Adsorption, interaction, and diffusion of adatoms on surfaces control growth and relaxation of epitaxial nanostructures and nanofilms. Previous reports of key diffusion barriers for Pb diffusion on low-index Pb surfaces are limited in scope and accuracy. Thus, we apply density functional theory (DFT) to calculate the adsorption and diffusion energetics for a Pb adatom on Pb(111), Pb(100), and Pb(110) nanofilms with different thicknesses. We find that these quantities exhibit damped oscillatory variation with increasing film thickness. For Pb(111) films, energetics along the minimum energy path for Pb adatom diffusion between adjacent fcc and hcp sites varies significantly with film thickness, its form differing from other metal-on-metal(111) systems. For Pb(111) and Pb(100) nanofilms, diffusion barriers obtained for both adatom hopping and exchange mechanism differ significantly from previous DFT results. Hopping is favored over exchange for Pb(111), and the opposite applies for Pb(100). For Pb(110) nanofilms, Pb adatom hopping over an in-channel bridge is most facile, then in-channel exchange, then cross-channel exchange, with cross-channel hopping least favorable. We also assess lateral Pb adatom interactions, and characterize island nucleation during deposition on Pb(111).

Starting from the Luttinger-Ward functional [J. M. Luttinger and J. C. Ward, Phys. Rev. 118, 1417 (1960)] we derive an expression for the oscillatory part of the grand potential of a two-dimensional Dirac system in a magnetic field. We perform the computation for the clean and the disordered system, and we study the effect of electron-electron interactions on the oscillations. Unlike in the two-dimensional electron gas (2DEG), a finite temperature and impurity scattering also affects the oscillation frequency. Furthermore, we find that in graphene, compared to the 2DEG, additional interaction induced damping effects occur: to two-loop order electron-electron interactions do lead to an additional damping factor in the amplitude of the Lifshitz-Kosevich formula.

We measure the onset of decomposition of silicon carbide, SiC, to silicon and carbon (e.g., diamond) at high pressures and high temperatures in a laser-heated diamond-anvil cell. We identify decomposition through x-ray diffraction and multiwavelength imaging radiometry coupled with electron microscopy analyses on quenched samples. We find that B3 SiC (also known as 3C or zinc blende SiC) decomposes at high pressures and high temperatures, following a phase boundary with a negative slope. The high-pressure decomposition temperatures measured are considerably lower than those at ambient, with our measurements indicating that SiC begins to decompose at $\sim 2000$ K at 60 GPa as compared to $\sim 2800$ K at ambient pressure. Once B3 SiC transitions to the high-pressure B1 (rocksalt) structure, we no longer observe decomposition, despite heating to temperatures in excess of $\sim 3200$ K. The temperature of decomposition and the nature of the decomposition phase boundary appear to be strongly influenced by the pressure-induced phase transitions to higher-density structures in SiC, silicon, and carbon. The decomposition of SiC at high pressure and temperature has implications for the stability of naturally forming moissanite on Earth and in carbon-rich exoplanets.

Direct experimental insights into the structural and dynamical mechanisms for ferroelectric β to paraelectric α phase transition in a poled PVDF-TrFE copolymer is obtained from in situ x-ray diffraction and quasielastic neutron scattering measurements at high temperatures. It is observed that the β-to-α phase transition proceeds through two energetically distinct processes, which are identified here as the nucleation and growth of an intermediate γ phase with random skew linkages followed by a γ-to-α transition. The two energetically distinct microscopic processes can explain the stages of evolution for β-to-α phase transition observed from heat flow measurements.

We characterize the information dynamics of strongly disordered systems using a combination of analytics, exact diagonalization, and matrix product operator (MPO) simulations. More specifically, we study the spreading of quantum information in three different scenarios: thermalizing, Anderson localized, and many-body localized. We qualitatively distinguish these cases by quantifying the amount of remnant information in a local region. The nature of the dynamics is further explored by computing the propagation of mutual information with respect to varying partitions. Finally, we demonstrate that classical simulability, as captured by the magnitude of MPO truncation errors, exhibits enhanced fluctuations near the localization transition, suggesting the possibility of its use as a diagnostic of the critical point.

We study the level repulsion and its relationship with the localization length in a disordered one-dimensional quantum wire excited with monochromatic linearly polarized light and described by the Anderson-Floquet model. In the high-frequency regime, the linear scaling between the localization length divided by the length of the system and the spectral repulsion is the same as in the one-dimensional Anderson model without driving, although both quantities depend on the parameters of the external field. In the low-frequency regime the level repulsion depends mainly on the value of the amplitude of the field, and the proportionality between level repulsion and localization length is lost.

We consider the XXZ spin chain with a magnetic field gradient and study the profiles of the magnetization as well as the entanglement entropy. For a slowly varying field, it is shown that, by means of a local density approximation, the ground-state magnetization profile can be obtained with standard Bethe ansatz techniques. Furthermore, it is argued that the low-energy description of the theory is given by a Luttinger liquid with slowly varying parameters. This allows us to obtain a very good approximation of the entanglement profile using a recently introduced technique of conformal field theory in curved spacetime. Finally, the front dynamics is also studied after the gradient field has been switched off, following arguments of generalized hydrodynamics for integrable systems. While for the XX chain the hydrodynamic solution can be found analytically, the XXZ case appears to be more complicated and the magnetization profiles are recovered only around the edge of the front via an approximate numerical solution.

We use frequency-resolved x-ray microscopy to fully characterize the potential well of a magnetic vortex in a soft ferromagnetic permalloy square. The vortex core is excited with magnetic broadband pulses and simultaneously displaced with a static magnetic field. We observe a frequency increase (blueshift) in the gyrotropic mode of the vortex core with increasing bias field. Supported by micromagnetic simulations, we show that this frequency increase is accompanied by internal deformation of the vortex core. The ability to modify the inner structure of the vortex core provides a mechanism to control the dynamics of magnetic vortices.

With few systems of technological interest having been studied as extensively as elemental silicon, there currently exists a wide disparity between the number of predicted low-energy silicon polymorphs and those that have been experimentally realized as metastable at ambient conditions. We put forward an explanation for this disparity wherein the likelihood of formation of a given polymorph under near-equilibrium conditions can be estimated on the basis of mean-field isothermal-isobaric $(N,p,T)$ ensemble statistics. The probability that a polymorph will be experimentally realized is shown to depend upon both the hypervolume of that structure's potential energy basin of attraction and a Boltzmann factor weight containing the polymorph's potential enthalpy per particle. Both attributes are calculated using density functional theory relaxations of randomly generated initial structures. We find that the metastable polymorphism displayed by silicon can be accounted for using this framework to the exclusion of a very large number of other low-energy structures.

Crystallization of liquid antimony has been studied at 600 K using six density functional/molecular dynamics simulations with up to 882 atoms and three scenarios: one completely disordered sample that did not crystallize even after 570 ps, four with fixed crystalline slab templates, and one with a fixed crystalline seed. Crystallization proceeded layer-by-layer in most cases and was rapid $(\sim 36$ m/s) with templates and somewhat slower with the seed. The seed simulation shows an unusual percolation asymmetry where the crystallite grows faster in the direction normal to the zigzag planes. Changes in pair distribution functions, bond angle distributions, ring statistics, nearest-neighbor distances, and cavity volumes were monitored. Diffusion plays a minor role in the process, and the evolution of bond lengths and ring statistics supports the bond-interchange model introduced to explain the rapid crystallization of Sb-rich phase change materials.

Muon spin rotation measurements were used to investigate the spin dynamics of heterometallic ${\mathrm{Cr}}_7\mathrm{Ni}$ and ${\mathrm{Cr}}_7\mathrm{Ni}$-Cu-${\mathrm{Cr}}_7\mathrm{Ni}$ molecular clusters. In ${\mathrm{Cr}}_7\mathrm{Ni}$ the magnetic ions are arranged in a quasiplanar ring and interact via an antiferromagnetic exchange coupling constant $J$, while ${\mathrm{Cr}}_7\mathrm{Ni}$-Cu-${\mathrm{Cr}}_7\mathrm{Ni}$ is composed of two ${\mathrm{Cr}}_7\mathrm{Ni}$ linked by a bridging moiety containing one Cu ion, that induces an inter-ring ferromagnetic interaction $J^{\prime }\ll J$. The longitudinal muon relaxation rate $\lambda$ collected at low magnetic fields ${\mu }_{0}H<0.15$ Tesla, shows that the two systems present differences in spin dynamics vs temperature. While both samples exhibit a main peak in the muon relaxation rate vs temperature, at $T\sim 10$ K for ${\mathrm{Cr}}_7\mathrm{Ni}$ and $T\sim 8$ K for ${\mathrm{Cr}}_7\mathrm{Ni}$-Cu-${\mathrm{Cr}}_7\mathrm{Ni}$, the two compounds have distinct additional features: ${\mathrm{Cr}}_7\mathrm{Ni}$ shows a shoulder in $\lambda \left(T\right)$ for $T<8$ K, while ${\mathrm{Cr}}_7\mathrm{Ni}$-Cu-${\mathrm{Cr}}_7\mathrm{Ni}$ shows a flattening of $\lambda \left(T\right)$ for $T<2$ K down to temperatures as low as $T=20$ mK. The main peak of both systems is explained by a Bloembergen-Purcell-Pound (BPP)-like heuristic fitting model that takes into account of a distribution of electronic spin characteristic times for $T>5$ K, while the shoulder presented by ${\mathrm{Cr}}_7\mathrm{Ni}$ can be reproduced by a BPP function that incorporates a single electronic characteristic time theoretically predicted to dominate for $T<5$ K. The flattening of $\lambda \left(T\right)$ in ${\mathrm{Cr}}_7\mathrm{Ni}$-Cu-${\mathrm{Cr}}_7\mathrm{Ni}$ occurring at very low temperature can be tentatively attributed to field-dependent quantum effects and/or to an inelastic term in the spectral density of the electronic spin fluctuations.

Motivated by recent experiments, we investigate Josephson scanning tunneling spectroscopy in an $s$-wave superconductor. We demonstrate that the spatial oscillations in the superconducting order parameter induced by defects can be spatially imaged through local measurements of the critical Josephson current, providing unprecedented insight into the nature of superconductivity. The spatial form of the Josephson current reflects the nature of the defects, and can be used to probe defect-induced phase transitions from an $S=0$ to an $S=1/2$ ground state.

We study vortex lattices (VLs) in superconducting weak-pinning platelet-like single crystals of $\beta \text{−}{\mathrm{Bi}}_2\mathrm{Pd}$ in tilted magnetic fields with a scanning tunneling microscope. We show that vortices exit the sample perpendicular to the surface and are thus bent beneath the surface. The structure and orientation of the tilted VLs in the bulk are, for large tilt angles, strongly affected by Coulomb-type intervortex repulsion at the surface due to stray magnetic fields.

Non-Fermi-liquid (NFL) phenomena associated with correlation effects have been widely observed in the phase diagrams of unconventional superconducting families. Exploration of the correlation between the normal state NFL, regardless of its microscopic origins, and the superconductivity has been argued as a key to unveiling the mystery of the high-$T_c$ pairing mechanism. Here we systematically investigate the pressure-dependent in-plane resistivity $\left(\rho \right)$ and Hall coefficient $\left(R_H\right)$ of a high-quality 112-type Fe-based superconductor ${\mathrm{Ca}}_{1-x}{\mathrm{La}}_x{\mathrm{Fe}}_{1-y}{\mathrm{Co}}_y{\mathrm{As}}_2$ $\left(x=0.2,y=0.02\right)$. With increasing pressure, the normal-state resistivity of the studied sample exhibits a pronounced crossover from non-Fermi-liquid to Fermi-liquid behaviors. Accompanied with this crossover, $T_c$ is gradually suppressed. In parallel, the extremum in the Hall coefficient $R_H\left(T\right)$ curve, possibly due to anisotropic scattering induced by spin fluctuations, is also gradually suppressed. The symbiosis of NFL and superconductivity implies that these two phenomena are intimately related. Further study on the pressure-dependent upper critical field reveals that the two-band effects are also gradually weakened with increasing pressure and reduced to the one-band Werthamer-Helfand-Hohenberg limit in the low-$T_c$ regime. Overall, our paper supports the picture that NFL, multigap, and extreme $R_H\left(T\right)$ are all of the same magnetic origin, i.e., the spin fluctuations in the 112 iron arsenide superconductors.

We improve the density-matrix renormalization group (DMRG) evaluation of the Kubo formula for the zero-temperature linear conductance of one-dimensional correlated systems. The dynamical DMRG is used to compute the linear response of a finite system to an applied ac source-drain voltage; then the low-frequency finite-system response is extrapolated to the thermodynamic limit to obtain the dc conductance of an infinite system. The method is demonstrated on the one-dimensional spinless fermion model at half filling. Our method is able to replicate several predictions of the Luttinger liquid theory such as the renormalization of the conductance in a homogeneous conductor, the universal effects of a single barrier, and the resonant tunneling through a double barrier.

We report absorption spectra of the 7.3- and 11.3-nm Co nanolayers and emission of a structured Co nanolayer. The structure contains a 7.3-nm Co nanolayer covering a $25\times 25\mathrm{m}{\mathrm{m}}^2$ fused silica substrate, with a thicker 11.3-nm Co track in the middle of the substrate. We report that the radiation energy absorbed by the entire Co nanolayer is transferred to the thicker nanotrack. The transferred energy is reemitted by the track, with the emission spectra containing well-defined emission bands, strongly dependent on the excitation wavelength. We report that the bands appearing in the emission spectra of the nanotrack correspond to the transitions from the higher electronic excited states of the nanotrack to its first excited state. We therefore identify the observed emission as the superemission of the Co nanotrack. The superemission quantum yield is dependent on the excitation wavelength, decreasing at higher excitation energies. We propose a theoretical model that explains the results obtained. The model analysis produced estimates of several model parameters.

We study the ground states of two-dimensional lattice bosons in an artificial gauge field. Using state-of-the-art density matrix renormalization group (DMRG) simulations we obtain the zero-temperature phase diagram for hard-core bosons at densities $n_b$ with flux $n_{\varphi }$ per unit cell, which determines a filling $\nu =n_b/n_{\varphi }$. We find the bosonic Jain sequence $[\nu =p/(p+1\left)\right]$ states, in particular, a bosonic integer quantum Hall phase at $\nu =2$, are fairly robust in the hard-core boson limit, In addition to identifying Hamiltonians whose ground states realize these phases, we discuss their preparation, beginning from independent chains, and ramping up interchain couplings. Using time-dependent DMRG simulations, these are shown to reliably produce states close to the ground state for experimentally relevant system sizes. Our proposal only utilizes existing experimental capabilities.

The dynamic polarization of nuclear spins by photoexcited electrons is studied in a high quality GaAs/AlGaAs quantum well. We find a surprisingly high efficiency of the spin transfer from the electrons to the nuclei as reflected by a maximum nuclear field of 0.9 T in a tilted external magnetic field of 1 T strength only. This high efficiency is due to a low leakage of spin out of the polarized nuclear system, because mechanisms of spin relaxation other than the hyperfine interaction are strongly suppressed, leading to a long nuclear relaxation time of up to 1000 s. A key ingredient to that end is the low impurity concentration inside the heterostructure, while the electrostatic potential from charged impurities in the surrounding barriers becomes screened through illumination by which the spin relaxation time is increased compared to keeping the system in the dark. This finding indicates a strategy for obtaining high nuclear spin polarization as required for long-lasting carrier spin coherence.

The design of electrically driven quantum dot devices for quantum optical applications asks for modeling approaches combining classical device physics with quantum mechanics. We connect the well-established fields of semiclassical semiconductor transport theory and the theory of open quantum systems to meet this requirement. By coupling the van Roosbroeck system with a quantum master equation in Lindblad form, we introduce a new hybrid quantum-classical modeling approach, which provides a comprehensive description of quantum dot devices on multiple scales: it enables the calculation of quantum optical figures of merit and the spatially resolved simulation of the current flow in realistic semiconductor device geometries in a unified way. We construct the interface between both theories in such a way, that the resulting hybrid system obeys the fundamental axioms of (non)equilibrium thermodynamics. We show that our approach guarantees the conservation of charge, consistency with the thermodynamic equilibrium and the second law of thermodynamics. The feasibility of the approach is demonstrated by numerical simulations of an electrically driven single-photon source based on a single quantum dot in the stationary and transient operation regime.