We report a thermally activated metastability in a GaAs double quantum dot exhibiting real-time charge switching in diamond shaped regions of the charge stability diagram. Accidental charge traps and sensor backaction are excluded as the origin of the switching. We present an extension of the canonical double dot theory based on an intrinsic, thermal electron exchange process through the reservoirs, giving excellent agreement with the experiment. The electron spin is randomized by the exchange process, thus facilitating fast, gate-controlled spin initialization. At the same time, this process sets an intrinsic upper limit to the spin relaxation time.

X-ray absorption by matter has long been described by the famous Beer-Lambert law. Here, we show how this fundamental law needs to be modified for high-intensity coherent x-ray pulses, now available at x-ray free electron lasers, due to the onset of stimulated elastic forward scattering. We present an analytical expression for the modified polarization-dependent Beer-Lambert law for the case of resonant core-to-valence electronic transitions and incident transform limited x-ray pulses. Upon transmission through a solid, the resonant absorption and dichroic contrasts are found to vanish with increasing x-ray intensity, with the stimulation threshold lowered by orders of magnitude through a resonant superradiantlike effect. Our results have broad implications for the study of matter with x-ray lasers.

Enzymes have been recently found to exhibit enhanced diffusion due to their catalytic activities. A recent experiment [C. Riedel et al., Nature (London) 517, 227 (2015)] has found evidence that suggests this phenomenon might be controlled by the degree of exothermicity of the catalytic reaction involved. Four mechanisms that can lead to this effect, namely, self-thermophoresis, boost in kinetic energy, stochastic swimming, and collective heating are critically discussed, and it is shown that only the last two can be strong enough to account for the observations. The resulting quantitative description is used to examine the biological significance of the effect.

We report the results of a search for neutrinoless double-beta decay in a 9.8 kg yr exposure of ${}^{130}\mathrm{Te}$ using a bolometric detector array, CUORE-0. The characteristic detector energy resolution and background level in the region of interest are $5.1\pm 0.3\mathrm{keV}$ FWHM and $0.058\pm 0.004(\text{stat})\pm 0.002(\text{syst})\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$, respectively. The median 90% C.L. lower-limit half-life sensitivity of the experiment is $2.9\times {10}^{24}\mathrm{yr}$ and surpasses the sensitivity of previous searches. We find no evidence for neutrinoless double-beta decay of ${}^{130}\mathrm{Te}$ and place a Bayesian lower bound on the decay half-life, $T_{1/2}^{0\nu }>2.7\times {10}^{24}\mathrm{yr}$ at 90% C.L. Combining CUORE-0 data with the 19.75 kg yr exposure of ${}^{130}\mathrm{Te}$ from the Cuoricino experiment we obtain $T_{1/2}^{0\nu }>4.0\times {10}^{24}\mathrm{yr}$ at 90% C.L. (Bayesian), the most stringent limit to date on this half-life. Using a range of nuclear matrix element estimates we interpret this as a limit on the effective Majorana neutrino mass, $m_{\beta \beta }<270–760\mathrm{meV}$.

The distribution function of suprathermal ions is found to be self-similar under conditions relevant to inertial confinement fusion hot spots. By utilizing this feature, interference between the hydrodynamic instabilities and kinetic effects is for the first time assessed quantitatively to find that the instabilities substantially aggravate the fusion reactivity reduction. The ion tail depletion is also shown to lower the experimentally inferred ion temperature, a novel kinetic effect that may explain the discrepancy between the exploding pusher experiments and rad-hydro simulations and contribute to the observation that temperature inferred from DD reaction products is lower than from DT at the National Ignition Facility.

The pressure-induced transformation of diatomic nitrogen into nonmolecular polymeric phases may produce potentially useful high-energy-density materials. We combine first-principles calculations with structure searching to predict a new class of nitrogen-rich boron nitrides with a stoichiometry of ${\mathrm{B}}_3{\mathrm{N}}_5$ that are stable or metastable relative to solid ${\mathrm{N}}_2$ and $h$-BN at ambient pressure. The most stable phase at ambient pressure has a layered structure ($h{\text{−}\mathrm{B}}_3{\mathrm{N}}_5$) containing hexagonal ${\mathrm{B}}_3{\mathrm{N}}_3$ layers sandwiched with intercalated freely rotating ${\mathrm{N}}_2$ molecules. At 15 GPa, a three-dimensional $C222_1$ structure with single N-N bonds becomes the most stable. This pressure is much lower than that required for triple-to-single bond transformation in pure solid nitrogen (110 GPa). More importantly, $C222_1\text{−}{\mathrm{B}}_3{\mathrm{N}}_5$ is metastable, and can be recovered under ambient conditions. Its energy density of $\sim 3.44\mathrm{kJ}/\mathrm{g}$ makes it a potential high-energy-density material. In addition, stress-strain calculations estimate a Vicker’s hardness of $\sim 44\mathrm{GPa}$. Structure searching reveals a new clathrate sodalitelike BN structure that is metastable under ambient conditions.

At low temperatures, the thermal conductivity of spin excitations in a magnetic insulator can exceed that of phonons. However, because they are charge neutral, the spin waves are not expected to display a thermal Hall effect. However, in the kagome lattice, theory predicts that the Berry curvature leads to a thermal Hall conductivity ${\kappa }_{xy}$. Here we report observation of a large ${\kappa }_{xy}$ in the kagome magnet Cu(1-3, bdc) which orders magnetically at 1.8 K. The observed ${\kappa }_{xy}$ undergoes a remarkable sign reversal with changes in temperature or magnetic field, associated with sign alternation of the Chern flux between magnon bands. The close correlation between ${\kappa }_{xy}$ and ${\kappa }_{xx}$ firmly precludes a phonon origin for the thermal Hall effect.

We performed high-resolution photon-energy and polarization-dependent ARPES measurements on ultrathin Bi(111) films [6–180 bilayers (BL), 2.5–70 nm thick] formed on Si(111). In addition to the extensively studied surface states (SSs), the edge of the bulk valence band was clearly measured by using $S$-polarized light. We found direct evidence that this valence band edge, which forms a hole pocket in the bulk Bi crystal, does not cross the Fermi level for the 180 BL thick film. This is consistent with the predicted semimetal-to-semiconductor transition due to the quantum-size effect [V.B. Sandomirskii, Sov. Phys. JETP 25, 101 (1967)]. However, it became metallic again when the film thickness was decreased (below 30 BL). A plausible explanation for this phenomenon is the modification of the charge neutrality condition due to the size effect of the SSs.

We report on microwave emission from linear parallel arrays of underdamped Josephson junctions, which are described by the Frenkel-Kontorova (FK) model. Electromagnetic radiation is detected from the arrays when biased on current singularities (steps) appearing at voltages $V_n={\mathrm{\Phi }}_0(n\overline{c}/L)$, where ${\mathrm{\Phi }}_0=2.07\times {10}^{-15}\mathrm{Wb}$ is the magnetic flux quantum, and $\overline{c}$, $L$, and $n$ are, respectively, the speed of light in the transmission line embedding the array, $L$ its physical length, and $n$ an integer. The radiation, detected at fundamental frequency $\overline{c}/2L$ when biased on different singularities, indicates shuttling of bunched $2\pi$ kinks (magnetic flux quanta). Resonance of flux-quanta motion with the small-amplitude oscillations induced in the arrays gives rise to fine structures in the radiation spectrum, which are interpreted on the basis of the FK model describing the resonance. The impact of our results on design and performances of new digital circuit families is discussed.

Density functional plus dynamical mean field calculations are used to show that in transition metal oxides, rotational and tilting (${\mathrm{GdFeO}}_3$-type) distortions of the ideal cubic perovskite structure produce a multiplicity of low-energy optical transitions which affect the conductivity down to frequencies of the order of 1 or 2 mV (terahertz regime), mimicking non-Fermi-liquid effects even in systems with a strictly Fermi-liquid self-energy. For ${\mathrm{CaRuO}}_3$, a material whose measured electromagnetic response in the terahertz frequency regime has been interpreted as evidence for non-Fermi-liquid physics, the combination of these band structure effects and a renormalized Fermi-liquid self-energy accounts for the low frequency optical response which had previously been regarded as a signature of exotic physics. Signatures of deviations from Fermi-liquid behavior at higher frequencies ($\sim 100\mathrm{meV}$) are discussed.

Multiferroics in nanoscale dimensions are promising for novel functional device paradigms, such as magnetoelectric memories, due to an intriguing cross-coupling between coexisting ferroelectric and (anti)ferromagnetic order parameters. However, the ferroic order is inevitably destroyed below the critical dimension of several nanometers. Here, we demonstrate a new path towards atomic-size multiferroics while resolving the controversial origin of dilute ferromagnetism that unexpectedly emerges in nanoparticles of nonmagnetic ferroelectric ${\mathrm{PbTiO}}_3$. Systematic exploration using predictive quantum-mechanical calculations demonstrates that oxygen vacancies formed at surfaces induce ferromagnetism due to local nonstoichiometry and orbital symmetry breaking. The localized character of the emerged magnetization allows an individual oxygen vacancy to act as an atomic-scale multiferroic element with a nonlinear magnetoelectric effect that involves rich ferromagnetic-antiferromagnetic-nonmagnetic phase transitions in response to switching of the spontaneous polarization.

We report the self-organization of microfluidic emulsions into anomalously homogeneous structures. Upon periodic driving confined emulsions undergo a first-order transition from a reversible to an irreversible dynamics. We evidence that this dynamical transition is accompanied by structural changes at all scales yielding macroscopic yet finite hyperuniform structures. Numerical simulations are performed to single out the very ingredients responsible for the suppression of density fluctuations. We show that, as opposed to equilibrium systems, the long-range nature of the hydrodynamic interactions are not required for the formation of hyperuniform patterns, thereby suggesting a robust relation between reversibility and hyperuniformity which should hold in a broad class of periodically driven materials.

We introduce a new class of nondiffracting optical pulses possessing orbital angular momentum. By generalizing the $X$-wave solution of the Maxwell equation, we discover the coupling between angular momentum and the temporal degrees of freedom of ultrashort pulses. The spatial twist of propagation invariant light pulse turns out to be directly related to the number of optical cycles. Our results may trigger the development of novel multilevel classical and quantum transmission channels free of dispersion and diffraction. They may also find application in the manipulation of nanostructured objects by ultrashort pulses and for novel approaches to the spatiotemporal measurements in ultrafast photonics.

We present a new test of the validity of the Friedmann-Lemaître-Robertson-Walker (FLRW) metric, based on comparing the distance from redshift 0 to $z_1$ and from $z_1$ to $z_2$ to the distance from 0 to $z_2$. If the Universe is described by the FLRW metric, the comparison provides a model-independent measurement of spatial curvature. The test relies on geometrical optics, it is independent of the matter content of the Universe and the applicability of the Einstein equation on cosmological scales. We apply the test to observations, using the Union2.1 compilation of supernova distances and Sloan Lens ACS Survey galaxy strong lensing data. The FLRW metric is consistent with the data, and the spatial curvature parameter is constrained to be $-1.22<{\mathrm{\Omega }}_{K0}<0.63$, or $-0.08<{\mathrm{\Omega }}_{K0}<0.97$ with a prior from the cosmic microwave background and the local Hubble constant, though modeling of the lenses is a source of significant systematic uncertainty.

Differential cross sections of isoscalar and isovector spin-$M1$ ($0^{+}\to 1^{+}$) transitions are measured using high-energy-resolution proton inelastic scattering at $E_p=295\mathrm{MeV}$ on ${}^{24}\mathrm{Mg}$, ${}^{28}\mathrm{Si}$, ${}^{32}\mathrm{S}$, and ${}^{36}\mathrm{Ar}$ at 0°–14°. The squared spin-$M1$ nuclear transition matrix elements are deduced from the measured differential cross sections by applying empirically determined unit cross sections based on the assumption of isospin symmetry. The ratios of the squared nuclear matrix elements accumulated up to $E_x=16\mathrm{MeV}$ compared to a shell-model prediction are 1.01(9) for isoscalar and 0.61(6) for isovector spin-$M1$ transitions, respectively. Thus, no quenching is observed for isoscalar spin-$M1$ transitions, while the matrix elements for isovector spin-$M1$ transitions are quenched by an amount comparable with the analogous Gamow-Teller transitions on those target nuclei.

We show that dynamic exchange is a dominant effect in strong field ionization of molecules. In ${\mathrm{CO}}_2$ it fixes the peak ionization yield at the experimentally observed angle of 45° between polarization direction and the molecular axis. For ${\mathrm{O}}_2$ it changes the angle of peak emission and for ${\mathrm{N}}_2$ the alignment dependence of yields is modified by up to a factor of 2. The effect appears on the Hartree-Fock level as well as in full ab initio solutions of the Schrödinger equation.

Broadband atmospheric phase spectra are acquired with a phase-sensitive dual-frequency-comb spectrometer by implementing adaptive compensation for the strong decoherence from atmospheric turbulence. The compensation is possible due to the pistonlike behavior of turbulence across a single spatial-mode path combined with the intrinsic frequency stability and high sampling speed associated with dual-comb spectroscopy. The atmospheric phase spectrum is measured across 2 km of air at each of the 70 000 comb teeth spanning $233{\mathrm{cm}}^{-1}$ across hundreds of near-infrared rovibrational resonances of ${\mathrm{CO}}_2$, ${\mathrm{CH}}_4$, and ${\mathrm{H}}_2\mathrm{O}$ with submilliradian uncertainty, corresponding to a ${10}^{-13}$ refractive index sensitivity. Trace gas concentrations extracted directly from the phase spectrum reach 0.7 ppm uncertainty, demonstrated here for ${\mathrm{CO}}_2$. While conventional broadband spectroscopy only measures intensity absorption, this approach enables measurement of the full complex susceptibility even in practical open path sensing.