Large-spin cold atomic systems can exhibit unique phenomena that do not appear in spin-$1/2$ systems. We report the observation of nearest-neighbor antiferromagnetic spin correlations of a Fermi gas with $\mathrm{SU}(\mathcal{N})$ symmetry trapped in an optical lattice. The precise control of the spin degrees of freedom provided by an optical pumping technique enables us a straightforward comparison between the cases of SU(2) and SU(4). Our important finding is that the antiferromagnetic correlation is enhanced for the SU(4)-spin system compared with SU(2) as a consequence of a Pomeranchuk cooling effect. This work is an important step towards the realization of novel $\mathrm{SU}(\mathcal{N}>2)$ quantum magnetism.

Theoretical studies of phase stability in solid materials with dynamic disorder are challenging due to the failure of the standard picture of atoms vibrating around fixed equilibrium positions. Dynamically disordered solid materials show immense potential in applications. In particular, superionic conductors, where the disorder results in exceptionally high ionic conductivity, are very promising as solid state electrolytes in batteries and fuel cells. The biggest obstacle in living up to this potential is the limited stability of the dynamically disordered phases. Here, we outline a method to obtain the free energy of a dynamically disordered solid. It is based on a stress-strain thermodynamic integration on a deformation path between a mechanically stable ordered variant of the disordered phase, and the dynamically disordered phase itself. We show that the large entropy contribution associated with the dynamic disorder is captured in the behavior of the stress along the deformation path. We apply the method to ${\mathrm{Bi}}_2{\mathrm{O}}_3$, whose superionic $\delta$ phase is the fastest known solid oxide ion conductor. We accurately reproduce the experimental transition enthalpy and the critical temperature of the phase transition from the low temperature ground state $\alpha$ phase to the superionic $\delta$ phase. The method can be used for a first-principles description of the phase stability of superionic conductors and other materials with dynamic disorder, when the disordered phase can be connected to a stable phase through a continuous deformation path.

By atom manipulation we performed on-surface chemical reactions of a single molecule on a multilayer insulating film using noncontact atomic force microscopy. The single-electron sensitivity of atomic force microscopy allows us to follow the addition of single electrons to the molecule and the investigation of the reaction products. By performing a novel strategy based on long-lived doubly charged states a single molecule is fragmented. The fragmentation can be reverted by again changing the charge state of the system, characterizing a reversible reaction. The experimental results in addition to density-functional theory provide insight into the charge states of the different products and reaction pathways. Similar molecular systems could be used as charge-transfer units and to induce reversible chemical reactions.

We experimentally demonstrate the formation of salt aggregations with unexpectedly high concentration inside multiwalled carbon nanotubes (CNTs) soaked only in dilute salt solution sand even in solutions containing only traces of salts. This finding suggests the blocking of fluid across CNTs by the salt aggregations when CNTs are soaked in a dilute salt solution with the concentration of seawater or even lower, which may open new avenues for the development of novel CNT-based desalination techniques. The high salt accumulation of CNTs also provides a new CNT-based strategy for the collection or extraction of noble metal salts in solutions containing traces of noble metal salts. Theoretical analyses reveal that this high salt accumulation inside CNTs can be mainly attributed to the strong hydrated cation-$\pi$ interactions of hydrated cations and $\pi$ electrons in the aromatic rings of CNTs.

Owing to their wide tunability, multiple internal degrees of freedom, and low disorder, graphene heterostructures are emerging as a promising experimental platform for fractional quantum Hall (FQH) studies. Here, we report FQH thermal activation gap measurements in dual graphite-gated monolayer graphene devices fabricated in an edgeless Corbino geometry. In devices with substrate-induced sublattice splitting, we find a tunable crossover between single- and multicomponent FQH states in the zero energy Landau level. Activation gaps in the single-component regime show excellent agreement with numerical calculations using a single broadening parameter $\mathrm{\Gamma }\approx 7.2\mathrm{K}$. In the first excited Landau level, in contrast, FQH gaps are strongly influenced by Landau level mixing, and we observe an unexpected valley-ordered state at integer filling $\nu =-4$.

Recently, two fundamental topological properties of a magnetic vortex at the interface of a superconductor (SC) and a strong topological insulator (TI) have been established: The vortex carries both a Majorana zero mode relevant for topological quantum computation and, for a time-reversal invariant TI, a charge of $e/4$. This fractional charge is caused by the axion term in the electromagnetic Lagrangian of the TI. Here we determine the angular momentum $J$ of the vortices, which in turn determines their mutual statistics. Solving the axion-London electrodynamic equations including screening in both a SC and a TI, we find that the elementary quantum of angular momentum of the vortex is $-n^2\hslash /8$, where $n$ is the flux quantum of the vortex line. Exchanging two elementary fluxes thus changes the phase of the wave function by $-\pi /4$.

We discuss noncollinear magnetic phenomena whose local order parameter is characterized by more than one spin vector. By focusing on the simple cases of 2D triangular and 3D pyrochlore lattices, we demonstrate that their low-energy theories can be described by a one-parametric class of sigma models continuously interpolating between the classical Heisenberg model and the principal chiral model $\mathrm{Tr}({\partial }_{a}U{\partial }_a{U}^{†})$ for all $U\in \mathrm{SU}(2)$. The target space can be viewed as a U(1) fibration over the $CP(1)$ space. The 3D version of our model is further generalized to break spatial and spin rotation symmetry $\mathrm{SO}(3)\times \mathrm{SO}(3)\to \mathrm{SO}(3)$.

We experimentally demonstrate that the radiative decay rate of a quantum emitter is determined by the combined electric and magnetic local density of optical states (LDOS). A Drexhage-style experiment was performed for two distinct quantum emitters, divalent nickel ions in magnesium oxide and trivalent erbium ions in yttrium oxide, which both support nearly equal mixtures of isotropic electric dipole and magnetic dipole transitions. The disappearance of lifetime oscillations as a function of emitter-interface separation distance confirms that the electromagnetic LDOS refers to the total mode density, and thus similar to thermal emission, these unique electronic emitters effectively excite all polarizations and orientations of the electromagnetic field.

Vortices are topological objects formed in coherent nonlinear systems. As such they are studied in a wide number of physical systems and promise applications in information storage, processing, and communication. In semiconductor microcavities, vortices in polariton condensates can be conveniently created, studied, and manipulated using solely optical means. For nonresonant excitation with a ring-shaped pump a stable vortex can be formed, leading to bistability with left- and right-handed vorticity. In the present work we report on a much richer vortex multistability, with optically addressable vortices with topological charges $m=\pm 1$, $\pm 2$, and $\pm 3$, all stable for the same system and excitation parameters. This unusual multistable behavior is rooted in the inherent nonlinear feedback between reservoir excitations and condensate in the microcavity. For larger radius of the ring-shaped pump we also find a Bessel vortex with its characteristic spiralling phase in the high density region and pronounced self-stabilization ability. Our theoretical results open up exciting possibilities for optical manipulation of vortex multiplets in a compact semiconductor system.

The non-Newtonian flow behavior of thermal and athermal disordered systems of dispersed uniform particles at high densities have strikingly similar features. By investigating the flow curves of yield-stress fluids and colloidal glasses having different volume fractions, particle sizes, and interactions, we show that both thermal and athermal systems exhibit power-law scaling with respect to the glass and jamming point, respectively, with the same exponents. All yield-stress flow curves can be scaled onto a single universal curve using the Laplace pressure as the stress scale for athermal systems and the osmotic pressure for the thermal systems. Strikingly, the details of interparticle interactions do not matter for the rescaling, showing that they are akin to usual phase transitions of the same universality class. The rescaling allows us to predict the flow properties of these systems from the volume fraction and known material properties.

Wrinkling instabilities appear in soft materials when a flat elastic layer on an elastic substrate is sufficiently stressed that it buckles with a wavy pattern to minimize the energy of the system. This instability is known to play an important role in engineering, but it also appears in many biological systems. In these systems, the stresses responsible for the wrinkling instability are often created through differential growth of the two layers. Beyond the instability, the upper and lower sides of the elastic layer are subject to different forces. This difference in forces leads to an interesting symmetry breaking whereby the thickness becomes larger at ridges than at valleys. Here we carry out an extensive analysis of this phenomenon by combining analytical, computational, and simple polymer experiments to show that symmetry breaking is a generic property of such systems. We apply our idea to the cortical folding of the brain for which it has been known for over a century that there is a thickness difference between gyri and sulci. An extensive analysis of hundreds of human brains reveals a systematic region-dependent thickness variation. Our results suggest that the evolving thickness patterns during brain development, similar to our polymer experiments, follow simple physics-based laws: Gyri are universally thicker than sulci.

We show that the symmetric portion of correlated coherence is always a valid quantifier of entanglement, and that this property is independent of the particular choice of coherence measure. This leads to an infinitely large class of coherence based entanglement monotones, which is always computable for pure states if the coherence measure is also computable. It is already known that every entanglement measure can be constructed as a coherence measure. The results presented here show that the converse is also true. The constructions that are presented can also be extended to include more general notions of nonclassical correlations, leading to quantifiers that are related to quantum discord, thus providing an avenue for unifying all such notions of quantum correlations under a single framework.

The universal Tan relations connect a variety of microscopic features of many-body quantum systems with two-body contact interactions to a single quantity, called the contact. The latter has become pivotal in the description of quantum gases. We provide a complete characterization of the Tan contact of the harmonically trapped Lieb-Liniger gas for arbitrary interactions and temperature. Combining thermal Bethe ansatz, local-density approximation, and exact quantum Monte Carlo calculations, we show that the contact is a universal function of only two scaling parameters, and determine the scaling function. We find that the temperature dependence of the contact, or equivalently the interaction dependence of the entropy, displays a maximum. The presence of this maximum provides an unequivocal signature of the crossover to the fermionized regime and it is accessible in current experiments.

We propose a mechanism that can convert a sizable fraction of neutron stars into black holes with mass $\sim 1M_{\odot }$, too light to be produced via stellar evolution. We show that asymmetric fermionic dark matter of mass on the teraelectron volt scale, with attractive self-interaction within the range that alleviates the problems of collisionless cold dark matter, can accumulate in a neutron star and collapse, forming a black hole that converts the rest of the star to a solar mass black hole. We estimate the fraction of neutron stars that can become black holes without contradicting neutron star observations. Such solar mass black holes could be in binary systems, which may be searched for by existing and forthcoming gravitational wave detectors. The (non-)observation of binary mergers of solar mass black holes may thus test the nature of dark matter.

We consider an interacting quantum field theory on a curved two-dimensional manifold that we construct by geometrically deforming a flat hexagonal lattice by the insertion of a defect. Depending on how the deformation is done, the resulting geometry acquires a locally nonvanishing curvature that can be either positive or negative. Fields propagating on this background are forced to satisfy boundary conditions modulated by the geometry and that can be assimilated by a nondynamical gauge field. We present an explicit example where curvature and boundary conditions compete in altering the way symmetry breaking takes place, resulting in a surprising behavior of the order parameter in the vicinity of the defect. The effect described here is expected to be generic and of relevance in a variety of situations.

We experimentally investigate the dynamic instability of Bose-Einstein condensates in an optical ring resonator that is asymmetrically pumped in both directions. We find that, beyond a critical resonator-pump detuning, the system becomes stable regardless of the pump strength. Phase diagrams and quenching curves are presented and described by numerical simulations. We discuss a physical explanation based on a geometric interpretation of the underlying nonlinear equations of motion.

We demonstrate, experimentally and theoretically, controlled loading of an exciton-polariton vortex chain into a 1D array of trapping potentials. Switching between two types of vortex chains, with topological charges of the same or alternating signs, is achieved by appropriately shaping an off-resonant pump beam that drives the system to the regime of bosonic condensation. In analogy to spin chains, these vortex sequences realize either a “ferromagnetic” or an “antiferromagnetic” order, whereby the role of spin is played by the orbital angular momentum. The ferromagnetic ordering of vortices is associated with the formation of a persistent chiral current. Our results pave the way for the controlled creation of nontrivial distributions of orbital angular momentum and topological order in a periodic exciton-polariton system.