Recent studies in the superconducting topological crystalline insulator (TCI) SnTe have reported signatures of multiple Majorana zero modes in a vortex. The energy and spatial characteristics of magnetic bound states in this platform are important for understanding their mechanism and building topological quantum states. Here, we investigate the Yu-Shiba-Rusinov (YSR) bound states induced by magnetic adatoms on a SnTe/Pb heterostructure, revealing their latticelike spatial extension, which is associated with the topological surface states of the TCI. We also reveal identical oscillation periods and energy-dependent spatial extensions of YSR states at different excitation energies. Moreover, we observe one-dimensional (1D) dispersive in-gap states with zero-energy crossings around the magnetic cluster, arising from the coupling of long-range magnetic bound states and suggesting possible 1D topologically nontrivial zero-energy states. Our work offers a comprehensive understanding of magnetic bound states in the superconducting TCIs, proposing a promising platform to engineer nonlocal topological quantum states through long-range magnetic coupling.

Intrinsic loss is typically regarded as a detrimental factor that impairs system performance, especially in systems with bound states in the continuum (BICs). Here, we propose and experimentally realize another type of loss-induced BICs (LBICs) in a non-Hermitian system consisting of a one-dimensional two-coupled-resonators chain. By engineering dissipative coupling introduced by loss, we highlight the role of loss and realize a topological phase transition of the energy band from discrete energy levels to a continuous spectrum, which results in the topological edge states being embedded into the continuous spectrum, thus forming a LBIC. Such topological LBIC, which inherits the robustness of topological edge states, is observed experimentally in a circuit system. Our work provides a physics mechanism to design topological BIC and establishes a bridge between intrinsic loss and radiation channels in non-Hermitian systems.

We calculate the crystal-field splitting, ground-state Kramers doublet, and intersite exchange interactions within the ground-state doublet manifold using an ab initio Hubbard-I based approach for a representative set of Ce and Yb triangular-lattice compounds. These include the putative quantum spin liquids (QSL) ${\mathrm{RbCeO}}_2$ and ${\mathrm{YbZn}}_2{\mathrm{GaO}}_5$ and the antiferromagnets ${\mathrm{KCeO}}_2$ and ${\mathrm{KCeS}}_2$. The calculated nearest-neighbor (NN) couplings are antiferromagnetic and exhibit noticeable anisotropy. The next-nearest-neighbor (NNN) couplings are ferromagnetic in the Ce systems and dominated by classical dipole-dipole interactions in the Yb case. Solving the resulting effective spin-1/2 models by exact diagonalization up to $N=36$ sites, we predict ordered magnetic ground states for all systems, including the two QSL candidates. We explore the phase space of an anisotropic NN $+$ isotropic NNN triangular-lattice model finding that a significant antiferromagnetic NNN coupling is required to stabilize QSL phases, while the NN exchange anisotropy is detrimental to them. Our findings highlight a possibly important role of deviations from the perfect triangular model—like atomic disorder—in real triangular-lattice materials.

Electronic quantum effects in mesoscopic plasmonic nanostructures significantly influence their optical properties. Here, by exciting plasmon, Bennett, and charge-transfer modes, we demonstrate that they can be strongly coupled in purely metallic devices. Using the Feibelman $d$ parameter framework, we derive an analytical expression for the coupling strength, showing its inverse dependence on the square root of the structure's length scale ($g\propto 1/\sqrt{L}$). Thus, we establish a nanophotonic platform where nonclassical states, such as Bennett and charge-transfer modes, interact strongly with purely classical ones, such as surface plasmons, providing an indirect strategy to probe and exploit quantum electronic phenomena in optical systems.

Helium and rare gases (RG: Ne, Ar, Kr, Xe) are typically considered chemically inert, yet under the extreme pressures of planetary interiors they may form compounds with unexpected properties. Using crystal structure prediction and first-principles calculations, we mapped the phase diagram of binary He–RG systems up to 1 TPa. We identify several previously unknown stoichiometric compounds that are both thermodynamically and vibrationally stable at subterapascal pressures, within the reach of modern high-pressure experiments. In particular, $A{\mathrm{He}}_2$ and $A\mathrm{He}$ $(A=\mathrm{Ar}, \mathrm{Kr}, \mathrm{Xe})$ adopt previously unreported orthorhombic, hexagonal and cubic phases that remain stable over wide pressure ranges. We further find that He–Xe systems host metallic and excitonic insulator phases at pressures nearly an order of magnitude lower than those required for pure helium, offering a pathway to realize these exotic quantum states experimentally. Finite-temperature simulations also reveal superionic He–Xe phases, in which helium ions diffuse either anisotropically or isotropically depending on the host lattice. These findings constitute the first prediction of helium-based systems that combine metallicity and superionicity, with profound implications for energy transport and planetary dynamo processes. Overall, our results demonstrate that mixing helium with heavier rare gases provides an effective strategy to stabilize metallic, excitonic insulator, and superionic phases at experimentally accessible pressures, opening new research directions for condensed matter physics and planetary science.

Altermagnets, an emerging class of magnetic materials, exhibit exotic chiral split magnons that are of great interest for both fundamental physics and spintronic applications. However, detecting and manipulating these magnons is challenging due to their THz frequency response. Here, we report the discovery of gapless chiral split magnons confined within altermagnetic domain walls. Unlike in conventional ferromagnets or antiferromagnets, their spectrum is highly sensitive to the domain wall orientation relative to the crystal axis. These magnons inherit the chiral splitting of their bulk counterparts and are detectable in the microwave regime, offering a distinctive signature for identifying altermagnets. We further show that the interfacial Dzyaloshinskii-Moriya interaction drives hybridization of magnons with opposite chiralities, enabling unidirectional strong magnon-magnon coupling. Moreover, we demonstrate that spin-orbit torque can control the domain wall orientation, providing a practical means to manipulate these chiral magnons. Our findings open pathways for novel magnonic nanocircuitry based on altermagnetic domain walls.

Semiconductor-superconductor interfaces play a crucial role in various applications, including hybrid circuits, thermometry, devices (bolometers, electronic coolers), detectors for high-energy particle physics, and quantum computing as potential hosts of topologically protected zero-energy modes. In this work, we solve the Kohn-Sham density-functional theory and Bogoliubov–de Gennes equations to describe the normal and superconducting properties of a PbTe/Pb heterostructure. We compute the anomalous charge density in real space, estimating its decay length and showing that the pairing potential is anisotropic. We demonstrate that superconductivity in the PbTe/Pb interface is resilient against strain. In the normal state we find a large Schottky barrier across the interface, resulting in charge transfer from PbTe to Pb. We resolve a proximity-induced superconducting gap on the PbTe side, which originates from hybridization between the Pb and PbTe states near the Fermi energy, which occurs in a weak-coupling regime. On the Pb side, the superconducting gap appears partially “poisoned,” namely less sharp and less wide than bulk Pb. Our first-principles simulations provide a quantitative prediction on emergent structural, electronic (charge transfer, potential drops, band offset), and superconducting properties of the PbTe/Pb interface, namely key information for the design of devices where the PbTe/Pb interface plays a central role as, for instance, in core/shell PbTe/Pb nanowires.

Doping tin surface epitaxially grown on silicon, Sn/Si(111), with boron atoms yields the appearance of a superconducting (SC) phase below $T_c\sim 4-9\mathrm{K}$. Even though the pairing mechanism remains unknown, experimental evidence of chiral $d-\mathrm{wave}$ superconductivity has been recently reported, thus ruling out a phonon-mediated pairing. Here, we study theoretically the SC phase of the doped Sn/Si(111) within a $t-J$ model investigating different symmetries of the order parameter. We analyze the photoexcitation of the system by intense terahertz pulses and show that the polarization dependence of the induced current can distinguish between different symmetries of the SC gap, thus providing an experimental means to investigate the spectroscopic features of the Sn/Si(111), and possibly to many other systems, across the SC transition.

The phenomenon of a field-induced superconductor-to-insulator transition in disordered two-dimensional electron systems has been a subject of controversy since its discovery in the early 1990s. Here we present a phenomenological quantitative theory of this phenomenon that is not based exclusively on the boson-vortex duality used commonly in the field. Within a new low-temperature framework of the time-dependent Ginzburg-Landau functional approach to superconducting fluctuations, we propose and develop a scenario in which bosons of Cooper-pair fluctuations (CPFs) condense and localize in real-space mesoscopic puddles under increasing magnetic field due to diminishing stiffness of the fluctuation modes at low temperatures in a broad range of momentum space. Quantum tunneled CPFs relieving the condensed mesoscopic puddles, which consequently pair break into fermionic quasiparticle excitations, reinforce the thermally activated interpuddles transport. The shrinking puddles of CPFs, embedded in expanding normal-state regions, upon further increasing field, suppress the quasiparticle excitation gap and so lead to high-field negative magnetoresistance (MR). Application to amorphous indium-oxide thin films shows good quantitative agreement with experimental sheet resistance data. In particular, in agreement with the experiment at low temperatures (i.e., well below the quantum tunneling pair breaking “temperature”), the sheet resistance isotherms are predicted to show a single crossing point at a quantum critical field not far below the MR peak.

We evaluate the quasiparticle contribution to the frequency shift and relaxation rates of a transmon with the Josephson junctions connecting superconductors that have unequal energy gaps. The gap difference substantially affects the transmon characteristics. We investigate their dependence on the density and effective temperature of the quasiparticles and on the nominal (unperturbed by the quasiparticles) transmon frequency. At temperatures low compared to the qubit frequency, the gap difference can induce an anomalous positive frequency shift, resulting in a nonmonotonic temperature dependence of the transmon frequency. The qubit relaxation rate exhibits a resonance when the qubit frequency matches the gap difference; the shape of the resonance is strongly temperature dependent. We propose to use these effects to access the details of the quasiparticle energy distribution.

Complex quantum networks are powerful tools in the modeling of transport phenomena, particularly for biological systems, and enable the study of emergent phenomena in many-body quantum systems. High connectivity and long-range interactions induce strong constraints on the system dynamics. Here, we study the transport properties of a quantum network described by the paradigmatic XXZ Hamiltonian, with nontrivial graph connectivity and topology, and long-range interactions. We show how long-range interactions induce memory-preserving effects and strongly affect the spreading of the excitations due to cooperative shielding. We describe the memory-preserving effect in all-to-all connected regular networks with distance-independent couplings. Indeed, the memory of the number of initially injected excitations is preserved over long times, encoded in the number of frequencies present in the dynamics. Interestingly, we find that memory-preserving effects occur also in less regular graphs, such as quantum networks with either power-law node connectivity or complex, small-world type, architectures. We discuss the implications of these properties in biology-related problems, such as an application to Weber's law in neuroscience, and their implementation in specific quantum technologies via biomimicry. We also show how the presence of long-range interaction strongly affects the dynamics of the excitations in small-world networks and power law all-to-all coupled networks. Indeed, because of cooperative shielding blue, as the connectivity or the range of interaction increases, the initial excitation spreads more slowly among the network and becomes strongly dependent on the initial conditions.

We study the elementary excitations and magnetization of a one-dimensional spin-1/2 XX chain comprising trimer-dimer units ($J_1-J_1-J_2-J_3-J_2$ topology) under a transverse magnetic field ($h$). Using Green's function theory and the Jordan-Wigner transformation, we map the system to spinless fermions and focus on antiferromagnetic (AFM) interactions. At zero temperature, distinct 1/5 and 3/5 magnetization plateaus emerge, determined by the overall periodicity $Q=5$, with the number of plateaus matching the number of excitation gaps above the Fermi level of spinless fermions. The magnetic phase diagram in the (h-J) plane features a Luttinger liquid (LL) state, a gapless AFM state, two magnetization plateau states, and a fully polarized gapped magnetic state. The widths of the LL and gapless AFM phases are found to be proportional to the bandwidths [$\gamma \propto \left|E\left(k=0\right)-E\left(k=\pi \right)\right|$] of the respective elementary excitations, whereas the widths of the magnetization plateau states are found to be linked to the gaps between excitations. Our study opens a path for exploring interacting trimer-dimer spin chains in quantum magnetism using experimental techniques, such as neutron scattering and/or through other theoretical or numerical approaches, including quantum Monte Carlo and density matrix renormalization group methods. Furthermore, our study extends the Oshikawa-Yamanaka-Affleck condition to generalized cluster chains, showing that the allowed magnetization plateau states are governed by the global periodicity of the chain (e.g., $Q=5$ for a trimer-dimer chain), rather than the local periodicity of individual units ($Q=3$ for a trimer or $Q=2$ for a dimer).

We discuss a class of lattice $S=\frac{1}{2}$ quantum Hamiltonians with bond-dependent Ising couplings and a mutually “anticommuting” algebra of extensively many local ${\mathbb{Z}}_2$ conserved charges that was explicated by Pujari [arXiv:2407.06236]. This mutual algebra is reminiscent of the spin-$\frac{1}{2}$ Pauli matrix algebra but encoded in the structure of local conserved charges. These models have finite residual entropy density in the ground state with a simple but nontrivial degeneracy counting and concomitant quantum spin liquidity as proved by Pujari [arXiv:2407.06236]. The spin liquidity relies on a geometrically site-interlinked character of the local conserved ${\mathbb{Z}}_2$ charges that is rather natural in the presence of an anticommuting structure. One may contrast this with, for example, the bond-interlinked character of the local conserved ${\mathbb{Z}}_2$ charges on the hexagonal plaquettes of the Kitaev honeycomb spin-$\frac{1}{2}$ model, which leads to a mutually commuting local algebra. In this work, we make several exact statements on the kinds of many-body orders that can be present within the class of anticommuting quantum spin liquids coexisting with extensive residual ground state entropy. We elucidate the differences between the many-body order in these models and that found in some gapped quantum spin liquids whose canonical example is the Kitaev toric code. The toric code belongs to the more general class of Levin-Wen or string net constructions that possess mutually commuting algebras for the local conserved charges. We also point out a mutually commuting algebra with local support that is naturally expressed as multilinear Majorana forms in the Kitaev representation of these quantum spin liquids. They capture quantum resonances spread across the lattice in anticommuting ${\mathbb{Z}}_2$ quantum spin liquids.

We use the Schrieffer-Wolff transformation (SWT) to analyze Josephson junctions between superconducting leads described by the charge-conserving BCS theory. Starting from the single-electron tunneling terms, we directly recover the conventional effective Hamiltonian, $-E_{J}cos\widehat{\phi }$, with an operator-valued phase bias $\widehat{\phi }$. The SWT approach has the advantage that it can be systematically extended to more complex scenarios. We show that if a Bogoliubov quasiparticle is present its motion couples to that of Cooper pairs, introducing correlated dynamics that reshape the energy spectrum of the junction. Furthermore, higher-order terms in the SWT naturally describe Josephson harmonics, whose amplitudes are directly related to the microscopic properties of the superconducting leads and the junction. We derive expressions that could facilitate tuning the ratio between the different harmonics in a controlled way.

Kagome-based magnetic metals are recognized as exemplary systems for the study of quantum materials, offering a distinctive framework to investigate the interrelation of topologically nontrivial electronic structures, geometrically frustrated magnetic moments ($f\approx 7$), and strongly correlated electron phenomena. The growth and detailed analysis of the $4d$ kagome metal $\mathrm{TbN}{\mathrm{b}}_6\mathrm{S}{\mathrm{n}}_6$ are reported, in which a kagome network of Nb atoms is integrated with a triangularly frustrated arrangement of localized ${\mathrm{Tb}}^{3+}$ moments. High-quality crystals are found to adopt the centrosymmetric $\mathrm{HfF}{\mathrm{e}}_6\mathrm{G}{\mathrm{e}}_6$-type structure ($P6$/mmm), with lattice constants precisely refined to $a=b=5.75791\AA$ and $c=9.55520\AA$. Striking uniaxial anisotropy is revealed by magnetization measurements, with the magnetic susceptibility along the $c$ direction exceeding the in-plane susceptibility by nearly 50-fold just above 3 K, indicating a strong out-of-plane alignment preference of the ${\mathrm{Tb}}^{3+}$ $4f$ moments. Two successive magnetic transitions are observed at zero magnetic field at $T_{\mathrm{N}}=2.91$ K and $T_2=2.32$ K. When a magnetic field is applied along the $c$ direction, four distinct metamagnetic transitions are observed at low temperatures, culminating in a fully polarized moment of 8.24 ${\mu }_{\mathrm{B}}$/Tb ion at 2 K above 3.6 T, as evidenced by both magnetization and resistivity measurements. A positive, nonsaturating magnetoresistance and a nonlinear Hall effect are exhibited by the compound across the full temperature range studied. First-principles calculations show that the Fermi level is dominated by Nb $4d$ orbitals, which generate kagome-derived bands featuring Dirac crossings and Van Hove singularities indicative of nontrivial topology. The potential of the $R\mathrm{N}{\mathrm{b}}_6\mathrm{S}{\mathrm{n}}_6$ family as a versatile platform for realizing emergent quantum states is highlighted by the combination of tunable magnetic anisotropy, complex spin textures, and multiband conduction.

The high-temperature series expansion for quantum spin models is a well-established tool to compute thermodynamic quantities and equal-time spin correlations, in particular for frustrated interactions. We extend the scope of this expansion to the dynamic Matsubara spin-spin correlator and develop an algorithm that yields exact expansion coefficients in the form of rational numbers. We focus on Heisenberg models with a single coupling constant $J$ and spin lengths $S\in \{1/2,1\}$. The expansion coefficients up to 12th order in $J/T$ are precomputed on all possible $\sim {10}^6$ graphs embeddable in arbitrary lattices and are provided in a repository. This enables calculation of static momentum-resolved susceptibilities for arbitrary site pairs or wave vectors. We test our results for the antiferromagnetic $S=1/2$ chain and triangular lattice model. An important application that we discuss in a companion letter is the calculation of real-frequency dynamic structure factors. This is achieved by identifying the high-frequency expansion coefficients of the Matsubara correlator with frequency moments of the spectral function.

The $GW$ approximation is a widely used framework for studying correlated materials, but it struggles with certain limitations, such as its inability to explain pseudogap phenomena. To overcome these problems, we propose a systematic theoretical framework for Green's function corrections and apply it specifically to the $GW$ approximation. In this new theory, the screened potential is reconnected to the physical response function, i.e., the covariant response function proposed by Li et al. [Phys. Rev. B 107, 085106 (2023)], rather than using the random phase approximation formula. We apply our scheme to calculate Green's function, the spectral function, and the charge compressibility in the two-dimensional Hubbard model. Our scheme yields significant qualitative and quantitative improvements over the standard $GW$ method and successfully captures the pseudogap behavior.

Altermagnets possess two key features: nonrelativistic alternating spin splitting (i.e., altermagnetism) and a material-dependent Néel vector. The former naturally coexists with Rashba spin-orbit coupling (SOC) in real materials on substrates, prompting the question of how SOC affects the magnetic properties of altermagnets. The latter is crucial for information storage, making it essential to determine its orientation. To address these issues, we study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in two-dimensional (2D) $d$-wave altermagnets by independently varying the Néel vector orientation and the SOC strength. Our results demonstrate that the Néel vector orientation can be accurately determined via the Ising term without SOC or qualitatively inferred via the Dzyaloshinskii-Moriya (DM) terms with SOC. Moreover, we observe a DM component distinct from previous reports, whose emergence is attributed to the synergy between altermagnetism and SOC. Additionally, by tuning the SOC strength, we reveal the evolution of the RKKY spin models governed by five distinct mechanisms: The spin model may be determined solely by altermagnetism, solely by SOC, or solely by the kinetic term; alternatively, altermagnetism may coincidentally yield the same moderately anisotropic spin model as SOC or compete with SOC to produce a spin model with maximal anisotropy. Beyond SOC strength, which mechanism operates also relies on the Néel vector orientation and impurity configurations. All results are numerically verified. These findings—which were inaccessible in prior studies due to the limitations of first-order SOC expansion and fixed Néel vector orientation—provide important insights into the magnetic properties of altermagnets.