Emergent Change of Phase for Electronics Takagi, Hidenori; Hwang, Harold Y
Science (American Association for the Advancement of Science),
03/2010, Volume:
327, Issue:
5973
Journal Article
Peer reviewed
Correlated electrons in transition metal oxides can form a variety of electronic phases. The phase change between these various states gives rise to novel device functions, including sensing, signal ...conversion, and nonvolatile memory, and is now at the frontier of research on "emergent research device materials." Those oxide devices may have an advantage over conventional semiconductor devices for added functionality and future downsizing to the nanoscale. The elucidation of the microscopic physics behind their operation is a key step for further development.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Using light to manipulate materials into desired states is one of the goals in condensed matter physics, since light control can provide ultrafast and environmentally friendly photonics devices. ...However, it is generally difficult to realise a photo-induced phase which is not merely a higher entropy phase corresponding to a high-temperature phase at equilibrium. Here, we report realisation of photo-induced insulator-to-metal transitions in Ta
Ni(Se
S
)
including the excitonic insulator phase using time- and angle-resolved photoemission spectroscopy. From the dynamic properties of the system, we determine that screening of excitonic correlations plays a key role in the timescale of the transition to the metallic phase, which supports the existence of an excitonic insulator phase at equilibrium. The non-equilibrium metallic state observed unexpectedly in the direct-gap excitonic insulator opens up a new avenue to optical band engineering in electron-hole coupled systems.
The identity of the fundamental broken symmetry (if any) in the underdoped cuprates is unresolved. However, evidence has been accumulating that this state may be an unconventional density wave. Here ...we carry out site-specific measurements within each CuO ₂ unit cell, segregating the results into three separate electronic structure images containing only the Cu sites Cu (r) and only the x / y axis O sites O ₓ(r) and O y(r). Phase-resolved Fourier analysis reveals directly that the modulations in the O ₓ(r) and O y(r) sublattice images consistently exhibit a relative phase of π . We confirm this discovery on two highly distinct cuprate compounds, ruling out tunnel matrix-element and materials-specific systematics. These observations demonstrate by direct sublattice phase-resolved visualization that the density wave found in underdoped cuprates consists of modulations of the intraunit-cell states that exhibit a predominantly d- symmetry form factor.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The layered oxysulfide Y2Ti2O5S2 (YTOS) is quite promising as a new generation anode material for Li-ion batteries (LIB) for power application. The charge-discharge curve of the YTOS/Li cell ...indicates that LixY2Ti2O5S has a capacity of 128 mAhg-1 (509 mAhcm-3) and a low voltage to Li/Li+ of 0.84V. The energy density for YTOS-based LIB is comparable to that of Li4Ti5O12 (LTO) based LIB. The electrical conductivity of LixY2Ti2O5S2 without any carbon additive was 5-50 mScm-1, orders of magnitude higher than that of LTO. The comparison of rate dependence of capacity between YTO without any carbon additive and LTO with carbon additive suggests excellent power performance of YTOS.
•Layered oxysulfideY2Ti2O5S is a promising candidate for anode for next generation Li ion batteries.•Y2Ti2O5S as anode has comparable or even better capacity and power performance in comparison with those of Li4Ti5O12.•Y2Ti2O5S dues to its high electric conductivity may be used free from carbon additives.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Gut‐associated lymphoid tissue (GALT) is the biggest lymphoid organ in the body. It plays a role in robust immune responses against invading pathogens while maintaining immune tolerance against ...nonpathogenic antigens such as foods. Oral vaccination can induce mucosal and systemic antigen‐specific immune reactions and has several advantages including ease of administration, no requirement for purification and ease of scale‐up of antigen. Thus far, taking advantage of these properties, various plant‐based oral vaccines have been developed. Seeds provide a superior production platform over other plant tissues for oral vaccines; they offer a suitable delivery vehicle to GALT due to their high stability at room temperature, ample and stable deposition space, high expression level, and protection from digestive enzymes in gut. A rice seed production system for oral vaccines was established by combining stable deposition in protein bodies or protein storage vacuoles and enhanced endosperm‐specific expression. Various types of rice‐based oral vaccines for infectious and allergic diseases were generated. Efficacy of these rice‐based vaccines was evaluated in animal models.
Full text
Available for:
BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
The excitonic insulator is an intriguing correlated electron phase formed of condensed excitons. A promising candidate is the small band gap semiconductor Ta2NiSe5. Here we investigate the ...quasiparticle and coherent phonon dynamics in Ta2NiSe5 in a time resolved pump probe experiment. Using the models originally developed by Kabanov et al for superconductors (Kabanov et al 1999 Phys. Rev. B 59 1497), we show that the material's intrinsic gap can be described as almost temperature independent for temperatures up to about 250 K to 275 K. This behavior supports the existence of the excitonic insulator state in Ta2NiSe5. The onset of an additional temperature dependent component to the gap above these temperatures suggests that the material is located in the BEC-BCS crossover regime. Furthermore, we show that this state is very stable against strong photoexcitation, which reveals that the free charge carriers are unable to effectively screen the attractive Coulomb interaction between electrons and holes, likely due to the quasi 1D structure of Ta2NiSe5.
A powder sample of pure H3LiIr2O6 was synthesized from α-Li2IrO3 powder by a soft chemical replacement of Li+ with H+. The crystal structure of H3LiIr2O6 consists of sheets of edge sharing LiO6- and ...IrO6-octahedra forming a honeycomb network with layers stacked in a monoclinic distorted HCrO2 type pattern. Heavy stacking faulting of the sheets is indicated by anisotropic peak broadening in the X-ray powder diffraction (XRPD) pattern. The ideal, faultless crystal structure was obtained by a Rietveld refinement of the laboratory XRPD pattern while using the LiIr2O63−-layers of α-Li2IrO3 as a starting model. The low radial distances of the PDF function, derived from synchrotron XRPD data, as constraints to stabilize the structural refinement. DIFFaX-simulations, structural considerations, high radial distances of the PDF function and a Rietveld compatible global optimization of a supercell were employed to derive a suitable faulting model and to refine the microstructure using the experimental data. We assumed that the overall stacking pattern of the layers in the structure of H3LiIr2O6 is governed by interlayer O–H⋯O contacts. From the constitution of the layers, different stacking patterns with similar amounts of strong O–H⋯O contacts are considered. Random transitions among these stacking patterns can occur as faults in the crystal structure of H3LiIr2O6, which quantitatively describe the observed XRPD.
PDF
