Unified energy law for fluctuating density wave orders in cuprate pseudogap phase

The quantum origin of the cuprate pseudogap is a central conundrum of condensed matter physics. Although many symmetry-broken scenarios were previously proposed, universal quantitative relationships have been rarely studied. Here, we report a unified energy law underlying the pseudogap, which determines the scattering rate, pseudogap energy, and its onset temperature, with a quadratic scaling of the wavevector of density wave order (DWO). The law is validated by data from over one hundred samples, and a further prediction that the master order of pseudogap transforms from fluctuating spin to charge DWO is also confirmed. Furthermore, the energy law enables our derivation of the well-known linear scalings for the resistivity of the strange metal phase and the transition temperature of the superconducting phase. Finally, it is concluded that fluctuating orders provide a critical bridge linking microscopic spectra to macroscopic transport, showing promise for the quantification of other strongly correlated materials.

Scattering Processes with the Emission of Longitudinal Optical Phonons in the Landau Level System In GaAs/AlGaAs Quantum Well

The scattering processes of longitudinal optical phonons in GaAs/AlGaAs quantum wells in a quantizing magnetic field are considered. The time of intrasubband scattering between Landau levels is calculated by using Fermi's golden rule. The dependence of the scattering rate on the magnitude of the magnetic field has been shown and the magnetic field can suppress scattering processes on longitudinal optical phonons. It is found that the scattering time depends linearly on the width of the quantum well.

Investigating the Threshold Conditions of Air Breakdown with Mode-Locked Q-Switched Laser Pulses, and the Temporal Dynamics of Induced Plasma with Self-Scattering Phenomenon

A Q-switched Nd:YAG laser with mode-locked modulations is utilized to explore the laser-induced air breakdown. The various modulation depths of the mode-locking within the Q-switched pulse can be utilized to investigate the threshold conditions. With the GHz high-speed detectors to accurately measure the temporal pulse shape pulse by pulse, it is verified that the air breakdown threshold is crucially determined by the peak-power density instead of the energy density from the statistic results, especially for mode-locked Q-switched lasers. The stability of the system for laser-induced breakdown can be evaluated by threshold width through fitting the statistical result. Otherwise, by measuring the temporal characteristics of the excitation pulse and the induced plasma, it is further found that the plasma radiation displays a few-nanoseconds time delay to the excitation pulse and shows a decaying tail to be 10 times longer than the plasma build-up time. Moreover, the incident laser pulse is observed to be self-scattered by the air breakdown, and a rapidly modulated scattering rate is found with a slight delay time to the excitation mode-locked subpulse modulations.

Search for sub-eV axion-like resonance states via stimulated quasi-parallel laser collisions with the parameterization including fully asymmetric collisional geometry

We have searched for axion-like resonance states by colliding optical photons in a focused laser field (creation beam) by adding another laser field (inducing beam) for stimulation of the resonance decays, where frequency-converted signal photons can be created as a result of stimulated photon-photon scattering via exchanges of axion-like resonances. A quasi-parallel collision system (QPS) in such a focused field allows access to the sub-eV mass range of resonance particles. In past searches in QPS, for simplicity, we interpreted the scattering rate based on an analytically calculable symmetric collision geometry in both incident angles and incident energies by partially implementing the asymmetric nature to meet the actual experimental conditions. In this paper, we present new search results based on a complete parameterization including fully asymmetric collisional geometries. In particular, we combined a linearly polarized creation laser and a circularly polarized inducing laser to match the new parameterization. A 0.10 mJ/31 fs Ti:sapphire laser pulse and a 0.20 mJ/9 ns Nd:YAG laser pulse were spatiotemporally synchronized by sharing a common optical axis and focused into the vacuum system. Under a condition in which atomic background processes were completely negligible, no significant scattering signal was observed at the vacuum pressure of 2.6 × 10−5 Pa, thereby providing upper bounds on the coupling-mass relation by assuming exchanges of scalar and pseudoscalar fields at a 95% confidence level in the sub-eV mass range.

Ion heat and parallel momentum transport by stochastic magnetic fields and turbulence

The theory of turbulent transport of parallel momentum and ion heat by the interaction of stochastic magnetic fields and turbulence is presented. Attention is focused on determining the kinetic stress and the compressive energy flux. A critical parameter is identified as the ratio of the turbulent scattering rate to the rate of parallel acoustic dispersion. For the parameter large, the kinetic stress takes the form of a viscous stress. For the parameter small, the quasilinear residual stress is recovered. In practice, the viscous stress is the relevant form, and the quasilinear limit is not observable. This is the principal prediction of this paper. A simple physical picture is developed and shown to recover the results of the detailed analysis.

Ultrafast carrier’s dynamics with scattering rate saturation in Ge thinfilms

<p>An innovative theoretical approach for deeper understanding of the ultrafast spectroscopy experiments through solution of the Boltzmann transport equation coupled with various nonlinear scattering mechanisms, overcoming the limitations offered by DFT, RT-TDDFT and molecular based methods, is reported. A clear advantage of the real-time approach is that it does not make a priori assumptions about specific scattering, relaxation mechanisms and has capabilities to capture the full real-time carrier’s dynamics, including the superposition of all electron–electron, electron-lattice and electron–phonon scatterings etc. No such method with advances in theoretical treatments to explain ultrafast spectroscopy has been reported previously as per the author’s knowledge.</p>

Ultrafast carrier’s dynamics with scattering rate saturation in Ge thinfilms

<p>An innovative theoretical approach for deeper understanding of the ultrafast spectroscopy experiments through solution of the Boltzmann transport equation coupled with various nonlinear scattering mechanisms, overcoming the limitations offered by DFT, RT-TDDFT and molecular based methods, is reported. A clear advantage of the real-time approach is that it does not make a priori assumptions about specific scattering, relaxation mechanisms and has capabilities to capture the full real-time carrier’s dynamics, including the superposition of all electron–electron, electron-lattice and electron–phonon scatterings etc. No such method with advances in theoretical treatments to explain ultrafast spectroscopy has been reported previously as per the author’s knowledge.</p>

Electron Conduction Processes in Tantalum-Germanium Multilayers

<p>An explosion of both theoretical and experimental research into structurally disordered materials in the late 1970s has greatly increased our understanding of these complex systems. A number of facets of the conduction processes remain unexplained, however, particularly in the area of non-simple metals. Multilayers of disordered tantalum and amorphous germanium with individual layer thicknesses of between 4 & 120A [Angstrom] and 13 & 220A [Angstrom]respectively have been prepared by vapour deposition and the in-plane resistance measured from 1.5 to 300K. Results for samples with germanium layers of sufficient thickness to prevent tunnelling between the conducting tantalum layers can be interpreted in terms of conduction in the tantalum layers alone. In these samples the behaviour of the resistance as a function of temperature and the tantalum layer thickness can be explained in terms of the interplay between quantum interference effects and disorder enhanced electron-electron interaction effects. At high temperatures the negative temperature coefficient of resistance arises from the destruction of coherent interference in the backscattered direction by phonons. From the data, the electron-phonon scattering rate is found to be comparable in magnitude to that expected for scattering in either the "clean" or "dirty" limits while the temperature dependence of the scattering rate lies between that expected for each of these limits. At lower temperatures a turn over to a positive temperature coefficient of resistance is seen as spin-orbit scattering and superconducting fluctuations become important. At still lower temperatures the resistance is dominated by electron-electron interaction effects and we have observed a transition from three-dimensional to two-dimensional behaviour as the tantalum layer thickness is reduced. Evidence for the onset of superconductivity is seen for samples with a low temperature sheet resistance of less than 3000 Omega/whitesquare. We have also investigated samples with thin germanium layers (<40A [Angstrom]) in which coupling between the layers causes an increase in the superconducting transition temperature. We present some preliminary measurements which suggest that the transition from isolated to coupled tantalum layers, as the germanium layer thickness is reduced, can be followed in the form of the fluctuation conductivity.</p>

Electron Conduction Processes in Tantalum-Germanium Multilayers

<p>An explosion of both theoretical and experimental research into structurally disordered materials in the late 1970s has greatly increased our understanding of these complex systems. A number of facets of the conduction processes remain unexplained, however, particularly in the area of non-simple metals. Multilayers of disordered tantalum and amorphous germanium with individual layer thicknesses of between 4 & 120A [Angstrom] and 13 & 220A [Angstrom]respectively have been prepared by vapour deposition and the in-plane resistance measured from 1.5 to 300K. Results for samples with germanium layers of sufficient thickness to prevent tunnelling between the conducting tantalum layers can be interpreted in terms of conduction in the tantalum layers alone. In these samples the behaviour of the resistance as a function of temperature and the tantalum layer thickness can be explained in terms of the interplay between quantum interference effects and disorder enhanced electron-electron interaction effects. At high temperatures the negative temperature coefficient of resistance arises from the destruction of coherent interference in the backscattered direction by phonons. From the data, the electron-phonon scattering rate is found to be comparable in magnitude to that expected for scattering in either the "clean" or "dirty" limits while the temperature dependence of the scattering rate lies between that expected for each of these limits. At lower temperatures a turn over to a positive temperature coefficient of resistance is seen as spin-orbit scattering and superconducting fluctuations become important. At still lower temperatures the resistance is dominated by electron-electron interaction effects and we have observed a transition from three-dimensional to two-dimensional behaviour as the tantalum layer thickness is reduced. Evidence for the onset of superconductivity is seen for samples with a low temperature sheet resistance of less than 3000 Omega/whitesquare. We have also investigated samples with thin germanium layers (<40A [Angstrom]) in which coupling between the layers causes an increase in the superconducting transition temperature. We present some preliminary measurements which suggest that the transition from isolated to coupled tantalum layers, as the germanium layer thickness is reduced, can be followed in the form of the fluctuation conductivity.</p>

Cosmic-Ray Transport in Simulations of Star-forming Galactic Disks

Cosmic-ray transport on galactic scales depends on the detailed properties of the magnetized, multiphase interstellar medium (ISM). In this work, we postprocess a high-resolution TIGRESS magnetohydrodynamic simulation modeling a local galactic disk patch with a two-moment fluid algorithm for cosmic-ray transport. We consider a variety of prescriptions for the cosmic rays, from a simple, purely diffusive formalism with constant scattering coefficient, to a physically motivated model in which the scattering coefficient is set by the critical balance between streaming-driven Alfvén wave excitation and damping mediated by local gas properties. We separately focus on cosmic rays with kinetic energies of ∼1 GeV (high-energy) and ∼30 MeV (low energy), respectively important for ISM dynamics and chemistry. We find that simultaneously accounting for advection, streaming, and diffusion of cosmic rays is crucial for properly modeling their transport. Advection dominates in the high-velocity, low-density hot phase, while diffusion and streaming are more important in higher-density, cooler phases. Our physically motivated model shows that there is no single diffusivity for cosmic-ray transport: the scattering coefficient varies by four or more orders of magnitude, maximal at density n H ∼ 0.01 cm−3. The ion-neutral damping of Alfvén waves results in strong diffusion and nearly uniform cosmic-ray pressure within most of the mass of the ISM. However, cosmic rays are trapped near the disk midplane by the higher scattering rate in the surrounding lower-density, higher-ionization gas. The transport of high-energy cosmic rays differs from that of low-energy cosmic rays, with less effective diffusion and greater energy losses for the latter.