11,967 research outputs found
Transport phenomenology for a holon-spinon fluid
We propose that the normal-state transport in the cuprate superconductors can
be understood in terms of a two-fluid model of spinons and holons. In our
scenario, the resistivity is determined by the properties of the holons while
magnetotransport involves the recombination of holons and spinons to form
physical electrons. Our model implies that the Hall transport time is a measure
of the electron lifetime, which is shorter than the longitudinal transport
time. This agrees with our analysis of the normal-state data. We predict a
strong increase in linewidth with increasing temperature in photoemission. Our
model also suggests that the AC Hall effect is controlled by the transport
time.Comment: 4 pages, 1 postscript figure. Uses RevTeX, epsf, multico
Optical investigation of the charge-density-wave phase transitions in
We have measured the optical reflectivity of the quasi
one-dimensional conductor from the far infrared up to the
ultraviolet between 10 and 300 using light polarized along and normal to
the chain axis. We find a depletion of the optical conductivity with decreasing
temperature for both polarizations in the mid to far-infrared region. This
leads to a redistribution of spectral weight from low to high energies due to
partial gapping of the Fermi surface below the charge-density-wave transitions
at 145 K and 59 K. We deduce the bulk magnitudes of the CDW gaps and discuss
the scattering of ungapped free charge carriers and the role of fluctuations
effects
Optimisation of Fine Pitch Contactor and Test Board for QFN Package
Fine pitch contactor describes a contactor with smaller air gap between the contact pins. It is used for testing small portable devices. This work presents the optimised way of designing the 0.4 mm pitch contactor and test board for QFN package. The signal integrity of fine pitch test contactor has become a concern due to the small air-gap between the pins that leads to signal crosstalk and impedance mismatch issues. The same challenge had been seen when designing the fine pitch test board because of the requirement to meet 0.4 mm pitch for typical hand-held devices. It restricts the trace routing with typical design rules at the contactor mounting area due to the limited spaces. This would bring to impedance discontinuity and crosstalk effect. Therefore, optimised design rules on the fine pitch contactor and test board are necessary. Full-wave modelling and system level simulation were demonstrated to study the fine pitch design rules. While the full-wave modelling was to construct the contactor and test board components, the system level simulation was intended to study the signal transmission when propagating from one component to another. Overall, designing the fine pitch contactor requires extra study on the signal integrity and layout design. This paper presents a method to study and design the fine pitch contactor design. It reports the test board to achieve minimum losses and distortion test system for functional testing. Our simulation results for finepitch contactor model show that the return loss is less than 12 dB at 4 GHz
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Enabling Thin and Flexible Solid-State Composite Electrolytes by the Scalable Solution Process
All solid-state batteries (ASSBs) have the potential to deliver higher energy densities, wider operating temperature range, and improved safety compared with today's liquid-electrolyte-based batteries. However, of the various solid-state electrolyte (SSE) classes - polymers, sulfides, or oxides - none alone can deliver the combined properties of ionic conductivity, mechanical, and chemical stability needed to address scalability and commercialization challenges. While promising strategies to overcome these include the use of polymer/oxide or sulfide composites, there is still a lack of fundamental understanding between different SSE-polymer-solvent systems and its selection criteria. Here, we isolate various SSE-polymer-solvent systems and study their molecular level interactions by combining various characterization tools. With these findings, we introduce a suitable Li7P3S11SSE-SEBS polymer-xylene solvent combination that significantly reduces SSE thickness (∼50 μm). The SSE-polymer composite displays high room temperature conductivity (0.7 mS cm-1) and good stability with lithium metal by plating and stripping over 2000 h at 1.1 mAh cm-2. This study suggests the importance of understanding fundamental SSE-polymer-solvent interactions and provides a design strategy for scalable production of ASSBs
Memory function approach to the Hall constant in strongly correlated electron systems
The anomalous properties of the Hall constant in the normal state of
high- superconductors are investigated within the single-band Hubbard
model. We argue that the Mori theory is the appropriate formalism to address
the Hall constant, since it aims directly at resistivities rather than
conductivities. More specifically, the frequency dependent Hall constant
decomposes into its infinite frequency limit and a memory function
contribution. As a first step, both terms are calculated perturbatively in
and on an infinite dimensional lattice, where is the correlation strength.
If we allow to be of the order of twice the bare band width, the memory
function contribution causes the Hall constant to change sign as a function of
doping and to decrease as a function of temperature.Comment: 35 pages, RevTex, 3 ps figures include
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