arXiv subjects

Yu-Han Gao

Publications and source records attributed to Yu-Han Gao.

4 recordsLinked to original sources

arXiv2026

Meson mass spectrum in isospin QCD medium from the $N_f=2+1$ quark-meson model

We study phase structures, meson mass spectra, and sound velocities at finite temperature and density in QCD with isospin chemical potential ($\mu_I$). We employ the quark-meson model with $N_f=2+1$, incorporating the Kobayashi-Maskawa-'t Hooft type coupling to capture dynamical effects of the $U(1)_A$ axial anomaly. Within the mean-field approximation at quark one-loop, we analyze the onset of pion condensation, which manifests as a second-order phase transition at low temperatures and may exhibit a first-order behavior at higher temperatures within this approximation. We examine the corresponding mass spectra of scalar and pseudoscalar singlet-octet mesons, in which the $\pi_+$ mass is exactly massless in the superfluid phase due to its Nambu-Goldstone boson nature. The neutral pion mass is, meanwhile, found to exhibit a strictly linear growth with $\mu_I$ in the pion condensed phase. We also investigate the isothermal squared sound velocity and identify characteristic structures associated with the phase transitions. Furthermore, we highlight how enhanced $U(1)_A$ anomaly effects facilitate the pion condensate to generate a less-pronounced sound velocity peak in cold medium. Our findings are expected to provide future lattice simulations with useful information on meson mass spectra from symmetry aspects.

hep-ph↗

arXiv2026

Ultrafast Demagnetization Governed by Spin Fluctuations in CaRuO$_{3}$/SrTiO$_{3}$ Superlattice

For ultrafast magnetization switching devices, critical slowing down in conventional ferromagnets near their Curie temperature constitutes a key challenge that must be overcome. In contrast to this typical behavior, we observe an anomalous acceleration of demagnetization in CaRuO$_{3}$/SrTiO$_{3}$ superlattices, a moderately correlated weak itinerant ferromagnet. The demagnetization rate increases with rising temperature, pump fluence, and applied magnetic field. To explain these anomalous phenomena, we develop a phenomenological model integrating the three-temperature model with self-consistent renormalization theory. Because the intrinsic gradient magnetism of the superlattice suppresses the typical divergence of specific heat, the conventional thermodynamic bottleneck is bypassed. Our model reveals that this decoupling enables the ultrafast dynamics to be predominantly governed by the spin-fluctuation-driven enhancement of the electron-spin scattering vertex. Our work demonstrates how spatial inhomogeneity can decouple macroscopic thermodynamic singularities from microscopic scattering processes, offering a new paradigm for manipulating ultrafast spin dynamics in correlated quantum materials. The pronounced sensitivity of the demagnetization rate to external parameters further suggests the potential for designing highly tunable ultrafast spintronic devices that leverage enhanced fluctuations near the magnetic instability.

cond-mat.mtrl-sci↗

arXiv2026

Polyakov-loop potential of accelerated gluonic matter and thermodynamic subtleties

We study the one-loop Polyakov-loop effective potential in pure gluonic matter under constant acceleration. We perform the computation in both the Euclidean Rindler spacetime and the optical spacetime, which are related via a conformal transformation. The results from the two formulations correspond to physically different observables, and we clarify their connection to specific components of the energy-momentum tensor. This identification resolves a discrepancy previously noted for fields on conical backgrounds. For the Polyakov-loop expectation value, we should minimize the effective potential computed in the optical metric formulation, which concludes that real acceleration strengthens deconfining properties. We also discuss analytic continuation from real to imaginary acceleration and find a perturbatively confined phase. We point out some suggestive similarities and differences between systems under imaginary acceleration and imaginary rotation.

hep-ph↗

arXiv2026

Ultrafast Magneto-optical Fingerprints of Altermagnetism in MnTe

Recently identified altermagnets exhibit a distinctive dual-space nature: they possess spin-split electronic bands akin to ferromagnets in momentum space while maintaining the fully compensated magnetization of antiferromagnets in real space. This inherent duality, originating from the same crystal symmetry, gives rise to various intriguing physical phenomena unique to altermagnets. Consequently, a robust and efficient experimental signature capable of revealing this dual character is critically needed. The magneto-optical Kerr and Voigt effects, given their high sensitivity to ferromagnetism and antiferromagnetism, respectively, are ideally suited to probe this duality. Here, using time-resolved pump-probe magneto-optical measurements, we report the coexistence of pronounced Kerr and Voigt effects in the altermagnet MnTe. Combining the magnetization measurement and first-principles calculations, we demonstrate that the Kerr effect originates from the intrinsic Berry curvature of altermagnetism distribution in momentum space, while the Voigt effect arises from an anisotropic permittivity induced by the in-plane N\'eel order in real space, directly revealing the dual-space nature of altermagnets. Furthermore, the transient Kerr signal exhibits faster relaxation dynamics than the transient Voigt signal, underscoring their distinct origins in Berry curvature and N\'eel order, respectively. These findings establish transient magneto-optical responses as distinctive fingerprints of altermagnetism and position altermagnets as promising platforms for manipulating magneto-optical phenomena in ultrafast spin optoelectronics.

cond-mat.mtrl-sci↗