Mechanical strain can lead to a synthetic gauge field that controls the dynamics of electrons in graphene sheets as well as light in photonic crystals. Here, we show how to engineer an analogous synthetic gauge field for lattice vibrations. Our approach relies on one of two strategies: shearing a honeycomb lattice of masses and springs or patterning its local material stiffness. As a result, vibrational spectra with discrete Landau levels are generated. Upon tuning the strength of the gauge field, we can control the density of states and transverse spatial confinement of sound in the metamaterial. We also show how this gauge field can be used to design waveguides in which sound propagates with robustness against disorder as a consequence of the change in topological polarization that occurs along a domain wall. By introducing dissipation, we can selectively enhance the domain-wall-bound topological sound mode, a feature that may potentially be exploited for the design of sound amplification by stimulated emission of radiation (SASER, the mechanical analogs of lasers).

The ability to control the plastic deformation of amorphous metals is based on the capacity to influence the percolation of the shear transformation zones (STZs). Despite the recent research progress, the mechanism of STZ self-assembly has so far remained elusive. Here, we identify the structural perturbation generated by an STZ in the surrounding material and show how such a perturbation triggers the activation of the neighboring STZ. The mechanism is based on the autocatalytic generation of successive strong strain and rotation fields, leading to STZ percolation and, ultimately, to the formation of a shear band.

We show that Be exhibits amphoteric behavior in GaN, involving switching between substitutional and interstitial positions in the lattice. This behavior is observed through the dominance of ${\mathrm{Be}}_{\mathrm{Ga}}$ in the positron annihilation signals in Be-doped GaN, while the emergence of $V_{\mathrm{Ga}}$ at high temperatures is a consequence of the Be impurities being driven to interstitial positions. The similarity of this behavior to that found for Na and Li in ZnO suggests that this could be a universal property of light dopants substituting for heavy cations in compound semiconductors.

The nuclear matrix elements for the spin operator and the momentum quadrupole operator are important for the interpretation of precision atomic physics experiments that search for violations of local Lorentz and $CPT$ symmetry and for new spin-dependent forces. We use the configuration-interaction nuclear shell model and self-consistent mean-field theory to calculate the momentum matrix elements for ${}^{21}\mathrm{Ne}$, ${}^{23}\mathrm{Na}$, ${}^{133}\mathrm{Cs}$, ${}^{173}\mathrm{Yb}$, and ${}^{201}\mathrm{Hg}$. We show that these momentum matrix are strongly suppressed by the many-body correlations, in contrast to the well-known enhancement of the spatial quadrupole nuclear matrix elements.

A free surface of a dilute ${}^3\mathrm{He}\text{−}{}^4\mathrm{He}$ liquid mixture is a unique system where two Fermi liquids with distinct dimensions coexist: a three-dimensional (3D) ${}^3\mathrm{He}$ Fermi liquid in the bulk and a two-dimensional (2D) ${}^3\mathrm{He}$ Fermi liquid at the surface. To investigate a novel effect generated by the interaction between the two Fermi liquids, the mobility of a Wigner crystal of electrons formed on the free surface of the mixture is studied. An anomalous enhancement of the mobility, compared with the case where the 3D and 2D systems do not interact with each other, is observed. The enhancement is explained by the nontrivial reflection of 3D quasiparticles from the surface covered with the 2D ${}^3\mathrm{He}$ system.

The first Weyl semimetal was recently discovered in the NbP class of compounds. Although the topology of these novel materials has been identified, the surface properties are not yet fully understood. By means of scanning tunneling spectroscopy, we find that NbP’s (001) surface hosts a pair of Dirac cones protected by mirror symmetry. Through our high-resolution spectroscopic measurements, we resolve the quantum interference patterns arising from these novel Dirac fermions and reveal their electronic structure, including the linear dispersions. Our data, in agreement with our theoretical calculations, uncover further interesting features of the Weyl semimetal NbP’s already exotic surface. Moreover, we discuss the similarities and distinctions between the Dirac fermions here and those in topological crystalline insulators in terms of symmetry protection and topology.

Combining ultrahigh sensitivity, spatial resolution, and the capability to resolve chemical information, tip-enhanced Raman spectroscopy (TERS) is a powerful tool to study molecules or nanoscale objects. Here we show that TERS can also be a powerful tool in studying two-dimensional materials. We have achieved a ${10}^9$ Raman signal enhancement and a 0.5 nm spatial resolution using monolayer silicene on Ag(111) as a prototypical 2D material system. Because of the selective enhancement on Raman modes with vertical vibrational components in TERS, our experiment provides direct evidence of the origination of Raman modes in silicene. Furthermore, the ultrahigh sensitivity of TERS allows us to identify different vibrational properties of silicene phases, which differ only in the bucking direction of the Si-Si bonds. Local vibrational features from defects and domain boundaries in silicene can also be identified.

Using a variational Monte Carlo method, we study the competition of strong electron-electron and electron-phonon interactions in the ground state of the Holstein-Hubbard model on a square lattice. At half filling, an extended intermediate metallic or weakly superconducting (SC) phase emerges, sandwiched between antiferromagnetic and charge order (CO) insulating phases. By carrier doping into the CO insulator, the SC order dramatically increases for strong electron-phonon couplings, but is largely hampered by wide phase separation (PS) regions. Superconductivity is optimized at the border to the PS.

Modulation and $\delta$-doping strategies, in which atomically thin layers of charged dopants are precisely deposited within a heterostructure, have played enabling roles in the discovery of new physical behavior in electronic materials. Here, we demonstrate a purely structural “$\delta$-doping” strategy in complex oxide heterostructures, in which atomically thin manganite layers are inserted into an isovalent manganite host, thereby modifying the local rotations of corner-connected ${\mathrm{MnO}}_6$ octahedra. Combining scanning transmission electron microscopy, polarized neutron reflectometry, and density functional theory, we reveal how local magnetic exchange interactions are enhanced within the spatially confined regions of suppressed octahedral rotations. The combined experimental and theoretical results illustrate the potential to utilize noncharge-based approaches to “doping” in order to enhance or suppress functional properties within spatially confined regions of oxide heterostructures.

We find that the multicritical fixed point structure of the $O(N)$ models is much more complicated than widely believed. In particular, we find new nonperturbative fixed points in three dimensions ($d=3$) as well as at $N=\infty$. These fixed points come together with an intricate double-valued structure when they are considered as functions of $d$ and $N$. Many features found for the $O(N)$ models are shared by the $O(N)\otimes O(2)$ models relevant to frustrated magnetic systems.

We report the first evidence for isospin violation in $B\to K^{*}\gamma$ and the first measurement of the difference of $CP$ asymmetries between $B^{+}\to K^{*+}\gamma$ and $B^0\to K^{*0}\gamma$. This analysis is based on the data sample containing $772\times {10}^{6}B\overline{B}$ pairs that was collected with the Belle detector at the KEKB energy-asymmetric $e^{+}{e}^{-}$ collider. We find evidence for the isospin violation with a significance of $3.1\sigma$, ${\mathrm{\Delta }}_{0+}=[+6.2\pm 1.5(\text{stat})\pm 0.6(\text{syst})\pm 1.2(f_{+-}/f_{00})]\%$, where the third uncertainty is due to the uncertainty on the fraction of $B^{+}{B}^{-}$ to $B^0{\overline{B}}^0$ production in $\mathrm{\Upsilon }(4S)$ decays. The measured value is consistent with predictions of the standard model. The result for the difference of $CP$ asymmetries is $\mathrm{\Delta }{A}_{CP}=[+2.4\pm 2.8(\text{stat})\pm 0.5(\text{syst})]\%$, consistent with zero. The measured branching fractions and $CP$ asymmetries for charged and neutral $B$ meson decays are the most precise to date. We also calculate the ratio of branching fractions of $B^0\to K^{*0}\gamma$ to $B_s^0\to \varphi \gamma$.

It is shown that inertial confinement fusion targets designed with low implosion velocities can be shock-ignited using laser-plasma interaction generated hot electrons (hot-$e$’s) to obtain high energy gains. These designs are robust to multimode asymmetries and are predicted to ignite even for significantly distorted implosions. Electron shock ignition requires tens of kilojoules of hot-$e$’s which can be produced only at a large laser facility like the National Ignition Facility, with the laser-to-hot-$e$ conversion efficiency greater than 10% at laser intensities $\sim {10}^{16}\mathrm{W}/{\mathrm{cm}}^2$.

The theory of generalized hydrodynamics (GHD) was recently developed as a new tool for the study of inhomogeneous time evolution in many-body interacting systems with infinitely many conserved charges. In this Letter, we show that it supersedes the widely used conventional hydrodynamics (CHD) of one-dimensional Bose gases. We illustrate this by studying “nonlinear sound waves” emanating from initial density accumulations in the Lieb-Liniger model. We show that, at zero temperature and in the absence of shocks, GHD reduces to CHD, thus for the first time justifying its use from purely hydrodynamic principles. We show that sharp profiles, which appear in finite times in CHD, immediately dissolve into a higher hierarchy of reductions of GHD, with no sustained shock. CHD thereon fails to capture the correct hydrodynamics. We establish the correct hydrodynamic equations, which are finite-dimensional reductions of GHD characterized by multiple, disjoint Fermi seas. We further verify that at nonzero temperature, CHD fails at all nonzero times. Finally, we numerically confirm the emergence of hydrodynamics at zero temperature by comparing its predictions with a full quantum simulation performed using the NRG-TSA-abacus algorithm. The analysis is performed in the full interaction range, and is not restricted to either weak- or strong-repulsion regimes.

We observe that the growth rate of ${\mathrm{Ga}}_2{\mathrm{O}}_3$ in plasma-assisted molecular beam epitaxy can be drastically enhanced by an additional In supply. This enhancement is shown to result from a catalytic effect, namely, the rapid formation of ${\mathrm{In}}_2{\mathrm{O}}_3$, immediately followed by a transformation of ${\mathrm{In}}_2{\mathrm{O}}_3$ to ${\mathrm{Ga}}_2{\mathrm{O}}_3$ due to an In-Ga interatomic exchange. We derive a simple model that quantitatively describes this process as well as its consequences on the formation rate of ${\mathrm{Ga}}_2{\mathrm{O}}_3$. Moreover, we demonstrate that the catalytic action of ${\mathrm{In}}_2{\mathrm{O}}_3$ allows the synthesis of the metastable hexagonal phase of ${\mathrm{Ga}}_2{\mathrm{O}}_3$. Since the ${\mathrm{Ga}}_2{\mathrm{O}}_3(0001)/{\mathrm{In}}_2{\mathrm{O}}_3(111)$ interface is closely lattice matched, this novel growth mode opens a new path for the fabrication of sesquioxide heterostructures.

It has been argued that the 0.7 anomaly in quantum point contacts (QPCs) is due to an enhanced density of states at the top of the QPC barrier (the van Hove ridge), which strongly enhances the effects of interactions. Here, we analyze their effect on dynamical quantities. We find that they pin the van Hove ridge to the chemical potential when the QPC is subopen, cause a temperature dependence for the linear conductance that qualitatively agrees with experiments, strongly enhance the magnitude of the dynamical spin susceptibility, and significantly lengthen the QPC traversal time. We conclude that electrons traverse the QPC via a slowly fluctuating spin structure of finite spatial extent.