949 research outputs found
Phase Diagram of the Half-Filled Ionic Hubbard Model
We study the phase diagram of the ionic Hubbard model (IHM) at half-filling
using dynamical mean field theory (DMFT), with two impurity solvers, namely,
iterated perturbation theory (IPT) and continuous time quantum Monte Carlo
(CTQMC). The physics of the IHM is governed by the competition between the
staggered potential and the on-site Hubbard U. In both the methods we
find that for a finite and at zero temperature, anti-ferromagnetic
(AFM) order sets in beyond a threshold via a first order phase
transition below which the system is a paramagnetic band insulator. Both the
methods show a clear evidence for a transition to a half-metal phase just after
the AFM order is turned on, followed by the formation of an AFM insulator on
further increasing U. We show that the results obtained within both the methods
have good qualitative and quantitative consistency in the intermediate to
strong coupling regime. On increasing the temperature, the AFM order is lost
via a first order phase transition at a transition temperature within both the methods, for weak to intermediate values of U/t. But
in the strongly correlated regime, where the effective low energy Hamiltonian
is the Heisenberg model, IPT is unable to capture the thermal (Neel) transition
from the AFM phase to the paramagnetic phase, but the CTQMC does. As a result,
at any finite temperature T, DMFT+CTQMC shows a second phase transition (not
seen within DMFT+IPT) on increasing U beyond . At , when
the Neel temperature for the effective Heisenberg model becomes lower
than T, the AFM order is lost via a second order transition. In the
3-dimensonal parameter space of , there is a line of
tricritical points that separates the surfaces of first and second order phase
transitions.Comment: Revised versio
Aerosol-Jet-Assisted Thin-Film Growth of CH3NH3PbI3 Perovskites—A Means to Achieve High Quality, Defect-Free Films for Efficient Solar Cells
AbstractA high level of automation is desirable to facilitate the lab‐to‐fab process transfer of the emerging perovskite‐based solar technology. Here, an automated aerosol‐jet printing technique is introduced for precisely controlling the thin‐film perovskite growth in a planar heterojunction p–i–n solar cell device structure. The roles of some of the user defined parameters from a computer‐aided design file are studied for the reproducible fabrication of pure CH3NH3PbI3 thin films under near ambient conditions. Preliminary power conversion efficiencies up to 15.4% are achieved when such films are incorporated in a poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate‐perovskite‐phenyl‐C71‐butyric acid methyl ester type device format. It is further shown that the deposition of atomized materials in the form of a gaseous mist helps to form a highly uniform and PbI2 residue‐free CH3NH3PbI3 film and offers advantages over the conventional two‐step solution approach by avoiding the detrimental solid–liquid interface induced perovskite crystallization. Ultimately, by integrating full 3D motion control, the fabrication of perovskite layers directly on a 3D curved surface becomes possible. This work suggests that 3D automation with aerosol‐jet printing, once fully optimized, could form a universal platform for the lab‐to‐fab process transfer of solution‐based perovskite photovoltaics and steer development of new design strategies for numerous embedded structural power applications
Room temperature giant baroresistance and magnetoresistance and its tunability in Pd doped FeRh
We report room temperature giant baro-resistance (128\%) in
. With the application of external pressure
and magnetic field the temperature range of giant baro-resistance
(600\% at 5K and 19.9 kbar and 8 Tesla) and magnetoresistance
(-85\% at 5K and 8 tesla) can be tuned from 5 K to well above room
temperature. As the AFM state is stabilized at room temperature under external
pressure, it shows giant room temperature magnetoresistance (-55\%)
with magnetic field. Due to coupled magnetic and latticel changes, the
isothermal change in room temperature resistivity with pressure (in the absence
of applied magnetic field) as well as magnetic field (under various constant
pressure) can be scaled together to a single curve when plotted as a function
of X = T + 12.8*H - 7.2*P
Germanium nanocrystals embedded in silicon dioxide for floating gate memory devices
Metal-oxide-semiconductor (MOS) capacitors with tri-layer structure consisting of rf magnetron sputtered grown germanium (Ge) nanocrystals (NCs) and silicon dioxide (SiO2) layers sandwiched between thermally grown tunnel and sputtered grown cap
oxide layers of SiO2 were fabricated on p-Si substrates. Plane view transmission electron micrographs revealed the formation of spherically shaped and uniformly distributed Ge NCs. The optical and electronic characteristics of tri-layer structures
were studied through photoluminescence (PL) spectroscopy and capacitance-voltage (C-V) measurements, respectively. Frequency dependent electrical properties of the structures have been studied. The optical emission characteristics support the
confinement of the carriers in Ge NCs embedded in oxide matrices. An anticlockwise hysteresis in C-V characteristics suggests electron injection and trapping in Ge NCs.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2785
Influence of Electron Transport Layer (TiO2) Thickness and Its Doping Density on the Performance of CH3NH3PbI3-Based Planar Perovskite Solar Cells
Simulation studies are vital to understanding solar cell performance and in optimal device design for high-efficiency solar cells. Cell performance is sensitive to many factors, including device architecture, energy band alignment at the interfaces, materials used for photogeneration, charge extraction, doping density and thickness of various layers. The role of electron transport layer (ETL) thickness and its doping density on device performance is explored in this work. As the ETL thickness is increased from 10 nm to 200 nm, both fill factor (FF) and efficiency remain high up to 40 nm, at 0.85 and 28.04%, respectively, and beyond 40 nm, they decrease gradually due to a sharp increase in series resistance, reaching zero at 200 nm. However, J(sc) and V-oc remained unchanged up to an ETL thickness of about 150 nm and 160 nm, respectively. These results were confirmed by contour plots of the simulated V-oc, J(sc), FF and efficiency results. We observed that when ETL approached 200 nm, J(sc) and V-oc decreased to zero and 0.88 V, respectively. This can be attributed to very high series resistance and recombination in the cell. Donor concentration variation in the ETL from 10(17)/cm(3) to 10(20)/cm(3) has much less impact on J(sc), and V-oc remains unchanged. However, fill factor and efficiency improved, which might be due to an increase in conductivity in the ETL. Our result shows that for an optimized device, with an AM 1.5 spectrum, a cell efficiency of 29.64% was achieved with V-oc, J(sc) and fill factor of 1.241 V, 28.70 mA/cm(2) and 0.83, respectively
Environment-induced dynamical chaos
We examine the interplay of nonlinearity of a dynamical system and thermal
fluctuation of its environment in the ``physical limit'' of small damping and
slow diffusion in a semiclassical context and show that the trajectories of
c-number variables exhibit dynamical chaos due to the thermal fluctuations of
the bath.Comment: Revtex, 4 pages and 4 figure
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