We show that the space-charge dynamics of high-intensity beams in the plane perpendicular to the magnetic field in cyclotrons is described by the two-dimensional Euler equations for an incompressible fluid. This analogy with fluid dynamics gives a unified and intuitive framework to explain the beam spiraling and beam breakup behavior observed in experiments and in simulations. Specifically, we demonstrate that beam breakup is the result of a classical instability occurring in fluids subject to a sheared flow. We give scaling laws for the instability and predict the nonlinear evolution of beams subject to it. Our work suggests that cyclotrons may be uniquely suited for the experimental study of shear layers and vortex distributions that are not achievable in Penning-Malmberg traps.

We consider periodically driven arrays of weakly coupled wires with conduction and valence bands of Rashba type and study the resulting Floquet states. This nonequilibrium system can be tuned into nontrivial phases such as topological insulators, Weyl semimetals, and dispersionless zero-energy edge mode regimes. In the presence of strong electron-electron interactions, we generalize these regimes to the fractional case, where elementary excitations have fractional charges $e/m$ with $m$ being an odd integer.

We report an atomic-scale characterization of ${\mathrm{ZrTe}}_5$ by using scanning tunneling microscopy. We observe a bulk band gap of $\sim 80\mathrm{meV}$ with topological edge states at the step edge and, thus, demonstrate that ${\mathrm{ZrTe}}_5$ is a two-dimensional topological insulator. We also find that an applied magnetic field induces an energetic splitting of the topological edge states, which can be attributed to a strong link between the topological edge states and bulk topology. The relatively large band gap makes ${\mathrm{ZrTe}}_5$ a potential candidate for future fundamental studies and device applications.

We report on a general principle using interlayer exchange coupling to extend the regime of chiral magnetic films in which stable or metastable magnetic Skyrmions can appear at a zero magnetic field. We verify this concept on the basis of a first-principles model for a Mn monolayer on a W(001) substrate, a prototype chiral magnet for which the atomic-scale magnetic texture is determined by the frustration of exchange interactions, impossible to unwind by laboratory magnetic fields. By means of ab initio calculations for the $\mathrm{Mn}/{\mathrm{W}}_m/{\mathrm{Co}}_n/\mathrm{Pt}/\mathrm{W}(001)$ multilayer system we show that for certain thicknesses $m$ of the W spacer and $n$ of the Co reference layer, the effective field of the reference layer fully substitutes the required magnetic field for Skyrmion formation.

We study the low-temperature physics of the SU(2)-symmetric spin-$1/2$ Heisenberg antiferromagnet on a pyrochlore lattice and find “fingerprint” evidence for the thermal spin-ice state in this frustrated quantum magnet. Our conclusions are based on the results of bold diagrammatic Monte Carlo simulations, with good convergence of the skeleton series down to the temperature $T/J=1/6$. The identification of the spin-ice state is done through a remarkably accurate microscopic correspondence for the static structure factor between the quantum Heisenberg, classical Heisenberg, and Ising models at all accessible temperatures, and the characteristic bowtie pattern with pinch points observed at $T/J=1/6$. The dynamic structure factor at real frequencies (obtained by the analytic continuation of numerical data) is consistent with diffusive spinon dynamics at the pinch points.

We report the first observation of two-phonon quantum coherences in a semiconductor. Two-dimensional terahertz (THz) spectra recorded with a sequence of three THz pulses display strong two-phonon signals, clearly distinguished from signals due to interband two-photon absorption and electron tunneling. The two-phonon coherences originate from impulsive off-resonant excitation in the nonperturbative regime of light-matter interaction. A theoretical analysis provides the relevant Liouville pathways, showing that nonlinear interactions using the large interband dipole moment generate stronger two-phonon excitations than linear interactions.

Electron spin plays important roles in determining the physical and chemical properties of matter. However, measurements of electron spin are of poor quality, impeding the development of material sciences, because the spin polarimeter has a low efficiency. Here, we show an imaging-type exchange-scattering spin polarimeter with 6786 channels and an $8.5\times {10}^{-3}$ single channel efficiency. As a demonstration, the fine spin structure of the electronic states in bismuth (111) is investigated, for which strong Rashba-type spin splitting behavior is seen in both the bulk and surface states. This improvement paves the way to study novel spin related phenomena with unprecedented accuracy.

We consider a thought experiment where two distinct species of 2D particles in a perpendicular magnetic field interact via repulsive potentials. If the magnetic field and the interactions are strong enough, one type of particles forms a Laughlin state and the other type couples to Laughlin quasiholes. We show that, in this situation, the motion of the second type of particles is described by an effective Hamiltonian, corresponding to the magnetic gauge picture for noninteracting anyons. The argument is in accord with, but distinct from, the Berry phase calculation of Arovas, Schrieffer, and Wilczek. It suggests possibilities to observe the influence of effective anyon statistics in fractional quantum Hall systems.

Based on quantum statistical mechanics and microscopic quantum dynamics, we prove Planck’s and Kelvin’s principles for macroscopic systems in a general and realistic setting. We consider a hybrid quantum system that consists of the thermodynamic system, which is initially in thermal equilibrium, and the “apparatus” which operates on the former, and assume that the whole system evolves autonomously. This provides a satisfactory derivation of the second law for macroscopic systems.

Results on two-particle angular correlations for charged particles produced in $pp$ collisions at a center-of-mass energy of 13 TeV are presented. The data were taken with the CMS detector at the LHC and correspond to an integrated luminosity of about $270{\mathrm{nb}}^{-1}$. The correlations are studied over a broad range of pseudorapidity ($|\eta |<2.4$) and over the full azimuth ($\varphi$) as a function of charged particle multiplicity and transverse momentum ($p_{\mathrm{T}}$). In high-multiplicity events, a long-range ($|\mathrm{\Delta }\eta |>2.0$), near-side ($\mathrm{\Delta }\varphi \approx 0$) structure emerges in the two-particle $\mathrm{\Delta }\eta$–$\mathrm{\Delta }\varphi$ correlation functions. The magnitude of the correlation exhibits a pronounced maximum in the range $1.0<p_{\mathrm{T}}<2.0\mathrm{GeV}/c$ and an approximately linear increase with the charged particle multiplicity, with an overall correlation strength similar to that found in earlier $pp$ data at $\sqrt{s}=7\mathrm{TeV}$. The present measurement extends the study of near-side long-range correlations up to charged particle multiplicities $N_{\mathrm{ch}}\sim 180$, a region so far unexplored in $pp$ collisions. The observed long-range correlations are compared to those seen in $pp$, $p\mathrm{Pb}$, and PbPb collisions at lower collision energies.

There is considerable fundamental and applicative interest in obtaining nondiffractive and nondispersive spatiotemporal localized wave packets propagating in optical cubic nonlinear or Kerr media. Here, we analytically predict the existence of a novel family of spatiotemporal dark lump solitary wave solutions of the $(2+1)\mathrm{D}$ nonlinear Schrödinger equation. Dark lumps represent multidimensional holes of light on a continuous wave background. We analytically derive the dark lumps from the hydrodynamic exact soliton solutions of the $(2+1)\mathrm{D}$ shallow water Kadomtsev-Petviashvili model, inheriting their complex interaction properties. This finding opens a novel path for the excitation and control of optical spatiotemporal waveforms of hydrodynamic footprint and multidimensional optical extreme wave phenomena.

We investigate the reflection of gravity-capillary surface waves by a plane vertical barrier. The size of the meniscus is found to strongly affect reflection: the energy of the reflected wave with a pinned contact line is around twice the one corresponding to a fully developed meniscus. To perform these measurements, a new experimental setup similar to an acousto-optic modulator is developed and offers a simple way to measure the amplitude, frequency and direction of propagation of surface waves.

Tokamak experiments at near-unity aspect ratio $A\lesssim 1.2$ offer new insights into the self-organized $H$-mode plasma confinement regime. In contrast to conventional $A\sim 3$ plasmas, the $L\text{−}H$ power threshold $P_{LH}$ is $\sim 15\times$ higher than scaling predictions, and it is insensitive to magnetic topology, consistent with modeling. Edge localized mode (ELM) instabilities shift to lower toroidal mode numbers as $A$ decreases. These ultralow-$A$ operations enable heretofore inaccessible $J_{\mathrm{edge}}(R,t)$ measurements through an ELM that show a complex multimodal collapse and the ejection of a current-carrying filament.

We explore the correlation between a boson peak and structural relaxation in a typical metallic glass. Consistent with enthalpy recovery, a boson peak shows a memory effect in an aging-and-scan procedure. Single-step isothermal aging produces a monotonic decrease of enthalpy and boson peak intensity; for double-step isothermal aging, both enthalpy and boson peak intensity experience, coincidently, an incipient increase to a maximum and a subsequent decrease toward the equilibrium state. Our results indicate a direct link between slow structural relaxation and fast boson peak dynamics, which presents a profound understanding of the two dynamic behaviors in glass.

By numerical simulations and analytical studies, we show that the phenomenon of microwave-induced resistance oscillations can be understood as a classical memory effect caused by recollisions of electrons with scattering centers after a cyclotron period. We develop a Drude-like approach to magnetotransport in the presence of a microwave field, taking into account memory effects, and find an excellent agreement between numerical and analytical results, as well as a qualitative agreement with experiment.

Measurements of the Hall and dissipative conductivity of a strained Ge quantum well on a $\mathrm{SiGe}/(001)\mathrm{Si}$ substrate in the quantum Hall regime are reported. We analyze the results in terms of thermally activated quantum tunneling of carriers from one internal edge state to another across saddle points in the long-range impurity potential. This shows that the gaps for different filling fractions closely follow the dependence predicted by theory. We also find that the estimates of the separation of the edge states at the saddle are in line with the expectations of an electrostatic model in the lowest spin-polarized Landau level (LL), but not in the spin-reversed LL where the density of quasiparticle states is not high enough to accommodate the carriers required.

We theoretically consider the superconductivity of the topological half-Heusler semimetals YPtBi and LuPtBi. We show that pairing occurs between $j=3/2$ fermion states, which leads to qualitative differences from the conventional theory of pairing between $j=1/2$ states. In particular, this permits Cooper pairs with quintet or septet total angular momentum, in addition to the usual singlet and triplet states. Purely on-site interactions can generate $s$-wave quintet time-reversal symmetry-breaking states with topologically nontrivial point or line nodes. These local $s$-wave quintet pairs reveal themselves as $d$-wave states in momentum space. Furthermore, due to the broken inversion symmetry in these materials, the $s$-wave singlet state can mix with a $p$-wave septet state, again with topologically stable line nodes. Our analysis lays the foundation for understanding the unconventional superconductivity of the half-Heuslers.