Taking chainlike $\mathrm{Tl}X{\mathrm{Se}}_2$ $(X=\mathrm{Tl}, \mathrm{In}, \mathrm{Al})$ as examples, we find that weak in-plane atomic interactions in these crystals intrinsically lead to extreme in-plane phonon blocking and heat flux confinement. We explicitly evaluate the propagative and diffusive lattice thermal transports based on the unified theory on top of the fourth-order lattice anharmonicity, and the results manifest that high-frequency phonons make negligible contributions to two channel heat transfer along the in-plane directions. This phenomenon provides a feasible approach for an effective suppression of the overall lattice thermal conductivity $\left({\kappa }_{\mathrm{L}}\right)$. The findings are also applicable to a series of quasi-one-dimensional solids with different crystal structures. This work provides fundamental insight into the understanding and minimization of low ${\kappa }_{\mathrm{L}}$ of quasi-one-dimensional crystals by focusing on their harmonic lattice dynamics.

We report strong damping enhancement in yttrium iron garnet (YIG) film due to spin inhomogeneity at the interface. The growth-induced thin interfacial gadolinium iron garnet (GdIG) layer antiferromagnetically (AFM) exchange couples with the top YIG layer. The out-of-plane angular variation of ferromagnetic resonance linewidth $\mathrm{\Delta }H$ reflects a large inhomogeneous distribution of the effective magnetization $\mathrm{\Delta }4\pi M_{\mathrm{eff}}$ due to the presence of the aforementioned AFM exchange coupling between the interfacial-GdIG and top-YIG layer. We probe the spin inhomogeneity at the YIG-GdIG interface by performing an in-plane angular variation of resonance field $H_r$, leading to a unidirectional feature. The large extrinsic $\mathrm{\Delta }4\pi M_{\mathrm{eff}}$ contribution, apart from the inherent intrinsic Gilbert contribution, manifests enhanced precessional damping in the YIG film.

A strain modulated ferromagnetic resonance technique was applied to determine two cubic magnetoelastic constants of the epitaxially grown 30-nm-thick ${\mathrm{Co}}_2{\mathrm{Fe}}_x{\mathrm{Mn}}_{1-x}\mathrm{Si}$ magnetic layers with different Fe and Mn contents, which were deposited on a MgO substrate with a 20-nm-thick Cr buffer layer—MgO (001) $\parallel$ Cr(001) $\parallel {\mathrm{Co}}_2{\mathrm{Fe}}_x{\mathrm{Mn}}_{1-x}\mathrm{Si}$ (001). It was found that, for the samples with the Fe content $x=0.4$ or higher, the magnitudes of the two cubic magnetoelastic constants are clearly different, showing that the magnetoelastic properties of these samples are different than in the case of isotropic samples for which these two constants are expected to be equal. The magnitude of the cubic magnetocrystalline anisotropy constant reveals an evident maximum at the composition of $x=0.4$, which corresponds to the minimum of the minor spin density of states, and thus the correlation between the cubic magnetocrystalline anisotropy and the electronic band structure. For all the investigated samples, a large perpendicular component of the magnetocrystalline anisotropy was observed as well as inhomogeneous broadening of the ferromagnetic resonance linewidth.

Spin fluctuations in the triangular-lattice Heisenberg antiferromagnet ${\mathrm{NaCrO}}_2$ are investigated by means of quasielastic neutron scattering with high energy resolution and a wide energy band. Two components with the following features are captured separately. They are pronounced at intermediate temperatures of 20–50 K. One, with quite an extended lifetime corresponding to $\sim 0.001E_{\mathrm{ex}}$ ($E_{\mathrm{ex}}$ is the exchange energy), nearly disappears at low temperature (10 K), and the other, with an extended lifetime of $\sim 0.01E_{\mathrm{ex}}$, survives there, identified as the free ${\mathbb{Z}}_2$ vortex and ${\mathbb{Z}}_2$-vortex pair, respectively, in agreement with the ${\mathbb{Z}}_2$-vortex theory.

High-pressure synthesis techniques have allowed for the growth of samples on the indium-rich side of (Pb,In)Te, which have increased superconducting transition temperatures compared to lead-rich compounds. In this paper we present measurements of the temperature dependence of the London penetration depth $\mathrm{\Delta }\lambda \left(T\right)$ in the compound ${\mathrm{In}}_{0.8}{\mathrm{Pb}}_{0.2}\mathrm{Te}$, which shows a bulk $T_{c,\mathrm{onset}}$ of $\sim 4.75$ K. The results indicate fully gapped BCS-like behavior, ruling out odd-parity topologically nontrivial $A_{2u}$ pairing, however, odd-parity $A_{1u}$ pairing is still possible. Critical field values measured below 1 K and other superconducting parameters are also presented.

Stripe domains in thin films form through a complex competition of perpendicular anisotropy and demagnetizing energy and are still lacking a complete micromagnetic description, despite being investigated since 50 years. This paper elucidates the formation of stripe domains with a special focus on the dependence of stripe domain width on film thickness with varying ratio of the two major energy contributions. An overview and review of the most established analytical models for the calculation of this dependency is given with respect to experimental data. For this purpose, new measurements on epitaxial Fe-Co-C films with perpendicular anisotropy have been performed. An efficient and rigorous micromagnetic simulations method is proposed, which proved to be comparable or better than previous models in describing experimental findings, especially for films with strongly dominating demagnetizing energy. Comprehensive simulations were performed to determine thickness-dependent stripe width for various material parameters, which can serve as a benchmark for analytical theories or can be used directly for comparison with experimental results. At a given combination of exchange constant and saturation polarization there exists a specific thickness at which the stripe width is independent of the uniaxial anisotropy.

Single magnetic molecules may be the smallest functional magnets. An electric-field controllable spin state of magnetic molecules is of fundamental importance for applications while its realization remains challenging. To date the observed spin-electric interaction based on spin-orbit coupling or spin dipole coupling is useful to tune fine spin structures but too weak to flip the spin state. In this work, we propose a mechanism to realize enhanced spin-electric coupling and flip the spin states by tuning the spin superexchange between local spins. Using first-principles calculations and the Heisenberg Hamiltonian, we demonstrate this effect in a family of magnetic molecules, transition metallic porphyrins. We show that their $d\text{−}\pi$ and $\pi \text{−}\pi$ spin superexchange couplings are determined by the relative energies of $d$ and $\pi$ electronic states, which are sensitive to the applied electric field. Therefore, applying electric field can tune a wide range of magnetic ground states, including ferromagnetic, ferrimagnetic, and antiferromagnetic configurations. This spin-electric coupling may provide a different approach for designing and controlling molecular spintronics.

In this work we study electromagnetic properties of a resonator recently suggested for the search of axions—a hypothetical candidate to explain dark matter. A wire medium loaded resonator (called a plasma haloscope when used to search for dark matter) consists of a box filled with a dense array of parallel wires electrically connected to top and bottom walls. We show that the homogenization model of a wire medium works for this resonator without mesoscopic corrections, and that the resonator quality factor $Q$ at the frequency of our interest drops versus the growth of the resonator volume $V$ until it is dominated by resistive losses in the wires. We find that even at room temperature metals like copper can give quality factors in the thousands—an order of magnitude higher than originally assumed. Our theoretical results for both loaded and unloaded resonator quality factors were confirmed by building an experimental prototype. We discuss ways to further improve wire medium loaded resonators.

We show evidence of many-body localization (MBL) transition in a one-dimensional isotropic XY chain with a weak next-nearest-neighbor frustration in a random magnetic field. We perform finite-size exact diagonalization calculations of level-spacing statistics and fractal dimensions to characterize the MBL transition with increasing the random field amplitude. An equivalent representation of the model in terms of spinless fermions explains the presence of the delocalized phase by the appearance of an effective nonlocal interaction between the fermions. This interaction appears due to frustration provided by the next-nearest-neighbor hopping.

In this paper, we demonstrate the existence of multiple photonic Fermi arcs with the same transmission direction at the interface between two different topological Weyl media. The surface waves are not affected by the type and number of defects and can bypass defects for robust one-way transportation, which confirms the disorder-immune property of Fermi arcs. The reconfigurable routing of Fermi arc surface waves can be well realized by changing the gyromagnetic and chiral parameters of Weyl metamaterials in H-shaped channels. Moreover, the unidirectional excitation and controllable transmission of Fermi arcs can be realized by adopting the different signs of the propagation constant and different interface configurations in T-shaped channels. Our paper provides an insight into the topological properties of Fermi arcs between two topological Weyl systems.

Due to its transparent and highly dispersive nature, plasmonically induced transparency (PIT) has become an attractive field in the on-chip control of light. Conventional methods to achieve PIT are only limited to the lowest dipole-dipole or dipole-combined quadrupole modes by breaking structural symmetry. Consequently, a general methodological framework for accurately designing all-order PIT remains absent. In this paper, we propose a theoretical scheme to achieve unidirectional odd-to-even order PIT by establishing a model with two layers of periodic graphene nanoribbons. The underlying physical principles are uncovered by defining the additional resonant phase of one mode over the other as phase difference, which predicts that the PIT effects appear (disappear) generally near the positions where the phase difference is around odd (even) multiple numbers of π. Full-wave simulations and theoretical analysis are used to demonstrate our proposal, revealing that the proposed PIT concept possesses good robustness against both the ribbon width and the relative ribbon positions. Our results serve to provide an effective method to realize all-order PIT and to design PIT-based photonic devices.

Two-dimensional ${\mathrm{CP}}_2$ and ${\mathrm{Li}}_x{\mathrm{CP}}_2$ ($x=1$ and 2) monolayers with high-mobility transport anisotropy, and tunable electronic and optical properties were identified through density-functional theory calculations. Our results indicate that the carrier mobility of ${\mathrm{CP}}_2$ monolayer is highly anisotropic with high hole mobility of $5.192\sim 6.826{\mathrm{m}}^2{\mathrm{V}}^{–1}{\mathrm{s}}^{–1}$ along the $x$ direction. The ${\mathrm{CP}}_2$ exhibits linear dichroism and extraordinary optical absorption in the ultraviolet- to visible-light spectrum range. More importantly, the electronic and optical properties of ${\mathrm{CP}}_2$ can be turned via lithiation. A semiconductor to semimetal transition is revealed by lithiated ${\mathrm{CP}}_2$ with the formation of ${\mathrm{LiCP}}_2$. The ${\mathrm{LiCP}}_2$ shows a high Fermi velocity of $0.69\times {10}^6\mathrm{m}/\mathrm{s}$ and strong optical absorbance in midwave-infrared regions. Further increasing the Li concentration leads to a semimetal to direct band-gap semiconductor transition with the formation of ${\mathrm{Li}}_2{\mathrm{CP}}_2$. The ${\mathrm{Li}}_2{\mathrm{CP}}_2$ has a high intrinsic conductivity with an anisotropic character (a high electron mobility of $4.665\sim 7.336{\mathrm{m}}^2{\mathrm{V}}^{–1}{\mathrm{s}}^{–1}$ along the $y$ direction) and intense optical absorbance in near-infrared regions. All these desirable properties make ${\mathrm{CP}}_2, {\mathrm{LiCP}}_2$, and ${\mathrm{Li}}_2{\mathrm{CP}}_2$ promising for a wide range of future applications in a variety of technologies, especially in electronics, and photovoltaic and optoelectronic devices.

In ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$, the competition of spin-orbit coupling $\zeta$ and tetragonal crystal-field splitting ${\mathrm{\Delta }}_{\mathrm{CF}}$ has been discussed controversially for many years. The orbital occupation depends on ${\mathrm{\Delta }}_{\mathrm{CF}}/\zeta$, which allows us to address this ratio via the optical spectral weights of the lowest intersite Mott-Hubbard excitations. We study the optical conductivity of ${\mathrm{Ca}}_2{\mathrm{Ru}}_{0.99}{\mathrm{Ti}}_{0.01}{\mathrm{O}}_4$ in the range of 0.75–5 eV by ellipsometry, using the large single crystals that can be grown for small Ti concentrations. Based on a local multiplet calculation, our analysis results in $2.4\le {\mathrm{\Delta }}_{\mathrm{CF}}/\zeta \lesssim 4$ at 15 K. The dominant crystal field yields a ground state close to $xy$ orbital order but spin-orbit coupling is essential for a quantitative description of the properties. Furthermore, we observe a pronounced decrease of ${\mathrm{\Delta }}_{\mathrm{CF}}$ with increasing temperature, as expected based on the reduction of octahedral distortions.

It is known that in two-dimensional relativistic Dirac systems placed in orthogonal uniform magnetic and electric fields, the Landau levels collapse as the applied in-plane electric field reaches a critical value $\pm E_c$. We study this phenomenon for a distinct field configuration with in-plane constant radial electric field. The Dirac equation for this configuration does not allow analytical solutions in terms of known special functions. The results are obtained by using both the WKB approximation and the exact diagonalization and shooting methods. It is shown that the collapse occurs for positive values of the total angular momentum quantum number, the hole (electron)-like Landau levels collapse as the electric field reaches the value $+(-)E_c/2$. The investigation of the Landau level collapse in the case of gapped graphene shows a number of distinctive features in comparison with the gapless case.

Coherent control steers a quantum system from an initial state to a target state by controlling quantum interference phenomena via an external field, which is central to vast applications ranging from quantum information processing to attosecond physics. Here, we analyze the quantum pathways interference in two-color coherent control of photoemission using exact analytical solutions of the time-dependent Schrödinger equation. The theory includes all possible quantum pathways and their interference terms. Constructive (or destructive) interferences among the pathways leads to the maximum (or minimum) emission with varying phase delay of the two-color lasers. It is found that increasing the intensity ratio of the second harmonic $\left(2\omega \right)$ to fundamental $\left(\omega \right)$ lasers results in less contribution from the $\omega$ pathway (absorption of $\omega$ photons only) and more contribution from multicolor pathway (simultaneous absorption of both $\omega$ and $2\omega$ photons) and $2\omega$ pathway (absorption of $2\omega$ photons only), and therefore stronger pathways interference and increased visibility larger than 95%. Increasing bias voltages shifts the dominant emission to processes with lower-order photon absorption, which sequentially decreases the interference between the $\omega$ and the $2\omega$ pathways, and between single-color and multicolor pathways, leading to two peaks in the visibility.

We report a succession of pressure-tuned structural transitions in the topological nodal-line superconductor ${\mathrm{PbTaSe}}_2$, evidenced from synchrotron x-ray diffraction, elastic neutron scattering, Raman spectroscopy, and electrical transport measurements up to 56 GPa, accompanied by first-principles calculations to uncover the evolution of the underlying electronic structure. In contrast to the previously proposed small shift of the Pb Wyckoff coordinate in the sub-GPa regime, our study reveals that it is rather a transition from $P\overline{6}m2$ ($\alpha$ phase) to $P{6}_{3}mc$ ($\beta$ phase), subsequently followed by a transition to $P6/mmm$ ($\gamma$ phase) at $\sim 7.5$ GPa and to $Pmmm$ ($\delta$ phase) at $\sim 44$ GPa. In addition, the first-principles calculations unambiguously demonstrate the multiple types of topological fermions associated with these different pressure-driven structures. Collectively, our results not only present the intriguing structural transitions in this topological ${\mathrm{PbTaSe}}_2$ superconductor, they also provide the impetus to study topological phase transitions and their physical consequences in a broader class of topological materials.

We theoretically investigate the critical bias current $j_c$ for a superconducting (SC) ring in a magnetic field. Based on the Ginzburg-Landau theory, we show that $j_c$ exhibits a Little-Parks (LP) oscillation as a function of the magnetic flux passing through the ring, similarly to the LP oscillation in the SC transition temperature. It is also found that for a spin-triplet SC ring, the $\mathbf{d}$ vector rotates to yield a larger $j_c$, forming a texture along the circumference of the ring. Experimental implications of our result are discussed.

Osmium, the least compressible metal, has recently been observed to undergo abrupt changes in the $c/a$ ratio at extreme pressures. These are claimed to provide evidence for two unusual electronic behaviors: a crossing of the semicore $4f$ and $5p$ levels, and an electronic topological transition. We demonstrate that these two electronic phenomena are readily reproduced and understood in density functional theory, but that neither perturbs the trend in $c/a$ ratio against pressure. Hence the observed anomalies in $c/a$ must have another cause. Osmium is also notable for its high yield stress: the $c/a$ anomalies lie well within the differential strains which osmium can support. We propose that observed $c/a$ changes can arise from mechanical yield of crystallites with strong preferred orientation under high deviatoric stress in the experimental data. We discuss what evidence remains for the more general hypothesis that core-level overlap under pressure can have measurable effects on the crystal structure in any material.

We theoretically and numerically demonstrate that Fano-like resonance can induce a left-handed optical torque on a dipolar plasmonic core-shell nanoparticle in the interference optical field composed of two linearly polarized plane waves. It is shown that the optical torque on the dipolar plasmonic nanoparticle is significantly enhanced at the Fano-like resonance, and its direction is opposite to that of the angular momentum of the incident field, termed Fano-like resonance-induced left-handed optical torque. The extinction spectra exhibit that the Fano-like resonance stems from the coupling between a narrow electric quadrupole dark mode and a broad electric dipole bright mode. In addition, such Fano-like resonance-induced left-handed optical torque can flexibly be tailored by the particle morphology. To further trace the physical origin of the left-handed optical torque, we derive an analytical expression of optical torques up to electric quadrupole in generic monochromatic optical fields based on the multipole expansion theory. The results obtained from our analytical expression show that the left-handed optical torque comes completely from the electric quadrupole terms while other terms from the electric dipole make no contribution. Our results may open a new avenue for tailoring optical torques on plasmonic structures.