We report on the control of the faceting of crystal surfaces by means of surface electromigration. When electromigration reinforces the faceting instability, we find perpetual coarsening with a wavelength increasing as $t^{1/2}$. For strongly stabilizing electromigration, the surface is stable. For weakly stabilizing electromigration, a cellular pattern is obtained, with a nonlinearly selected wavelength. The selection mechanism is not caused by an instability of steady states, as suggested by previous works in the literature. Instead, the dynamics is found to exhibit coarsening before reaching a continuous family of stable nonequilibrium steady states.

The correlated electronic structure of ${\mathrm{SrVO}}_3$ has been investigated by angle-resolved photoemission spectroscopy using in situ prepared thin films. Pronounced features of band renormalization have been observed: a sharp kink $\sim 60\mathrm{meV}$ below the Fermi level ($E_F$) and a broad so-called “high-energy kink” $\sim 0.3\mathrm{eV}$ below $E_F$ as in the high-$T_c$ cuprates, although ${\mathrm{SrVO}}_3$ does not show magnetic fluctuations. We have deduced the self-energy in a wide energy range by applying the Kramers-Kronig relation to the observed spectra. The obtained self-energy clearly shows a large energy scale of $\sim 0.7\mathrm{eV}$, which is attributed to electron-electron interaction and gives rise to the $\sim 0.3\mathrm{eV}$ kink in the band dispersion as well as the incoherent peak $\sim 1.5\mathrm{eV}$ below $E_F$. The present analysis enables us to obtain a consistent picture for both the incoherent spectra and the band renormalization.

We realize and investigate an all-semiconductor quantized voltage source which generates quantized output voltages $V_{\mathrm{out}}=f(h/e)$ linked only to two fundamental constants, the electron’s charge $e$ and Planck’s constant $h$, and to an applied excitation frequency $f$. The device is based on an integrated quantized circuit of a single-electron pump operated at pumping frequency $f$ and a quantum Hall device monolithically integrated in series. Robust output voltages up to several $\mu \mathrm{V}$ are generated, which are expected to be scalable by orders of magnitude using present technology. The device might open a new route towards the closure of the quantum metrology triangle.

We report an inelastic neutron scattering investigation of phonons with energies up to 159 meV in the conventional superconductor ${\mathrm{YNi}}_2{\mathrm{B}}_2\mathrm{C}$. Using the sweep mode, a newly developed time-of-flight technique involving the continuous rotation of a single crystal specimen, allowed us to measure a four-dimensional volume in ($\mathbf{Q}$, $E$) space and, thus, determine the dispersion surface and linewidths of the $A_{1g}$ ($\approx 102\mathrm{meV}$) and $A_u$ ($\approx 159\mathrm{meV}$) type phonon modes over the whole Brillouin zone. Despite of having linewidths of $\Gamma =10\mathrm{meV}$, $A_{1g}$ modes do not strongly contribute to the total electron-phonon coupling constant $\lambda$. However, experimental linewidths show a remarkable agreement with ab initio calculations over the complete phonon energy range, demonstrating the accuracy of such calculations in a rare comparison to a comprehensive experimental data set.

We study charge transport through a metallic dot coupled to a superconducting and a ferromagnetic lead with a precessing magnetization due to ferromagnetic resonance. Using the quasiclassical theory, we find that the magnetization precession induces a dc current in the subgap regime even in the absence of a bias voltage. This effect is due to the rectification of the ac spin currents at the interface with the ferromagnet; it exists in the absence of spin current in the superconductor. When the dot is strongly coupled to the superconductor, we find a strong enhancement in a wide range of parameters as compared to the induced current in the normal state.

We elucidate the existing controversies in the newly discovered K-doped iron selenide (${\mathrm{K}}_x{\mathrm{Fe}}_{2-y}{\mathrm{Se}}_{2-z}$) superconductors. The stoichiometric ${\mathrm{KFe}}_2{\mathrm{Se}}_2$ with $\sqrt{2}\times \sqrt{2}$ charge ordering was identified as the parent compound of ${\mathrm{K}}_x{\mathrm{Fe}}_{2-y}{\mathrm{Se}}_{2-z}$ superconductor using scanning tunneling microscopy and spectroscopy. The superconductivity is induced in ${\mathrm{KFe}}_2{\mathrm{Se}}_2$ by either Se vacancies or interacting with the antiferromagnetic ${\mathrm{K}}_2{\mathrm{Fe}}_4{\mathrm{Se}}_5$ compound. In total, four phases were found to exist in ${\mathrm{K}}_x{\mathrm{Fe}}_{2-y}{\mathrm{Se}}_{2-z}$: parent compound ${\mathrm{KFe}}_2{\mathrm{Se}}_2$, superconducting ${\mathrm{KFe}}_2{\mathrm{Se}}_2$ with $\sqrt{2}\times \sqrt{5}$ charge ordering, superconducting ${\mathrm{KFe}}_2{\mathrm{Se}}_{2-z}$ with Se vacancies, and insulating ${\mathrm{K}}_2{\mathrm{Fe}}_4{\mathrm{Se}}_5$ with $\sqrt{5}\times \sqrt{5}$ Fe vacancy order. The phase separation takes place at the mesoscopic scale under standard molecular beam epitaxy conditions.

We show in the case of a superconducting Nb ladder that a mesoscopic superconductor typically exhibits magnetoresistance oscillations whose amplitude and temperature dependence are different from those stemming from the Little-Parks effect. We demonstrate that these large resistance oscillations (as well as the monotonic background on which they are superimposed) are due to current-excited moving vortices, where the applied current in competition with the oscillating Meissner currents imposes or removes the barriers for vortex motion in an increasing magnetic field. Because of the ever present current in transport measurements, this effect should be considered in parallel with the Little-Parks effect in low-critical temperature ($T_c$) samples, as well as with recently proposed thermal activation of dissipative vortex-antivortex pairs in high-$T_c$ samples.

The temporal evolution of the exchange-split ${\Delta }_2$-like $\Sigma$ valence bands of the $4f$-ferromagnet gadolinium after femtosecond laser excitation has been studied using angle-resolved photoelectron spectroscopy based on high-order harmonic generation. The ultrafast drop of the exchange splitting reflects the magnetic response seen in femtosecond magnetic dichroism experiments. However, while the minority valence band reacts immediately, the response of the majority counterpart is delayed by 1 picosecond and is only half as fast. These findings demonstrate that laser excitation drives the valence band structure out of magnetic equilibrium.

Guanine-rich sequences in nucleic acids can fold into $G$ quadruplexes, in which four guanines on a single strand combine to form $G$-tetrad planes stabilized by metallic ions. Sequence motifs which are predicted to form a $G$ quadruplex are found throughout the genome and are believed to regulate a variety of biological processes. Detailed knowledge of the kinetics of $G$-quadruplex folding and unfolding would provide critical insight into these processes. To probe its structural stability, we used optical tweezers to disrupt single molecules of a single-stranded DNA $G4$ quadruplex. Dynamic force spectroscopy was employed, in which the distribution of rupture forces was measured for different loading rates and used to infer the nature of the transition state barrier for unfolding of the structure. The distance and height of the energy barriers were extracted for two observed conformations. The energy barrier was found to be close to the folded conformation, resulting in a high disruption force despite the relatively low energy barrier height.

Thickness fluctuations have long been predicted in biological membranes but never directly observed experimentally. Here, we utilize neutron spin echo spectroscopy to experimentally reveal such fluctuations in a pure, fully saturated, phosphocholine lipid bilayer system. These fluctuations appear as an excess in the dynamics of undulation fluctuations. Like the bending rigidity, the thickness fluctuations change dramatically as the lipid transition temperature is crossed, appearing to be completely suppressed below the transition. Above the transition, the relaxation rate is on the order of 100 ns and is independent of temperature. The amplitude of the thickness fluctuations is $3.7\AA \pm 0.7\AA$, which agrees well with theoretical calculations and molecular dynamics simulations. The dependence of the fluctuations on lipid tail lengths is also investigated and determined to be minimal in the range of 14 to 18 carbon tails.

We experimentally investigate the structural behavior of an interacting colloidal monolayer being driven across a decagonal quasiperiodic potential landscape created by an optical interference pattern. When the direction of the driving force is varied, we observe the monolayer to be directionally locked on angles corresponding to the symmetry axes of the underlying potential. At such locking steps, we observe a dynamically ordered smectic phase in agreement with recent simulations. We demonstrate that such dynamical ordering is due to the interaction of particle lanes formed by interstitial and noninterstitial particles.

We analyze quantum interference and decoherence effects in single-molecule junctions both experimentally and theoretically by means of the mechanically controlled break junction technique and density-functional theory. We consider the case where interference is provided by overlapping quasidegenerate states. Decoherence mechanisms arising from electronic-vibrational coupling strongly affect the electrical current flowing through a single-molecule contact and can be controlled by temperature variation. Our findings underline the universal relevance of vibrations for understanding charge transport through molecular junctions.

We report on transport properties of Josephson junctions in hybrid superconducting-topological insulator devices, which show two striking departures from the common Josephson junction behavior: a characteristic energy that scales inversely with the width of the junction, and a low characteristic magnetic field for suppressing supercurrent. To explain these effects, we propose a phenomenological model which expands on the existing theory for topological insulator Josephson junctions.

We report a precise determination of the ${}^{19}\mathrm{Ne}$ half-life to be $T_{1/2}=17.262\pm 0.007\mathrm{s}$. This result disagrees with the most recent precision measurements and is important for placing bounds on predicted right-handed interactions that are absent in the current standard model. We are able to identify and disentangle two competing systematic effects that influence the accuracy of such measurements. Our findings prompt a reassessment of results from previous high-precision lifetime measurements that used similar equipment and methods.

Neutrinoless double-$\beta$ decay is of fundamental importance for the determining neutrino mass. By combining a calculation of nuclear matrix elements within the framework of the microscopic interacting boson model with an improved calculation of phase space factors, we set limits on the average light neutrino mass and on the average inverse heavy neutrino mass (flavor-violating parameter).

The $1s2s{}^{3}S_1\to 1s^2{}^{1}S_0$ relativistic magnetic dipole transition in heliumlike argon, emitted by the plasma of an electron-cyclotron resonance ion source, has been measured using a double-flat crystal x-ray spectrometer. Such a spectrometer, used for the first time on a highly charged ion transition, provides absolute (reference-free) measurements in the x-ray domain. We find a transition energy of 3104.1605(77) eV (2.5 ppm accuracy). This value is the most accurate, reference-free measurement done for such a transition and is in good agreement with recent QED predictions.

A significant fraction of high-harmonic fast-wave (HHFW) power applied to NSTX can be lost to the scrape-off layer (SOL) and deposited in bright and hot spirals on the divertor rather than in the core plasma. We show that the HHFW power flows to these spirals along magnetic field lines passing through the SOL in front of the antenna, implying that the HHFW power couples across the entire width of the SOL rather than mostly at the antenna face. This result will help guide future efforts to understand and minimize these edge losses in order to maximize fast-wave heating and current drive.

At a pressure of $\sim 25.7\mathrm{bar}$, the flux $F$ carried by solid ${}^4\mathrm{He}$ for $T>100\mathrm{mK}$ depends on the net chemical potential difference between two reservoirs in series with the solid, $\Delta \mu$, and obeys $F\sim (\Delta \mu {)}^b$, where $b\approx 0.3$ is independent of temperature. At fixed $\Delta \mu$ the temperature dependence of the flux $F$ can be adequately represented by $F\sim -\ln (T/\tau )$, $\tau \approx 0.6\mathrm{K}$, for $0.1\le T\le 0.5\mathrm{K}$. A single function $F=F_0(\Delta \mu {)}^b\ln (T/\tau )$ fits all of the available data sets in the range 25.6–25.8 bar reasonably well. We suggest that the mass flux in solid ${}^4\mathrm{He}$ for $T>100\mathrm{mK}$ may have a Luttinger liquidlike behavior in this bosonic system.

Functionalization of thin-film heterostructures on the basis of their electrical, optical and magnetic properties, requires precise control of the film stresses that develop during the growth process. By using real-time in situ stress measurements, the present study reveals strikingly that the in-plane film stress oscillates with increasing film thickness at the initial stage of epitaxial Al(111) film growth on a $\mathrm{Si}(111)\mathrm{\text{−}}\sqrt{3}\times \sqrt{3}\mathrm{\text{−}}\mathrm{Al}$ surface, with a periodicity of 2 times the Fermi wavelength of bulk Al and a stress variation from maximum to minimum as large as 100 MPa. Such macroscopic stress oscillations are shown to be caused by quantum confinement of the free electrons in the ultrathin epitaxial metal film. The amplitude, period, and phase of the observed stress oscillations are consistent with predictions based on the free electron model and continuum elasticity.

Motivated to understand the nature of the strongly insulating $\nu =0$ quantum Hall state in bilayer graphene, we develop the theory of the state in the framework of quantum Hall ferromagnetism. The generic phase diagram, obtained in the presence of the isospin anisotropy, perpendicular electric field, and Zeeman effect, consists of the spin-polarized ferromagnetic (F), canted antiferromagnetic (CAF), and partially (PLP) and fully (FLP) layer-polarized phases. We address the edge transport properties of the phases. Comparing our findings with the recent data on suspended dual-gated devices, we conclude that the insulating $\nu =0$ state realized in bilayer graphene at lower electric field is the CAF phase. We also predict a continuous and a sharp insulator-metal phase transition upon tilting the magnetic field from the insulating CAF and FLP phases, respectively, to the F phase with metallic edge conductance $2e^2/h$, which could be within the reach of available fields and could allow one to identify and distinguish the phases experimentally.