We study the Mott transition from a metal to cluster Mott insulators in the $1/4$- and $1/8$-filled pyrochlore lattice systems. It is shown that such Mott transitions can arise due to charge localization in clusters or in tetrahedron units, driven by the nearest-neighbor repulsive interaction. The resulting cluster Mott insulator is a quantum spin liquid with a spinon Fermi surface, but at the same time a novel fractionalized charge liquid with charge excitations carrying half the electron charge. There exist two emergent U(1) gauge fields or “photons” that mediate interactions between spinons and charge excitations, and between fractionalized charge excitations themselves, respectively. In particular, it is suggested that the emergent photons associated with the fractionalized charge excitations can be measured in x-ray scattering experiments. Various other experimental signatures of the exotic cluster Mott insulator are discussed in light of candidate materials with partially filled bands on the pyrochlore lattice.

It is demonstrated that the threshold current for damping compensation can be reached in a $5\mu \mathrm{m}$ diameter $\mathrm{YIG}(20\mathrm{nm})|\mathrm{Pt}(7\mathrm{nm})$ disk. The demonstration rests upon the measurement of the ferromagnetic resonance linewidth as a function of $I_{\mathrm{dc}}$ using a magnetic resonance force microscope (MRFM). It is shown that the magnetic losses of spin-wave modes existing in the magnetic insulator can be reduced or enhanced by at least a factor of 5 depending on the polarity and intensity of an in-plane dc current $I_{\mathrm{dc}}$ flowing through the adjacent normal metal with strong spin-orbit interaction. Complete compensation of the damping of the fundamental mode by spin-orbit torque is reached for a current density of $\sim 3\times {10}^{11}\mathrm{A}·{\mathrm{m}}^{-2}$, in agreement with theoretical predictions. At this critical threshold the MRFM detects a small change of static magnetization, a behavior consistent with the onset of an auto-oscillation regime.

We consider general locally interacting arbitrary-dimensional lattice spin systems that are gapped for any system size. We show under reasonable conditions that nondegenerate ground states of such systems obey the entanglement area law. In so doing, we offer an intuitive picture on how a spectral gap restricts the correlations that a ground state can accommodate and leads to such a special feature.

The quantum spin liquid is an exotic quantum state of matter in magnets. This state is a spin analog of liquid helium that does not solidify down to the lowest temperature due to strong quantum fluctuations. In conventional fluids, the liquid and gas possess the same symmetry and adiabatically connect to each other by bypassing the critical end point. We find that the situation is qualitatively different in quantum spin liquids realized in a three-dimensional Kitaev model; both gapless and gapped quantum spin liquid phases at low temperatures are always distinguished from the high-temperature paramagnet (spin gas) by a phase transition. The results challenge the common belief that the absence of thermodynamic singularity down to the lowest temperature is a symptom of a quantum spin liquid.

The use of Bell’s theorem in any application or experiment relies on the assumption of free choice or, more precisely, measurement independence, meaning that the measurements can be chosen freely. Here, we prove that even in the simplest Bell test—one involving 2 parties each performing 2 binary-outcome measurements—an arbitrarily small amount of measurement independence is sufficient to manifest quantum nonlocality. To this end, we introduce the notion of measurement dependent locality and show that the corresponding correlations form a convex polytope. These correlations can thus be characterized efficiently, e.g., using a finite set of Bell-like inequalities—an observation that enables the systematic study of quantum nonlocality and related applications under limited measurement independence.

The Berry curvature is a geometrical property of an energy band which acts as a momentum space magnetic field in the effective Hamiltonian describing single-particle quantum dynamics. We show how this perspective may be exploited to study systems directly relevant to ultracold gases and photonics. Given the exchanged roles of momentum and position, we demonstrate that the global topology of momentum space is crucially important. We propose an experiment to study the Harper-Hofstadter Hamiltonian with a harmonic trap that will illustrate the advantages of this approach and that will also constitute the first realization of magnetism on a torus.

Composite fermions (CFs), exotic particles formed by pairing an even number of flux quanta to each electron, provide a fascinating description of phenomena exhibited by interacting two-dimensional electrons at high magnetic fields. At and near Landau level filling $\nu =1/2$, CFs occupy a Fermi sea and exhibit commensurability effects when subjected to a periodic potential modulation. We observe a pronounced asymmetry in the magnetic field positions of the commensurability resistance minima of CFs with respect to the field at $\nu =1/2$. This unexpected asymmetry is consistent with the CFs’ Fermi wave vector being determined by the minority carriers in the lowest Landau level, and suggests a breaking of the particle-hole symmetry for CFs near $\nu =1/2$.

Exploration and manipulation of electronic states in low-dimensional systems are of great importance in the fundamental and practical aspects of nanomaterial and nanotechnology. Here, we demonstrate that the incorporation of vacancy defects into monatomic indium wires on $n$-type Si(111) can stabilize electronically phase-separated ground states where the insulating $8\times 2$ and metallic $4\times 1$ phases coexist. Furthermore, the areal ratio of the two phases in the phase-separated states can be tuned reversibly by electric field or charge doping, and such tunabilities can be quantitatively captured by first principles-based modeling and simulations. The present results extend the realm of electronic phase separation from strongly correlated $d$-electron materials typically in bulk form to weakly interacting $sp$-electron systems in reduced dimensionality.

Quantum spin Hall–superconductor hybrids are promising sources of topological superconductivity and Majorana modes, particularly given recent progress on HgTe and InAs/GaSb. We propose a new method of revealing topological superconductivity in extended quantum spin Hall Josephson junctions supporting “fractional Josephson currents.” Specifically, we show that as one threads magnetic flux between the superconductors, the critical current traces an interference pattern featuring sharp fingerprints of topological superconductivity—even when noise spoils parity conservation.

Materials that realize Kitaev spin models with bond-dependent anisotropic interactions have long been searched for, as the resulting frustration effects are predicted to stabilize novel forms of magnetic order or quantum spin liquids. Here, we explore the magnetism of $\gamma \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$, which has the topology of a three-dimensional Kitaev lattice of interconnected Ir honeycombs. Using magnetic resonant x-ray diffraction, we find a complex, yet highly symmetric incommensurate magnetic structure with noncoplanar and counterrotating Ir moments. We propose a minimal Kitaev-Heisenberg Hamiltonian that naturally accounts for all key features of the observed magnetic structure. Our results provide strong evidence that $\gamma \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ realizes a spin Hamiltonian with dominant Kitaev interactions.

We study the dynamics of phase relaxation between a pair of one-dimensional condensates created by a supersonic unzipping of a single condensate. We use the Lorentz invariance of the low energy sector of such systems to show that dephasing results in an unusual prethermal state, in which right- and left-moving excitations have different, Doppler-shifted temperatures. The chirality of these modes can be probed experimentally by measuring the interference fringe contrasts with the release point of the split condensates moving at another supersonic velocity. Further, an accelerated motion of the release point can be used to observe a spacelike analog of the Unruh effect. A concrete experimental realization of the quantum zipper for a BEC of trapped atoms on an atom chip is outlined.

We derive a strong bound on the axion-photon coupling $g_{a\gamma }$ from the analysis of a sample of 39 Galactic Globular Clusters. As recognized long ago, the $R$ parameter, i.e., the number ratio of stars in horizontal over red giant branch of old stellar clusters, would be reduced by the axion production from photon conversions occurring in stellar cores. In this regard, we have compared the measured $R$ with state-of-the-art stellar models obtained under different assumptions for $g_{a\gamma }$. We show that the estimated value of $g_{a\gamma }$ substantially depends on the adopted He mass fraction $Y$, an effect often neglected in previous investigations. Taking as a benchmark for our study the most recent determinations of the He abundance in H ii regions with $\mathrm{O}/\mathrm{H}$ in the same range of the Galactic Globular Clusters, we obtain an upper bound $g_{a\gamma }<0.66\times {10}^{-10}{\mathrm{GeV}}^{-1}$ at 95% confidence level. This result significantly improves the constraints from previous analyses and is currently the strongest limit on the axion-photon coupling in a wide mass range.

We explore the sensitivity of the Higgs decay to four leptons, the so-called golden channel, to higher dimensional loop-induced couplings of the Higgs boson to $ZZ$, $Z\gamma$, and $\gamma \gamma$ pairs, allowing for general $CP$ mixtures. The larger standard model tree level coupling $h{Z}^{\mu }{Z}_{\mu }$ is the dominant “background” for the loop-induced couplings. However, this large background interferes with the smaller loop-induced couplings, enhancing the sensitivity. We perform a maximum likelihood analysis based on analytic expressions of the fully differential decay width for $h\to 4\ell$ ($4\ell \equiv 2e2\mu ,4e,4\mu$), including all interference effects. We find that the spectral shapes induced by Higgs couplings to photons are particularly different than the $h{Z}^{\mu }{Z}_{\mu }$ background leading to enhanced sensitivity to these couplings. We show that even if the $h\to \gamma \gamma$ and $h\to 4\ell$ rates agree with that predicted by the standard model, the golden channel has the potential to probe both the $CP$ nature as well as the overall sign of the Higgs coupling to photons well before the end of a high-luminosity LHC.

We employ a small $x$ color glass condensate (CGC)+ nonrelativistic QCD (NRQCD) formalism to compute $J/\psi$ production at low $p_{\perp }$ in proton-proton collisions at collider energies. Very good agreement is obtained for total cross sections, rapidity distributions, and low momentum $p_{\perp }$ distributions. Similar agreement is obtained for ${\psi }^{\prime }$ production. We observe an overlap region in $p_{\perp }$ where our results match smoothly to those obtained in a next-to-leading order collinearly factorized NRQCD formalism. The relative contribution of color singlet and color octet contributions can be quantified in the $\mathrm{CGC}+\mathrm{NRQCD}$ framework, with the former contributing approximately 10% of the total cross section.

We present the first Green’s function Monte Carlo calculations of light nuclei with nuclear interactions derived from chiral effective field theory up to next-to-next-to-leading order. Up to this order, the interactions can be constructed in a local form and are therefore amenable to quantum Monte Carlo calculations. We demonstrate a systematic improvement with each order for the binding energies of $A=3$ and $A=4$ systems. We also carry out the first few-body tests to study perturbative expansions of chiral potentials at different orders, finding that higher-order corrections are more perturbative for softer interactions. Our results confirm the necessity of a three-body force for correct reproduction of experimental binding energies and radii, and pave the way for studying few- and many-nucleon systems using quantum Monte Carlo methods with chiral interactions.

We present the first ab initio calculations for $p$-shell single-$\mathrm{\Lambda }$ hypernuclei. For the solution of the many-baryon problem, we develop two variants of the no-core shell model with explicit $\mathrm{\Lambda }$ and ${\mathrm{\Sigma }}^{+},{\mathrm{\Sigma }}^0,{\mathrm{\Sigma }}^{-}$ hyperons including $\mathrm{\Lambda }\text{−}\mathrm{\Sigma }$ conversion, optionally supplemented by a similarity renormalization group transformation to accelerate model-space convergence. In addition to state-of-the-art chiral two- and three-nucleon interactions, we use leading-order chiral hyperon-nucleon interactions and a recent meson-exchange hyperon-nucleon interaction. We validate the approach for $s$-shell hypernuclei and apply it to $p$-shell hypernuclei, in particular to ${}_{\mathrm{\Lambda }}{}^7\mathrm{Li}$, ${}_{\mathrm{\Lambda }}{}^9\mathrm{Be}$, and ${}_{\mathrm{\Lambda }}{}^{13}\mathrm{C}$. We show that the chiral hyperon-nucleon interactions provide ground-state and excitation energies that generally agree with experiment within the cutoff dependence. At the same time we demonstrate that hypernuclear spectroscopy provides tight constraints on the hyperon-nucleon interactions.