1,947 research outputs found
The deformation and elastic anisotropy of a new gyroid-based honeycomb made by laser sintering
© 2020 The Author(s) The stiffness, anisotropy and structural deformation of three gyroid-based lattices was investigated, with particular focus on a newly proposed honeycomb gyroid. This honeycomb is based on a modified triply periodic minimal surface (TPMS) equation with reduced periodicity. Using the numerical homogenisation method, the anisotropy of the gyroid lattice types was found to differ greatly, as was the dependence of this anisotropy on the volume fraction. From compression testing of laser sintered polyamide PA2200 specimens, the honeycomb gyroid was found to possess extremely high anisotropy, with Emax*/Emin*, the ratio of the highest to the lowest direction-dependent modulus, ∼250 at low volume fraction. The stiffness and anisotropy of the honeycomb gyroid are compared to equivalent results from the square honeycomb, the closest analogue in the set of conventional honeycomb types. The honeycomb gyroid lattice exhibited novel deformation and post-yield stiffening under in-plane loading; it underwent reorientation into a second, stiffer geometry following plastic bending and contact of its cell walls. The unique deformation behaviour and extremely high anisotropy of the honeycomb gyroid provide strong motivation for further investigations into this new family of reduced periodicity TPMS-based honeycombs
Temperature dependent correlations in covalent insulators
Motivated by the peculiar behavior of FeSi and FeSb2 we study the effect of
local electronic correlations on magnetic, transport and optical properties in
a specific type of band insulator, namely a covalent insulator. Investigating a
minimum model of covalent insulator within a single-site dynamical mean-field
approximation we are able to obtain the crossover from low temperature
non-magnetic insulator to high-temperature paramagnetic metal with parameters
realistic for FeSi and FeSb2 systems. Our results show that the behavior of
FeSi does not imply microscopic description in terms of Kondo insulator
(periodic Anderson model) as can be often found in the literature, but in fact
reflects generic properties of a broader class of materials.Comment: 4 pages, 4 figure
Theory of Diamagnetism in the Pseudogap Phase: Implications from the Self energy of Angle Resolved Photoemission
In this paper we apply the emerging- consensus understanding of the fermionic
self energy deduced from angle resolved photoemisssion spectroscopy (ARPES)
experiments to deduce the implications for orbital diamagnetism in the
underdoped cuprates. Many theories using many different starting points have
arrived at a broadened BCS-like form for the normal state self energy
associated with a d-wave excitation gap, as is compatible with ARPES data.
Establishing compatibility with the f-sum rules, we show how this self energy,
along with the constraint that there is no Meissner effect in the normal phase
are sufficient to deduce the orbital susceptibility. We conclude, moreover,
that diamagnetism is large for a d-wave pseudogap. Our results should apply
rather widely to many theories of the pseudogap, independent of the microscopic
details.Comment: 15 pages, 8 figure
Large bulk resistivity and surface quantum oscillations in the topological insulator Bi2Te2Se
Topological insulators are predicted to present novel surface transport
phenomena, but their experimental studies have been hindered by a metallic bulk
conduction that overwhelms the surface transport. We show that a new
topological insulator, Bi2Te2Se, presents a high resistivity exceeding 1 Ohm-cm
and a variable-range hopping behavior, and yet presents Shubnikov-de Haas
oscillations coming from the surface Dirac fermions. Furthermore, we have been
able to clarify both the bulk and surface transport channels, establishing a
comprehensive understanding of the transport in this material. Our results
demonstrate that Bi2Te2Se is the best material to date for studying the surface
quantum transport in a topological insulator.Comment: 4 pages, 3 figure
Effect of pressure on the polarized infrared optical response of quasi-one-dimensional LaTiO
The pressure-induced changes in the optical properties of the
quasi-one-dimensional conductor LaTiO were studied by
polarization-dependent mid-infrared micro-spectroscopy at room temperature. For
the polarization of the incident radiation parallel to the conducting
direction, the optical conductivity spectrum shows a pronounced mid-infrared
absorption band, exhibiting a shift to lower frequencies and an increase in
oscillator strength with increasing pressure. On the basis of its pressure
dependence, interpretations of the band in terms of electronic transitions and
polaronic excitations are discussed. Discontinuous changes in the optical
response near 15 GPa are in agreement with a recently reported pressure-induced
structural phase transition and indicate the onset of a dimensional crossover
in this highly anisotropic system.Comment: 7 pages, 7 figure
Proximity Effect in Nb/Au/CoFe Trilayers
We have investigated the superconducting critical temperatures of Nb/Au/CoFe
trilayers as a function of Au and CoFe thicknesses. Without the CoFe layer the
superconducting critical temperatures of Nb/Au bilayers as a function of Au
thickness follow the well-known proximity effect between a superconductor and a
normal metal. The superconducting critical temperatures of Nb/Au/CoFe trilayers
as a function of Au thickness exhibit a rapid initial increase in the small Au
thickness region and increase slowly to a limiting value above this region,
accompanied by a small oscillation of Tc. On the other hand, the
superconducting critical temperatures of Nb/Au/CoFe trilayers as a function of
CoFe thickness show non-monotonic behavior with a shallow dip feature. We
analyzed the Tc behavior in terms of Usadel formalism and found that most
features are consistent with the theory, although the small oscillation of Tc
as a function of the Au thickness cannot be accounted for. We have also found
quantitative values for the two interfaces: Nb/Au and Au/CoFe.Comment: 25 pages, 6 figure
Entanglement of indistinguishable particles in condensed matter physics
The concept of entanglement in systems where the particles are
indistinguishable has been the subject of much recent interest and controversy.
In this paper we study the notion of entanglement of particles introduced by
Wiseman and Vaccaro [Phys. Rev. Lett. 91, 097902 (2003)] in several specific
physical systems, including some that occur in condensed matter physics. The
entanglement of particles is relevant when the identical particles are
itinerant and so not distinguished by their position as in spin models. We show
that entanglement of particles can behave differently to other approaches that
have been used previously, such as entanglement of modes (occupation-number
entanglement) and the entanglement in the two-spin reduced density matrix. We
argue that the entanglement of particles is what could actually be measured in
most experimental scenarios and thus its physical significance is clear. This
suggests entanglement of particles may be useful in connecting theoretical and
experimental studies of entanglement in condensed matter systems.Comment: 13 pages, 6 figures, comments welcome, published version (minor
changes, added references
Skew scattering due to intrinsic spin-orbit coupling in a two-dimensional electron gas
We present the generalization of the two-dimensional quantum scattering
formalism to systems with Rashba spin-orbit coupling. Using symmetry
considerations, we show that the differential scattering cross section depends
on the spin state of the incident electron, and skew scattering may arise even
for central spin-independent scattering potentials. The skew scattering effect
is demonstrated by exact results of a simple hard wall impurity model. The
magnitude of the effect for short-range impurities is estimated using the first
Born approximation. The exact formalism we present can serve as a foundation
for further theoretical investigations.Comment: 4 pages, 3 figur
Localization and entanglement of two interacting electrons in a quantum-dot molecule
The localization of two interacting electrons in a coupled-quantum-dots
semiconductor structure is demonstrated through numerical calculations of the
time evolution of the two-electron wave function including the Coulomb
interaction between the electrons. The transition from the ground state to a
localized state is induced by an external, time-dependent, uniform electric
field. It is found that while an appropriate constant field can localize both
electrons in one of the wells, oscillatory fields can induce roughly equal
probabilities for both electrons to be localized in either well, generating an
interesting type of localized and entangled state. We also show that shifting
the field suddenly to an appropriate constant value can maintain in time both
types of localization.Comment: 4 pages, 4 figure
A quantum hydrodynamics approach to the formation of new types of waves in polarized two-dimension systems of charged and neutral particles
In this paper we explicate a method of quantum hydrodynamics (QHD) for the
study of the quantum evolution of a system of polarized particles. Though we
focused primarily on the two-dimension physical systems, the method is valid
for three-dimension and one-dimension systems too. The presented method is
based upon the Schr\"{o}dinger equation. Fundamental QHD equations for charged
and neutral particles were derived from the many-particle microscopic
Schr\"{o}dinger equation. The fact that particles possess the electric dipole
moment (EDM) was taken into account. The explicated QHD approach was used to
study dispersion characteristics of various physical systems. We analyzed
dispersion of waves in a two-dimension (2D) ion and hole gas placed into an
external electric field which is orthogonal to the gas plane. Elementary
excitations in a system of neutral polarized particles were studied for 1D, 2D
and 3D cases. The polarization dynamics in systems of both neutral and charged
particles is shown to cause formation of a new type of waves as well as changes
in the dispersion characteristics of already known waves. We also analyzed wave
dispersion in 2D exciton systems, in 2D electron-ion plasma and 2D
electron-hole plasma. Generation of waves in 3D system neutral particles with
EDM by means of the beam of electrons and neutral polarized particles is
investigated.Comment: 15 pages, 7 figure
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