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Condens. Matter, Volume 2, Issue 1 (March 2017)

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Editorial

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Open AccessEditorial Acknowledgement to Reviewers of Condensed Matter in 2016
Condens. Matter 2017, 2(1), 5; doi:10.3390/condmat2010005
Received: 11 January 2017 / Revised: 11 January 2017 / Accepted: 11 January 2017 / Published: 11 January 2017
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Research

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Open AccessArticle Discovery of BiS2-Based Superconductor and Material Design Concept
Condens. Matter 2017, 2(1), 6; doi:10.3390/condmat2010006
Received: 25 November 2016 / Accepted: 26 January 2017 / Published: 31 January 2017
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Abstract
In 2012, we discovered new layered superconductors whose superconducting states emerge in the BiS2 layers. Since their crystal structure, composed of alternate stacks of BiS2 conduction layers and electrically insulating (blocking) layers, is similar to those of cuprate and Fe-based superconductors, many researchers
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In 2012, we discovered new layered superconductors whose superconducting states emerge in the BiS2 layers. Since their crystal structure, composed of alternate stacks of BiS2 conduction layers and electrically insulating (blocking) layers, is similar to those of cuprate and Fe-based superconductors, many researchers have explored new BiS2-based superconductors and have studied the physical and chemical properties of the BiS2-based superconductors. In this paper, we present the histories of the discovery of the first BiS2-based superconductor, Bi4O4S3, and the second one, LaO1−xFxBiS2. The structural variation of the BiS2-based superconductor family is briefly introduced. Then, we show the material design concept for the emergence of bulk superconductivity in BiS2-based compounds. At the end, a possible strategy for the enhancement of the transition temperature in the BiS2-based superconductors is proposed. Full article
(This article belongs to the Special Issue Layered Superconductors)
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Open AccessArticle Effects of Domain Boundaries on the Diffraction Patterns of One-Dimensional Structures
Condens. Matter 2017, 2(1), 7; doi:10.3390/condmat2010007
Received: 10 November 2016 / Revised: 17 January 2017 / Accepted: 18 January 2017 / Published: 31 January 2017
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Abstract
Motivated by diffraction experiments on the (2√3 x √3) R30◦ reconstructed Si(111) surface due to deposition of rare earth elements (Dy, Tb) and silicide formation, we analyse the splitting and non-splitting of superstructure diffraction spots. For this purpose, we model diffraction patterns for
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Motivated by diffraction experiments on the (2√3 x √3) R30◦ reconstructed Si(111) surface due to deposition of rare earth elements (Dy, Tb) and silicide formation, we analyse the splitting and non-splitting of superstructure diffraction spots. For this purpose, we model diffraction patterns for one-dimensional structures generated by the binary surface technique and use supercell models to keep the analysis simple. Diffraction patterns are calculated in the framework of the kinematical diffraction theory, and they are analyzed as a function of the domains and domain boundaries. Basic properties of the diffraction pattern are analyzed for model systems of a two-fold and a three-fold periodicity. The rules derived from these calculations are applied to the “real-world” system of Si(111)-(2√3 × √3) R30◦-RESix (RE = Dy or Tb). Depending on the combination of domains and domain boundaries of different types, a plethora of different features are observed in the diffraction patterns. These are analyzed to determine the sizes of both domain boundaries and domains from experimentally observed splitting of specific superstructure spots. Full article
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Open AccessArticle Experimental Study of Particle Interactions in Moderate to Dense Granular Shear Flows of Disks
Condens. Matter 2017, 2(1), 2; doi:10.3390/condmat2010002
Received: 14 September 2016 / Revised: 10 December 2016 / Accepted: 21 December 2016 / Published: 28 December 2016
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Abstract
To find the status of multiple collisions in transitional granular flow, moderate to densely packed monosized plastic disks were sheared in experimental 2D shear flow apparatus by applying shear strain rate in the range of 14.8 s−1 to 34.6 s−1.
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To find the status of multiple collisions in transitional granular flow, moderate to densely packed monosized plastic disks were sheared in experimental 2D shear flow apparatus by applying shear strain rate in the range of 14.8 s−1 to 34.6 s−1. Application of high speed video camera and subsequent image processing techniques precisely measure the spatial positions of the particles involved in making the flow. Collision detection and contact duration finding algorithms were formulated to detect inter particle collision in each time step. The proportion of binary and multiple collisions was quantified in each time step. It is found that the contribution of multi particle collision is 13% for the lowest normalized solid fraction ( ν * = 0.50) and 68% for the highest normalized solid fraction ( ν * = 0.85) under consideration. The inter particle collision time is also found greater than binary collision time in all the flows under consideration. The group size is determined for each time step as an additional length scale associated with multi-particle interactions. Number of groups was made of more than two particles in all the flows under consideration, and the amount of such groups increased on increasing the solid fraction irrespective of the shear rate. In the dense cases (solid fraction > 0.60), rapid increase in the group size and the formation of occasional force chains should be attributed for the change in the stress generation pattern. Full article
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Open AccessArticle Metastability Phenomena in VO2 Thin Films
Condens. Matter 2017, 2(1), 10; doi:10.3390/condmat2010010
Received: 1 December 2016 / Revised: 10 February 2017 / Accepted: 15 February 2017 / Published: 18 February 2017
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Abstract
VO2 is a transition metal oxide in which complex electronic phases appear near the metal-to-insulator transition due to electron correlation and electron–lattice interactions. This system is characterized by a metal-to-insulator transition (MIT) at around 341 K. The metal (high T) phase is
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VO2 is a transition metal oxide in which complex electronic phases appear near the metal-to-insulator transition due to electron correlation and electron–lattice interactions. This system is characterized by a metal-to-insulator transition (MIT) at around 341 K. The metal (high T) phase is tetragonal while the insulator (low T) phase is monoclinic and the resistivity changes at the MIT by about five orders of magnitude. Here, we report investigations of the MIT in a thin VO2 film deposited on a sapphire substrate showing hysteresis. The MIT has been characterized by resistance measurements versus temperature and a DC magnetic field. The thin sample shows different final resistance values in both the insulating and metallic state after different temperature cycles. Moreover, some cycles do not close in the insulating phase. An unexpected magnetic dependence of the temperature cycle in the sample was also observed. The results show that the MIT of VO2 can be controlled by reducing the thickness below 40 nm in micron-sized ribbons since MIT is associated with the emergence of coexisting metastable conformations controlled by the thickness-dependent misfit strain and stress distributions induced by the mismatch between thin ribbon film and the substrate. Full article
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Open AccessArticle Influence of the Lattice Mismatch on the Atomic Ordering of ZnO Grown by Atomic Layer Deposition onto Single Crystal Surfaces with Variable Mismatch (InP, GaAs, GaN, SiC)
Condens. Matter 2017, 2(1), 3; doi:10.3390/condmat2010003
Received: 10 November 2016 / Revised: 12 December 2016 / Accepted: 19 December 2016 / Published: 8 January 2017
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Abstract
It has previously been reported that epitaxial growth of ZnO can be obtained at low temperatures by atomic layer deposition (ALD) onto a GaN (0001-Ga) surface, corresponding to a ~2.3% compressive lattice mismatch of the deposited ZnO. The question addressed here is the
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It has previously been reported that epitaxial growth of ZnO can be obtained at low temperatures by atomic layer deposition (ALD) onto a GaN (0001-Ga) surface, corresponding to a ~2.3% compressive lattice mismatch of the deposited ZnO. The question addressed here is the atomic ordering of deposited ZnO as a function of the lattice mismatch between ZnO and several single-crystal seeding surfaces. We have deposited ZnO using ALD onto either the (111) cubic or (0001) hexagonal surfaces of a set of available single-crystal substrates (GaAs, InP, GaN, SiC), for which the lattice mismatch varies over a wide range of values, positive and negative. It is found that deposition onto surfaces with very high extensive lattice mismatch (GaAs, InP) leads to polycrystalline ZnO, similar to the configuration obtained on an amorphous SiO2 surface. In contrast, ZnO ALD deposition onto both 2H-GaN (0001-Ga) and 4H-SiC (0001-Si) surfaces with lower and compressive mismatch leads to epitaxial ordering over the whole substrate temperature range of 180–250 °C. Full article
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Open AccessArticle Photoluminescence of Rare-Earth Ions in the Nanocrystalline GaAs/SnO2 Heterostructure and the Photoinduced Electrical Properties Related to the Interface
Condens. Matter 2017, 2(1), 9; doi:10.3390/condmat2010009
Received: 31 October 2016 / Revised: 4 January 2017 / Accepted: 24 January 2017 / Published: 7 February 2017
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Abstract
Deposition of an SnO2 thin film was carried out by sol–gel-dip-coating and doped with Ce3+ or Eu3+, and a GaAs layer was deposited by resistive evaporation or sputtering. This investigation combines the emission properties of these rare-earth ions with
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Deposition of an SnO2 thin film was carried out by sol–gel-dip-coating and doped with Ce3+ or Eu3+, and a GaAs layer was deposited by resistive evaporation or sputtering. This investigation combines the emission properties of these rare-earth ions with the unique transport properties generated by the heterostructure assembly. Illumination with light with energy above the GaAs bandgap and below the SnO2 bandgap drastically increases the GaAs/SnO2 heterostructure conductance, which becomes practically temperature-independent. This was associated with the presence of interface conduction, possibly a two-dimensional electron gas at the GaAs/SnO2 interface. This feature takes place only for the sample where the GaAs bottom layer is deposited via sputtering. Irradiation with energies above the SnO2 bandgap only excites the top oxide layer. The heterostructure assembly GaAs/SnO2:Eu leads to emission from Eu3+, unlike SnO2 deposition directly on a glass substrate, where the Eu3+ transitions are absent. Eu emission comes along a broad band, located at a higher energy compared to Eu3+ transitions, which are blue-shifted as the thermal annealing temperature increases. Luminescence from Ce3+ ions in the heterostructure can be detected, but the ions overlap with emission from the matrix, and a cleaning procedure helps to identify Ce3+ transitions. Full article
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Open AccessArticle Facile Design of a Plasmonic Nanolaser
Condens. Matter 2017, 2(1), 8; doi:10.3390/condmat2010008
Received: 10 November 2016 / Revised: 15 January 2017 / Accepted: 27 January 2017 / Published: 4 February 2017
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Abstract
A spaser consists of a plasmonic noble-metal nanostructure that acts as nanocavity, when incorporated or surface-coupled two-level emitters constitute the nanoscale gain medium. Suited two-level emitters are, for instance, laser dyes. Optical pumping may provide efficient excitation energy transfer between the two-level emitters
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A spaser consists of a plasmonic noble-metal nanostructure that acts as nanocavity, when incorporated or surface-coupled two-level emitters constitute the nanoscale gain medium. Suited two-level emitters are, for instance, laser dyes. Optical pumping may provide efficient excitation energy transfer between the two-level emitters in the gain medium and the surface plasmons sustained in the nanocavity. Strong resonant coupling of the surface plasmon modes to the gain medium may establish an inherent feedback amplification mechanism which finally drives the spaser action. In this contribution, we demonstrate that spaser emission can be generated by amplifying longitudinal surface plasmon modes in gold nanorods by optically pumping surface-attached resonantly-coupled laser dyes. Therefore, we synthesized gold nanorods whose longitudinal surface plasmon resonance peak was adjusted between 680 and 700 nm. The gain medium was realized by electrostatically attaching the laser dye phthalocyanine tetrasulfonate via the positively-charged CTAB (cetyltrimethylammonium bromide) bilayer to the gold-nanorod surface. Phthalocyanine tetrasulfonate exhibits fluorescence at 700 nm. Fluorescence quenching experiments unambiguously gave indication of resonant excitation energy transfer. The fluorescence intensity ratio I F 0 / I F follows the Stern–Volmer relationship, and the Stern–Volmer coefficient was determined as KSV = 1.22 × 106 M−1. The spaser emission was observed in fs transient absorption spectra as an ultrafast decaying narrow emission peak around 716 nm. Full article
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Open AccessArticle Tuning the Electronic Structure of Hydrogen-Decorated Silicene
Condens. Matter 2017, 2(1), 1; doi:10.3390/condmat2010001
Received: 9 November 2016 / Revised: 15 December 2016 / Accepted: 19 December 2016 / Published: 23 December 2016
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Abstract
The effects of strain, charge doping, and external electric field on the electronic structure of a free-standing silicene layer decorated by hydrogen atoms are studied by first-principles density functional theory. Various phases, including insulating, metallic, spin-polarized, and half-metallic have been found, depending on
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The effects of strain, charge doping, and external electric field on the electronic structure of a free-standing silicene layer decorated by hydrogen atoms are studied by first-principles density functional theory. Various phases, including insulating, metallic, spin-polarized, and half-metallic have been found, depending on these external factors. The most efficient way of switching the system between these phases is charge doping. The character of the energy gap of the H/silicene system can also be modified, and for charged or for strained systems, the originally indirect gap can be tuned to become direct. The obtained results are very promising in view of the silicene functionalization and potential applications of silicene in the fields of spintronics and optoelectronics. Full article
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Open AccessArticle Unraveling the Peculiarities in the Temperature-Dependent Structural Evolution of Black Phosphorus
Condens. Matter 2017, 2(1), 11; doi:10.3390/condmat2010011
Received: 9 January 2017 / Revised: 10 February 2017 / Accepted: 16 February 2017 / Published: 20 February 2017
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Abstract
Black phosphorous (BP) is one of the important emerging two-dimensional systems. We have undertaken a structural investigation of BP in the temperature range of 320 K to 85 K using synchrotron X-ray diffraction (XRD) studies. The XRD pattern of BP is heavily influenced
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Black phosphorous (BP) is one of the important emerging two-dimensional systems. We have undertaken a structural investigation of BP in the temperature range of 320 K to 85 K using synchrotron X-ray diffraction (XRD) studies. The XRD pattern of BP is heavily influenced by the preferred orientation effects. Collection of the diffraction pattern in a standard capillary geometry with controlled capillary rotations perpendicular to the X-ray direction permitted us to provide insights to the effects of the preferred orientation. In the range of 320 K to 85 K, BP remains in the so-called “A17” orthorhombic structure. Lattice parameters show a regular shrinkage with the lowering of the temperature as expected for any elemental metallic system. Dense temperature sampling permitted us to observe a small but clear deviation from the linear behavior in of one of the in-plane lattice parameters. This temperature-dependent structural evolution seems to provide some insights into the temperature dependence of the macroscopic properties of BP such as the Hall coefficient, thermal conductivity, etc. Full article
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Open AccessArticle Ultrafast Transport Transient in n-Doped ZnS in Wurtzite and Zincblende Phases
Condens. Matter 2017, 2(1), 12; doi:10.3390/condmat2010012
Received: 26 January 2017 / Revised: 25 February 2017 / Accepted: 2 March 2017 / Published: 5 March 2017
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Abstract
In this paper, we analyzed the ultrafast transient transport in n-doped ZnS in wurtzite and zincblende phases, driven far away from equilibrium by an electric field. Through the numerical solution of associate quantum transport equations based on the Non-Equilibrium Statistical Operator Method,
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In this paper, we analyzed the ultrafast transient transport in n-doped ZnS in wurtzite and zincblende phases, driven far away from equilibrium by an electric field. Through the numerical solution of associate quantum transport equations based on the Non-Equilibrium Statistical Operator Method, the time evolution of the electron drift velocity and the non-equilibrium temperature of electrons and phonons were obtained, analyzing the dependence on the electric field strength. Full article
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Review

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Open AccessReview Titanium Pnictide Oxide Superconductors
Condens. Matter 2017, 2(1), 4; doi:10.3390/condmat2010004
Received: 1 December 2016 / Revised: 30 December 2016 / Accepted: 3 January 2017 / Published: 12 January 2017
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Abstract
In 2012, a novel superconductor BaTi2Sb2O was found in the layered titanium pnictide oxides ATi2Pn2O. A related superconductor BaTi2Bi2O was subsequently discovered in 2013. The structure of these materials consists
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In 2012, a novel superconductor BaTi2Sb2O was found in the layered titanium pnictide oxides ATi2Pn2O. A related superconductor BaTi2Bi2O was subsequently discovered in 2013. The structure of these materials consists of alternate stacking of superconducting Ti2Pn2O layers and Ba blocking layers, which is somewhat similar to high-Tc cuprates since the Ti2Pn2O layer contains an anti-CuO2-type Ti2O square lattice. In addition to the structural similarity to the well-known high-Tc superconductors, BaTi2Pn2O shows unique physical properties: two superconducting domes appear in the electronic phase diagram for solid solutions of BaTi2(Sb1‒xBix)2O and a unique density-wave instability which coexists with superconductivity. In this short review, the early studies of titanium pnictide oxides, the discovery of novel superconductors BaTi2Pn2O, and recent progress are summarized. Full article
(This article belongs to the Special Issue Layered Superconductors)
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