| 1. |
- Abergel, David, et al.
(författare)
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Infrared absorption of closely aligned heterostructures of monolayer and bilayer graphene with hexagonal boron nitride
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : AMER PHYSICAL SOC. - 1098-0121 .- 1550-235X. ; 92:11
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Tidskriftsartikel (refereegranskat)abstract
- We model optical absorption of monolayer and bilayer graphene on hexagonal boron nitride for the case of closely aligned crystal lattices. We show that perturbations with different spatial symmetry can lead to similar absorption spectra. We suggest that a study of the absorption spectra as a function of the doping for an almost completely full first miniband is necessary to extract meaningful information about the moire characteristics from optical absorption measurements and to distinguish between various theoretical proposals for the physically realistic interaction. Also, for bilayer graphene, the ability to compare spectra for the opposite signs of electric-field-induced interlayer asymmetry might provide additional information about the moire parameters.
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| 2. |
- Ahmed, T., et al.
(författare)
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G W quasiparticle calculations with spin-orbit coupling for the light actinides
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:3, s. 035104-
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Tidskriftsartikel (refereegranskat)abstract
- We report on the importance of GW self-energy corrections for the electronic structure of light actinides in the weak-to-intermediate coupling regime. Our study is based on calculations of the band structure and total density of states of Np, U, and Pu using a one-shot GW approximation that includes spin-orbit coupling within a full potential LAPW framework. We also present RPA screened effective Coulomb interactions for the f-electron orbitals for different lattice constants, and show that there is an increased contribution from electron-electron correlation in these systems for expanded lattices. We find a significant amount of electronic correlation in these highly localized electronic systems.
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| 3. |
- B. Arnardottir, Kristin, et al.
(författare)
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Hall effect for indirect excitons in an inhomogeneous magnetic field
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:24
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Tidskriftsartikel (refereegranskat)abstract
- We study the effect of an inhomogeneous out-of-plane magnetic field on the behavior of two-dimensional (2D) spatially indirect excitons. Due to the difference of the magnetic field acting on electrons and holes, the total Lorentz force affecting the center of mass motion of an indirect exciton appears. Consequently, an indirect exciton acquires an effective charge proportional to the gradient of the magnetic field. The appearance of the Lorentz force causes the Hall effect for neutral bosons, which can be detected by measurement of the spatially inhomogeneous blueshift of the photoluminescence using a counterflow experiment.
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| 4. |
- B. Arnardottir, Kristin, et al.
(författare)
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One-dimensional Van Hove polaritons
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:12
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Tidskriftsartikel (refereegranskat)abstract
- We study the light-matter coupling of microcavity photons and an interband transition in a one-dimensional (1D) nanowire. Due to the Van Hove singularity in the density of states, resulting in a resonant character of the absorption line, the achievement of strong coupling becomes possible even without the formation of a bound state of an electron and a hole. The calculated absorption in the system and corresponding energy spectrum reveal anticrossing behavior characteristic of the formation of polariton modes. In contrast to the case of conventional exciton polaritons, the formation of 1D Van Hove polaritons will not be restricted to low temperatures and can be realized in any system with a singularity in the density of states.
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| 5. |
- Balakrishna, S. G., et al.
(författare)
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Preferential sliding directions on graphite
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:24, s. 245440-
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Tidskriftsartikel (refereegranskat)abstract
- The anisotropy of friction on graphitic surfaces is investigated by a combined friction force microscopy and modeling study. Friction vectors deviate up to 15 degrees from pulling directions. The strongest deviations are found for pulling directions which lie almost along one zigzag direction of the honeycomb structure, the preferred sliding direction on graphite surfaces and epitaxial graphene grown on SiC(0001). Atomic stick-slip events along and across molecular rows determine direction and magnitude of friction. Simulation and modeling reveal the role of temperature and of the two-dimensional character of the surface potential for the friction anisotropy.
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| 6. |
- Baym, Gordon, et al.
(författare)
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Transport in ultradilute solutions of He-3 in superfluid He-4
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:2
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Tidskriftsartikel (refereegranskat)abstract
- We calculate the effect of a heat current on transporting He-3 dissolved in superfluid He-4 at ultralow concentration, as will be utilized in a proposed experimental search for the electric dipole moment of the neutron (nEDM). In this experiment, a phonon wind will be generated to drive (partly depolarized) 3He down a long pipe. In the regime of 3He concentrations less than or similar to 10(-9) and temperatures similar to 0.5 K, the phonons comprising the heat current are kept in a flowing local equilibrium by small angle phonon-phonon scattering, while they transfer momentum to the walls via the He-4 first viscosity. On the other hand, the phonon wind drives the 3He out of local equilibrium via phonon-He-3 scattering. For temperatures below 0.5 K, both the phonon and He-3 mean free paths can reach the centimeter scale, and we calculate the effects on the transport coefficients. We derive the relevant transport coefficients, the phonon thermal conductivity, and the He-3 diffusion constants from the Boltzmann equation. We calculate the effect of scattering from the walls of the pipe and show that it may be characterized by the average distance from points inside the pipe to the walls. The temporal evolution of the spatial distribution of the He-3 atoms is determined by the time dependent He-3 diffusion equation, which describes the competition between advection by the phonon wind and He-3 diffusion. As a consequence of the thermal diffusivity being small compared with the He-3 diffusivity, the scale height of the final He-3 distribution is much smaller than that of the temperature gradient. We present exact solutions of the time dependent temperature and He-3 distributions in terms of a complete set of normal modes.
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| 7. |
- Baym, Gordon, et al.
(författare)
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Transport in very dilute solutions of He-3 in superfluid He-4
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:1, s. 014512-
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by a proposed experimental search for the electric dipole moment of the neutron (nEDM) utilizing neutron-He-3 capture in a dilute solution of He-3 in superfluid He-4, we derive the transport properties of dilute solutions in the regime where the He-3 are classically distributed and rapid He-3-He-3 scatterings keep the He-3 in equilibrium. Our microscopic framework takes into account phonon-phonon, phonon-He-3, and He-3-He-3 scatterings. We then apply these calculations to measurements by Rosenbaum et al. [J. Low Temp. Phys. 16, 131 (1974)] and by Lamoreaux et al. [Europhys. Lett. 58, 718 (2002)] of dilute solutions in the presence of a heat flow. We find satisfactory agreement of theory with the data, serving to confirm our understanding of the microscopics of the helium in the future nEDM experiment.
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| 8. |
- Bergholtz, E. J., et al.
(författare)
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Pfaffian quantum Hall state made simple : Multiple vacua and domain walls on a thin torus
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:8, s. 081308-
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the Moore-Read Pfaffian state on a thin torus. The known sixfold degeneracy is realized by two inequivalent crystalline states with a four- and twofold degeneracy, respectively. The fundamental quasihole and quasiparticle excitations are domain walls between these vacua, and simple counting arguments give a Hilbert space of dimension 2n−1 for 2n−k holes and k particles at fixed positions and assign each a charge ±e∕4. This generalizes the known properties of the hole excitations in the Pfaffian state as deduced using conformal field theory techniques. Numerical calculations using a model Hamiltonian and a small number of particles support the presence of a stable phase with degenerate vacua and quarter-charged domain walls also away from the thin-torus limit. A spin-chain Hamiltonian encodes the degenerate vacua and the various domain walls.
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| 9. |
- Björnson, Kristofer, et al.
(författare)
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Spin-polarized edge currents and Majorana fermions in one- and two-dimensional topological superconductors
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 92:21
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the persistent currents, spin-polarized local density of states, and spectral functions of topological superconductors constructed by placing ferromagnetic impurities on top of an s-wave superconductor with Rashba spin-orbit interaction. We solve self-consistently for the superconducting order parameter and investigate both two-dimensional blocks and one-dimensional wires of ferromagnetic impurities, with the magnetic moments pointing both perpendicular and parallel to the surface. We find that the topologically protected edge states of ferromagnetic blocks give rise to spin-polarized edge currents, but that the total persistent current flows in opposite direction to what is expected from the dispersion relation of the edge states. We also show that the Majorana fermions at the end points of one-dimensional wires are spin polarized, which can be directly related to the spin polarization of the edge currents of two-dimensional blocks. Connections are also made to the physics of the Yu-Shiba-Rusinov states for zero-dimensional impurities.
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| 10. |
- Black-Schaffer, Annica M., et al.
(författare)
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Odd-frequency superconducting pairing in multiband superconductors
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:10, s. 104514-
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Tidskriftsartikel (refereegranskat)abstract
- We point out that essentially all multiband superconductors have an odd-frequency pairing component, as follows from a general symmetry analysis of even- and odd-frequency pairing states. We show that odd-frequency superconducting pairing requires only a finite band hybridization, or scattering, and nonidentical intraband order parameters, of which only one band needs to be superconducting. Under these conditions odd-frequency odd-interband pairing is always present. From a symmetry analysis we establish a complete reciprocity between parity in band index and frequency.
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