We report the direct observation of a single quantized vortex vanishing from a microcavity exciton-polariton superfluid. Exciton-polariton vortices generated by a nonresonant Laguerre-Gaussian optical pumping beam reveal themselves in the energy-integrated emission image, representing a multimode entity consisting of the ground- and excited states. From the time-resolved spectroscopy measurements utilizing various Laguerre-Gaussian beam sizes, we find that the two lowest-energy states get populated and compete with each other, manifested by the change in their mutual population with the beam diameter. Furthermore, we study the transition from the excited state characterized by the finite orbital angular momentum (and a vortex in the direct space) to the ground state under pulsed excitation conditions. Our experimental findings are in excellent agreement with the numerical calculations employing the driven-dissipative Gross-Pitaevskii equation coupled with pumping reservoirs. Thus, our study provides an experimental and theoretical platform to investigate nonequilibrium vortex dynamics and manipulate multistate polariton condensates in semiconductor microcavities.

Topological corner states are zero-dimensional localized excitations whose existence is protected by the bulk properties of the system. This feature makes them robust to disorder unveiling intriguing physics. Canonical realizations of higher-order topology in two-dimensional systems typically rely on tight-binding models with the nearest-neighbor couplings. Here, in contrast, we propose a $D_4$-symmetric system where the topological band gap opens due to the additional long-range interactions, which are controllably incorporated in our setup based on a resonant electrical circuit. In our experiments, we probe the response of the designed circuit at every node, reconstruct the eigenmode profiles, and directly extract the topological invariant demonstrating the topological origin of the observed symmetry-protected corner states.

We propose a scheme to create an electronic Floquet vortex state by irradiating a two-dimensional semiconductor with a laser light carrying nonzero orbital angular momentum. We analytically and numerically study the properties of the Floquet vortex states, with methods analogous to the ones previously applied to the analysis of superconducting vortex states. We show that such Floquet vortex states are similar to superconducting vortex states, and they exhibit a wide range of tunability. To illustrate the potential utility of such tunability, we show how such states could be used for quantum state engineering.

Domain walls, topological defects that define the frontier between regions of different stacking order in multilayer graphene, have proved to host exciting physics. The ability to tune these topological defects in situ in an electronic transport experiment brings a wealth of possibilities in terms of fundamental understanding of domain walls as well as for electronic applications. Here, we demonstrate, through a MEMS (microelectromechanical system) actuator and magnetoresistance measurements, the effect of domain walls in multilayer graphene quantum Hall effect. Reversible and controlled uniaxial strain triggers the topological defects, manifested as addtional quantum Hall effect plateaus as well as a discrete and reversible modulation of the current across the device. Our findings are supported by theoretical calculations and constitute indication of the in situ tuning of topological defects in multilayer graphene probed through electronic transport, opening the way for the use of reversible topological defects in electronic applications.

All optical switching (AOS) of magnetization exhibits a high potential for ultrafast and energy-efficient memory applications. Many works have been carried out in the area of AOS, including its observation in a wide variety of ferromagnetic or ferrimagnetic materials, and the exploration of the parameters for the achievements of AOS such as the laser fluence and helicity, and duration of laser pulses. A large majority of all optical helicity-independent single-shot switching (AO-HIS) has been observed in Gd-based rare-earth transition-metal ferrimagnets. It is then necessary to explore the unique role of Gd in AO-HIS mechanism, compared with other rare-earth elements. Here, we engineered ${\mathrm{Gd}}_{1-x-y}{\mathrm{Tb}}_y{\mathrm{Co}}_x$ alloys and investigated the influence of the Tb concentration on the magnetization dynamics via static Kerr microscope and time-resolved magneto-optical Kerr effect (TR-MOKE) measurements. The ultrafast demagnetization time at low fluence is found to be independent of Tb concentration, while both the range of laser fluence and pulse duration allowing for AO-HIS becomes narrower with increasing the Tb concentration. The TR-MOKE signal $\mathrm{\Delta }{\mathrm{\Theta }}_K/{\mathrm{\Theta }}_{K\_\mathrm{sat}}\sim 10\mathrm{ps}$ after the laser pulse excitation decreases with increasing either the Tb concentration or the pulse duration. The fact that AO-HIS is prohibited by increasing the Tb content is explained by considering a larger damping for Tb than Gd in atomistic simulations. Our results are well explained by the fact that angular momentum can be transferred from Gd to Co resulting in the magnetization switching, whereas for Tb it is dissipated through the lattice due to the large spin-orbit coupling, instead of being transferred between Tb and Co.

Nanoscale skyrmions enable ultralow-power nonvolatile logic gate designs due to their current-driven motion and topological protection. A key building block in skyrmion-based digital spintronics is the logic inverter (not) gate. Despite recent computational and practical demonstrations, a skyrmion-based low-power, wideband, and cascadable inverter gate is still a long way off. For skyrmion-based logic circuits, a systematic design and analysis of an inverter gate is essential. Here we present a skyrmion logic inverter design and analyze its full operation using micromagnetic modeling. Because of the substrate thermal conductivity, our investigations reveal that the all-metallic inverter gate can function with direct current drive, wide bandwidth, submicron footprint, no or low external magnetic field, cascadability, and with room-temperature thermal stability despite Joule heating. Using magnetic insulators for eliminating Joule heating and lowering the exchange stiffness, magnetic moment and other factors might further assist in reducing power consumption by more than four orders of magnitude.

Large-scale nonequilibrium molecular dynamic simulations of impact-induced shock propagation in defect-free single-crystal Ta along the [001] direction is presented, paying particular attention to the formation of elastic-plastic two-wave structures. Plastic deformation and elastic limits of Ta single crystals for various crystal orientations were investigated in a recent paper [R. Ravelo et al., Phys. Rev. B 88, 134101 (2013)]. In the present paper, a comprehensive study on the Hugoniot elastic limit (HEL) and its dependence on associated physical parameters is reported. The observed attenuation of an elastic precursor in a stress-wave profile led to proposing wide-range scaling relations for HEL decay applicable for ultrahigh strain rates. The influence of a lateral dimension on the spatial profile of a stress wave and time profile of free surface velocity (FSV) in the distinct appearance of a spike-valley feature and its consequence on scaling relations is investigated. Further, it is shown that the commonly used method of calculating HEL from a FSV profile is inadequate for submicron-thick samples at high strain rates. The necessary modifications are incorporated that resulted in comparable HEL values by two complimentary approaches of stress and FSV profiles. Simulations carried out for increasing impact strength revealed a power law dependence of HEL with strain rate. A methodology based on extrapolation of stress decay law and strain rate scaling constructed by us is proposed here for prediction of HEL pertaining to larger length samples. Very good agreement between the predicted values and available experimental results makes the modeling robust and applicable for a wide range of strain rates and length scales. Finally, the study is extended for elevated sample temperatures up to melting. Interestingly, yield strength is shown to follow an increasing trend up to a certain temperature, beyond which it decreases. An empirical relation is proposed here for expressing temperature dependence of HEL that explains the observed yield strength anomaly. Results are justified through thermal analysis of shear stress and evolution of dislocation density.

The trigonal layered quaternary tellurate ${\mathrm{Na}}_2\mathrm{MnTe}{\mathrm{O}}_6$ has been studied by means of various techniques to clarify its magnetic properties. The crystal structure of this compound is based on the triangular arrangement of all cations in the parallel layers with the space group $P\overline{3}1c$. By using symmetry analysis of the magnetic neutron scattering data, we have found that the solution for the magnetic structure corresponds to the magnetic Shubnikov group $R{\overline{3}}^{\prime }{c}^{\prime }$ (No. 167.4.1337). ${\mathrm{Mn}}^{4+}$ ions in an octahedral environment form a triangular network where all spins are directed from the center of each triangle. Overall magnetic structure in ${\mathrm{Na}}_2\mathrm{MnTe}{\mathrm{O}}_6$ is commensurate $120{}^{\circ }$ spin helix with propagation vector $\mathit{k}=\left(1/3,1/3,1/3\right)$ in variance with planar spin structure in structurally equivalent ${\mathrm{Li}}_2\mathrm{MnTe}{\mathrm{O}}_6$ with magnetic propagation vector $\mathbf{k}=\left(1/3,1/3,0\right)$. The magnetization measurements show that ${\mathrm{Na}}_2\mathrm{MnTe}{\mathrm{O}}_6$ experiences an antiferromagnetic order at $T_{\mathrm{N}}=5.5\mathrm{K}$. NMR, electron spin resonance, and thermodynamics experiments demonstrate the extended temperature region of 2D short-range correlations well above the ordering temperature.

A comprehensive study of the structural, magnetic, and transport properties of double-substituted ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{Co}}_{1-y}{\mathrm{Ni}}_y{\mathrm{O}}_{3-\gamma }$ ($0.1\le x\le 0.5, 0.05\le y\le 0.25$) perovskite systems was carried out. The average oxidation number of Co ions was found to be $3+$ for the most subsystems. The existence of several characteristic concentration regions for various degrees of substitution in the A (La, Sr) and B (Co, Ni) sublattices is shown. Low levels of Sr and Ni ion substitution subsystems demonstrate cluster spin-glass behavior with a semiconducting character of the conductivity and a diamagnetic low-spin (LS) ${\mathrm{Co}}^{3+}$ matrix. An increase of Ni substitution leads to the stabilization of intermediate-spin (IS) ${\mathrm{Co}}^{3+}$ ions in ${\mathrm{CoO}}_6$ octahedra, approaching the percolation threshold of ferromagnetic clusters. For strongly Sr-substituted subsystems an effect of stabilization of IS ${\mathrm{Co}}^{3+}$ is not observed, since the contribution of this effect is smaller than the effect of the dilution by antiferromagnetically interacting Ni ions. In this case, an increase of Ni content leads to a decrease in the magnetic ordering temperature $T_{\text{mo}}$ and magnetization values. For weakly Sr-substituted systems, on the contrary, it leads to their growth. Anomalies in the conductivity dependences for several subsystems are due to the thermally induced spin crossover of the part of ${\mathrm{Co}}^{3+}$ ions, first from the LS to the IS state, and then to the mixed IS/high-spin (HS) state, similar to the parent ${\mathrm{LaCoO}}_3$.

The quasiclassical theory of superconductivity provides a methodology to study emergent phenomena in hybrid structures comprised of superconductors interfaced with other materials. A key component in this theory is the boundary condition that the Green functions describing the materials must satisfy. Recently, progress has been made toward formulating such a boundary condition for interfaces with spin-orbit coupling, the latter playing an important role for several phenomena in spintronics. Here we derive a boundary condition for spin-orbit coupled interfaces that includes gradient terms, which enables the description of spin-Hall-like effects with superconductors due to such interfaces. As an example, we show that the boundary conditions predict that a supercurrent flowing through a superconductor that is coupled to a normal metal via a spin-orbit interface can induce a nonlocal magnetization in the normal metal.

Two-dimensional Rashba superconductor $\mathrm{Si}\left(111\right)-\sqrt{3}\times \sqrt{3}-(\mathrm{Tl},\mathrm{Pb})$ is a candidate platform of mixed spin-singlet and -triplet superconductivity. A recent scanning tunneling microscope (STM) experiment revealed a pseudogap at the vortex core, suggesting the finite triplet component [Nakamura et al., Phys. Rev. B 98, 134505 (2018)]. Detailed spectroscopic information of the superconducting gap and the low-energy band structure is necessary to establish the putative triplet superconductivity. Here, we performed high-energy-resolution spectroscopic imaging experiments on $\mathrm{Si}\left(111\right)-\sqrt{3}\times \sqrt{3}-(\mathrm{Tl},\mathrm{Pb})$ using an ultralow temperature STM. We found that various spectroscopic features, including the vortex-core spectrum, are consistent with spin-singlet $s$-wave superconductivity, having no sign of the triplet component. The apparent contradiction with the previous STM result suggests that the nature of superconductivity changes within the same system. From the analysis of the quasiparticle interference patterns, we found that the Fermi energy is in the close vicinity of the saddle point near the $\overline{\mathrm{M}}$ point. We speculate that the nature of superconductivity varies depending on the saddle-point energy with respect to the Fermi energy, which is sample-dependent due to different band filling.

Stark many-body localization (SMBL) is a phenomenon observed in interacting systems with a nearly uniform spatial gradient applied field. Contrasting to the traditional many-body localization phenomenon, SMBL does not require disorder. Here we investigate SMBL in a spin-$1/2$ described by a Heisenberg model including a next-nearest-neighbor exchange coupling. By employing an exact diagonalization approach and time evolution calculation we analyze both level spacing ratio (LSR) statistics of the Hamiltonian model as well as the dynamics of the system from a given initial state. Our results reveals that for zero field in our finite system, LSR statistics suggest localization while the dynamics shows thermalization, which has been attributed to a finite-size effect. Slightly nonuniform field gradient, LSR statistic predictions agree very well with the dynamics of the physical quantities indicating delocalization and localization for small and large field gradient, respectively. More interestingly, we find that localization is robust in the presence of next-nearest-neighbor coupling in the Hamiltonian. Moreover, this coupling can be tuned to enhance SMBL in the system, meaning that localized regimes can be obtained for smaller field gradient as compared to the traditional nearest-neighbor isotropic Heisenberg model.

In this paper, we apply the angle-resolved optically detected magnetic resonance (ODMR) technique to study a series of strained (Cd, Mn)Te/(Cd, Mg)Te quantum wells (QWs) produced by molecular beam epitaxy. By analyzing characteristic features of ODMR angular scans, we determine the strain-induced axial-symmetry spin Hamiltonian parameter $D$ with neV precision. Furthermore, we use low-temperature optical reflectivity measurements and x-ray diffraction scans to evaluate the local strain present in the QW material. In our analysis, we take into account different thermal expansion coefficients of the GaAs substrate and CdTe buffer. The additional deformation due to the thermal expansion effects has the same magnitude as the deformation that originates from the different compositions of the samples. Based on the evaluated deformations and values of the strain-induced axial-symmetry spin Hamiltonian parameter $D$, we find the strain spin-lattice coefficient $G_{11}=(72.2\pm 1.9)$ neV for ${\mathrm{Mn}}^{2+}$ in CdTe and shear deformation potential $b=(-0.94\pm 0.11)$ eV for CdTe.

We study the non-trivial phase of the two-dimensional breathing kagome lattice, displaying both edge and corner modes. The corner localized modes of a two-dimensional flake were initially identified as a signature of a higher-order topological phase but later shown to be trivial for perturbations that were thought to protect them. Using various theoretical and simulation techniques, we confirm that it does not display higher-order topology the corner modes are of trivial nature. Nevertheless, they might be protected. First, we show a set of perturbations within a tight-binding model that can move the corner modes away from zero energy, also repeat some perturbations that were used to show that the modes are trivial. In addition, we analyze the protection of the corner modes in more detail and find that only perturbations respecting the sublattice or generalized chiral and crystalline symmetries, and the lattice connectivity, pin the corner modes to zero energy robustly. A destructive interference model corroborates the results. Finally, we analyze a muffin-tin model for the bulk breathing kagome lattice. Using topological and symmetry markers, such as Wilson loops and Topological Quantum Chemistry, we identify the two breathing phases as adiabatically disconnected different obstructed atomic limits.

We investigate, using a first-principles density functional methodology, the nature of magnetism in monolayer $1T$ phase of tantalum disulfide ($1T\text{−}\mathrm{Ta}{\mathrm{S}}_2$). Magnetism in the insulating phase of $\mathrm{Ta}{\mathrm{S}}_2$ is a longstanding puzzle and has led to a variety of theoretical proposals including notably the realization of a two-dimensional quantum-spin-liquid (QSL) phase. By means of noncollinear spin calculations, we derive ab initio spin Hamiltonians including two-spin bilinear Heisenberg exchange as well as biquadratic and four-spin ring-exchange couplings, the latter being relevant for the stabilization of putative QSL states. We find that both quadratic and quartic interactions are consistently ferromagnetic for all the functionals considered. Relativistic calculations predict substantial magnetocrystalline anisotropy. Altogether, our results suggest that this material may realize an easy-plane XXZ quantum ferromagnet with large anisotropy.

Combining mean-field and renormalization group analyses, here we unveil the nature of recently observed superconductivity and parent metallic states in chemically doped rhombohedral trilayer graphene, subject to external electric displacement fields ($D$) [H. Zhou et al., Nature (London) 598, 434 (2021)]. We argue that close to the charge neutrality, on site Hubbard repulsion favors layer antiferromagnet, which when combined with the $D$-field induced layer polarization, produces a spin-polarized, but valley-unpolarized half metal, conducive to the nucleation of spin-triplet $f$-wave pairing (SC2). At larger doping valence bond order emerges as a prominent candidate for isospin coherent paramagent, boosting condensation of spin-singlet Cooper pairs in the $s$-wave channel (SC1), manifesting a “selection rule” among competing orders. Responses of these paired states to displacement and in-plane magnetic fields show qualitative similarities with experimental observation. With the onset of the quantum anomalous Hall order, the valley degeneracy of half metal gets lifted, forming a quarter metal at lower doping [H. Zhou et al., Nature (London) 598, 429 (2021)].

The Hugoniot equation-of-state, Grüneisen parameter, and structure of laser-shocked polyimide were measured. The polyimide Hugoniots were measured in the pressure range 80–600 GPa and found to be consistent with the extrapolation of previously reported data below 60 GPa. The structural measurements of polyimide shock compressed to pressures of 28–163 GPa were performed using the in situ x-ray diffraction technique, and the results show that the melting pressure of polyimide along its Hugoniot is below 32(±3) GPa, indicating that the discontinuous volume change of the polyimide Hugoniot at ∼26 GPa observed in previous gas-gun experiments denotes the onset of melting. The consistency of the melting pressure between the previous gas-gun results and the present laser experiments suggests that the shock-melting process of polyimide is independent of the duration of the compression, revealing its rapid melting kinetics.

We have studied the magnetization, dielectric permittivity, thermal expansion, and magnetostriction of ${\mathrm{Ni}}_2{\mathrm{NbBO}}_6$ single crystals. Different from that of the $ab$ plane, the $c$ axis magnetization approaches zero at low magnetic fields and a spin-flop transition happens around $H_{\mathrm{SF}}=3.65\mathrm{T}$. The results indicate that the $c$ axis is the hard axis and the $ab$ plane is the easy plane. The high-field isothermal magnetization measured at $T=4.2\mathrm{K}$ reveals that the saturation magnetic field is $H_s=17\mathrm{T}$, above which the magnetic structure changes from canted-antiferromagnetic order to ferromagnetic order with the saturation magnetic moment ${\mu }_{\mathrm{eff}}=2.40 {\mu }_{\mathrm{B}}/{\mathrm{Ni}}^{2+}$ Below antiferromagnetic transition temperature $T_N$, an unusual negative thermal expansion phenomenon is detected along the $b$ axis and it can be interpreted by the magnetic structural variation. Based on the magnetization and the magnetostriction data, the magnetic field–temperature phase diagram of ${\mathrm{Ni}}_2{\mathrm{NbBO}}_6$ is constructed. The magnetodielectric effect confirms the existence of magnetoelectric coupling in ${\mathrm{Ni}}_2{\mathrm{NbBO}}_6$.

An $A{A}_3^{\prime }{B}_4{\mathrm{O}}_{12}$-type transition-metal-only quadruple perovskite oxide $\mathrm{Mn}{\mathrm{Cu}}_3{\mathrm{Mn}}_4{\mathrm{O}}_{12}$ was prepared by high-pressure and high-temperature methods. The compound has a cubic $Im$-3 symmetry with charge distribution of ${\mathrm{Mn}}^{2+}{\mathrm{Cu}}_3^{2+}{\mathrm{Mn}}_4^{4+}{\mathrm{O}}_{12}$. A long-range ferrimagnetic phase transition caused by ${\mathrm{Cu}}^{2+}(\uparrow ){\mathrm{Mn}}^{4+}(\downarrow )$ spin interaction is found to occur at a Curie temperature $T_{\mathrm{C}}\approx 365\mathrm{K}$ . Different from the isostructural compound $\mathrm{Ca}{\mathrm{Cu}}_3{\mathrm{Mn}}_4{\mathrm{O}}_{12}$, the susceptibility of $\mathrm{Mn}{\mathrm{Cu}}_3{\mathrm{Mn}}_4{\mathrm{O}}_{12}$ experiences a second anomaly ∼200 K due to the effects of $A$-site ${\mathrm{Mn}}^{2+}$ spin ordering. Moreover, the $A$-site ${\mathrm{Mn}}^{2+}$ spins also considerably decrease the magnitude of resistivity. Theoretical calculations reveal that the $A$-site Mn $3d$ orbitals locate near the Fermi level and hybridize with the Cu $3d$ and O $2p$ orbitals, playing a crucial role on the magnetic and electrical transport properties of $\mathrm{Mn}{\mathrm{Cu}}_3{\mathrm{Mn}}_4{\mathrm{O}}_{12}$. In this paper, we provide an interesting example using $A$-site magnetic ions to significantly tune the physical properties in $A{A}_3^{\prime }{B}_4{\mathrm{O}}_{12}$-type quadruple perovskite oxides.

We report a doping study directed to intentionally induce disorder in ${\mathrm{PdTe}}_2$ by the isoelectronic substitution of Pt. Two single-crystalline batches ${\mathrm{Pd}}_{1-x}{\mathrm{Pt}}_x{\mathrm{Te}}_2$ have been prepared with nominal doping concentrations $x=0.05$ and $x=0.10$. Sample characterization by energy dispersive x-ray spectroscopy revealed Pt did not dissolve homogeneously in the crystals. For the nominal value $x=0.10$ small single crystals cut from the batch appeared to have $x=0.09$, as well as the nonstoichiometric composition ${\mathrm{Pd}}_{0.97}{\mathrm{Pt}}_{<0.004}{\mathrm{Te}}_{2.03}$. Magnetic and heat capacity measurements demonstrate a transition from type-I to type-II superconducting behavior upon increasing disorder. From transport measurements we calculate a residual resistivity ${\rho }_0=1.4\mu \mathrm{\Omega }\mathrm{cm}$ suffices to turn ${\mathrm{PdTe}}_2$ into a superconductor of the second kind.