Electronic Phase Diagram Research Articles

Ni doping effect and phase diagram of Ni-doped [formula omitted

Transport properties of Ni-doped BaFe2-xNixAs2 single crystals have been investigated and the electronic phase diagram is derived. Tc reaches 20K at the optimal doping level x=0.10. There is a small doping range around x=0.055 where superconductivity and spin-density wave order coexist. The Hall coefficient shows a strong temperature dependence at the optimal doping level, suggesting non-Fermi liquid behavior.

Phase diagram of thePrFeAsO1−xFxsuperconductor

The electronic phase diagram of PrFeAsO$_{1-x}$F$_{x}$ (0$\leq$x$\leq$0.225) has been determined using synchrotron X-ray powder diffraction, magnetization and resistivity measurements. The structural transition temperature is suppressed from 154 K to $\approx$120 K and the magnetic phase transitions of both iron and praseodymium ions are completely suppressed by x$\approx$0.08 fluorine doping, coinciding with the emergence of superconductivity. The optimal doping is x$\approx$0.15 when T$_{C}$=47 K, while the maximum solubility of fluorine in PrFeAsO$_{1-x}$F$_{x}$ is reached around x=0.22. The structural, magnetic and superconducting phase diagram is presented.

Electronic phase diagram of the layered cobalt oxide systemLixCoO2(0.0≤x≤1.0)

Here we report the magnetic properties of the layered cobalt oxide system, ${\text{Li}}_{x}{\text{CoO}}_{2}$, in the whole range of Li composition, $0\ensuremath{\le}x\ensuremath{\le}1$. Based on dc-magnetic-susceptibility data, combined with results of $^{59}\text{Co}$ nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) observations, the electronic phase diagram of ${\text{Li}}_{x}{\text{CoO}}_{2}$ has been established. As in the related material ${\text{Na}}_{x}{\text{CoO}}_{2}$, a magnetic critical point is found to exist between $x=0.35$ and 0.40, which separates the Pauli-paramagnetic and Curie-Weiss metals. In the Pauli-paramagnetic regime $(x\ensuremath{\le}0.35)$, the antiferromagnetic spin correlations systematically increase with decreasing $x$. Nevertheless, ${\text{CoO}}_{2}$, the $x=0$ end member is a noncorrelated metal in the whole temperature range studied. In the Curie-Weiss regime $(x\ensuremath{\ge}0.40)$, on the other hand, various phase transitions are observed. For $x=0.40$, a susceptibility hump is seen at 30 K, suggesting the onset of static antiferromagnetic order. A magnetic jump, which is likely to be triggered by charge ordering, is clearly observed at ${T}_{\text{t}}\ensuremath{\approx}175\text{ }\text{K}$ in samples with $x=0.50$ $(=1/2)$ and 0.67 $(=2/3)$, while only a tiny kink appears at $T\ensuremath{\approx}210\text{ }\text{K}$ in the sample with an intermediate Li composition, $x=0.60$. Thus, the phase diagram of the ${\text{Li}}_{x}{\text{CoO}}_{2}$ system is complex and the electronic properties are sensitively influenced by the Li content $(x)$.

Cracking Mechanism of Laser Cladding Rapid Manufacturing 316L Stainless Steel

Laser cladding rapid manufacturing technology is a kind of new developed advanced manufacturing technology integrating the advantages of rapid prototyping manufacturing and laser cladding surface modification. Due to the complex thermo-physical and metallurgical factors in the deposition process, the cladding layer is liable to crack, which seriously impedes the industrial application of this technology. Experiments of laser cladding rapid manufacturing 316L stainless steel were carried out. The cracking behavior and phenomena has been observed, cracking mechanism of 316L stainless steel was investigated by means of microstructure characterization and phase analysis with optical microscopy (OM), X-Ray diffraction (XRD), scan electronic microscopy (SEM) and phase diagram analysis. Factors influencing the cracking susceptibility has also been studied. Results show that the cracks of 316L stainless steel were hot solidification cracks caused by the high residual stress and separating of the liquid films among dendrites. Through the optimization of process parameters, adding protective atmosphere, etc. cracking sensitivity has been effectively reduced and crack free 316L stainless steel components have been obtained.

New correlated electron physics from new materials

Many important advances in the physics of strongly correlated electron systems have been driven by the development of new materials: for instance the filled skutterudites MT4X12 (M=alkali metal, alkaline earth, lanthanide, or actinide; T=Fe, Ru, or Os; X=P, As, or Sb), certain lanthanide and actinide intermetallic compounds such as URu2-xRexSi2 and CeTIn5 (T=Co, Rh, or Ir), and layered oxypnictides and related materials. These types of complex multinary d- and f-electron compounds have proven to be a vast reservoir of novel strongly correlated electron ground states and phenomena. In these materials, the occurrence of such a wide range of ground states and phenomena arises from a delicate interplay between competing interactions that can be tuned by partial or complete substitution of one element for another, as well as the application of pressure, and magnetic fields, resulting in rich and complex electronic phase diagrams in the hyperspace of temperature, chemical composition, pressure and magnetic field. It seems clear that this type of “materials driven physics” will continue to play a central role in the development of the field of strongly correlated electron systems in the future, through the discovery of new materials that exhibit unexpected phenomena and experiments on known materials in an effort to optimize their physical properties and test relevant theories.

Duration dependences of electric and crystal structures of bi layer hydrated NaxCoO2·yH2O

Abstract We succeeded in synthesizing the bi layer hydrated superconducting Na x CoO 2 · y H 2 O powder samples with different T c 's by systematically changing the duration in a high humidity atmosphere after intercalation of water molecules. From the results of 59Co nuclear quadrupole resonance measurements, it was found that resonance frequency ν Q monotonically decreased with increasing the duration after filtration. The electronic states of samples were found being well characterized by the ν Q , and we succeeded in drawing the electronic phase diagram in which there exist two superconducting phases and an in-between magnetic phase. On the other hand, a lattice parameter along c-axis was found to decrease monotonically with increasing the time duration. This result indicates that shrinkage of CoO 2 planes is caused by changes of arrangements and/or contents of ions between CoO 2 planes which evolve during kept in a high humidity atmosphere.

Insulator to correlated metal transition inV1−xMoxO2

Although many materials display the transition from insulating to metallic behavior on doping, only a few, such as VO2, have the right combination of crystal structure and physical properties to serve as model systems. Here we report the electronic and structural characteristics of the insulator to metal transition in V1?xMoxO2, which we have studied over the range 0.0?x?0.50 through characterization of the electrical resistivity, magnetic susceptibility, specific heat, and average- and short-range crystal structures. We find that metal-metal pairing exists in small domains in the doped metallic phases and an unexpected phenomenology for the crossover between a Curie-Weiss insulating regime and an intermediate mass metallic regime. An electronic phase diagram is presented.

Electronic and magnetic phase diagram of β-Fe1.01Se with superconductivity at 36.7 K under pressure

The discovery of new high-temperature superconductors based on FeAs has led to a new 'gold rush' in high-T(C) superconductivity. All of the new superconductors share the same common structural motif of FeAs layers and reach T(C) values up to 55 K (ref. 2). Recently, superconductivity has been reported in FeSe (ref. 3), which has the same iron pnictide layer structure, but without separating layers. Here, we report the magnetic and electronic phase diagram of beta-Fe(1.01)Se as a function of temperature and pressure. The superconducting transition temperature increases from 8.5 to 36.7 K under an applied pressure of 8.9 GPa. It then decreases at higher pressures. A marked change in volume is observed at the same time as T(C) rises, owing to a collapse of the separation between the Fe(2)Se(2) layers. No static magnetic ordering is observed for the whole p-T phase diagram. We also report that at higher pressures (starting around 7 GPa and completed at 38 GPa), Fe(1.01)Se transforms to a hexagonal NiAs-type structure and exhibits non-magnetic behaviour.

Phase diagram of electron–hole systems: Interplay between exciton Mott transition and quantum pair condensation

Quasi-thermal-equilibrium states of electron–hole (e–h) systems in photoexcited insulators are studied from a theoretical viewpoint, stressing the exciton Bose–Einstein condensation (BEC), the e–h BCS-type pair-condensed state, and the exciton Mott transition between an insulating exciton/biexciton gas phase and a metallic e–h plasma phase. We determine the quasi-equilibrium phase diagram of the e–h system at zero and finite temperatures with applying the dynamical mean-field theory (DMFT) to the e–h Hubbard model with both repulsive and attractive on-site interactions. Effects of inter-site interactions on the exciton Mott transition are also clarified with applying the extended DMFT to the extended e–h Hubbard model.

WDX-Analysis of the New Superconductors RO1−x F x FeAs and Its Consequences on the Electronic Phase Diagram

WDX-Analysis of the New Superconductors RO1−x F x FeAs and Its Consequences on the Electronic Phase Diagram

Scenario for fractional quantum Hall effect in bulk isotropic materials

We investigate the possibility of a strongly correlated Fractional Quantum Hall (FQH) state in bulk three dimensional isotropic (not layered) materials. We find that a FQH state can exist at low densities only if it is accompanied by a staging transition in which the electrons re-organize themselves in layers, perpendicular to the magnetic field, at distances of order the magnetic length apart. The Hartree energy associated to the staging transition is off-set by the correlation Fock energy of the 3D FQH state. We obtain the phase diagram of bulk electrons in a magnetic field subject to Coulomb interactions as a function of carrier density and lattice constant. At very low densities, the 3D FQH state exhibits a transition to a 3D Wigner crystal state stabilized by phonon correlations.

Coverage-dependent faceting of Au chains on Si(557)

The structural and electronic phase diagrams of Au on Si(557) are established using scanning tunneling microscopy (STM) and angle-resolved photoemission. Five phases consisting of altogether seven facets are observed in the submonolayer regime. With increasing Au coverage one observes $\text{Si}(111)7\ifmmode\times\else\texttimes\fi{}7+\text{Si}(112)$, Si(557)-Au, $\text{Si}(111)5\ifmmode\times\else\texttimes\fi{}2\text{-Au}+\text{Si}(335)\text{-Au}$, $\text{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\text{-Au}+\text{Si}(335)\text{-Au}$, and $\text{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\text{-Au}+\text{Si}(5 5 11)\text{-Au}$. The relative surface areas of the five phases and seven facets are determined accurately by depositing a Au wedge ranging from 0 to 0.7 monolayer and performing automatic pattern recognition on large-scale STM images. Angle-resolved photoemission spectra are decomposed into contributions from the five phases. The Fermi wave vectors and the band filling of various facets are identified. Using Si(557)-Au as reference we find a coverage of three Au chains per unit cell for the frequently studied $\text{Si}(111)5\ifmmode\times\else\texttimes\fi{}2\text{-Au}$ surface (instead of the widely used value of two Au chains). Likewise a coverage of two Au chains per unit cell is found for Si(553)-Au (instead of one Au chain), in agreement with x-ray diffraction. A structural model with three Au rows per unit cell is developed for $\text{Si}(111)5\ifmmode\times\else\texttimes\fi{}2\text{-Au}$ using density-functional-theory calculations.

The peculiar physical properties and phase diagram of BaFe2- xCoxAs2 single crystals

In this paper, we systematically study the transport, susceptibility and heat capacity of single crystals of BaFe2−xCoxAs2. In the underdoped region, spin density wave (SDW) transition was observed in both resistivity and susceptibility. The magnetic susceptibility shows unusual T-linear dependence above the SDW transition up to 700 K. With Co doping, SDW ordering is gradually suppressed and superconductivity emerges with a dome-like shape. The electrical transport, specific heat and magnetic susceptibility indicate that the SDW and superconductivity coexist in the BaFe2−xCoxAs2 sample around x=0.17, similar to the case of (Ba,K)Fe2As2. The superconductivity completely disappears for samples with x>0.34. A crossover from the SDW state to the Fermi-liquid state is observed with an increase in Co doping. A detailed electronic phase diagram of the evolution from the SDW to the superconducting state is given.

Charge Transport in Interpenetrating Networks of Semiconducting and Metallic Carbon Nanotubes

Carbon nanotube network field effect transistors (CNTN-FETs) are promising candidates for low cost macroelectronics. We investigate the microscopic transport in these devices using electric force microscopy and simulations. We find that in many CNTN-FETs the voltage drops abruptly at a point in the channel where the current is constricted to just one tube. We also model the effect of varying the semiconducting/metallic tube ratio. The effect of Schottky barriers on both conductance within semiconducting tubes and conductance between semiconducting and metallic tubes results in three possible types of CNTN-FETs with fundamentally different gating mechanisms. We describe this with an electronic phase diagram.

The electronic phase diagram of the LaO1−xFxFeAs superconductor

The competition of magnetic order and superconductivity is a key element in the physics of all unconventional superconductors, for example in high-transition-temperature cuprates, heavy fermions and organic superconductors. Here superconductivity is often found close to a quantum critical point where long-range antiferromagnetic order is gradually suppressed as a function of a control parameter, for example charge-carrier doping or pressure. It is believed that dynamic spin fluctuations associated with this quantum critical behaviour are crucial for the mechanism of superconductivity. Recently, high-temperature superconductivity has been discovered in iron pnictides, providing a new class of unconventional superconductors. Similar to other unconventional superconductors, the parent compounds of the pnictides show a magnetic ground state and superconductivity is induced on charge-carrier doping. In this Letter the structural and electronic phase diagram is investigated by means of X-ray scattering, muon spin relaxation and Mössbauer spectroscopy on the series LaO(1-x)F(x)FeAs. We find a discontinuous first-order-like change of the Néel temperature, the superconducting transition temperature and the respective order parameters. Our results strongly question the relevance of quantum critical behaviour in iron pnictides and prove a strong coupling of the structural orthorhombic distortion and the magnetic order both disappearing at the phase boundary to the superconducting state.

Spin Susceptibility, Phase Diagram, and Quantum Criticality in the Eelctron-Doped High Tc Superconductor Ba(Fe1-xCox)2As2

We report a systematic investigation of Ba(Fe 1- x Co x ) 2 As 2 based on transport and 75 As NMR measurements, and establish the electronic phase diagram. We demonstrate that doping progressively suppresses the uniform spin susceptibility and low frequency spin fluctuations. The optimum superconducting phase emerges at x c ≃0.08 when the tendency toward spin ordering completely diminishes. Our findings point toward the presence of a quantum critical point near x c between the SDW (spin density wave) and superconducting phases.

Exploration of Novel Electronic and Magnetic Phase Diagrams in Transition Metal Oxides by Heat Capacity Measurements

Exploration of Novel Electronic and Magnetic Phase Diagrams in Transition Metal Oxides by Heat Capacity Measurements

Muon-spin-relaxation studies of magnetic order and superfluid density in antiferromagnetic NdFeAsO,BaFe2As2, and superconductingBa1−xKxFe2As2

Recently, high-transition-temperature (high-T(c)) superconductivity was discovered in the iron pnictide RFeAsO(1-x)F(x) (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO(1-x)F(x) as the system is tuned from a semimetal to a high-T(c) superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x D 0 : 10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x > 0.06, resulting in an electronic phase diagram remarkably similar to that of the high-T(c) copper oxides. Comparison of the structural evolution of CeFeAsO(1-x)F(x) with other Fe-based superconductors suggests that the structural perfection of the Fe-As tetrahedron is important for the high-T(c) superconductivity in these Fe pnictides.

Structural and magnetic phase diagram of CeFeAsO1− xFx and its relation to high-temperature superconductivity

Recently, high-transition-temperature (high-Tc) superconductivity was discovered in the iron pnictide RFeAsO(1-x)F(x) (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO(1-x)F(x) as the system is tuned from a semimetal to a high-Tc superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x=0.10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x>0.06, resulting in an electronic phase diagram remarkably similar to that of the high-Tc copper oxides. Comparison of the structural evolution of CeFeAsO(1-x)F(x) with other Fe-based superconductors suggests that the structural perfection of the Fe-As tetrahedron is important for the high-Tc superconductivity in these Fe pnictides.

Tuning the charge density wave and superconductivity inCuxTaS2

We report the characterization of layered 2H-type CuxTaS2 for 0?x?0.12. The charge density wave (CDW), at 70 K for TaS2, is destabilized with Cu doping. The sub-1 K superconducting transition in undoped 2H-TaS2 jumps quickly to 2.5 K at low x, increases to 4.5 K at the optimal composition Cu0.04TaS2, and then decreases at higher x. The electronic contribution to the specific heat, first increasing and then decreasing as a function of Cu content, is 12 mJ mol?1 K?2 at Cu0.04TaS2. Electron-diffraction studies show that the CDW remains present at the optimal superconducting composition but with both a changed q vector and decreased coherence length. We present an electronic phase diagram for the system.