The nonlinear electron dynamics in metallic nanoparticles is studied using a hydrodynamic model that incorporates most quantum many-body features, including spill-out and nonlocal effects as well as electron exchange and correlations. We show that, by irradiating the nanoparticle with a chirped laser pulse of modest intensity (autoresonance), it is possible to drive the electron dynamics far into the nonlinear regime, leading to enhanced energy absorption and complete ionization of the nanoparticle on a time scale of the order of 100 fs. The accompanying radiated power spectrum is rich in high-order harmonics.

We consider a square lattice configuration of circular gate-defined quantum dots in an unbiased graphene sheet and calculate the electronic, particularly spectral properties of finite albeit actual sample sized systems by means of a numerically exact kernel polynomial expansion technique. Analyzing the local density of states and the momentum resolved photoemission spectrum we find clear evidence for a series of quasibound states at the dots, which can be probed by optical measurements. We further analyze the interplay of the superlattice structure with dot-localized modes on the electron energy dispersion. Effects of disordered dot lattices are discussed too.

Neutron and x-ray diffraction, magnetic susceptibility, and specific heat measurements have been used to investigate the magnetic and structural phase transitions of the spinel system ${\mathrm{Fe}}_{1+x}$${\mathrm{Cr}}_{2-x}$$O_4$ ($0.0$ $\le$ $x$ $\le$ $1.0$). The temperature versus Fe concentration ($x$) phase diagram features two magnetically ordered states and four structural states below 420 K. The complexity of the phase diagram is closely related to the change in the spin and orbital degrees of freedom induced by substitution of Fe ions for Cr ions. The systematic change in the crystal structure is explained by the combined effects of Jahn-Teller distortion, spin-lattice interaction, ${\mathrm{Fe}}^{2+}$${\mathrm{-Fe}}^{3+}$ hopping, and disorder among ${\mathrm{Fe}}^{2+}$, ${\mathrm{Fe}}^{3+}$, and ${\mathrm{Cr}}^{3+}$ ions.

We examine the magnetostriction in amorphous SmCo thin films with a composition in the range 4–27 at. % Sm. The magnetostriction increases significantly with increasing Sm content but is small compared to terbium-based ferromagnetic compounds, despite the large imprinted anisotropy. The magnetostriction and anisotropy both increase approximately linearly as the temperature is reduced. The magnetoelastic energy is found to be far smaller than the anisotropy energy so the magnetoelastic atomic displacements during growth cannot be the origin of the imprinted anisotropy. The anisotropy is only slightly altered by the application of large tensile stresses, indicating that the local strain fields involved in magnetostriction are not equivalent to the global strain produced by mechanical bending.

We calculate the switching voltages for MgO-based magnetic tunnel junctions taking into account both the in-plane and the fieldlike spin-torque terms. To this end, we analytically solve the Landau-Lifshitz-Gilbert equation for a generalized geometry. We assume that the in-plane spin-torque varies linearly with the applied voltage, while the fieldlike torque exhibits a quadratic voltage dependence. Specifically, we consider that the free layer has two generic, orthogonal anisotropy components, one of which is along the direction defined by the magnetization of the reference layer, which also serves as a polarizer. The resulting formalism is applied to three different, experimentally relevant geometries: tunnel junctions with both the free and the reference layers magnetized in the plane of the layers, junctions with fully perpendicular anisotropy, and perpendicular junctions with an additional in-plane easy axis, respectively. We find that for in-plane devices, the quadratic dependence of the fieldlike torque on the applied voltage can lead to back hopping, which remains possible if we insert an additional linear term for the bias dependence of the fieldlike spin-torque comparable to current experimental results. For perpendicular anisotropy junctions neither back hopping nor spin-transfer-driven steady-state precession are expected. An additional in-plane shape anisotropy component stabilizes canted states in tunnel junctions with perpendicular anisotropy for specific values of voltage and field. The results are consistent with numerical integration of the Landau-Lifshitz-Gilbert equation and in good agreement with recent experiments involving perpendicular magnetic anisotropy magnetic tunnel junctions.

The influence of external pressure on the charge-density-wave (CDW) ground state of the quasi-one-dimensional two-leg ladder compound ${\mathrm{Sr}}_{10}$${\mathrm{Ca}}_4$${\mathrm{Cu}}_{24}$$o_{41}$ has been studied by optical reflectivity measurements as a function of temperature (10–300 K) and pressure $P$ (0.3–4.3 GPa) over the spectral range 580–6000 cm${}^1$. With increasing pressure the CDW transition temperature $T_{\text{CDW}}$ decreases with the linear pressure coefficient $\approx -$70 K/GPa, and above $\approx$3 GPa the CDW phase is suppressed at all temperatures. This behavior is similar to that in compounds ${\mathrm{Sr}}_{14-x}$${\mathrm{Ca}}_x$${\mathrm{Cu}}_{24}$$o_{41}$ with increasing Ca content $x$ at ambient pressure, with the simple scaling $x\approx 3\times P\left(\text{GPa}\right)$. The size of the CDW gap decreases with increasing pressure, whereas the dimensionality of the high-temperature insulating phase in ${\mathrm{Sr}}_{10}$${\mathrm{Ca}}_4$${\mathrm{Cu}}_{24}$$o_{41}$ within the ladder plane is hardly affected by external pressure.

A spin current is usually detected by converting it into a charge current through the inverse spin Hall effect (ISHE) in thin layers of a nonmagnetic metal with large spin-orbit coupling, such as Pt, Pd, and Ta. Here we demonstrate that ${\mathrm{Ir}}_{20}$${\mathrm{Mn}}_{80}$, a high-temperature antiferromagnetic metal that is commonly employed in spin-valve devices, exhibits a large inverse spin Hall effect, as recently predicted theoretically. We present results of experiments in which the spin currents are generated either by microwave spin pumping or by the spin Seebeck effect in bilayers of singe-crystal yttrium iron garnet (YIG)/${\mathrm{Ir}}_{20}$${\mathrm{Mn}}_{80}$ and compare them with measurements in YIG/Pt bilayers. The results of both measurements are consistent, showing that ${\mathrm{Ir}}_{20}$${\mathrm{Mn}}_{80}$ has a spin Hall angle similar to Pt, and that it is an efficient spin-current detector.

We demonstrate a self-consistent and versatile method to determine the relative spin Hall angle ${\theta }_{\text{SH}}$ and spin diffusion length ${\lambda }_{\text{SF}}$ of selected $5d$ metals (Pt, Au, Ta, and W) by thermal spin injection from a common ferromagnetic insulator, yttrium iron garnet, into thin metal films of various thicknesses. The values of ${\theta }_{\text{SH}}$ for Pt and Au are opposite in sign to those of Ta and W. The inverse spin Hall effect voltage depends on spin Hall resistivity, which is the product of ${\theta }_{\text{SH}}$ and electrical resistivity. We also show evidence of magnetic proximity effects including magnetoresistance and the anomalous Hall effect in these $5d$ metals, except for Au.

Transport coefficients, the elements of the so-called Onsager matrix, are essential quantities for modeling solid-state kinetics controlled by diffusion. In a face-centered-cubic structure, drag of solute atoms by vacancies can be caused by solute-vacancy binding at nearest neighbors. In order to investigate solute drag in alloys with interactions up to the third-nearest-neighbor sites, we extend an analytic method: the self-consistent mean field method. With this method, we calculate the Onsager matrix of model alloys to identify kinetic effects arising from individual and collective jump frequencies and assess the results on select cases using atomic kinetic Monte Carlo simulations. Using preexisting density functional theory data from various sources, we show that many impurities have low-temperature solute drag before changing to solute exchange at high temperatures. We evaluate the transition temperature for these alloys between these two regimes and compare the results with available experimental data. Some disagreement is found, which can be due both to experimental and numerical shortcomings. In order to guide diffusion calculations, the sensitivity of the Onsager matrix to the range of the kinetic correlation and to the input density functional theory data is studied.

Neutron diffraction is used to examine the polarization of weak static antiferromagnetism in high quality single crystalline ${\mathrm{URu}}_2$${\mathrm{Si}}_2$. As previously documented, elastic Bragg-like diffraction develops for temperature $T<T_{HO}=17.5$ K at $\mathbf{q}=\left(100\right)$ but not at wave vector transfer $\mathbf{q}=\left(001\right)$. The peak width indicates correlation lengths ${\xi }_c=230\left(12\right)$ Å and ${\xi }_a=240\left(15\right)$ Å. The integrated intensity of the $T$-dependent peaks corresponds to a sample averaged $c$-oriented staggered moment of ${\mu }_c=0.022\left(1\right){\mu }_B$ at $T=1.7$ K. The absence of $T$-dependent diffraction at $\mathbf{q}=\left(001\right)$ places a limit ${\mu }_{\perp }<0.0011{\mu }_B$ on an $f$- or $d$-orbital-based in-plane staggered magnetic dipole moment, which is associated with multipolar orders proposed for ${\mathrm{URu}}_2$${\mathrm{Si}}_2$.

We report the magnetic-field-dependent far-infrared reflectivity of polycrystalline bismuth. We observe four distinct absorptions that we attribute to magnetoplasmon resonances, which are collective modes of an electron-hole liquid in a magnetic field and become optical and acoustic resonances of the electron-hole system in the small-field limit. Acoustic mode are only when the masses of distinct components are very different, which is the case in bismuth. In a polycrystal, where the translational symmetry is broken, a big shift of spectral weight to an acoustic plasmon is possible. This enables us to detect an associated plasma edge. Although the polycrystal sample has grains of randomly distributed orientations, our reflectivity results can be explained by invoking only two, clearly distinct, series of resonances. In the limit of zero field, the optical modes of these two series converge onto plasma frequencies measured in a monocrystal along the main optical axes.

A first-principles density functional theory study of the Bechgaard salts ${\left(\mathrm{TMTSF}\right)}_2$${\text{ClO}}_4$ and ${\left(\mathrm{TMTSF}\right)}_2$${\text{NO}}_3$, with special emphasis on the anion ordering transition, is reported. It is found that the main effect of the anion ordering on the band structure occurs through the deformations induced in the TMTSF layers and not through the Coulomb potential of the anions, as it has been almost invariably assumed. It is shown that the anion ordering in ${\left(\mathrm{TMTSF}\right)}_2$${\text{ClO}}_4$ leads to a modulation of the dimerization in successive chains and to a noteworthy polarization of the two partially filled bands around the Fermi level into either the TMTSF A or TMTSF B donors. The calculated anion ordering half gap ${\Delta }_{AO}$ is found to be small but definitely non-nil, $\sim$14 meV. The suppression of the SDW instability in the relaxed samples is attributed to the deterioration of the Fermi surface nesting in the anion ordered phase. The possible nodal structure of the superconducting gap is discussed in relation with the newly calculated split Fermi surface. Anion ordering in ${\left(\mathrm{TMTSF}\right)}_2$${\text{NO}}_3$ leads to a smaller half gap, 8.9 meV. The anion ordering in this salt leads to a larger charge transfer between the two donors but to a smaller polarization of the two partially filled electron and hole bands. The weak influence of anion ordering into the low-temperature physics of this salt is related to the different periodicity of the anion ordering which leaves the nested parts of the Fermi surface almost unaltered.

Using scanning tunneling microscopy and ab initio simulations, we have identified several configurations for Cu dopants in ${\text{Cu}}_x$${\text{Bi}}_2$${\text{Se}}_3$, with Cu intercalants being the most abundant. Through statistical analysis, we show strong short-range repulsive interactions between Cu intercalants. At intermediate range (>5 nm), the pair distribution function shows oscillatory structure along the $\langle 10\overline{1}\rangle$ directions, which appear to be influenced by different diffusion barriers along the $\langle 10\overline{1}\rangle$ and $\langle 2\overline{1}\overline{1}\rangle$ directions.

We fabricated an etched hole quantum dot in a Si-doped (311)A AlGaAs/GaAs heterostructure to study disorder effects via magnetoconductance fluctuations (MCF) at millikelvin temperatures. Recent experiments in electron quantum dots have shown that the MCF are sensitive to the disorder potential created by remote ionized impurities. We utilize this to study the temporal/thermal stability of Si acceptors in $p$-type AlGaAs/GaAs heterostructures. In particular, we use a surface gate to cause charge migration between Si acceptor sites at $T=40$ mK, and detect the ensuing changes in the disorder potential using the MCF. We show that Si acceptors are metastable at $T=40$ mK and that raising the device to a temperature $T=4.2$ K and returning to $T=40$ mK is sufficient to produce complete decorrelation of the MCF. The same decorrelation occurs at $T\sim 165$ K for electron quantum dots; by comparing with the known trap energy for Si DX centers, we estimate that the shallow acceptor traps in our heterostructures have an activation energy $E_A\sim 3$ meV. Our method can be used to study charge noise and dopant stability towards optimization of semiconductor materials and devices.

We observe microwave-induced nonlocal resistance in magnetotransport in single and bilayer electronic systems. The obtained results provide evidence for an edge-state current stabilized by microwave irradiation due to nonlinear resonances. Our observation is closely related to microwave-induced oscillations and zero resistance states in a two-dimensional electron system.

We study the relaxation mechanism of a highly excited charge carrier propagating in the antiferromagnetic background modeled by the $t$-$J$ Hamiltonian on a square lattice. We show that the relaxation consists of two distinct stages. The initial ultrafast stage with the relaxation time $\tau \sim (\hslash /t_0){(J/t_0)}^{-2/3}$ (where $t_0$ is the hopping integral and $J$ is the exchange interaction) is based on the generation of string states in the close proximity of the carrier. This unusual scaling of $\tau$ is obtained by means of the comparison of numerical results with a simplified $t$-$J_z$ model on a Bethe lattice. In the subsequent (much slower) stage, local antiferromagnetic excitations are carried away by magnons. The relaxation time on the two-legged ladder system is an order of magnitude longer due to the lack of string excitations. This further reinforces the importance of string excitations for the ultrafast relaxation in the two-dimensional system.

Migdal's theorem plays a central role in the physics of electron-phonon interactions in metals and semiconductors, and has been extensively studied theoretically for parabolic band electronic systems in three-, two-, and one-dimensional systems over the last fifty years. In the current work, we theoretically study the relevance of Migdal's theorem in graphene and Weyl semimetals which are examples of 2D and 3D Dirac materials, respectively, with linear and chiral band dispersion. Our work also applies to 2D and 3D topological insulator systems. In Fermi liquids, the renormalization of the electron-phonon vertex scales as the ratio of sound ($v_s$) to Fermi ($v_F$) velocity, which is typically a small quantity. In two- and three-dimensional quasirelativistic systems, such as undoped graphene and Weyl semimetals, the one loop electron-phonon vertex renormalization, which also scales as $\eta =v_s/v_F$ as $\eta \to 0$, is, however, enhanced by an ultraviolet logarithmic divergent correction, arising from the linear, chiral Dirac band dispersion. Such enhancement of the electron-phonon vertex can be significantly softened due to the logarithmic increment of the Fermi velocity, arising from the long range Coulomb interaction, and therefore, the electron-phonon vertex correction does not have a logarithmic divergence at low energy. Otherwise, the Coulomb interaction does not lead to any additional renormalization of the electron-phonon vertex. Therefore, electron-phonon vertex corrections in two- and three-dimensional Dirac fermionic systems scale as $v_s/v_F^0$, where $v_F^0$ is the bare Fermi velocity, and small when $v_s\ll v_F^0$. These results, although explicitly derived for the intrinsic undoped systems, should hold even when the chemical potential is tuned away from the Dirac points.

We employ a magnetic-field driven antiferromagnetic to the fully polarized state transition in ${\text{Ni}}_3$${\text{V}}_2$${\text{O}}_8$ to investigate the interaction between spin ordering and driven charge excitations, with special emphasis on the color properties. Our measurements reveal field-induced blue shifts of the band gap that are much larger than that of the Zeeman effect in isolation, anticipating a more greenish appearance in the fully polarized state. This color change is verified with direct photographic images and emanates from charge density differences around the Ni and O centers in high fields.

The corrugation feature of potential energy surfaces (PESs) for rare-gas (RG) adlayers on metal surfaces has been extensively explored in the positive adsorption energy part. Here, we show that opposite corrugation features may also happen in the negative adsorption energy side for Ne and Xe on Cu(111). While the PES of Ne/Cu(111) is corrugated near the equilibrium adsorption geometry, i.e., Ne prefers the hollow site, the PES of Xe/Cu(111) is anticorrugated, i.e., Xe prefers the atop site. The weak hybridization of RG $p$ and Cu $d$ states is critical for this qualitative difference. Furthermore, the calculated activation energies indicate that Ne may move on Cu(111) at a very low temperature, whereas Xe motion can be activated only above 35 K. We found that the inclusion of the nonlocal van der Waals correction is essential for the correct determination of adsorption and motion energetics for RG adatoms on metals through density functional calculations.

The symmetry of boundaries between ferroelectric, ferroelastic, and antiphase domains is a key element for a theoretical understanding of their properties. Here, we derive this symmetry from their organic relation to the symmetry of the primary transition order parameters. The domain wall symmetries are shown to coincide with directions of the order-parameter $n$-dimensional vector space, corresponding to sum of the vectors associated with adjacent domain states. This property is illustrated by the determination of the maximal symmetries of domain walls in ${\mathrm{BaTiO}}_3$, ${\mathrm{LaAlO}}_3$, ${\mathrm{SrTiO}}_3$, and ${\mathrm{Gd}}_2$(${\mathrm{MoO}}_4$)${}_3$. Besides, the domain pattern in ${\mathrm{YMnO}}_3$ is interpreted as resulting from an annihilation-creation process, the annihilation of the antiphase domain walls creating six ferroelectric domain walls merging at a single point.