arXiv subjects

J. J. Lin

Publications and source records attributed to J. J. Lin.

9 recordsLinked to original sources

arXiv2013

Phase diagram and physical properties of NaFe$_{1-x}$Cu$_x$As single crystals

A series of high quality NaFe$_{1-x}$Cu$_x$As single crystals has been grown by a self-flux technique, which were systematically characterized via structural, transport, thermodynamic, and high pressure measurements. Both the structural and magnetic transitions are suppressed by Cu doping, and bulk superconductivity is induced by Cu doping. Superconducting transition temperature ($T_c$) is initially enhanced from 9.6 to 11.5 K by Cu doping, and then suppressed with further doping. A phase diagram similar to NaFe$_{1-x}$Co$_x$As is obtained except that insulating instead of metallic behavior is observed in extremely overdoped samples. $T_c$'s of underdoped, optimally doped, and overdoped samples are all notably enhanced by applying pressure. Although a universal maximum transition temperature ($T_c^{max}$) of about 31 K under external pressure is observed in underdoped and optimally doped NaFe$_{1-x}$Co$_x$As, $T_c^{max}$ of NaFe$_{1-x}$Cu$_x$As is monotonously suppressed by Cu doping, suggesting that impurity potential of Cu is stronger than Co in NaFeAs. The comparison between Cu and Co doping effect in NaFeAs indicates that Cu serves as an effective electron dopant with strong impurity potential, but part of the doped electrons are localized and do not fill the energy bands as predicted by the rigid-band model.

cond-mat.supr-con↗

arXiv2009

Spin bottleneck in resonant tunneling through double quantum dots with different Zeeman splittings

We investigated the electron transport property of the InGaAs/GaAs double quantum dots, the electron g-factors of which are different from each other. We found that in a magnetic field, the resonant tunneling is suppressed even if one of the Zeeman sublevels is aligned. This is because the other misaligned Zeeman sublevels limit the total current. A finite broadening of the misaligned sublevel partially relieves this bottleneck effect, and the maximum current is reached when interdot detuning is half the Zeeman energy difference.

cond-mat.mes-hall↗

arXiv2007

Observation of strong electron dephasing in disordered Cu$_{93}$Ge$_4$Au$_3$ thin films

We report the observation of strong electron dephasing in a series of disordered Cu$_{93}$Ge$_4$Au$_3$ thin films. A very short electron dephasing time possessing very weak temperature dependence around 6 K, followed by an upturn with further decrease in temperature below 4 K, is found. The upturn is progressively more pronounced in more disordered samples. Moreover, a ln$T$ dependent, but high-magnetic-field-insensitive, resistance rise persisting from above 10 K down to 30 mK is observed in the films. These results suggest a nonmagnetic dephasing process which is stronger than any known mechanism and may originate from the coupling of conduction electrons to dynamic defects.

cond-mat.mes-hall↗

arXiv2007

Low-temperature electron dephasing time in AuPd revisited

Ever since the first discoveries of the quantum-interference transport in mesoscopic systems, the electron dephasing times, $τ_ϕ$, in the concentrated AuPd alloys have been extensively measured. The samples were made from different sources with different compositions, prepared by different deposition methods, and various geometries (1D narrow wires, 2D thin films, and 3D thickfilms) were studied. Surprisingly, the low-temperature behavior of $τ_ϕ$ inferred by different groups over two decades reveals a systematic correlation with the level of disorder of the sample. At low temperatures, where $τ_ϕ$ is (nearly) independent of temperature, a scaling $τ_ϕ^{\rm max} \propto D^{-α}$ is found, where $tau_ϕ^{\rm max}$ is the maximum value of $τ_ϕ$ measured in the experiment, $D$ is the electron diffusion constant, and the exponent $α$ is close to or slightly larger than 1. We address this nontrivial scaling behavior and suggest that the most possible origin for this unusual dephasing is due to dynamical structure defects, while other theoretical explanations may not be totally ruled out.

cond-mat.mes-hall↗

arXiv2007

Fabrication and Low Temperature Thermoelectric Properties of Na_xCoO_2 (x = 0.68 and 0.75) Epitaxial Films by the Reactive Solid-Phase Epitaxy

We have fabricated Na_xCoO_2 thin films via lateral diffusion of sodium into Co_3O_4 (111) epitaxial films (reactive solid-phase epitaxy: Ref. 4). The environment of thermal diffusion is key to the control of the sodium content in thin films. From the results of x-ray diffraction and in-plane resistivity, the epitaxial growth and the sodium contents of these films were identified. The thermoelectric measurements show a large thermoelectric power similar to that observed in single crystals. The quasiparticle scattering rate is found to approach zero at low temperatures, consistent with the small residual resistivity, indicating high quality of the Na_xCoO_2 thin films.

cond-mat.str-el↗

arXiv2002

Electron dephasing near zero temperature: an experimental review

The behavior of the electron dephasing time near zero temperature, $τ_ϕ^0$, has recently attracted vigorous attention. This renewed interest is primarily concerned with whether $τ_ϕ^0$ should reach a finite or an infinite value as $T \to$ 0. While it is accepted that $τ_ϕ^0$ should diverge if there exists only electron-electron (electron-phonon) scattering, several recent measurements have found that $τ_ϕ^0$ depends only very weakly on temperature, if at all, when $T$ is sufficiently low. This article discusses the current experimental status of "the saturation problem", and concludes that the origin(s) for this widely observed saturation are still unresolved.

cond-mat.mes-hall↗

arXiv2002

Effect of microstructures on the electron-phonon interaction in the disordered metals Pd$_{60}$Ag$_{40}$

Using the weak-localization method, we have measured the electron-phonon scattering times $τ_{ep}$ in Pd$_{60}$Ag$_{40}$ thick films prepared by DC- and RF-sputtering deposition techniques. In both series of samples, we find an anomalous $1/τ_{ep} \propto T^2\ell$ temperature and disorder dependence, where $\ell$ is the electron elastic mean free path. This anomalous behavior cannot be explained in terms of the current concepts for the electron-phonon interaction in impure conductors. Our result also reveals that the strength of the electron-phonon coupling is much stronger in the DC than RF sputtered films, suggesting that the electron-phonon interaction not only is sensitive to the total level of disorder but also is sensitive to the microscopic quality of the disorder.

cond-mat.dis-nn↗

arXiv2001

Effect of annealing on electron dephasing in three-dimensional polycrystalline metals

We have studied the effect of thermal annealing on electron dephasing times $τ_ϕ$ in three-dimensional polycrystalline metals. Measurements are performed on as-sputtered and annealed AuPd and Sb thick films, using weak-localization method. In all samples, we find that $τ_ϕ$ possesses an extremely weak temperature dependence as $T \to 0$. Our results show that the effect of annealing is non-universal, and it depends strongly on the amount of disorder quenched in the microstructures during deposition. The observed "saturation" behavior of $τ_ϕ$ cannot be easily explained by magnetic scattering. We suggest that the issue of saturation can be better addressed in three-dimensional, rather than lower-dimensional, structures.

cond-mat.mes-hall↗

arXiv2000

Universal saturation of electron dephasing in three-dimensional disordered metals

We have systematically investigated the low-temperature electron dephasing times $τ_ϕ$ in more than 40 three-dimensional polycrystalline impure metals with distinct material characteristics. In all cases, a saturation of the dephasing time is observed below about a (few) degree(s) Kelvin, depending on samples. The value of the saturated dephasing time $τ_0$ [$\equiv τ_ϕ(T \to 0 {\rm K})$] falls basically in the range 0.005 to 0.5 ns for all samples. Particularly, we find that $τ_0$ scales with the electron diffusion constant $D$ as $τ_0 \sim D^{- α}$, with $α$ close to or slightly larger than 1, for over two decades of $D$ from about 0.1 to 10 cm$^2$/s. Our observation suggests that the saturation behavior of $τ_ϕ$ is universal and intrinsic in three-dimensional polycrystalline impure metals. A complete theoretical explanation is not yet available.

cond-mat.dis-nn↗