Entanglement of spatial bipartitions, used to explore lattice models in condensed matter physics, may be insufficient to fully describe itinerant quantum many-body systems in the continuum. We introduce a procedure to measure the Rényi entanglement entropies on a particle bipartition, with general applicability to continuum Hamiltonians via path integral Monte Carlo methods. Via direct simulations of interacting bosons in one spatial dimension, we confirm a logarithmic scaling of the single-particle entanglement entropy with the number of particles in the system. The coefficient of this logarithmic scaling increases with interaction strength, saturating to unity in the strongly interacting limit. Additionally, we show that the single-particle entanglement entropy is bounded by the condensate fraction, suggesting a practical route towards its measurement in future experiments.

The crossover from antidot to dot magnetic behavior on arrays patterned in a ferromagnetic thin film has been achieved by modifying only the geometry. A series of antidot arrays has been fabricated on cobalt with fixed diameter $d$ and by reducing the period of the array $p$ from $p\gg d$ to $p<d$. A dramatic change in the coercivity dependence with $p$, correlated with a significant modification in the magnetic domain structure observed by x-ray photoemission electron microscopy, evidences the crossover. An intermediate regime has been found between the superdomain structure present in antidot arrays and the array of astroid-state noncorrelated dots. The study has been reproduced for a different ferromagnetic material, permalloy, and supported by micromagnetic simulations.

Luminescence in Eu${}^{2+}$ activated materials corresponds to a transition from an excited state where the lowest Eu 5$d$ level is filled with one electron [often called the (Eu${}^{2+}$)${}^{*}$ state] to the ground state with a half-filled 4$f$ shell with seven electrons of the same spin. We have performed theoretical calculations based on density functional theory to determine the ground state band structure of Eu-doped materials as well as study the (Eu${}^{2+}$)${}^{*}$ excited state. Calculations were performed on Eu-doped materials, experimentally known to be either scintillators or nonscintillators, in order to relate theoretically calculable parameters to experimentally observed properties. Applying criteria previously developed for Ce-doped systems [A. Canning, A. Chaudhry, R. Boutchko, and N. Grønbech-Jensen, Phys. Rev. B 83, 125115 (2011)] to new Eu-doped materials, we developed a list of candidate materials for new bright Eu-activated scintillators. Ba${}_2$CsBr${}_5$:Eu is an example of a new bright scintillator from our candidate list that has been synthesized in microcrystalline powder form. As discussed in our previous paper on Ce-doped materials, this approach was designed as a systematic high-throughput method to aid in the discovery of new bright scintillator materials by prioritization and down-selection on the large number of potential new materials.

Image potential states (IPSs) on monolayer, bilayer, and trilayer graphene epitaxially grown on SiC(0001) have been studied by time- and angle-resolved two-photon photoemission (2PPE) spectroscopy. The free-electron-like dispersions of even and odd symmetry IPSs with a quantum number of $n$ = 1${}^{+}$, 1${}^{-}$, 2, 3 were observed. All observed IPSs showed the dispersions with effective masses of $m^{*}=1.0\pm 0.1m_e$. The 2PPE intensity of the lowest IPS ($n$ = 1${}^{+}$) was attenuated with an increasing number of graphene layers. The time-resolved 2PPE measurements revealed that these IPSs have significantly shorter lifetimes, suggesting a coupling of IPSs with electronic states in the buffer layer and the SiC substrate.

We study the entanglement of magnetic impurities in an environment of electrons through successive scattering while an external magnetic field is applied. We show that the dynamics of the problem can be approximately described by a reduced model of three interacting spins, which reveals an intuitive view on how spins can be entangled by controlled electron scattering. The role of the magnetic field is rather crucial. Depending on the initial state configuration, the magnetic field can either increase or decrease the resulting entanglement but more importantly it can allow the impurities to be maximally entangled.

Starting from the extended Su-Schrieffer-Heeger model, multiband semiconductor Bloch equations are formulated in momentum space and applied to the analysis of the linear optical response of semiconducting carbon nanotubes (SCNTs). This formalism includes the coupling of electron-hole pair excitations between different valence and conduction bands, originating from the electron-hole Coulomb attraction. The influence of these couplings, which are referred to as nondiagonal interband Coulomb interaction (NDI-CI), on the linear excitonic absorption spectra is investigated and discussed for light fields polarized parallel to the tube direction. The results show that the intervalley NDI-CI leads to a significant increase of the band gap and a decrease of the exciton binding energy that results in a blueshift of the lowest-frequency excitonic absorption peak. The strength of these effects depends on the symmetry of the SCNT. Furthermore, for zigzag SCNTs with higher symmetry other nonintervalley NDI-CI terms also affect the spectral positions of excitonic absorption peaks.

The long-range surface structure of the dichalcogenide $\mathrm{Mo}{\mathrm{S}}_2$ is probed with nanometer-length spatial resolution using low-energy electron microscopy (LEEM) and microprobe low-energy electron diffraction (μ-LEED). The quality of two differently prepared types of $\mathrm{Mo}{\mathrm{S}}_2$, single-layer and multilayer exfoliated crystals, as well as single-layer chemical-vapor-deposition (CVD)–grown crystals, is examined. The effects induced by a supporting interface are examined by utilizing two different substrates, $\mathrm{Si}{\mathrm{O}}_2$ and native-oxide-covered Si. In addition, the role of impurities is also studied by way of in situ deposition of the alkali-metal potassium. Microprobe measurements reveal that, unlike exfoliated $\mathrm{Mo}{\mathrm{S}}_2$, CVD-grown $\mathrm{Mo}{\mathrm{S}}_2$ may, in some instances, exhibit large-scale grain-boundary alterations due to the presence of surface strain during growth. However, real-space probing by LEEM in conjunction with $k$-space probing by μ-LEED shows that the quality of CVD-grown $\mathrm{Mo}{\mathrm{S}}_2$ can be comparable to that of exfoliated $\mathrm{Mo}{\mathrm{S}}_2$.

The Ce$T_2$Al${}_{10}$ family of orthorhombic compounds exhibits a very peculiar evolution from a Kondo insulator ($T$: Fe) to an unconventional long-range magnetic order ($T$: Ru, Os). Inelastic neutron-scattering experiments performed on single-crystal CeFe${}_2$Al${}_{10}$ reveal that this material develops a spin gap in its magnetic spectral response below $\sim$50 K, with a magnetic excitation dispersing from $E=10.2\pm 0.5$ meV at the $Y$ zone-boundary point [$\mathit{q}=(0,1,0)$] to $\approx$12 meV at the top of the branch. The excitation shows a pronounced polarization of the magnetic fluctuations along $a$, the easy anisotropy axis. Its behavior is contrasted with that of the (magnonlike) modes previously reported for CeRu${}_2$Al${}_{10}$, which have transverse character and exist only in the antiferromagnetic state. The present observation is ascribed to a “magnetic exciton” mechanism invoked to explain a similar magnetic response previously discovered in YbB${}_{12}$.

We propose the interaction of two electrons in a triple quantum dot as a minimal system to control long-range superexchange transitions. These are probed by transport spectroscopy. Narrow resonances appear indicating the transfer of charge from one side of the sample to the other with the central one being occupied only virtually. We predict that two different intermediate states establish the two arms of a one-dimensional interferometer. We find configurations where destructive interference of the two superexchange trajectories totally blocks the current through the system. We emphasize the role of spin correlations giving rise to lifetime-enhanced resonances.

In a magnetic field, graphene trilayers support a special multiplet of 12 zero(-energy)-mode Landau levels with a threefold degeneracy in Landau orbitals. A close look is made into such zero-mode levels in $ABA$-stacked trilayers, with the Coulomb interaction taken into account. It turns out that the zero-mode Landau levels of $ABA$ trilayers are greatly afflicted with electron-hole and valley asymmetries, which come from general hopping parameters and which are enhanced by the Coulomb interaction and the associated vacuum effect, the orbital Lamb shift, that lifts the zero-mode degeneracy. These asymmetries substantially affect the way the zero-mode levels evolve with filling via Coulomb interactions, and its consequences are discussed in the light of experiments.

The recent development of hybrid circuit quantum electrodynamics allows one to study how cavity photons interact with a system driven out of equilibrium by fermionic reservoirs. We study here one of the simplest combination: a double quantum dot coupled to a single mode of the electromagnetic field. We are able to couple resonantly the charge levels of a carbon-nanotube-based double dot to cavity photons. We perform a microwave readout of the charge states of this system, which allows us to unveil features of the out-of-equilibrium charge dynamics, otherwise invisible in the DC current. We extract the relaxation rate, dephasing rate, and photon number of the hybrid system using a theory based on a master equation technique. These findings open the path for manipulating other degrees of freedom, e.g., the spin and/or the valley in nanotube-based double dots using microwave light.

The ferrimagnetic spinels $\mathrm{Mn}{B}_2{\mathrm{O}}_4$ ($B=\mathrm{Mn}$,V) exhibit a similar series of closely spaced magnetic and structural phase transitions at low temperatures, reflecting both magnetic frustration and a strong coupling between the spin and lattice degrees of freedom. Careful studies of excitations in $\mathrm{Mn}{B}_2{\mathrm{O}}_4$ ($B=\mathrm{Mn}$,V), and the evolution of these excitations with temperature, are important for obtaining a microscopic description of the role that magnetic excitations and spin-lattice coupling play in the low-temperature phase transitions of these materials. We report an inelastic light (Raman) scattering study of the temperature and magnetic-field dependences of one- and two-magnon excitations in $\mathrm{Mn}{\mathrm{V}}_2{O}_4$ and ${\mathrm{Mn}}_3{\mathrm{O}}_4$. We observe a pair of $\mathbf{q}=0$ one-magnon modes at 74 and 81 cm${}^{-1}$ in $\mathrm{Mn}{\mathrm{V}}_2{O}_4$, which is in contrast with the single 80-cm${}^{-1}$ $\mathbf{q}=0$ magnon that has been reported for $\mathrm{Mn}{\mathrm{V}}_2{O}_4$ based on previous neutron-scattering measurements and spin-wave calculations. Additionally, we find that the two-magnon energy of $\mathrm{Mn}{\mathrm{V}}_2{O}_4$ decreases (“softens”) with decreasing temperature below $T_N$, which we attribute to strong coupling between magnetic and vibrational excitations near the zone boundary.

Topological defects such as quantized vortices are one of the most striking manifestations of the superfluid nature of Bose-Einstein condensates and typical examples of quantum mechanical phenomena on a macroscopic scale. Here we demonstrate the formation of a lattice of vortex-antivortex pairs and study its properties in the nonlinear regime at high polariton-density where polariton-polariton interactions dominate the behavior of the system. In this work first we demonstrate that the array of vortex-antivortex pairs can be generated in a controllable way in terms of size of the array and in terms of size and shape of its fundamental unit cell. Then we demonstrate that polariton-polariton repulsion can strongly deform the lattice unit cell and determine the pattern distribution of the vortex-antivortex pairs, reaching a completely new behavior with respect to geometrically generated vortex lattices whose shape is determined only by the geometry of the system.

Impurity-helium condensates created by injection of hydrogen (deuterium) atoms and molecules as well as rare gas (RG) atoms (Ne and Kr) into superfluid ${}^4\mathrm{He}$ have been studied via electron spin resonance (ESR) techniques. Measurements of the ground-state spectroscopic parameters of hydrogen and deuterium atoms show that the nanoclusters have a shell structure. H and D atoms reside in solid molecular layers of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$, respectively. These layers form on the surfaces of RG (Ne or Kr) nanoclusters. By monitoring the recombination of H atoms in the collection of hydrogen-neon nanoclusters, we show that nanoclusters form a gel-like porous structure which enables the H atoms to be transported through the structure via percolation. Observation of percolation in the collection of nanoclusters containing stabilized hydrogen atoms may open possibilities for a search for macroscopic collective quantum phenomena at ultralow temperatures accessible by a dilution refrigerator.

Since the discovery of all-optical magnetization switching in rare-earth transition-metal alloys the underlying magnetization dynamics of multisublattice magnets has become a hot topic of modern magnetism. We studied the ultrafast magnetization dynamics in TbCo alloys as a function of the alloy composition and the laser fluence using either 800 nm or 400 nm probe pulses. Direct comparison between TbCo samples with different compositions for equal excitation conditions demonstrates that the magnetization dynamics of the Co sublattice strongly depends on the Tb concentration. For ${\mathrm{Tb}}_{32}{\mathrm{Co}}_{68}$ the magnetization of the sublattices can even transiently be reversed on a subpicosecond time scale.

We present a theory of the intrinsic anomalous Hall effect in a model of a doped Weyl semimetal, which serves here as the simplest toy model of a generic three-dimensional metallic ferromagnet with Weyl nodes in the electronic structure. We analytically evaluate the anomalous Hall conductivity as a function of doping, which allows us to explicitly separate the Fermi-surface and non-Fermi-surface contributions to the Hall conductivity by carefully evaluating the zero-frequency and zero wave-vector limits of the corresponding response function. We show that this separation agrees with the one suggested a long time ago in the context of the quantum Hall effect by Streda [J. Phys. C 15, L717 (1982)].