Employing inelastic x-ray scattering and neutron scattering techniques, we observed nematic and magnetic phase transitions with distinct characters in ${\mathrm{K}}_5{\mathrm{Fe}}_4{\mathrm{Ag}}_6{\mathrm{Te}}_{10}$. Upon cooling, the nematic order undergoes a strongly first-order phase transition followed by a magnetic transition at $T_{\text{N}}\approx 34.7\mathrm{K}$ that is consistent with a second-order transition. The temperature difference between these two phase transitions is $\sim 1.0\left(8\right)$ K. The observed phenomenon can be attributed to a distinctive first-order preemptive Ising-nematic transition, a characteristic unique to a quasi-two-dimensional scenario marked by strong out-of-plane spatial anisotropy due to weak coupling. Our studies establish ${\mathrm{K}}_5{\mathrm{Fe}}_4{\mathrm{Ag}}_6{\mathrm{Te}}_{10}$ as the first material in the family of iron pnictides and chalcogenides that possesses a nematic tricritical point preceding the magnetic one upon decreasing nematic coupling.

Through a combination of crystal symmetry analysis and density functional theory calculations we unveil a possible microscopic origin of the unexpected insulating behavior reported in the honeycomb Kitaev material ${\mathrm{Cu}}_2{\mathrm{IrO}}_3$. Our study suggests that this material hosts an instability towards charge ordering of the Ir ions, with alternating magnetic ${\mathrm{Ir}}^{4+}$ and nonmagnetic ${\mathrm{Ir}}^{3+}$ ions arranged on the honeycomb lattice. In this case, the next-nearest-neighbor interactions that couple magnetic ${\mathrm{Ir}}^{4+}$ ions form an enlarged triangular lattice, instead of the expected honeycomb lattice. The magnetic ${\mathrm{Cu}}^{2+}$ ions located at the center of the iridium honeycomb voids also form a triangular lattice, and additionally contribute to the magnetization of the system. Together, the interpenetrated ${\mathrm{Ir}}^{4+}$ and ${\mathrm{Cu}}^{2+}$ triangular lattices present a novel type of honeycomb Kitaev lattice composed of two types of magnetic ion.

The universal oscillation of the tunnel magnetoresistance (TMR) ratio as a function of the insulating barrier thickness in crystalline magnetic tunnel junctions (MTJs) is a long-standing unsolved problem in condensed matter physics. To explain this, we here introduce a superposition of wave functions with opposite spins and different Fermi momenta, based on the fact that spin-flip scattering near the interface provides a hybridization between majority- and minority-spin states. In a typical Fe/MgO/Fe MTJ, we solve the tunneling problem and show that the TMR ratio oscillates with a period of $\sim 3$Å by varying the MgO thickness, consistent with previous and present experimental observations.

The kagome metals $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ ($A=\mathrm{K}$, Cs, Rb) have become a fascinating materials platform following the discovery of many novel quantum states due to the interplay between electronic correlation, topology, and geometry. Understanding their physical origin requires constructing effective theories that capture the low-energy electronic structure and electronic interactions. Here, we point out the unusual and puzzling properties of the DFT electronic structure, including the sublattice type of the van Hove singularities, the geometric shape of the Fermi surface, and the orbital content of the low-energy band dispersion, which cannot be described by the commonly used one-orbital or multiorbital kagome tight-binding models. We address these fundamental puzzles and develop an extended Slater-Koster formalism that can successfully resolve these issues. We discover the important role of site-symmetry and interorbital hopping structure and provide a concrete multiorbital tight-binding model description of the electronic structure for $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ and the family of “135” compounds with other transition metals.

We present a constructive method utilizing the Cartan decomposition to characterize topological properties and their connection to two-qubit quantum entanglement in the framework of the tenfold classification and Wootters concurrence. This relationship is comprehensively established for the two-qubit system through the antiunitary time reversal (TR) operator. The TR operator is shown to identify concurrence and differentiate between entangling and nonentangling operators. This distinction is of a topological nature, as the inclusion or exclusion of certain operators alters topological characteristics. Proofs are presented which demonstrate that the two-qubit system can be described in the framework of the tenfold classification, unveiling aspects of the connection between entanglement and a geometrical phase. Topological features are obtained systematically by a mapping to a quantum graph, allowing for a direct computation of topological integers and of the two-qubit equivalent of topological zero modes. An additional perspective is provided regarding the extension of this approach to condensed matter systems, illustrated through examples involving indistinguishable fermions and arrays of quantum dots.

We study the magnetic properties of the metallic kagome system $\left({\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\right)\mathrm{Sn}$ by a combination of muon spin relaxation ($\mu \mathrm{SR}$), magnetic susceptibility, and scanning tunneling microscopy (STM) measurements in single crystal specimens with Co concentrations $x=0,0.11,0.8$. In the undoped antiferromagnetic compound FeSn, we find possible signatures for a previously unidentified phase that sets in at $T^{*}\sim 50\mathrm{K}$, well beneath the Neel temperature $T_N\sim 376\mathrm{K}$, as indicated by a peak in the relaxation rate $1/T_1$ observed in zero field (ZF) and longitudinal field (LF) $\mu \mathrm{SR}$ measurements, with a corresponding anomaly in the ac and dc susceptibility, and an increase in the static width $1/T_2$ in ZF-µSR measurements. No signatures of spatial symmetry breaking are found in STM down to 7 K. Related to the location and motion of muons in FeSn, we confirm a previous report that about $40\%$ of the implanted muons reside at a field-cancelling high symmetry site at $T<250\mathrm{K}$, while an onset of thermal hopping changes the site occupancy at higher temperatures. In ${\mathrm{Fe}}_{0.89}{\mathrm{Co}}_{0.11}\mathrm{Sn}$, where disorder eliminates the field-cancellation effect, all the implanted muons exhibit precession and/or relaxation in the ordered state. In ${\mathrm{Fe}}_{0.2}{\mathrm{Co}}_{0.8}\mathrm{Sn}$, we find canonical spin glass behavior with freezing temperature $T_g\sim 3.5\mathrm{K}$; the ZF- and LF-µSR time spectra exhibit results similar to those observed in dilute alloy spin glasses CuMn and AuFe, with a critical behavior of $1/T_1$ at $T_g$ and $1/T_1\to 0$ as $T\to 0$. The absence of spin dynamics at low temperatures makes a clear contrast to the spin dynamics observed by $\mu \mathrm{SR}$ in many geometrically frustrated spin systems on insulating kagome, pyrochlore, and triangular lattices. The spin glass behavior of CoSn doped with dilute Fe moments is shown to originate primarily from the randomness of doped Fe moments rather than due to geometrical frustration of the underlying lattice.

Superconducting circuits incorporating Josephson elements represent a promising hardware platform for quantum technologies. Potential applications include scalable quantum computing, microwave quantum networks, and quantum-limited amplifiers. However, progress in Josephson junction–based quantum technologies is facing the ongoing challenge of minimizing loss channels. This is also true for parametric superconducting devices based on nonlinear Josephson resonators. In this work, we report on the fabrication and characterization of low-loss Josephson parametric devices operated in the GHz frequency range, showing record internal quality factors. Specifically, we achieve internal quality factors $Q_{\mathrm{int}}$ significantly exceeding ${10}^5$ for both Josephson parametric converters and Josephson parametric amplifiers in the single-photon regime by fitting the scattering data. We confirm the extracted $Q_{\mathrm{int}}$ values by analyzing purity of squeezed vacuum states generated by these devices. These low-loss devices mark a significant step forward in realizing high-performance quantum circuits, enabling further advancements in superconducting quantum technologies.

A key feature of the newly discovered altermagnet is that its spin degeneracy is lifted, although it has an antiferromagnetic order and zero net magnetization. In this work, we investigate a frustrated spin-$\frac{1}{2} J_1\text{−}{J}_2\text{−}\delta$ Heisenberg model on the square lattice by the tensor network method in combination with the linear spin-wave theory, with our focus on both the magnon excitations and longitudinal excitations. For a small $J_2$ and a finite range of $\delta$, we demonstrate that such a model hosts an altermagnetic ground state. Its magnon spectrum is split into two branches and the largest splitting occurs at $(\pm \pi /2,\pm \pi /2)$ in the Brillouin zone. The magnitudes of splitting in the two magnon modes are equal with respect to the case of $\delta =0$. Dynamical spin structure factors show that the low-energy peak in the longitudinal spectral weight around $(\pi /2,\pi /2)$ is also split, and thus the relative positions of the magnon modes and the longitudinal modes in energy may change in the presence of a finite $\delta$. These findings demonstrate that altermagnets harbor quantum dynamics that are more complex than the quantum dynamics of conventional collinear antiferromagnets.

We discuss the Josephson effect in a spin-singlet superconductor/spin-triplet superconductor junction fabricated on a substrate. Due to inversion symmetry breaking on top of the substrate, Rashba spin-orbit interaction works on electrons in the superconductors. As a result, spin-triplet (spin-singlet) Cooper pairs are induced in a spin-singlet (spin-triplet) superconductor. The presence of such induced Cooper pairs enables the lowest-order Josephson coupling between the two superconductors. Based on the theoretical results and recent experimental findings [X. Xu et al., Phys. Rev. Lett. 132, 056001 (2024)], we analyze the pair potential of $\beta \text{−}{\mathrm{Bi}}_2\mathrm{Pd}$.

Ferroelectric oxide films are known for superior electromechanical properties and extensive applications but are prone to brittleness and fracture in preparation, transferring, and integration for device fabrications, highlighting the contradiction between high coupling of physical properties and low ability of mechanical deformation. Dislocations, as one general form of plasticity, can be introduced to enhance ductility of ferroelectric films and yet remain to degrade performance and stability. It is crucial and challenging to control the nucleation and annihilation of dislocations in preparations and operations for ferroelectric oxide films, resolving the contradiction and satisfying the needs of different stages. Here we performed molecular dynamics to study the evolution of dislocations in $\mathrm{PbTi}{\mathrm{O}}_3$ films. The junctions of surface and domain walls triggered the nucleation of screw dislocations under compression. Combining with mechanical loading, the external electric field that moved the ferroelectric domain walls controlled the nucleation sites of screw dislocations. The screw dislocations in $\mathrm{PbTi}{\mathrm{O}}_3$ films glided and escaped under electric or mechanical fields. The stress induced by compressed or tensile deformation enabled the screw dislocations surrounded by asymmetric stress distribution to glide towards different directions. More interestingly, the damped oscillation of stress caused by the sudden change of electric field led to the ratchet movements of screw dislocations. The design of the changing rates of electric field could accelerate the annihilation of dislocations. These findings provide strategies for defect engineering in ferroelectric oxide films, precisely modulate the nucleation and annihilation of dislocations, and tackle the trade-off between the performance and deformability.

We construct an exactly solvable $\mathcal{PT}$-symmetric non-Hermitian model where a spin-$\frac{1}{2}$ isotropic quantum Heisenberg spin chain is coupled to two spin-$\frac{1}{2}$ Kondo impurities at its boundaries with coupling strengths that are complex conjugates of each other. Solving the model by means of a combination of the Bethe ansatz and density matrix renormalization group (DMRG) techniques, we show that the model exhibits three distinct boundary phases: a $\mathcal{PT}$-symmetric phase with a dissipative Kondo effect, a phase with bound modes and spontaneously broken $\mathcal{PT}$-symmetry, and a phase with an effectively unscreened spin (i.e., a free local moment). In the Kondo and the unscreened phases, the $\mathcal{PT}$-symmetry is unbroken, and hence all states have real energies, whereas in the bound-mode phases, in addition to the states with real energies, there exist states with complex energy eigenvalues that appear in complex conjugate pairs, signaling spontaneous breaking of the $\mathcal{PT}$-symmetry. The exact solution is used to provide an accessible benchmark for DMRG with a non-Hermitian matrix product operator representation that demonstrates an accuracy comparable to its Hermitian limit, thus showing the power of DMRG to handle non-Hermitian many-body calculations.

The nature of the magnetic ground state of highly frustrated systems remains puzzling to this day. Here, we have performed multifrequency electron spin resonance (ESR) measurements on a putative quantum spin liquid compound $\kappa \text{−}{\left(\mathrm{BEDT}\text{−}\mathrm{TTF}\right)}_2{\mathrm{Ag}}_2{\left(\mathrm{CN}\right)}_3$, which is a rare example of $S=1/2$ spins on a triangular lattice. At high temperatures, the spin susceptibility exhibits a weak temperature dependence which can be described by the Heisenberg model with an antiferromagnetic exchange interaction of strength $J/k_B\approx 175\mathrm{K}$. At low temperatures, however, the rapid drop of the static spin susceptibility, together with monotonic decrease of the ESR linewidth, indicates that strong singlet correlations develop below a pairing energy scale $T^{*}$ accompanied by a spin gap. On the other hand, a weak Curie-like spin susceptibility and the angular dependence of the linewidth suggest additional contributions from impurity spins. We propose the gradual formation of spin singlets with an inhomogeneous spin gap at low temperatures.

The usual one-way inequalities of the Rashba and Dresselhaus spin-orbit (SO) couplings in semiconductor heterostructures set a severe restriction for spin manipulation. Here, by resorting to a realistic system and a dual-gate multisubband model the following occurs. (i) We overcome this long-standing bottleneck and release unconventional SO manipulation, and so render it feasible for achieving universal SO control and for guiding experiments in unlocking new frontiers in spintronics. (ii) We also reveal the emergence of both aligned and crossed spin helices embracing nontopological and topological (TP) swirling textures, respectively, thus opening up a unique possibility for harnessing robust (either non-TP or TP) spin textures in device designs. Finally, (iii) we achieve the interconversion between the two distinct (TP and non-TP) phases through in situ electrical means, further facilitating possible applications in practice. Our findings may hold broad relevance across multiple fields of physics including spintronics, orbitronics, topological manner, and even quantum computing and quantum information science, particularly in the broad heterostructure community.

Minimal Kitaev chains, composed of two quantum dots connected via a superconductor, have emerged as an attractive platform to realize Majorana bound states (MBSs). These excitations exist when the ground state is degenerate. The additional requirement of isolating the MBS wave functions further restricts the parameter space to discrete sweet spots. While scaling up to Kitaev chains with more than two sites has the potential to improve the stability of the MBSs, longer chains offer more features to optimize, including the MBS localization length and the excitation gap. In this work, we theoretically investigate three-site Kitaev chains and show that there are three different types of sweet spots, obtained by maximizing distinct MBS properties: genuine three-site sweet spots with well-localized MBSs at the ends, effective two-site sweet spots, where the middle site acts as a barrier, and sweet spots with delocalized MBSs that overlap in the middle of the chain. These three cases feature different degrees of robustness against perturbations, with the genuine three-site being the most stable. We analyze the energy spectrum, transport, and microwave absorption associated with these three cases, showing how to distinguish them.

Incompressible insulating phases of electronic systems at partial filling of a lattice are often associated with charge ordering that breaks lattice symmetry. The resulting phases have an enlarged unit cell with an effective integer filling. Here we explore the possibility of insulating states—which we dub “quantum charge liquids” (QCLs)—at partial lattice filling that preserve lattice translation symmetry. Such QCL phases must necessarily either have gapped fractionally charged excitations and associated topological order or have gapless neutral excitations. We establish some general constraints on gapped fermionic QCL phases that restrict the nature of their topological order. We prove a number of results on the minimal topological order that is consistent with the lattice filling. In particular we show that, at rational fillings $\nu =p/q$ with $q$ an even integer, the minimal ground-state degeneracy on a torus of the fermionic QCL is $4q^2$, four times larger than that of the bosonic QCL at the same filling. We comment on models and physical systems which may host fermionic QCL phases and discuss the phenomenology of these phases.

Weyl semimetals can emerge from Dirac semimetals when the time-reversal or spatial-inversion symmetries are broken. Recently, it has been proposed based on Floquet theory that Dirac semimetals can be converted into Weyl semimetals even by shining circularly polarized light (CPL). Here we have investigated the possibility of such a Dirac-Weyl conversion by measuring the CPL-induced anomalous Hall conductivity (AHC) in a massive 3D Dirac semimetal ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$ in the paramagnetic phase using ultrafast midinfrared pump-terahertz Faraday rotation probe spectroscopy. We find that the field-strength and driving frequency dependence of the observed AHC is well accounted for by CPL-induced nonzero Berry curvature associated with the splitting of the Dirac bands as predicted by the Floquet theory. The estimated splitting of the Dirac bands reaches about 60% of the mass gap and the calculated CPL-induced AHC quantitatively reproduces the experimental observation, demonstrating a promising route toward the realization of Floquet-Weyl states from massive Dirac semimetals.

We propose a nanodevice based on multiterminal Josephson junctions for the creation and detection of poor man's Majorana (PMM) modes. The device consists of a double three-terminal Josephson junction (3TJJ) embedded in a planar semiconductor that engineers a two-site Kitaev chain. We identify the conditions necessary for the emergence of PMM modes by precisely tuning the superconducting phases of the terminals and the interjunction coupling between the 3TJJs. To validate our findings, we perform numerical simulations that account for disorder in a more general geometry and test experimentally feasible protocols based on conductance measurements to reliably detect these modes. Unlike traditional approaches that rely on magnetic fields, our design eliminates the need for such fields, potentially increasing the energy-level resolution and significantly expanding the range of compatible semiconductor materials, such as Ge-based heterostructures.

Neon is the fifth most abundant element and is found in the interior of stars and gas giant planets. Neon's noble, atomic fluid nature and large bandgap makes it an excellent candidate for comparison of experiment and theory at extreme conditions. We performed a combined computational and experimental study on shock compressed cryogenic liquid neon. Experiments at the Omega laser facility measured the principal Hugoniot to 600 GPa and provided temperature data along the principal Hugoniot. Magnetically accelerated, plate impact experiments at Sandia's Z machine demonstrate consistent results with the laser-driven data and emphasize the importance of using well-characterized impedance matching standards on the two experimental platforms. Additionally, density functional theory based molecular dynamics simulations reproduced the experimental Hugoniot data up to 500 GPa. We developed a new neon equation of state model based on the combined experimental data and simulation results at extreme conditions. This new equation of state significantly improves our understanding of the high pressure properties of neon compared to legacy models.

We performed single-crystal magnetic susceptibility and ${}^1\mathrm{H}$ NMR measurements on a quasi-1D, spin-1 antiferromagnet ${\mathrm{NiC}}_2{\mathrm{O}}_4·2{\mathrm{NH}}_3$, with temperature down to 100 mK and with field up to 26 T. With field applied along the chain direction (crystalline $b$ direction), a spin gap is determined at low fields. Our susceptibility and spin-lattice relaxation measurements reveal a Haldane phase at low field, with an intrachain exchange coupling $J\approx 35$ K and an easy-plane single-ion anisotropy of 17 K. A field-induced antiferromagnetic (AFM) ordering emerges at a field of 2.28 T, which sets a quantum critical point (QCP). The high-temperature spin-lattice relaxation rates $1/T_1$ resolves an onset of Tomonaga-Luttinger liquid behavior at field above 3.5 T.

We provide solid evidence for the long-standing presumption that model Hamiltonians with short-range interactions faithfully reproduce the physics of the long-range Coulomb interaction in real materials. For this aim, we address a generic Hubbard model that captures the quantum phase transitions between metal, Mott insulator, and charge-density-wave (CDW) insulator, in the absence of Fermi-surface nesting. By comparing the quantum phase diagrams for the $1/r$-Hubbard model on a half-filled chain with nearest-neighbor and $1/r$-long-range interactions, we argue that the inclusion of long-range interactions is not crucial for a proper description of interacting many-electron systems. To this end, we employ the density matrix renormalization group method on finite lattices and antiperiodic boundary conditions to determine the quantum phase transitions between the metallic Luttinger liquid for weak interactions, the Mott-Hubbard insulator for dominant on-site interactions, and the CDW insulator for dominant intersite interactions. The two phase diagrams qualitatively agree inasmuch as the quantum phase transitions are continuous in both cases. Moreover, simple Hartree-Fock theory and the atomic limit provide renormalization factors that allow us to quantitatively map the two phase diagrams onto each other. As a practical advantage, our findings imply that computational efforts can be reduced tremendously by using models with short-range interactions only.