Incoherent Carriers Research Articles

Strange metal behavior from incoherent carriers scattered by local moments

Strange metal behavior from incoherent carriers scattered by local moments

Possible superconductivity from incoherent carriers in overdoped cuprates

There is now compelling evidence that the normal state of superconducting overdoped cuprates is a strange metal comprising two distinct charge sectors, one governed by coherent quasiparticle excitations, the other seemingly incoherent and characterized by non-quasiparticle (Planckian) dissipation. The zero-temperature superfluid density n_s(0)ns(0) of overdoped cuprates exhibits an anomalous depletion with increased hole doping pp, falling to zero at the edge of the superconducting dome. Over the same doping range, the effective zero-temperature Hall number n_{\rm H}(0) transitions from pp to 1 + pp. By taking into account the presence of these two charge sectors, we demonstrate that in the overdoped cuprates Tl_22Ba_22CuO_{6+\delta}6+δ and La_{2-x}2−xSr_xxCuO_44, the growth in n_s(0)ns(0) as pp is decreased from the overdoped side may be compensated by the loss of carriers in the coherent sector. Such a correspondence is contrary to expectations from conventional BCS theory and implies that superconductivity in overdoped cuprates emerges uniquely from the sector that exhibits incoherent transport in the normal state.

Infrared Hall conductivity ofNa0.7CoO2

We report infrared Hall conductivity $\sigma_{xy}(\omega)$ of Na$_{0.7}$CoO$_2$ thin films determined from Faraday rotation angle $\theta_{F}$ measurements. $\sigma_{xy}(\omega)$ exhibits two types of hole conduction, Drude and incoherent carriers. The coherent Drude carrier shows a large renormalized mass and Fermi liquid-like behavior of Hall scattering rate, $\gamma_{H} \sim aT^{2}$. The spectral weight is suppressed and disappears at T = 120K. The incoherent carrier response is centered at mid-IR frequency and shifts to lower energy with increasing T. Infrared Hall constant is positive and almost independent of temperature in sharp contrast with the dc-Hall constant.

Influence of Coulomb and phonon interaction on the exciton formation dynamics in semiconductor heterostructures

A microscopic theory is developed to analyze the dynamics of exciton formation out of incoherent carriers in semiconductor heterostructures. The carrier Coulomb and phonon interaction is included consistently. A cluster expansion method is used to systematically truncate the hierarchy problem. By including all correlations up to the four-point (i.e. two-particle) level, the fundamental fermionic substructure of excitons is fully included. The analysis shows that the exciton formation is an intricate process where Coulomb correlations rapidly build up on a picosecond time scale while phonon dynamics leads to true exciton formation on a slow nanosecond time scale.

Studies on some methods of communication using pulse-modulated incoherent carriers †

Abstract The possibility of the use of incoherent carriers with compound pulse modulation has been established. The video SNR's for different pulse-modulation systems using gaus-sian and clipped noise carriers have been evaluated and the results have been used to calculate finally the message SNR's of the systems. Some of these results have boon experimentally verified. Experimental results show that message SNR's of 60-70 dB are obtained with clipped noise carrier systems. The design of some of the practical systems using noise carriers has been indicated. It has been shown that the PFM-AM and PPM-AM systems provide best message SNR's for the carrier bandwidth Bn ≪fr and for Bn ≥fr /2, PPM-AM systems provide the best message SNR. The PPM-AM system however requires minimum r.f. bandwidth to provide the same message SNR and message bandwidth. The results of incoherent carrier systems have been extended to laser communication systems, and it has been shown that by clipping the received signal at the receiver input, semiconductor lasers can be used to transmit information with a message SNR of 60-70 dB. †An incoherent carrier whose amplitude distribution is gaussian will be called the noise carrier.

The Incoherent-carrier Communication Systems

Possibilities of the use of incoherent carriers for transmission of analogue and digital signals have been established. It has been shown that for analogue signals a message SNR of 60–70 db, with incoherent carrier, can be obtained by using compound pulse modulation and carrier clipping. The use of incoherent carriers eliminates the fading distortion, normally very disturbing with the coherent-carrier systems.For On-Off digital transmission through noisy fading channels, an error rate of 1 × 10−5 has been obtained with incoherent carriers for a CNR of 17 db, the sine wave carriers under similar conditions require 53 db CNR for the single channel reception. Thus in effect, the noise carrier provides a signal gain of 36 db. Minimum noise-carrier bandwidths required to obtain fading protection have been obtained, and it was found to depend on the method of noise-carrier generation. Different methods of noise-carrier generation have been studied. The diversity effectiveness of noise-carrier systems has been e...

Digital communication in fading channels using incoherent carriers

Possibilities of efficient digital communication through a fading channel, using a narrowband noise carrier, have been investigated both theoretically and experimentally. It is shown that, for a carrier spread Bn ≥ 0.9 f2c (fc, being the mean carrier frequency in megahertz), the system performs better than a 4-fold equal-gain diversity system. Error rates against the channel carrier/noise ratio (c.n.r.) and channel separation (for multiplexed systems) are also shown.

Some results for an r.f.- and p.l.-modulated incoherent carrier

Possibilities of using incoherent carriers, amplitude-modulated by the message-modulated p.f.m., r.f.m. and p.l.m. have been investigated. It has been shown that, for noise bandwidths much smaller than the transmission bandwidth, efficient communication is possible, and s.n.r.s of 50?60dB are obtained for practical p.f.m.-a.m. and r.f.m.-a.m. systems. Some comparisons are also given.

Synchronous detection of microwave-modulated incoherent optical carriers

Synchronous detection of microwave-modulated incoherent optical carriers