We report the observation of weak ferromagnetism and possible non-Fermi-liquid behavior in itinerant electronic material ${\mathrm{Co}}_3\mathrm{SnC}$ via magnetic properties, electrical transport, and specific heat under various magnetic fields. The analysis of magnetic properties suggests that ${\mathrm{Co}}_3\mathrm{SnC}$ undergoes a noncollinear itinerant ferromagnetic-paramagnetic phase transition around 3.6 K. With this transition, non-Fermi-liquid (NFL) behavior appears at low temperature covering a wide temperature range. The features of NFL are revealed by the power-law temperature dependence of resistivity and also proved by the $–T\log T$ dependence upturn in specific heat and the $T^{4/3}$ dependence of inverse susceptibility. With increasing the fields, the temperature coefficient of the $T^2$ term in the resistivity data shows a ${\left(H–H_{\mathrm{c}}\right)}^{-0.5}$ divergence approaching the $H_{\mathrm{c}}$ and reduces monotonously with increasing the field further, apart from the usual $1/\left(H–H_{\mathrm{c}}\right)$ dependence with the whole Fermi surface under the singular scattering. The exponent $n$ in the temperature dependence of resistivity shows an increase from $n=1.0$ to 2.0 with increasing the field as the evidence for the field-induced crossover from NFL to FL behavior; it is thought that field dependence of magnetic ground states should be responsible for this crossover; the relative mass enhancement factor $\lambda \left(H\right)/\lambda \left(0\right)$ reduces monotonically to nearly 60% at 9.0 T, indicating the gradual suppression of magnetic fluctuations and electron-electron scattering. Our results indicate that ${\mathrm{Co}}_3\mathrm{SnC}$ is a candidate for exploring itinerant quantum materials.

Peculiar temporal intermittent microscopic dynamics has been recently reported during structural relaxation in metallic glasses, though its origin is poorly understood. By using x-ray photon correlation spectroscopy, we have investigated the atomic motions in a model system of metallic glass with distinct stability and in situ stress states. We find that the microscopic dynamics can be tuned from dramatically nonmonotonous to monotonous. The intermittent dynamics is always accompanied by the activation of a secondary relaxation process, as indicated by the drop of the initial nonergodic plateau of the intensity-intensity correlation function. Both phenomena depend on the material state and can be suppressed by simultaneously lowering the fictive temperature and external loading, leading the glass in a stationary metastable state which appears independent on the thermal history of the system.

We present a thorough investigation of the collective dynamics of liquid Ag combining neutron Brillouin scattering and ab initio molecular dynamics (AIMD) determinations of the dynamic structure factor $S(Q,\omega )$. The main scope of this work is not only to provide experimental results for some important dynamical properties of this liquid metal in the wave-vector range $4<Q<16{\mathrm{nm}}^{-1}$, but also to inquire about the scarce detectability of shear waves apparently characterizing two elements of group IB, differently from other metals. In fact, as in the case of Au, a transverse-like dynamics is not deducible from the experimental $S(Q,\omega )$ of Ag, despite the indisputable quality of the neutron data collected on the BRISP spectrometer at the Institut Laue Langevin in Grenoble. However, the significant agreement between experiment and AIMD calculations allowed for an in-depth study of the simulated $S(Q,\omega )$ in a $Q$ range overlapping and extending the experimental one. A multimode analysis, already proven very successful in the description of various dynamical properties of fluid systems, is shown to be extremely effective also to analyze the intermediate scattering function predicted by AIMD at the various $Q$ values, and eventually enables a reliable determination of both longitudinal and transverse branches in the dispersion curve of this liquid. Throughout the paper we highlight the importance of referring to theoretically well-founded models for $S(Q,\omega )$ and of imposing physical constraints in a fit-based analysis: These ensure that the used models obey fundamental properties of the dynamic structure factor.

We study the geometrical conditions for stabilizing magnetic skyrmions in cylindrical nanostrips and nanotubes of ferromagnetic materials with chiral interactions. We obtain the low-temperature equilibrium state of the system implementing a simulation annealing technique for a classical spin Hamiltonian with competing isotropic exchange and chiral interactions, radial anisotropy and an external field. We address the impact of surface curvature on the formation, the shape and the size of magnetic skyrmions. We demonstrate that the evolution of the skyrmion phase with the curvature is controlled by the competition between two characteristic lengths, namely the curvature radius, $R$ (geometrical length) and the skyrmion radius, $R_{\text{sk}}$ (physical length). In narrow nanotubes $(R<R_{\text{sk}})$ the skyrmion phase evolves to a stripe phase, while in wide nanotubes $(R>R_{\text{sk}})$ a mixed skyrmion-stripe phase emerges. Most interestingly, the mixed phase is characterized by spatially separated skyrmions from stripes owing to the direction of the applied field relative to the surface normal. In the stability regime $(R\gtrsim R_{\text{sk}})$ skyrmions remain circular and preserve their size as a consequence of their topological protection. Zero-field skyrmions are shown to be stable on curved nanoelements with free boundaries within the same stability region $(R\gtrsim R_{\text{sk}})$. The experimental and technological perspectives from the stability of skyrmions on cylindrical surfaces are discussed.

We study the superconducting instability mediated by spin fluctuations in the Eliashberg theory for a minimal two-band model of iron-based superconductors. While antiferromagnetic spin fluctuations can drive superconductivity (SC) as is well established, we find that spin fluctuations necessarily contain a contribution to suppress SC even though SC can eventually occur at lower temperatures. This self-restraint effect stems from a general feature of the spin-fluctuation mechanism, namely, the repulsive pairing interaction, which leads to phase frustration of the pairing gap and consequently the suppression of SC.

Detailed ${}^{31}\mathrm{P}$ nuclear magnetic resonance (NMR) measurements are presented on well-characterized single-crystals of antiferromagnetic van der Waals ${\mathrm{Ni}}_2{\mathrm{P}}_2{\mathrm{S}}_6$. An anomalous breakdown is observed in the proportionality of the NMR shift $K$ with the bulk susceptibility $\chi$. This so-called $K$–$\chi$ anomaly occurs in close proximity to the broad peak in $\chi \left(T\right)$, thereby implying a connection to quasi-two-dimensional (2D) magnetic correlations known to be responsible for this maximum. Quantum chemistry calculations show that crystal field energy level depopulation effects cannot be responsible for the $K$–$\chi$ anomaly. Appreciable transferred hyperfine coupling is observed, which is consistent with the proposed Ni–S–Ni super- and Ni–S–S–Ni super-super-exchange coupling mechanisms. Magnetization and spin-lattice relaxation rate ($T_1^{-1}$) measurements indicate little to no magnetic field dependence of the Néel temperature. Finally, $T_1^{-1}\left(T\right)$ evidences relaxation driven by three-magnon scattering in the antiferromagnetic state.

In Phys. Rev. B 93, 140206(R) (2016), electron transport governed by nuclear tunneling was claimed to be a more realistic transport mechanism in semiconducting polymers as compared to Marcus and Miller-Abrahams transport mechanisms. The conclusion was based on the analysis of the field-dependent charge carrier mobility. We point out the unjustified simplification in the theoretical description of the electron transport governed by nuclear tunneling which caused such a conclusion.

The authors reply to the Comment by Nenashev et al.

We study how multiple charge excitations appear in the resonant inelastic x-ray scattering (RIXS) spectra of metals. Typically, the focus is upon single excitations in the problem, the plasmons and electron-hole pairs, while the multiexcitation processes are neglected. However, at small momentum transfer the multiexcitation contributions may dominate the signal and one needs to understand how to interpret the data in such cases. In particular, we demonstrate how to “decode” the total multiexcitation intensity and extract the plasmon dispersion. While our calculations are based on the random phase approximation for jellium, which does not allow us to obtain quantitatively precise results in the entire region of parameters, we expect them to capture semiqualitatively all features expected for charged Fermi-liquid states, including universal and singular properties of the RIXS spectra.

We report the synthesis and systematic studies of a new layered ternary telluride ${\mathrm{TaPdTe}}_5$ with quasi-one-dimensional ${\mathrm{PdTe}}_2$ chains. This compound crystalizes in a layered orthorhombic structure with space group $Cmcm$. Analysis of its curved field-dependent Hall resistivity, using the two-band model, indicates the hole-dominated transport with a high mobility ${\mu }_h=2.38\times {10}^3{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ at low temperatures. The in-plane magnetoresistance (MR) displays significant anisotropy with field applied along the crystallographic $b$ axis. The MR with the current applied along the $c$ axis is also measured in high magnetic fields up to 51.7 T. Remarkably, it follows a power-law dependence and reaches $(9.5\times {10}^3)\%$ at 2.1 K without any signature of saturation. The de Haas–van Alphen oscillations show a small Fermi surface pocket with a nontrivial Berry phase. The Shubnikov–de Haas (SdH) oscillations are detected at low temperatures and under magnetic fields above 28.5 T. Two effective masses $m^{*}$ ($0.26m_e$ and $0.41m_e$) are extracted from the oscillatory SdH data. Our first-principles calculations unveil a topological Dirac cone in its surface states, and, in particular, the topological index indicates that ${\mathrm{TaPdTe}}_5$ is a topologically nontrivial material.

We investigate the relationship between ion implantation and the optical linewidth of the nitrogen vacancy (NV) zero-phonon line (ZPL) in bulk and structured samples. We also propose a novel approach to ion implantation that we name postimplantation, in which nitrogen is implanted after all fabrication processes have been completed. We examine three post-implanted samples, one implanted with ${}^{14}\mathrm{N}$ and two with ${}^{15}\mathrm{N}$ isotopes. We perform photoluminescence excitation (PLE) spectroscopy to assess optical linewidths and optically detected magnetic resonance (ODMR) measurements to isotopically classify the NV centers. From this, we find that NV centers formed from nitrogen naturally occurring in the diamond lattice are characterized by a linewidth distribution peaked at an optical linewidth nearly two orders of magnitude smaller than the distribution characterizing most of the NV centers formed from implanted nitrogen. Surprisingly, we also observe a number of ${}^{15}\mathrm{NV}$ centers with narrow ($<500\mathrm{MHz}$) linewidths, implying that implanted nitrogen can yield NV centers with narrow optical linewidths. We further use a Bayesian approach to statistically model the linewidth distributions, to accurately quantify the uncertainty of fit parameters in our model, and to predict future linewidths within a particular sample. Our model is designed to aid comparisons between samples and research groups, in order to determine the best methods of achieving narrow NV linewidths in structured samples.

We present that the hexagonal boron nitride ($h$-BN) layer is a platform that facilitates strong light-matter interactions. We calculate the emission spectrum of a quantum emitter (QE) interacting with the $h$-BN layer at the strong-coupling regime. The $h$-BN layer supports phonon polariton modes at the far-infrared part of the spectrum that lead to a ${10}^4$ confinement of light. The phonon polaritons are the main channel of relaxation of the QE, where the Purcell factor of the QE shows an enhancement of the relaxation rate above three orders of magnitude, compared to the free space value, when it is placed $100\mathrm{nm}$ above the $h$-BN layer. At smaller separation distances of the QE with the $h$-BN layer the total system operates in the strong-coupling regime, which appears as two peaks in the emission spectrum, splitting the single emission peak of the QE emitting in the free space. This energy splitting is the Rabi splitting $\hslash \mathrm{\Omega }$ that depends on the transition energy $\hslash {\omega }_0$ of the QE, the position and the free-space relaxation rate of the QE, reaching values of $\mathrm{\Omega }/{\omega }_0=23.5\%$.

We derive a simple formula for the real-space chirality of twisted bilayer graphene that can be related to the cross product of its sheet currents. This quantity shows well-defined plateaus for the first remote band as a function of the gate voltage which are approximately quantized for commensurate twist angles. The zeroth plateau corresponds to the first magic angle where a sign change occurs due to an emergent $C_6$ symmetry. Our observation offers a new definition of the magic angle based on a macroscopic observable which is accessible in typical transport experiments.

Within the expanding field of non-Hermitian physics, non-Hermitian pumping has emerged as a key phenomenon, epitomized through the skin effect via extensive boundary mode accumulation modifying the conventional Bloch picture. Beyond redefining bulk-boundary correspondences, we show that non-Hermitian pumping induces an unprecedented type of spectral topology: It admits a classification in terms of graph topology, which is distinct from conventional topological classifications of the eigenstate or energy Riemann surface. Each topological class is characterized by a conformally invariant configuration of spectral branching singularities, with gap-preserving transitions giving rise to emergent band geometry and Berry curvature discontinuities physically manifested as anomalous response kinks. By placing all Hermitian and non-Hermitian lattice Hamiltonians on equal footing, our comprehensive framework also enables the first analytic construction of topological phase diagrams in the presence of multiple nonreciprocal coupling scales, as prototypically demonstrated for the extended non-Hermitian Chern and Kitaev models. Based on general algebraic geometry properties of the energy dispersion, our framework can be directly generalized to multiple bands, dimensions, and even interacting systems. Overall, it reveals the conspiracy of band representations, spectral topology, and complex geometry as it unfolds in directly measurable quantities.

We develop a theory of finite-temperature momentum-resolved tunneling spectroscopy (MRTS) for disordered, interacting, two-dimensional, topological-insulator edges. The MRTS complements conventional electrical transport measurement in characterizing the properties of the helical Luttinger liquid edges. Using the standard bosonization technique, we study low-energy spectral function and the MRTS tunneling current, providing a detailed description controlled by disorder, interaction, and temperature, taking into account Rashba spin-orbit coupling, interedge interaction, and distinct edge velocities. Our theory provides a systematic description of the spectroscopic signals in the MRTS measurement we hope will stimulate future experimental studies on the two-dimensional time-reversal invariant topological insulator.

The spin polarization in centrosymmetric molybdenum disulfide ($\mathrm{Mo}{\mathrm{S}}_2$) bulk crystal is recorded by helicity dependent photocurrent exposed as elliptically polarized terahertz (THz) emission. We assign this observation to hidden spin polarization due to the local Dresselhaus effect induced by the molybdenum atomic site asymmetry. This spin polarization induces ultrafast optically controlled circular photogalvanic current that results in elliptically polarized THz emission. Furthermore, this THz radiation exhibits a helicity dependent bleaching effect under opposite circularly polarized excitations due to the spin relaxation. Our results demonstrate the viability of all-optical control of hidden spin polarization in two-dimensional materials and propose the applicability of the THz emission spectroscopy as a sensitive and contactless method to study spintronic physics in two-dimensional materials.

The effect of high tensile strain and low dimensionality on the magnetic and electronic properties of $\mathrm{Ca}\mathrm{Mn}{\mathrm{O}}_3$ ultrathin films, epitaxially grown on $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ substrates, are experimentally studied and theoretically analyzed. By means of ab initio calculations, we find that both the high strain produced by the substrate and the presence of the free surface contribute to the stabilization of an in-plane ferromagnetic coupling, giving rise to a nonzero net magnetic moment in the ultrathin films. Coupled with this change in the magnetic order we find an insulator-metal transition triggered by the quantum confinement and the tensile epitaxial strain. Accordingly, our magnetic measurements in 3-nm ultrathin films show a ferromagnetic hysteresis loop, absent in the bulk compound due to its G-type antiferromagnetic structure.

We study the electronic transport properties at the intersection of three topological zero lines as the elementary current partition node that arises in minimally twisted bilayer graphene. Unlike the partition laws of two intersecting zero lines, we find that (i) the incoming current can be partitioned into both left-right adjacent topological channels and (ii) the forward-propagating current is nonzero. By tuning the Fermi energy from the charge-neutrality point to a band edge, the currents partitioned into the three outgoing channels become nearly equal. Moreover, we find that the current partition node can be designed as a perfect valley filter and energy splitter controlled by electric gating. By changing the relative electric-field magnitude, the intersection of three topological zero lines can transform smoothly into a single zero line, and the current partition can be controlled precisely. We explore the available methods for modulating this device systematically by changing the Fermi energy, the energy gap size, and the size of the central gapless region. The current partition is also influenced by magnetic fields and the system size. Our results provide a microscopic depiction of the electronic transport properties around a unit cell of minimally twisted bilayer graphene and have far-reaching implications in the design of electron-beam splitters and interferometer devices.