Heusler compounds are widely studied due to their variety of magnetic properties making them ideal candidates for spintronic and magnetoelectronic applications. ${\mathrm{V}}_3\mathrm{Al}$ in its metastable ${\mathrm{D}0}_3$-type Heusler structure is a prototype for a rare antiferromagnetic gapless behavior. We provide an extensive study on the electronic and magnetic properties of ${\mathrm{V}}_3\mathrm{Al}, {\mathrm{V}}_3\mathrm{Ga}$, and ${\mathrm{V}}_3\mathrm{In}$ compounds based on electronic structure calculations. We show that the ground state for all three is a $G$-type itinerant antiferromagnetic gapless semiconductor. The large antiferromagnetic exchange interactions lead to very high Néel temperatures, which are predicted to be around 1000 K. The coexistence of the gapless and antiferromagnetic behaviors in these compounds can be explained considering the simultaneous presence of three V atoms at the unit cell using arguments which have been employed for usual inverse Heusler compounds. We expect our study on these compounds to enhance further the interest on them towards the optimization of their growth conditions and their eventual incorporation in devices.

This study demonstrates the effect of antiferromagnet-induced perpendicular magnetic anisotropy (PMA) on ferromagnetic/antiferromagnetic/ferromagnetic (FM/AFM/FM) trilayers and reveals its interplay with a long-range interlayer coupling between separated FM layers. In epitaxially grown 12 monolayer (ML) Ni/Co/Mn/5 ML Co/Cu(001) films, magnetic hysteresis loops and element-resolved magnetic domain imaging showed that the magnetization direction of the top layers of 12 ML Ni/Co films could be changed from the in-plane direction to the perpendicular direction, when the thickness of the Mn films (${\mathrm{t}}_{\mathrm{Mn}}$) was greater than a critical value close to the thickness threshold associated with the onset of AFM ordering (${\mathrm{t}}_{\mathrm{Mn}}=3.5$ ML). The top FM layers exhibited a significantly enhanced PMA when ${\mathrm{t}}_{\mathrm{Mn}}$ increased further, and this enhancement can be attributed to a strengthened AFM ordering of the volume moments of the Mn films, as evidenced by the presence of induced domain frustration. By contrast, the long-range interlayer coupling presented clear effects only when ${\mathrm{t}}_{\mathrm{Mn}}$ was at a lower coverage.

Isotropic and anisotropic magnetic behavior of the frustrated spin-chain compound $\beta -{\mathrm{TeVO}}_4$ is reported. Three magnetic transitions observed in zero magnetic field are tracked in fields applied along different crystallographic directions using magnetization, heat capacity, and magnetostriction measurements. Qualitatively different temperature-field diagrams are obtained below 10 T for the field applied along $a$ or $b$ and along $c$, respectively. In contrast, a nearly isotropic high-field phase emerges above 18 T and persists up to the saturation that occurs around 22.5 T. Upon cooling in low fields, the transitions at $T_{\mathrm{N}1}$ and $T_{\mathrm{N}2}$ toward the spin-density-wave and stripe phases are of the second order, whereas the transition at $T_{\mathrm{N}3}$ toward the helical state is of the first order and entails a lattice component. Our microscopic analysis identifies frustrated $J_1\text{−}{J}_2$ spin chains with a sizable antiferromagnetic interchain coupling in the $bc$ plane and ferromagnetic couplings along the $a$ direction. The competition between these ferromagnetic interchain couplings and the helical order within the chain underlies the incommensurate order along the $a$ direction, as observed experimentally. While a helical state is triggered by the competition between $J_1$ and $J_2$ within the chain, the plane of the helix is not uniquely defined because of competing magnetic anisotropies. Using high-resolution synchrotron diffraction and ${}^{125}\mathrm{Te}$ nuclear magnetic resonance, we also demonstrate that the crystal structure of $\beta -{\mathrm{TeVO}}_4$ does not change down to 10 K, and the orbital state of ${\mathrm{V}}^{4+}$ is preserved.

We explore the stability of the hybridization gap in ${\mathrm{SmB}}_6$ to the presence of a small number of Sm vacancies typical for this material, and demonstrate the extreme fragility of the Kondo insulating state. For the most stoichiometric sample we detect the hybridization gap which appears below 50 K as a depressed electronic Raman intensity below about 30 meV. The spectral weight that shifts to higher frequencies on the opening of the hybridization gap forms two electronic maxima at 100 and 41 meV. We assign these maxima to the excitations between hybridized $4f-5d$ bands using recent band structure calculations. Below 30 K, in-gap exciton modes with long lifetimes protected by the hybridization gap develop at 16–18 meV. With the increase of the number of Sm vacancies the exciton features broaden, evidencing a decrease in the lifetime due to the presence of electronic states in the gap. At a concentration of Sm vacancies of only about 1% the in-gap exciton is completely quenched, and the hybridization gap is not fully opened. We suggest that only the most stoichiometric ${\mathrm{SmB}}_6$ samples possess a bulk gap necessary for the topological Kondo insulator state.

We study bosonic atoms with two internal states in artificial gauge potentials whose strengths are different for the two components. A series of topological phases for such systems is proposed using the composite fermion theory and the parton construction. It is found in exact diagonalization that some of the proposed states may be realized for simple contact interaction between bosons. The ground states and low-energy excitations of these states are modeled using trial wave functions. The effective field theories for these states are also constructed and reveal some interesting properties.

We demonstrate how a Dirac-like magnon spectrum is generated for localized magnetic moments forming a two-dimensional honeycomb lattice. The Dirac crossing point is proven to be robust against magnon-magnon interactions, as these only shift the spectrum. Local defects induce impurity resonances near the Dirac point, as well as magnon Friedel oscillations. The energy of the Dirac point is controlled by the exchange coupling, and thus a two-dimensional array of magnetic dots is an experimentally feasible realization of Dirac magnons with tunable dispersion.

We investigate the transmission properties of a spin transistor coupled to two quantum point contacts acting as a spin injector and detector. In the Fabry-Pérot regime, transport is mediated by quasibound states formed between tunnel barriers. Interestingly, the spin-orbit interaction of the Rashba type can be tuned in such a way that nonuniform spin-orbit fields can point along distinct directions at different points of the sample. We discuss both spin-conserving and spin-flipping transitions as the spin-orbit angle of orientation increases from parallel to antiparallel configurations. Spin precession oscillations are clearly seen as a function of the length of the central channel. Remarkably, we find that these oscillations combine with the Fabry-Pérot motion, giving rise to quasiperiodic transmissions in the purely one-dimensional case. Furthermore, we consider the more realistic case of a finite width in the transverse direction and find that the coherent oscillations become deteriorated for moderate values of the spin-orbit strength. Our results then determine the precise role of the spin-orbit intersubband coupling potential in the Fabry-Pérot-Datta-Das intermixed oscillations.

We report on the study of terahertz radiation-induced MIRO-like oscillations of magnetoresistivity in GaAs heterostructures. Our experiments provide an answer on two most intriguing questions—effect of radiation helicity and the role of the edges—yielding crucial information for an understanding of the MIRO (microwave-induced resistance oscillations) origin. Moreover, we demonstrate that the range of materials exhibiting radiation-induced magneto-oscillations can be largely extended by using high-frequency radiation.

We have evaluated as-grown $\mathrm{Mo}{\mathrm{S}}_2$ crystals, epitaxially grown on a monocrystalline sapphire by chemical vapor deposition (CVD), with direct electronic band-structure measurements by energy-filtered $k$-space photoelectron emission microscopy performed with a conventional laboratory vacuum ultraviolet He I light source under off-normal illumination. The valence states of the epitaxial $\mathrm{Mo}{\mathrm{S}}_2$ were mapped in momentum space down to 7 eV below the Fermi level. Despite the high nucleation density within the imaged area, the CVD $\mathrm{Mo}{\mathrm{S}}_2$ possesses an electronic structure similar to the free-standing monolayer $\mathrm{Mo}{\mathrm{S}}_2$ single crystal, and it exhibits hole effective masses of $2.41\pm 0.05m_0$, and $0.81\pm 0.05m_0$, respectively, at Γ and $K$ high-symmetry points that are consistent with the van der Waals epitaxial growth mechanism. This demonstrates the excellent ability of the $\mathrm{Mo}{\mathrm{S}}_2$ CVD on sapphire to yield a highly aligned growth of well-stitched grains through epitaxial registry with a strongly preferred crystallographic orientation.

In 1+1-dimensional conformal-field theory, the thermal state on a circle is related to a certain quotient of the vacuum on a line. We explain how to take this quotient in the MERA tensor network representation of the vacuum and confirm the validity of the construction in the critical Ising model. This result suggests that the tensors comprising MERA can be interpreted as performing local scale transformations, so that adding or removing them emulates conformal maps. In this sense, the optimized MERA recovers local conformal invariance that is broken by the choice of lattice.

We combine electron energy-loss spectroscopy (EELS) and density functional theory (DFT) calculations to study the dispersion and effective mass of excitons in the bulk of ${\mathrm{WSe}}_2$. Our EELS data suggest substantial deviations from the generic quadratic momentum dependence along the $\mathrm{\Gamma }K$ direction. From the DFT-derived Kohn-Sham states we deduce the EELS response without the inclusion of particle-hole attraction to study the possible role of the single-particle band structure on the exciton behavior. Based on this analysis we argue in favor of a strongly momentum dependent particle-hole interaction in ${\mathrm{WSe}}_2$ and other group-VI-transition-metal dichalcogenides.

The phase separation occurring in Fe-Ni thin films near the Invar composition is studied by using high-resolution spectromicroscopy techniques and density functional theory calculations. Annealed at temperatures around $300{}^{\circ }\mathrm{C},{\mathrm{Fe}}_{0.70}{\mathrm{Ni}}_{0.30}$ films on W(110) break into micron-sized bcc and fcc domains with compositions in agreement with the bulk Fe-Ni phase diagram. Ni is found to be the diffusing species in forming the chemical heterogeneity. The experimentally determined energy barrier of $1.59\pm 0.09$ eV is identified as the vacancy formation energy via density functional theory calculations. Thus, the principal role of the surface in the phase separation process is attributed to vacancy creation without interstitials.

Strain effects on epitaxial thin films of $\mathrm{LaNi}{\mathrm{O}}_3$ grown on different single crystalline substrates are studied by Raman scattering and first-principles simulation. New Raman modes, not present in bulk or fully relaxed films, appear under both compressive and tensile strains, indicating symmetry reductions. Interestingly, the Raman spectra and the underlying crystal symmetry for tensile and compressively strained films are different. Extensive mapping of $\mathrm{LaNi}{\mathrm{O}}_3$ phase stability is addressed by simulations, showing that a variety of crystalline phases are indeed stabilized under strain. The calculated Raman frequencies reproduce the principal features of the experimental spectra, supporting the validity of the multiple strain-driven structural transitions predicted by the simulations.

It is shown that direct information from surface acoustic waves (SAWs) of bulk transparent materials can be obtained by using Brillouin light scattering (BLS). The study of surface phonons by means of an optical spectroscopy such as BLS has been historically constrained to nontransparent and highly reflecting bulk and film samples or even to very thin films deposited on reflecting substrates. Probably due to its low signal and to the narrow window in experimental conditions, it was assumed for years that bulk transparent samples were not suited for Brillouin spectroscopy in order to get information on SAWs, negating this optical technique in the search for SAW properties. The reported experiments on transparent glasses and single crystals (cubic MgO and trigonal sapphire) prove that there is no intrinsic physical reason not to collect SAW propagation velocity data from transparent bulk samples and opens a challenge to apply the Brillouin spectroscopy in a wider scenario to obtain direct information, in a nondestructive and contactless way, about SAWs in bulk materials.

Inelastic neutron scattering experiments have been carried out to determine the crystal-field states of the Kondo lattice heavy fermions ${\mathrm{CeRuSn}}_3$ and ${\mathrm{CeRhSn}}_3$. Both the compounds crystallize in ${\mathrm{LaRuSn}}_3$-type cubic structure (space group $Pm\overline{3}n$) in which the Ce atoms occupy two distinct crystallographic sites with cubic $\left(m\overline{3}\right)$ and tetragonal $\left(\overline{4}m.2\right)$ point symmetries. The INS data of ${\mathrm{CeRuSn}}_3$ reveal the presence of a broad excitation centered around 6–8 meV, which is accounted by a model based on crystal electric field (CEF) excitations. On the other hand, the INS data of isostructural ${\mathrm{CeRhSn}}_3$ reveal three CEF excitations around 7.0, 12.2, and 37.2 meV. The neutron intensity sum rule indicates that the Ce ions at both cubic and tetragonal Ce sites are in ${\mathrm{Ce}}^{3+}$ state in both ${\mathrm{CeRuSn}}_3$ and ${\mathrm{CeRhSn}}_3$. The CEF level schemes for both the compounds are deduced. We estimate the Kondo temperature $T_{\mathrm{K}}=3.1\left(2\right)$ K for ${\mathrm{CeRuSn}}_3$ from neutron quasielastic linewidth in excellent agreement with that determined from the scaling of magnetoresistance which gives $T_{\mathrm{K}}=3.2\left(1\right)$ K. For ${\mathrm{CeRhSn}}_3$, the neutron quasielastic linewidth gives $T_{\mathrm{K}}\approx 4.6$ K. For both ${\mathrm{CeRuSn}}_3$ and ${\mathrm{CeRhSn}}_3$, the ground state of ${\mathrm{Ce}}^{3+}$ turns out to be a quartet for the cubic site and a doublet for the tetragonal site.