial charges also appear in oxide heterojunctions such as LaAlO
3
/SrTiO
3
and (Nd
0.35
Sr
0.65
)MnO
3
/SrTiO
3
. How the localized strain field of one-dimensional misfit dislocations, defects resulting from the intrinsic misfit strains, would affect the extended oxide-interfacial charges is intriguing and remains unresolved. Here we show the atomic-scale observation of one-dimensional electron chains formed in (Nd
0.35
Sr
0.65
)MnO
3
/SrTiO
3
by the condensation of characteristic two-dimensional interfacial charges into the strain field of periodically arrayed misfit dislocations, using chemical mapping and quantification by scanning transmission electron microscopy. The strain-relaxed inter-dislocation regions are readily charge depleted, otherwise decorated by the pristine charges, and the corresponding total-energy calculations unravel the undocumented charge-reservoir role played by the dislocation-strain field. This two-dimensional-to-one-dimensional electronic condensation represents a novel electronic-inhomogeneity mechanism at oxide interfaces and could stimulate further studies of one-dimensional electron density in oxide heterostructures.
Strain is one of the parameters used to control electron densities in semiconductor devices. Here, the authors show that strain at the interface of two oxide thin films can lead to the condensation of the two-dimensional interfacial electron density into one-dimensional chains.
Journal Article
Observation of half-quantum flux in the unconventional superconductor β-Bi 2 Pd
At sufficiently low temperatures, superconductors expel an applied magnetic field. However, if the topology of the superconductor is nontrivial—for example, if there is a hole in the sample—there can be a nonzero magnetic flux inside the hole. This flux can only take certain discrete values, and the superconducting critical temperature has maxima at the corresponding values of the magnetic field. Li et al. studied these so-called Little-Parks oscillations in superconducting rings made out of polycrystalline thin films of β-Bi 2 Pd. They found that the phase of the oscillations was shifted by π compared with oscillations observed in most superconductors, as predicted for certain unconventional pairing symmetries. Science , this issue p. 238 Little-Parks oscillations in rings of polycrystalline β-Bi 2 Pd suggest unconventional superconductivity. Magnetic flux quantization is one of the defining properties of a superconductor. We report the observation of half-integer magnetic flux quantization in mesoscopic rings of superconducting β-Bi 2 Pd thin films. The half-quantum fluxoid manifests itself as a π phase shift in the quantum oscillation of the superconducting critical temperature. This result verifies unconventional superconductivity of β-Bi 2 Pd and is consistent with a spin-triplet pairing symmetry. Our findings may have implications for flux quantum bits in the context of quantum computing.
Journal Article
Off-Stoichiometry Driven Carrier Density Variation at the Interface of LaAlO3/SrTiO3
The interface between LaAlO
3
(LAO) and SrTiO
3
(STO) has attracted enormous interests due to its rich physical phenomena, such as metallic nature, magnetism and superconductivity. In this work, we report our experimental investigations on the influence of the LAO stoichiometry to the metallic interface. Taking advantage of the oxide molecular beam epitaxy (MBE) technique, a series of high quality LAO films with different nominal La/Al ratios and LAO thicknesses were grown on the TiO
2
-terminated STO substrates, where systematic variations of the LAO lattice constant and transport property were observed. In particular, the sheet density can be largely reduced by nearly an order of magnitude with merely about 20% increase in the nominal La/Al ratio. Our finding provides an effective method on tuning the electron density of the two-dimensional electron liquid (2DEL) at the LAO/STO interface.
Journal Article
Large single crystal growth, transport property and spectroscopic characterizations of three-dimensional Dirac semimetal Cd3As2
The three dimensional (3D) Dirac semimetal is a new quantum state of matter that has attracted much attention recently in physics and material science. Here, we report on the growth of large plate-like single crystals of Cd
3
As
2
in two major orientations by a self-selecting vapor growth (SSVG) method and the optimum growth conditions have been experimentally determined. The crystalline imperfections and electrical properties of the crystals were examined with transmission electron microscopy (TEM), scanning tunneling microscopy (STM) and transport property measurements. This SSVG method makes it possible to control the as-grown crystal compositions with excess Cd or As leading to mobilities near 5–10
5
cm
2
V
−1
s
−1
. Zn-doping can effectively reduce the carrier density to reach the maximum residual resistivity ratio (RRR
ρ
300K
/ρ
5K
) of 7.6. A vacuum-cleaved single crystal has been investigated using angle-resolved photoemission spectroscopy (ARPES) to reveal a single Dirac cone near the center of the surface Brillouin zone with a binding energy of approximately 200 meV.
Journal Article