The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
Amir Yacoby - One of the best experts on this subject based on the ideXlab platform.
-
Broken-Symmetry States in Doubly Gated Suspended Bilayer Graphene
Science (New York N.Y.), 2010Co-Authors: Ralf Thomas Weitz, Monica Allen, Benjamin E. Feldman, Jens Martin, Amir YacobyAbstract:The single-particle energy spectra of graphene and its bilayer counterpart exhibit multiple degeneracies that arise through inherent symmetries. Interactions among charge carriers should spontaneously break these symmetries and lead to ordered states that exhibit energy gaps. In the quantum Hall regime, these states are predicted to be ferromagnetic in nature, whereby the system becomes spin polarized, layer polarized, or both. The parabolic dispersion of bilayer graphene makes it susceptible to interaction-induced Symmetry breaking even at zero magnetic field. We investigated the underlying order of the various Broken-Symmetry states in bilayer graphene suspended between top and bottom gate electrodes. We deduced the order parameter of the various quantum Hall ferromagnetic states by controllably breaking the spin and sublattice symmetries. At small carrier density, we identified three distinct Broken-Symmetry states, one of which is consistent with either spontaneously Broken time-reversal Symmetry or spontaneously Broken rotational Symmetry.
-
Broken Symmetry states and divergent resistance in suspended bilayer graphene
Nature Physics, 2009Co-Authors: Benjamin E. Feldman, Jens Martin, Amir YacobyAbstract:The presence of disorder makes it difficult to determine the intrinsic properties of graphene in its ideal form. Measurements of high-quality bilayer graphene flakes suspended above a substrate identify the persistence of quantum Hall behaviour at magnetic fields an order of magnitude lower than seen before, and previously unseen Symmetry breaking of the lowest Landau level is also observed. Mono- and bilayer graphene have generated tremendous excitement owing to their unique and potentially useful electronic properties1. Suspending single-layer graphene flakes above the substrate2,3 has been shown to greatly improve sample quality, yielding high-mobility devices with little charge inhomogeneity. Here we report the fabrication of suspended bilayer graphene devices with very little disorder. We observe quantum Hall states that are fully quantized at a magnetic field of 0.2 T, as well as Broken-Symmetry states at intermediate filling factors ν=0, ±1, ±2 and ±3. In the ν=0 state, the devices show extremely high magnetoresistance that scales as magnetic field divided by temperature. This resistance is predominantly affected by the perpendicular component of the applied field, and the extracted energy gap is significantly larger than expected for Zeeman splitting. These findings indicate that the Broken-Symmetry states arise from many-body interactions and underscore the important part that Coulomb interactions play in bilayer graphene.
François Englert - One of the best experts on this subject based on the ideXlab platform.
-
Broken Symmetry and Yang–Mills Theory
Asia Pacific Physics Newsletter, 2014Co-Authors: François EnglertAbstract:From its inception in statistical physics to its role in the construction and in the development of the asymmetric Yang–Mills phase in quantum field theory, the notion of spontaneous Broken Symmetry permeates contemporary physics. This is reviewed with particular emphasis on the conceptual issues.
-
Spontaneous Broken Symmetry
Comptes Rendus Physique, 2007Co-Authors: Robert Brout, François EnglertAbstract:The concept of spontaneous Broken Symmetry is reviewed in the presence of global symmetries both in matter and particle physics. This concept is then taken over to confront local symmetries in relativistic field theory. Emphasis is placed on the basic concepts where, in the former case, the vacuum of spontaneous Broken Symmetry is degenerate whereas that of local (or gauge) Symmetry is gauge invariant. To cite this article: R. Brout, F. Englert, C. R. Physique 8 (2007). © 2007 Academie des sciences.
-
Broken Symmetry and Yang-Mills theory
50 Years of Yang-Mills Theory, 2005Co-Authors: François EnglertAbstract:From its inception in statistical physics to its role in the construction and in the development of the asymmetric Yang-Mills phase in quantum field theory, the notion of spontaneous Broken Symmetry permeates contemporary physics. This is reviewed with particular emphasis on the conceptual issues.
Wolfgang Lubitz - One of the best experts on this subject based on the ideXlab platform.
-
Dimanganese catalase—spectroscopic parameters from Broken-Symmetry density functional theory of the superoxidized Mn^III/Mn^IV state
JBIC Journal of Biological Inorganic Chemistry, 2005Co-Authors: Sebastian Sinnecker, Frank Neese, Wolfgang LubitzAbstract:Broken-Symmetry density functional theory was used to study the catalytic center of manganese catalase in the superoxidized Mn^III/Mn^IV state. Heisenberg exchange coupling constants, ^55Mn and ^14N hyperfine coupling constants (hfcs) and nuclear quadrupole splittings, as well as the electronic g tensors were evaluated for different model systems of the active site after complete geometry optimizations in the high-spin and Broken-Symmetry states. A comparison of the experimental data with the spectroscopic parameters computed for the models with unprotonated and protonated μ -oxo bridges shows best agreement between theory and experiment for a Mn_2( μ -O)_2( μ -OAc) core. The calculated Mn–Mn distances and ^55Mn hfcs clearly support a dimanganese cluster with unprotonated μ -oxo bridges in the superoxidized state. Furthermore, it is shown that an interchange of the Mn^III and Mn^IV oxidation states in this trapped valence system leads to specific changes in the molecular and electronic structure of the manganese clusters.
-
calculating the electron paramagnetic resonance parameters of exchange coupled transition metal complexes using Broken Symmetry density functional theory application to a mniii mniv model compound
Journal of the American Chemical Society, 2004Co-Authors: Sebastian Sinnecker, Frank T Neese, Louis Noodleman, Wolfgang LubitzAbstract:The capability of the density functional Broken Symmetry approach for the calculation of various EPR parameters of exchange coupled metal clusters is demonstrated by studying the experimentally well-investigated [MnIIIMnIV(μ-O)2(μ-OAc)DTNE]2+ complex. Geometry optimizations of the complex in its Broken Symmetry and high spin states yielded structures with two distinct manganese sites and geometrical parameters in good agreement with the X-ray structure. Exchange coupling constants were calculated from the energy differences between the high spin and Broken Symmetry states using the Heisenberg spin Hamiltonian. Very good agreement between theory and experiment was achieved with the B3LYP hybrid functional. The g-tensor calculations were performed employing the coupled perturbed Kohn−Sham equations. A strategy for the computation of g-tensor site values is presented and provides single-site g-tensors that are in good agreement with the expectations for MnIII and MnIV, respectively. Spin projection gave the ...
Zhigang Jiang - One of the best experts on this subject based on the ideXlab platform.
-
Landau quantization in tilted Weyl semimetals with Broken Symmetry
Journal of Applied Physics, 2021Co-Authors: Luojia Zhang, Yuxuan Jiang, Dmitry Smirnov, Zhigang JiangAbstract:Broken Symmetry and tilting effects are ubiquitous in Weyl semimetals (WSMs). Therefore, it is crucial to understand their impacts on the materials’ electronic and optical properties. Here, using a realistic four-band model for WSMs, which incorporates both the Symmetry breaking and tilting effects, we study its Landau quantization and the associated magneto-absorption spectrum. We show that the Landau bands in tilted WSMs can be obtained by considering a non-tilt Hamiltonian through Lorentz boost. However, Broken Symmetry effects can generate an additional term in the Hamiltonian, which equivalently lead to band reconstruction. Our work provides a more realistic view of the magnetic field response of WSMs that shall be taken into account in relevant future device applications.
Allan H. Macdonald - One of the best experts on this subject based on the ideXlab platform.
-
Gapped Broken Symmetry states in ABC-stacked trilayer graphene
Physical Review B, 2013Co-Authors: Jeil Jung, Allan H. MacdonaldAbstract:We use a self-consistent Hartree-Fock approximation with realistic Coulomb interactions for $\ensuremath{\pi}$-band electrons to explore the possibility of Broken Symmetry states in weakly disordered ABC-stacked trilayer graphene. The competition between gapped and gapless Broken Symmetry states and normal states is studied by comparing total energies. We find that gapped states are favored and that, unlike the bilayer case, gapless nematic Broken Symmetry states are not metastable. Among the gapped states, the layer antiferromagnetic state is favored over anomalous and spin Hall states.
-
Broken-Symmetry states in quantum Hall superlattices
Physical Review B, 2002Co-Authors: Charles B. Hanna, J. C. Díaz-vélez, Allan H. MacdonaldAbstract:We argue that Broken-Symmetry states with either spatially diagonal or spatially off-diagonal order are likely in the quantum Hall regime, for clean multiple-quantum-well (MQW) systems with small layer separations. We find that for MQW systems, unlike bilayers, charge order tends to be favored over spontaneous interlayer coherence. We estimate the size of the interlayer-tunneling amplitude needed to stabilize superlattice Bloch minibands by comparing the variational energies of interlayer-coherent superlattice miniband states with those of states with charge order and states with no Broken symmetries. We predict that when coherent miniband ground states are stable, strong interlayer electronic correlations will strongly enhance the growth-direction tunneling conductance and promote the possibility of Bloch oscillations.
