Conductivity in quasi two-dimensional systems

The conductivity in quasi two-dimensional systems is calculated using the quantum kinetic equation. Linearizing the Lenard-Balescu collision integral with the extension to include external field dependences allows one to calculate the conductivity with diagrams beyond the GW approximation including maximally crossed lines. Consequently the weak localization correction as an interference effect appears here from the field dependence of the collision integral (the latter dependence sometimes called intra-collisional field effect). It is shown that this weak localization correction has the same origin as the Debye-Onsager relaxation effect in plasma physics. The approximation is applied to a system of quasi two-dimensional electrons in hetero-junctions which interact with charged and neutral impurities and the low temperature correction to the conductivity is calculated analytically. It turns out that the dynamical screening due to charged impurities leads to a linear temperature dependence, while the scattering from neutral impurities leads to the usual Fermi-liquid behavior. By considering an appropriate mass action law to determine the ratio of charged to neutral impurities we can describe the experimental metal-insulator transition at low temperatures as a Mott-Hubbard transition.Comment: 7 pages 7 pages appendix 11 figure

Steady states of a chi-three parametric oscillator with coupled polarisations

Polarisation effects in the microcavity parametric oscillator are studied using a simple model in which two chi-three optical parametric oscillators are coupled together. It is found that there are, in general, a number of steady states of the model under continuous pumping. There are both continuous and discontinuous thresholds, at which new steady-states appear as the driving intensity is increased: at the continuous thresholds, the new state has zero output intensity, whereas at the discontinuous threshold it has a finite output intensity. The discontinuous thresholds have no analog in the uncoupled device. The coupling also generates rotations of the linear polarisation of the output compared with the pump, and shifts in the output frequencies as the driving polarisation or intensity is varied. For large ratios of the interaction between polarisations to the interaction within polarisations, of the order of 5, one of the thresholds has its lowest value when the pump is elliptically polarised. This is consistent with recent experiments in which the maximum output was achieved with an elliptically polarised pump.Comment: 7 pages, 4 figure

An estimate of the flavour singlet contributions to the hyperfine splitting in charmonium

We explore the splitting between flavour singlet and non-singlet mesons in charmonium. This has implications for the hyperfine splitting in charmonium

Effect of intravalley and intervalley electron-hole exchange on the nonlinear optical response of monolayer MoSe2

The coherent third-order nonlinear response of monolayer transition-metal dichalcogenide semiconductors, such as MoSe2, is dominated by the nonlinear exciton response, as well as biexciton and trion resonances. The fact that these resonances may be spectrally close together makes identification of the signatures, for example in differential transmission (DT), challenging. Instead of focusing on explaining a given set of experimental data, a systematic study aimed at elucidating the roles of intravalley and intervalley long-range electron-hole (e-h) exchange on the DT spectra is presented. Previous works have shown that the e-h long-range exchange introduces a linear leading-order term in the exciton dispersion. Based on a generalized Lippmann-Schwinger equation, we show that the presence of this linear dispersion term can reduce the biexciton binding energy to zero, contrary to the conventional situation of quadratic dispersion where an arbitrarily weak (well-behaved) attractive interaction always supports bound state(s). The effects of spin scattering and the spin-orbit interaction caused by e-h exchange are also clarified, and the DT line shape at the exciton and trion resonance is studied as a function of e-h exchange strength. In particular, as the exciton line shape is determined by the interplay of linear exciton susceptibility and the bound-state two-exciton resonance in the T matrix, the line shape at the trion is similarly determined by the interplay of the linear trion susceptibility and the bound-state exciton-trion resonance in the T matrix. ©2021 American Physical SocietyImmediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Terahertz spectroscopy of semiconductor microcavity lasers: Photon lasers

Semiconductor microcavities can exhibit various macroscopic quantum phenomena, including Bose-Einstein condensation of polaritons, Bardeen-Cooper-Schrieffer (BCS) states of polaritons, and photon lasing (lasing with negligible Coulombic exciton effects). An important aspect of possible experimental identification of these states is a gap in the excitation spectrum (the BCS gap in the case of a polaritonic BCS state). Similar to the polaritonic BCS gap, a light-induced gap can exist in photon lasers. Although polaritonic BCS states have been observed on the basis of spectroscopy in the vicinity of the laser frequency, the direct observation of polaritonic BCS gaps using light spectrally centered at or around the emission frequency has not been achieved. It has been conjectured that low-frequency (terahertz) spectroscopy should be able to identify such gaps. In this first of two studies, a theory aimed at identifying features of light-induced gaps in the linear terahertz spectroscopy of photon lasers is developed and numerically evaluated. It is shown that spectral features in the intraband conductivity, and therefore in the system's transmissivity and absorptivity, can be related to the light-induced gap. For sufficiently small Drude damping this includes spectral regions of THz gain. A future study will generalize the present formalism to include Coulomb effects. © 2021 American Physical Society.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Gapless fluctuations and exceptional points in semiconductor lasers

We analyze the spectrum of spatially uniform, single-particle fluctuation modes in the linear electromagnetic response of a semiconductor laser. We show that if the decay rate of the interband polarization, γp, and the relaxation rate of the occupation distribution, γf, are different, a gapless regime exists in which the order parameter Δ(0)(k) (linear in the coherent photon field amplitude and the interband polarization) is finite but there is no gap in the real part of the single-particle fluctuation spectrum. As the laser is an open, pumped, and dissipative system, this regime may be considered a nonequilibrium analog of gapless superconductivity. We analyze the fluctuation spectrum in both the photon laser limit, where the interactions among the charged particles are ignored, and the more general model with interacting particles. In the photon laser model, the order parameter is reduced to a momentum-independent quantity, which we denote by Δ. We find that, immediately above the lasing threshold, the real part of the fluctuation spectrum remains gapless when 0<|Δ|<2/27|γf-γp| and becomes gapped when |Δ| exceeds the upper bound of this range. Viewed as a complex function of |Δ| and the electron-hole energy, the eigenvalue set displays some interesting exceptional point (EP) structure around the gapless-gapped transition. The transition point is a third-order EP, where three eigenvalues (and eigenvectors) coincide. Switching on the particle interactions in the full model modifies the spectrum of the photon laser model and, in particular, leads to a more elaborate EP structure. However, the overall spectral behavior of the continuous (noncollective) modes of the full model can be understood on the basis of the relevant results of the photon laser model. © 2024 American Physical Society.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Data of Figure 1 of "Gapless fluctuations and exceptional points in semiconductor lasers"

Data of Figure 1 of "Gapless fluctuations and exceptional points in semiconductor lasers" by N.H. Kwong, M.Em. Spotnitz and R. Binder, University of Arizona. The figure shows fluctuation mode spectra (real and imaginary part) of semiconductor lasers. Refer to the publication in Physical Review B for details.For inquiries regarding the contents of this dataset, please contact the Corresponding Author listed in the README.txt file. Administrative inquiries (e.g., removal requests, trouble downloading, etc.) can be directed to [email protected]</p

Supplementary Material for: A Clinical Score for Predicting Atrial Fibrillation in Patients with Cryptogenic Stroke or Transient Ischemic Attack

<strong><em>Objectives:</em></strong> Detection of atrial fibrillation (AF) in post-cryptogenic stroke (CS) or transient ischemic attack (TIA) patients carries important therapeutic implications. <b><i>Methods:</i></b> To risk stratify CS/TIA patients for later development of AF, we conducted a retrospective cohort study using data from 1995 to 2015 in the Stanford Translational Research Integrated Database Environment (STRIDE). <b><i>Results:</i></b> Of the 9,589 adult patients (age ≥40 years) with CS/TIA included, 482 (5%) patients developed AF post CS/TIA. Of those patients, 28.4, 26.3, and 45.3% were diagnosed with AF 1-12 months, 1-3 years, and >3 years after the index CS/TIA, respectively. Age (≥75 years), obesity, congestive heart failure, hypertension, coronary artery disease, peripheral vascular disease, and valve disease are significant risk factors, with the following respective odds ratios (95% CI): 1.73 (1.39-2.16), 1.53 (1.05-2.18), 3.34 (2.61-4.28), 2.01 (1.53-2.68), 1.72 (1.35-2.19), 1.37 (1.02-1.84), and 2.05 (1.55-2.69). A risk-scoring system, i.e., the HAVOC score, was constructed using these 7 clinical variables that successfully stratify patients into 3 risk groups, with good model discrimination (area under the curve = 0.77). <b><i>Conclusions:</i></b> Findings from this study support the strategy of looking longer and harder for AF in post-CS/TIA patients. The HAVOC score identifies different levels of AF risk and may be used to select patients for extended rhythm monitoring