In this Letter we discuss physical mechanisms for delocalization of the magnetic field of the Abrikosov vortex in superconductors in the presence of planar defects of various electronic transparency. The resulting strong perturbation of the supercurrent can significantly affect the local flux measurements and mimic the vortices that carried only part of a flux quantum.

The de Haas–van Alphen (dHvA) oscillations are oscillations in the magnetization as a function of the inverse magnetic field. These oscillations are usually considered to be a property of the Fermi surface and, hence, a metallic property. Recently, however, such oscillations have been shown to arise, both experimentally and theoretically, in certain insulators which have a narrow gap and an inverted band structure. In this Letter, we develop a theory to study the effect of many-body interactions on these unconventional oscillations. We consider a weak interaction, focusing on the effect of renormalization of the quasiparticle spectrum on these oscillations. We find that the interaction has an unusual effect: Unlike in metals, in a certain regime the amplitude of oscillations may be enhanced substantially, both at zero and nonzero temperatures, even when the interaction is perturbatively weak.

We report the design and observation of an ideal weak topological insulator in a quasi-one-dimensional bismuth halide, ${\mathrm{Bi}}_4{\mathrm{I}}_{1.2}{\mathrm{Br}}_{2.8}$. Via angle-resolved photoemission spectroscopy, we identify that ${\mathrm{Bi}}_4{\mathrm{I}}_{1.2}{\mathrm{Br}}_{2.8}$ hosts topological surface states on the ${\left(100\right)}^{\prime }$ side surface in the form of two anisotropic $\pi$-offset Dirac cones while topologically dark on the (001) top surface. The results fully determine a unique side-surface Hamiltonian and thereby identify two pairs of nondegenerate helical saddle points. The fact that both the surface Dirac and helical saddle points are in the global bulk band gap of 195 meV suggests the potential of this system to be a fertile ground for topological many-body physics.

We report a comprehensive experimental investigation of the phase diagram of ammonia hemihydrate (AHH) in the range of 2–30 GPa and 300–700 K, based on Raman spectroscopy and x-ray diffraction experiments and visual observations. Four solid phases, denoted AHH-II, DIMA, $p\mathrm{bcc}$, and $q\mathrm{bcc}$, are present in this domain, one of which, AHH-$q\mathrm{bcc}$ was discovered in this work. We show that, unlike previously thought, the body-centered cubic (bcc) phase obtained on heating AHH-II below 10 GPa, denoted here as AHH-$p\mathrm{bcc}$, is distinct from the DIMA phase, although both present the same bcc structure and O/N positional disorder. Our results actually indicate that AHH-$p\mathrm{bcc}$ is a plastic form of DIMA, characterized by free molecular rotations. AHH-$q\mathrm{bcc}$ is observed in the intermediate $P-T$ range between AHH-II and DIMA. It presents a complex x-ray pattern reminiscent of the “quasibcc” structures that have been theoretically predicted, although none of these structures is consistent with our data. The transition lines between all solid phases as well as the melting curve have been mapped in detail, showing that (1) the new $q\mathrm{bcc}$ phase is the stable one in the intermediate $P-T$ range 10–19 GPa, 300–450 K, although the II-$q\mathrm{bcc}$ transition is kinetically hindered for $T<450$ K, and II directly transits to DIMA in a gradual fashion from 25 to 35 GPa at 300 K. (2) The stability domain of $q\mathrm{bcc}$ shrinks above 450 K and eventually terminates at a $p\mathrm{bcc}$-qbcc-DIMA triple point at 21.5 GPa-630 K. (3) A direct and reversible transition occurs between AHH-$p\mathrm{bcc}$ and DIMA above 630 K. (4) The $p\mathrm{bcc}$ solid stability domain extends up to the melting line above 3 GPa, and a II-$p\mathrm{bcc}$-liquid triple point is identified at 3 GPa-320 K.

This paper reports on the hysteresis and frequency tuning (electrical and magnetic) of the Bragg resonance in the spectrum of spin waves in a multiferroic structure based on YIG (100 nm thick) and HZO (10 nm thick) with a periodic modulation of parameters. The resonance can be tuned in a wide frequency range of 1–4 GHz by a magnetic field $H$ and in a narrow frequency range of $\sim 3$ MHz by an electric field $E$. Electrical tuning was carried out due to a combination of the magnetostriction of the ferromagnetic layer and the piezoelectric effect in the ferroelectric due to mechanical coupling between the layers. The direction of the resonance shift caused by the electric field changed at the coercive field, and the alteration characteristic is of “butterfly” type.

Magnonics, an emerging field of magnetism, studies spin waves (SWs) in nanostructures, with an aim towards possible applications. As information may be eventually transmitted with efficiency stored in the phase and amplitude of spin waves, a topic of interest within magnonics is the propagation of SW modes. Thus understanding mechanisms that may influence SW propagation is of interest. Here the effect of localized surface geometric defects on magnetostatic surface modes propagation is studied in ferromagnetic films and semi-infinite media. Theoretical results are developed that allow one to calculate the scattering of these surface or Damon-Eshbach (DE) modes. A Green's-extinction theorem extension is used to determine the scattering of incident surface modes through the determination of phase shifts of associated modes that are symmetric and antisymmetric under inversion in the same geometry with geometric defects. Choosing localized symmetric depressions as geometric defects, scattering transmission coefficients are determined that show perfect transmission at specific frequencies or wavelengths that we associate with resonances in the system: they do occur when appropriate fractions of the incoming wavelength “fit” with the approximate depression's sizes, i.e., depressions are effectively similar to “potential wells.” Interestingly the system also shows the appearance of localized modes in the depression regions, with associated discrete frequencies immersed in the continuum spectrum of these surface DE modes. These localized modes have a short wavelength content and appear similarly in semi-infinite surfaces with depressions. The latter indicates that these types of scattering effects should appear in all surfaces with roughness or more pronounced geometric defects.

The pairing symmetry of superconducting state is a critical topic in the realm of topological superconductivity. However, the pairing symmetry of the $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ family, wherein $A=\mathrm{K},\mathrm{Rb},\mathrm{Cs}$, remains indeterminate. To address this issue, we formulate an effective model on the kagome lattice to describe topological superconducting states featuring chiral charge density waves. Through this model, we explore the topological phase diagrams and thermal Hall conductivity under various parameters, with and without spin-orbit coupling. Our analysis reveals that the disparities in thermal Hall conductivity curves among different pairing symmetry states are safeguarded by the topology resulting from the interplay of spin-orbital coupling and superconductivity. Remarkably, this theoretical prediction can potentially enable the differentiation of various superconducting pairing symmetry states in materials via experimental measurements of thermal Hall conductivity curves.

The upper critical field of multiband superconductors can be an essential quantity to unravel the nature of superconducting pairing and its interplay with the electronic structure. Here we experimentally map out the complete upper critical field phase diagram of FeSe for different magnetic field orientations at temperatures down to $0.3\mathrm{K}$ using both resistivity and torque measurements. The temperature dependence of the upper critical field reflects that of a multiband superconductor and requires a two-band description in the clean limit with band coupling parameters favoring interband over intraband interactions. Despite the relatively small Maki parameter in FeSe of $\alpha \sim 1.6$, the multiband description of the upper critical field is consistent with the stabilization of a Fulde-Ferrell-Larkin-Ovchinnikov state below $T/T_{\mathrm{c}}\sim 0.3$. We find that the anomalous behavior of the upper critical field is linked to a departure from the single-band picture, and FeSe provides a clear example of where multiband effects and the strong anisotropy of the superconducting gap need to be taken into account.

This work investigates the out-of-equilibrium dynamics of dipole and higher-moment-conserving systems with long-range interactions, drawing inspiration from trapped ion experiments in strongly tilted potentials. We introduce a hierarchical sequence of multipole-conserving models characterized by power-law decaying couplings. Although the moments are always globally conserved, adjusting the power-law exponents of the couplings induces various regimes in which only a subset of multipole moments are effectively locally conserved. We examine the late-time hydrodynamics analytically and numerically using an effective classical framework, uncovering a rich dynamical phase diagram that includes subdiffusion, conventional diffusion, and Lévy flights. Our results are unified in an analytic reciprocal rule that captures the nested hierarchy of hydrodynamics in multipole conserving systems where only a subset of the moments are locally conserved. Moreover, we extend our findings to higher dimensions and explore the emergence of long timescales, reminiscent of prethermal regimes, in systems with low charge density. Lastly, we corroborate our results through state-of-the-art numerical simulations of a fully quantum long-range dipole-conserving system and discuss their relevance to trapped-ion experimental setups.

We study the plaquette valence bond solid phase in an XXZ-type spin-1/2 model in the kagome lattice. The low-energy theory for this phase is a U(1) lattice gauge theory on the honeycomb lattice. We find that there is an emergent 1-form U(1) symmetry at low energy and there is a mixed anomaly. We also show that this 1-form symmetry restricts the longitudinal dynamical structure factor and leads to the selection rule relating to the vanishing intensity along some high-symmetry momentum paths (e.g., the $\mathrm{\Gamma }\text{−}M$ path). Since this emergent 1-form symmetry is robust in the presence of local UV perturbation, the selection rule will also apply to the model which is obtained by perturbing the classical limit of our model.

We observe radiative recombination from an electron-hole liquid (EHL) in a thin film of $FA\mathrm{Pb}{\mathrm{Br}}_3$, a metal halide perovskite used in transparent photovoltaics and light emitters. Photoluminescence (PL) at low excitation intensity and low temperatures only shows the free-exciton (FE) signal. As the excitation intensity increases, two additional signals in PL emerge: the electron-hole plasma (EHP) and the EHL recombination bands. For both the FE-EHP and the EHP-EHL phase transitions, a critical carrier density is established and a phase diagram is presented.

Driven-dissipative condensates, such as those formed from polaritons, expose how the coherence of Bose-Einstein condensates evolves far from equilibrium. We consider the phase and frequency ordering in the steady-states of a one-dimensional lattice of condensates, described by a coupled oscillator model with nonodd couplings, including both time-dependent noise and a static random potential. We present numerical results for the phase and frequency distributions, and discuss them in terms of the Kardar-Parisi-Zhang equation and the physics of spacetime vortices. We find that the nucleation of spacetime vortices causes the breakdown of the single-frequency steady state and produces a variation in the frequency with position. Such variation would provide an experimental signature of spacetime vortices. More generally, our results expose the nature of synchronization in oscillator chains with nonodd couplings, random frequencies, and noise.

We develop here a theory of the electronic properties of a finite number of valence holes in gated ${\text{WSe}}_{\text{2}}$ quantum dots, considering the influence of spin, valley, electronic orbitals, and many-body interactions. The single-particle wave functions are constructed by combining the spin-up and spin-down states of the highest valence bulk bands employing a multi-million-atom ab initio based tight-binding model solved in the wave-vector space, allowing to study up to 100-nm-radius quantum dots atomistically. The effects of the many-body interactions are determined using the configuration interaction technique, applied up to $N=6$ holes occupying up to six electronic shells with 42 orbitals. Our results show that $N=2$ holes are in the valley and spin antiferromagnetic ground state, independent of the interaction strength and the quantum dot size. However, we predict that a higher number of holes can undergo a transition to spontaneously broken symmetry valley- and spin-polarized ferromagnetic phases, highlighting the interplay between the many-body effects and the quantum dot lateral size and confining potential depth.

The quantum dynamics of correlated fermionic or bosonic many-body systems following external excitation can be successfully studied using nonequilibrium Green functions (NEGFs) or reduced density matrix methods. Approximations are introduced via a proper choice of the many-particle self-energy or decoupling of the BBGKY-hierarchy, respectively. These approximations are based on Feynman's diagram approaches or on cluster expansions into single-particle and correlation operators. In a recent paper [E. Schroedter, J.-P. Joost, and M. Bonitz, Condens. Matter Phys. 25, 23401 (2022)] we presented a different approach in which, instead of equations of motion for the many-particle NEGF (or density operators), equations for the correlation functions of fluctuations are analyzed. In particular, we derived the stochastic $GW$ and polarization approximations that are closely related to the nonequilibrium $GW$ approximation. Here, we extend this approach to the computation of two-time observables depending on the specific ordering of the underlying operators. In particular, we apply this extension to the calculation of the density correlation function and dynamic structure factor of correlated Hubbard clusters in and out of equilibrium.

Monolayer germanium sulfide (GeS) has gained significant attention for its exceptional anisotropic electronic conductance, notable excitonic effects, and wide range of applications. In this study we used density functional theory, the nonequilibrium Green's function, and many-body perturbation theory to investigate electronic transport properties and exciton radiative lifetime of single-layer germanium sulfide. Our theoretical findings showed that applying up to 8% compressive strain yielded a nearly threefold increase in carrier mobility and dramatically enhanced device's current intensity. Moreover, we observed that strain engineering allowed for fine-tuning of the electron-hole recombination time. At 6% tensile strain, the effective radiative lifetime was as short as 0.81 ps, which is 4 times faster than the intrinsic case and 24 times faster than at 8% compressive strain. These results highlight the potential of strain engineering to customize the electronic and optical properties of GeS monolayer for specific electronic, optoelectronic, and photovoltaic applications.

We propose the spin-swapping effect for an exchange magnon spin current in a perpendicularly magnetized ferromagnetic medium with in-plane anisotropy on the surface. The excitation of a magnon current flowing along an in-plane direction with an out-of-plane spin polarization leads to the generation of an exchange spin current propagating along the out-of-plane direction, characterized by an in-plane spin polarization. The resulting exchange magnon spin current can induce an inverse spin Hall voltage of microvolts. The exchange coupling at the interface between regions with different magnetic anisotropies plays a crucial role in generating the spin-swapping effect. This is in contrast to the recently reported spin swapping for an exchange spin current in a canted antiferromagnet due to the Dzyaloshiskii-Moriya interaction.

Antiferromagnetic (AFM) materials are robust to external magnetic perturbation due to the absence of net magnetic moment, which also eliminates spin splitting in the band structures. Altermagnetism provides a route to resurrect the spin-split bands in a collinear symmetry-compensated antiferromagnet with special magnetic space group. Here we propose an alternative mechanism to achieve spin splitting in a two-dimensional (2D) Janus A-type AFM material. Since the built-in electric field intrinsic to the Janus structure creates a layer-dependent electrostatic potential, the electronic bands in different layers stagger to produce the spin-splitting effect, resulting in the electric potential difference antiferromagnetism (EPD-AFM). We demonstrate that Janus monolayer ${\mathrm{Mn}}_2\mathrm{ClF}$ is a candidate material for achieving EPD-AFM by first-principles calculations. We further show that the spin splitting in EPD-AFM can be tuned by the piezoelectric effect. This work reveals a different class of 2D AFM materials with spin polarization.

We study the energies and optical spectra of excitons in twisted bilayers of anisotropic van der Waals semiconductors exhibiting moiré patterns, taking phosphorene as a case study. Leveraging the scale separation between the moiré length scale and the exciton Bohr radii, we introduce a continuous model for Wannier excitons that incorporates the spatial variation of their binding energies. Our calculations reveal a dimensionality crossover for the exciton states, driven by the combined dispersion and moiré potential anisotropies, from quantum dot lattices at twist angles $\theta <{\theta }_{*}$, to quantum wire arrays at $\theta >{\theta }_{*}$, with crossover angle ${\theta }_{*}=4^{\circ }$. We identify clear signatures of this dimensionality crossover in the twist angle dependence of the excitonic absorption spectra, which allows experimental verification of our theoretical results through standard optical measurements. Our results establish two-dimensional anisotropic moiré semiconductors as versatile solid-state platforms for exploring bosonic correlations across different dimensionalities.

We investigate the effect of an additional modulation parameter $\delta$ on the mobility properties of quasiperiodic lattices described by a generalized Ganeshan-Pixley-Das Sarma model with two onsite modulation parameters. For the case with bounded quasiperiodic potential, we unveil the existence of self-duality relation, independent of $\delta$. By applying Avila's global theory, we analytically derive Lyapunov exponents in the whole parameter space, which enables us to determine mobility edges or anomalous mobility edges exactly. Our analytical results indicate that the mobility edge equation is described by two curves and their intersection with the spectrum gives the true mobility edge. Tuning the strength parameter $\delta$ can change the spectrum of the quasiperiodic lattice, and thus engineers the mobility of quasiperiodic systems, giving rise to completely extended, partially localized, and completely localized regions. For the case with unbounded quasiperiodic potential, we also obtain the analytical expression of the anomalous mobility edge, which separates localized states from critical states. By increasing the strength parameter $\delta$, we find that the critical states can be destroyed gradually and finally vanish.