A novel effect of fast heating and charging a finite-radius plasma is discovered in the context of plasma wakefield acceleration. As the plasma wave breaks, most of its energy is transferred to plasma electrons. The electrons gain substantial transverse momentum and escape the plasma radially, which gives rise to a strong charge-separation electric field and azimuthal magnetic field around the plasma. The slowly varying field structure is preserved for hundreds of wakefield periods and contains (together with hot electrons) up to 80% of the initial wakefield energy.

We study monolayers of noble gas atoms (Xe, Kr, Ar, and Ne) deposited on individual ultraclean suspended nanotubes. For this, we record the resonance frequency of the mechanical motion of the nanotube, since it provides a direct measure of the coverage. The latter is the number of adsorbed atoms divided by the number of the carbon atoms of the suspended nanotube. Monolayers form when the temperature is lowered in a constant pressure of noble gas atoms. The coverage of Xe monolayers remains constant at $1/6$ over a large temperature range. This finding reveals that Xe monolayers are solid phases with a triangular atomic arrangement, and are commensurate with the underlying carbon nanotube. By comparing our measurements to theoretical calculations, we identify the phases of Ar and Ne monolayers as fluids, and we tentatively describe Kr monolayers as solid phases. These results underscore that mechanical resonators made from single nanotubes are excellent probes for surface science.

We introduce a nonequilibrium density-functional theory of local temperature and associated local energy density that is suited for the study of thermoelectric phenomena. The theory rests on a local temperature field coupled to the energy-density operator. We identify the excess-energy density, in addition to the particle density, as the basic variable, which is reproduced by an effective noninteracting Kohn-Sham system. A novel Kohn-Sham equation emerges featuring a time-dependent and spatially varying mass which represents local temperature variations. The adiabatic contribution to the Kohn-Sham potentials is related to the entropy viewed as a functional of the particle and energy density. Dissipation can be taken into account by employing linear response theory and the thermoelectric transport coefficients of the electron gas.

We present a novel scheme for an unbiased, nonperturbative treatment of strongly correlated fermions. The proposed approach combines two of the most successful many-body methods, the dynamical mean field theory and the functional renormalization group. Physically, this allows for a systematic inclusion of nonlocal correlations via the functional renormalization group flow equations, after the local correlations are taken into account nonperturbatively by the dynamical mean field theory. To demonstrate the feasibility of the approach, we present numerical results for the two-dimensional Hubbard model at half filling.

Lithium is one of the simplest metals, with negative charge carriers and a close reproduction of free-electron dispersion. Experimentally, however, Li is one of a handful of elemental solids (along with Cu, Ag, and Au) where the sign of the Seebeck coefficient ($S$) is opposite to that of the carrier. This counterintuitive behavior still lacks a satisfactory interpretation. We calculate $S$ fully from first principles, within the framework of Allen’s formulation of Boltzmann transport theory. Here it is crucial to avoid the constant relaxation time approximation, which gives a sign for $S$ which is necessarily that of the carriers. Our calculated $S$ are in excellent agreement with experimental data, up to the melting point. In comparison with another alkali metal, Na, we demonstrate that within the simplest nontrivial model for the energy dependency of the electron lifetimes, the rapidly increasing density of states (DOS) across the Fermi energy is related to the sign of $S$ in Li. The exceptional energy dependence of the DOS is beyond the free-electron model, as the dispersion is distorted by the Brillouin zone edge; this has a stronger effect in Li than other alkali metals. The electron lifetime dependency on energy is central, but the details of the electron-phonon interaction are found to be less important, contrary to what has been believed for several decades. Band engineering combined with the mechanism exposed here may open the door to new “ambipolar” thermoelectric materials, with a tunable sign for the thermopower even if either $n$- or $p$-type doping is impossible.

We investigate the magnetotransport properties of strained 80 nm thick HgTe layers featuring a high mobility of $\mu \sim 4\times 10^5{\mathrm{cm}}^2/\mathrm{V}·\mathrm{s}$. By means of a top gate, the Fermi energy is tuned from the valence band through the Dirac-type surface states into the conduction band. Magnetotransport measurements allow us to disentangle the different contributions of conduction band electrons, holes, and Dirac electrons to the conductivity. The results are in line with previous claims that strained HgTe is a topological insulator with a bulk gap of $\approx 15\mathrm{meV}$ and gapless surface states.

Here we study the electronic properties of cuprate-manganite interfaces. By means of atomic resolution electron microscopy and spectroscopy, we produce a subnanometer scale map of the transition metal oxidation state profile across the interface between the high Tc superconductor ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ and the colossal magnetoresistance compound (La,Ca)${\mathrm{MnO}}_3$. A net transfer of electrons from manganite to cuprate with a peculiar nonmonotonic charge profile is observed. Model calculations rationalize the profile in terms of the competition between standard charge transfer tendencies (due to band mismatch), strong chemical bonding effects across the interface, and Cu substitution into the Mn lattice, with different characteristic length scales.

We theoretically study transport through a semiconducting Rashba nanowire (NW) in the presence of uniform and spatially modulated magnetic fields. The system is fully gapped, and the interplay between the spin orbit interaction and the magnetic fields leads to fractionally charged fermion (FF) bound states of the Jackiw-Rebbi type at each end of the nanowire. We investigate the transport and noise behavior of a $\mathrm{N}/\mathrm{NW}/\mathrm{N}$ system, where the wire is contacted by two normal leads (N), and we look for possible signatures that could help in the experimental detection of such states. We find that the differential conductance and the shot noise exhibit a subgap structure which fully reveals the presence of the FF state. Alternatively, another confirmation of the presence of the FFs is provided by a conductance measurement in an Aharonov-Bohm setup, where the FFs are responsible for oscillations with double period. Our predictions can be tested in $\mathrm{InSb}/\mathrm{InAs}$ nanowires and are within reach of the present technology.

The transition-metal dichalcogenide $1T\text{−}{\mathrm{TiSe}}_2$ is a quasi-two-dimensional layered material with a charge density wave (CDW) transition temperature of $T_{\mathrm{CDW}}\approx 200\mathrm{K}$. Self-doping effects for crystals grown at different temperatures introduce structural defects, modify the temperature-dependent resistivity, and strongly perturbate the CDW phase. Here, we study the structural and doping nature of such native defects combining scanning tunneling microscopy or spectroscopy and ab initio calculations. The dominant native single atom dopants we identify in our single crystals are intercalated Ti atoms, Se vacancies, and Se substitutions by residual iodine and oxygen.

Based on first-principles calculations, we predict the use of pure silicon nanocrystals as nano-oscillators in the giga- and terahertz region. Small- and large-amplitude, one-dimensional vibrations are observed. The former are spontaneously excited thermally at frequencies around 3 THz. Large-amplitude vibrations originate from oscillations between the inversion geometries of the nanocrystal and can be caused either classically by an external excitation or by quantum tunneling. The latter causes a ground-state splitting of 4.2 GHz, suggesting the use of the proposed nanocrystals as laser elements in a configuration analogous to that of the ammonia maser.

While memory effects have been reported for dense enough disordered systems such as glasses, we show here by a combination of analytical and simulation techniques that they are also intrinsic to the dynamics of dilute granular gases. By means of a certain driving protocol, we prepare the gas in a state where the granular temperature $T$ coincides with its long time limit. However, $T$ does not subsequently remain constant but exhibits a nonmonotonic evolution before reaching its nonequilibrium steady value. The corresponding so-called Kovacs hump displays a normal behavior for weak dissipation (as observed in molecular systems) but is reversed under strong dissipation, where it, thus, becomes anomalous.

We describe a new and experimentally feasible protocol for performing fundamental tests of quantum mechanics with massive objects. In our approach, a single two-level system is used to probe the motion of a nanomechanical resonator via multiple Ramsey interference measurements. This scheme enables the measurement of modular variables of macroscopic continuous-variable systems; we show that correlations thereof violate a Leggett-Garg inequality and can be applied for tests of quantum contextuality. Our method can be implemented with a variety of different solid-state or photonic qubit-resonator systems, and it provides a clear experimental signature to distinguish the predictions of quantum mechanics from those of other alternative theories at a macroscopic scale.

Using first-principles density functional theory calculations, we explore the chemical activity of epitaxial heterostructures of ${\mathrm{TiO}}_2$ anatase on strained polar ${\mathrm{SrTiO}}_3$ films focusing on the oxygen evolution reaction (OER), the bottleneck of water splitting. Our results show that the reactivity of the ${\mathrm{TiO}}_2$ surface is tuned by electric dipoles dynamically induced by the adsorbed species during the intermediate steps of the reaction while the initial and final steps remain unaffected. Compared to the OER on unsupported ${\mathrm{TiO}}_2$, the combined effects of the dynamically induced dipoles and epitaxial strain strongly reduce rate-limiting thermodynamic barriers and significantly improve the efficiency of the reaction.

The fractal spectrum of magnetic minibands (Hofstadter butterfly), induced by the moiré superlattice of graphene on a hexagonal crystal substrate, is known to exhibit gapped Dirac cones. We show that the gap can be closed by slightly misaligning the substrate, producing a hierarchy of conical singularities (Dirac points) in the band structure at rational values $\mathrm{\Phi }=(p/q)(h/e)$ of the magnetic flux per supercell. Each Dirac point signals a switch of the topological quantum number in the connected component of the quantum Hall phase diagram. Model calculations reveal the scale-invariant conductivity $\sigma =2q{e}^2/\pi h$ and Klein tunneling associated with massless Dirac fermions at these connectivity switches.

We report on a new analysis of neutrino oscillations in MINOS using the complete set of accelerator and atmospheric data. The analysis combines the ${\nu }_{\mu }$ disappearance and ${\nu }_e$ appearance data using the three-flavor formalism. We measure $|\mathrm{\Delta }{m}_{32}^2|=[2.28–2.46]\times 10^{-3}{\mathrm{eV}}^2$ (68% C.L.) and ${\sin }^2{\theta }_{23}=0.35–0.65$ (90% C.L.) in the normal hierarchy, and $|\mathrm{\Delta }{m}_{32}^2|=[2.32–2.53]\times 10^{-3}{\mathrm{eV}}^2$ (68% C.L.) and ${\sin }^2{\theta }_{23}=0.34–0.67$ (90% C.L.) in the inverted hierarchy. The data also constrain ${\delta }_{CP}$, the ${\theta }_{23}$ octant degeneracy and the mass hierarchy; we disfavor 36% (11%) of this three-parameter space at 68% (90%) C.L.

We present a detailed experimental investigation which uncovers the nature of light bullets generated from self-focusing in a bulk dielectric medium with Kerr nonlinearity in the anomalous group velocity dispersion regime. By high dynamic range measurements of three-dimensional intensity profiles, we demonstrate that the light bullets consist of a sharply localized high-intensity core, which carries the self-compressed pulse and contains approximately 25% of the total energy, and a ring-shaped spatiotemporal periphery. Subdiffractive propagation along with dispersive broadening of the light bullets in free space after they exit the nonlinear medium indicate a strong space-time coupling within the bullet. This finding is confirmed by measurements of a spatiotemporal energy density flux that exhibits the same features as a stationary, polychromatic Bessel beam, thus highlighting the nature of the light bullets.