Hard x-ray absorption and magnetic circular dichroism spectroscopy have been applied to study the consequential changes of the local environment around Fe atoms and their orbital polarizations in 40 nm thick ${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$ thin films along the order-disorder $\left(B2\to A2\right)$ phase transition initiated by 20-keV ${\mathrm{Ne}}^{+}$ ion irradiation with fluences of $(0.75–6)\times {10}^{14}\text{ions}{\mathrm{cm}}^{-2}$. The analysis of the extended x-ray absorption fine structure spectra measured at the Fe K edge at room temperature revealed an increased number of Fe-Fe nearest neighbors from 3.47(7) to 5.0(1) and $\sim 1\%$ of volume expansion through the transition. The visualization of the Fe and Al nearest-neighbor rearrangement in the first coordination shell of Fe absorbers via the transition was carried out by wavelet transformations. The obtained changes in Fe coordination are evidently reflected in the x-ray magnetic circular dichroism spectra which show an increased orbital magnetic moment of Fe atoms and a pronounced magnetic multielectronic excitations peak at $\sim 60$ eV above the edge. The amplitudes of both peaks demonstrated similar dependencies on the irradiation fluence. The results of self-consistent density functional calculations on relaxed ${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$ model structures for the ordered $\left(B2\right)$ and the disordered $\left(A2\right)$ phases are consistent with the experimental findings and point to the formation of Fe-rich regions in the films studied.

We study spin-photon coupling in a cavity in the presence of a relative phase shift between two ferromagnetic resonance driving forces. We show that the anticrossing gap can be manipulated by varying the relative phase. Increasing the phase difference leads to narrowing the anticrossing gap between two hybridized modes and eventually phase-locked coupling when the relative phase equals $\pi$. The ferromagnetic resonance (FMR) and cavity modes become phase locked and oscillate at the same frequency near the resonance frequency. The characteristic FMR linewidth drop and transmission amplitude enhancement are demonstrated. The phase-resolved spin-photon coupling can be used both for phase imaging and for controlling coupling parameters.

We study the one-dimensional $t\text{−}{t}^{\prime }\text{−}J$ model for generic couplings using two complementary theories, the extremely correlated Fermi liquid theory and time dependent density matrix renormalization group over a broad energy scale. The two methods provide a unique insight into the strong momentum dependence of the self-energy of this prototypical non-Fermi liquid, described at low energies as a Tomonaga-Luttinger liquid. We also demonstrate its intimate relationship to spin-charge separation, i.e., the splitting of Landau quasiparticles of higher dimensions into two constituents, driven by strong quantum fluctuations inherent in one dimension. The momentum distribution function, the spectral function, and the excitation dispersion of these two methods also compare well.

We investigate the equilibrium and real-time properties of the spin-correlation function $\langle {\vec{S}}_1{\vec{S}}_2\rangle$ in the two-impurity Kondo model for different distances $R$ between the two-impurity spins. It is shown that the competition between the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction and the Kondo effect governs the amplitude of $\langle {\vec{S}}_1{\vec{S}}_2\rangle$. For distances $R$ exceeding the Kondo length scale, the Kondo effect also has a profound effect on the sign of the correlation function. For ferromagnetic Heisenberg couplings $J$ between the impurities and the conduction band, the Kondo effect is absent and the correlation function only decays for distances beyond a certain length scale introduced by finite temperature. The real-time dynamics after a sudden quench of the system reveals that correlations propagate through the conduction band with Fermi velocity. We identify two distinct timescales for the long-time behavior, which reflects that for small $J$ the system is driven by the RKKY interaction while for large $J$ the Kondo effect dominates. Interestingly, we find that at certain distances a one-dimensional dispersion obeying $\epsilon \left(k\right)=\epsilon (-k)$ may lead to a local parity conservation of the impurities such that $\langle {\vec{S}}_1{\vec{S}}_2\rangle$ becomes a conserved quantity for long times and does not decay to its equilibrium value.

Topological insulators exhibit gapless edge or surface states that are topologically protected by time-reversal symmetry. However, several promising candidates for topologically insulating materials (such as ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ and HgTe) contain spinful nuclei or other types of magnetic impurities that break time-reversal symmetry. We investigate the consequences of such impurities coupled to the electronic edge states of a topological insulator ring or circular quantum dot in the presence of a magnetic flux. We use spin conservation and additional symmetry arguments to derive a universal formula for the spectrum of propagating edge modes in terms of the amplitude of transmission through the impurity. Our results apply for impurities of arbitrary spin. We show that there exists an energy regime in which the spectrum becomes nearly independent of the flux and significant spectral gaps form. We further analyze the electron-impurity entanglement entropy, finding that maximal entanglement occurs near the gaps in the spectrum. Our predictions can be investigated with quantum ring transport interference experiments or through spin-resolved STM measurements, providing a new approach to understand the role of impurities in topological insulator edge transport.

Stochastic systems feature, in general, both coherent dynamics and incoherent transitions between different states. We propose a method to identify the coherent part in the full counting statistics for the transitions. The proposal is illustrated for electron transfer through a quantum-dot spin valve, which combines quantum-coherent spin precession with electron tunneling. We show that by counting the number of transferred electrons as a function of time, it is possible to distill out the coherent dynamics from the counting statistics even in transport regimes, in which other tools such as the frequency-dependent current noise and the waiting-time distribution fail.

Herein, the repulsive-attractive transition, regarded as a stable equilibrium, between gold and dielectric metamaterials (based on Mie resonance) immersed in various fluids was studied. This transition is owing to the interplay of the gravitational, buoyant, and Casimir forces among different geometries containing parallel plates and spheres levitated over substrates. It was found that Mie metamaterials allowed a wider range of separation distance for stable equilibrium than was possible with natural materials. The relationship between the separation distance for stable equilibrium and the constructive parameters of the Mie metamaterial and the geometric parameters of the system was investigated, and simple rules for tuning the equilibrium position by modifying the constructive parameters of the Mie metamaterial was provided. These results are promising for potential applications in frictionless suspension in micro/nanofabrication technologies.

We present a density functional theory parametrized hybrid $\mathrm{k}·\mathrm{p}$ tight-binding model for electronic properties of atomically thin films of transition-metal dichalcogenides, $2\mathrm{H}-M{X}_2(M=\mathrm{Mo},\mathrm{W};X=\mathrm{S}$, Se). We use this model to analyze intersubband transitions in $p$- and $n$-doped $2\mathrm{H}\text{−}M{X}_2$ films and predict the line shapes of the intersubband excitations, determined by the subband-dependent two-dimensional electron and hole masses, as well as excitation lifetimes due to emission and absorption of optical phonons. We find that the intersubband spectra of atomically thin films of the 2H-$M{X}_2$ family with thicknesses of $N=2$ to 7 layers densely cover the infrared spectral range of wavelengths between 2 and $30\mu \mathrm{m}$. The detailed analysis presented in this paper shows that for thin $n$-doped films, the electronic dispersion and spin-valley degeneracy of the lowest-energy subbands oscillate between odd and even number of layers, which may also offer interesting opportunities for quantum Hall effect studies in these systems.

Lateral two-dimensional (2D) transition-metal dichalcogenide (TMD) heterostructures have recently attracted wide attention as promising materials for optoelectronic nanodevices. Due to the nanoscale width of lateral heterojunctions, the study of their optical properties is challenging and requires using subwavelength optical characterization techniques. We investigated the photoresponse of a lateral 2D $\mathrm{WS}{\mathrm{e}}_2/\mathrm{MoS}{\mathrm{e}}_2$ heterostructure using tip-enhanced photoluminescence (TEPL) with nanoscale spatial resolution and with picoscale tip-sample distance dependence. We demonstrate the observation of quantum plasmonic effects in 2D heterostructures on a nonmetallic substrate, and we report the nano-optical measurements of the lateral 2D TMD heterojunction width of $\sim 150$ nm and the charge tunneling distance of $\sim 20$ pm. Controlling the plasmonic tip location allows for both nano-optical imaging and plasmon-induced hot-electron injection into the heterostructure. By adjusting the tip-sample distance, we demonstrated the controllability of the hot-electron injection via the competition of two quantum plasmonic photoluminescence (PL) enhancement and quenching mechanisms. The directional charge transport in the depletion region leads to the increased hot-electron injection, enhancing the $\mathrm{MoS}{\mathrm{e}}_2$ PL signal. The properties of the directional hot-electron injection in the quantum plasmonic regime make the lateral 2D $\mathrm{MoS}{\mathrm{e}}_2/\mathrm{WS}{\mathrm{e}}_2$ heterostructures promising for quantum nanodevices with tunable photoresponse.

A typical quantum state obeying the area law for entanglement on an infinite two-dimensional (2D) lattice can be represented by a tensor network Ansatz, known as an infinite projected entangled pair state (iPEPS), with a finite bond dimension $D$. Its real-imaginary time evolution can be split into small time steps. An application of a time step generates a new iPEPS with a bond dimension $k$ times the original one. The new iPEPS does not make optimal use of its enlarged bond dimension $kD$; hence, in principle, it can be represented accurately by a more compact Ansatz, preferably with the original $D$. In this work we show how the more compact iPEPS can be optimized variationally to maximize its overlap with the new iPEPS. To compute the overlap we use the corner-transfer-matrix renormalization group. By simulating sudden quench of the transverse field in the 2D quantum Ising model with the proposed algorithm, we provide a proof of principle that real-time evolution can be simulated with iPEPS. A similar proof is provided with the same model for imaginary-time evolution of purification of its thermal states.

We consider the $d$-dimensional transverse-field Ising model with power-law interactions $J/r^{d+\sigma }$ in the presence of a noisy longitudinal field with zero average. We study the longitudinal-magnetization dynamics of an initial paramagnetic state after a sudden switch-on of both the interactions and the noisy field. While the system eventually relaxes to an infinite-temperature state with vanishing magnetization correlations, we find that two-time correlation functions show aging at intermediate times. Moreover, for times shorter than the inverse noise strength $\kappa$ and distances longer than $a{(J/\kappa )}^{2/\sigma }$ with $a$ being the lattice spacing, we find a critical scaling regime of correlation and response functions consistent with the model A dynamical universality class with an initial-slip exponent $\theta =1$ and dynamical critical exponent $z=\sigma /2$. We obtain our results analytically by deriving an effective action for the magnetization field including the noise in a nonperturbative way. The above scaling regime is governed by a nonequilibrium fixed point dominated by the noise fluctuations.

We numerically investigate the electronic properties of magnetic domain walls formed in a Weyl semimetal. Electric charge distribution is computed from the electron wave functions, by numerically diagonalizing the Hamiltonian under several types of domain walls. We find a certain amount of electric charge localized around the domain wall, depending on the texture of the domain wall. This localized charge stems from the degeneracy of Landau states under the axial magnetic field, which corresponds to the curl in the magnetic texture. The localized charge enables one to drive the domain wall motion by applying an external electric field without injecting an electric current, which is distinct from the ordinary spin-transfer torque and is free from Joule heating.

We consider graphene on monolayer ${\mathrm{WSe}}_2$ and the spin-orbit coupling induced by the transition-metal dichalcogenide substrate for application to spin-active devices. We study quantum dots and graphene quantum rings as tunable spin filters and inverters. We use an atomistic tight-binding model as well as the Dirac equation to determine stationary states confined in quantum dots and rings. Next, we solve the spin-transport problem for dots and rings connected to nanoribbon leads. The systems connected to zigzag nanoribbons at low magnetic fields act as spin filters and provide strongly spin polarized current.

Glassy carbon is a disordered carbon allotrope consisting of $s{p}^2$-hybridized bonds, which can be transformed to mixed $s{p}^2\text{−}s{p}^3$ forms with completely different mechanical and electrical properties. The transformation from an $s{p}^2$-rich to $s{p}^3$-rich structure under pressure has been extensively studied, while the effect of shear strain on the transformation remains unexplored. In this work, we use a first-principles calculation method to study the phase transitions of glassy carbon under both shear strain and pressure. We find that shear strain can significantly reduce the external pressure needed to transform the structure from $s{p}^2$ rich to $s{p}^3$ rich. Compared with the initial $s{p}^2$-rich structure, $s{p}^3$-rich structures recovered to ambient condition have a much higher mechanical strength and lower electronic density of states near the Fermi level. Our results demonstrate that applying large shear strain is a promising approach for industrial production of superhard amorphous carbon under lower pressures.

The thermal expansion behavior of metal fluorides can be tuned by choosing an appropriate metal cation. We present ab initio lattice dynamical studies on the metal fluorides $(\mathrm{CaZr}{\mathrm{F}}_6,\mathrm{MgZr}{\mathrm{F}}_6$, and $\mathrm{SrZr}{\mathrm{F}}_6)$ and identify the anharmonic phonon modes responsible for the negative thermal expansion (NTE) in these materials. These phonon modes involve $\mathrm{Zr}{\mathrm{F}}_6$ polyhedral rotational motion, which leads to large transverse amplitude of the vibrations of the fluorine atom in the Zr-F-M bond in these compounds. The compounds with larger anisotropy in the thermal amplitude of the fluorine atom show larger NTE behavior. This has enabled us to understand the substantial variation in thermal expansion behavior of these compounds at high temperature. We have also calculated the potential energy profile of selected phonon modes, which enables us to derive the cubic and quartic anharmonic coefficients.

We study spin-dependent electron transport through a ferromagnetic-antiferromagnetic-normal metal tunneling junction subject to a voltage or temperature bias, in the absence of spin-orbit coupling. We derive microscopic formulas for various types of spin torque acting on the antiferromagnet as well as for charge and spin currents flowing through the junction. The obtained results are applicable in the limit of slow magnetization dynamics. We identify a parameter regime in which an unconventional dampinglike torque can become comparable in magnitude to the equivalent of the conventional Slonczewski's torque generalized to antiferromagnets. Moreover, we show that the antiferromagnetic sublattice structure opens up a channel of electron transport which does not have a ferromagnetic analog and that this mechanism leads to a pronounced fieldlike torque. Both charge conductance and spin current transmission through the junction depend on the relative orientation of the ferromagnetic and the antiferromagnetic vectors (order parameters). The obtained formulas for charge and spin currents allow us to identify the microscopic mechanisms responsible for this angular dependence and to assess the efficiency of an antiferromagnetic metal acting as a spin current polarizer.

The magnetic ground states of the diluted $\alpha -{\mathrm{Ru}}_{1-x}{\mathrm{Ir}}_x{\mathrm{Cl}}_3$ are systematically investigated by magnetization, specific heat, and muon spin rotation measurements. Introduction of moderate spin vacancies leads to a destabilization of the zigzag antiferromagnetic order towards a short-range ordered state. It is remarkable that the $x=0.2$ sample located near a quantum critical point shows an extremely short correlation length of the magnitude of magnetic moments ${\zeta }_{\mathrm{mag}}\sim 1.2a$ ($a=\mathrm{lattice}$ spacing) and a power-law behavior of the magnetic susceptibility $\chi \left(T\right)\sim T^{-p}$ below 14 K for ${\mu }_{0}H\parallel ab$ and below 30 K for ${\mu }_{0}H\parallel c$. Our work demonstrates that the $\alpha -{\mathrm{Ru}}_{1-x}{\mathrm{Ir}}_x{\mathrm{Cl}}_3$ system hosts a short-range, quasistatic order characterized by critical spin correlations.

We report a new multiferroic family of $(R,\mathrm{Y}){\mathrm{CrO}}_4(R=\mathrm{Sm},\mathrm{Gd},\text{and} \mathrm{Ho})$. The ferroelectric ordering temperatures are observed at much higher temperatures than their corresponding magnetic ordering temperatures for all the members. The values of electric polarization ($P$) are significantly high, which vary from $\sim 217$ to $\sim 640\mu {\mathrm{C}/\mathrm{m}}^2$ for a 4 kV/cm poling field. The large value of $P(\sim 590\mu {\mathrm{C}/\mathrm{m}}^2)$ for ${\mathrm{YCrO}}_4$ compared to the smallest $P$ value in the series for ${\mathrm{GdCrO}}_4$ signifies that the magnetic rare-earth element does not directly influence the $P$ value. Our careful analysis of the low-temperature synchrotron diffraction studies confirms that the distortion of ${\mathrm{CrO}}_4$ tetrahedra directs the $P$ value. The structural transformation from the centrosymmetric $I{4}_1/amd$ structure to a noncentrosymmetric $I\overline{4}2d$ space group at the onset of polar order is found to be correlated with the appearance of spontaneous electric polarization.

We report the generation and transport of thermal spin currents in fully epitaxial $\gamma \text{−}\mathrm{F}{\mathrm{e}}_2{\mathrm{O}}_3/\mathrm{NiO}\left(001\right)/\mathrm{Pt}$ and $\mathrm{F}{\mathrm{e}}_3{\mathrm{O}}_4/\mathrm{NiO}\left(001\right)/\mathrm{Pt}$ trilayers. A thermal gradient, perpendicular to the plane of the sample, generates a magnonic spin current in the ferrimagnetic maghemite $\left(\gamma \text{−}\mathrm{F}{\mathrm{e}}_2{\mathrm{O}}_3\right)$ and magnetite $\left(\mathrm{F}{\mathrm{e}}_3{\mathrm{O}}_4\right)$ thin films by means of the spin Seebeck effect. The spin current propagates across the epitaxial, antiferromagnetic insulating NiO layer, before being detected in the Pt layer by the inverse spin Hall effect. The transport of the spin signal is studied as a function of the NiO thickness, temperature, and ferrimagnetic material where the spin current is generated. In epitaxial NiO grown on maghemite, the spin Seebeck signal decays exponentially as a function of the NiO thickness, with a spin-diffusion length for thermally generated magnons of ${\lambda }_{\mathrm{MSDL}}=1.6\pm 0.2\mathrm{nm}$ (where MSDL is mean spin-diffusion length), largely independent of temperature. We see no enhancement of the spin-current signal as previously reported for certain temperatures and thicknesses of the NiO. In epitaxial NiO grown on magnetite, the temperature-averaged spin-diffusion length is ${\lambda }_{\mathrm{MSDL}}=3.8\pm 0.3\mathrm{nm}$, and we observe an enhancement of the spin signal when the NiO thickness is 0.8 nm, demonstrating that the growth conditions dramatically affect the spin-transport properties of the NiO even for full epitaxial growth. In contrast to theoretical predictions for coherent spin transport, we do not see vastly different spin-diffusion lengths between epitaxial and polycrystalline NiO layers.

We report a study of the magnetic and electronic properties of the ${\mathrm{U}}_{0.15}\mathrm{N}{\mathrm{p}}_{0.85}{\mathrm{O}}_2$ solid solution, based on dc- and ac magnetization, ${}^{237}\mathrm{Np}$ Mössbauer spectroscopy, ${}^{17}\mathrm{O}$ nuclear magnetic resonance, and specific heat measurements. The compound orders antiferromagnetically at $T_{\mathrm{N}}=17\mathrm{K}$. The different techniques reveal the complexity of this system with: $\left(i\right)$ a spatial distribution of ordered moments, $\left(ii\right)$ a small Np ordered moment $\left({\mu }_{\mathrm{Np}}=0.3{\mu }_{\mathrm{B}}\right)$, and (iii) an additional specific heat anomaly at 7.4 K, with a residual value at very low temperature and a reduced magnetic entropy. The results are compared to the end members of the series, $\mathrm{U}{\mathrm{O}}_2$ and $\mathrm{Np}{\mathrm{O}}_2$, as well as to the other solid solutions previously reported in this system. We discuss how the properties of ${\mathrm{U}}_{0.15}\mathrm{N}{\mathrm{p}}_{0.85}{\mathrm{O}}_2$ add input to the trend previously reported for the series in view of the models that have been proposed.