arXiv subjects

Helios Y. Li

Publications and source records attributed to Helios Y. Li.

3 recordsLinked to original sources

arXiv2025

Generalized causality constraint based on duality symmetry reveals untapped potential of sound absorption

Causality constraints are known to bind sound absorption to a limit that can only be achieved by optimizing the system bandwidth for a specific material thickness. This limit is defined on the assumption of a one-port system, generally causing duality symmetry to be overlooked. Here, we define a generalized causality constraint of sound absorption by investigating reflection and transmission of a two-port hybrid monopole-dipole resonator. With our theory, we show that the absorption limit is approached by relying on the well-established critical coupling as well as by matching effective compressibility and density. We experimentally show that the designed resonator absorbance follows the duality symmetry condition embodied in the large bandwidth reported. A comparison with a traditional foam liner and other competitive works further validates our findings, confirming an intrinsic connection between duality symmetry and scattering causality. Our results untap unexplored absorption potential in broadband acoustic metamaterials.

physics.app-ph↗

arXiv2025

Tailoring 4H-SiC Surface Electronic States by Atomic-Layer Deposition for Ideal Peta-Ohm Resistors

High resolution resistors capable of detecting minuscule currents are vital for advanced sensors, but existing off-shelf models struggle with inconsistent resistance under varying voltages. The underlying physics of this issue is rooted in unstable surface charges and intrinsic inhomogeneity of surface potential caused by spontaneous polarization (SP) in commercial semi-insulating silicon carbide (SiC) devices. In this work, we found that coating SiC surfaces with an ultrathin zinc oxide layer immobilizes the dangling surface charges in place and balances the natural electric field of the material, ensuring stable resistance even at extreme voltages up to 1000 V. The resulting SiC resistor maintains a record-high resistance of one peta-ohm (10^15 Ω) with negligible voltage fluctuations, outperforming conventional options. Additionally, these devices can switch states when exposed to light or heat, making them dual-purpose tools for ultra-sensitive measurements and sensors. This breakthrough combines high stability, scalability for mass production, and multifunctionality, opening doors to next-generation precision technologies in fields like quantum sensing and environmental monitoring.

physics.app-ph↗

arXiv2025

Phase amplification microscopy with femtometer-level accuracy

We demonstrate a major breakthrough in laser interferometry and microscopy achieving femtometer-level measurement accuracy and beyond, termed Phase Amplification microscopy ({\Phi}-Amp). By exploiting the native silicide substrate as a phase cavity, our phase-gain theory predicts that weak sub-atomic phase signals can be magnified over 1000-fold, thus bypassing the shot-noise limit. We experimentally achieved a 158.2-fold phase gain for graphene in ambient air, corresponding ~ 730 femtometer accuracy. To fully unleash the potential of {\Phi}-Amp for atomic fabrication and quantum measurement, we quantified interlayer spacing differences between AB-stacked and 30-degree-twisted bilayer graphene to be ~ 0.77 Angstroms and further detected atomic impurities and defects on large atomic structures. As the first wide-field metrology tool, we envision {\Phi}-Amp may accelerate the scaling up of atomic quantum devices.

physics.optics↗