Various unusual behaviors of artificial materials are governed by their topological properties, among which the edge state at the boundary of a photonic or phononic lattice has been captivated as a popular notion. However, this remarkable bulk-bounda
ry correspondence and the related phenomena are missing in thermal materials. One reason is that heat diffusion is described in a non-Hermitian framework because of its dissipative nature. The other is that the relevant temperature field is mostly composed of modes that extend over wide ranges, making it difficult to be rendered within the tight-binding theory as commonly employed in wave physics. Here, we overcome the above challenges and perform systematic studies on heat diffusion in thermal lattices. Based on a continuum model, we introduce a state vector to link the Zak phase with the existence of the edge state, and thereby analytically prove the thermal bulk-boundary correspondence. We experimentally demonstrate the predicted edge states with a topologically protected and localized heat dissipation capacity. Our finding sets up a solid foundation to explore the topology in novel heat transfer manipulations.
Using the state-of-art dynamical mean-field theory combined with density functional theory method, we have performed systematic study on the temperature and pressure dependent electronic structure of ferromagnetic quantum critical material candidate
CeRh$_6$Ge$_4$. At -3.9 GPa and -8.3 GPa, the Ce-4$f$ occupation variation, the local magnetic susceptibility, and the low-frequency electronic self-energy behaviors suggest the Ce-4$f$ electrons are in the localized state; whereas at 6.5 GPa and 13.1 GPa, these quantities indicate the Ce-4$f$ electrons are in the itinerant state. The characteristic temperatures associated with the coherent Kondo screening is gradually suppressed to 0 around 0.8 GPa upon releasing external pressure, indicative of a local quantum critical point. Interestingly, the momentum-resolved spectrum function shows that even at the localized state side, highly anisotropic $mathbf{k}$-dependent hybridization between Ce-4$f$ and conduction electrons is still present along $Gamma$-A, causing hybridization gap in between. The calculations predict 8 Fermi surface sheets at the local-moment side and 6 sheets at the Kondo coherent state. Finally, the self-energy at 0.8 GPa can be well fitted by marginal Fermi-liquid form, giving rise to a linearly temperature dependent resistivity.
We predict that CeBi in the ferromagnetic state is a Weyl semimetal. Our calculations within density functional theory show the existence of two pairs of Weyl nodes on the momentum path $(0, 0, k_z)$ at $15$ meV} above and $100$ meV below the Fermi l
evel. Two corresponding Fermi arcs are obtained on surfaces of mirror-symmetric (010)-oriented slabs at $E=15$ meV and both arcs are interrupted into three segments due to hybridization with a set of trivial surface bands. By studying the spin texture of surface states, we find the two Fermi arcs are strongly spin-polarized but in opposite directions, which can be detected by spin-polarized ARPES measurements. Our theoretical study of quasiparticle interference (QPI) for a nonmagnetic impurity at the Bi site also reveals several features related to the Fermi arcs. Specifically, we predict that the spin polarization of the Fermi arcs leads to a bifurcation-shaped feature only in the spin-dependent QPI spectrum, serving as a fingerprint of the Weyl nodes.
We investigate the electronic structure of nickelate superconductor NdNiO2 upon hole doping, by means of density-functional theory and dynamical mean-field theory. We demonstrate the strong intrinsic hybridization between strongly correlated states f
ormed by Ni-3dx2-y2 orbital and itinerant electrons due to Nd-5d and Ni-3dz2 orbitals, producing a valence-fluctuating correlated metal as the normal state of hole-doped NdNiO2. The Hunds rule appears to play a dominating role on multi-orbital physics in the lightly doped compound, while its effect is gradually reduced by increasing the doping level. Crucially, the hole-doping leads to intricate effects on Ni-3d orbitals, such as a non-monotonic change of electron occupation in lightly doped level, and a flipping orbital configuration in the overdoped regime. Additionaly, we also map out the topology of Fermi surface at different doping levels. These findings render a preferred window to peek into electron pairing and superconductivity.
We report the first-principles study on the H-intercalated Cr-based superconductor KCr$_3$As$_3$H$_x$. Our results show a paramagnetic ground state for KCr$_3$As$_3$H. The electronic structure consists of two quasi-one-dimensional (Q1D) Fermi-surface
s and one 3D Fermi-surface which are mainly contributed by Cr-d$_{z^2}$, d$_{x^2-y^2}$ and d$_{xy}$ orbitals. The bare electron susceptibility shows a $Gamma$-centered imaginary peak, indicating possible ferromagnetic spin fluctuations. Upon moderate hole doping, the system undergoes a Lifshitz transition, which may enhance the Q1D feature of the system. The Bader charge analysis and electron localization functions reveal a strong bonding nature of hydrogen in KCr$_3$As$_3$H, which results in a nontrivial electron doping in KCr$_3$As$_3$H.
An aging population is bringing new challenges to the management of escape routes and facility design in many countries. This paper investigates pedestrian movement properties of crowd with different age compositions. Three pedestrian groups are cons
idered: young student group, old people group and mixed group. It is found that traffic jams occur more frequently in mixed group due to the great differences of mobilities and self-adaptive abilities among pedestrians. The jams propagate backward with a velocity 0.4 m/s for global density around 1.75 m-1 and 0.3 m/s for higher than 2.3 m-1. The fundamental diagrams of the three groups are obviously different from each other and cannot be unified into one diagram by direct non-dimensionalization. Unlike previous studies, three linear regimes in mixed group but only two regimes in young student group are observed in the headway-velocity relation, which is also verified in the fundamental diagram. Different ages and mobilities of pedestrians in a crowd cause the heterogeneity of system and influence the properties of pedestrian dynamics significantly. It indicates that the density is not the only factor leading to jams in pedestrian traffic. The composition of crowd has to be considered in understanding pedestrian dynamics and facility design.
The physical properties of CsNi$_{2}$Se$_{2}$ were characterized by electrical resistivity, magnetization and specific heat measurements. We found that the stoichiometric CsNi$_{2}$Se$_{2}$ compound is a superconductor with a transition temperature t
extit{T$_{c}$}=2.7K. A large Sommerfeld coefficient $gamma$$_{n}$ ($sim$77.90 mJ/mol$cdot$K$^{-2}$), was obtained from the normal state electronic specific heat. However, the Kadowaki-Woods ratio of CsNi$_{2}$Se$_{2}$ was estimated to be about 0.041$times$10$^{-5}$ $muOmega$$cdot$cm(mol$cdot$K/mJ)$^{2}$, indicating the absence of strong electron-electron correlations in this compound. In the superconducting state, we found that the zero-field electronic specific heat data, $C_{es}(T)$ (0.5K $leq$ T $<$ 2.6K), can be well fitted with a two-gap BCS model. The comparison with the results of the density functional theory (DFT) calculations suggested that the large $gamma$$_{n}$ in the nickel-selenide superconductors may be related to the large Density of States (DOS) at the fermi surface.
Motivated by the rich interplay among electronic correlation, spin-orbit coupling (SOC), crystal-field splitting, and geometric frustrations in the honeycomb-like lattice, we systematically investigated the electronic and magnetic properties of Li$_2
$RhO$_3$. The material is semiconducting with a narrow band gap of $Deltasim$78 meV, and its temperature dependence of resistivity conforms to 3D variable range hopping mechanism. No long-range magnetic ordering was found down to 0.5 K, due to the geometric frustrations. Instead, single atomic spin-glass behavior below the spin-freezing temperature ($sim$6 K) was observed and its spin dynamics obeys the universal critical slowing down scaling law. First principle calculations suggested it to be a relativistic Mott insulator mediated by both electronic correlation and SOC. With moderate strength of electronic correlation and SOC, our results shed new light to the research of Heisenberg-Kitaev model in realistic materials.
The electronic structure of the vacancy-ordered K$_{0.5}$Fe$_{1.75}$Se$_2$ iron-selenide compound (278 phase) is studied using the first-principles density functional method. The ground state of the 278 phase is stripe-like antiferromagnetic, and its
bare electron susceptibility shows a large peak around $(pi, pi)$ in the folded Brillouin zone. Near Fermi level, the density of states are dominated by the Fe-3d orbitals, and both electron-like and hole-like Fermi surfaces appear in the Brillouin zone. Unfolded band structure shows limited similarities to a hole doped 122 phase. With 0.1e electron doping, the susceptibility peak is quickly suppressed and broadened; while the two-dimensionality of the electron-like Fermi surfaces are greatly enhanced, resulting in a better nesting behavior. Our study should be relevant to the recently reported superconducting phase K$_{0.5+x}$Fe$_{1.75+y}$Se$_2$ with both $x$ and $y$ very tiny.
The holographic principle asserts that the entropy of a system cannot exceed its boundary area in Planck units. However, conventional quantum field theory fails to describe such systems. In this Letter, we assume the existence of large $n$ extra dime
nsions and propose a relationship between UV and IR cutoffs in this case. We find that if $n=2$, this effective field theory could be a good description of holographic systems. If these extra dimensions are detected in future experiments, it will help to prove the validity of the holographic principle. We also discuss implications for the cosmological constant problem.
