Yang Liu

Bio: Yang Liu is an academic researcher from Pennsylvania State University. The author has contributed to research in topics: Dielectric & Electroactive polymers. The author has an hindex of 30, co-authored 106 publications receiving 3574 citations.

Superconductivity close to magnetic instability in Fe ( Se 1 − x Te x ) 0.82

Abstract: We report our study of the evolution of superconductivity and the phase diagram of the ternary $\text{Fe}{({\text{Se}}_{1\ensuremath{-}x}{\text{Te}}_{x})}_{0.82}$ $(0\ensuremath{\le}x\ensuremath{\le}1.0)$ system. We discovered a superconducting phase with ${T}_{c,\text{max}}=14\text{ }\text{K}$ in the $0.3lxl1.0$ range. This superconducting phase is suppressed when the sample composition approaches the end member ${\text{FeTe}}_{0.82}$, which exhibits an incommensurate antiferromagnetic order. We discuss the relationship between the superconductivity and magnetism of this material system in terms of recent results from neutron-scattering measurements. Our results and analyses suggest that superconductivity in this class of Fe-based compounds is associated with magnetic fluctuations and therefore may be unconventional in nature.

High-Temperature Dielectric Materials for Electrical Energy Storage

Abstract: The demand for high-temperature dielectric materials arises from numerous emerging applications such as electric vehicles, wind generators, solar converters, aerospace power conditioning, and downhole oil and gas explorations, in which the power systems and electronic devices have to operate at elevated temperatures. This article presents an overview of recent progress in the field of nanostructured dielectric materials targeted for high-temperature capacitive energy storage applications. Polymers, polymer nanocomposites, and bulk ceramics and thin films are the focus of the materials reviewed. Both commercial products and the latest research results are covered. While general design considerations are briefly discussed, emphasis is placed on material specifications oriented toward the intended high-temperature applications, such as dielectric properties, temperature stability, energy density, and charge-discharge efficiency. The advantages and shortcomings of the existing dielectric materials are identif...

High-Energy-Density Dielectric Polymer Nanocomposites with Trilayered Architecture

Abstract: The development of advanced dielectric materials with high electric energy densities is of crucial importance in modern electronics and electric power systems. Here, a new class of multilayer-structured polymer nanocomposites with high energy and power densities is presented. The outer layers of the trilayered structure are composed of boron nitride nanosheets dispersed in poly(vinylidene fluoride) (PVDF) matrix to provide high breakdown strength, while PVDF with barium strontium titanate nanowires forms the central layer to offer high dielectric constant of the resulting composites. The influence of the filler contents on the electrical polarization, breakdown strength, and energy density is examined. Simulations are carried out to model the electrical tree formation in the layered nanocomposites and to verify the experimental breakdown results. The trilayered polymer nanocomposite with an optimized filler content displays a discharged energy density of 20.5 J cm−3 at Weibull breakdown strength of 588 MV m−1, which is among the highest discharged energy densities reported so far. Moreover, the nanocomposite exhibits a superior power density of 0.91 MW cm−3, more than nine times that of the commercially available biaxially oriented polypropylene. The findings of this research provide a new design paradigm for high-performance dielectric polymer nanocomposites.

Charge-carrier localization induced by excess Fe in the superconductor Fe 1 + y Te 1 − x Se x

Abstract: We have investigated the effect of Fe nonstoichiometry on properties of the ${\text{Fe}}_{1+y}(\text{Te},\text{Se})$ superconductor system by means of resistivity, Hall coefficient, magnetic susceptibility, and specific-heat measurements. We find that the excess Fe at interstitial sites of the (Te, Se) layers not only suppresses superconductivity but also results in a weakly localized electronic state. We argue that these effects originate from the magnetic coupling between the excess Fe and the adjacent Fe square-planar sheets, which favors a short-range magnetic order.

Dielectric polymers for high-temperature capacitive energy storage.

Abstract: Polymers are the preferred materials for dielectrics in high-energy-density capacitors. The electrification of transport and growing demand for advanced electronics require polymer dielectrics capable of operating efficiently at high temperatures. In this review, we critically analyze the most recent development in the dielectric polymers for high-temperature capacitive energy storage applications. While general design considerations are discussed, emphasis is placed on the elucidation of the structural dependence of the high-field dielectric and electrical properties and the capacitive performance, including discharged energy density, charge-discharge efficiency and cyclability, of dielectric polymers at high temperatures. Advantages and limitations of current approaches to high-temperature dielectric polymers are summarized. Challenges along with future research opportunities are highlighted at the end of this article.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Non-Abelian Anyons and Topological Quantum Computation

Abstract: Topological quantum computation has emerged as one of the most exciting approaches to constructing a fault-tolerant quantum computer. The proposal relies on the existence of topological states of matter whose quasiparticle excitations are neither bosons nor fermions, but are particles known as non-Abelian anyons, meaning that they obey non-Abelian braiding statistics. Quantum information is stored in states with multiple quasiparticles, which have a topological degeneracy. The unitary gate operations that are necessary for quantum computation are carried out by braiding quasiparticles and then measuring the multiquasiparticle states. The fault tolerance of a topological quantum computer arises from the nonlocal encoding of the quasiparticle states, which makes them immune to errors caused by local perturbations. To date, the only such topological states thought to have been found in nature are fractional quantum Hall states, most prominently the $\ensuremath{ u}=5∕2$ state, although several other prospective candidates have been proposed in systems as disparate as ultracold atoms in optical lattices and thin-film superconductors. In this review article, current research in this field is described, focusing on the general theoretical concepts of non-Abelian statistics as it relates to topological quantum computation, on understanding non-Abelian quantum Hall states, on proposed experiments to detect non-Abelian anyons, and on proposed architectures for a topological quantum computer. Both the mathematical underpinnings of topological quantum computation and the physics of the subject are addressed, using the $\ensuremath{ u}=5∕2$ fractional quantum Hall state as the archetype of a non-Abelian topological state enabling fault-tolerant quantum computation.

Ultracapacitors: Why, How, and Where is the Technology

Abstract: The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

New directions in the pursuit of Majorana fermions in solid state systems.

Abstract: The 1937 theoretical discovery of Majorana fermions-whose defining property is that they are their own anti-particles-has since impacted diverse problems ranging from neutrino physics and dark matter searches to the fractional quantum Hall effect and superconductivity. Despite this long history the unambiguous observation of Majorana fermions nevertheless remains an outstanding goal. This review paper highlights recent advances in the condensed matter search for Majorana that have led many in the field to believe that this quest may soon bear fruit. We begin by introducing in some detail exotic 'topological' one- and two-dimensional superconductors that support Majorana fermions at their boundaries and at vortices. We then turn to one of the key insights that arose during the past few years; namely, that it is possible to 'engineer' such exotic superconductors in the laboratory by forming appropriate heterostructures with ordinary s-wave superconductors. Numerous proposals of this type are discussed, based on diverse materials such as topological insulators, conventional semiconductors, ferromagnetic metals and many others. The all-important question of how one experimentally detects Majorana fermions in these setups is then addressed. We focus on three classes of measurements that provide smoking-gun Majorana signatures: tunneling, Josephson effects and interferometry. Finally, we discuss the most remarkable properties of condensed matter Majorana fermions-the non-Abelian exchange statistics that they generate and their associated potential for quantum computation.

Carbon Nanotubes: Synthesis, Integration, and Properties

Abstract: Synthesis of carbon nanotubes by chemical vapor deposition over patterned catalyst arrays leads to nanotubes grown from specific sites on surfaces. The growth directions of the nanotubes can be controlled by van der Waals self-assembly forces and applied electric fields. The patterned growth approach is feasible with discrete catalytic nanoparticles and scalable on large wafers for massive arrays of novel nanowires. Controlled synthesis of nanotubes opens up exciting opportunities in nanoscience and nanotechnology, including electrical, mechanical, and electromechanical properties and devices, chemical functionalization, surface chemistry and photochemistry, molecular sensors, and interfacing with soft biological systems.