查看更多>>摘要：The origin of fast radio bursts(FRBs),the brightest cosmic explosion in radio bands,remains unknown.We introduce here a novel method for a comprehensive analysis of active FRBs'behaviors in the time-energy domain.Using"Pincus Index"and"Maximum Lyapunov Exponent",we were able to quantify the randomness and chaoticity,respectively,of the bursting events and put FRBs in the context of com-mon transient physical phenomena,such as pulsar,earthquakes,and solar flares.In the bivariate time-energy domain,repeated FRB bursts'behaviors deviate significantly(more random,less chaotic)from pulsars,earthquakes,and solar flares.The waiting times between FRB bursts and the corresponding energy changes exhibit no correlation and remain unpredictable,suggesting that the emission of FRBs does not exhibit the time and energy clustering observed in seismic events.The pronounced stochasticity may arise from a singular source with high entropy or the combination of diverse emission mechanisms/sites.Consequently,our methodology serves as a pragmatic tool for illustrating the congruities and dis-tinctions among diverse physical processes.
查看更多>>摘要：Electron-phonon interactions and electron-electron correlations represent two crucial facets of condensed matter physics.For instance,in a half-filled spin-1/2 anti-ferromagnetic chain,the lattice dimerization induced by electron-nucleus interaction can be intensified by onsite Coulomb repulsion,resulting in a spin-Peierls state.Through first-principles calculations and crystal structure prediction methods,we have identified that under mild pressures,potassium and ammonia can form stable compounds:R3m K(NH3)2,Pm3m K(NH3)2,and Cm K2(NH3)3.Our predictions suggest that the R3 m K(NH3)2 exhibits electride characteristics,marked by the formation of interstitial anionic electrons(IAEs)in the interlayer space.These IAEs are arranged in quasi-two-dimensional triangular arrays.With increasing pressure,the electronic van-Hove singularity shifts toward the Fermi level,resulting in an augmented density of states and the onset of both Peierls and magnetic instabilities.Analyzing these instabilities,we determine that the ground state of the R3 m K(NH3)2 is the dimerized P2i/m phase with zigzag-type anti-ferromagnetic IAEs.This state can be described by the triangular-lattice antiferromag-netic Heisenberg model with modulated magnetic interactions.Furthermore,we unveil the coexistence and positive interplay between magnetic and Peierls instability,constituting a scenario of spin-Peierls instability unprecedented in realistic 2D materials,particularly involving IAEs.This work provides valuable insights into the coupling of IAEs with the adjacent lattice and their spin correlations in quantum materials.
查看更多>>摘要：In thermoelectrics,doping is essential to augment the figure of merit.Traditional strategy,predominantly heavy doping,aims to optimize carrier concentration and restrain lattice thermal conductivity.However,this tactic can severely hamper carrier transport due to pronounced point defect scattering,particularly in materials with inherently low carrier mean-free-path.Conversely,dilute doping,although minimally affecting carrier mobility,frequently fails to optimize other vital thermoelectric parameters.Herein,we present a more nuanced dilute doping strategy in GeTe,leveraging the multifaceted roles of small-size metal atoms.A mere 4％CuPbSbTe3 introduction into GeTe swiftly suppresses rhombohedral distortion and optimizes carrier concentration through the aid of Cu interstitials.Additionally,the formation of multiscale microstructures,including zero-dimensional Cu interstitials,one-dimensional dislocations,two-dimensional planar defects,and three-dimensional nanoscale amorphous GeO2 and Cu2GeTe3 pre-cipitates,along with the ensuing lattice softening,contributes to an ultralow lattice thermal conductivity.Intriguingly,dilute CuPbSbTe3 doping incurs only a marginal decrease in carrier mobility.Subsequent trace Cd doping,employed to alleviate the bipolar effect and align the valence bands,yields an impressive figure-of-merit of 2.03 at 623 K in(Ge0.97Cd0.03Te)0.96(CuPbSbTe3)0.04.This leads to a high energy-conversion efficiency of 7.9％and a significant power density of 3.44 W cm-2 at a temperature difference of 500 K.These results underscore the invaluable insights gained into the constructive role of nuanced dilute doping in the concurrent tuning of carrier and phonon transport in GeTe and other thermoelectric materials.
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