1
|
Hong YL, Tang GH, Peng RW, Fan RH, Ma ZL, Wang Z, Jiang Y, Chen LD, Wang M. Direct observation of terahertz topological valley transport. OPTICS EXPRESS 2022; 30:14839-14850. [PMID: 35473219 DOI: 10.1364/oe.454750] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Accepted: 03/30/2022] [Indexed: 06/14/2023]
Abstract
Topological photonics offers the possibility of robust transport and efficiency enhancement of information processing. Terahertz (THz) devices, such as waveguides and beam splitters, are prone to reflection loss owing to their sensitivity to defects and lack of robustness against sharp corners. Thus, it is a challenge to reduce backscattering loss at THz frequencies. In this work, we constructed THz photonic topological insulators and experimentally demonstrated robust, topologically protected valley transport in THz photonic crystals. The THz valley photonic crystal (VPC) was composed of metallic cylinders situated in a triangular lattice. By tuning the relevant location of metallic cylinders in the unit cell, mirror symmetry was broken, and the degenerated states were lifted at the K and K' valleys in the band structure. Consequently, a bandgap of THz VPC was opened, and a nontrivial band structure was created. Based on the calculated band structure, THz field distributions, and valley Berry curvature, we verified the topological phase transition in such type of THz photonic crystals. Further, we showed the emergence of valley-polarized topological edge states between the topologically distinct VPCs. The angle-resolved transmittance measurements identified the bulk bandgap in the band structure of the VPC. The measured time-domain spectra demonstrated the topological transport of valley edge states between distinct VPCs and their robustness against bending and defects. Furthermore, experiments conducted on a topological multi-channel intersectional device revealed the valley-polarized characteristic of the topological edge states. This work provides a unique approach to reduce backscattering loss at the THz regime. It also demonstrates potential high-efficiency THz functional devices such as topologically protected beam splitters, low-loss waveguides, and robust delay lines.
Collapse
|
2
|
Bahrami M, Vasilopoulos P. Inhomogeneous linear responses and transport in armchair graphene nanoribbons in the presence of elastic scattering. NANOTECHNOLOGY 2022; 33:195201. [PMID: 35090140 DOI: 10.1088/1361-6528/ac4fe2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Accepted: 01/28/2022] [Indexed: 06/14/2023]
Abstract
Within linear-response theory we derive a response function that thoroughly accounts for the influence of elastic scattering and is valid beyond the long-wavelength limit. We use the theory to evaluate the polarization function and the conductivity in metallic armchair graphene nanoribbons in the Lindhard approximation for intra-band and inter-band transitions and for a relaxation timeτthat is not constant. We obtain a logarithmic behaviour in the scattering-independent polarization function not only for intra-band transitions, as is usually the case for one-dimensional systems, but also for inter-band transitions. Modifying the screening wave vector and the impurity density in the long-wavelength limit strongly influences the relaxation time. In contrast, for large wave vectors, this modification leads to a conservative value ofτ. We show that the imaginary part of the impurity-dependent conductivity varies with the wave vector while its scattering-independent part exists only for a single value of the wave vector.
Collapse
Affiliation(s)
- Mousa Bahrami
- Bita Quantum AI Inc., 2021 Av. Atwater, Montréal, Québec, H3H 2P2, Canada
| | - Panagiotis Vasilopoulos
- Department of Physics, Concordia University, 7141 Sherbrooke Ouest, Montréal, Québec, H4B 1R6, Canada
| |
Collapse
|
3
|
Xiong L, Li Y, Jung M, Forsythe C, Zhang S, McLeod AS, Dong Y, Liu S, Ruta FL, Li C, Watanabe K, Taniguchi T, Fogler MM, Edgar JH, Shvets G, Dean CR, Basov DN. Programmable Bloch polaritons in graphene. SCIENCE ADVANCES 2021; 7:eabe8087. [PMID: 33962941 PMCID: PMC8104864 DOI: 10.1126/sciadv.abe8087] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Accepted: 03/19/2021] [Indexed: 05/10/2023]
Abstract
Efficient control of photons is enabled by hybridizing light with matter. The resulting light-matter quasi-particles can be readily programmed by manipulating either their photonic or matter constituents. Here, we hybridized infrared photons with graphene Dirac electrons to form surface plasmon polaritons (SPPs) and uncovered a previously unexplored means to control SPPs in structures with periodically modulated carrier density. In these periodic structures, common SPPs with continuous dispersion are transformed into Bloch polaritons with attendant discrete bands separated by bandgaps. We explored directional Bloch polaritons and steered their propagation by dialing the proper gate voltage. Fourier analysis of the near-field images corroborates that this on-demand nano-optics functionality is rooted in the polaritonic band structure. Our programmable polaritonic platform paves the way for the much-sought benefits of on-the-chip photonic circuits.
Collapse
Affiliation(s)
- Lin Xiong
- Department of Physics, Columbia University, New York, NY 10027, USA
| | - Yutao Li
- Department of Physics, Columbia University, New York, NY 10027, USA
| | - Minwoo Jung
- Department of Physics, Cornell University, Ithaca, NY 14853, USA
| | - Carlos Forsythe
- Department of Physics, Columbia University, New York, NY 10027, USA
| | - Shuai Zhang
- Department of Physics, Columbia University, New York, NY 10027, USA
| | | | - Yinan Dong
- Department of Physics, Columbia University, New York, NY 10027, USA
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA
| | - Song Liu
- The Tim Taylor Department of Chemical Engineering, Kansas State University, Manhattan, KS 66506, USA
| | - Frank L Ruta
- Department of Physics, Columbia University, New York, NY 10027, USA
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA
| | - Casey Li
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
| | - Michael M Fogler
- Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA
| | - James H Edgar
- The Tim Taylor Department of Chemical Engineering, Kansas State University, Manhattan, KS 66506, USA
| | - Gennady Shvets
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
| | - Cory R Dean
- Department of Physics, Columbia University, New York, NY 10027, USA
| | - D N Basov
- Department of Physics, Columbia University, New York, NY 10027, USA.
| |
Collapse
|
4
|
Xiong L, Forsythe C, Jung M, McLeod AS, Sunku SS, Shao YM, Ni GX, Sternbach AJ, Liu S, Edgar JH, Mele EJ, Fogler MM, Shvets G, Dean CR, Basov DN. Photonic crystal for graphene plasmons. Nat Commun 2019; 10:4780. [PMID: 31636265 PMCID: PMC6803641 DOI: 10.1038/s41467-019-12778-2] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2019] [Accepted: 09/26/2019] [Indexed: 11/22/2022] Open
Abstract
Photonic crystals are commonly implemented in media with periodically varying optical properties. Photonic crystals enable exquisite control of light propagation in integrated optical circuits, and also emulate advanced physical concepts. However, common photonic crystals are unfit for in-operando on/off controls. We overcome this limitation and demonstrate a broadly tunable two-dimensional photonic crystal for surface plasmon polaritons. Our platform consists of a continuous graphene monolayer integrated in a back-gated platform with nano-structured gate insulators. Infrared nano-imaging reveals the formation of a photonic bandgap and strong modulation of the local plasmonic density of states that can be turned on/off or gradually tuned by the applied gate voltage. We also implement an artificial domain wall which supports highly confined one-dimensional plasmonic modes. Our electrostatically-tunable photonic crystals are derived from standard metal oxide semiconductor field effect transistor technology and pave a way for practical on-chip light manipulation. Traditional photonic crystals consist of periodic media with a pre-defined optical response. Here, the authors combine nanostructured back-gate insulators with a continuous layer of graphene to demonstrate an electrically tunable two-dimensional photonic crystal suitable for controlling the propagation of surface plasmon polaritons.
Collapse
Affiliation(s)
- L Xiong
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - C Forsythe
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - M Jung
- Department of Physics, Cornell University, Ithaca, NY, 14853, USA
| | - A S McLeod
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - S S Sunku
- Department of Physics, Columbia University, New York, NY, 10027, USA.,Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, 10027, USA
| | - Y M Shao
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - G X Ni
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - A J Sternbach
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - S Liu
- The Tim Taylor Department of Chemical Engineering, Kansas State University, Manhattan, KS, 66506, USA
| | - J H Edgar
- The Tim Taylor Department of Chemical Engineering, Kansas State University, Manhattan, KS, 66506, USA
| | - E J Mele
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - M M Fogler
- Department of physics, University of California San Diego, La Jolla, CA, 92093, USA
| | - G Shvets
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, 14853, USA
| | - C R Dean
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - D N Basov
- Department of Physics, Columbia University, New York, NY, 10027, USA.
| |
Collapse
|
5
|
Ke S, Zhao D, Liu J, Liu Q, Liao Q, Wang B, Lu P. Topological bound modes in anti-PT-symmetric optical waveguide arrays. OPTICS EXPRESS 2019; 27:13858-13870. [PMID: 31163844 DOI: 10.1364/oe.27.013858] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Accepted: 04/21/2019] [Indexed: 06/09/2023]
Abstract
We investigate the topological bound modes in a binary optical waveguide array with anti-parity-time (PT) symmetry. The anti-PT-symmetric arrays are realized by incorporating additional waveguides to the bare arrays, such that the effective coupling coefficients are imaginary. The systems experience two kinds of phase transition, including global topological order transition and quantum phase transition. As a result, the system supports two kinds of robust bound modes, which are protected by the global topological order and the quantum phase, respectively. The study provides a promising approach to realizing robust light transport by utilizing mediating components.
Collapse
|
6
|
Yan M, Lu J, Li F, Deng W, Huang X, Ma J, Liu Z. On-chip valley topological materials for elastic wave manipulation. NATURE MATERIALS 2018; 17:993-998. [PMID: 30349029 DOI: 10.1038/s41563-018-0191-5] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2018] [Accepted: 09/10/2018] [Indexed: 05/19/2023]
Abstract
Valley topological materials, in which electrons possess valley pseudospin, have attracted a growing interest recently. The additional valley degree of freedom offers a great potential for its use in information encoding and processing. The valley pseudospin and valley edge transport have been investigated in photonic and phononic crystals for electromagnetic and acoustic waves, respectively. In this work, by using a micromanufacturing technology, valley topological materials are fabricated on silicon chips, which allows the observation of gyral valley states and valley edge transport for elastic waves. The edge states protected by the valley topology are robust against the bending and weak randomness of the channel between distinct valley Hall phases. At the channel intersection, a counterintuitive partition of the valley edge states manifests for elastic waves, in which the partition ratio can be freely adjusted. These results may enable the creation of on-chip high-performance micro-ultrasonic materials and devices.
Collapse
Affiliation(s)
- Mou Yan
- School of Physics and Optoelectronics, South China University of Technology, Guangzhou, Guangdong, China
| | - Jiuyang Lu
- School of Physics and Optoelectronics, South China University of Technology, Guangzhou, Guangdong, China
| | - Feng Li
- School of Physics and Optoelectronics, South China University of Technology, Guangzhou, Guangdong, China
| | - Weiyin Deng
- School of Physics and Optoelectronics, South China University of Technology, Guangzhou, Guangdong, China
| | - Xueqin Huang
- School of Physics and Optoelectronics, South China University of Technology, Guangzhou, Guangdong, China
| | - Jiahong Ma
- School of Physics and Optoelectronics, South China University of Technology, Guangzhou, Guangdong, China
| | - Zhengyou Liu
- Key Laboratory of Artificial Micro- and Nanostructures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan, China.
- Institute for Advanced Studies, Wuhan University, Wuhan, China.
| |
Collapse
|
7
|
Song Z, Liu H, Huang N, Wang Z. Plasmonic topological edge states in ring-structure gate graphene. APPLIED OPTICS 2018; 57:8503-8507. [PMID: 30461915 DOI: 10.1364/ao.57.008503] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 09/04/2018] [Indexed: 06/09/2023]
Abstract
Topological photonic states exhibit unique robustness against defects, facilitating fault-tolerant photonic device applications. However, existing proposals either involve a sophisticated and bulky structure or can only operate in the microwave regime. We show a theoretical demonstration for highly confined topologically protected plasmonic states to be realized at infrared frequencies in monolayer graphene with a ring-structure gate. With a suitable bias voltage, the combined gate-graphene structure is shown to produce sufficiently strong Bragg scattering of graphene surface plasmons and to impart them with nontrivial topological properties. Our design is compact and could pave the way for dynamically reconfigurable, robust, nanoscale, integrated photonic devices.
Collapse
|