We present the nuclear matrix element for the neutrinoless double-beta decay of ${}^{48}\mathrm{Ca}$ based on large-scale shell-model calculations including two harmonic oscillator shells ($sd$ and $pf$ shells). The excitation spectra of ${}^{48}\mathrm{Ca}$ and ${}^{48}\mathrm{Ti}$, and the two-neutrino double-beta decay of ${}^{48}\mathrm{Ca}$ are reproduced in good agreement to the experimental data. We find that the neutrinoless double-beta decay nuclear matrix element is enhanced by about 30% compared to $pf$-shell calculations. This reduces the decay lifetime by almost a factor of 2. The matrix-element increase is mostly due to pairing correlations associated with cross-shell $sd\text{−}pf$ excitations. We also investigate possible implications for heavier neutrinoless double-beta decay candidates.

Two-nucleon systems are shown to exhibit large scattering lengths in strong magnetic fields at unphysical quark masses, and the trends toward the physical values indicate that such features may exist in nature. Lattice QCD calculations of the energies of one and two nucleons systems are performed at pion masses of $m_{\pi }\sim 450$ and 806 MeV in uniform, time-independent magnetic fields of strength $|\mathbf{B}|\sim {10}^{19}–{10}^{20}\mathrm{G}$ to determine the response of these hadronic systems to large magnetic fields. Fields of this strength may exist inside magnetars and in peripheral relativistic heavy ion collisions, and the unitary behavior at large scattering lengths may have important consequences for these systems.

Two pairs of positive-and negative-parity doublet bands together with eight strong electric dipole transitions linking their yrast positive- and negative-parity bands have been identified in ${}^{78}\mathrm{Br}$. They are interpreted as multiple chiral doublet bands with octupole correlations, which is supported by the microscopic multidimensionally-constrained covariant density functional theory and triaxial particle rotor model calculations. This observation reports the first example of chiral geometry in octupole soft nuclei.

We propose a control scheme which can stabilize and fix the position of chimera states in small networks. Chimeras consist of coexisting domains of spatially coherent and incoherent dynamics in systems of nonlocally coupled identical oscillators. Chimera states are generally difficult to observe in small networks due to their short lifetime and erratic drifting of the spatial position of the incoherent domain. The control scheme, like a tweezer, might be useful in experiments, where usually only small networks can be realized.

Owing to the rapid progress in laser technology, very high-contrast femtosecond laser pulses of relativistic intensities have become available. These pulses allow for interaction with microstructured solid-density plasma without destroying the structure by parasitic prepulses. This opens a new realm of possibilities for laser interaction with micro- and nanoscale photonic materials at relativistic intensities. Here we demonstrate, for the first time, that when coupled with a readily available 1.8 J laser, a microplasma waveguide (MPW) may serve as a novel compact x-ray source. Electrons are extracted from the walls and form a dense helical bunch inside the channel. These electrons are efficiently accelerated and wiggled by the waveguide modes in the MPW, which results in a bright, well-collimated emission of hard x rays in the range of $1\sim 100\mathrm{keV}$.

The phase separation in binary mixtures of charged particles has been investigated in a dusty plasma under microgravity on parabolic flights. A method based on the use of fluorescent dust particles was developed that allows us to distinguish between particles of slightly different size. A clear trend towards phase separation even for smallest size (charge) disparities is observed. The diffusion flux is directly measured from the experiment and uphill diffusion coefficients have been determined.

We investigate coupled spin and heat transport in easy-plane magnetic insulators. These materials display a continuous phase transition between normal and condensate states that is controlled by an external magnetic field. Using hydrodynamic equations supplemented by Gross-Pitaevski phenomenology and magnetoelectric circuit theory, we derive a two-fluid model to describe the dynamics of thermal and condensed magnons, and the appropriate boundary conditions in a hybrid normal-metal–magnetic-insulator–normal-metal heterostructure. We discuss how the emergent spin superfluidity can be experimentally probed via a spin Seebeck effect measurement.

In this study we show from first principles calculations the possibility to induce multiferroic and magnetoelectric functional properties in the $Pnma$ ${\text{NaMnF}}_3$ fluoroperovskite by means of epitaxial strain engineering. Surprisingly, we found a very strong nonlinear polarization-strain coupling that drives an atypical amplification of the ferroelectric polarization for either compression or expansion of the cell. This property is associated with a noncollinear antiferromagnetic ordering, which induces a weak ferromagnetism phase and makes the strained ${\text{NaMnF}}_3$ fluoroperovskite multiferroic. The magnetoelectric response was calculated and it was found to be composed of linear and nonlinear components with amplitudes similar to the ones of ${\mathrm{Cr}}_2{\mathrm{O}}_3$. These findings show that it is possible to move the fluoride family toward functional applications with unique responses.

The formation of temporal dissipative Kerr solitons in microresonators driven by a continuous-wave laser enables the generation of coherent, broadband, and spectrally smooth optical frequency combs as well as femtosecond pulse sources with compact form factors. Here we report the observation of a Raman-induced soliton self-frequency shift for a microresonator dissipative Kerr soliton also referred to as the frequency-locked Raman soliton. In amorphous silicon nitride microresonator-based single soliton states the Raman effect manifests itself by a spectrum that is ${\text{sech}}^2$ in shape and whose center is spectrally redshifted from the continuous wave pump laser. The shift is theoretically described by the first-order shock term of the material’s Raman response, and we infer a Raman shock time of $\sim 20\mathrm{fs}$ for amorphous silicon nitride. Moreover, we observe that the Raman-induced frequency shift can lead to a cancellation or overcompensation of the soliton recoil caused by the formation of a coherent dispersive wave. The observations are in agreement with numerical simulations based on the Lugiato-Lefever equation with a Raman shock term. Our results contribute to the understanding of Kerr frequency combs in the soliton regime, enable one to substantially improve the accuracy of modeling, and are relevant to the understanding of the fundamental timing jitter of microresonator solitons.

${\mathrm{PbCuTe}}_2{\mathrm{O}}_6$ is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of ${\mathrm{Cu}}^{2+}$ ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature ($T$) evolution of the $1/T_1$ NMR relaxation rate at low $T$ point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.

Recent nondetection of gravitational-wave backgrounds from pulsar timing arrays casts further uncertainty on the evolution of supermassive black hole binaries. We study the capabilities of current gravitational-wave observatories to detect individual binaries and demonstrate that, contrary to conventional wisdom, some are, in principle, detectable throughout the Universe. In particular, a binary with rest-frame mass $\gtrsim {10}^{10}{M}_{\odot }$ can be detected by current timing arrays at arbitrarily high redshifts. The same claim will apply for less massive binaries with more sensitive future arrays. As a consequence, future searches for nanohertz gravitational waves could be expanded to target evolving high-redshift binaries. We calculate the maximum distance at which binaries can be observed with pulsar timing arrays and other detectors, properly accounting for redshift and using realistic binary waveforms.

The $ZZ$ production cross section in proton-proton collisions at 13 TeV center-of-mass energy is measured using $3.2{\mathrm{fb}}^{-1}$ of data recorded with the ATLAS detector at the Large Hadron Collider. The considered $Z$ boson candidates decay to an electron or muon pair of mass 66–116 GeV. The cross section is measured in a fiducial phase space reflecting the detector acceptance. It is also extrapolated to a total phase space for $Z$ bosons in the same mass range and of all decay modes, giving $16.7_{-2.0}^{+2.2}(\mathrm{stat})\genfrac{}{}{0ex}{}{+0.9}{-0.7}(\mathrm{syst})\genfrac{}{}{0ex}{}{+1.0}{-0.7}(\mathrm{lumi})\mathrm{pb}$. The results agree with standard model predictions.

Giant impurity excitations are powerful probes for exploring new regimes of far out of equilibrium dynamics in few- and many-body quantum systems, and in situ observations of correlations. Motivated by recent experimental progress in spectroscopic studies of Rydberg excitations in ultracold atoms, we develop a new theoretical approach for describing multiscale dynamics of Rydberg excitations in quantum Bose gases. We find that the crossover from few- to many-body dynamics manifests in a dramatic change in spectral profile from resolved molecular lines to broad Gaussian distributions representing a superpolaronic state in which many atoms bind to the Rydberg impurity. We discuss signatures of this crossover in the temperature and density dependence of the spectra.

By measuring the prototypical antiferromagnet $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$, we show that it is possible to determine the static spin orientation and dynamic spin correlations within nanometers from an antiferromagnetic surface using the nuclear spin polarization of implanted ${}^8{\mathrm{Li}}^{+}$ ions detected with $\beta$-NMR. Remarkably, the first-order Morin spin reorientation in single crystal $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ occurs at the same temperature at all depths between 1 and 100 nm from the (110) surface; however, the implanted nuclear spin experiences an increased $1/T_1$ relaxation rate at shallow depths revealing soft-surface magnons. The surface-localized dynamics decay towards the bulk with a characteristic length of $\epsilon =11\pm 1\mathrm{nm}$, closely matching the finite-size thresholds of hematite nanostructures.

Systems with topologically protected ground-state degeneracies are currently of great interest due to their potential applications in quantum computing. In practice, this degeneracy is never exact, and the magnitude of the ground-state degeneracy splitting imposes constraints on the time scales over which information is topologically protected. In this Letter, we use an instanton approach to evaluate the splitting of topological ground-state degeneracy in quasi-1D systems with parafermion zero modes, in the specific case where parafermions are realized by inducing a superconducting gap in pairs of fractional quantum Hall edges. We show that, like 1D topological superconducting wires, this splitting has an oscillatory dependence on the chemical potential, which arises from an intrinsic Berry phase that produces interference between distinct instanton tunneling events. These Berry phases can be mapped to chiral phases in a (dual) quantum clock model using a Fradkin-Kadanoff transformation. Comparing our low-energy spectrum to that of phenomenological parafermion models allows us to evaluate the real and imaginary parts of the hopping integral between adjacent parafermionic zero modes as functions of the chemical potential.

Light emission by inelastic tunneling has been known for many years. Recently, this technique has been used to generate surface plasmons using a scanning tunneling microscope tip. The emission process suffers from a very low efficiency lower than a photon in ${10}^4$ electrons. We introduce a resonant plasmonic nanoantenna that allows both enhancing the power conversion to surface plasmon polaritons by more than 2 orders of magnitude and narrowing the emission spectrum. The physics of the emission process is analyzed in terms of local density of states and the efficiency of the nanoantenna to radiate surface plasmon polaritons.