The optical activity of achiral nonmagnetic uniaxial metasurfaces caused by the extrinsic chirality arising from the mutual orientation of their anisotropy axis and the light plane of incidence is studied. The hyperbolic regime of the metasurfaces manifests in the amplification of the polarization rotation in transmitted light and in the giant enhancement of the effect in reflected light. The transition to this regime is frequency dependent and has a topological nature. The key role in the optical activity enhancement belongs to the $\sigma$-near-pole and hyperbolic $\sigma$-near-zero regimes of the metasurfaces. The hyperbolic metasurfaces based on graphene strips or metal disks, and a black phosphorus thin film as a natural hyperbolic layer are considered. The efficiency of the predicted effects depends on the metasurface implementation and the role of a substrate. By varying the metasurface parameters and choosing the physical realizations it is possible to design such a hyperbolic metasurface polarizer for the THz, infrared, and visible working ranges. Our findings may help to improve metasurface polarizers by using them in the hyperbolic regime.

The phonon-assisted sticking rate of slow moving atoms impinging on an elastic membrane at nonzero temperature is studied analytically using a model with linear atom-phonon interactions, valid in the weak-coupling regime. A perturbative expansion of the adsorption rate in the atom-phonon coupling is infrared divergent at zero temperature, and this infrared problem is exacerbated by finite temperature. The use of a coherent-state phonon basis in the calculation, however, yields infrared-finite results even at finite temperature. The sticking probability with the emission of any finite number of phonons is seen explicitly to be exponentially small, and it vanishes as the membrane size grows, a result that was found previously at zero temperature; in contrast to the zero-temperature case, this exponential suppression of the sticking probability persists even with the emission of an infinite number of soft phonons. Explicit closed-form expressions are obtained for the effects of soft-phonon emission at finite temperature on the adsorption rate. For slowly moving atoms, the model predicts that there is zero probability of sticking to a large elastic membrane at nonzero temperature and weak coupling.

The two-dimensional electron system in an InAs quantum well has emerged as a prime candidate for hosting exotic quasiparticles with non-Abelian statistics such as Majorana fermions and parafermions. To attain its full promise, however, the electron system has to be clean enough to exhibit electron-electron interaction phenomena. Here, we report the observation of the fractional quantum Hall effect in a very low disorder InAs quantum well with a well width of 24 nm, containing a two-dimensional electron system with a density $n=7.8\times {10}^{11}{\mathrm{cm}}^{-2}$ and low-temperature mobility $1.8\times {10}^6{\mathrm{cm}}^2$/Vs. At a temperature of $\simeq 35$ mK and $B\simeq 24$ T, we observe a deep minimum in the longitudinal resistance, accompanied by a nearly quantized Hall plateau at a Landau level filling factor $\nu =4/3$.

Motivated by the physics of Pr-based cobaltites, we study the effect of the external magnetic field in the hole-doped two-band Hubbard model close to instabilities toward the excitonic condensation and ferromagnetic ordering. Using the dynamical mean-field theory we observe a field-driven suppression of the excitonic condensate. The onset of a magnetically ordered phase at the fixed chemical potential is accompanied by a sizable change of the electron density. This leads us to predict that ${\mathrm{Pr}}^{3+}$ abundance increases on the high-field side of the transition.

The idea of renormalization and scale invariance is pervasive across disciplines. It has not only drawn numerous surprising connections between physical systems under the guise of holographic duality, but has also inspired the development of wavelet theory now widely used in signal processing. Synergizing on these two developments, we describe in this paper a generalized exact holographic mapping that maps a generic $N$-dimensional lattice system to a ($N+1$)-dimensional holographic dual, with the emergent dimension representing scale. In previous works, this was achieved via the iterations of the simplest of all unitary mappings, the Haar mapping, which fails to preserve the form of most Hamiltonians. By taking advantage of the full generality of biorthogonal wavelets, our new generalized holographic mapping framework is able to preserve the form of a large class of lattice Hamiltonians. By explicitly separating features that are fundamentally associated with the physical system from those that are basis specific, we also obtain a clearer understanding of how the resultant bulk geometry arises. For instance, the number of nonvanishing moments of the high-pass wavelet filter is revealed to be proportional to the radius of the dual anti–de Sitter space geometry. We conclude by proposing modifications to the mapping for systems with generic Fermi pockets.

Here, we present an alternative approach for the description of quantum critical fluctuations. These are described by Langevin random fields, which are then related to the susceptibility using the fluctuation-dissipation theorem. We use this approach to characterize the physical properties arising in the vicinity of two coupled quantum phase transitions. We consider a phenomenological model based on two scalar order parameter fields locally coupled biquadratically and having a common quantum critical point as a function of a quantum tuning parameter such as pressure or magnetic field. A self-consistent treatment shows that the uniform static susceptibilities of the two order parameter fields have the same qualitative form at low temperature even where the forms are different in the absence of the biquadratic coupling.

We study the emergence of two-dimensional conformal symmetry in critical quantum spin chains on the finite circle. Our goal is to characterize the conformal field theory (CFT) describing the universality class of the corresponding quantum phase transition. As a means to this end, we propose and demonstrate automated procedures which, using only the lattice Hamiltonian $H={\sum }_j{h}_j$ as an input, systematically identify the low-energy eigenstates corresponding to Virasoro primary and quasiprimary operators, and assign the remaining low-energy eigenstates to conformal towers. The energies and momenta of the primary operator states are needed to determine the primary operator scaling dimensions and conformal spins, an essential part of the conformal data that specifies the CFT. Our techniques use the action, on the low-energy eigenstates of $H$, of the Fourier modes $H_n$ of the Hamiltonian density $h_j$. The $H_n$ were introduced as lattice representations of the Virasoro generators by Koo and Saleur [Nucl. Phys. B 426, 459 (1994)]. In this paper, we demonstrate that these operators can be used to extract conformal data in a nonintegrable quantum spin chain.

The observation of giant Rydberg excitons in cuprous oxide $\left({\mathrm{Cu}}_2\mathrm{O}\right)$ up to a principal quantum number of $n=25$ by T. Kazimierczuk et al. [Nature (London) 514, 343 (2014)] inevitably raises the question whether these quasiparticles must be described within a multipolariton framework since excitons and photons are always coupled in the solid. In this paper we present the theory of exciton-polaritons in ${\mathrm{Cu}}_2\mathrm{O}$. To this end we extend the Hamiltonian which includes the complete valence-band structure, the exchange interaction, and the central-cell corrections effects, and which has been recently deduced by F. Schweiner et al. [Phys. Rev. B 95, 195201 (2017)], for finite values of the exciton momentum $\hslash K$. We derive formulas to calculate not only dipole but also quadrupole oscillator strengths when using the complete basis of F. Schweiner et al., which has recently been proven as a powerful tool to calculate exciton spectra. Very complex polariton spectra for the three orientations of $\mathit{K}$ along the axes $\left[001\right]$, $\left[110\right]$, and $\left[111\right]$ of high symmetry are obtained and a strong mixing of exciton states is reported. The main focus is on the $1S$ ortho-exciton-polariton, for which pronounced polariton effects have been measured in experiments. We set up a $5\times 5$ matrix model, which accounts for both the polariton effect and the $K$-dependent splitting, and which allows treating the anisotropic polariton dispersion for any direction of $\mathit{K}$. We especially discuss the dispersions for $\mathit{K}$ being oriented in the planes perpendicular to $\left[1\overline{1}0\right]$ and $\left[111\right]$, for which experimental transmission spectra have been measured. Furthermore, we compare our results with experimental values of the $K$-dependent splitting, the group velocity, and the oscillator strengths of this exciton-polariton. The results are in good agreement. This proves the validity of the $5\times 5$ matrix model as a useful theoretical model for further investigations on the $1S$ ortho-exciton-polariton.

Achieving high charge-carrier mobility is the holy grail of organic electronics. In this paper we report an ultrahigh charge-carrier mobility of $14.93{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ through a coronene stack encapsulated in a single-walled carbon nanotube (CNT) by using a multiscale modeling technique which combines molecular dynamics simulations, first-principle calculations, and kinetic Monte Carlo simulations. For a CNT having a diameter of 1.56 nm we find a highly ordered defect-free organization of coronene molecules inside the CNT which is responsible for the high charge-carrier mobility. The encapsulated coronene molecules are correlated with a large correlation length of $\sim 18\AA$, which is independent of the length of the coronene column. Our simulation further suggests that coronene molecules can spontaneously enter the CNT, suggesting that the encapsulation is experimentally realizable.

The metastable $1T^{\prime }$ phase of layered transition metal dichalcogenides has recently attracted considerable interest due to electronic properties, possible topological phases, and catalytic activity. We report a comprehensive theoretical investigation of intrinsic point defects in the $1T^{\prime }$ crystalline phase of single-layer molybdenum disulfide ($1T^{\prime }\text{−}{\mathrm{MoS}}_2$) and provide comparison to the well-studied semiconducting $2H$ phase. Based on density functional theory calculations, we explore a large number of configurations of vacancy, adatom, and antisite defects and analyze their atomic structure, thermodynamic stability, and electronic and magnetic properties. The emerging picture suggests that, under thermodynamic equilibrium, $1T^{\prime }\text{−}{\mathrm{MoS}}_2$ is more prone to hosting lattice imperfections than the $2H$ phase. More specifically, our findings reveal that the S atoms that are closer to the Mo atomic plane are the most reactive sites. Similarly to the $2H$ phase, S vacancies and adatoms in $1T^{\prime }\text{−}{\mathrm{MoS}}_2$ are very likely to occur while Mo adatoms and antisites induce local magnetic moments. Contrary to the $2H$ phase, Mo vacancies in $1T^{\prime }\text{−}{\mathrm{MoS}}_2$ are expected to be an abundant defect due to the structural relaxation that plays a major role in lowering the defect formation energy. Overall, our study predicts that the realization of high-quality flakes of $1T^{\prime }\text{−}{\mathrm{MoS}}_2$ should be carried out under very careful laboratory conditions but at the same time the facile defects introduction can be exploited to tailor physical and chemical properties of this polymorph.

We explore the limitations and validity of semiclassically formulated spin equations of motion. Using a single-molecule magnet as a test model, we employ three qualitatively different approximation schemes. From a microscopic model, we derive a generalized spin equation of motion in which the parameters have a nonlocal time dependence. This dynamical equation is simplified to the Landau-Lifshitz-Gilbert equation with (i) time-dependent and (ii) time-independent parameters. We show that transient dynamics is essentially nonexisting in the latter approximation, while the former breaks down in the regime of strong coupling between the spin and the itinerant electrons.

Magnetic skyrmions are nanoscale windings of the spin structure that can be observed in chiral magnets and hold promise for potential applications in storing or processing information. Pinning due to ever-present material imperfections crucially affects the mobility of skyrmions. Therefore, a proper understanding of how magnetic skyrmions pin to defects is necessary for the development and performance of spintronic devices. Here we present a fundamental analysis on the interactions of single skyrmions with atomic defects of distinctly different origins, in a Co monolayer on Pt, based on minimum-energy paths considerations and atomic-spin simulations. We first report the preferred pinning loci of the skyrmion as a function of its nominal size and the type of defect being considered, to further reveal the manipulation and “breathing” of skyrmion core in the vicinity of a defect. We also show the behavior of skyrmions in the presence of an extended defect of particular geometry, that can lead to ratcheted skyrmion motion or a facilitated guidance on a defect “trail.” We close the study with reflections on the expected thermal stability of the skyrmion against collapse on itself for a given nature of the defect, and discuss the applications where control of skyrmions by defects is of particular interest.

We investigate the necessary conditions for the emergence of complex, noncoplanar magnetic configurations in a Kondo lattice model with classical local moments on the geometrically frustrated Shastry-Sutherland lattice and their evolution in an external magnetic field. We demonstrate that topologically nontrivial spin textures, including a new canted flux state, with nonzero scalar chirality arise dynamically from realistic short-range interactions. Our results establish that a finite Dzyaloshinskii-Moriya (DM) interaction is necessary for the emergence of these novel magnetic states when the system is at half filling, for which the ground state is insulating. We identify the minimal set of DM vectors that are necessary for the stabilization of chiral magnetic phases. The noncoplanarity of such structures can be tuned continually by applying an external magnetic field. This is the first part in a series of two papers; in the following paper the effects of frustration, thermal fluctuations, and magnetic field on the emergence of novel noncollinear states at metallic filling of itinerant electrons are discussed. Our results are crucial in understanding the magnetic and electronic properties of the rare-earth tetraboride family of frustrated magnets with separate spin and charge degrees of freedom.

We explore the magnetic phases in a Kondo lattice model on the geometrically frustrated Shastry-Sutherland lattice at metallic electron densities, searching for noncollinear and noncoplanar spin textures. Motivated by experimental observations in many rare-earth-based frustrated metallic magnets, we treat the local moments as classical spins and set the coupling between the itinerant electrons and local moments as the largest energy scale in the problem. Our results show that a noncollinear flux state is stabilized over an extended range of Hamiltonian parameters. These spin states can be quenched efficiently by external fields like temperature and magnetic field as well as by varying the degree of frustration in the electronic itinerancy and exchange coupling between local moments. Interestingly, unlike insulating electron densities that we discussed in paper I of this sequence, a Dzyaloshinskii-Moriya interaction between the local moments is not essential for the emergence of their noncollinear ordering.

Controlling the magnetic anisotropy in epitaxial ${\mathrm{Y}}_3\mathrm{F}{\mathrm{e}}_5{\mathrm{O}}_{12}$ (YIG) thin films is critical for magnonic and photonic device applications. In this paper, we report the crystal structure, magnetic properties, and magnetic anisotropy of epitaxial ${\mathrm{Y}}_3\left(\mathrm{F}{\mathrm{e}}_{5-x}\mathrm{M}{\mathrm{n}}_x\right){\mathrm{O}}_{12}$ (Mn:YIG) thin films grown on $\mathrm{G}{\mathrm{d}}_3\mathrm{G}{\mathrm{a}}_5{\mathrm{O}}_{12}$ (111) (GGG) substrates by pulsed-laser deposition. Mn doping is observed to strongly enhance the magnetoelastic coefficient of YIG thin films, which leads to large tunability of the thin film magnetic anisotropy by lattice strain. With increasing Mn concentration from $x=0$ to $x=1.25$, a continuous increase of out-of-plane magnetic anisotropy ranging from −644.4 Oe to 1337.5 Oe is observed. In particular, a perpendicular magnetic anisotropy (PMA) is achieved in Mn:YIG thin films with a high Mn concentration of $x=1.12$. Ferromagnetic resonance (FMR) measurements show low FMR linewidths of 3.4 Oe to 129 Oe at 9.5 GHz in Mn:YIG thin films. Our paper demonstrates manganese doping as an effective way to enhance the magnetoelastic anisotropy of YIG thin films by strain, which is useful for magnonic and magneto-optical device applications.

By using the high pressure synthesis method, we fabricated the potassium-doped para-terphenyl. The temperature dependence of magnetization measured in both zero-field-cooled and field-cooled processes shows step-like transitions at about 125 K. This confirms an earlier report about the possible superconductivity-like transition in the same system. However, the magnetization hysteresis loop exhibits a weak ferromagnetic background. The estimate on the diamagnetization of this step shows that the diamagnetic volume is only about 0.04% at low temperatures, if we assume that the penetration depth is much smaller than the size of possible superconducting grains. This magnetization transition does not shift with magnetic field, but is suppressed and becomes almost invisible above 1.0 T. The resistivity measurements fail because of an extremely large resistance. By using the same method, we also fabricated the potassium-doped para-quaterphenyl. A similar step-like transition at about 125 K was also observed by using a magnetization measurement. Since there is an unknown positive background and the diamagnetic volume is too small, it is insufficient to conclude that this step is derived from superconductivity although it appears so.

Beside the spin density wave (SDW) order inside the superconducting phase in ${\mathrm{CeCoIn}}_5$ at high magnetic fields, recent neutron scattering measurements have found Bragg peaks in $5\%$ Nd-doped ${\mathrm{CeCoIn}}_5$ at low fields. The intensity of Bragg peaks in low fields is suppressed by increasing field. Based on the phenomenological and microscopic modeling, we show that for the Pauli limited $d$-wave superconductors in the vicinity of SDW instability relevant for ${\mathrm{CeCoIn}}_5$, magnetic impurities locally induce droplets of SDW order. Because of the strong anisotropy in the momentum space in the spin fluctuations guaranteed by the $d$-wave pairing symmetry, sharp peaks in spin structure factor at $\mathbf{Q}\mathrm{s}$ are produced by the impurities, even when the droplets of SDW do not order. At zero field, the Nd impurity spins are along the $c$ axis due to the coupling to the conduction electrons with an easy $c$ axis, besides their own crystal field effect. The in-plane magnetic field cants the impurity moments toward the $ab$ plane, which suppress the droplets of SDW order. At high fields, the long-range SDW inside the superconducting phase is stabilized as a consequence of magnon condensation. Our results are consistent with the recent neutron scattering and thermal conductivity measurements.

We study the validity of Hund's first rule for the spin multiplicity in circular molecules—made of real or artificial atoms such as quantum dots—by considering a perturbative approach in the Coulomb interaction in the extended Hubbard model with both on-site and long-range interactions. In this approximation, we show that an anti-Hund rule always defines the ground state in a molecule with $4N$ atoms at half-filling. In all other cases (i.e., number of atoms not a multiple of four, or a $4N$ molecule away from half-filling) both the singlet and the triplet outcomes are possible, as determined primarily by the total number of electrons in the system. In some instances, the Hund rule is always obeyed and the triplet ground state is realized mathematically for any values of the on-site and long-range interactions, while for other filling situations the singlet is also possible but only if the long-range interactions exceed a certain threshold, relatively to the on-site interaction.

The fully spin-polarized composite-fermion (CF) Fermi sea at the half-filled lowest Landau level has a Fermi wave vector $k_{\mathrm{F}}^{*}=\sqrt{4\pi {\rho }_e}$, where ${\rho }_e$ is the density of electrons or composite fermions, supporting the notion that the interaction between composite fermions can be treated perturbatively. Away from $\nu =1/2$, the area is seen to be consistent with $k_{\mathrm{F}}^{*}=\sqrt{4\pi {\rho }_e}$ for $\nu <1/2$ but $k_{\mathrm{F}}^{*}=\sqrt{4\pi {\rho }_h}$ for $\nu >1/2$, where ${\rho }_h$ is the density of holes in the lowest Landau level. This result is consistent with particle-hole symmetry in the lowest Landau level. We investigate in this article the Fermi wave vector of the spin-singlet CF Fermi sea (CFFS) at $\nu =1/2$, for which particle-hole symmetry is not a consideration. Using the microscopic CF theory, we find that for the spin-singlet CFFS the Fermi wave vectors for up- and down-spin CFFSs at $\nu =1/2$ are consistent with $k_{\mathrm{F}}^{*\uparrow ,\downarrow }=\sqrt{4\pi {\rho }_e^{\uparrow ,\downarrow }}$, where ${\rho }_e^{\uparrow }={\rho }_e^{\downarrow }={\rho }_e/2$, which implies that the residual interactions between composite fermions do not cause a nonperturbative correction for spin-singlet CFFS either. Our results suggest the natural conjecture that for arbitrary spin polarization the CF Fermi wave vectors are given by $k_{\mathrm{F}}^{*\uparrow }=\sqrt{4\pi {\rho }_e^{\uparrow }}$ and $k_{\mathrm{F}}^{*\downarrow }=\sqrt{4\pi {\rho }_e^{\downarrow }}$.

We demonstrate that intersubband (ISB) polaritons are robust to inhomogeneous effects originating from the presence of multiple quantum wells (MQWs). In a series of samples that exhibit mid-infrared ISB absorption transitions with broadenings varying by a factor of 5 (from 4 to 20 meV), we observed polariton linewidths always lying in the 4 to 7 meV range only. We experimentally verified the dominantly inhomogeneous origin of the broadening of the ISB transition, and that the linewidth reduction effect of the polariton modes persists up to room-temperature. This immunity to inhomogeneous broadening is a direct consequence of the coupling of the large number of ISB oscillators to a single photonic mode. It is a precious tool to gauge the natural linewidth of the ISB plasmon that is otherwise masked in such MQWs system, and is also beneficial in view of perspective applications such as intersubband polariton lasers.