publications

2026

1. AIP Advances

   Reservoir computing using a Si-integrated electro-optic oxide: A numerical study

   Xiaoru Zhang and Alexander A. Demkov

   AIP Advances, May 2026

   Abs DOI

   Reservoir computing is a compelling neuromorphic architecture due to its natural compatibility with many physical systems. Among available implementations, the electro-optic reservoir, where an optical delay feedback loop serves as the reservoir, offers energy-efficient computation without the need for a separate memory, making its chip-scale implementation very appealing. Barium titanate, with its exceptionally large Pockels coefficient, has recently enabled significant advances in compact electro-optic modulators, positioning it as a suitable platform for such a chip-scale electro-optic reservoir. Here, we numerically investigate the performance of an electro-optic reservoir under the practical constraints of a Si-integrated photonic design. We also introduce a method of constructing reservoir states that results in a significant performance improvement. Furthermore, we demonstrate the superior energy efficiency of barium titanate-based devices, owing to their very efficient electro-optic modulation. Our results show that compact, energy-efficient electro-optic reservoirs are feasible using barium titanate-based integrated Si photonic devices.

2. Phys. Rev. Applied

   Gigahertz quantum spin Hall effect in nanoelectromechanical phononic crystals

   Yue Jiang, Shizai Chu, Xiaoru Zhang, and 4 more authors

   Physical Review Applied, May 2026

   Accepted 2 September 2026

   DOI
3. Under review

   How to Choose a Gate Dielectric for Rutile GeO\textsubscript2

   Xiaoru Zhang and Alexander A. Demkov

   Physical Review B, May 2026

   Manuscript under review

2024

1. Device

   Klein tunneling of gigahertz elastic waves in nanoelectromechanical metamaterials

   Daehun Lee, Yue Jiang, Xiaoru Zhang, and 5 more authors

   Device, May 2024

   Abs DOI

   The Klein tunneling effect describes the transmission of a relativistic particle with normal incidence through an energy barrier. It has been observed and tested in various electronic, photonic, and phononic systems, but its potential in guiding and filtering classical waves in the ultrahigh frequency regime has not been explored. Here, we report the realization of acoustic Klein tunneling in a nanoelectromechanical metamaterial system operating at gigahertz frequencies. The piezoelectric potential profiles are obtained by transmission-mode microwave impedance microscopy, from which reciprocal-space maps are extracted. The transmission rate of normally incident elastic waves is near unity in the Klein tunneling regime and drops significantly outside this frequency range, consistent with microwave network analysis. Strong angular dependent transmission is possible by controlling the launching angle of the emitter interdigital transducer. This work broadens the horizon for exploiting high-energy-physics phenomena for practical circuit applications in both classical and quantum regimes.

2022

1. Adv. Photonics Res.

   Detection and demultiplexing of cylindrical vector beams enabled by rotational Doppler effect

   Xiaoru Zhang, Junliang Jia, Kaiyi Zhai, and 3 more authors

   Advanced Photonics Research, May 2022

   Abs DOI

   Cylindrical vector beams (CVBs) detection is of vital significance in various kinds of studies such as particle observation and mode-division multiplexing (MDM). Herein, a comprehensive detection of CVBs based on the rotational Doppler effect (RDE) including analysis of topological charge (TC), relative amplitude module, and phase for superimposed mode bases is realized. A mode demultiplexing scheme is constructed through the complex amplitude of the harmonic terms in the beating signal. The method resolves both absolute values and signs of the TC of CVB simultaneously, which cannot be simply realized by existing polarization examination techniques. It may be of big potential in related research since an efficient, quantitative, and complete scheme to detect CVBs is verified starting from this work.