Motivated by recent experimental and numerical evidence of deconfined quantum critical points and quantum spin liquid states in the spin-$1/2$ Heisenberg model on the Shastry-Sutherland lattice, we studied possible symmetric spin liquid states and their proximate ordered states under Schwinger boson formalism. We found a symmetric gapped $Z_2$ spin liquid state for intermediate model parameter $0.66<J_1/J_2<0.71$ under the mean-field approximation. The Schwinger boson mean-field picture is partially supported by exact-diagonalization and self-consistent spin wave theory results.

${\mathrm{FePSe}}_3$ is a collinear honeycomb antiferromagnet with an easy-axis anisotropy and large spins $S=2$. It belongs to a family of magnetic van der Waals materials which recently attracted considerable attention. In this work we present an experimental magneto-optical study of the low-energy excitation spectrum in ${\mathrm{FePSe}}_3$, together with its theoretical description. The observed response contains several types of magnon excitations. Two of them are conventional transverse magnons described by a classical theory of antiferromagnetic resonance. Two other modes are identified as multimagnon hexadecapole excitations with an anomalous $g$ factor approximately equal to 4 times the $g$ factor of a single ${\mathrm{Fe}}^{2+}$ ion. These quasiparticles correspond to full reversals of iron spins that coherently propagate in the up-down antiferromagnetic structure. They constitute a novel type of collective excitations in anisotropic magnetic solids, called longitudinal magnons. Comparison between theory and experiment allows us to estimate the microscopic parameters of ${\mathrm{FePSe}}_3$, including exchange coupling constants and the single-ion anisotropy.

We probed a gate-tunable InAs nanowire Josephson weak link by coupling it to a microwave resonator. Tracking the resonator frequency shift when the weak link is close to pinch-off, we observe that the ground state of the latter alternates between a singlet and a doublet when varying either the gate voltage or the superconducting phase difference across it. The corresponding microwave absorption spectra display lines that approach zero energy close to the singlet-doublet boundaries, suggesting parity-flipping transitions, which are in principle forbidden in microwave spectroscopy and expected to arise only in tunnel spectroscopy. We tentatively interpret them by means of an ancillary state isolated in the junction acting as a reservoir for individual electrons.

Energy is stored in a ${\mathrm{LiFePO}}_4$ battery electrode through the intercalation of Li. As Li incorporate into the crystal lattice of $\mathrm{Fe}\left(\mathrm{III}\right){\mathrm{PO}}_4$, electrons reduce Fe(III) into Fe(II). The interactions of Li and its vacant site (Va) with these localized electrons (holes), so-called polarons, cause phase separation during battery operation. These fundamental interactions are however difficult to quantify using standard electronic structure calculations. In this paper, we utilize $\mathrm{DFT}+U$ with occupation matrix control to compute interaction energies at varying Li-Fe(II) and Va-Fe(III) pair separations. The increased energy with separation warrants the use of an electrostatic description. The $\mathrm{DFT}+U$ data are fitted to a Coulombic potential with two-body corrections and used in a Monte Carlo scheme. The coordination of the species determines their short-range ordering, showing that the Li and Va create chains bridged by their associated polarons which dissociate into dimers at higher temperatures. This dissociation happens at higher temperatures for Va than for Li, indicating a more pronounced clustering behavior during the formation of ${\mathrm{FePO}}_4$. Notably, a significant amount of uncoordinated Li exists at elevated temperatures, challenging the simplified picture of complete Li-Fe(II) pairing.

We report on Raman scattering and ${}^{23}\mathrm{Na}$ nuclear magnetic resonance (NMR) investigations of $j_{\mathrm{eff}}=1/2$ hyperkagome antiferromagnet ${\mathrm{Na}}_{4-x}{\mathrm{Ir}}_3{\mathrm{O}}_8$, which lies in the Mott insulating state. Our Raman scattering experiments unveil remarkable parallels between the magnetic excitations of the pristine ${\mathrm{Na}}_4{\mathrm{Ir}}_3{\mathrm{O}}_8$ and the Kitaev honeycomb material ${\mathrm{Na}}_2{\mathrm{IrO}}_3$, which are characterized by dominant fractional spinon excitations. In the case of moderate Na-deficient ${\mathrm{Na}}_{4-x}{\mathrm{Ir}}_3{\mathrm{O}}_8$, however, a substantial suppression of the magnetic excitations is observed, alluding to the notable influence of charge fluctuations on spin dynamics. In addition, our site-specific ${}^{23}\mathrm{Na}$ NMR measurements offer further insights into the spin dynamics when a minor concentration of holes is introduced into a spin-orbit coupled Mott insulator. Specifically, the spin-lattice relaxation rate $1/T_1$ reveals the emergence of pseudogaplike correlations at the Na(2) site, alongside a critical slowing down behavior at the Na(1) and Na(3) sites. These findings showcase the intricate interplay between itinerant holes and magnetic correlations in a spin-liquid-like background.

The search for materials exhibiting multiple topological transport properties such as large anomalous Hall effect (AHE) and robust topological Hall effect (THE) are crucial for novel nanospintronic devices. However, such multiple unconventional Hall responses materials are rare in nature. Here, we report the coexistence of a giant AHE and robust THE in single crystals of $\mathrm{SmM}{\mathrm{n}}_2\mathrm{G}{\mathrm{e}}_2$ with a noncoplanar spin texture. A giant anomalous Hall conductivity of $1715{\mathrm{\Omega }}^{-1}\mathrm{c}{\mathrm{m}}^{-1}$ is observed for $H\text{//}a$ and $I\text{//}b$ whereas a large THE is observed for $H\text{//}c$ and $I\text{//}b$. A scaling analysis suggests that the giant AHE in this compound has an overwhelmingly large extrinsic contribution due to the unconventional skew scattering induced by short-range conical spin clusters with scalar spin chirality. The large THE originates from the real-space magnetic skyrmionic bubbles which are observed using the Lorenz transmission electron microscopy. Additionally, a planar topological Hall effect (PTHE) is observed when the magnetic field and the current are coplanar. The PTHE is related to a noncoplanar spin texture with nonzero spin chirality. These observations of multiple topological transport responses contribute to a deeper understanding of the noncoplanar $\mathrm{SmM}{\mathrm{n}}_2\mathrm{G}{\mathrm{e}}_2$ material and advance their application in spintronic devices.

Hydrostatic pressure transforms the superconductor ${\mathrm{MoTe}}_2$ from a type-II Weyl semimetallic $T_d$ phase to a topologically trivial $1T^{\prime }$ phase at low temperature, serving as an ideal platform to explore the interplay between topology and superconductivity (SC). We report a soft point-contact-spectroscopy (SPCS) study on single-crystalline ${\mathrm{MoTe}}_2$ under hydrostatic pressure up to 2.5 GPa, where the local SC transition temperature $T_c$ of ${\mathrm{MoTe}}_2$ in the contact region shows the same behavior as the reported pressure phase diagram. Excess current extracted from the integrated conductance subtracted by the normal state shows a positive correlation with the $1T^{\prime }$ phase volume fraction as a function of pressure, supporting that the probed SC under pressure is mainly contributed by the $1T^{\prime }$ phase of ${\mathrm{MoTe}}_2$. Our SPCS spectra are better fitted by a two-gap $s$-wave Blonder-Tinkham-Klapwijk model in the whole pressure range, yielding $2{\mathrm{\Delta }}_1/k_B{T}_c=2.0\text{–}2.5$ and $2{\mathrm{\Delta }}_2/k_B{T}_c=4.15\text{–}5.0$, respectively, and suggesting a strong-coupling SC for $1T^{\prime }\text{−}{\mathrm{MoTe}}_2$.

We study the two-channel Kondo problem in the context of two interacting helical liquids coupled to a spin-$\frac{1}{2}$ magnetic impurity. We show that the interactions between the two helical liquids significantly affect the phase diagram and other observable properties. Using a multichannel Luttinger liquid formalism, we analyze both the Toulouse limit, where an exact solution is available, and the weak coupling limit, which can be studied via a perturbative renormalization group (RG) approach. We recover the results for the decoupled limit (interactions between the helical liquids switched off) and point out deviations from the known results due to this coupling. The model under study is mapped to a model of two effectively decoupled helical liquids coupled to an impurity. The perturbative RG study shows that each of these channels can flow to either a ferromagnetic or an antierromagnetic fixed point. We obtain the phase diagram of the coupled system as a function of the system parameters. The observable consequences of the interaction between the two channels are captured using linear response theory. We compute the negative correction to the conductance due to the Kondo scattering processes and show how it scales with the temperature as a function of interchannel interaction.

In the quest for exotic phases of matter due to the interplay of various interactions, iridates hosting a spin-orbit entangled $j_{\mathrm{eff}}=1/2$ ground state have been in the spotlight in recent years. Also in view of parallels with the low-energy physics of high-temperature superconducting cuprates, the validity of a single- or few-band picture in terms of the $j_{\mathrm{eff}}$ states is key. However, in particular, for its structurally simple member ${\mathrm{Ba}}_2{\mathrm{IrO}}_4$, such a systematic construction and subsequent analysis of minimal low-energy models are still missing. Here we show by means of a combination of different ab initio techniques with dynamical mean-field theory that a three-band model in terms of Ir-$j_{\mathrm{eff}}$ states fully retains the low-energy physics of the system as compared to a full Ir-$5d$ model. Providing a detailed study of the three-band model in terms of spin-orbit coupling, Hund's coupling, and Coulomb interactions, we map out a rich phase diagram and identify a region of an effective one-band metal-insulator transition relevant to ${\mathrm{Ba}}_2{\mathrm{IrO}}_4$. Compared to available angle-resolved photoemission spectra, we find good agreement of salient aspects of the calculated spectral function and identify features which require the inclusion of nonlocal fluctuations. In a broader context, we envisage the three- and five-band models developed in this paper to be relevant for the study of doped ${\mathrm{Ba}}_2{\mathrm{IrO}}_4$ and to further clarify the similarities and differences with cuprates.

A wide array of unusual phenomena has recently been uncovered in kagome solids. The charge density wave (CDW) state in the kagome superconductor ${A\mathrm{V}}_3{\mathrm{Sb}}_5$, in particular, intrigued the community; the CDW phase appears to break the time-reversal symmetry despite the absence of spin magnetism, which has been tied to exotic orbital loop currents possibly intertwined with magnetic field tunable crystal distortions. To test this connection, precise determination of the lattice response to an applied magnetic field is crucial but can be challenging at the atomic scale. We establish a scanning tunneling microscopy (STM) based method to study the evolution of the ${A\mathrm{V}}_3{\mathrm{Sb}}_5$ atomic structure as a function of magnetic field. The method substantially reduces the errors of typical STM measurements, which are at the order of 1% when measuring an in-plane lattice constant change. We find that the out-of-plane lattice constant of ${A\mathrm{V}}_3{\mathrm{Sb}}_5$ remains unchanged (within ${10}^{-6}$) by the application of both in-plane and out-of-plane magnetic fields. We also reveal that the in-plane lattice response to magnetic field is at most at the order of 0.05%. Our experiments provide further constraints on time-reversal symmetry breaking in kagome metals and establish a tool for higher-resolution extraction of the field-lattice coupling at the nanoscale applicable to other quantum materials.

The layered perovskite ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ has attracted a great deal of attention recently due to the observation of unconventional superconductivity $(T_c\approx 80\mathrm{K}$) at high pressures. Motivated thereby, we present a computational study based on density functional plus dynamical mean-field theory calculations for the normal-state electronic reconstruction of a pressurized ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ superconductor. We show how a coherence-incoherence crossover behavior manifests itself due to sizable electron correlation effects in the $e_g$-shell one-particle spectral functions. Our results capture the $T$ dependence of the resistance, providing a many-particle interpretation for the emergent strange metal behavior seen in experiment. Our findings call for more studies on unconventional high-temperature superconductors to unearth the consequences of proximity to marginal Fermi liquidness as the prominent candidate in governing the transport anomalies of a strange metal.

With high enough doping concentrations, organic dye–doped polymer materials exhibit a negative real part of the permittivity within an energy range just above their material absorption, incurring surface exciton (SE) modes at these energies. Here, we report on how such modes can be used to realize strong light-matter coupling with photoactive molecules. Our simulations reveal that SEs can facilitate strong coupling by sustaining the energy-splitting-induced transparency; however, the polaritons may not be visible in the absorption since they can easily be located outside of the narrow negative permittivity regime. Moreover, we show that the SE modes cannot couple strongly with the surface plasmons. Our findings shed light on the weak and strong coupling properties of SEs.

Off-axis twisted waveguides possess unique optical properties such as circular and orbital angular momentum (OAM) birefringence, setting them apart from their straight counterparts. Analyzing mode formation in such helical waveguides relies on the use of specific coordinate frames that follow the twist of the structure. In this paper, the differences between modes forming in high-contrast off-axis twisted waveguides defined in the three most important coordinate systems—the Frenet-Serret, the helicoidal, or the Overfelt frame—are investigated through numerical simulations. We explore modal characteristics up to high twist rates (pitch: $50\mu \mathrm{m}$) and clarify a transformation allowing us to map the modal fields and the effective index back to the laboratory frame. In case the waveguide is single-mode, the fundamental modes of the three types of waveguides show significant differences in terms of birefringence, propagation loss, and polarization. Conversely, the modal characteristics of the investigated waveguides are comparable in the multimode domain. Furthermore, our paper examines the impact of twisting on spatial mode properties. At high twist rates, a separation of modes with different spins is observed, suggesting a potential influence of the photonic spin Hall effect. Additionally, twisting induces OAM-dependent changes in the intensity distribution, indicating the presence of the photonic orbital Hall effect. Lastly, modes of single-mode helical waveguides were found to exhibit superchiral fields on their surfaces. These findings provide a comprehensive basis for further research into the physics of twisted off-axis waveguides. Implementation approaches such as 3D nanoprinting or fiber-preform twisting open the doors to potential applications of such highly twisted waveguides, including chip-integrated devices for broadband spin- and OAM-preserving optical signal transport, as well as applications in chiral spectroscopy or nonlinear frequency conversion.

The realization of quantum gates in topological quantum computation still confronts significant challenges in both fundamental and practical aspects. Here, we propose an ancilla-free, deterministic, and topologically protected measurement-based scheme to realize the implementation of Clifford quantum gates on the Majorana qubits. Our scheme is based on a rigorous proof that the single-qubit gate can be performed by leveraging the neighboring Majorana qubit but not disturbing its carried quantum information, enabling an ancilla-free scheme for the topological quantum computing with Majorana qubits. Benefiting from the ancilla-free construction, we show the minimum measurement sequences with four steps to achieve two-qubit Clifford gates by constructing their geometric visualization. The uncertainty of the current strategy can be avoided by manipulating the Majorana modes in their parameter space, as shown in a concrete Majorana platform, correcting the undesired measurement outcomes while maintaining topological protection. Our scheme identifies the minimal operations of measurement-based topological and deterministic Clifford gates and offers an ancilla-free design of topological quantum computation.

The melting temperature of the quantum electron solid in double-layer two-dimensional ${\mathrm{MoS}}_2$ stacked on opposite sides of a thin layer of BN is larger than previous single-layer results in Si-MOSFETs and bilayer estimates by four orders of magnitude. This giant enhancement of the stability of the solid comes from a shear modulus $\mu$ that is an order of magnitude larger than expected and comes from a weakened electron-electron interaction due to the screening by the polarization charges at the interfaces of the experimental structure. We found that the short-range part of the interelectron Coulomb potential actually provides for a negative contribution to $\mu$ and makes the lattice less stable. The weakening of this short-range contribution enhances $\mu$ by an order of magnitude. This large $\mu$, together with a larger energy scale $e^2/a_b$ for a smaller Bohr radius $a_b$ for the experimental structure, leads to a high melting temperature and makes possible using the structure as a practical logic device. Our understanding of this phenomenon guides us in optimizing its design. The large melting temperature and the small zero-temperature critical density agrees with experimental results extracted from the density and temperature dependence of the Coulomb drag resistance.

Efficient thermal management in nanoscale electronic devices presents a pressing challenge. The two-dimensional (2D) materials, notably bilayer black phosphorus, exhibit unique thermal properties that hold promise for addressing this challenge. In this study, we explore the impact of the strain on phonon hydrodynamics in bilayer black phosphorus, providing insight into its intricate thermal behavior. By employing first-principles calculations and the Boltzmann transport equation, we uncover that the thermal conductivity generally decreases with increasing strain. However, a nonmonotonic behavior emerges at small strains, challenging conventional expectations. This behavior is attributed to the intricate interplay among the softening of optical phonons induced by strain, the subsequent enhancement of phonon scattering, and the maintenance/strengthening of the quadratic Z-axis acoustic (ZA) mode through reinforced quasicovalent bonds, ultimately contributing to improved phonon hydrodynamics. Our findings underscore the pivotal role of interlayer thickness in governing these effects. Our research pioneers the modulation of phonon hydrodynamics, offering transformative insight into the 2D materials’ thermal behavior.

The bond-dependent Kitaev model offers a playground in which one can search for quantum spin liquids. In these Kitaev materials, a symmetric off-diagonal $\mathrm{\Gamma }$ term emerges, hosting a number of remarkable features, which has been particularly challenging to fully understand. One primary question that arises after recognizing a new phase is how information will spread in it. Out-of-time-ordered commutators and entanglement entropy describe processes whereby information about the initial condition of a unitarily evolving system propagates over the system. A possible way to investigate dynamics in such systems is by considering one-dimensional models. We investigate here the one-dimensional spin-1/2 $XY$ model in a transverse field with a $\mathrm{\Gamma }$ interaction with periodic boundary conditions imposed. We will show that the $\mathrm{\Gamma }$ interaction constructs an asymmetric “light-cone” with different butterfly velocities. In addition, it leads to faster information propagation in the spiral phase and slower propagation in the ferromagnetic and paramagnetic phases. Interestingly, we observe a pronounced effect in the entanglement entropy, explicitly showing up as a two-stage linear growth in time as fast/slow then slow/fast for quenches originating from the spiral phase. We hope our work paves the way for studying more about the spreading of information in one-dimensional Kitaev materials, which can in turn help to discover unknown aspects of higher-dimensional models.