Prof. Xiang Zhang Profile

Prof. Xiang Zhang

Chair/Director & Professor at Univ of California Berkeley

SPIE Involvement:

Conference Program Committee | Author

Publications (46)

Proceedings Article | 9 September 2019

Light-matter interactions in perovskites (Conference Presentation)

Wei Bao, Xiaoze Liu, Sui Yang, Fei Xue, Allan MacDonald, Yuan Wang, Xiang Zhang

Proc. SPIE. 11081, Active Photonic Platforms XI

KEYWORDS: Electronics, Chemical species, Molecules, Control systems, Energy harvesting, Light-matter interactions, Molecular electronics, Photonic nanostructures, Catalysis, Perovskite

Read Abstract +

Proceedings Article | 8 March 2019

Two-way asymmetric flat optics with nonlinear metasurfaces (Conference Presentation)

Nir Shitrit, Jeongmin Kim, David Barth, Hamidreza Ramezani, Yuan Wang, Xiang Zhang

Proc. SPIE. 10928, High Contrast Metastructures VIII

KEYWORDS: Optical components, Electronics, Wavefronts, Refraction, Nonlinear optics, Diodes, Free space optics, Acoustics, Optical isolators, Phase shifts

Read Abstract +

Proceedings Article | 4 March 2019

The interplay of magnetism and chirality in van der Waals crystals (Conference Presentation)

Shoufeng Lan, Xiang Zhang

Proc. SPIE. 10927, Photonic and Phononic Properties of Engineered Nanostructures IX

KEYWORDS: Metamaterials, Thin films, Molecules, Crystals, Organisms, Magnetism, Physics, Dichroic materials, Anisotropy

Read Abstract +

Proceedings Article | 27 February 2019

Experimental observation of chiral phonons in monolayer WSe2

Hanyu Zhu, Jun Yi, Ming-Yang Li, Jun Xiao, Lifa Zhang, Chih-Wen Yang, Sui Yang, Robert Kaindl, Lain-Jong Li, Yuan Wang, Xiang Zhang

Proc. SPIE. 10916, Ultrafast Phenomena and Nanophotonics XXIII

KEYWORDS: Polarization, Scattering, Luminescence, Photons, Materials science, Infrared radiation, Phonons, Raman scattering, Picosecond phenomena, Absorption

Read Abstract +

Proceedings Article | 22 February 2019

Oblique lightsheet STORM for tissue samples

Jeongmin Kim, Michal Wojcik, Yuan Wang, Ke Xu, Xiang Zhang

Proc. SPIE. 10884, Single Molecule Spectroscopy and Superresolution Imaging XII

KEYWORDS: Super resolution, Tissues, Microscopy, Super resolution microscopy

Read Abstract +

Proceedings Article | 18 September 2018

Valley-optomechanics in a monolayer semiconductor (Conference Presentation)

King Yan Fong, Hao-Kun Li, Hanyu Zhu, Quanwei Li, Siqi Wang, Sui Yang, Yuan Wang, Xiang Zhang

Proc. SPIE. 10733, Quantum Photonic Devices 2018

KEYWORDS: Semiconductors, Modulation, Resonators, Polarization, Mechanics, Magnetism, Physics, Raman spectroscopy, Data processing, Information technology

Read Abstract +

The interaction of macroscopic mechanical object with electron charge and spin plays a vital role in today’s information technology and fundamental studies of the quantum-classical boundary. Recently emerged valleytronics encodes information to the valley degree-of-freedom and promises exciting applications in communication and computation. Exploring the interplay between the valley physics and macroscopic mechanics will bring new perspectives for valley information processing and exploration of the quantum-classical boundary. Recently discovered two-dimensional (2D) transition metal dichalcogenides (TMDs) provide an appealing platform to explore valley-mechanical interaction. Their honeycomb lattice supports two valleys (namely K and K’) and thus forms a spin-like binary system called valley-pseudospin. The broken inversion symmetry together with the strong spin-orbit coupling give rise to a unique optical selection rule, which provides a powerful tool for optical generation and manipulation of the valley. On the other hand, nano-mechanical systems made of 2D materials have shown high mechanical strength, high quality-factor, and extraordinary mass and force sensitivities. Their extremely small mass also leads to large quantum zero-point motion and thus facilitates its use in quantum system. Because of the broken inversion symmetry in monolayer TMDs, electrons in the K and K’ valleys possess total magnetic moments that are equal in magnitude but opposite in sign. When a magnetic field gradient is applied perpendicular to the monolayer, it experiences a net force whose direction depends on which valley is populated and therefore allows transduction of the valley information (K or K’) into the mechanical motion (upward or downward displacement). We fabricate the valley-resonators by dry-transferring an exfoliated monolayer MoS2 onto pre-patterned square hole structures, which are conformally coated with a film of high permeability permalloy (Ni/Fe). Under an external magnetic field, the permalloy film distorts the field and generates a strong local magnetic field gradient. For an applied magnetic field of 26 mT, the magnetic field gradient in the central region of the suspended MoS2 reaches ~4000 T/m. The monolayer nature of the MoS2 membrane is confirmed by Raman and photoluminescence (PL) spectroscopy. A PL scan across the sample shows that the emission from the suspended regions is much stronger than that from the metal substrate, which confirms that the membrane is freestanding. The square structure has a lateral dimension of 5.2 × 5.2 um^2 and the resonator has an effective mass of 21 fg. The mechanical resonance frequency is ~35.7 MHz and the quality factor is 22,000 at 30 K. We observe the valley-mechanical actuation of the monolayer MoS2 at low temperature. We detect the resonator motion by an optical interferometric scheme using a probe laser (654 nm) and excite the K and K’ valleys alternatingly by modulating the polarization of the pump laser (633 nm) between left- and right-circular (LCP and RCP) while keeping the optical intensity constant. This exerts an oscillating push-pull force to drive the resonator. The measured displacement of the resonator shows a clear Lorentzian response. Meanwhile, a linearly-polarized pump light shows no driving effect because it equally populates both valleys and thus results in zero net force. The mechanical displacement shows an opposite phase when the pump laser polarization is switched to opposite helicity, which confirms that the excitation of carriers at different valleys exerts opposite forces onto the monolayer. In the measurement, the polarization modulation frequency is close to the mechanical resonance (~35.7 MHz) which is much slower than the decay of the valley carriers, whose timescale is in the range of picoseconds to a few nanoseconds. Therefore, the valley carrier population adiabatically follows the polarization modulation. The probe light is kept linearly-polarized throughout the measurement to eliminate its effect on the net valley population. Utilizing the fact that the direction of the force depends on which valley is populated, we demonstrate transduction of the valley information into the mechanical state of the nano-resonator. We examine the mechanical quadratures of the device when it is resonantly driven by opposite valley population. Two distinct mechanical states of opposite phase are clearly resolved within the measurement uncertainty and the confidence level of differentiating the two states is close to 100%. This result demonstrates that the valley information of the monolayer is unambiguously transferred into the mechanical states. In conclusion, our experiment demonstrates direct transduction of valley information to mechanical states of a MoS2 monolayer resonator. The valley-mechanical interaction lays the foundation for a new class of valley-controlled mechanical devices. It also facilitates hybridization of valley pseudospin with other quantum information carriers such as two-level qubits and microwave photons.

Proceedings Article | 17 September 2018

Chiral domain-boundary magnetoplasmons: magnetically cast topological edge excitations in edgeless electron gas (Conference Presentation)

Dafei Jin, Yang Xia, Thomas Christensen, Siqi Wang, Kingyan Fong, Matthew Freeman, Geoffrey Gardner, Saeed Fallahi, Qing Hu, Yuan Wang, Lloyd Engel, Michael Manfra, Nicholas Fang, Xiang Zhang

Proc. SPIE. 10721, Active Photonic Platforms X

KEYWORDS: Photonics

Read Abstract +

Proceedings Article | 17 September 2018

Physics and controllability of phase transitions in two-dimensional materials (Conference Presentation)

Ying Wang, Xiang Zhang

Proc. SPIE. 10721, Active Photonic Platforms X

KEYWORDS: Second-harmonic generation, Optical properties, Microscopy, Crystals, Physics, Doping, Raman spectroscopy, Optoelectronics, Harmonic generation, Molybdenum

Read Abstract +

Proceedings Article | 14 March 2018

Control of coherently-coupled exciton-polaritons in monolayer tungsten disulphide (Conference Presentation)

Xiaoze Liu, Wei Bao, Quanwei Li, Chad Ropp, Yuan Wang, Xiang Zhang

Proc. SPIE. 10534, 2D Photonic Materials and Devices

Read Abstract +

Proceedings Article | 14 March 2018

2D valleytronics: from material exploration to device engineering (Conference Presentation)

Xiang Zhang

Proc. SPIE. 10541, Photonic and Phononic Properties of Engineered Nanostructures VIII

Read Abstract +

Proceedings Article | 14 March 2018

Observation of solid-state Rydberg exciton polariton and its condensate in a single-crystal perovskite (Conference Presentation)

Wei Bao, Xiaoze Liu, Fan Zheng, Yang Xia, Mervin Zhao, Jeongmin Kim, Sui Yang, Ying Wang, Yuan Wang, Lin-Wang Wang, Xiang Zhang

Proc. SPIE. 10526, Physics and Simulation of Optoelectronic Devices XXVI

Read Abstract +

Proceedings Article | 22 September 2017

Quantum self-organized criticality and nonequilibrium light localization (Conference Presentation)

Kosmas Tsakmakidis, Pankaj Jha, Xiang Zhang, Hatice Altug, Robert Boyd

Proc. SPIE. 10345, Active Photonic Platforms IX

KEYWORDS: Photons, Complex systems, Physics, Geology, Biology, Nanophotonics, Dynamical systems, Technetium, Probability theory, Thermodynamics

Read Abstract +

Proceedings Article | 11 May 2017

Experimental observation of wave modulation and Dirac cone in acoustic double zero refractive index metamaterials (Conference Presentation)

Chengzhi Shi, Marc Dubois, Xuefeng Zhu, Yuan Wang, Xiang Zhang

Proc. SPIE. 10170, Health Monitoring of Structural and Biological Systems 2017

KEYWORDS: Metamaterials, Refractive index, Modulation, Optical testing, Wave propagation, Structural design, Waveguide modes, Acoustics, Current controlled current source

Read Abstract +

Proceedings Article | 9 November 2016

Molding the spin flow of light in valley photonic crystals (Conference Presentation)

Jian-Wen Dong, Xiao-Dong Chen, Hanyu Zhu, Yuan Wang, Xiang Zhang

Proc. SPIE. 9918, Metamaterials, Metadevices, and Metasystems 2016

KEYWORDS: Metamaterials, Sun, Modulation, Dispersion, Crystals, Physics, Photonic crystals, Optoelectronics, Optoelectronic devices, Solid state physics

Read Abstract +

Proceedings Article | 9 November 2016

Macroscale transformation optics enabled by photoelectrochemical etching of silicon (Conference Presentation)

David Barth, Christopher Gladden, Alessandro Salandrino, Kevin O'Brien, Ziliang Ye, Michael Mrejen, Yuan Wang, Xiang Zhang

Proc. SPIE. 9918, Metamaterials, Metadevices, and Metasystems 2016

KEYWORDS: GRIN lenses, Optical components, Refractive index, Optical design, Visible radiation, Optical properties, Etching, Dielectrics, Silicon, Electromagnetism

Read Abstract +

Proceedings Article | 9 November 2016

Parity-time symmetric optical cavities (Conference Presentation)

Zi Jing Wong, Xiang Zhang

Proc. SPIE. 9920, Active Photonic Materials VIII

KEYWORDS: Modulation, Optical resonators, Microrings, Resonance enhancement, Current controlled current source, Absorption

Read Abstract +