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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Microstructural and preliminary optical and microwave characterization of erbium-doped CaMoO 4 thin films

This work explores erbium-doped calcium molybdate (Er:CaMoO4) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the ∼1.5 μm Er 3+ 4f–4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction, and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO 4 formation that can be in situ doped with Er (typically 2–100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology, while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO 4 films. We perform preliminary optical and microwave characterization on the suspected Y 1 –Z 1 transition of 2 ppm, 200 nm epitaxial Er:CaMoO 4 annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz.

Masiulionis, Ignas [Univ. of Chicago, IL (United S↗
DOE OSTI2016

The study of structural phase transitions and static properties using transition metal model pseudopotential (TMMP) for Ca and Sr

In the present communication, we have computed static and dynamic properties (binding energy-E, bulk modulus-B and second moment- <ω{sup 2}>) as well as first order pressure induced phase transition (FCC-BCC) using local form of pseudopotential for Calcium and Strontium. The form of pseudopotential used for the computation is directly extracted from Generalized Pseudopotential Theory (GPT) which contains three parameters (r{sub c}, r{sub d} and β). We have suggested a simple method using which pseudopotential is determined by single parameter (β). Our computed results for binding energy and bulk modulii are in excellent agreement with experimental findings and are better than other theoretical results. The present study confirms that s-d hybridization is accounted properly in the presently used pseudopotential and can be extended for the study of lattice mechanical properties of these metals.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Solid State Quantum Refrigeration Superconducting, Absorption and Measurement Based (Final Technical Report)

During this DOE grant, DE-SC0017890, in place for the past six years, all proposed research was carried out and published in peer-reviewed papers, as well as other projects that emerged during the research. In that effort the research team accomplished all proposed research, as well as many closely related research projects discovered and conceived of during the grant. These works included “Efficient Quantum Measurement Engines”, a work published in Physical Review Letters, giving a theory of quantum measurement-based engines, which uses quantum measurement as a resource. These engines are designed to efficiently convert energy from the stochastic quantum measurement process into useful work. Further publications include “Experimental Realization of a Quantum Dot Energy Harvester”, a joint theory and experimental work in collaboration with the group of Charles Smith in Cambridge, UK, as well as long time theoretical collaborators, Rafael Sánchez and Björn Sothmann. This work, featured as an Editor’s Suggestion in Physical Review Letters, realized an earlier theoretical proposal of ours, whereby two resonant tunneling quantum dots are connected to a central electronic cavity that is heated by a hot energy source. We also published “Superconducting Quantum Refrigerator: Breaking and Rejoining Cooper Pairs with Magnetic Field Cycles” a work done in collaboration with experimentalist Francesco Giazotto from ENS Pisa, Italy, which also resulted in a patent. This paper, published in Phys. Rev. Applied, advanced the concept of a cyclic fridge based on the normal/superconducting phase transition together with layered materials separated by tunnel junctions. We also completed the proposed research on a heat transistor, publishing “Thermal transistor and thermometer based on Coulomb-coupled conductors”, carried out as a collaboration between my group and theorists Splettstoesser (Lund U., Sweden), Sothmann (U. Duisburg-Essen, Germany), and Sánchez (U. Autónoma de Madrid, Spain). We carried out an analysis of a quantum coupled to a quantum point contact as a sensitive thermometer and heat transistor. We found the optimal statistical estimator for the temperature and compared it with experiments on the same type of devices. We also investigated autonomous quantum absorption refrigerators using quantum dots to cool by using a very hot thermal reservoir to drive heat between two other reservoirs. In the article “Quantifying the quantum heat contribution from a driven superconducting circuit”, we demonstrated that for a driven superconducting circuit, we showed heat flow provided by a hot source to the qubit can be switched on and off by varying external parameters, the frequency and the intensity of the driving. In the work “Stochastic thermodynamic cycles of a mesoscopic thermoelectric engine”, we reconsidered the autonomous thermoelectric heat engine in terms of underlying cycles. Rather than periodic behavior, the cycles were stochastic in nature. Nevertheless, by undertaking a graph theoretical analysis of the elementary transport processed, great quantitative and qualitative insight could be found. We also considered the quantum measurement process and showed that a quantum version of Maxwell’s demon could be related to the work extraction of a quantum system, closely related to arrow-of-time measures for quantum measurement, as described in our article “Thermodynamics of quantum measurement and Maxwell's demon's arrow of time”. This work was selected in Phys. Rev. A as an Editor’s Suggestion. A recent preprint titled “Cyclic Superconducting Quantum Refrigerators Using Guided Fluxon Propagation” accomplished an important piece of this grant: to propose a new kind of quantum refrigerator using the dynamics of fluxons in a type II superconductor. This invention envisioned a race-track type geometry where fluxons are confined. By applying a gradient of magnetic field together with electric current in a Corbino geometry, the circulating fluxons can actively cool a cold reservoir, realizing a new type of cyclic superconducting refrigerator. We also investigated the possibility of thermal control from different points of view. The application of quantum measurement to the system gives a new kind of control on the system of interest – we have pioneered this approach and shown that measurement can boost the thermal power of quantum engines as described in “Continuous measurement boosted adiabatic quantum thermal machines”. The ability to have heat flows on demand is an outstanding challenge, and we have provided new solutions to this problem in Thermal control across a chain of electronic nanocavities” for a chain of electron cavities using gating voltage control. The control methods using qubit/qubit coupling to create absorption fridges at their most fundamental level have also been developed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Computer simulation of liquid-vapor coexistence of confined quantum fluids

The liquid-vapor coexistence (LV) of bulk and confined quantum fluids has been studied by Monte Carlo computer simulation for particles interacting via a semiclassical effective pair potential V{sub eff}(r) = V{sub LJ} + V{sub Q}, where V{sub LJ} is the Lennard-Jones 12-6 potential (LJ) and V{sub Q} is the first-order Wigner-Kirkwood (WK-1) quantum potential, that depends on β = 1/kT and de Boer's quantumness parameter Λ=h/σ√(mε), where k and h are the Boltzmann's and Planck's constants, respectively, m is the particle's mass, T is the temperature of the system, and σ and ε are the LJ potential parameters. The non-conformal properties of the system of particles interacting via the effective pair potential V{sub eff}(r) are due to Λ, since the LV phase diagram is modified by varying Λ. We found that the WK-1 system gives an accurate description of the LV coexistence for bulk phases of several quantum fluids, obtained by the Gibbs Ensemble Monte Carlo method (GEMC). Confinement effects were introduced using the Canonical Ensemble (NVT) to simulate quantum fluids contained within parallel hard walls separated by a distance L{sub p}, within the range 2σ ⩽ L{sub p} ⩽ 6σ. The critical temperature of the system is reduced by decreasing L{sub p} and increasing Λ, and the liquid-vapor transition is not longer observed for L{sub p}/σ < 2, in contrast to what has been observed for the classical system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Impurity-generated non-Abelions

Two classes of topological superconductors and Majorana modes in condensed matter systems are known to date: one in which disorder induced by impurities strongly suppresses topological superconducting gap and is detrimental to Majorana modes, and another where Majorana fermions are protected by a disorder-robust topological superconductor gap. Observation and control of Majorana fermions and other non-Abelions often requires a symmetry of an underlying system leading to a gap in the single-particle or quasiparticle spectra. In semiconductor structures, impurities that provide charge carriers introduce states into the gap and enable conductance and proximity-induced superconductivity via the in-gap states. Thus a third class of topological superconductivity and Majorana modes emerges, in which topological superconductivity and Majorana fermions appear exclusively when impurities generate in-gap states. We show that impurity-enabled topological superconductivity is realized in a quantum Hall ferromagnet, when a helical domain wall is coupled to an 𝑠-wave superconductor. As an example of emergence of topological superconductivity in quantum Hall ferromagnets, we consider the integer quantum Hall effect in Mn-doped CdTe quantum wells. Recent experiments on transport through the quantum Hall ferromagnet domain wall in this system indicated a vital role of impurities in the conductance, but left unresolved the question whether impurities preclude generation of Majorana fermions and other non-Abelions in such systems in general. Here, solving a general quantum-mechanical problem of impurity bound states in a system of spin-orbit coupled Landau levels, we demonstrate that impurity-induced Majorana modes emerge at boundaries between topological and conventional superconducting states generated in a domain wall due to proximity to an 𝑠 superconductor. We consider both short-range disorder and a smooth random potential. The phase diagram of the system is defined by characteristic disorder, gate voltage induced angular momentum splitting of impurity levels, and by a proximity superconducting gap. The phase diagram exhibits two ranges of gate voltage with conventional superconducting order separated by a gate voltage range with topological superconductivity. We show that electrostatic control of domain walls in an integer quantum Hall ferromagnet allows manipulation of Majorana fermions. Ferromagnetic transitions in the fractional quantum Hall regime may lead to the formation and electrostatic control of higher order non-Abelian excitations.

Edge states↗
DOE OSTI2013

Lattice distortion-induced phase transformations in La{sub 1-y}Pr{sub y}MnO{sub 3+{delta}} manganites

The structural and magnetic phase transformations that occur in the system of self-doped La{sub 1-y}Pr{sub y}MnO{sub 3+{delta}} ({delta} Almost-Equal-To 0.1, 0 {<=} y {<=} 1) manganites in the temperature range 4.2-300 K are studied by X-ray diffraction and measuring the temperature and field dependences of dc magnetization. The low-temperature magnetic phase transformations induced by the substitution of Pr for La correlate well with the structural phase transformations at T = 300 K, which indicates a strong coupling of the electronic and magnetic subsystems of La{sub 1-y}Pr{sub y}MnO{sub 3+{delta}} manganites with the crystal lattice. The anomalies of the magnetic and structural properties detected in this work in the form of peaks and inflection points in the concentration dependences of the magnetization and lattice parameters of the pseudocubic phase of La{sub 1-y}Pr{sub y}MnO{sub 3+{delta}} (0.1 {<=} y {<=} 0.7) in the temperature range 4.2-300 K are explained in terms of the existing concepts of the effect of Fermi surface nesting on the renormalization of the density of states and the hole dispersion near E{sub F} in the presence of a strong coupling of holes with low-frequency optical phonons, which results in their transformation into quasiparticles. The narrow peak in the magnetization curve M(y) of La{sub 1-y}Pr{sub y}MnO{sub 3+{delta}} that is detected near y = 0.3 at T = 4.2 K is assumed to correspond to the peak of coherence of quasiparticles with a low energy of coupling with the crystal lattice near E{sub F}, which was found earlier in the photoelectron emission spectra of manganites. The disappearance of the narrow magnetization peak with increasing Pr concentration is explained by the transition of charge carriers from the mode of 'light' holes weakly coupled to one of the soft phonons to the mode of 'heavy' holes strongly coupled to several phonons. The transition between phases with strongly different effective quasiparticle masses proceeds jumpwise; that is, it has features of the metal-insulator Mott transition and is accompanied by the transition from 3D to 2D quasiparticle motion in planes ab.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

High pressure polymorphs and amorphization of upconversion host material NaY(WO 4 ) 2

The pressure effect on the structural change of upconversion host material NaY(WO 4 ) 2 was studied in this paper by using in-situ synchrotron X-ray diffraction. A transition from the initial scheelite phase to the M-fergusonite phase occurs near 10 GPa, and another phase transition is found near 27.5 GPa, which could be an isostructural transition without symmetry change. The sample becomes amorphous when the pressure is fully released from high pressure. Finally, this work demonstrates the possibility of synthesizing various polymorph structures for non-linear optical applications with a high pressure, chemical doping, or strained thin-film nanostructure process.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Directed assembly of magnetic and semiconducting nanoparticles with tunable and synergistic functionality

The ability to fabricate new materials using nanomaterials as building blocks, and with meta functionalities, is one of the most intriguing possibilities in the area of materials design and synthesis. Semiconducting quantum dots (QDs) and magnetic nanoparticles (MNPs) are co-dispersed in a liquid crystalline (LC) matrix and directed to form self-similar assemblies by leveraging the host’s thermotropic phase transition. These co-assemblies, comprising 6 nm CdSe/ZnS QDs and 5–20 nm Fe 3 O 4 MNPs, bridge nano- to micron length scales, and can be modulated in situ by applied magnetic fields <250 mT, resulting in an enhancement of QD photoluminescence (PL). This effect is reversible in co-assemblies with 5 and 10 nm MNPs but demonstrates hysteresis in those with 20 nm MNPs. Transmission electron microscopy (TEM) and energy dispersive spectroscopy reveal that at the nanoscale, while the QDs are densely packed into the center of the co-assemblies, the MNPs are relatively uniformly dispersed through the cluster volume. Using Lorentz TEM, it is observed that MNPs suspended in LC rotate to align with the applied field, which is attributed to be the cause of the observed PL increase at the micro-scale. This study highlights the critical role of correlating multiscale spectroscopy and microscopy characterization in order to clarify how interactions at the nanoscale manifest in microscale functionality.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Quasielastic neutron scattering with in situ humidity control: Water dynamics in uranyl fluoride

The structural phase diagram of uranyl fluoride (UO{sub 2}F{sub 2}), while incomplete, contains at least one anhydrous crystal structure and a second, zeolite-like structure with the formula [(UO{sub 2}F{sub 2})(H{sub 2}O)]{sub 7} ⋅ (H{sub 2}O){sub 4} that can be produced by adding water to the anhydrous structure. While traditional diffraction measurements can easily differentiate these crystals, additional aqueous structures (in general of the form UO{sub 2}F{sub 2} + xH{sub 2}O) have been proposed as well. We present results using a novel sample environment setup to intercalate water during a quasielastic neutron scattering measurement over the course of 86 h. Our sample environment allows low-pressure (<2 atm) humid air flow across the sample coupled with a system to control the relative humidity of this air flow between 10% and 70%. The water dynamics in UO{sub 2}F{sub 2} and [(UO{sub 2}F{sub 2})(H{sub 2}O)]{sub 7} ⋅ (H{sub 2}O){sub 4} are sufficiently different to distinguish them, with water in the latter executing a restricted diffusion (D = 2.7 × 10{sup −6} cm{sup 2}/s) within the structure's accessible pores (r = 3.17 Å) such that the dynamics can be used as a fingerprinting tool. We confirm that water vapor pressure is the driving thermodynamic force for the conversion of the anhydrous structure to [(UO{sub 2}F{sub 2})(H{sub 2}O)]{sub 7} ⋅ (H{sub 2}O){sub 4}, and we demonstrate the feasibility of extending this approach to aqueous forms of UO{sub 2}F{sub 2} + xH{sub 2}O. This method has general applicability to systems in which water content itself is a driving variable for structural or dynamical phase transitions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Stacking disorder and thermal transport properties of α-RuCl 3

α-RuCl 3 , a well-known candidate material for Kitaev quantum spin liquid, is prone to stacking disorder due to the weak van der Waals bonding between the honeycomb layers. After a decade of intensive experimental and theoretical studies, the detailed correlation between stacking degree of freedom, structure transition, magnetic, and thermal transport properties remains unresolved. In this work, we reveal the effects of a small amount of stacking disorder inherent even in high quality α-RuCl 3 crystals. This small amount of stacking disorder results in the variation of the magnetic ordering temperature, and it suppresses the structure transition and thermal conductivity. Crystals with a minimal amount of stacking disorder have a T N > 7.4 K and exhibit a well-defined structure transition around 140 K upon cooling. For those with more stacking faults and a T N below 7 K, the structure transition occurs well below 140 K upon cooling and is incomplete, manifested by the diffuse streaks and the coexistence of both high-temperature and low-temperature phases down to the lowest measurement temperature. Both types of crystals exhibit oscillatory field-dependent thermal conductivity and a plateaulike feature in thermal Hall resistivity in the field-induced quantum spin liquid state. However, α-RuCl 3 crystals with a minimal amount of stacking disorder have a higher thermal conductivity that pushes the thermal Hall conductivity to be closer to the half-integer quantized value. Importantly, these findings demonstrate a strong correlation between layer stacking, structure transition, magnetic, and thermal transport properties, underscoring the importance of interlayer coupling in α-RuCl3 despite the weak van der Waals bonding.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Models of quark-hadron matter and compact stars

Phenomenological approaches to Quantum Chromodynamics covering the whole region of low and high temperatures and/or densities must address the problem that the effective degrees of freedom change from hadrons to quarks and gluons. We approach this task with a unified description of hadronic and quark matter allowing for cross-over as well as first or second-order phase transitions. As a further benefit of such an approach, a quantitatively satisfactory description of nuclear ground state matter as well as nuclear and hypernuclear properties can be achieved. We apply this model to neutron stars and consider potential constraints on star properties arising from lattice gauge results in relation with the observation of 2 solar mass stars.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Cosmological perturbations in teleparallel Loop Quantum Cosmology

Cosmological perturbations in Loop Quantum Cosmology (LQC) are usually studied incorporating either holonomy corrections, where the Ashtekar connection is replaced by a suitable sinus function in order to have a well-defined quantum analogue, or inverse-volume corrections coming from the eigenvalues of the inverse-volume operator. In this paper we will develop an alternative approach to calculate cosmological perturbations in LQC based on the fact that, holonomy corrected LQC in the flat Friedmann-Lemaître-Robertson-Walker (FLRW) geometry could be also obtained as a particular case of teleparallel F(T) gravity (teleparallel LQC). The main idea of our approach is to mix the simple bounce provided by holonomy corrections in LQC with the non-singular perturbation equations given by F(T) gravity, in order to obtain a matter bounce scenario as a viable alternative to slow-roll inflation. In our study, we have obtained an scale invariant power spectrum of cosmological perturbations. However, the ratio of tensor to scalar perturbations is of order 1, which does not agree with the current observations. For this reason, we suggest a model where a transition from the matter domination to a quasi de Sitter phase is produced in order to enhance the scalar power spectrum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Roles of grain boundaries on the semiconductor to metal phase transition of VO{sub 2} thin films

Vanadium dioxide (VO{sub 2}) thin films with controlled grain sizes are deposited on amorphous glass substrates by pulsed laser deposition. The grain boundaries (GBs) are found as the dominating defects in the thin films. The semiconductor to metal transition (SMT) properties of VO{sub 2} thin films are characterized and correlated to the GB density. The VO{sub 2} films with lower GB density exhibit a sharper SMT with a larger transition amplitude. A high resolution TEM study at GB area reveals the disordered atomic structures along the boundaries and the distorted crystal lattices near the boundaries. The VO{sub 2} SMT amplitude and sharpness could be directly related to these defects at and near the boundaries.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Giant reversible barocaloric response of (MnNiSi) 1- x (FeCoGe) x ( x = 0.39, 0.40, 0.41)

MnNiSi-based alloys and isostructural systems have traditionally demonstrated impressive magnetocaloric properties near room temperature associated with a highly tunable first-order magnetostructural transition that involves large latent heat. However, these materials are limited by a small field-sensitivity of the transition, preventing significant reversible effects usable for cooling applications. Instead, the concomitant large transition volume changes prompt a high pressure-sensitivity, and therefore, promise substantial barocaloric performances, but they have been sparsely studied in these materials. Here, we study the barocaloric response in a series of composition-related (MnNiSi) 1-x (FeCoGe) x (x = 0.39, 0.40, 0.41) alloys that span continuously over a wide temperature range around ambient. We report on giant reversible effects of ~40 J K -1 kg -1 and up to ~4 K upon application of ~2 kbar and find a degradation of the first-order transition properties with pressure that limits the barocaloric effects at high pressures. Our results confirm the potential of this type of alloys for barocaloric applications, where multicaloric and composite possibilities, along with the high density and relatively high thermal conductivity, constructively add to the magnitude of the caloric effects.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2012

Field-induced length changes in the spin-liquid candidate kappa{BEDT-TTF){<_2}Cu{<_2}(CN){<_3}.

Measurements of the coefficient of thermal expansion on the spin-liquid candidate {kappa}-(BEDT-TTF){sub 2}Cu{sub 2}(CN){sub 3} have revealed distinct and strongly anisotropic lattice effects around 6 K - a possible spin liquid instability. In order to study the effects of a magnetic field on the low-temperature spin-liquid state, dilatometric measurements have been conducted both as a function of temperature at B = const. and as a function of field at T = const. While the 6 K anomaly is found to be insensitive to magnetic fields B {le} 10 T, the maximum field applied, surprisingly strong B-induced effects are observed for magnetic fields applied along the in-plane b-axis. Above a threshold field of 0.5 T < B{sub c} {le} 1 T, a jump-like anomaly is observed in the b-axis lattice parameter. This anomaly, which is located at 8.7 K at B = 1 T, grows in size and shifts to lower temperatures with increasing the magnetic field. Although the anomaly bears resemblance to a first-order phase transition, the lack of hysteresis suggests otherwise.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Phase transitions in twin Higgs models

We study twin Higgs models at non-zero temperature and discuss cosmological phase transitions as well as their implications on electroweak baryogenesis and gravitational waves. It is shown that the expectation value of the Higgs field at the critical temperature of the electroweak phase transition is much smaller than the critical temperature, which indicates two important facts: (i) the electroweak phase transition cannot be analyzed perturbatively (ii) the electroweak baryogenesis is hardly realized in the typical realizations of twin Higgs models. We also analyze the phase transition associated with the global symmetry breaking, through which the Standard Model Higgs is identified with one of the pseudo-Nambu-Goldstone bosons in terms of its linear realization, with and without supersymmetry. For this phase transition, we show that, only in the supersymmetric case, there are still some parameter spaces, in which the perturbative approach is validated and the phase transition is the first order. We find that the stochastic gravitational wave background is generated through this first order phase transition, but it is impossible to be detected by DECIGO or BBO in the linear realization and the decoupling limit. The detection of stochastic gravitational wave background with the feature of first order phase transition, therefore, will give strong constraints on twin Higgs models.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Structural, optical, and electrical properties of phase-controlled cesium lead iodide nanowires

Cesium lead iodide (CsPbI 3 ), in its black perovskite phase, has a suitable bandgap and high quantum efficiency for photovoltaic applications. However, CsPbI 3 tends to crystalize into a yellow non-perovskite phase, which has poor optoelectronic properties, at room temperature. Therefore, controlling the phase transition in CsPbI 3 is critical for practical application of this material. Here we report a systematic study of the phase transition of one-dimensional CsPbI 3 nanowires and their corresponding structural, optical, and electrical properties. We show the formation of perovskite black phase CsPbI 3 nanowires from the non-perovskite yellow phase through rapid thermal quenching. Post-transformed black phase CsPbI 3 nanowires exhibit increased photoluminescence emission intensity with a shrinking of the bandgap from 2.78 to 1.76 eV. The perovskite nanowires were photoconductive and showed a fast photoresponse and excellent stability at room temperature. Finally, these promising optical and electrical properties make the perovskite CsPbI 3 nanowires attractive for a variety of nanoscale optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Error controlling of the combined Cluster-Expansion and Wang–Landau Monte-Carlo method and its application to FeCo

Simulating order–disorder phase transitions in magnetic materials requires the accurate treatment of both the atomic and magnetic interactions, which span a vast configuration space. Taking FeCo as a prototype system, we demonstrate that this can be accurately and efficiently addressed by the combined Cluster-Expansion method and Wang–Landau algorithm. All involved key parameters in this method are carefully tested. Based on these tests, error controlling approaches are also developed. Furthermore our method is readily applicable to the study of similar second-order phase transitions in other binary and multi-component systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗