Showing papers on "Phase transition published in 2021"
TL;DR: This work uncovers an unconventional entanglement transition in an elementary, physically realistic model for weak continuous measurements and demonstrates that the measurement aspect in the dynamics is crucial for whether or not a phase transition takes place.
Abstract: We analyze the quantum trajectory dynamics of free fermions subject to continuous monitoring. For weak monitoring, we identify a novel dynamical regime of subextensive entanglement growth, reminiscent of a critical phase with an emergent conformal invariance. For strong monitoring, however, the dynamics favors a transition into a quantum Zeno-like area-law regime. Close to the critical point, we observe logarithmic finite size corrections, indicating a Berezinskii-Kosterlitz-Thouless mechanism underlying the transition. This uncovers an unconventional entanglement transition in an elementary, physically realistic model for weak continuous measurements. In addition, we demonstrate that the measurement aspect in the dynamics is crucial for whether or not a phase transition takes place.
171 citations
TL;DR: In this paper, a machine learning model is used to predict the electronic properties of amorphous silicon, showing that polyamorphic low-and high-density regions are found to coexist, rather than appearing sequentially.
Abstract: Structurally disordered materials pose fundamental questions1–4, including how different disordered phases (‘polyamorphs’) can coexist and transform from one phase to another5–9. Amorphous silicon has been extensively studied; it forms a fourfold-coordinated, covalent network at ambient conditions and much-higher-coordinated, metallic phases under pressure10–12. However, a detailed mechanistic understanding of the structural transitions in disordered silicon has been lacking, owing to the intrinsic limitations of even the most advanced experimental and computational techniques, for example, in terms of the system sizes accessible via simulation. Here we show how atomistic machine learning models trained on accurate quantum mechanical computations can help to describe liquid–amorphous and amorphous–amorphous transitions for a system of 100,000 atoms (ten-nanometre length scale), predicting structure, stability and electronic properties. Our simulations reveal a three-step transformation sequence for amorphous silicon under increasing external pressure. First, polyamorphic low- and high-density amorphous regions are found to coexist, rather than appearing sequentially. Then, we observe a structural collapse into a distinct very-high-density amorphous (VHDA) phase. Finally, our simulations indicate the transient nature of this VHDA phase: it rapidly nucleates crystallites, ultimately leading to the formation of a polycrystalline structure, consistent with experiments13–15 but not seen in earlier simulations11,16–18. A machine learning model for the electronic density of states confirms the onset of metallicity during VHDA formation and the subsequent crystallization. These results shed light on the liquid and amorphous states of silicon, and, in a wider context, they exemplify a machine learning-driven approach to predictive materials modelling. Machine learning models enable atomistic simulations of phase transitions in amorphous silicon, predict electronic fingerprints, and show that the pressure-induced crystallization occurs over three distinct stages.
145 citations
30 Mar 2021
TL;DR: This work introduces theoretical approaches to measurement-induced phase transitions (MPT) and also to entanglement transitions in random tensor networks, and proposes Landau-Ginsburg-Wilson-like field theories for the MPT, the FMPT, and for entanglements in Tensor networks.
Abstract: A quantum many-body system whose dynamics includes local measurements at a nonzero rate can be in distinct dynamical phases, with differing entanglement properties We introduce theoretical approaches to measurement-induced phase transitions (MPTs) and also to entanglement transitions in random tensor networks Many of our results are for “all-to-all” quantum circuits with unitaries and measurements, in which any qubit can couple to any other, and related settings where some of the complications of low-dimensional models are reduced We also propose field-theory descriptions for spatially local systems of any finite dimensionality To build intuition, we first solve the simplest “minimal cut” toy model for entanglement dynamics in all-to-all circuits, finding scaling forms and exponents within this approximation We then show that certain all-to-all measurement circuits allow exact results by exploiting local treelike structure in the circuit geometry For this reason, we make a detour to give general universal results for entanglement phase transitions in a class of random tree tensor networks with bond dimension 2, making a connection with the classical theory of directed polymers on a tree We then compare these results with numerics in all-to-all circuits, both for the MPT and for the simpler “forced-measurement phase transition” (FMPT) We characterize the two different phases in all-to-all circuits using observables that are sensitive to the amount of information that is propagated between the initial and final time We demonstrate signatures of the two phases that can be understood from simple models Finally we propose Landau-Ginsburg-Wilson-like field theories for the measurement phase transition, the forced-measurement phase transition, and for entanglement transitions in random tensor networks This analysis shows a surprising difference between the measurement phase transition and the other cases We discuss variants of the measurement problem with additional structure (for example free-fermion structure), and questions for the future
136 citations
TL;DR: In this article, the authors discuss the thermodynamic and kinetic features of 2D phase transitions arising from dimensionality confinement, elasticity, electrostatics, defects and chemistry unique to 2D materials.
Abstract: The discovery and control of new phases of matter is a central endeavour in materials research. The emergence of atomically thin 2D materials, such as transition-metal dichalcogenides and monochalcogenides, has allowed the study of diffusive, displacive and quantum phase transitions in 2D. In this Review, we discuss the thermodynamic and kinetic features of 2D phase transitions arising from dimensionality confinement, elasticity, electrostatics, defects and chemistry unique to 2D materials. We highlight polymorphic, ferroic and high-temperature diffusive phase changes, and examine the technological potential of controlled 2D phase transitions. Finally, we give an outlook to future opportunities in the study and applications of 2D phase transitions, and identify key challenges that remain to be addressed. Phase transformations in 2D materials have distinct kinetic and thermodynamic features, resulting from their reduced dimensionality and unique interactions. This Review discusses the properties of phase transitions and defects in 2D materials, and examines technological applications and challenges in the study of 2D phase transitions.
126 citations
TL;DR: In this paper, an out-of-plane electric field controls not only the bandwidth but also the band topology by intertwining moire bands centered at different high-symmetry stacking sites.
Abstract: Electron correlation and topology are two central threads of modern condensed matter physics. Semiconductor moire materials provide a highly tunable platform for studies of electron correlation. Correlation-driven phenomena, including the Mott insulator, generalized Wigner crystals, stripe phases and continuous Mott transition, have been demonstrated. However, nontrivial band topology has remained elusive. Here we report the observation of a quantum anomalous Hall (QAH) effect in AB-stacked MoTe2/WSe2 moire heterobilayers. Unlike in the AA-stacked structures, an out-of-plane electric field controls not only the bandwidth but also the band topology by intertwining moire bands centered at different high-symmetry stacking sites. At half band filling, corresponding to one particle per moire unit cell, we observe quantized Hall resistance, h/e2 (with h and e denoting the Planck's constant and electron charge, respectively), and vanishing longitudinal resistance at zero magnetic field. The electric-field-induced topological phase transition from a Mott insulator to a QAH insulator precedes an insulator-to-metal transition; contrary to most known topological phase transitions, it is not accompanied by a bulk charge gap closure. Our study paves the path for discovery of a wealth of emergent phenomena arising from the combined influence of strong correlation and topology in semiconductor moire materials.
123 citations
TL;DR: In this article, a detailed analysis of stochastic gravitational wave production from cosmological phase transitions in an expanding universe was performed, where the authors studied both a standard radiation as well as a matter dominated history.
Abstract: We undertake a careful analysis of stochastic gravitational wave production from cosmological phase transitions in an expanding universe, studying both a standard radiation as well as a matter dominated history. We analyze in detail the dynamics of the phase transition, including the false vacuum fraction, bubble lifetime distribution, bubble number density, mean bubble separation, etc., for an expanding universe. We also study the full set of differential equations governing the evolution of plasma and the scalar field during the phase transition and generalize results obtained in Minkowski spacetime. In particular, we generalize the sound shell model to the expanding universe and determine the velocity field power spectrum. This ultimately provides an accurate calculation of the gravitational wave spectrum seen today for the dominant source of sound waves. For the amplitude of the gravitational wave spectrum visible today, we find a suppression factor arising from the finite lifetime of the sound waves and compare with the commonly used result in the literature, which corresponds to the asymptotic value of our suppression factor. We point out that the asymptotic value is only applicable for a very long lifetime of the sound waves, which is highly unlikely due to the onset of shocks, turbulence and other damping processes. We also point out that features of the gravitational wave spectral form may hold out the tantalizing possibility of distinguishing between different expansion histories using phase transitions.
103 citations
92 citations
TL;DR: Polar skyrmions are topologically protected structures that can exist in (PbTiO 3 ) n /(SrTiO3 ) n superlattices and it is shown that they have negative permittivity at the surface, and that they can undergo a reversible phase transition with large dielectric tunability under an electric field.
Abstract: Topological solitons such as magnetic skyrmions have drawn attention as stable quasi-particle-like objects. The recent discovery of polar vortices and skyrmions in ferroelectric oxide superlattices has opened up new vistas to explore topology, emergent phenomena and approaches for manipulating such features with electric fields. Using macroscopic dielectric measurements, coupled with direct scanning convergent beam electron diffraction imaging on the atomic scale, theoretical phase-field simulations and second-principles calculations, we demonstrate that polar skyrmions in (PbTiO3)n/(SrTiO3)n superlattices are distinguished by a sheath of negative permittivity at the periphery of each skyrmion. This enhances the effective dielectric permittivity compared with the individual SrTiO3 and PbTiO3 layers. Moreover, the response of these topologically protected structures to electric field and temperature shows a reversible phase transition from the skyrmion state to a trivial uniform ferroelectric state, accompanied by large tunability of the dielectric permittivity. Pulsed switching measurements show a time-dependent evolution and recovery of the skyrmion state (and macroscopic dielectric response). The interrelationship between topological and dielectric properties presents an opportunity to simultaneously manipulate both by a single, and easily controlled, stimulus, the applied electric field.
89 citations
TL;DR: In this article, the authors studied the possibility of observing the gravitational wave spectrum created in a first-order phase transition (in beyond the standard model theories) in upcoming space-based detectors like LISA.
Abstract: Building on previous work (https://journals.aps.org/prd/abstract/10.1103/PhysRevD.97.123513), the authors study through extensive numerical simulations the possibility of observing the gravitational wave spectrum created in a first-order phase transition (in beyond the standard model theories) in upcoming space-based detectors like LISA. Different effective potentials are considered and it is shown that the potential could be determined by the form of the gravitational wave spectrum.
86 citations
TL;DR: This work identifies the transition as well as the nontrivial steady state that emerges at late times in the mixed phase using exact diagonalization and an approximate, analytically tractable mean-field theory; these methods yield consistent conclusions.
Abstract: A quantum system subject to continuous measurement and postselection evolves according to a non-Hermitian Hamiltonian. We show that, as one increases the strength of postselection, this non-Hermitian Hamiltonian can undergo a spectral phase transition. On one side of this phase transition (for weak postselection), an initially mixed density matrix remains mixed at all times, and an initially unentangled state develops volume-law entanglement; on the other side, an arbitrary initial state approaches a unique pure state with low entanglement. We identify this transition with an exceptional point in the spectrum of the non-Hermitian Hamiltonian, at which $PT$ symmetry is spontaneously broken. We characterize the transition as well as the nontrivial steady state that emerges at late times in the mixed phase using exact diagonalization and an approximate, analytically tractable mean-field theory; these methods yield consistent conclusions.
82 citations
15 Feb 2021
TL;DR: Hindmarsh et al. as mentioned in this paper provided the necessary basics to understand first-order phase transitions in the early universe, to outline how they leave imprints in gravitational waves, and advertise how those gravitational waves could be detected in the future.
Abstract: These lecture notes are based on a course given by Mark Hindmarsh at the 24th Saalburg Summer School 2018 and written up by Marvin Luben, Johannes Lumma and Martin Pauly. The aim is to provide the necessary basics to understand first-order phase transitions in the early universe, to outline how they leave imprints in gravitational waves, and advertise how those gravitational waves could be detected in the future. A first-order phase transition at the electroweak scale is a prediction of many theories beyond the Standard Model, and is also motivated as an ingredient of some theories attempting to provide an explanation for the matter-antimatter asymmetry in our Universe.
Starting from bosonic and fermionic statistics, we derive Boltzmann's equation and generalise to a fluid of particles with field dependent mass. We introduce the thermal effective potential for the field in its lowest order approximation, discuss the transition to the Higgs phase in the Standard Model and beyond, and compute the probability for the field to cross a potential barrier. After these preliminaries, we provide a hydrodynamical description of first-order phase transitions as it is appropriate for describing the early Universe. We thereby discuss the key quantities characterising a phase transition, and how they are imprinted in the gravitational wave power spectrum that might be detectable by the space-based gravitational wave detector LISA in the 2030s.
TL;DR: In this article, the influence of the superficial Bi and Ga2O3 layers during surface solidification was investigated and the pattern-formation mechanism involved surface-catalysed heterogeneous nucleation.
Abstract: It is well-understood that during the liquid-to-solid phase transition of alloys, elements segregate in the bulk phase with the formation of microstructures. In contrast, we show here that in a Bi–Ga alloy system, highly ordered nanopatterns emerge preferentially at the alloy surfaces during solidification. We observed a variety of transition, hybrid and crystal-defect-like patterns, in addition to lamellar and rod-like structures. Combining experiments and molecular dynamics simulations, we investigated the influence of the superficial Bi and Ga2O3 layers during surface solidification and elucidated the pattern-formation mechanisms, which involve surface-catalysed heterogeneous nucleation. We further demonstrated the dynamic nature and robustness of the phenomenon under different solidification conditions and for various alloy systems. The surface patterns we observed enable high-spatial-resolution nanoscale-infrared and surface-enhanced Raman mapping, which reveal promising potential for surface- and nanoscale-based applications. During a liquid-to-solid phase transition, a Bi–Ga alloy forms ordered nanostructured patterns on its surface.
TL;DR: In this paper, the authors consider a non-Hermitian extension of the Aubry-Andr\'e-Harper model, and show that the dynamical localization-delocalization transition is discontinuous, not only in the diffusion exponent, but also in the speed $v$ of ballistic transport.
Abstract: The Aubry-Andr\'e-Harper model provides a paradigmatic example of aperiodic order in a one-dimensional lattice displaying a delocalization-localization phase transition at a finite critical value ${V}_{c}$ of the quasiperiodic potential amplitude $V$. In terms of the dynamical behavior of the system, the phase transition is discontinuous when one measures the quantum diffusion exponent $\ensuremath{\delta}$ of wave-packet spreading, with $\ensuremath{\delta}=1$ in the delocalized phase $Vl{V}_{c}$ (ballistic transport), $\ensuremath{\delta}\ensuremath{\simeq}1/2$ at the critical point $V={V}_{c}$ (diffusive transport), and $\ensuremath{\delta}=0$ in the localized phase $Vg{V}_{c}$ (dynamical localization). However, the phase transition turns out to be smooth when one measures, as a dynamical variable, the speed $v(V)$ of excitation transport in the lattice, which is a continuous function of potential amplitude $V$ and vanishes as the localized phase is approached. Here we consider a non-Hermitian extension of the Aubry-Andr\'e-Harper model, in which hopping along the lattice is asymmetric, and show that the dynamical localization-delocalization transition is discontinuous, not only in the diffusion exponent $\ensuremath{\delta}$, but also in the speed $v$ of ballistic transport. This means that even very close to the spectral phase transition point, rather counterintuitively, ballistic transport with a finite speed is allowed in the lattice. Also, we show that the ballistic velocity can increase as $V$ is increased above zero, i.e., surprisingly, disorder in the lattice can result in an enhancement of transport.
Massachusetts Institute of Technology1, University of Mainz2, European XFEL3, Technical University of Berlin4, University of Göttingen5, University of Hamburg6, Heidelberg University7, Polytechnic University of Milan8, Istituto Nazionale di Fisica Nucleare9, Radboud University Nijmegen10, University of Liège11
TL;DR: Atomistic simulations indicate that the fluctuation state largely reduces the topological energy barrier and thereby enables the observed rapid and homogeneous nucleation of the skyrmion phase, and suggest a path towards ultrafast topological switching in a wide variety of materials through intermediate fluctuating states.
Abstract: Topological states of matter exhibit fascinating physics combined with an intrinsic stability. A key challenge is the fast creation of topological phases, which requires massive reorientation of charge or spin degrees of freedom. Here we report the picosecond emergence of an extended topological phase that comprises many magnetic skyrmions. The nucleation of this phase, followed in real time via single-shot soft X-ray scattering after infrared laser excitation, is mediated by a transient topological fluctuation state. This state is enabled by the presence of a time-reversal symmetry-breaking perpendicular magnetic field and exists for less than 300 ps. Atomistic simulations indicate that the fluctuation state largely reduces the topological energy barrier and thereby enables the observed rapid and homogeneous nucleation of the skyrmion phase. These observations provide fundamental insights into the nature of topological phase transitions, and suggest a path towards ultrafast topological switching in a wide variety of materials through intermediate fluctuating states. Time-resolved X-ray scattering is utilized to demonstrate an ultrafast 300 ps topological phase transition to a skyrmionic phase. This transition is enabled by the formation of a transient topological fluctuation state.
TL;DR: In this article, measurement-induced phase transitions in the quantum Ising chain coupled to a monitoring environment were investigated and two different limits of the measurement problem, the stochastic quantum-state diffusion protocol corresponding to infinite small jumps per unit of time and the no-click limit, corresponding to post-selection and described by a non-Hermitian Hamiltonian, were compared.
Abstract: We investigate measurement-induced phase transitions in the Quantum Ising chain coupled to a monitoring environment. We compare two different limits of the measurement problem, the stochastic quantum-state diffusion protocol corresponding to infinite small jumps per unit of time and the no-click limit, corresponding to post-selection and described by a non-Hermitian Hamiltonian. In both cases we find a remarkably similar phenomenology as the measurement strength $\gamma$ is increased, namely a sharp transition from a critical phase with logarithmic scaling of the entanglement to an area-law phase, which occurs at the same value of the measurement rate in the two protocols. An effective central charge, extracted from the logarithmic scaling of the entanglement, vanishes continuously at the common transition point, although with different critical behavior possibly suggesting different universality classes for the two protocols. We interpret the central charge mismatch near the transition in terms of noise-induced disentanglement, as suggested by the entanglement statistics which displays emergent bimodality upon approaching the critical point. The non-Hermitian Hamiltonian and its associated subradiance spectral transition provide a natural framework to understand both the extended critical phase, emerging here for a model which lacks any continuous symmetry, and the entanglement transition into the area law.
TL;DR: A superconducting phase transition with a critical temperature that scales linearly with the interaction strength is found and is substantiate the validity of the topological bound beyond the mean-field regime and further stress the importance of fragile topology for flat-band superconductivity.
Abstract: In flat bands, superconductivity can lead to surprising transport effects. The superfluid ``mobility'', in the form of the superfluid weight ${D}_{s}$, does not draw from the curvature of the band but has a purely band-geometric origin. In a mean-field description, a nonzero Chern number or fragile topology sets a lower bound for ${D}_{s}$, which, via the Berezinskii-Kosterlitz-Thouless mechanism, might explain the relatively high superconducting transition temperature measured in magic-angle twisted bilayer graphene (MATBG). For fragile topology, relevant for the bilayer system, the fate of this bound for finite temperature and beyond the mean-field approximation remained, however, unclear. Here, we numerically use exact Monte Carlo simulations to study an attractive Hubbard model in flat bands with topological properties akin to those of MATBG. We find a superconducting phase transition with a critical temperature that scales linearly with the interaction strength. Then, we investigate the robustness of the superconducting state to the addition of trivial bands that may or may not trivialize the fragile topology. Our results substantiate the validity of the topological bound beyond the mean-field regime and further stress the importance of fragile topology for flat-band superconductivity.
TL;DR: In this article, the authors present a non-thermal mechanism for producing the observed Dark Matter (DM) relic abundance during the First Order Phase Transition (FOPT) in the early universe.
Abstract: In this paper we present a novel mechanism for producing the observed Dark Matter (DM) relic abundance during the First Order Phase Transition (FOPT) in the early universe. We show that the bubble expansion with ultra-relativistic velocities can lead to the abundance of DM particles with masses much larger than the scale of the transition. We study this non-thermal production mechanism in the context of a generic phase transition and the electroweak phase transition. The application of the mechanism to the Higgs portal DM as well as the signal in the Stochastic Gravitational Background are discussed.
TL;DR: In this article, the dynamics of the relativistic bubble expansion during the first order phase transition focusing on the ultra-relativistic velocities was analyzed and it was shown that fields much heavier than the scale of the phase transition can significantly contribute to the friction and modify the motion of the bubble wall leading to interesting phenomenological consequences.
Abstract: We analyse the dynamics of the relativistic bubble expansion during the first order phase transition focusing on the ultra relativistic velocities $\gamma\gg 1$. We show that fields much heavier than the scale of the phase transition can significantly contribute to the friction and modify the motion of the bubble wall leading to interesting phenomenological consequences. NLO effects on the friction due to the soft vector field emission are reviewed as well.
TL;DR: In this article, the authors show that the apparent phase separation is a dynamical artefact occurring in a many-particle system driven by autocatalytic electrochemical reactions, that is, an interfacial exchange current that increases with the extent of delithiation.
Abstract: Layered oxides widely used as lithium-ion battery electrodes are designed to be cycled under conditions that avoid phase transitions. Although the desired single-phase composition ranges are well established near equilibrium, operando diffraction studies on many-particle porous electrodes have suggested phase separation during delithiation. Notably, the separation is not always observed, and never during lithiation. These anomalies have been attributed to irreversible processes during the first delithiation or reversible concentration-dependent diffusion. However, these explanations are not consistent with all experimental observations such as rate and path dependencies and particle-by-particle lithium concentration changes. Here, we show that the apparent phase separation is a dynamical artefact occurring in a many-particle system driven by autocatalytic electrochemical reactions, that is, an interfacial exchange current that increases with the extent of delithiation. We experimentally validate this population-dynamics model using the single-phase material Lix(Ni1/3Mn1/3Co1/3)O2 (0.5 < x < 1) and demonstrate generality with other transition-metal compositions. Operando diffraction and nanoscale oxidation-state mapping unambiguously prove that this fictitious phase separation is a repeatable non-equilibrium effect. We quantitatively confirm the theory with multiple-datastream-driven model extraction. More generally, our study experimentally demonstrates the control of ensemble stability by electro-autocatalysis, highlighting the importance of population dynamics in battery electrodes (even non-phase-separating ones). Although layered oxides electrodes in lithium-ion batteries are designed under conditions avoiding phase transitions, phase separation during delithiation has been observed. This apparent phase separation is shown to be a dynamical artefact occurring in a many-particle system driven by autocatalytic electrochemical reactions.
TL;DR: More than 200 different spinels, with the general formula AB 2 X 4, have been identified or synthesized in polycrystalline or single-celline form as discussed by the authors.
11 Mar 2021
TL;DR: In this paper, the solid-liquid phase transition of Ga-Sn/Ga-In alloys can induce an instant and radical transformation of their atomic and electronic structures during electrocatalysis, which dramatically impacts their catalytic properties.
Abstract: Conventional strategies for modifying electrocatalysts for efficient CO2 reduction are mainly based on doping, defect/morphology engineering, substrate design and so on. In most cases, these methods can only tune their structures, electronic states and thereby catalytic properties in a gradual way. Here we report that the solid–liquid phase transition of Ga–Sn/Ga–In alloys can induce an instant and radical transformation of their atomic and electronic structures during electrocatalysis, which dramatically impacts their catalytic properties. The transition of Sn/In active components from phase-segregated clusters to dispersed single atoms during melting results in a unique electronic structure through further reduction of both metallic Sn/In and Ga. Such atomic/electronic structure transitions can correlate well with suppression of the hydrogen evolution reaction and an enhanced formate Faradaic efficiency from 95%. This two-state switching strategy may be extended to other catalytic reactions to determine correlations between their structures and catalytic properties. Common strategies for catalyst design explore ways of fine-tuning continuous structure–property relationships. Here, the abrupt solid–liquid transition of Ga–In and Ga–Sn alloys is shown to have a profound impact on the CO2 electroreduction performance, with the molten alloy achieving a Faradaic efficiency of 95% formate production.
TL;DR: In this paper, the effect of uniaxial heterostrain on the interacting phase diagram of magic-angle twisted bilayer graphene was investigated, and it was shown that small strain values (e∼0.1%-0.2%) drive a zero-temperature phase transition between the symmetry-broken "Kramer intervalley-coherent" insulator and a nematic semimetal.
Abstract: We investigate the effect of uniaxial heterostrain on the interacting phase diagram of magic-angle twisted bilayer graphene. Using both self-consistent Hartree-Fock and density-matrix renormalization group calculations, we find that small strain values (e∼0.1%-0.2%) drive a zero-temperature phase transition between the symmetry-broken "Kramers intervalley-coherent" insulator and a nematic semimetal. The critical strain lies within the range of experimentally observed strain values, and we therefore predict that strain is at least partly responsible for the sample-dependent experimental observations.
TL;DR: In this article, a stearic acid/palmitic acid binary eutectic phase change material (SA/PA-PCM) was used in asphalt binder by conducting a series of tests.
TL;DR: In this article, an experimental demonstration of a phase transition in the quantum Rabi model using a 171Yb+ ion in a Paul trap is presented. But the phase transition is not associated with many-body systems in the thermodynamic limit.
Abstract: Quantum phase transitions (QPTs) are usually associated with many-body systems in the thermodynamic limit when their ground states show abrupt changes at zero temperature with variation of a parameter in the Hamiltonian. Recently it has been realized that a QPT can also occur in a system composed of only a two-level atom and a single-mode bosonic field, described by the quantum Rabi model (QRM). Here we report an experimental demonstration of a QPT in the QRM using a 171Yb+ ion in a Paul trap. We measure the spin-up state population and the average phonon number of the ion as two order parameters and observe clear evidence of the phase transition via adiabatic tuning of the coupling between the ion and its spatial motion. An experimental probe of the phase transition in a fundamental quantum optics model without imposing the thermodynamic limit opens up a window for controlled study of QPTs and quantum critical phenomena.
TL;DR: In this article, the superconducting property and structural stability of kagome CsV3Sb5 under in-situ high pressures were investigated and a two-dome-like variation of Tc was concluded.
Abstract: Here we present the superconducting property and structural stability of kagome CsV3Sb5 under in-situ high pressures. For the initial SC-I phase, its Tc is quickly enhanced from 3.5 K to 7.6 K and then totally suppressed at P~10 GPa. Further increasing the applied pressures, an SC-II phase emerges at P~15 GPa and persists up to 100 GPa. The Tc rapidly increases to the maximal value of 5.2 K at P=53.6 GPa and rather slowly decreases to 4.7 K at P=100 GPa. A two-dome-like variation of Tc in CsV3Sb5 is concluded here. The Raman measurements demonstrate that weakening of E2g model and strengthening of A1g model occur without phase transition as entering the SC-II phase, which is supported by the results of phonon spectra calculations. Electronic structure calculations reveal that exertion of pressure may bridge the gap of topological surface nontrivial states near EF, i. e. Z2 invariant. Meanwhile, it enlarges Fermi surface significantly, consistent with the increased carrier density. The findings here point out the change of electronic structure and strengthened electron-phonon coupling should be responsible for the pressure-induced reentrant SC.
TL;DR: In this article, a sp2 carbon-conjugated three-dimensional (3D) covalent organic framework (COF) (BUCT-COF-4) is synthesized via the Knoevenagel condensation of the saddle-shaped aldehyde-substituted cyclooctatetrathiophene and 1,4-phenylenediacetonitrile.
Abstract: A first example of an sp2 carbon-conjugated three-dimensional (3D) covalent organic framework (COF) (BUCT-COF-4) is synthesized via the Knoevenagel condensation of the saddle-shaped aldehyde-substituted cyclooctatetrathiophene and 1,4-phenylenediacetonitrile. Ascribed to the extended π-conjugation and long-range ordered structures, BUCT-COF-4 displays high Hall electron mobility of 1.97 cm2 V-1 s-1 at room temperature. After it is doped with iodine, the material not only exhibits an enhanced electron mobility up to 2.62 cm2 V-1 s-1 in ambient air but also presents an unexpected metal-free ferromagnetic phase transition arising from the formation of aligned spins unidirectional across the whole sp2 carbon-conjugated 3D framework. This is the first report of a ferromagnetic phenomenon in 3D COF materials, which would broaden promising applications and open a new frontier in COF materials.
TL;DR: In this paper, both pure and mixed state Floquet dynamical quantum phase transitions (FDQFTs) in the one-dimensional $p$-wave superconductor with a time-driven pairing phase were studied.
Abstract: We explore both pure and mixed state Floquet dynamical quantum phase transitions (FDQFTs) in the one-dimensional $p$-wave superconductor with a time-driven pairing phase. In the Fourier space the model is recast to the noninteracting quasispins subjected to a time-dependent effective magnetic field. We show that FDQFTs occur within a range of driving frequency without resorting to any quenches. Moreover, FDQFTs appear in the region where quasispins are in the resonance regime. In the resonance regime, the population completely cycles the population between the spin down and up states. Additionally, we study the conditions for the appearance of FDQFTs using the entanglement spectrum and purity entanglement measure. Our results imply that the entanglement spectrum can truly capture the resonance regime where FDQFTs occur. Particularly, the dynamical topological region results in the degeneracy of the entanglement spectrum. It is shown that the boundary of the driven frequency range, over which the system reveals FDQFTs, is signaled by the purity entanglement measure.
TL;DR: In this paper, the authors investigated the localization and topological transitions in a one-dimensional (interacting) non-Hermitian quasiperiodic lattice, which is described by a generalized Aubry-Andr\'e-Harper model with irrational modulations in the off-diagonal hopping and on-site potential and with non-hermiticities from the non-reciprocal hopping and complex potential phase.
Abstract: We investigate the localization and topological transitions in a one-dimensional (interacting) non-Hermitian quasiperiodic lattice, which is described by a generalized Aubry-Andr\'e-Harper model with irrational modulations in the off-diagonal hopping and on-site potential and with non-Hermiticities from the nonreciprocal hopping and complex potential phase. For noninteracting cases, we reveal that the nonreciprocal hopping (the complex potential phase) can enlarge the delocalization (localization) region in the phase diagrams spanned by two quasiperiodic modulation strengths. We show that the localization transition is always accompanied by a topological phase transition characterized the winding numbers of eigenenergies in three different non-Hermitian cases. Moreover, we find that a real-complex eigenenergy transition in the energy spectrum coincides with (occurs before) these two phase transitions in the nonreciprocal (complex potential) case, while the real-complex transition is absent with the coexistence of the two non-Hermiticities. For interacting spinless fermions, we demonstrate that the extended phase and the many-body localized phase can be identified by the entanglement entropy of eigenstates and the level statistics of complex eigenenergies. By making the critical scaling analysis, we further show that the many-body localization transition coincides with the real-complex transition and occurs before the topological transition in the nonreciprocal case, which are absent in the complex phase case.
TL;DR: In this article, a simulation of a two-dimensional second-order topological phase in a superconducting qubit was carried out, where the pseudo-spin texture was measured in momentum space of the bulk for the first time.
Abstract: Higher-order topological phases give rise to new bulk and boundary physics, as well as new classes of topological phase transitions. While the realization of higher-order topological phases has been confirmed in many platforms by detecting the existence of gapless boundary modes, a direct determination of the higher-order topology and related topological phase transitions through the bulk in experiments has still been lacking. To bridge the gap, in this work we carry out the simulation of a two-dimensional second-order topological phase in a superconducting qubit. Owing to the great flexibility and controllability of the quantum simulator, we observe the realization of higher-order topology directly through the measurement of the pseudo-spin texture in momentum space of the bulk for the first time, in sharp contrast to previous experiments based on the detection of gapless boundary modes in real space. Also through the measurement of the evolution of pseudo-spin texture with parameters, we further observe novel topological phase transitions from the second-order topological phase to the trivial phase, as well as to the first-order topological phase with nonzero Chern number. Our work sheds new light on the study of higher-order topological phases and topological phase transitions.
TL;DR: Two-step electroweak phase transition is found to occur in a narrow region of allowed parameter space with the second transition always being first order in a non-negligible portion of the two-step parameter space.
Abstract: New field content beyond that of the standard model of particle physics can alter the thermal history of electroweak symmetry breaking in the early Universe. In particular, the symmetry breaking may have occurred through a sequence of successive phase transitions. We study the thermodynamics of such a scenario in a real triplet extension of the standard model, using nonperturbative lattice simulations. Two-step electroweak phase transition is found to occur in a narrow region of allowed parameter space with the second transition always being first order. The first transition into the phase of nonvanishing triplet vacuum expectation value is first order in a non-negligible portion of the two-step parameter space. A comparison with two-loop perturbative calculation is provided and significant discrepancies with the nonperturbative results are identified.