arXiv subjects

S. M. Liu

Publications and source records attributed to S. M. Liu.

3 recordsLinked to original sources

arXiv2025

Transition from antiferromagnets to altermagnets: Symmetry-Breaking Theory

Considering the similarity of the real-space configurations for the opposite spin sublattices in both antiferromagnets (AFM) and altermagnets (AM), the relationship between them should be profound. In this work, we demonstrate that AFM and AM can be connected with spin groups and their subgroups. Consequently, the breaking of the combined inversion or translation operation with time-reversal symmetry (PT or tT) in AFM will induce transition from AFM to AM. We systematically list all collinear spin point groups and space groups that can realize the transition for the three types of AFMs: PT-type, tT-type and PT-tT-type. Moreover, we propose that Floquet engineering using circularly polarized light and surface cutting engineering are effective approaches to break PT and tT symmetries of AFM, respectively, achieving the transition. Interestingly, the features and magnitude of altermagnetic spin splitting can be tuned by adjusting various parameters of Floquet engineering. Our work not only establishes a theoretical framework for the transition from AFM to AM, but also provides practical approaches utilizing the achievements in AFM for a hundred years to obtain AM, significantly expanding the scope of altermagnetic materials for both theoretical studies and future practical applications.

cond-mat.mtrl-sci↗

arXiv2021

Non-thermal electron energization during the impulsive phase of an X9.3 flare revealed by Insight-HXMT

The X9.3 flare SOL20170906T11:55 was observed by the CsI detector aboard the first Chinese X-ray observatory Hard X-ray Modulation telescope (Insight-HXMT). By using wavelets method, we report about 22 s quasiperiodic pulsations(QPPs) during the impulsive phase. And the spectra from 100 keV to 800 keV showed the evolution with the gamma-ray flux, of a power-law photon index from $\sim 1.8$ before the peak, $\sim 2.0$ around the flare peak, to $\sim 1.8$ again. The gyrosynchrotron microwave spectral analysis reveals a $36.6 \pm 0.6 \arcsec$ radius gyrosynchrotron source with mean transverse magnetic field around 608.2 Gauss, and the penetrated $\ge$ 10 keV non-thermal electron density is about $10^{6.7} \mathrm{cm}^{-3}$ at peak time. The magnetic field strength followed the evolution of high-frequency radio flux. Further gyrosynchrotron source modeling analysis implies that there exists a quite steady gyrosynchrotron source, the non-thermal electron density and transverse magnetic field evolution are similar to higher-frequency light curves. The temporally spectral analysis reveals that those non-thermal electrons are accelerated by repeated magnetic reconnection, likely from a lower corona source.

astro-ph.SR↗

arXiv2004

A Radio Outburst Nearly Coincident with the Large X-ray Flare from Sgr A* on 2002-10-03

A large radio outburst from Sgr A* was observed during the VLA weekly monitoring program at 2 cm, 1.3 cm and 7 mm, nearly coincident with the brightest X-ray flare detected to date with the XMM-Newton X-ray Observatory on 2002-10-03. The flux density of 1.9$\pm$0.2 Jy measured at 7 mm exceeds the mean value (1.00$\pm$0.01 Jy) by a factor of $\sim 2$, one of the two highest increases observed during the past three years (June 2000-October 2003), while less significant increases in flux densities were observed at 1.3 cm and 2 cm. The radio observation started 13.5 hrs after the onset of the X-ray flare (which had occurred over a 45 min duration) and continued for 1.3 hrs. During the observation, there was no significant ($<3σ$) change in the radio flux densities at all the three wavelengths, indicating that the radio outburst varied on a timescale of $>1$hr. A spectral index of $α=2.4^{+0.3}_{-0.6}$ (${\rm S \proptoν^α}$) was derived for the outburst component, consistent with an optically thick nonthermal synchrotron source. These results suggest that energetic electrons responsible for the radio outburst might be produced via a process associated with the X-ray flare, then transported to large radii, producing the observed radio outburst. The observation is the first evidence for a correlated variation in the radio and X-ray emissions from Sgr A*.

astro-ph↗