Showing papers on "Phase transition published in 2014"
TL;DR: In situ scanning transmission electron microscopy can be used to follow the structural transformation between semiconducting (2H) and metallic (1T) phases in single-layered MoS2, with atomic resolution.
Abstract: Phase transitions can be used to alter the properties of a material without adding any additional atoms and are therefore of significant technological value. In a solid, phase transitions involve collective atomic displacements, but such atomic processes have so far only been investigated using macroscopic approaches. Here, we show that in situ scanning transmission electron microscopy can be used to follow the structural transformation between semiconducting (2H) and metallic (1T) phases in single-layered MoS2, with atomic resolution. The 2H/1T phase transition involves gliding atomic planes of sulphur and/or molybdenum and requires an intermediate phase (α-phase) as a precursor. The migration of two kinds of boundaries (β- and γ-boundaries) is also found to be responsible for the growth of the second phase. Furthermore, we show that areas of the 1T phase can be controllably grown in a layer of the 2H phase using an electron beam.
1,129 citations
TL;DR: Perovskite solar cells with power conversion efficiencies exceeding 16% at AM 1.5 G one sun illumination are developed using the black polymorph of formamidnium lead iodide, HC(NH2)2 PbI3, which exhibits photostability and little I-V hysteresis.
Abstract: Perovskite solar cells with power conversion efficiencies exceeding 16% at AM 15 G one sun illumination are developed using the black polymorph of formamidnium lead iodide, HC(NH2)2 PbI3 Compared with CH3 NH3 PbI3 , HC(NH2 )2 PbI3 extends its absoprtion to 840 nm and shows no phase transition between 296 and 423 K Moreover, a solar cell based on HC(NH2 )2 PbI3 exhibits photostability and little I-V hysteresis
817 citations
TL;DR: This work discovers that mechanical deformations provide a route to switching thermodynamic stability between a semiconducting and a metallic crystal structure in these monolayer materials and finds that MoTe2 is an excellent candidate phase change material.
Abstract: Mo- and W-dichalcogenide compounds have a two-dimensional monolayer form that differs from graphene in an important respect: it can potentially have more than one crystal structure. Some of these monolayers exhibit tantalizing hints of a poorly understood structural metal-to-insulator transition with the possibility of long metastable lifetimes. If controllable, such a transition could bring an exciting new application space to monolayer materials beyond graphene. Here we discover that mechanical deformations provide a route to switching thermodynamic stability between a semiconducting and a metallic crystal structure in these monolayer materials. Based on state-of-the-art density functional and hybrid Hartree–Fock/density functional calculations including vibrational energy corrections, we discover that MoTe2 is an excellent candidate phase change material. We identify a range from 0.3 to 3% for the tensile strains required to transform MoTe2 under uniaxial conditions at room temperature. The potential for mechanical phase transitions is predicted for all six studied compounds. 2D transition metal dichalcogenide materials can potentially exist in more than one monolayer crystal structure, a feature likely to be useful for electronics that is absent in graphene. Here, the authors present calculations showing that such phase transitions may be readily accessible in MoTe2.
804 citations
TL;DR: A reversible 2H-to-1T phase transition in a MoS2 monolayer is realized by plasmonic hot electrons, resulting in an effective shift of photoluminescence.
Abstract: A reversible 2H-to-1T phase transition in a MoS2 monolayer is realized by plasmonic hot electrons. This transition can be actively controlled by the incident light intensity, wavelength, sample areas, and perimeters, resulting in an effective shift of photoluminescence. The suggested configuration paves the way for plasmonic optoelectronic device applications of MoS2 in the future.
515 citations
TL;DR: It is shown that two metastable liquid phases and a stable crystal phase exist at the same deeply supercooled thermodynamic condition, and that the transition between the two liquids satisfies the thermodynamic criteria of a first-order transition.
Abstract: A stable crystal phase and two metastable liquid phases of the ST2 model of water exist at the same deeply supercooled condition, and the two liquids undergo a first-order liquid–liquid transition that meets stringent thermodynamic criteria Water's anomalous physical properties become markedly enhanced upon supercooling below the freezing point and even seem to diverge towards infinity at around 228 K Two papers in this issue use contrasting techniques to study this little-explored 'no-man's land' of water where extremely fast ice formation has prohibited measurements of the liquid state Jonas Sellberg et al use femtosecond X-ray laser pulses to measure bulk liquid water structure in droplets evaporatively cooled to 227 K Even at this temperature some droplets remained liquid on a millisecond timescale Pushing this technique further can shed light on controversial scenarios that aim to describe and explain the many anomalous properties of water Jeremy Palmer et al use six advanced computational methods to demonstrate the existence of two metastable liquid phases of ST2 water at the same deeply supercooled condition, undergoing a liquid–liquid transition that meets stringent thermodynamic criteria and could explain the behavior of water in this regime Liquid water’s isothermal compressibility1 and isobaric heat capacity2, and the magnitude of its thermal expansion coefficient3, increase sharply on cooling below the equilibrium freezing point Many experimental4,5,6,7,8, theoretical9,10,11 and computational12,13 studies have sought to understand the molecular origin and implications of this anomalous behaviour Of the different theoretical scenarios9,14,15 put forward, one posits the existence of a first-order phase transition that involves two forms of liquid water and terminates at a critical point located at deeply supercooled conditions9,12 Some experimental evidence is consistent with this hypothesis4,16, but no definitive proof of a liquid–liquid transition in water has been obtained to date: rapid ice crystallization has so far prevented decisive measurements on deeply supercooled water, although this challenge has been overcome recently16 Computer simulations are therefore crucial for exploring water’s structure and behaviour in this regime, and have shown13,17,18,19,20,21 that some water models exhibit liquid–liquid transitions and others do not However, recent work22,23 has argued that the liquid–liquid transition has been mistakenly interpreted, and is in fact a liquid–crystal transition in all atomistic models of water Here we show, by studying the liquid–liquid transition in the ST2 model of water24 with the use of six advanced sampling methods to compute the free-energy surface, that two metastable liquid phases and a stable crystal phase exist at the same deeply supercooled thermodynamic condition, and that the transition between the two liquids satisfies the thermodynamic criteria of a first-order transition25 We follow the rearrangement of water’s coordination shell and topological ring structure along a thermodynamically reversible path from the low-density liquid to cubic ice26 We also show that the system fluctuates freely between the two liquid phases rather than crystallizing These findings provide unambiguous evidence for a liquid–liquid transition in the ST2 model of water, and point to the separation of time scales between crystallization and relaxation as being crucial for enabling it
456 citations
TL;DR: It is found that the compression waves in the fluid continue to be a source of GWs long after the bubbles have merged, a new effect not taken properly into account in previous modeling of the GW source.
Abstract: We report on the first three-dimensional numerical simulations of first-order phase transitions in the early Universe to include the cosmic fluid as well as the scalar field order parameter. We calculate the gravitational wave (GW) spectrum resulting from the nucleation, expansion, and collision of bubbles of the low-temperature phase, for phase transition strengths and bubble wall velocities covering many cases of interest. We find that the compression waves in the fluid continue to be a source of GWs long after the bubbles have merged, a new effect not taken properly into account in previous modeling of the GW source. For a wide range of models, the main source of the GWs produced by a phase transition is, therefore, the sound the bubbles make.
436 citations
TL;DR: Using first-principle calculations combined with Boltzmann transport equation, Wang et al. as mentioned in this paper have extensively studied the geometry, energetics, electronic structure, optical absorption, and carrier mobility of various phases of MoS2.
Abstract: As an inorganic cousin of graphene, MoS2 monolayer has attracted considerable attention. However, a full understanding of its structure and stability is still lacking due to its dependence on experimental synthesis conditions. Using first-principle calculations combined with Boltzmann transport equation, we have extensively studied the geometry, energetics, electronic structure, optical absorption, and carrier mobility of various phases of MoS2. We have not only identified the stable phases of a MoS2 monolayer, but also clarified the specific conditions under which different phases are formed. The possible pathways for transitions among different phases are also discussed.
432 citations
TL;DR: It is demonstrated that femtosecond X-ray laser pulses can be used to probe the structure of liquid water in micrometre-sized droplets that have been evaporatively cooled below TH, and experimental evidence is found for the existence of metastable bulk liquid water down to temperatures of kelvin in the previously largely unexplored no man’s land.
Abstract: Water has a number of anomalous physical properties, and some of these become drastically enhanced on supercooling below the freezing point. Particular interest has focused on thermodynamic response functions that can be described using a normal component and an anomalous component that seems to diverge at about 228 kelvin (refs 1-3). This has prompted debate about conflicting theories that aim to explain many of the anomalous thermodynamic properties of water. One popular theory attributes the divergence to a phase transition between two forms of liquid water occurring in the 'no man's land' that lies below the homogeneous ice nucleation temperature (TH) at approximately 232 kelvin and above about 160 kelvin, and where rapid ice crystallization has prevented any measurements of the bulk liquid phase. In fact, the reliable determination of the structure of liquid water typically requires temperatures above about 250 kelvin. Water crystallization has been inhibited by using nanoconfinement, nanodroplets and association with biomolecules to give liquid samples at temperatures below TH, but such measurements rely on nanoscopic volumes of water where the interaction with the confining surfaces makes the relevance to bulk water unclear. Here we demonstrate that femtosecond X-ray laser pulses can be used to probe the structure of liquid water in micrometre-sized droplets that have been evaporatively cooled below TH. We find experimental evidence for the existence of metastable bulk liquid water down to temperatures of 227(-1)(+2) kelvin in the previously largely unexplored no man's land. We observe a continuous and accelerating increase in structural ordering on supercooling to approximately 229 kelvin, where the number of droplets containing ice crystals increases rapidly. But a few droplets remain liquid for about a millisecond even at this temperature. The hope now is that these observations and our detailed structural data will help identify those theories that best describe and explain the behaviour of water.
392 citations
11 Jan 2014
TL;DR: In this article, a review of recent developments on the thermodynamics of black holes in extended phase space is presented, where the cosmological constant is interpreted as thermodynamic pressure and treated as a thermodynamic variable in its own right.
Abstract: In this review we summarize, expand, and set in context recent developments on the thermodynamics of black holes in extended phase space, where the cosmological constant is interpreted as thermodynamic pressure and treated as a thermodynamic variable in its own right. We specifically consider the thermodynamics of higher-dimensional rotating asymptotically flat and AdS black holes and black rings in a canonical (fixed angular momentum) ensemble. We plot the associated thermodynamic potential—the Gibbs free energy—and study its behavior to uncover possible thermodynamic phase transitions in these black hole spacetimes. We show that the multiply-rotating Kerr-AdS black holes exhibit a rich set of interesting thermodynamic phenomena analogous to the “every day thermodynamics” of simple substances, such as reentrant phase transitions of multicomponent liquids, multiple first-order solid/liquid/gas phase transitions, and liquid/gas phase transitions of the van derWaals type. Furthermore, the reentrant phase transitions also occur for multiply-spinning asymptotically flat Myers–Perry black holes. These phenomena do not require a variable cosmological constant, though they are more naturally understood in the context of the extended phase space. The thermodynamic volume, a quantity conjugate to the thermodynamic pressure, is studied for AdS black rings and demonstrated to satisfy the reverse isoperimetric inequality; this provides a first example of calculation confirming the validity of isoperimetric inequality conjecture for a black hole with non-spherical horizon topology. The equation of state P = P(V,T) is studied for various black holes both numerically and analytically—in the ultraspinning and slow rotation regimes.
359 citations
TL;DR: Large-scale lattice simulations are used to compute the rate of baryon number violating processes (the sphaleron rate), the Higgs field expectation value, and the critical temperature in the standard model across the electroweak phase transition temperature.
Abstract: We use large-scale lattice simulations to compute the rate of baryon number violating processes (the sphaleron rate), the Higgs field expectation value, and the critical temperature in the standard model across the electroweak phase transition temperature. While there is no true phase transition between the high-temperature symmetric phase and the low-temperature broken phase, the crossover is sharp and located at temperature T c = ( 159.5 ± 1.5 ) GeV . The sphaleron rate in the symmetric phase ( T > T c ) is Γ / T 4 = ( 18 ± 3 ) α W 5 , and in the broken phase in the physically interesting temperature range 130 GeV T T c it can be parametrized as log ( Γ / T 4 ) = ( 0.83 ± 0.01 ) T / GeV - ( 147.7 ± 1.9 ) . The freeze-out temperature in the early Universe, where the Hubble rate wins over the baryon number violation rate, is T * = ( 131.7 ± 2.3 ) GeV . These values, beyond being intrinsic properties of the standard model, are relevant for, e.g., low-scale leptogenesis scenarios.
349 citations
TL;DR: The controversial phase transition from semiconductive 2H to metallic 1T phase and occupancy of the intercalated sodium (Na) upon electrochemical Na intercalation into MoS2 are clarified at the atomic scale by aberration-corrected scanning transmission electron microscope.
Abstract: Two-dimensional (2D) transition-metal dichalcogenides hold enormous potential for applications in electronic and optoelectronic devices. Their distinctive electronic and chemical properties are closely related to the structure and intercalation chemistry. Herein, the controversial phase transition from semiconductive 2H to metallic 1T phase and occupancy of the intercalated sodium (Na) upon electrochemical Na intercalation into MoS2 are clarified at the atomic scale by aberration-corrected scanning transmission electron microscope. In addition, a series of other complicated phase transitions along with lattice distortion, structural modulation, and even irreversible structural decomposition are recognized in MoS2 depending on the content of Na ion intercalation. It is shown that x = 1.5 in NaxMoS2 is a critical point for the reversibility of the structural evolution. Our findings enrich the understanding of the phase transitions and intercalation chemistry of the MoS2 and shed light on future material des...
TL;DR: In this article, the authors provide a brief introduction to quantum thermalization, paying particular attention to the ''Eigenstate Thermalization Hypothesis' (ETH), and the resulting ''single-eigenstate statistical mechanics''.
Abstract: We review some recent developments in the statistical mechanics of isolated quantum systems. We provide a brief introduction to quantum thermalization, paying particular attention to the `Eigenstate Thermalization Hypothesis' (ETH), and the resulting `single-eigenstate statistical mechanics'. We then focus on a class of systems which fail to quantum thermalize and whose eigenstates violate the ETH: These are the many-body Anderson localized systems; their long-time properties are not captured by the conventional ensembles of quantum statistical mechanics. These systems can locally remember forever information about their local initial conditions, and are thus of interest for possibilities of storing quantum information. We discuss key features of many-body localization (MBL), and review a phenomenology of the MBL phase. Single-eigenstate statistical mechanics within the MBL phase reveals dynamically-stable ordered phases, and phase transitions among them, that are invisible to equilibrium statistical mechanics and can occur at high energy and low spatial dimensionality where equilibrium ordering is forbidden.
TL;DR: In this paper, a new P2-type layered oxide, Na5/6[Li 1/4Mn3/4]O2 is prepared using a solid-state method.
Abstract: A new and promising P2-type layered oxide, Na5/6[Li1/4Mn3/4]O2 is prepared using a solid-state method. Detailed crystal structures of the sample are analyzed by synchrotron X-ray diffraction combined with high-resolution neutron diffraction. P2-type Na5/6[Li1/4Mn3/4]O2 consists of two MeO2 layers with partial in-plane √3a × √3a-type Li/Mn ordering. Na/Li ion-exchange in a molten salt results in a phase transition accompanied with glide of [Li1/4Mn3/4]O2 layers without the destruction of in-plane cation ordering. P2-type Na5/6[Li1/4Mn3/4]O2 translates into an O2-type layered structure with staking faults as the result of ion-exchange. Electrode performance of P2-type Na5/6[Li1/4Mn3/4]O2 and O2-type Lix[Li1/4Mn3/4]O2 is examined and compared in Na and Li cells, respectively. Both samples show large reversible capacity, ca. 200 mA h g−1, after charge to high voltage regardless of the difference in charge carriers. Structural analysis suggests that in-plane structural rearrangements, presumably associated with partial oxygen loss, occur in both samples after charge to a high-voltage region. Such structural activation process significantly influences electrode performance of the P2/O2-type phases, similar to O3-type Li2MnO3-based materials. Crystal structures, phase-transition mechanisms, and the possibility of the P2/O2-type phases as high-capacity and long-cycle-life electrode materials with the multi-functionality for both rechargeable Li/Na batteries are discussed in detail.
TL;DR: In this article, a model for network failure recovery reveals spontaneous phase flipping between high-activity and low-activity modes, in analogy with first-order phase transitions near a critical point.
Abstract: Networks that fail can sometimes recover spontaneously—think of traffic jams suddenly easing or people waking from a coma. A model for such recoveries reveals spontaneous ‘phase flipping’ between high-activity and low-activity modes, in analogy with first-order phase transitions near a critical point.
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TL;DR: In this article, the thermodynamics of higher-dimensional rotating asymptotically flat and AdS black holes and black rings in a canonical (fixed angular momentum) ensemble were studied.
Abstract: In this review we summarize, expand, and set in context recent developments on the thermodynamics of black holes in extended phase space, where the cosmological constant is interpreted as thermodynamic pressure and treated as a thermodynamic variable in its own right. We specifically consider the thermodynamics of higher-dimensional rotating asymptotically flat and AdS black holes and black rings in a canonical (fixed angular momentum) ensemble. We plot the associated thermodynamic potential-the Gibbs free energy-and study its behaviour to uncover possible thermodynamic phase transitions in these black hole spacetimes. We show that the multiply-rotating Kerr-AdS black holes exhibit a rich set of interesting thermodynamic phenomena analogous to the "every day thermodynamics" of simple substances, such as reentrant phase transitions of multicomponent liquids, multiple first-order solid/liquid/gas phase transitions, and liquid/gas phase transitions of the Van der Waals type. Furthermore, the reentrant phase transitions also occur for multiply-spinning asymptotically flat Myers-Perry black holes. The thermodynamic volume, a quantity conjugate to the thermodynamic pressure, is studied for AdS black rings and demonstrated to satisfy the reverse isoperimetric inequality; this provides a first example of calculation confirming the validity of isoperimetric inequality conjecture for a black hole with non-spherical horizon topology. The equation of state P=P(V,T) is studied for various black holes both numerically and analytically-in the ultraspinning and slow rotation regimes.
TL;DR: This work detects the phase transitions of individual palladium nanocrystals during hydrogen absorption and desorption, using in situ electron energy-loss spectroscopy in an environmental transmission electron microscope and finds that palladium Nanocrystals undergo sharp transitions between the α and β phases.
Abstract: Many energy- and information-storage processes rely on phase changes of nanomaterials in reactive environments. Compared to their bulk counterparts, nanostructured materials seem to exhibit faster charging and discharging kinetics, extended life cycles, and size-tunable thermodynamics. However, in ensemble studies of these materials, it is often difficult to discriminate between intrinsic size-dependent properties and effects due to sample size and shape dispersity. Here, we detect the phase transitions of individual palladium nanocrystals during hydrogen absorption and desorption, using in situ electron energy-loss spectroscopy in an environmental transmission electron microscope. In contrast to ensemble measurements, we find that palladium nanocrystals undergo sharp transitions between the α and β phases, and that surface effects dictate the size dependence of the hydrogen absorption pressures. Our results provide a general framework for monitoring phase transitions in individual nanocrystals in a reactive environment and highlight the importance of single-particle approaches for the characterization of nanostructured materials.
TL;DR: The Kibble-Zurek mechanism as mentioned in this paper was developed to describe the associated nonequilibrium dynamics and to estimate the density of defects as a function of the quench rate through the transition.
Abstract: In the course of a nonequilibrium continuous phase transition, the dynamics ceases to be adiabatic in the vicinity of the critical point as a result of the critical slowing down (the divergence of the relaxation time in the neighborhood of the critical point). This enforces a local choice of the broken symmetry and can lead to the formation of topological defects. The Kibble–Zurek mechanism (KZM) was developed to describe the associated nonequilibrium dynamics and to estimate the density of defects as a function of the quench rate through the transition. During recent years, several new experiments investigated the formation of defects in phase transitions induced by a quench both in classical and quantum mechanical systems. At the same time, some established results were called into question. We review and analyze the Kibble–Zurek mechanism focusing in particular on this surge of activity, and suggest possible directions for further progress.
TL;DR: The partial substitution of B for P in MnFe(P,Si,B) compounds is found to be an ideal parameter to control the latent heat observed at the Curie point without deteriorating the magnetic properties, which results in promising magnetocaloric properties suitable for magnetic refrigeration.
Abstract: Large magnetically driven temperature changes are observed in MnFe(P,Si,B) materials simultaneously with large entropy changes, limited (thermal or magnetic) hysteresis, and good mechanical stability. The partial substitution of B for P in MnFe(P,Si) compounds is found to be an ideal parameter to control the latent heat observed at the Curie point without deteriorating the magnetic properties, which results in promising magnetocaloric properties suitable for magnetic refrigeration.
TL;DR: In this article, the authors studied the thermodynamic behavior of multi-spinning d = 6 Kerr-anti de Sitter black holes in the canonical ensemble of fixed angular momenta J1 and J2, and found, dependent on the ratio q = J2/J1, qualitatively different interesting phenomena known from the ‘every day thermodynamics of simple substances.
Abstract: We study the thermodynamic behavior of multi-spinning d = 6 Kerr-anti de Sitter black holes in the canonical ensemble of fixed angular momenta J1 and J2. We find, dependent on the ratio q = J2/J1, qualitatively different interesting phenomena known from the ‘every day thermodynamics’ of simple substances. For q = 0 the system exhibits recently observed reentrant large/small/large black hole phase transitions, but for 0 0.0985 we observe the ‘standard liquid/gas behavior’ of the Van der Waals fluid.
TL;DR: X-ray diffraction, Raman spectroscopy, and electrical conductivity measurements of molybdenum disulfide MoS(2) are performed at pressures up to 81 GPa, which provide evidence for isostructural phase transition from 2H(c) to2H(a) modification through layer sliding previously predicted theoretically.
Abstract: X-ray diffraction, Raman spectroscopy, and electrical conductivity measurements of molybdenum disulfide MoS(2) are performed at pressures up to 81 GPa in diamond anvil cells. Above 20 GPa, we find discontinuous changes in Raman spectra and x-ray diffraction patterns which provide evidence for isostructural phase transition from 2H(c) to 2H(a) modification through layer sliding previously predicted theoretically. This first-order transition, which is completed around 40 GPa, is characterized by a collapse in the c-lattice parameter and volume and also by changes in interlayer bonding. After the phase transition completion, MoS(2) becomes metallic. The reversibility of the phase transition is identified from all these techniques.
TL;DR: Time-resolved X-ray diffraction is applied to directly measure the changes in long-range order during ultrafast melting of the charge and orbitally ordered phase in a perovskite manganite to find the dynamics of the phase transformation can be well described using a single time-dependent 'order parameter' that depends exclusively on the electronic excitation.
Abstract: Strongly correlated electron systems often exhibit very strong interactions between structural and electronic degrees of freedom that lead to complex and interesting phase diagrams. For technological applications of these materials it is important to learn how to drive transitions from one phase to another. A key question here is the ultimate speed of such phase transitions, and to understand how a phase transition evolves in the time domain. Here we apply time-resolved X-ray diffraction to directly measure the changes in long-range order during ultrafast melting of the charge and orbitally ordered phase in a perovskite manganite. We find that although the actual change in crystal symmetry associated with this transition occurs over different timescales characteristic of the many electronic and vibrational coordinates of the system, the dynamics of the phase transformation can be well described using a single time-dependent 'order parameter' that depends exclusively on the electronic excitation.
TL;DR: The strain dynamics of ultrathin VO2 film on TiO2 substrate are directly recorded and the intrinsic modulation process is revealed by means of synchrotron radiation and first-principles calculations, showing that the MIT process of the obtained VO2 films can be modulated continuously via the interfacial strain.
Abstract: Tuning the metal insulator transition (MIT) behavior of VO2 film through the interfacial strain is effective for practical applications. However, the mechanism for strain-modulated MIT is still under debate. Here we directly record the strain dynamics of ultrathin VO2 film on TiO2 substrate and reveal the intrinsic modulation process by means of synchrotron radiation and first-principles calculations. It is observed that the MIT process of the obtained VO2 films can be modulated continuously via the interfacial strain. The relationship between the phase transition temperature and the strain evolution is established from the initial film growth. From the interfacial strain dynamics and theoretical calculations, we claim that the electronic orbital occupancy is strongly affected by the interfacial strain, which changes also the electron–electron correlation and controls the phase transition temperature. These findings open the possibility of an active tuning of phase transition for the thin VO2 film through...
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14 Apr 2014TL;DR: In this article, near-equilibrium critical dynamics: 1. Equilibrium critical phenomena 2. Stochastic dynamics 3. Dynamic scaling 4. Dynamic perturbation theory 5. Dynamic renormalization group 6. Hydrodynamic modes and reversible mode couplings 7. Scale invariance in Non-Equilibrium Systems 8. Nonequilibrium Critical dynamics 9. Reaction-diffusion systems 10. Active to absorbing state transitions 11. Driven diffusive systems and growing interfaces Index
Abstract: Part I. Near-Equilibrium Critical Dynamics: 1. Equilibrium critical phenomena 2. Stochastic dynamics 3. Dynamic scaling 4. Dynamic perturbation theory 5. Dynamic renormalization group 6. Hydrodynamic modes and reversible mode couplings 7. Phase transitions in quantum systems Part II. Scale Invariance in Non-Equilibrium Systems 8. Non-equilibrium critical dynamics 9. Reaction-diffusion systems 10. Active to absorbing state transitions 11. Driven diffusive systems and growing interfaces Index.
TL;DR: In this article, a temperature-dependent study of optical absorption and photoluminescence (PL) emission of vapor-deposited CH3NH3PbI3−xClx exploring the nature of recombination channels in the room- and low-temperature phase of the material was performed.
Abstract: The optoelectronic properties of the mixed hybrid lead halide perovskite CH3NH3PbI3−xClx have been subject to numerous recent studies related to its extraordinary capabilities as an absorber material in thin film solar cells. While the greatest part of the current research concentrates on the behavior of the perovskite at room temperature, the observed influence of phonon-coupling and excitonic effects on charge carrier dynamics suggests that low-temperature phenomena can give valuable additional insights into the underlying physics. Here, we present a temperature-dependent study of optical absorption and photoluminescence (PL) emission of vapor-deposited CH3NH3PbI3−xClx exploring the nature of recombination channels in the room- and the low-temperature phase of the material. On cooling, we identify an up-shift of the absorption onset by about 0.1 eV at about 100 K, which is likely to correspond to the known tetragonal-to-orthorhombic transition of the pure halide CH3NH3PbI3. With further decreasing temperature, a second PL emission peak emerges in addition to the peak from the room-temperature phase. The transition on heating is found to occur at about 140 K, i.e., revealing significant hysteresis in the system. While PL decay lifetimes are found to be independent of temperature above the transition, significantly accelerated recombination is observed in the low-temperature phase. Our data suggest that small inclusions of domains adopting the room-temperature phase are responsible for this behavior rather than a spontaneous increase in the intrinsic rate constants. These observations show that even sparse lower-energy sites can have a strong impact on material performance, acting as charge recombination centres that may detrimentally affect photovoltaic performance but that may also prove useful for optoelectronic applications such as lasing by enhancing population inversion.
TL;DR: It is shown that any discrete symmetry-breaking aspect of the charge order—nematicity in the case of the unidirectional CDW the authors consider explicitly—generically survives up to a nonzero critical disorder strength.
Abstract: The cuprate high-temperature superconductors have been the focus of unprecedentedly intense and sustained study not only because of their high superconducting transition temperatures, but also because they represent the most exquisitely investigated examples of highly correlated electronic materials. In particular, the pseudogap regime of the phase diagram exhibits a variety of mysterious emergent behaviors. In the last few years, evidence from NMR and scanning tunneling microscopy (STM) studies, as well as from a new generation of X-ray scattering experiments, has accumulated, indicating that a general tendency to short-range–correlated incommensurate charge density wave (CDW) order is “intertwined” with the superconductivity in this regime. Additionally, transport, STM, neutron-scattering, and optical experiments have produced evidence—not yet entirely understood—of the existence of an associated pattern of long-range–ordered point-group symmetry breaking with an electron-nematic character. We have carried out a theoretical analysis of the Landau–Ginzburg–Wilson effective field theory of a classical incommensurate CDW in the presence of weak quenched disorder. Although the possibilities of a sharp phase transition and long-range CDW order are precluded in such systems, we show that any discrete symmetry-breaking aspect of the charge order—nematicity in the case of the unidirectional (stripe) CDW we consider explicitly—generically survives up to a nonzero critical disorder strength. Such “vestigial order,” which is subject to unambiguous macroscopic detection, can serve as an avatar of what would be CDW order in the ideal, zero disorder limit. Various recent experiments in the pseudogap regime of the hole-doped cuprates are readily interpreted in light of these results.
TL;DR: This work creates supercurrents in annular two-dimensional Bose gases through a temperature quench of the normal-to-superfluid phase transition and measures their distribution for different quench times to demonstrate the stochastic nature of the super currents.
Abstract: We create supercurrents in annular two-dimensional Bose gases through a temperature quench of the normal-to-superfluid phase transition We detect the magnitude and the direction of these supercurrents by measuring spiral patterns resulting from the interference of the cloud with a central reference disk These measurements demonstrate the stochastic nature of the supercurrents We further measure their distribution for different quench times and compare it with predictions based on the Kibble-Zurek mechanism
TL;DR: In this paper, the effects of higher curvature corrections from Lovelock gravity on the phase structure of asymptotically AdS black holes, treating the cosmological constant as a thermodynamic pressure, were investigated.
Abstract: We investigate the effects of higher curvature corrections from Lovelock gravity on the phase structure of asymptotically AdS black holes, treating the cosmological constant as a thermodynamic pressure. We examine how various thermodynamic phenomena, such as Van der Waals behaviour, reentrant phase transitions (RPT), and tricritical points are manifest for U(1) charged black holes in Gauss-Bonnet and 3rd-order Lovelock gravities. We furthermore observe a new phenomenon of "multiple RPT" behaviour, in which for fixed pressure the small/large/small/large black hole phase transition occurs as the temperature of the system increases. We also find that when the higher-order Lovelock couplings are related in a particular way, a peculiar isolated critical point emerges for hyperbolic black holes and is characterized by non-standard critical exponents.
TL;DR: In this article, the authors used molecular dynamics simulations with recently developed importance sampling methods to show that the differential capacitance of a model ionic liquid based double-layer capacitor exhibits an anomalous dependence on the applied electrical potential.
Abstract: Using molecular dynamics simulations with recently developed importance sampling methods, we show that the differential capacitance of a model ionic liquid based double-layer capacitor exhibits an anomalous dependence on the applied electrical potential. Such behavior is qualitatively incompatible with standard mean-field theories of the electrical double layer, but is consistent with observations made in experiment. The anomalous response results from structural changes induced in the interfacial region of the ionic liquid as it develops a charge density to screen the charge induced on the electrode surface. These structural changes are strongly influenced by the out-of-plane layering of the electrolyte and are multifaceted, including an abrupt local ordering of the ions adsorbed in the plane of the electrode surface, reorientation of molecular ions, and the spontaneous exchange of ions between different layers of the electrolyte close to the electrode surface. The local ordering exhibits signatures of a first-order phase transition, which would indicate a singular charge-density transition in a macroscopic limit.
TL;DR: In this paper, the authors show that a Weyl semimetal always exists as an intermediate phase regardless of any constriant from lattice symmetries, although the interval of the critical region is sensitive to the choice of path in the parameter space and can be very narrow.
Abstract: We study the problem of phase transitions from three-dimensional topological to normal insulators without inversion symmetry. In contrast with the conclusions of some previous work, we show that a Weyl semimetal always exists as an intermediate phase regardless of any constriant from lattice symmetries, although the interval of the critical region is sensitive to the choice of path in the parameter space and can be very narrow. We demonstrate this behavior by carrying out first-principles calculations on the noncentrosymmetric topological insulators LaBiTe3 and LuBiTe3 and the trivial insulator BiTeI. We find that a robust Weyl-semimetal phase exists in the solid solutions LaBi1−xSbxTe3 and LuBi1−xSbxTe3 for x ≈ 38.5%‐41.9% and x ≈40.5%‐45.1%, respectively. A low-energy effective model is also constructed to describe the critical behavior in these two materials. In BiTeI, a Weyl semimetal also appears with applied pressure, but only within a very small pressure range, which may explain why it has not been experimentally observed.
TL;DR: The results reveal that the nucleation process is multi-step in nature and proceeds by Ostwald's step rule through which coalescence of soluble monomers leads to the formation of nanospheres, which then undergo ripening and structural conversions to form the final supramolecular assemblies.
Abstract: The self-assembly of molecular building blocks into nano- and micro-scale supramolecular architectures has opened up new frontiers in polymer science. Such supramolecular species not only possess a rich set of dynamic features as a consequence of the non-covalent nature of their core interactions, but also afford unique structural characteristics. Although much is now known about the manner in which such structures adopt their morphologies and size distributions in response to external stimuli, the kinetic and thermodynamic driving forces that lead to their transformation from soluble monomeric species into ordered supramolecular entities have remained elusive. Here we focus on Boc-diphenylalanine, an archetypical example of a peptide with a high propensity towards supramolecular self-organization, and describe the pathway through which it forms a range of nano-assemblies with different structural characteristics. Our results reveal that the nucleation process is multi-step in nature and proceeds by Ostwald's step rule through which coalescence of soluble monomers leads to the formation of nanospheres, which then undergo ripening and structural conversions to form the final supramolecular assemblies. We characterize the structures and thermodynamics of the different phases involved in this process and reveal the intricate nature of the transitions that can occur between discrete structural states of this class of supramolecular polymers.