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JournalISSN: 0034-6861

Reviews of Modern Physics

About: Reviews of Modern Physics is an academic journal. The journal publishes majorly in the area(s): Scattering & Superconductivity. It has an ISSN identifier of 0034-6861. Over the lifetime, 3166 publication(s) have been published receiving 1035226 citation(s).

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Topics: Scattering, Superconductivity, Electron ...read more
Papers
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Open accessJournal ArticleDOI: 10.1103/REVMODPHYS.81.109
Abstract: This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.

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Topics: Graphene nanoribbons (67%), Silicene (64%), Graphene (64%) ...read more

18,972 Citations


Open accessJournal ArticleDOI: 10.1103/REVMODPHYS.74.47
Abstract: The emergence of order in natural systems is a constant source of inspiration for both physical and biological sciences. While the spatial order characterizing for example the crystals has been the basis of many advances in contemporary physics, most complex systems in nature do not offer such high degree of order. Many of these systems form complex networks whose nodes are the elements of the system and edges represent the interactions between them. Traditionally complex networks have been described by the random graph theory founded in 1959 by Paul Erdohs and Alfred Renyi. One of the defining features of random graphs is that they are statistically homogeneous, and their degree distribution (characterizing the spread in the number of edges starting from a node) is a Poisson distribution. In contrast, recent empirical studies, including the work of our group, indicate that the topology of real networks is much richer than that of random graphs. In particular, the degree distribution of real networks is a power-law, indicating a heterogeneous topology in which the majority of the nodes have a small degree, but there is a significant fraction of highly connected nodes that play an important role in the connectivity of the network. The scale-free topology of real networks has very important consequences on their functioning. For example, we have discovered that scale-free networks are extremely resilient to the random disruption of their nodes. On the other hand, the selective removal of the nodes with highest degree induces a rapid breakdown of the network to isolated subparts that cannot communicate with each other. The non-trivial scaling of the degree distribution of real networks is also an indication of their assembly and evolution. Indeed, our modeling studies have shown us that there are general principles governing the evolution of networks. Most networks start from a small seed and grow by the addition of new nodes which attach to the nodes already in the system. This process obeys preferential attachment: the new nodes are more likely to connect to nodes with already high degree. We have proposed a simple model based on these two principles wich was able to reproduce the power-law degree distribution of real networks. Perhaps even more importantly, this model paved the way to a new paradigm of network modeling, trying to capture the evolution of networks, not just their static topology.

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Topics: Degree distribution (73%), Evolving networks (70%), Hierarchical network model (68%) ...read more

17,463 Citations


Open accessJournal ArticleDOI: 10.1103/REVMODPHYS.82.3045
M. Z. Hasan1, Charles L. Kane2Institutions (2)
Abstract: Topological insulators are electronic materials that have a bulk band gap like an ordinary insulator but have protected conducting states on their edge or surface. These states are possible due to the combination of spin-orbit interactions and time-reversal symmetry. The two-dimensional (2D) topological insulator is a quantum spin Hall insulator, which is a close cousin of the integer quantum Hall state. A three-dimensional (3D) topological insulator supports novel spin-polarized 2D Dirac fermions on its surface. In this Colloquium the theoretical foundation for topological insulators and superconductors is reviewed and recent experiments are described in which the signatures of topological insulators have been observed. Transport experiments on $\mathrm{Hg}\mathrm{Te}∕\mathrm{Cd}\mathrm{Te}$ quantum wells are described that demonstrate the existence of the edge states predicted for the quantum spin Hall insulator. Experiments on ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}$, ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$, and ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ are then discussed that establish these materials as 3D topological insulators and directly probe the topology of their surface states. Exotic states are described that can occur at the surface of a 3D topological insulator due to an induced energy gap. A magnetic gap leads to a novel quantum Hall state that gives rise to a topological magnetoelectric effect. A superconducting energy gap leads to a state that supports Majorana fermions and may provide a new venue for realizing proposals for topological quantum computation. Prospects for observing these exotic states are also discussed, as well as other potential device applications of topological insulators.

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  • FIG. 2. Color online The interface between a quantum Hall state and an insulator has chiral edge mode. a The skipping cyclotron orbits. b The electronic structure of a semi-infinite strip described by the Haldane model. A single edge state connects the valence band to the conduction band.
    FIG. 2. Color online The interface between a quantum Hall state and an insulator has chiral edge mode. a The skipping cyclotron orbits. b The electronic structure of a semi-infinite strip described by the Haldane model. A single edge state connects the valence band to the conduction band.
  • FIG. 5. Color online Edge states in the quantum spin Hall insulator QSHI . a The interface between a QSHI and an ordinary insulator. b The edge state dispersion in the graphene model in which up and down spins propagate in opposite directions.
    FIG. 5. Color online Edge states in the quantum spin Hall insulator QSHI . a The interface between a QSHI and an ordinary insulator. b The edge state dispersion in the graphene model in which up and down spins propagate in opposite directions.
  • FIG. 10. Color online Topological spin textures: Spin resolved photoemission directly probes the nontrivial spin textures of the topological insulator surface. a A schematic of spin-ARPES measurement setup that was used to measure the spin distribution on the 111 surface Fermi surface of Bi0.91Sb0.09. b Spin orientations on the surface create a vortexlike pattern around point. A net Berry phase is extracted from the full Fermi-surface data. c Net polarizations along x, y, and z directions are shown. Pz 0 suggests that spins lie mostly within the surface plane. Adapted from Hsieh, Xia, Wray, Qian, et al., 2009a, 2009b and Hsieh et al., 2010.
    FIG. 10. Color online Topological spin textures: Spin resolved photoemission directly probes the nontrivial spin textures of the topological insulator surface. a A schematic of spin-ARPES measurement setup that was used to measure the spin distribution on the 111 surface Fermi surface of Bi0.91Sb0.09. b Spin orientations on the surface create a vortexlike pattern around point. A net Berry phase is extracted from the full Fermi-surface data. c Net polarizations along x, y, and z directions are shown. Pz 0 suggests that spins lie mostly within the surface plane. Adapted from Hsieh, Xia, Wray, Qian, et al., 2009a, 2009b and Hsieh et al., 2010.
  • FIG. 9. Color online Topological surface states in Bi1−xSbx: a ARPES data on the 111 surface of Bi0.9Sb0.1 which probes the occupied surface states as a function of momentum on the line connecting the T invariant points ̄ and M̄ in the surface Brillouin zone. Only the surface bands cross the Fermi energy five times. This, along with further detailed ARPES results Hsieh et al., 2008 , establishes that the semiconducting alloy Bi1−xSbx is a strong topological insulator in the 1;111 class. b A schematic of the 3D Brillouin zone and its 111 surface projection. c The resistivity of semimetallic pure Bi contrasted with the semiconducting alloy. Adapted from Hsieh et al., 2008.
    FIG. 9. Color online Topological surface states in Bi1−xSbx: a ARPES data on the 111 surface of Bi0.9Sb0.1 which probes the occupied surface states as a function of momentum on the line connecting the T invariant points ̄ and M̄ in the surface Brillouin zone. Only the surface bands cross the Fermi energy five times. This, along with further detailed ARPES results Hsieh et al., 2008 , establishes that the semiconducting alloy Bi1−xSbx is a strong topological insulator in the 1;111 class. b A schematic of the 3D Brillouin zone and its 111 surface projection. c The resistivity of semimetallic pure Bi contrasted with the semiconducting alloy. Adapted from Hsieh et al., 2008.
  • FIG. 20. Color online Majorana fermions on topological insulators. a A superconducting vortex or antidot with flux h /2e on a topological insulator is associated with a Majorana zero mode. b A superconducting trijunction on a topological insulator. Majorana modes at the junction can be controlled by adjusting the phases 1,2,3. 1D chiral Majorana modes exist at a superconductor-magnet interface on a topological insulator. c A 1D chiral Dirac mode on a magnetic domain wall that splits into two chiral Majorana modes around a superconducting island. When =h /2e interference of the Majorana modes converts an electron into a hole. d Majorana modes at a superconductor-magnet junction on a 2D QSHI.
    FIG. 20. Color online Majorana fermions on topological insulators. a A superconducting vortex or antidot with flux h /2e on a topological insulator is associated with a Majorana zero mode. b A superconducting trijunction on a topological insulator. Majorana modes at the junction can be controlled by adjusting the phases 1,2,3. 1D chiral Majorana modes exist at a superconductor-magnet interface on a topological insulator. c A 1D chiral Dirac mode on a magnetic domain wall that splits into two chiral Majorana modes around a superconducting island. When =h /2e interference of the Majorana modes converts an electron into a hole. d Majorana modes at a superconductor-magnet junction on a 2D QSHI.
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12,967 Citations


Open accessJournal ArticleDOI: 10.1103/REVMODPHYS.83.1057
Xiao-Liang Qi1, Shou-Cheng Zhang2Institutions (2)
Abstract: Topological insulators are new states of quantum matter which cannot be adiabatically connected to conventional insulators and semiconductors. They are characterized by a full insulating gap in the bulk and gapless edge or surface states which are protected by time-reversal symmetry. These topological materials have been theoretically predicted and experimentally observed in a variety of systems, including HgTe quantum wells, BiSb alloys, and Bi2Te3 and Bi2Se3 crystals. Theoretical models, materials properties, and experimental results on two-dimensional and three-dimensional topological insulators are reviewed, and both the topological band theory and the topological field theory are discussed. Topological superconductors have a full pairing gap in the bulk and gapless surface states consisting of Majorana fermions. The theory of topological superconductors is reviewed, in close analogy to the theory of topological insulators.

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9,145 Citations


Open accessJournal ArticleDOI: 10.1103/REVMODPHYS.76.323
Abstract: Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

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  • FIG. 4. (Color in online edition) Pedagogical illustration of the concept of electrical spin injection from a ferromagnet (F) into a normal metal (N). Electrons flow from F to N: (a) schematic device geometry; (b) magnetization M as a function of position—nonequilibrium magnetization dM (spin accumulation) is injected into a normal metal; (c) contribution of different spin-resolved densities of states to both charge and spin transport across the F/N interface. Unequal filled levels in the density of states depict spin-resolved electrochemical potentials different from the equilibrium value m0 .
    FIG. 4. (Color in online edition) Pedagogical illustration of the concept of electrical spin injection from a ferromagnet (F) into a normal metal (N). Electrons flow from F to N: (a) schematic device geometry; (b) magnetization M as a function of position—nonequilibrium magnetization dM (spin accumulation) is injected into a normal metal; (c) contribution of different spin-resolved densities of states to both charge and spin transport across the F/N interface. Unequal filled levels in the density of states depict spin-resolved electrochemical potentials different from the equilibrium value m0 .
  • FIG. 7. (Color in online edition) Spatial variation of the electrochemical potentials near a spin-selective resistive interface at an F/N junction. At the interface x50 both the spinresolved electrochemical potentials (ml , l5↑ ,↓ , denoted with solid lines) and the average electrochemical potential (mF , mN , dashed lines) are discontinuous. The spin diffusion lengths LsF and LsN characterize the decay of ms5m↑2m↓ (or equivalently the decay of spin accumulation and the nonequilibrium magnetization) away from the interface and into the bulk F and N regions, respectively.
    FIG. 7. (Color in online edition) Spatial variation of the electrochemical potentials near a spin-selective resistive interface at an F/N junction. At the interface x50 both the spinresolved electrochemical potentials (ml , l5↑ ,↓ , denoted with solid lines) and the average electrochemical potential (mF , mN , dashed lines) are discontinuous. The spin diffusion lengths LsF and LsN characterize the decay of ms5m↑2m↓ (or equivalently the decay of spin accumulation and the nonequilibrium magnetization) away from the interface and into the bulk F and N regions, respectively.
  • FIG. 31. (Color in online edition) Giant magnetoresistance (GMR) effect in magnetic diodes. Current/spin-splitting characteristics (I2z) are calculated self-consistently at V50.8 V for the diode from Fig. 30. Spin splitting 2qz on the p side is normalized to kBT . The solid curve corresponds to a switchedoff spin source. The current is symmetric in z. With spin source on (the extreme case of 100% spin polarization injected into the n region is shown), the current is a strongly asymmetric function of z, displaying large GMR, shown by the dashed curve. Materials parameters of GaAs were applied. Adapted from Žutić et al., 2002.
    FIG. 31. (Color in online edition) Giant magnetoresistance (GMR) effect in magnetic diodes. Current/spin-splitting characteristics (I2z) are calculated self-consistently at V50.8 V for the diode from Fig. 30. Spin splitting 2qz on the p side is normalized to kBT . The solid curve corresponds to a switchedoff spin source. The current is symmetric in z. With spin source on (the extreme case of 100% spin polarization injected into the n region is shown), the current is a strongly asymmetric function of z, displaying large GMR, shown by the dashed curve. Materials parameters of GaAs were applied. Adapted from Žutić et al., 2002.
  • FIG. 16. Measured and calculated ts in Al. The low-T measurements are the conduction-electron spin resonance (Lubzens and Schultz, 1976b) and spin injection (Johnson and Silsbee, 1985). Only the phonon contribution is shown, as adapted from Johnson and Silsbee (1985). The solid line is the first-principles calculation, not a fit to the data (Fabian and Das Sarma, 1998). The data at T5293 K are results from room-temperature spin injection experiments of Jedema et al. (2002a, 2003). Adapted from Fabian and Das Sarma, 1999b.
    FIG. 16. Measured and calculated ts in Al. The low-T measurements are the conduction-electron spin resonance (Lubzens and Schultz, 1976b) and spin injection (Johnson and Silsbee, 1985). Only the phonon contribution is shown, as adapted from Johnson and Silsbee (1985). The solid line is the first-principles calculation, not a fit to the data (Fabian and Das Sarma, 1998). The data at T5293 K are results from room-temperature spin injection experiments of Jedema et al. (2002a, 2003). Adapted from Fabian and Das Sarma, 1999b.
  • FIG. 27. (Color in online edition) Electric-field control of ferromagnetism. RHall vs field curves under three different gate biases. Application of VG50, 1125, and 2125 V results in a qualitatively different field dependence of RHall measured at 22.5 K (sample B): almost horizontal dash-dotted line, paramagnetic response when holes are partially depleted from the channel (VG51125 V); dashed lines, clear hysteresis at low fields (,0.7 mT) as holes are accumulated in the channel (VG52125 V); solid line, RHall curve measured at VG50 V before application of 6125 V; dotted line, RHall curve after application of 6125 V. Inset, the same curves shown at higher magnetic fields. From Ohno, Chiba, et al., 2000.
    FIG. 27. (Color in online edition) Electric-field control of ferromagnetism. RHall vs field curves under three different gate biases. Application of VG50, 1125, and 2125 V results in a qualitatively different field dependence of RHall measured at 22.5 K (sample B): almost horizontal dash-dotted line, paramagnetic response when holes are partially depleted from the channel (VG51125 V); dashed lines, clear hysteresis at low fields (,0.7 mT) as holes are accumulated in the channel (VG52125 V); solid line, RHall curve measured at VG50 V before application of 6125 V; dotted line, RHall curve after application of 6125 V. Inset, the same curves shown at higher magnetic fields. From Ohno, Chiba, et al., 2000.
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Topics: Spin engineering (75%), Spin polarization (70%), Spin Hall effect (67%) ...read more

8,325 Citations


Performance
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No. of papers from the Journal in previous years
YearPapers
202130
202033
201940
201841
201741
201648

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