arXiv subjects

Haiyun Huang

Publications and source records attributed to Haiyun Huang.

10 recordsLinked to original sources

arXiv2026

High-energy electronic excitations in La3Ni2O7 by time-resolved optical spectroscopy

Recently, high-temperature superconductivity has been established in bilayer La3Ni2O7, which exhibits a density-wave (DW) transition at ~ 150 K under ambient pressure. The DW order is believed to be linked to superconductivity, as it is suppressed upon the emergence of superconductivity at high pressures. Here, we explore the ultrafast dynamics of high-energy electronic excitations from 10 K to room temperature under ambient pressure using time-resolved optical spectroscopy. Two high-energy electronic excitations at ~1.8 and ~ 2.4 eV, arising from distinct interband transitions, are identified. They exhibit different DW gaps of approximately 54 and 67 meV, respectively, along with relaxation dynamics that can be well described by the Rothwarf-Taylor model. In addition, we observe four coherent Raman-active phonon modes that exhibit distinct coupling with different electronic excitations. The phonon softening with increasing temperature can be well described between ~100 K and room temperature by a semi-quantitative model, which includes thermal expansion and anharmonic phonon-phonon coupling. At cryogenic temperatures, deviations from the measured temperature-dependent phonon frequencies and the model fits suggest an additional contribution from electron-phonon coupling. Our study provides direct evidence of the complex gap structure and phonon dynamics in this material, offering critical insights into the DW mechanism and many-body effects.

cond-mat.supr-con↗

arXiv2025

Low-frequency interlayer phonon dynamics and photoinduced terahertz absorption in black phosphorus

The strong interlayer coupling in black phosphorus (BP), arising from wavefunction overlap between layers, is critical for understanding its electronic and optical properties. Here, we utilize terahertz (THz) spectroscopy to study phonon dynamics in BP. We identify two peaks at 6 and 8.5 meV in steady-state THz spectra, which are attributed to low-frequency interlayer phonon modes. Both modes exhibit anharmonic phonon coupling behavior below 150 K, manifesting as temperature-dependent red-shifts. Using time-resolved THz spectroscopy, we observe significantly increased THz absorption under photoexcitation, arising from the transient enhancements of the extended Drude component and the oscillator strengths of interlayer phonons in non-equilibrium. These findings highlight the critical role of interlayer phonon dynamics in understanding many-body physics in BP.

cond-mat.str-el↗

arXiv2025

Alleviating Seasickness through Brain-Computer Interface-based Attention Shift

Seasickness poses a widespread problem that adversely impacts both passenger comfort and the operational efficiency of maritime crews. Although attention shift has been proposed as a potential method to alleviate symptoms of motion sickness, its efficacy remains to be rigorously validated, especially in maritime environments. In this study, we develop an AI-driven brain-computer interface (BCI) to realize sustained and practical attention shift by incorporating tasks such as breath counting. Forty-three participants completed a real-world nautical experiment consisting of a real-feedback session, a resting session, and a pseudo-feedback session. Notably, 81.39\% of the participants reported that the BCI intervention was effective. EEG analysis revealed that the proposed system can effectively regulate motion sickness EEG signatures, such as an decrease in total band power, along with an increase in theta relative power and a decrease in beta relative power. Furthermore, an indicator of attentional focus, the theta/beta ratio, exhibited a significant reduction during the real-feedback session, providing further evidence to support the effectiveness of the BCI in shifting attention. Collectively, this study presents a novel nonpharmacological, portable, and effective approach for seasickness intervention, which has the potential to open up a brand-new application domain for BCIs.

cs.HC↗

arXiv2025

Ultrafast charge-transfer dynamics in Ca$_2$CuO$_2$Cl$_2$ from time-resolved optical reflectivity

We employ time-resolved optical reflectivity to investigate the ultrafast dynamics of the charge-transfer gap (CTG) in a parent cuprate compound Ca$_2$CuO$_2$Cl$_2$ (CCOC). We observe a persistent photoinduced red shift of the CTG that lasts up to 1000 ps. The red shift during the slow decay after 10 ps can be well modeled by the localized picture, whereas its maximum value at ~0.9 ps involves additional contribution from the renormalization of the Hubbard U due to screening effect from delocalized electrons. Furthermore, coupling between the mid-gap absorption and a slow acoustic phonon launches coherent oscillations below the CTG, observed as a ~20 GHz modulation with a dispersion independent of the pump fluence. These results demonstrate the tunning of the CTG by light, unveil complex interplay between multiple degrees of freedom, and contribute to a deeper understanding of superconductivity and correlated materials.

cond-mat.str-el↗

arXiv2025

Ultrafast Chirality-dependent Dynamics from Helicity-resolved Transient Absorption Spectroscopy

Chirality, a pervasive phenomenon in nature, is widely studied across diverse fields including the origins of life, chemical catalysis, drug discovery, and physical optoelectronics. The investigations of natural chiral materials have been constrained by their intrinsically weak chiral effects. Recently, significant progress has been made in the fabrication and assembly of low-dimensional micro and nanoscale chiral materials and their architectures, leading to the discovery of novel optoelectronic phenomena such as circularly polarized light emission, spin and charge flip, advocating great potential for applications in quantum information, quantum computing, and biosensing. Despite these advancements, the fundamental mechanisms underlying the generation, propagation, and amplification of chirality in low-dimensional chiral materials and architectures remain largely unexplored. To tackle these challenges, we focus on employing ultrafast spectroscopy to investigate the dynamics of chirality evolution, with the aim of attaining a more profound understanding of the microscopic mechanisms governing chirality generation and amplification. This review thus provides a comprehensive overview of the chiral micro-/nano-materials, including two-dimensional transition metal dichalcogenides (TMDs), chiral halide perovskites, and chiral metasurfaces, with a particular emphasis on the physical mechanism. This review further explores the advancements made by ultrafast chiral spectroscopy research, thereby paving the way for innovative devices in chiral photonics and optoelectronics.

cond-mat.mes-hall↗

arXiv2022

A Novel Semi-supervised Meta Learning Method for Subject-transfer Brain-computer Interface

Brain-computer interface (BCI) provides a direct communication pathway between human brain and external devices. Before a new subject could use BCI, a calibration procedure is usually required. Because the inter- and intra-subject variances are so large that the models trained by the existing subjects perform poorly on new subjects. Therefore, effective subject-transfer and calibration method is essential. In this paper, we propose a semi-supervised meta learning (SSML) method for subject-transfer learning in BCIs. The proposed SSML learns a meta model with the existing subjects first, then fine-tunes the model in a semi-supervised learning manner, i.e. using few labeled and many unlabeled samples of target subject for calibration. It is significant for BCI applications where the labeled data are scarce or expensive while unlabeled data are readily available. To verify the SSML method, three different BCI paradigms are tested: 1) event-related potential detection; 2) emotion recognition; and 3) sleep staging. The SSML achieved significant improvements of over 15% on the first two paradigms and 4.9% on the third. The experimental results demonstrated the effectiveness and potential of the SSML method in BCI applications.

eess.SP↗

arXiv2022

Vacuum Decay Induced by Quantum Fluctuations

We treat the effects of quantum field fluctuations on the decay of a meta-stable state of a self-coupled scalar field. We consider two varieties of field fluctuations and their potential effects in a semiclassical description. The first are the fluctuations of the time derivative a free massive scalar field operator, which has been averaged over finite regions of space and time. These fluctuations obey a Gaussian probability distribution. A sufficiently large fluctuation is assumed to produce an effect analogous to a classical initial field velocity, which can cause a finite region to fly over the barrier separating the meta-stable state from the stable vacuum state. Here we find a contribution to the decay rate which is comparable to the decay rate by quantum tunneling, as computed in an instanton approximation. This result is consistent with those of other authors. We next consider the effects of the fluctuations of operators which are quadratic in the time derivative of the free scalar field. The quadratic operator is also averaged over finite regions of space and of time. Now the probability distribution for the averaged operator falls more slowly than an exponential function, allowing for the possibility of very large fluctuations. We find a contribution to the decay rate which is much larger than those coming from either quantum tunneling or linear field fluctuations, and hence appears to be the dominant decay mechanism.

hep-th↗

arXiv2018

Vacuum Radiation Pressure Fluctuations and Barrier Penetration

We apply recent results on the probability distribution for quantum stress tensor fluctuations to the problem of barrier penetration by quantum particles. The probability for large stress tensor fluctuations decreases relatively slowly with increasing magnitude of the fluctuation, especially when the quantum stress tensor operator has been averaged over a finite time interval. This can lead to large vacuum radiation pressure fluctuations on charged or polarizable particles, which can in turn push the particle over a potential barrier. The rate for this effect depends sensitively upon the details of the time averaging of the stress tensor operator, which might be determined by factors such as the shape of the potential. We make some estimates for the rate of barrier penetration by this mechanism and argue that in some cases this rate can exceed the rate for quantum tunneling through the barrier. The possibility of observation of this effect is discussed.

quant-ph↗

arXiv2015

Quantum Electric Field Fluctuations and Potential Scattering

Some physical effects of time averaged quantum electric field fluctuations are discussed. The one loop radiative correction to potential scattering are approximately derived from simple arguments which invoke vacuum electric field fluctuations. For both above barrier scattering and quantum tunneling, this effect increases the transmission probability. It is argued that the shape of the potential determines a sampling function for the time averaging of the quantum electric field operator. We also suggest that there is a nonperturbative enhancement of the transmission probability which can be inferred from the probability distribution for time averaged electric field fluctuations.

hep-th↗

arXiv2011

Path Integral and Effective Hamiltonian in Loop Quantum Cosmology

We study the path integral formulation of Friedmann universe filled with a massless scalar field in loop quantum cosmology. All the isotropic models of $k=0,+1,-1$ are considered. To construct the path integrals in the timeless framework, a multiple group-averaging approach is proposed. Meanwhile, since the transition amplitude in the deparameterized framework can be expressed in terms of group-averaging, the path integrals can be formulated for both deparameterized and timeless frameworks. Their relation is clarified. It turns out that the effective Hamiltonian derived from the path integral in deparameterized framework is equivalent to the effective Hamiltonian constraint derived from the path integral in timeless framework, since they lead to same equations of motion. Moreover, the effective Hamiltonian constraints of above models derived in canonical theory are confirmed by the path integral formulation.

gr-qc↗