In this study, we investigate the problem of Anderson localization in a one-dimensional flat band lattice with a non-Hermitian quasiperiodic on-site potential. First of all, we discuss the influences of non-Hermitian potentials on the existence of critical states. Our findings show that, unlike in Hermitian cases, the non-Hermiticity of the potential leads to the disappearance of critical states and critical regions. Furthermore, we are able to accurately determine the Lyapunov exponents and the mobility edges. Our results reveal that the mobility edges form mobility lines and mobility rings in the complex energy plane. Within the mobility rings, the eigenstates are extended, while the localized states are located outside the mobility rings. For mobility line cases, only when the eigenenergies lie on the mobility lines, their corresponding eigenstates are extended states. As the energy approaches the mobility edges, we observe that, differently from Hermitian cases, here the critical index of the localization length is not a constant, but rather varies depending on the positions of the mobility edges. In addition, we conducted a comprehensive study on the effects of different parameter changes on the phase diagram of the system. Finally, we find that the changes of parameters can lead to changes of the topological structure of the mobility rings.

Information scrambling plays a pivotal role in comprehending the dynamics of quantum many-body systems. In this work, we investigate information scrambling in a one-dimensional topological system using tripartite mutual information (TMI). We consider the one-dimensional Su-Schrieffer-Heeger model as an example and implement it using a Gaussian stroboscopic simulator, verifying its validity through both dynamical studies and effective Hamiltonian analysis, confirming the presence of topological edge states. We then discuss the dynamical behavior of TMI using this simulator as a prototype. Our results reveal that information scrambling can serve as a probe of the system's topological properties, with its presence or absence distinctly characterizing the topologically nontrivial and trivial phases. Moreover, we introduce the standardized mean TMI as a measure of topological phase transitions, demonstrating its effectiveness in determining the phase diagram. Our findings not only elucidate the interplay between topological properties and quantum information dynamics but also propose methods for detecting topological phase transitions through information dynamics.

The garnet compound ${\mathrm{Yb}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ is a fascinating material that is considered highly suitable for low-temperature refrigeration, via the magnetocaloric effect, in addition to enabling the exploration of quantum states with long-range dipolar interactions. It has previously been theorized that the magnetocaloric effect can be enhanced in ${\mathrm{Yb}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ via magnetic soft mode excitations, which in the hyperkagome structure would be derived from an emergent magnetic structure formed from nanosized ten-spin loops. We study the magnetic field dependence of bands of magnetic soft mode excitations in the effective spin $S=1/2$ hyperkagome compound ${\mathrm{Yb}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ using single-crystal inelastic neutron scattering. We probe the magnetically short-ranged ordered state, in which we determine magnetic nanoscale structures coexisting with a fluctuating state, and the magnetically saturated state, from which we determine the relevant magnetic interactions. We determine that ${\mathrm{Yb}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ can be described as a quantum dipolar magnet with perturbative weak near-neighbor and interhyperkagome exchange interaction. The magnetic excitations, under the application of a magnetic field, reveal highly robust soft modes with distinctive signatures of the quantum nature of the ${\mathrm{Yb}}^{3+}$ spins. Our results enhance our understanding of soft modes in topological frustrated magnets that drive both the unusual physics of quantum dipolar systems and future refrigerant material design.

The voltage-current ($V\text{–}I$) characteristics of a submicron-wide superconducting bridge made of granular Nb-film exhibit puzzling regions characterized by negative differential resistance (NDR), $\partial V/\partial I<0$. Our local magnetic force microscopy studies suggest that above the critical current, the voltage develops across the bridge owing to the quantum vortices moving along the weakest intergranular links, which form a nanoscale network. The simulations based on the time-dependent Ginzburg-Landau model show that in such a network, the interaction between vortices may slow down the global vortex dynamics, leading to a flattening and even NDR regions in $V\text{–}I$ characteristics.

Unlike conventional oxide ferroelectrics with rigid lattices, van der Waals (vdW) ferroelectrics feature covalently bonded monolayers interconnected by vdW interactions across the interlayer. The structural discontinuity introduced by vdW interlayer distance may lead to the anisotropic switching dynamics along in plane and out of plane, directly impacting the performance of ferroelectric devices. However, the anisotropic switching mechanisms of the domain walls (DWs) in vdW ferroelectrics remain unclear, constrained by the spatial-temporal resolution limitations in both theoretical simulations and experimental observations. Here, we employ the machine-learning potential molecular dynamics to investigate the atomic structure and the dynamics of DWs in multilayer $2H$ α-$\mathrm{I}{\mathrm{n}}_2\mathrm{S}{\mathrm{e}}_3$. Our results reveal that the in-plane DWs of $2H$ α-$\mathrm{I}{\mathrm{n}}_2\mathrm{S}{\mathrm{e}}_3$ contain a nonpolarized layer sandwiched between two oppositely polarized layers, which avoids an abrupt polarization reversal with high electrostatic energy. Such nonpolarized layer enables layer-by-layer domain switching dynamics in a multilayer structure under external field. We further reveal that two types of out-of-plane DWs exhibit distinct switching behaviors due to the difference in DW motion energy barriers. Notably, the motion of out-of-plane DWs precedes that of the in-plane DWs under an external electric field. These findings reveal the anisotropic switching dynamics in multilayer $2H$ α-$\mathrm{I}{\mathrm{n}}_2\mathrm{S}{\mathrm{e}}_3$ and provide critical insight for designing vdW ferroelectric devices based on DW engineering.

The structure and stability of iron near melting at multi-megabar pressures are of significant interest in high-pressure physics and earth and planetary sciences. While the body-centered cubic (bcc) phase is generally recognized as unstable at lower temperatures, its stability relative to the hexagonal close-packed (hcp) phase at high temperatures (approximately 0.5 eV) in the Earth's inner core (IC) remains a topic of ongoing theoretical and experimental debate. Motivated by a series of studies attempting to understand the state of the IC and resulting in contradictory findings, we aim to explore the physical factors that may contribute to this confusion in a broader context. Our ab initio calculations show a significant drop in energy, the emergence of a plateau and a local minimum in the potential energy surface, and stabilization of all phonon modes of bcc iron at elevated electron temperatures ($>$1–1.5 eV). These effects increase the competition among the bcc, hcp, and face-centered cubic (fcc) phases and lead to the metastability of the bcc structure. Furthermore, at pressure-temperature conditions relevant to the IC, we can expect substantial coexistence of fcc and hcp iron due to their similar free energies and low transition barrier ($\sim 0.2$ eV/atom), and the thermodynamic stability of bcc iron is enhanced by its substantial lattice vibration entropy. These findings provide a clear theoretical framework for understanding iron phase relations and solidification processes, both experimentally and in the IC.

Altermagnets are known in spintronics for their intrinsic spin-splitting and unconventional magnetic responses, particularly to magnetic impurities. However, effectively controlling the magnetic exchange interactions in altermagnets is challenging for practical applications. Here, we propose using circularly polarized light to tune the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in two-dimensional $d$-wave altermagnets. Using the real-space retarded Green's functions approach, our results show that while the Heisenberg and Ising exchanges dominate, a notable Dzyaloshinskii–Moriya (DM) interaction also plays a key role. Furthermore, the inherent strength of altermagnetism imprints chirp-like signatures into the magnetic responses, which can be dynamically tuned via light. We mainly demonstrate that gate-induced Rashba spin-orbit coupling is essential in response to light—light selectively and anisotropically adjusts the DM interaction without affecting the other exchanges. Our findings further indicate that rotating the altermagnet by ${45}^{\circ }$ relative to the light's polarization direction generates a Dirac-like dispersion and different DM interactions. We finally extract critical thresholds where light reverses DM interactions along one axis or balances both in-plane components. The anisotropic light-driven control of RKKY interactions in altermagnets not only highlights their unique properties but also opens new avenues for engineering tailored magnetic characteristics in spintronic applications.

We employ polarization-resolved Raman spectroscopy to study the lattice dynamics of the polar charge density wave phase of the superconductor ${\mathrm{Mo}}_3{\mathrm{Al}}_2\mathrm{C}$ with structural chirality. We show the phononic signatures of the charge density wave transition at $T^{*}$ = 155 K in ${\mathrm{Mo}}_3{\mathrm{Al}}_2\mathrm{C}$. The detailed temperature dependence of these phonon modes' frequency, half width at half maximum, and integrated area below $T^{*}$ reveal anomalies at an intermediate temperature $T^{\prime }\sim$ 100 K, especially for the low-energy modes at 130 and 180 ${\mathrm{cm}}^{-1}$. We discuss the origin of these phonon anomalies within the polar charge density wave phase of ${\mathrm{Mo}}_3{\mathrm{Al}}_2\mathrm{C}$.

Exciton transport and charge transfer in donor-acceptor (D-A) heterojunctions are critical in governing the power conversion efficiency in organic photovoltaics (OPVs). Despite advances in organic photovoltaic materials, exciton transport is hindered by structural disorder that limits device efficiency. Exciton polaritons, formed through the strong coupling of cavity-coupled organic materials, exhibit delocalized states that enhance exciton transport and reduce the effects of disorder. Using transient absorption spectroscopy, we explore strong coupling in D-A heterojunctions integrated with a distributed Bragg reflector “open cavity.” The delocalized hybrid polariton state slows charge transfer compared to non-cavity-coupled control samples. These findings underscore the role that polaritons play in exciton transport and charge transfer. Understanding and controlling this interaction, along with the optimization of photonic structures, may lead to increased performance of OPVs and polaritonic devices.

We employ first-principles electronic structure calculations to explore the effects of Bi doping at the As site of ${\mathrm{BaFe}}_2{\mathrm{As}}_2$, predicting significant changes in band topology and surface states. The negative chemical pressure induced by Bi doping, which has also been observed experimentally, is shown to drive distinct Lifshitz transitions that effectively act as electron doping, modifying the Fermi surface topology. These theoretical predictions suggest potential impacts on superconducting properties, with optimal superconductivity likely near $x=0.01$. Additionally, Dirac-cone-type surface states at the $\overline{\mathrm{\Gamma }}$ point progressively shift towards the Fermi level with increasing Bi concentration. This evolution is pivotal for the realization of topological superconducting surface states, the observation of Majorana zero-energy modes, and potential practical applications, including quantum computation. Using symmetry indicators derived from wavefunction symmetry at high-symmetry momenta, we confirm a nontrivial topological phase across all studied doping levels, from $x=0.005$ to $x=0.05$. The nontrivial nature of the ${\mathbb{Z}}_2$-topological invariant, while a topological phase transition corresponding to a higher topological index is predicted at $x=0.03$. These findings highlight that Bi-doped ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ retains a nontrivial topological phase throughout the studied doping range and suggest its potential as a platform for exploring Majorana zero-energy modes in its low-doping superconducting state.

We perform microscopic numerical simulations of the Josephson effect through short junctions between two full-shell hybrid nanowires, comprised of a semiconductor core fully wrapped by a thin superconductor shell, both in the trivial and topological regimes. We explore the behavior of the current-phase relation and the critical current $I_c$ as a function of a threading flux for different models of the semiconductor core and different transparencies of the weak link. We find that $I_c$ is modulated with flux due to the Little-Parks (LP) effect and displays a characteristic skewness towards large fluxes within nonzero LP lobes, which is inherited from the skewness of a peculiar kind of subgap states known as Caroli-de Gennes-Matricon (CdGM) analogs. The appearance of Majorana zero modes at the junction in the topological phase is revealed in $I_c$ as fin-shaped peaks that stand out from the background at low junction transparencies. The competition between CdGMs of opposite electron- and holelike character produces steps and dips in $I_c$. A rich phenomenology results, which includes 0-, $\pi$-, and $\varphi$-junction behaviors depending on the charge distribution across the wire core and the junction transparency.

The nitrogen-vacancy (NV) color centers in nanodiamonds can be utilized as low-cost, highly versatile quantum sensors for studying surface properties in condensed matter physics through the application of relaxometry protocols. For such applications, a detailed knowledge of the intrinsic relaxation processes of NV centers in nanodiamonds is necessary. Here, we study the spin-lattice relaxation rates of NV ensembles in nanodiamonds with average diameters of 40 nm and 3 $\mu \mathrm{m}$ between room temperature and $\sim 6\mathrm{K}$. The NV relaxation curves fit to a stretched-exponential form with a stretching exponent $\alpha \approx 0.7$, implying the large distribution of relaxation times of individual centers within nanodiamonds. We determine the Orbach-like scattering on phonons as the leading relaxation mechanism. Finally, we discuss the viability of nanodiamonds as surface sensors when deposited on a metallic substrate and emphasize the need for well-controlled surface preparation techniques.

The form of the entanglement Hamiltonian varies with the parameters of the original system. Whether there is a singularity is the key problem for demonstrating/negating the universality of the relation between the entanglement spectrum and edge energy spectrum. We carefully study the phase diagram of a 1D Ising entanglement Hamiltonian as an example to clarify the long-standing controversy of the general relation between the entanglement Hamiltonian and original Hamiltonian. Interestingly, even if the singularities indeed exist, the Li-Haldane-Poilblanc conjecture, i.e., the general relation between the entanglement spectrum and edge energy spectrum, seemingly still holds.

The ferromagnetic-semiconductor rare-earth nitrides have coupled magnetism/conductivity responses that promise facility to support superconducting spintronics, for which it is urgent to improve their electron mobility. We report exactly that advance, showing an order-of-magnitude enhanced mobility in GdN, the prototypical rare-earth nitride, enabling ballistic-transport barriers in magnetic Josephson junctions. To achieve the enhancement, the film was grown on the square net presented by the (001) surface of ${\mathrm{LaAlO}}_3$. The film's crystal structure was characterized by in situ reflection high-energy electron diffraction and ex situ x-ray diffraction and x-ray reflectivity to show the best crystallinity and smoothest surfaces we have accomplished to date. It shows a clear ferromagnetic transition at $\sim 70$ K with a saturation magnetization within uncertainty of $7{\mu }_B$/${\mathrm{Gd}}^{3+}$ ion, a remanence of $5{\mu }_B$/${\mathrm{Gd}}^{3+}$ ion, and a coercive field of $\sim 5$ mT. It is doped by $\sim 1$% nitrogen vacancies that introduce $\sim 3\times {10}^{20}{\mathrm{cm}}^{-3}$ electrons into the conduction band. The resistivity shows transport in a conduction band doped to degeneracy by $\sim 0.01$ electrons/formula unit with a residual resistance ratio of 2 and a Hall resistivity permitting easily separated ordinary and anomalous Hall components. The electron transport resides in the strongly spin-split $5d$ conduction band that ensures purely majority-spin transport.

Discovery of polar skyrmions on the ${\left({\mathrm{PbTiO}}_3\right)}_n/{\left({\mathrm{SrTiO}}_3\right)}_n$ superlattice in the absence of any known interaction, which can orient electric polarizations at a point with respect to its neighboring points, is enigmatic. We here show that the coupling of the electric polarization and strain at each layer is responsible for orienting polarizations. We formulate coupled Euler equations for electric polarization and elastic displacement vectors, and solve to find skyrmion solution for a range of electric fields with a unique topological number in each layer. The types of skyrmions vary from Neel to Bloch depending on the position of the layers in the superlattice, as observed in the experiments. A phase diagram for skyrmions in the electric field and temperature space is obtained.

Several prior attempts to formulate the laws of thermodynamics for a small region within a larger quantum system led to inconsistencies and unexplained infinities. The entropy and external work, in particular, require careful analysis when partitioning over the various subsystems. In this work, we analyze the thermodynamics of a quantum subsystem driven quasistatically by external forces. We show that the thermodynamic functions of a quantum subsystem can be defined dynamically in terms of its local spectrum. The external work is found to be intrinsically nonlocal due to the nonlocal character of the underlying quantum states. This nonlocal quantum work can be harnessed in a “quantum lever” to provide up to 100% amplification of the local work done on a quantum subsystem.

Higher-order topological insulators have expanded the conventional bulk-boundary correspondence by hosting lower-dimensional boundary states, in which Benalcazar-Bernevig-Hughes model is pivotal in unraveling quadrupole topological phases in two-dimensional systems. Recent theoretical study has revealed that multilayer systems with engineered interlayer couplings can host a richer variety of topological phases compared to their monolayer counterparts. However, such multilayer Benalcazar-Bernevig-Hughes system with heterogeneous topological layers remains underexplored in experiments. Here, we experimentally realize a trilayer Benalcazar-Bernevig-Hughes sonic crystal comprising two topological nontrivial outer layers and a trivial middle layer. By modulating the interlayer coupling strength, we induce a topological phase transition characterized by the multipole chiral number and obtain hybrid topological corner states with different pressure field patterns. Leveraging 3D-printed cavity-tube structures, we experimentally observe these distinct acoustic corner states and distinguish them via the symmetric rules of the acoustic phase distributions. Our work not only establishes a framework for realizing multilayer topological systems, but also demonstrates the potential for designing topological acoustic devices.

TaOsSi has been identified as a material with both topological surface states and signatures of unconventional superconductivity, while at the same time showing indications of two-gap superconductivity. We report investigation of electronic and superconducting properties of TaOsSi and the related superconductor NbOsSi based on electron-phonon coupling. We find that these materials are not near magnetism, which implies that spin-fluctuation pairing is unlikely to be operative. There is a momentum-dependent electron-phonon coupling on a multisheet Fermi surface leading to a superconducting state with a highly anisotropic gap in the clean limit. The state is fully gapped in accord with experimental results. We do not find a conventional two-gap state but rather a continuous variation of the gap on the Fermi surfaces. Thus, it is possible to explain the occurrence of superconductivity in these compounds within a conventional electron-phonon picture. Both NbOsSi and TaOsSi show a Dirac point very close to the Fermi energy, $E_F$, along the X-S line near the $S$ point. In the case of NbOsSi, this is 16 meV below $E_F$ at k = (0.5,0.48,0) and in TaOsSi it is 23 meV below $E_F$ at k = (0.5,0.46,0). Thus, these materials are superconductors with strong spin orbit, topological superconductivity, and substantial anisotropy of the superconducting order parameter.