We measure the electrical resistivity of hcp iron up to $\sim 170\mathrm{GPa}$ and $\sim 3000\mathrm{K}$ using a four-probe van der Pauw method coupled with homogeneous flattop laser heating in a DAC, and compute its electrical and thermal conductivity by first-principles molecular dynamics including electron-phonon and electron-electron scattering. We find that the measured resistivity of hcp iron increases almost linearly with temperature, and is consistent with our computations. The results constrain the resistivity and thermal conductivity of hcp iron to $\sim 80\pm 5\mu \mathrm{\Omega }\mathrm{cm}$ and $\sim 100\pm 10\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$, respectively, at conditions near the core-mantle boundary. Our results indicate an adiabatic heat flow of $\sim 10\pm 1\mathrm{TW}$ out of the core, supporting a present-day geodynamo driven by thermal and compositional convection.

Finite-temperature spin transport in the quantum Heisenberg spin chain is known to be superdiffusive, and has been conjectured to lie in the Kardar-Parisi-Zhang (KPZ) universality class. Using a kinetic theory of transport, we compute the KPZ coupling strength for the Heisenberg chain as a function of temperature, directly from microscopics; the results agree well with density-matrix renormalization group simulations. We establish a rigorous quantum-classical correspondence between the “giant quasiparticles” that govern superdiffusion and solitons in the classical continuous Landau-Lifshitz ferromagnet. We conclude that KPZ universality has the same origin in classical and quantum integrable isotropic magnets: a finite-temperature gas of low-energy classical solitons.

Dicke-like models can describe a variety of physical systems, such as atoms in a cavity or vibrating ion chains. In equilibrium these systems often feature a radical change in their behavior when switching from weak to strong spin-boson interaction. This usually manifests in a transition from a “dark” to a “superradiant” phase. However, understanding the out-of-equilibrium physics of these models is extremely challenging, and even more so for strong spin-boson coupling. Here we show that the nonequilibrium strongly interacting multimode Dicke model can mimic some fundamental properties of an associative memory—a system which permits the recognition of patterns, such as letters of an alphabet. Patterns are encoded in the couplings between spins and bosons, and we discuss the dynamics of the spins from the perspective of pattern retrieval in associative memory models. We identify two phases, a “paramagnetic” and a “ferromagnetic” one, and a crossover behavior between these regimes. The “ferromagnetic” phase is reminiscent of pattern retrieval. We highlight similarities and differences with the thermal dynamics of a Hopfield associative memory and show that indeed elements of “machine learning behavior” emerge in the strongly coupled multimode Dicke model.

Cosmic microwave background (CMB) temperature and polarization anisotropies from Planck have estimated a lower value of the optical depth to reionization ($\tau$) compared to WMAP. A significant period in the reionization history would then fall within $6<\text{redshift}(z)<10$, where detection of galaxies with Hubble frontier fields program and independent estimation of neutral hydrogen in the inter galactic medium by Lyman-$\alpha$ observations are also available. This overlap allows an analysis of cosmic reionization which utilizes a direct combination of CMB and these astrophysical measurements and potentially breaks degeneracies in parameters describing the physics of reionization. For the first time we reconstruct reionization histories by assuming photoionization and recombination rates to be free-form and by allowing underlying cosmological parameters to vary with CMB (temperature and polarization anisotropies and lensing) data from Planck 2018 release and a compilation of astrophysical data. We find an excellent agreement between the low-$\ell$ Planck 2018 High Frequency Instrument polarization likelihood and astrophysical data in determining the integrated optical depth. By combining both data, we report for a minimal reconstruction $\tau =0.051_{-0.0012-0.002}^{+0.001+0.002}$ at 68% and 95% C.L., which, for the errors in the current astrophysical measurements quoted in the literature, is nearly twice better than the projected cosmic variance limited CMB measurements. For the duration of reionization, redshift interval between 10%, and complete ionization, we get ${2.9}_{-0.16-0.26}^{+0.12+0.29}$ at 68% and 95% C.L., which improves significantly on the corresponding result obtained by using Planck 2015 data. By a Bayesian analysis of the combined results we do not find evidence beyond monotonic reionization histories, therefore a multiphase reionization scenario such as a first burst of reionization followed by recombination plateau and thereafter complete reionization is disfavored compared to minimal alternatives.

We investigate the role of partonic degrees of freedom in high-multiplicity $p\text{−}\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ carried out at the Large Hadron Collider (LHC) by studying the production and collective flow of identified hadrons at intermediate $p_T$ via the coalescence of soft partons from the viscous hydrodynamics ($\mathrm{VISH}2+1$) and hard partons from the energy loss model, linear Boltzmann transport (LBT). We find that combining these intermediate $p_T$ hadrons with the low $p_T$ hadrons from the hydrodynamically expanding fluid and high $p_T$ hadrons from the fragmentation of quenched jets, the resulting hydro-dynamics-coalescence-fragmentation model provides a nice description of measured $p_T$ spectra and differential elliptic flow $v_2(p_T)$ of pions, kaons, and protons over the $p_T$ range from 0 to 6 GeV. We further demonstrate the necessity of including the quark coalescence contribution to reproduce the experimentally observed approximate number of constituent quark scaling of hadron $v_2$ at intermediate $p_T$. Our results thus indicate the importance of partonic degrees of freedom and also hint at the possible formation of quark-gluon plasma in high-multiplicity $p\text{−}\mathrm{Pb}$ collisions at the LHC.

The critical phases, being delocalized but nonergodic, are fundamental phases different from both the many-body localization and ergodic extended quantum phases, and have so far not been realized in experiment. Here we propose an incommensurate topological insulating model of AIII symmetry class to realize such critical phases through an optical Raman lattice scheme, which possesses a one-dimensional (1D) spin-orbit coupling and an incommensurate Zeeman potential. We show the existence of both noninteracting and many-body critical phases, which can coexist with the topological phase, and show that the critical-localization transition coincides with the topological phase boundary in noninteracting regime. The dynamical detection of the critical phases is proposed and studied in detail based on the available experimental techniques. Finally, we demonstrate how the proposed critical phases can be achieved within the current ultracold atom experiments. This work paves the way to observe the novel critical phases.

Wall-bounded turbulent flows can take different statistically stationary turbulent states, with different transport properties, even for the very same values of the control parameters. What state the system takes depends on the initial conditions. Here we analyze the multiple states in large-aspect ratio ($\mathrm{\Gamma }$) two-dimensional turbulent Rayleigh-Bénard flow with no-slip plates and horizontally periodic boundary conditions as model system. We determine the number $n$ of convection rolls, their mean aspect ratios ${\mathrm{\Gamma }}_r=\mathrm{\Gamma }/n$, and the corresponding transport properties of the flow (i.e., the Nusselt number Nu), as function of the control parameters Rayleigh (Ra) and Prandtl number. The effective scaling exponent $\beta$ in $\mathrm{Nu}\sim {\mathrm{Ra}}^{\beta }$ is found to depend on the realized state and thus ${\mathrm{\Gamma }}_r$, with a larger value for the smaller ${\mathrm{\Gamma }}_r$. By making use of a generalized Friedrichs inequality, we show that the elliptical shape of the rolls and viscous damping determine the ${\mathrm{\Gamma }}_r$ window for the realizable turbulent states. The theoretical results are in excellent agreement with our numerical finding $2/3\le {\mathrm{\Gamma }}_r\le 4/3$, where the lower threshold is approached for the larger Ra. Finally, we show that the theoretical approach to frame ${\mathrm{\Gamma }}_r$ also works for free-slip boundary conditions.

In nodal-line semimetals, linearly dispersing states form Dirac loops in the reciprocal space with a high degree of electron-hole symmetry and a reduced density of states near the Fermi level. The result is reduced electronic screening and enhanced correlations between Dirac quasiparticles. Here we investigate the electronic structure of ZrSiSe, by combining time- and angle-resolved photoelectron spectroscopy with ab initio density functional theory (DFT) complemented by an extended Hubbard model ($\mathrm{DFT}+U+V$) and by time-dependent $\mathrm{DFT}+U+V$. We show that electronic correlations are reduced on an ultrashort timescale by optical excitation of high-energy electrons-hole pairs, which transiently screen the Coulomb interaction. Our findings demonstrate an all-optical method for engineering the band structure of a quantum material.

A striking consequence of the Hohenberg-Kohn theorem of density functional theory is the existence of a bijection between the local density and the ground-state many-body wave function. Here we study the problem of constructing approximations to the Hohenberg-Kohn map using a statistical learning approach. Using supervised deep learning with synthetic data, we show that this map can be accurately constructed for a chain of one-dimensional interacting spinless fermions in different phases of this model including the charge ordered Mott insulator and metallic phases and the critical point separating them. However, we also find that the learning is less effective across quantum phase transitions, suggesting an intrinsic difficulty in efficiently learning nonsmooth functional relations. We further study the problem of directly reconstructing complex observables from simple local density measurements, proposing a scheme amenable to statistical learning from experimental data.

Temperature- and frequency-dependent infrared spectroscopy identifies two contributions to the electronic properties of the magnetic kagome metal ${\mathrm{Fe}}_3{\mathrm{Sn}}_2$: two-dimensional Dirac fermions and strongly correlated flat bands. The interband transitions within the linearly dispersing Dirac bands appear as a two-step feature along with a very narrow Drude component due to intraband contribution. Low-lying absorption features indicate flat bands with multiple van Hove singularities. Localized charge carriers are seen as a Drude peak shifted to finite frequencies. The spectral weight is redistributed when the spins are reoriented at low temperatures; a sharp mode appears suggesting the opening of a gap due to the spin reorientation as the sign of additional Weyl nodes in the system.

The topological Hall effect (THE) and its thermoelectric counterpart, the topological Nernst effect (TNE), are hallmarks of the skyrmion lattice phase (SkL). We observed the giant TNE of the SkL in centrosymmetric ${\mathrm{Gd}}_2{\mathrm{PdSi}}_3$, comparable in magnitude to the largest anomalous Nernst signals in ferromagnets. Significant enhancement (suppression) of the THE occurs when doping electrons (holes) to ${\mathrm{Gd}}_2{\mathrm{PdSi}}_3$. On the electron-doped side, the topological Hall conductivity approaches the characteristic threshold $\sim 1000{(\mathrm{\Omega }\mathrm{cm})}^{-1}$ for the intrinsic regime. We use the filling-controlled samples to confirm Mott’s relation between TNE and THE and discuss the importance of Gd-5d orbitals for transport in this compound.

Fractional conductance is measured by partitioning a $\nu =1$ edge state using gate-tunable fractional quantum Hall (FQH) liquids of filling $1/3$ or $2/3$ for current injection and detection. We observe two sets of FQH plateaus $1/9$, $2/9$, $4/9$ and $1/6$, $1/3$, $2/3$ at low and high magnetic field ends of the $\nu =1$ plateau, respectively. The findings are explained by magnetic field dependent equilibration of three FQH edge modes with conductance $e^2/3h$ arising from edge reconstruction. The results reveal a remarkable enhancement of the equilibration lengths of the FQH edge modes with increasing magnetic field.

A central idea in strongly correlated systems is that doping a Mott insulator leads to a superconductor by transforming the resonating valence bonds (RVBs) into spin-singlet Cooper pairs. Here, we argue that a spin-triplet RVB (tRVB) state, driven by spatially, or orbitally anisotropic ferromagnetic interactions can provide the parent state for triplet superconductivity. We apply this idea to the iron-based superconductors, arguing that strong on site Hund’s interactions develop intra-atomic tRVBs between the $t_{2g}$ orbitals. On doping, the presence of two iron atoms per unit cell allows these interorbital triplets to coherently delocalize onto the Fermi surface, forming a fully gapped triplet superconductor. This mechanism gives rise to a unique staggered structure of on site pair correlations, detectable as an alternating $\pi$ phase shift in a scanning Josephson tunneling microscope.

The sedimentation of solid objects into granular matter near boundaries is an almost virgin field of research. Here we describe in detail the penetration dynamics of a cylindrical object into a quasi-2D granular medium. By tracking the trajectory of the cylinder as it penetrates the granular bed, we characterize two distinct kinds of motion: its center of mass moves horizontally away from the lateral wall, and it rotates around its symmetry axis. While the repulsion is caused by the loading of force chains between the intruder and the wall, the rotation can be associated to the frictional forces between the grains and the intruder. Finally, we show the analogies between the sedimentation of twin intruders released far from any boundaries, and that of one intruder released near a vertical wall.

Determining the positions of lattice defects on bounded elastic surfaces with Gaussian curvature is a nontrivial task of mechanical energy optimization. We introduce a simple way to predict the onset of disclination disorder from the shape of the surface. The criterion fixes the value of a weighted integral Gaussian curvature to a universal constant and proves accurate across a great variety of shapes. It provides improved understanding of the limitations to crystalline order in many natural and engineering contexts, such as the assembly of viral capsids.

The friction between cytoskeletal filaments is of central importance for the formation of cellular structures such as the mitotic spindle and the cytokinetic ring. This friction is caused by passive cross-linkers, yet the underlying mechanism and the dependence on cross-linker density are poorly understood. Here, we use theory and computer simulations to study the friction between two filaments that are cross-linked by passive proteins, which can hop between discrete binding sites while physically excluding each other. The simulations reveal that filaments move via rare discrete jumps, which are associated with free-energy barrier crossings. We identify the reaction coordinate that governs the relative microtubule movement and derive an exact analytical expression for the free-energy barrier and the friction coefficient. Our analysis not only elucidates the molecular mechanism underlying cross-linker-induced filament friction, but also predicts that the friction coefficient scales superexponentially with the density of cross-linkers.

Generalized hydrodynamics is a recent theory that describes the large scale transport properties of one dimensional integrable models. At the heart of this theory lies an exact quantum-classical correspondence, which states that the flows of the conserved quantities are essentially quasiclassical even in the interacting quantum many body models. We provide the algebraic background to this observation, by embedding the current operators of the integrable spin chains into the canonical framework of Yang-Baxter integrability. Our construction can be applied in a large variety of models including the $XXZ$ spin chains, the Hubbard model, and even in models lacking particle conservation such as the $XYZ$ chain. Regarding the $XXZ$ chain we present a simplified proof of the recent exact results for the current mean values, and explain how their quasiclassical nature emerges from the exact computations.