The search for a novel superconductor exhibiting a high critical temperature (high $T_c$) or even near room temperature at an accessible synthetic pressure is a persistent objective for both experimental and theoretical physicists. Here, we conduct a systematic high-throughput structure search on boron-carbon clathrates at ambient pressure and uncover two stable 1166-type superconductors, ${\mathrm{RbYbB}}_6{\mathrm{C}}_6$ and ${\mathrm{RbBaB}}_6{\mathrm{C}}_6$, both exhibiting maximum $T_c\sim 70$ K. The high-$T_c$ superconductivity in 1166-type superconductors is attributed to two key factors: an enhanced density of states at the Fermi level and the strong B-C covalent framework in boron-carbon clathrates, which enhance the electron-phonon coupling and facilitate superconductivity at temperatures near the boiling point of liquid nitrogen. These results provide a significant advancement in understanding the underlying mechanisms of superconductivity in 1166-type boron-carbon based superconductors and offer valuable avenues for the design and synthesis of advanced high-temperature superconductors at ambient conditions.

We analyze the spectral and transport properties of the interacting disordered Tavis-Cummings model at half excitation filling. We demonstrate that a Poissonian-level statistics coexists with eigenfunctions that are multifractal (extended, but nonergodic) in the Hilbert space, for all strengths of light-matter interactions. This is associated with a lack of thermalization for a local perturbation. We find that the bipartite entanglement entropy grows logarithmically with time, similarly to many-body localized systems, while the spin imbalance tends to zero for strong coupling, in analogy to ergodic phases. We show that these effects are due to the combination of finite interactions and integrability of the model. When a small integrability-breaking perturbation (nearest-neighbor hopping) is introduced, typical eigenfunctions become ergodic, seemingly turning the system into a near-perfect conductor, contrary to the single-excitation noninteracting case. We propose a realization of this model with cold atoms.

Periodically driven quantum systems host exotic phenomena that often do not have any analog in undriven systems. Floquet prethermalization and dynamical freezing of certain observables, via the emergence of conservation laws, are realized by controlling the drive frequency. Recent experimental developments in synthetic quantum matter, such as superconducting qubits and cold atoms, have opened avenues for implementing local Floquet engineering which can achieve spatially modulated quantum control of states. Here, we uncover the novel memory effects of local periodic driving in a nonintegrable spin-half staggered Heisenberg chain. For a boundary-driven protocol at the dynamical freezing frequency, we show the formation of an approximate strong zero mode, a prethermal quasilocal operator, due to the emergence of a discrete global ${\mathbb{Z}}_2$ symmetry. This is captured by constructing an accurate effective Floquet Hamiltonian using a higher-order partially resummed Floquet-Magnus expansion. The lifetime of the boundary spin can be exponentially enhanced by enlarging the set of suitably chosen driven sites. We demonstrate that in the asymptotic limit, achieved by increasing the number of driven sites, a strong zero mode emerges, where the lifetime of the boundary spin grows exponentially with system size. The nonlocal processes in the Floquet Hamiltonian play a pivotal role in the total freezing of the boundary spin in the thermodynamic limit. The novel dynamics of the boundary spin is accompanied by a rich structure of entanglement in the Floquet eigenstates where specific bipartitions yield an area-law scaling while the entanglement for random bipartitions scales as a volume-law. Our work addresses the long-standing question of the existence of a strong zero mode in a nonintegrable model and elucidates the complex nature of thermalization in locally driven systems.

We demonstrate phase control of magnons in the van der Waals antiferromagnet ${\mathrm{NiPS}}_3$ using optical excitation by polarized light. The sign of the coherent precession of spin amplitude changes upon (i) reversing the helicity of a circularly polarized pump beam, or (ii) rotating the polarization of a linearly polarized pump by $\pi /2$. Because these two excitation pathways have comparable generation efficiency, the phase of spin precession can be continuously tuned from 0 to $2\pi$ by controlling the polarization state of the pump pulse. The ability to excite magnons with a desired phase has potential applications in the design of a spin-wave phased array and ultrafast spin information processing.

Using the density-matrix renormalization group, we determine the different topological phases and low-energy excitations of a time-reversal invariant topological superconducting (TRITOPS) wire with extended $s$-wave superconductivity, Rashba spin-orbit coupling (SOC) and on-site repulsion $U$, under an externally applied Zeeman field $J$. For the case in which $J$ is perpendicular to the SOC, the model describes a chain of Shiba impurities on top of a superconductor with extended superconductor pairing. We identify the different topological phases of the model at temperature $T=0$, and in particular we study the stability of the TRITOPS phase against the Zeeman field $J$ and the chemical potential $\mu$, for different values of $U$. In the case where the magnetic field $J$ is perpendicular to the SOC axis, the pair of Kramers degenerate Majorana zero modes at the edges of the system that exist for $J=0$, remain degenerate until a critical value of the magnetic field is reached. For $J$ parallel to the SOC and up to moderate values of $U$, the fractional spin projection $\langle S_y\rangle =1/4$ at the ends, found for noninteracting wires at $U=0$, is recovered. In addition, the analytic expression that relates $\langle S_y\rangle$ with $J$ for finite noninteracting chains is shown to be universal up to moderate values of $U$.

We study a superconducting Kitaev ring pierced by a magnetic flux, with and without disorder, in a quantum ring configuration, and in a rf-SQUID one, where a weak link is present. In the rf-SQUID configuration, in the topological phase, the supercurrent shows jumps at specific values of the flux ${\mathrm{\Phi }}^{*}=\frac{hc}{e}(1/4+n)$, with $n\in \mathbb{N}$. In the thermodynamic limit ${\mathrm{\Phi }}^{*}$ are constant inside the topological phase, independently of disorder, and we analytically predict this fact using a perturbative approach in the weak-link coupling. The weak link breaks the topological ground-state degeneracy, and opens a spectral gap for $\mathrm{\Phi }\ne {\mathrm{\Phi }}^{*}$, that vanishes at ${\mathrm{\Phi }}^{*}$ with a cusp providing the current jump. Looking at the quasiparticle excitations, we see that they are Anderson localized, so they cannot carry a resistive contribution to the current, and the localization length shows a peculiar behavior at a flat-band point for the quasiparticles. In the absence of disorder, we analytically and numerically find that the chemical-potential derivative of the supercurrent logarithmically diverges at the topological-to-trivial transition, in agreement with the transition being of the second order.

Finite-depth quantum circuits preserve the long-range entanglement structure in quantum states and map between states within a gapped phase. To map between states of different gapped phases, we can use sequential quantum circuits, which apply unitary transformations to local patches, strips, or other subregions of a system in a sequential way. The sequential structure of the circuit, on the one hand, preserves entanglement area law and hence the gappedness of the quantum states. On the other hand, the circuit has generically a linear depth, hence, it is capable of changing the long-range correlation and entanglement of quantum states and the phase they belong to. In this paper, we systematically discuss the definition, basic properties, and prototypical examples of sequential quantum circuits that map product states to Greenberger-Horne-Zeilinger states, symmetry-protected topological states, intrinsic topological states, and fracton states. We discuss the physical interpretation of the power of the circuits through connection to condensation, Kramers-Wannier duality, and the notion of foliation for fracton phases.

Bicomponent magnonic crystals (BMCs) are engineered metamaterials comprised of magnetic materials with contrasting properties that offer a wide range of tunability in spin-wave (SW) dynamics, making them highly relevant for modern magnonic and spintronic devices. Herein, the magnetic configuration driven SW dynamics of BMC, having Permalloy (${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$) inclusion of circular and square shapes in ${\mathrm{Co}}_{50}{\mathrm{Fe}}_{50}$ matrix, have been extensively studied using ferromagnetic resonance spectroscopy and micromagnetic simulation. The experimentally obtained magnetic field dispersion confirms the theoretically predicted SW mode reversal. In this phenomenon, the SW mode with the highest frequency, typically excited in the region of high saturation magnetization under a higher applied bias field, undergoes a transition, becoming the mode with the lowest frequency as the applied field decreases. Furthermore, we observed mode splitting and mode merging alongside the conventional monotonic variation of SW modes with changes in the applied bias field. The numerically simulated mode profile shows the bias field dependent preferential spatial excitation of SW modes, originating from the spatial distribution of the demagnetizing field. The magnetic microstate dependent spatial distribution of the demagnetizing field leads to the creation, distortion, and annihilation of positively and negatively demagnetized channels, which act as roadways for SW propagation.

The combination of a superconductor (SC) and a topological insulator (TI) nanowire was proposed as a potential candidate for realizing Majorana zero modes (MZMs). In this study, we adopt the Schrödinger-Poisson formalism to incorporate the electrostatic environment inside the nanowire and systematically explore its topological properties. Our calculations reveal that the proximity to the SC induces a band bending effect, leading to a nonuniform potential across the TI nanowire. As a consequence, there is an upward shift of the Fermi level within the conduction band. This gives rise to the coexistence of surface and bulk states, localized in an accumulation layer adjacent to the TI-SC interface. When magnetic flux is applied, these occupied states have different flux-penetration areas, suppressing the superconducting gap. However, this impact can be mitigated by increasing the radius of the nanowire. Finally, we demonstrate that MZMs can be achieved across a wide range of parameters centered around one applied flux quantum, ${\varphi }_0=h/2e$. Within this regime, MZMs can be realized even in the presence of conduction bands. Moreover, the realization of MZMs is not affected by the band bending effect. These findings provide valuable insights into the practical realization of MZMs in TI nanowire-based devices, especially in the presence of a complicated electrostatic environment.

In gapped Dirac materials, the topological current associated with each valley can flow in opposite directions creating long-range charge-neutral valley currents. We report valley currents in hexagonal boron nitride (hBN)/bilayer-graphene heterostructures with an energy gap, which is tunable by a perpendicular electric (displacement) field in a dual-gated structure. We observed significant nonlocal resistance, consistent with the scaling theory of the valley Hall effect. In the low-temperature limit, the nonlocal resistance approaches a saturated value near the “quantum limit,” indicating the emergence of quantum valley currents.

The interplay between topology and electronic correlations offer a rich avenue for discovering emergent quantum phenomena in condensed matter systems. In this work, starting from the Weyl-Hubbard model, we investigate the quantum Hall effect to explore the consequence of onsite Hubbard repulsion on nontrivial Weyl band topology in the presence of an external magnetic field. Within the Gutzwiller projected wavefunction method, we find the system to undergo multiple topological phase transitions by tuning on-site Coulomb interaction, including two distinct Weyl phases with different numbers of Weyl node pairs and a trivial narrow band insulator. Crucially, these two Weyl phases may be identified by the sign of their chiral Landau levels. The possible experimental signature of these topological phases and correlation effects is provided by the magnetic-field dependent quantum Hall conductivity within the Kubo response theory.

We present here the steps enabling the microscopic design of a synthetic spin-1 chain in an InAsP quantum dot (QD) array embedded in an InP nanowire. The chain is described by a two-leg multiorbital Hubbard Kanamori (HK) model with parameters obtained from the microscopic calculations of up to eight electrons in a single and double QD. In this HK model describing long arrays of QDs, using both exact diagonalization and matrix product state (MPS) tools, we demonstrate a fourfold quasidegenerate ground state separated from excited states by a finite energy gap similar to a Heisenberg spin-1 chain in the Haldane phase. We demonstrate characteristic behavior of spin-$\frac{1}{2}$ quasiparticles at the edges of the chain by observing the magnetic field dependence of the low-energy spectrum as a function of the applied magnetic field. The applied magnetic field isolates the singlet and $S^z=0$ triplet states from the other triplet components emulating a singlet-triplet qubit but with macroscopic quantum states. Most importantly, the regions in parameter space where the low-energy spectrum of the multiorbital Hubbard chain yields a Heisenberg spin-1 chain spectrum are mapped out.

We introduce a two-dimensional non-Hermitian lattice model with an imaginary magnetic field and elucidate various unique features which are absent in Hermitian lattice models with real magnetic fields. To describe the imaginary magnetic field, we consider both the Landau gauge and the symmetric gauge, which are related by a generalized gauge transformation, changing not only the phase but also the amplitude of the wave function. We discuss the complex energy spectrum and the non-Hermitian Aharonov-Bohm effect as examples of properties which are due to the imaginary magnetic field independent of the generalized gauge transformation. We show that the energy spectrum does not converge as the lattice size is made larger, which comes from the intrinsic nonperiodicity of the model. However, we have found that the energy spectrum does converge if one fixes the length of one side and makes the other side longer; this asymptotic behavior can be understood in the framework of the non-Bloch band theory. We also find an analog of the Aharonov-Bohm effect; the net change of the norm of the wave function upon adiabatically forming a closed path is determined by the imaginary magnetic flux enclosed by the path, which provides an experimentally observable feature of the imaginary magnetic field.

We introduce an energy-resolved variant of quantum thermodynamics for open systems strongly coupled to their baths. The approach generalizes the Landauer-Buttiker inside-outside duality method [Phys. Rev. Lett. 120, 107701 (2018)] to interacting systems subjected to arbitrary external driving. It is consistent with the underlying dynamical quantum transport description and is capable of overcoming limitations of the only other consistent approach [New J. Phys. 12, 013013 (2010)]. We illustrate viability of the generalized inside-outside method with numerical simulations for generic junction models.

Despite the long and extensive history of melting studies, experiments to determine the dependence of melting on crystal orientation are lacking. Using longitudinal sound speed measurements in aluminum single crystals shock compressed along $\langle 100\rangle$ and $\langle 110\rangle$ to 168 GPa, we address this need and show that the melting transition (both onset and completion) is strongly anisotropic. The present findings demonstrate the need to consider the role of deformation induced lattice defects on the melting transition and provide a general approach to examine melting anisotropy in crystalline solids.

CoSn is a prototypical kagome compound showing lattice-born flat bands with suppressed bandwidth over large parts of the Brillouin zone. Here, by means of time- and angle-resolved photoelectron spectroscopy, we provide direct evidence of the response to photoexcitation of the flat bands, which underlie information about localization in real space. In particular, we detect a sudden shift and broadening of the flat bands, while after one picosecond only a broadening survives. We ascribe both these effects to an ultrafast disruption of electron localization, which renormalizes the effect of electron-electron interaction and affects the flat band dispersion. Since both variations are in the order of a few meV for an excitation fluence of a few hundreds of $\mu \mathrm{J}/{\mathrm{cm}}^2$, our measurements suggest that the flat bands are resilient to near-infrared photoexcitation in a moderate fluence reégime.

We numerically study the effect of spatial inhomogeneity on quantum information scrambling, a process of spreading and locally hiding quantum information in quantum many-body systems. As a paradigmatic example, we consider the quantum chaotic Ising spin chain and its inhomogeneous counterpart that is obtained by modulating the Hamiltonian density. Specifically, we consider the so-called Möbius and sine-square deformations that were previously studied in the context of ($1+1$)-dimensional conformal field theories ($1+1$ d CFTs). In the spatial region where the modulated energy density is small, these deformations prevent the spreading of quantum information while in the region where the modulated energy density is large quantum information scrambling is accelerated. This suggests that we can control the scrambling and butterfly effect by spatially modulating the Hamiltonian density. We also find that the time dependence of energy density exhibits the signature of black-hole-like excitation found in the $1+1$ d CFTs even in the chaotic spin chain.

Using atomistic simulations, we investigate the dynamical behavior of a single skyrmion interacting with an asymmetric linear protrusion array under external ac driving. The linear protrusion array is placed in the $xy$ plane and is composed of magnetic walls near the edge of the nanotrack that have angled linear protrusions into the nanotrack. The structure forms a hard axis for $-x$ direction motion and an easy axis for $+x$ direction motion. When the ac drive is applied along the $x$ direction, the skyrmion moves along the hard direction of the substrate asymmetry in three phases: a pinned phase with localized skyrmion orbits, a constant velocity phase where the orbits become delocalized, and a reentrant pinned phase with larger localized orbits. We measure the dependence of the skyrmion velocity on the frequency and amplitude of the ac drive. All three phases appear for all frequency values simulated here, and in the constant velocity phase the skyrmion velocity depends only on the frequency and not on the amplitude of the ac drive. When ac driving is applied in the $y$ direction, the skyrmion moves along the easy direction of the substrate asymmetry and exhibits the same three phases as for $x$-direction driving along with a fourth phase which, at high driving frequencies, consists of a series of constant velocity phases, each with different average skyrmion velocities. For low frequencies, the constant velocity phase is lost and the skyrmion speed increases linearly with increasing ac drive amplitude due to a Magnus boost effect. Our findings suggest new ways to create reliable data transport for spintronic devices using skyrmions as information carriers, where the skyrmion direction and speed can be controlled by varying only the ac drive amplitude and frequency.

A general theory for the melting of two-dimensional (2D) solids that explains the universal and nonuniversal properties remains an open problem. Although the celebrated Kosterlitz-Thouless-Halperin-Nelson-Young theory was able to predict the critical properties of the melting transition in a variety of cases, it is already known that it could not capture the occurrence of first-order transitions observed in certain systems, nor does it provide a clear way to calculate the melting temperature for a specific model. In the present work, we have developed an analytical method that combines the self-consistent variational approximation with the renormalization group in order to deal simultaneously with the phonon fluctuations and the topological defects that are present in the melting process of 2D crystals. The method was applied with impressive success to a study of the phase diagram of the Gaussian core model, capturing not only the reentrant feature of its 2D solid phase, but also the related critical temperatures as a function of the density in quantitative detail. The developed method can be directly applied to study the melting of any hexagonal simple crystal formed by particles interacting through any finite pairwise interaction potential. Additionally, it has the potential to explain the occurrence of first-order transitions in the melting process of 2D crystals.