Latest Papers in Condensed Matter Physics

Mesoscale And Nanoscale Physics

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Accelerating, guiding, and compressing skyrmions by defect rails (1808.09689v2)

Josep Castell-Queralt, Leonardo G. González-Gómez, Nuria Del-Valle, Alvaro Sanchez, Carles Navau

2018-08-29

Magnetic skyrmions are promising candidates as information carriers in spintronic devices. The transport of individual skyrmions in a fast and controlled way is a key issue in this field. Here we introduce a novel platform for accelerating, guiding and compressing skyrmions along predefined paths. The guiding mechanism is based on two parallel defect-lines (rails), one attractive and the other repulsive. Numerical simulations, using parameters from state-of-the-art experiments, show that the speed of the skyrmions along the rails is increased up to a factor of ten with respect to the non-defect case whereas the distance between rails can be as small as the initial radius of the skyrmions. In this way, the flux of information that can be coded and transported with magnetic skyrmions could be significantly increased.

Nonlinear optics in the electron-hole continuum in 2D semiconductors: two-photon transition, second harmonic generation and valley current injection (1903.05588v1)

Pu Gong, Hongyi Yu, Yong Wang, Wang Yao

2019-03-13

We investigate two-photon transitions to the electron-hole scattering continuum in monolayer transition-metal dichalcogenides, and identify two contributions to this nonlinear optical process with opposite circularly polarized valley selection rules. In the non-interacting limit, the competition between the two contributions leads to a crossover of the selection rule with the increase of the two-photon energy. With the strong Coulomb interaction between the electron and hole, the two contributions excite electron-hole scattering states in orthogonal angular momentum channels, while the strength of the transition can be substantially enhanced by the interaction. Based on this picture of the two-photon transition, the second harmonic generation (SHG) in the electron-hole continuum is analyzed, where the Coulomb interaction is shown to greatly alter the relative strength of different cross-circular polarized SHG processes. Valley current injection by the quantum interference of one-photon and two-photon transition is also investigated in the presence of the strong Coulomb interaction, which significantly enhances the injection rate.

Diamagnetism of metallic nanoparticles as the result of strong spin-orbit interaction (1903.05584v1)

B. Murzaliev, M. Titov, M. I. Katsnelson

2019-03-13

The magnetic susceptibility of an ensemble of clean metallic nanoparticles is shown to change from paramagnetic to diamagnetic one with the onset of spin-orbit interaction. The effect is quantified on the basis of symmetry analysis with the help of the random matrix theory. In particular, the magnetic susceptibility is investigated as the function of symmetry breaking parameter representing magnetic flux in the crossover from symplectic to unitary and from orthogonal to unitary ensembles. Corresponding analytical and numerical results provide a qualitative explanation to the experimental data on diamagnetism of an ensemble of gold nanorods.

Observation of weakened V-V dimers in the monoclinic metallic phase of strained VO2 (1903.05576v1)

J. Laverock, V. Jovic, A. A. Zakharov, Y. R. Niu, S. Kittiwatanakul, B. Westhenry, J. W. Lu, S. A. Wolf, K. E. Smith

2019-03-13

Emergent order at mesoscopic length scales in condensed matter can provide fundamental insight into the underlying competing interactions and their relationship with the order parameter. Using spectromicroscopy, we show that mesoscopic stripe order near the metal-insulator transition (MIT) of strained VO2 represent periodic modulations in both crystal symmetry and V-V dimerization. Above the MIT, we unexpectedly find the long range order of V-V dimer strength and crystal symmetry become dissociated beyond ~ 200 nm, whereas the conductivity transition proceeds homogeneously in a narrow temperature range.

Optical orientation with linearly polarized light in transition metal dichalcogenides (1811.04003v2)

G. Catarina, J. Have, J. Fernández-Rossier, N. M. R. Peres

2018-11-09

We study the optical properties of semiconducting transition metal dichalcogenide monolayers under the influence of strong out-of-plane magnetic fields, using the effective massive Dirac model. We pay attention to the role of spin-orbit coupling effects, doping level and electron-electron interactions, treated at the Hartree-Fock level. We find that optically-induced valley and spin imbalance, commonly attained with circularly polarized light, can also be obtained with linearly polarized light in the doped regime. Additionally, we explore an exchange-driven mechanism to enhance the spin-orbit splitting of the conduction band, in n-doped systems, controlling both the carrier density and the intensity of the applied magnetic field.

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