arXiv subjects

P. Ji

Publications and source records attributed to P. Ji.

4 recordsLinked to original sources

arXiv2025

Magnetic brightening of light-like excitons in a monolayer semiconductor

Monolayer transition-metal dichalcogenides, such as WSe$_2$, are direct gap, multi-valley semiconductors. Long-range electron-hole exchange interactions mix the valleys, yielding dispersion relations for massive ($\propto Q^2$) as well as light-like ($\propto Q$) excitons. We report magneto-photoluminescence spectroscopy of excitons in the monolayer semiconductor WSe$_2$ to $B = \pm25$T. The magnetic field-dependent line shape of the neutral exciton reveals the emergence of a new blue-detuned emission peak in both field orientations. Analyzing the distinct magnetic field-dependent shifts of both peaks facilitates the identification of the emergent feature as a spin-singlet with a significantly smaller reduced exciton mass as compared to the neutral exciton. The intensity of the emergent feature increases with magnetic field according to $\propto B^2$, as expected for a linear dispersion relation. The density-dependent diamagnetic shift ratios of both features follow the expected density dependence of the electron-hole exchange interactions. We interpret our observations within a picture of magnetic-field-induced coupling between the bright massive and quasi dark light-like exciton, leading to its brightening.

cond-mat.mes-hall↗

arXiv2020

Reaction rate weighted multilayer nuclear reaction network

Nuclear reaction rate ($\lambda$) is a significant factor in the process of nucleosynthesis. A multi-layer directed-weighted nuclear reaction network in which the reaction rate as the weight, and neutron, proton, $^4$He and the remainder nuclei as the criterion for different reaction-layers is for the first time built based on all thermonuclear reactions in the JINA REACLIB database. Our results show that with the increase of the stellar temperature ($T_{9}$), the distribution of nuclear reaction rates on the $R$-layer network demonstrates a transition from unimodal to bimodal distributions. Nuclei on the $R$-layer in the region of $\lambda = [1,2.5\times10^{1}]$ have a more complicated out-going degree distribution than the one in the region of $\lambda = [10^{11},10^{13}]$, and the number of involved nuclei at $T_{9} = 1$ is very different from the one at $T_{9} = 3$. The redundant nuclei in the region of $\lambda = [1, 2.5\times10^{1}]$ at $T_{9} = 3$ prefer $(\gamma,p)$ and $({\gamma,\alpha})$ reactions to the ones at $T_{9}=1$, which produce nuclei around the $\beta$ stable line. This work offers a novel way to the big-data analysis on nuclear reaction network at stellar temperatures.

nucl-th↗

arXiv2018

Bistable firing pattern in a neural network model

Excessively high, neural synchronisation has been associated with epileptic seizures, one of the most common brain diseases worldwide. A better understanding of neural synchronisation mechanisms can thus help control or even treat epilepsy. In this paper, we study neural synchronisation in a random network where nodes are neurons with excitatory and inhibitory synapses, and neural activity for each node is provided by the adaptive exponential integrate-and-fire model. In this framework, we verify that the decrease in the influence of inhibition can generate synchronisation originating from a pattern of desynchronised spikes. The transition from desynchronous spikes to synchronous bursts of activity, induced by varying the synaptic coupling, emerges in a hysteresis loop due to bistability where abnormal (excessively high synchronous) regimes exist. We verify that, for parameters in the bistability regime, a square current pulse can trigger excessively high (abnormal) synchronisation, a process that can reproduce features of epileptic seizures. Then, we show that it is possible to suppress such abnormal synchronisation by applying a small-amplitude external current on less than 10% of the neurons in the network. Our results demonstrate that external electrical stimulation not only can trigger synchronous behaviour, but more importantly, it can be used as a means to reduce abnormal synchronisation and thus, control or treat effectively epileptic seizures.

physics.bio-ph↗

arXiv2002

The classical wormhole solution and wormhole wavefunction with a nonlinear Born-Infeld scalar field

On this paper we consider the classical wormhole solution of the Born-Infeld scalar field. The corresponding classical wormhole solution can be obtained analytically for both very small and large $\dotϕ$. At the extreme limits of small $\dotϕ$ the wormhole solution has the same format as one obtained by Giddings and Strominger[10]. At the extreme limits of large $\dotϕ$ the wormhole solution is a new one. The wormhole wavefunctions can also be obtained for both very small and large $\dotϕ$. These wormhole wavefunctions are regarded as solutions of quantum-mechanical Wheeler--Dewitt equation with certain boundary conditions.

gr-qc↗