Topic
Spin-½
About: Spin-½ is a research topic. Over the lifetime, 40423 publications have been published within this topic receiving 796639 citations.
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TL;DR: Ozawa et al. as discussed by the authors constructed a minimal effective spin model composed of the bilinear and biquadratic interactions with particular wave numbers dictated by the Fermi surface.
Abstract: Noncollinear and noncoplanar magnetic textures including Skyrmions and vortices act as emergent electromagnetic fields and give rise to novel electronic and transport properties. We here report a unified understanding of noncoplanar magnetic orderings emergent from the spin-charge coupling in itinerant magnets. The mechanism has its roots in effective multiple spin interactions beyond the conventional Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism, which are ubiquitously generated in itinerant electron systems with local magnetic moments. By carefully examining the higher-order perturbations in terms of the spin-charge coupling, we construct a minimal effective spin model composed of the bilinear and biquadratic interactions with particular wave numbers dictated by the Fermi surface. Taking two-dimensional systems as examples, we find that our effective model captures the underlying physics of the instability toward noncoplanar multiple-$Q$ states discovered recently: a single-$Q$ helical state expected from the RKKY theory is replaced by a double-$Q$ vortex crystal with chirality density waves even for an infinitely small spin-charge coupling on generic lattices [R. Ozawa et al., J. Phys. Soc. Jpn. 85, 103703 (2016)], and a triple-$Q$ Skyrmion crystal with a high topological number of two appears while increasing the spin-charge coupling on a triangular lattice [R. Ozawa, S. Hayami, and Y. Motome, Phys. Rev. Lett. 118, 147205 (2017)]. We find that by introducing an external magnetic field, our effective model exhibits a plethora of multiple-$Q$ states. Our effective model will serve as a guide for exploring further exotic magnetic orderings in itinerant magnets, not only in two dimensions but also in three dimensions.
160 citations
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TL;DR: In this article, the charge, valley, and spin transports in a normal/ferromagnetic/normal silicene junction were investigated, and it was shown that the charge and spin conductances in this junction oscillate with the length of the ferromagnetic silicenes.
Abstract: We investigate charge, valley, and spin transports in a normal/ferromagnetic/normal silicene junction. We show that the charge, valley, and spin conductances in this junction oscillate with the length of the ferromagnetic silicene. It is also found that the current through this junction is valley and spin polarized due to the coupling between valley and spin degrees of freedom, and the valley and spin polarizations can be tuned by local application of a gate voltage. In particular, we find a fully valley and spin polarized current by applying the electric field. We also obtain the condition for observing the fully valley and spin polarized current.
160 citations
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29 Jun 2012
TL;DR: The Bottom-Up Approach Introductory concepts: Why Electrons Flow The Elastic Resistor The New Ohm's Law Where is the Resistance? Transverse Modes Drude Formula Kubo Formula How Realistic is an Elastic Resonistor? Semiclassical & Quantum Transport: The Nanotransistor Semiclassesical Transport and the SCF Method Resistance and Uncertainty Quantum Transport, Schrodinger to NEGF Resonant Tunneling and Anderson Localization Coulomb Blockade and Mott Transition Spin Blockade Hall Effect / QHE Beyond Voltages and Currents: Ther
Abstract: The Bottom-Up Approach Introductory Concepts: Why Electrons Flow The Elastic Resistor The New Ohm's Law Where is the Resistance? Transverse Modes Drude Formula Kubo Formula How Realistic is an Elastic Resistor? Semiclassical & Quantum Transport: The Nanotransistor Semiclassical Transport and the SCF Method Resistance and Uncertainty Quantum Transport: Schrodinger to NEGF Resonant Tunneling and Anderson Localization Coulomb Blockade and Mott Transition Spin Blockade Hall Effect / QHE Beyond Voltages and Currents: Thermoelectricity Heat Flow Spin Flow Spin Transistor Entropy Flow And Maxwell's Demon Epilogue: Physics in a Grain of Sand Solutions to Exercises Additional Problems.
160 citations
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TL;DR: This work uses a solid-state quantum register realized in a nitrogen-vacancy defect in diamond to compute the bond dissociation curve of the minimal basis helium hydride cation, HeH(+), with an energy uncertainty of 10(-14) hartree, which is 10 orders of magnitude below the desired chemical precision.
Abstract: Ab initio computation of molecular properties is one of the most promising applications of quantum computing. While this problem is widely believed to be intractable for classical computers, efficient quantum algorithms exist which have the potential to vastly accelerate research throughput in fields ranging from material science to drug discovery. Using a solid-state quantum register realized in a nitrogen-vacancy (NV) defect in diamond, we compute the bond dissociation curve of the minimal basis helium hydride cation, HeH+. Moreover, we report an energy uncertainty (given our model basis) of the order of 10–14 hartree, which is 10 orders of magnitude below the desired chemical precision. As NV centers in diamond provide a robust and straightforward platform for quantum information processing, our work provides an important step toward a fully scalable solid-state implementation of a quantum chemistry simulator.
160 citations
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TL;DR: In this article, the exact diagonalization method applied to the extended Hubbard model with interaction parameters was used to handle the competing interactions among Wannier orbitals owing to their significant overlap, which is a crucial but overlooked aspect of the magic-angle twisted bilayer graphene.
Abstract: We investigate correlated insulating states in magic-angle twisted bilayer graphene (TBG) by the exact diagonalization method applied to the extended Hubbard model with interaction parameters recently evaluated in the realistic effective model. Our model can handle the competing interactions among Wannier orbitals owing to their significant overlap, which is a crucial but overlooked aspect of the magic-angle TBG. We propose two candidates for the correlated insulating states: spin- and valley-ferromagnetic band insulator and the Dirac semimetallic state for two flavors with peculiar renormalization, where a flavor denotes a combined degree of freedom with spin and valley. One of the important consequences for the latter candidate is that it allows van Hove singularity near half-filling of the whole band structure (i.e., near the Dirac points) to play some role in superconductivity. The consistency between the two flavor degrees of freedom for the Dirac semimetallic state and the twofold degeneracy of the Landau level observed in the experiment is also noteworthy.
160 citations