arXiv subjects

T. Jiang

Publications and source records attributed to T. Jiang.

8 recordsLinked to original sources

arXiv2026

Room-temperature local strain control of moir\'e excitons in MoS$_2$/WSe$_2$ heterobilayers

Moir\'e superlattices in heterobilayers of atomically thin transition metal dichalcogenides provide a versatile platform for exploring quantum many-body physics as they can trap excitons, leading to the formation of quantized moir\'e exciton states. However, such moir\'e excitons have been predominantly studied at cryogenic temperatures, which severely limits their practical applications. Here, we demonstrate room-temperature activation and control of moir\'e excitons in MoS$_2$/WSe$_2$ heterobilayers using local strain engineering. Applying mechanical strain with a modified atomic force microscopy tip, we observe a series of resonances attributed to interlayer exciton states confined in the moir\'e potential. Power-dependent photoluminescence measurements elucidate the population dynamics of the moir\'e exciton states, while controlled local strain enables continuous tuning of their emission wavelength to the center of the second telecom window. We provide a theoretical model that captures all experimentally observed features, including the unconventional spectral shape of the moir\'e exciton emission. Our findings establish local tip-induced strain as a powerful tool for the on-demand manipulation of moir\'e excitons, paving the way for room-temperature quantum excitonic devices.

cond-mat.mes-hall↗

arXiv2026

Magnetic switching of self-hybridized exciton-polaritons in CrSBr photonic crystal slabs

Layered van der Waals antiferromagnet CrSBr supports strong light--matter coupling and formation of magnetically tunable exciton-polaritons, yet active magnetic control over polariton propagation direction has remained elusive. Here, we investigate self-hybridized exciton-polaritons in photonic crystal slabs fabricated from CrSBr flakes and their evolution across the antiferromagnetic-to-ferromagnetic spin-flip transition induced by moderate in-plane magnetic fields. Using angle-resolved reflectance and photoluminescence spectroscopy supported by modeling, we show that the polariton energy continuously tracks the layer-by-layer magnetization switching, revealing a gradual redistribution of oscillator strength from antiferromagnetic to ferromagnetic excitons near the critical field. Most notably, we demonstrate that the sign of the polariton group velocity can be reversed by a small change in the external magnetic field of only 40 mT, resulting in complete switching of the polariton propagation direction. Our results establish CrSBr photonic crystal slabs as a platform for magnetically controlled polariton transport, opening opportunities for active integrated photonic and polaritonic devices.

physics.optics↗

arXiv2024

Quantum geometry embedded in unitarity of evolution: revealing its impacts as geometric oscillation and dephasing in spin resonance and crystal bands

Quantum Hall effects provide intuitive ways of revealing the topology in crystals, i.e., each quantized "step" represents a distinct topological state. Here, we seek a counterpart for "visualizing" quantum geometry, which is a broader concept. We show how geometry emerges in quantum as an intrinsic consequence of unitary evolution, composing a frame work compatible with quantum metric and independent of specific details or approximations, suggesting quantum geometry may have widespread applicability. Indeed, we exemplify geometric observables, such as oscillation, dephasing, in spin and band scenarios. Anomalies, supported by both analytic and numerical solutions, underscore the advantages of adopting a geometric perspective, potentially yielding distinguishable experimental signatures.

quant-ph↗

arXiv2024

Coherent Transfer of Lattice Entropy via Extreme Nonlinear Phononics in Metal Halide Perovskites

Entropy transfer in metal halide perovskites, characterized by significant lattice anharmonicity and low stiffness, underlies the remarkable properties observed in their optoelectronic applications, ranging from solar cells to lasers. The conventional view of this transfer involves stochastic processes occurring within a thermal bath of phonons, where lattice arrangement and energy flow from higher to lower frequency modes. Here we unveil a comprehensive chronological sequence detailing a conceptually distinct, coherent transfer of entropy in a prototypical perovskite CH$_3$NH$_3$Pbl$_3$. The terahertz periodic modulation imposes vibrational coherence into electronic states, leading to the emergence of mixed (vibronic) quantum beat between approximately 3 THz and 0.3 THz. We highlight a well-structured, bi-directional time-frequency transfer of these diverse phonon modes, each developing at different times and transitioning from high to low frequencies from 3 to 0.3 THz, before reversing direction and ascending to around 0.8 THz. First-principles molecular dynamics simulations disentangle a complex web of coherent phononic coupling pathways and identify the salient roles of the initial modes in shaping entropy evolution at later stages. Capitalizing on coherent entropy transfer and dynamic anharmonicity presents a compelling opportunity to exceed the fundamental thermodynamic (Shockley-Queisser) limit of photoconversion efficiency and to pioneer novel optoelectronic functionalities.

cond-mat.mtrl-sci↗

arXiv2021

Lattice points in stretched finite type domains

We study an optimal stretching problem, which is a variant lattice point problem, for convex domains in $\mathbb{R}^d$ ($d\geq 2$) with smooth boundary of finite type that are symmetric with respect to each coordinate hyperplane/axis. We prove that optimal domains which contain the most positive (or least nonnegative) lattice points are asymptotically balanced.

math.NT↗

arXiv2020

Onset of Cosmic Reionization: Evidence of An Ionized Bubble Merely 680 Myrs after the Big Bang

While most of the inter-galactic medium (IGM) today is permeated by ionized hydrogen, it was largely filled with neutral hydrogen for the first 700 million years after the Big Bang. The process that ionized the IGM (cosmic reionization) is expected to be spatially inhomogeneous, with fainter galaxies playing a significant role. However, we still have only a few direct constraints on the reionization process. Here we report the first spectroscopic confirmation of two galaxies and very likely a third galaxy in a group (hereafter EGS77) at redshift z = 7.7, merely 680 Myrs after the Big Bang. The physical separation among the three members is < 0.7 Mpc. We estimate the radius of ionized bubble of the brightest galaxy to be about 1.02 Mpc, and show that the individual ionized bubbles formed by all three galaxies likely overlap significantly, forming a large yet localized ionized region, which leads to the spatial inhomogeneity in the reionization process. It is striking that two of three galaxies in EGS77 are quite faint in the continuum, thanks to our selection of reionizing sources using their Lyman-alpha line emission. Indeed, one is the faintest spectroscopically confirmed galaxy yet discovered at such high redshifts. Our observations provide direct constraints in the process of cosmic reionization, and allow us to investigate the properties of sources responsible for reionizing the universe.

astro-ph.GA↗

arXiv2014

Human Bipedalism, Evolved from Arboreal Locomotion of Two-arm Brachiation

Among all kinds of apes, only gibbons have the slim body as human. Gibbons can move in the forest by cross arm swing, what was the locomotion mode of our arboreal ancestor. Since our ancestor had much heavier body but weaker arms than gibbons, we suppose they had to move with two arm brachiation. Such mode of locomotion can account reasonably for the transition to bipedalism. Firstly, it needed our ancestor to straighten knee and hip joints and flex their lumbar spine. secondly, it evolved the feet of our ancestor with longitudinal arche. And most importantly, it made the ratio of the length of the upper limbs to that of the lower limbs unsuitable for quadruped walking.

q-bio.PE↗

arXiv2014

Human Hunting Evolved as an Adaptated Result of Arboreal Locomotion Model of Two-arm Brachiation

Various fossil evidences show that hunting is one of major means of ancient human to get foods. But the running speed of our ancestors was much slower than quadruped animals, and they did not have sharp claws and canines. So, they have to rely heavily on stone and wooden tools when they hunting or fighting against other predators, which are very different from the hunting behaviors of other carnivores. There are mainly two types of attack and defense action during human hunting, front or side hit with a wooden stick in hands and stone or wooden spears throwing, and throwing had play an important role in human evolution process. But there is almost no work to study the why only human chose to hunting by this way. Here we suppose that ancient human chose two-arm brachiation as main arboreal locomotion mode because of their suitable body weight. Human body traits include slim body, parallel arranged scapulas, long thumb and powerful grip ability are all evolved as results of two arm brachiation. The relevant adaptive evolution of the shoulder bone structure make human arms with a large range of movement and the long thumb makes human activities to be more accurate and controllable. These are two important body structure advantages of ancient human which makes them could get from arboreal life into a whole new hunting and fighting stage.

q-bio.PE↗