Searcharxiv⌕ Search

arXiv subjects

J. Dai

Publications and source records attributed to J. Dai.

44 records · Page 3Linked to original sources
arXiv2011

Local spin fluctuations in iron-based superconductors: 77Se and 87Rb NMR measurements of Tl0.47Rb0.34Fe1.63Se2

We report nuclear magnetic resonance (NMR) studies of the intercalated iron selenide superconductor (Tl, Rb)$_{y}$Fe$_{2-x}$Se$_2$ ($T_c = 32$ K). Single-crystal measurements up to 480 K on both $^{77}$Se and $^{87}$Rb nuclei show a superconducting phase with no magnetic order. The Knight shifts $K$ and relaxation rates $1/T_1T$ increase very strongly with temperature above $T_c$, before flattening at 400 K. The quadratic $T$-dependence and perfect proportionality of both $K$ and $1/T_1T$ data demonstrate their origin in paramagnetic moments. A minimal model for this pseudogap-like response is not a missing density of states but two additive contributions from the itinerant electronic and local magnetic components, a framework unifying the $K$ and $1/T_1 T$ data in many iron-based superconductors.

cond-mat.supr-con↗
arXiv2011

Visible light induced ocular delayed bioluminescence as a possible origin of negative afterimage

The delayed luminescence of biological tissues is an ultraweak reemission of absorbed photons after exposure to external monochromatic or white light illumination. Recently, Wang, Bókkon, Dai and Antal (Brain Res. 2011) presented the first experimental proof of the existence of spontaneous ultraweak biophoton emission and visible light induced delayed ultraweak photon emission from in vitro freshly isolated rat's whole eye, lens, vitreous humor and retina. Here, we suggest that the photobiophysical source of negative afterimage can also occur within the eye by delayed bioluminescent photons. In other words, when we stare at a colored (or white) image for few seconds, external photons can induce excited electronic states within different parts of the eye that is followed by a delayed reemission of absorbed photons for several seconds. Finally, these reemitted photons can be absorbed by nonbleached photoreceptors that produce a negative afterimage. Although this suggests the photobiophysical source of negative afterimages is related retinal mechanisms, cortical neurons have also essential contribution in the interpretation and modulation of negative afterimages.

physics.bio-ph↗
arXiv2006

Two-Electron Linear Intersubband Light Absorption in a Biased Quantum Well

We point out a novel manifestation of many-body correlations in the linear optical response of electrons confined in a quantum well. Namely, we demonstrate that along with conventional absorption peak at frequency close to intersubband energy, there exists an additional peak at double frequency. This new peak is solely due to electron-electron interactions, and can be understood as excitation of two electrons by a single photon. The actual peak lineshape is comprised of a sharp feature, due to excitation of pairs of intersubband plasmons, on top of a broader band due to absorption by two single-particle excitations. The two-plasmon contribution allows to infer intersubband plasmon dispersion from linear absorption experiments.

cond-mat.mes-hall↗
arXiv1996

Detection of Neutral MSSM Higgs Bosons in Four-$b$ Final States at the Tevatron and the LHC: An Update

We update our earlier results regarding detection of $gg\to b\anti b h\to 4b$ ($h=h^0,H^0,A^0$) to incorporate the very high $b$-tagging efficiencies and purities that are now anticipated at the LHC. New results for the Tev$^*$ are given, and indicate substantial potential for these modes. The complementarity of the $H^0\to h^0h^0 \to 4b$ final state mode is illustrated for the LHC. The latest radiative corrections to the Higgs sector are incorporated.

hep-ph↗
arXiv1995

Detection of the Minimal Supersymmetric Model Higgs Boson $H^0$ in its $h^0h^0\to 4b$ and $A^0A^0\to 4b$ Decay Channels

We demonstrate that detection of the heavier minimal supersymmetric model CP-even Higgs boson $H^0$ will be possible at the LHC via its $H^0\to h^0h^0\to 4b$ and/or $H^0\to A^0A^0\to 4b$ decay channels for significant portions of the $( m_{A^0},\tanβ)$ model parameter space. At low $ m_{A^0}$ ($\lsim 60\gev$), {\it both} the $H^0\to A^0A^0\to 4b$ and $H^0\to h^0h^0\to 4b$ modes yield a viable signal for most $\tanβ$ values; viability for the $h^0h^0$ channel extends up to $\mhh\sim 2\mt$ when the model parameter $\tanβ$ is not large. At the Tevatron, the $h^0h^0$ and $A^0A^0$ channels are both potentially viable at low $ m_{A^0}$ for sufficiently good $b$-tagging efficiency and purity.

hep-ph↗
arXiv1994

LHC Detection of Neutral MSSM Higgs Bosons via $gg\rta b\anti b \h\rta b\anti b b\anti b$

We demonstrate that simultaneous detection of two of the neutral Higgs bosons of the Minimal Supersymmetric Model will be possible at the LHC in the $b\anti b b\anti b$ final state, provided $\tanb$ is large and $b$-tagging can be performed with good efficiency and purity. This mode enhances the already established guarantee that there is no region of supersymmetric parameter space for which {\it none} of the Higgs bosons of the model can be seen at the LHC.

hep-ph↗
arXiv1993

Guaranteed Detection of a Minimal Supersymmetric Model Higgs Boson at Hadron Supercolliders

We demonstrate that expected efficiencies and purities for $b$-tagging at SSC/LHC detectors should allow detection of at least one of the Higgs bosons of the Minimal Supersymmetric Model in $t\anti t$~Higgs production, with Higgs$\rta b\anti b$ decay, over a substantial range of supersymmetric parameter space. In particular, with the addition of this mode to those previously considered, there is no region of supersymmetric parameter space for which {\it none} of the Higgs bosons of the model can be seen at the SSC/LHC.

hep-ph↗