The experimental and theoretical study of electrostatically driven granular material are reported. It is shown that the charged granular medium undergoes a hysteretic first order phase transition from the immobile condensed state (granular solid) to a fluidized dilated state (granular gas) with a changing applied electric field. In addition a spontaneous precipitation of dense clusters from the gas phase and subsequent coarsening--coagulation of these clusters is observed. Molecular dynamics simulations shows qualitative agreement with experimental results.
Compact solid-state sources of terahertz (THz) radiation are being sought for sensing, imaging, and spectroscopy applications across the physical and biological sciences. We demonstrate that coherent continuous-wave THz radiation of sizable power can be extracted from intrinsic Josephson junctions in the layered high-temperature superconductor Bi2Sr2CaCu2O8. In analogy to a laser cavity, the excitation of an electromagnetic cavity resonance inside the sample generates a macroscopic coherent state in which a large number of junctions are synchronized to oscillate in phase. The emission power is found to increase as the square of the number of junctions reaching values of 0.5 microwatt at frequencies up to 0.85 THz, and persists up to approximately 50 kelvin. These results should stimulate the development of superconducting compact sources of THz radiation.
We investigate the electronic specific heat of superoptimally substituted ${\mathrm{BaFe}}_{2}{({\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{P}}_{x})}_{2}$ single crystals in the superconducting state using high-resolution nanocalorimetry. From the measurements, we extract the substitution dependence of the condensation energy, superconducting gap $\mathrm{\ensuremath{\Delta}}$, and related microscopic parameters. We find that the anomalous scaling of the specific heat jump $\mathrm{\ensuremath{\Delta}}C\ensuremath{\propto}{T}_{\mathrm{c}}^{3}$, found in many iron-based superconductors, in this system originates from a ${T}_{\mathrm{c}}$-dependent ratio $\mathrm{\ensuremath{\Delta}}/{k}_{\mathrm{B}}{T}_{\mathrm{c}}$ in combination with a substitution-dependent density of states $N({\ensuremath{\varepsilon}}_{\mathrm{F}})$. A clear enhancement is seen in the effective mass ${m}^{*}$ as the composition approaches the value that has been associated with a quantum critical point at optimum substitution. However, a simultaneous increase in the superconducting carrier concentration ${n}_{\mathrm{s}}$ yields a penetration depth $\ensuremath{\lambda}$ that decreases with increasing ${T}_{\mathrm{c}}$ without sharp divergence at the quantum critical point. Uemura scaling indicates that ${T}_{\mathrm{c}}$ is governed by the Fermi temperature ${T}_{\mathrm{F}}$ for this multiband system.
The dynamic and thermodynamic experimental evidence supporting first order vortex melting in clean crystals of YBa{sub 2}Cu{sub 3}O{sub 7} is reviewed.
YBa$_{2}$Cu$_{3}$O$_{7-{\delta}}$ coated conductors (CCs) have achieved high critical current densities ($\textit{J}_{c}$) that can be further increased through the introduction of additional defects using particle irradiation. However, these gains are accompanied by increases in the flux creep rate, a manifestation of competition between the different types of defects. Here, we study this competition to better understand how to design pinning landscapes that simultaneously increase $\textit{J}_{c}$ and reduce creep. CCs grown by metal organic deposition show non-monotonic changes in the temperature-dependent creep rate, $\textit{S}(\textit{T})$. Notably, in low fields, there is a conspicuous dip to low $\textit{S}$ as temperature ($\textit{T}$) increases from ~20 K to ~65 K. Oxygen-, proton-, and Au-irradiation substantially increase $\textit{S}$ in this temperature range. Focusing on an oxygen-irradiated CC, we investigate the contribution of different types of irradiation-induced defects to the flux creep rate. Specifically, we study $\textit{S}(\textit{T})$ as we tune the relative density of point defects to larger defects by annealing both an as-grown and an irradiated CC in O$_{2}$ at temperatures $\textit{T}_{A}$ = 250${\deg}$C to 600${\deg}$C. We observe a steady decrease in $\textit{S}$($\textit{T}$ > 20 K) with increasing $\textit{T}_{A}$, unveiling the role of pre-existing nanoparticle precipitates in creating the dip in $\textit{S}(\textit{T})$ and point defects and clusters in increasing $\textit{S}$ at intermediate temperatures.
The Hall coefficient of the heavy fermion compounds CePd 3 , CeCu 2 Si 2 , CeAl 3 , CeCu 6 , URu 2 Si 2 and UCu 5 manifests an extremely large positive value due to skew scattering by Kondo sites. The Hall coefficient increases with decreasing temperature, making a maximum and decreases steeply. At low temperatures it becomes constant, suggesting a band of heavy electrons.
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