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We identify a mechanism to convert skyrmions and antiskyrmions into their antiferromagnetic (AFM) counterparts via interfacial engineering. The key idea is to combine properties of an antiferromagnet and a spin-orbit (SO) coupled metal. Utilizing hybrid Monte Carlo (HMC) simulations for a generic microscopic electronic Hamiltonian for the interfacial layers, we explicitly show the emergence of AFM skyrmions and AFM antiskyrmions. We further show that an effective spin Hamiltonian provides a simpler understanding of the results. We discuss the role of electronic itinerancy in determining the nature of magnetic textures, and demonstrate that the mechanism also allows for a tuning of antiskyrmion size without changing the SO coupling., Comment: 10 pages including supplemental material, 6 figures in manuscript, and 3 figures in supplemental material

We discover magnetic phases hosting highly elusive and technologically important antiferromagnetic skyrmion quasiparticles in a model for a Rashba-coupled Hund insulator. The results are based on unbiased simulations of a classical superexchange model derived, in this work, from a realistic microscopic electronic Hamiltonian. We also discover a skyrmion density wave ground state characterized by a $(Q,Q)$ modulation in the local skyrmion density map. A unique inhomogeneous state characterized by a circular pattern in the spin structure factor and filamentary real-space textures is identified as the parent of sparse antiferromagnetic skyrmions. We predict that the magnetic states reported here can be realized in thin films of multiorbital systems involving $4d$ or $5d$ transition metals.

Motivated by the importance of antiferromagnetic skyrmions as building blocks of next-generation data storage and processing devices, we report theoretical and computational analysis of a model for a spin-orbit coupled correlated magnet on a triangular lattice. We find that two distinct antiferromagnetic skyrmion crystal (AF-SkX) states can be stabilized at low temperatures in the presence of external magnetic field. The results are obtained via Monte Carlo simulations on an effective magnetic model derived from the microscopic electronic Hamiltonian consisting of Rashba spin-orbit coupling, as well as the Hund’s rule coupling of electrons to large classical spins. The two AF-SkX phases are understood to originate from a classical spin liquid state that exists at low but finite temperatures. These AF-SkX states can be easily distinguished from each other in experiments as they are characterized by peaks at distinct momenta in the spin structure factor which is directly measured in neutron scattering experiments. We also discuss examples of materials where the model as well as the two AF-SkX states can be realized.

We report a microscopic electronic mechanism for nanoscale skyrmion formation and topological metalicity originating from Rashba and double-exchange physics. The results are based on hybrid simulations in a model that explicitly retains itinerant electronic degrees of freedom. A simple physical picture is provided via an effective short-range spin model. We identify hexagonal and square lattice arrangements of skyrmions in two different regimes of the parameter space. Sparse skyrmions emerge at finite temperatures as excitations of the ferromagnetic phase. The skyrmion states are characterized as topological metals via explicit calculations of the Bott index and the Hall conductivity. Oscillations in local density of states are shown to arise from a combination of confinement effects and emergent gauge-fields. We also emphasize the importance of a consistent treatment of spin-orbit coupling for calculating electronic properties of metals hosting unconventional magnetic textures such as skyrmions.

We present a microscopic electronic description of how antiskyrmions can be stabilized in a Dresselhaus spin-orbit coupled magnetic metal. Furthermore, we show that the antiskyrmions can be tuned into Bloch skyrmions via a change in sign of hopping integral. The results are based on the state of the art hybrid Monte Carlo simulations. Origin of such topological textures is understood via an effective spin-only model. Our results uncover a novel connection between two very distinct topological spin textures of immense current interest, and present a microscopic explanation of skyrmion formation reported recently in certain magnetic Weyl semimetals.

We derive a new microscopic spin Hamiltonian for Rashba-coupled double exchange metals. The Hamiltonian consists of anisotropic interactions of the Dzyaloshinskii-Moriya (DM) and Kitaev form, in addition to the standard isotropic term. We validate the spin Hamiltonian by comparing results with those on the exact spin-fermion model, and present its phase diagram using large scale Monte Carlo simulations. In addition to ferromagnetic, planar spiral and flux states, the model hosts skyrmion crystal and classical spin-liquid states characterized, respectively, by multiple peaks and a diffuse ring pattern in the spin structure factor. The filamentary domain wall structures in the spin-liquid state are in remarkable agreement with experimental data on thin films of MnSi-type B20 metals and transition metals and their alloys., Comment: A sign mistake in the derivation is corrected in the 2nd version. Figures have been updated

In doped polyaniline (PANI), the charge transport properties are determined by mesoscopic morphology, which in turn is controlled by the molecular recognition interactions among polymer chain, dopant and solvent Molecular recognition plays a significant role in chain conformation and charge delocalization. The resistivity of PANI doped by camphor sulfonic acid (CSA)/2-acrylo-amido-1-propane sulfonic acid (AMPSA)/dodecyl benzene sulfonic acid (DBSA) is around $0.02\Omega$ cm. PANI-CSA and PANI-AMPSA show a metallic positive temperature coefficient of resistivity above 150 K, with a finite value of conductivity at 1.4 K; whereas, PANI-DBSA shows hopping transport at low temperatures. The magnetoresistance is positive (negative) for PANI-CSA (PANI-AMPSA); and PANI-DBSA has a large positive MR. The behavior of MR suggests subtle variations in mesoscopic morphology between PANI-CSA and PANI-AMPSA.

Molecular recognition plays a significant role in the counterion-induced processibility, morphological features, and physical properties of doped polyaniline (PANI). The interaction of the counterion and solvent controls the chain conformation and, as a result, the formation of extended and localized electronic states; hence, it holds the key for tuning a wide range of electrical and optical properties of doped PANI. The combined effects of counterion, solvent, and processing conditions tune the metal-insulator transition, temperature dependence of conductivity, magnetoresistance, and so forth in doped PANI. The typical examples are shown in the case of PANI doped by camphor sulfonic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, and dodecylbenzoyl sulfonic acid.

Using THz time-domain spectroscopy (THz-TDS), we have measured the absorption and dispersion of 7.5/( \Omega cm) conducting poly-3-methylthiophene film from low frequencies up to 4 THz. From these measurements the complex conductance that increases with increasing frequency was obtained over this frequency range. The results do not follow simple Drude theory and are not comparable with normal metal and semiconductors; the results were well fit by the localization-modified Drude theory.

Using an optoelectronic THz beam system for THz time-domain spectroscopy (THz TDS), we have measured the absorption and index of refraction of a conducting polypyrrole film from low frequencies to 2.5 THz. From these measurements, the dc conductivity of 215/( \Omega cm) and the complex conductance were obtained over this frequency range. All of the results were well fit by Drude theory, which gives a carrier scattering time of only 12.6 fs, less than 1/10 that of the semiconductors, thereby illustrating the disorder and low mobility of the polymer.

The evolution of the density of states (DOS) and conductivity as function of well controlled doping levels in OC_1C_10-poly(p-phenylene vinylene) [OC_1C_10-PPV] doped by FeCl_3 and PF_6, and PF_6 doped polypyrrole (PPy-PF_6 have been investigated. At a doping level as high as 0.2 holes per monomer, the former one remains non-metallic, while the latter crosses the metal-insulator transition. In both systems a similar almost linear increase in DOS as function of charges per unit volume c* has been observed from the electrochemical gated transistor data. In PPy-PF_6, when compared to doped OC_1C_10-PPV, the energy states filled at low doping are closer to the vacuum level; by the higher c* at high doping more energy states are available, which apparently enables the conduction to change to metallic. Although both systems on the insulating side show log(sigma) proportional to T^-1/4 as in variable range hopping, for highly doped PPy-PF_6 the usual interpretation of the hopping parameters leads to seemingly too high values for the density of states., 4 pages (incl. 6 figures) in Phys. Rev. B

10596 Background: Ifosfamide is commonly used to treat bone and soft tissue sarcomas (STS) and its efficacy appears to increase with doses >9g/m2/cycle. Due to the toxicity associated with bolus do...