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Uría-Álvarez AJ, Palacios JJ. Topologically Protected Photovoltaics in Bi Nanoribbons. NANO LETTERS 2024; 24:6651-6657. [PMID: 38804328 PMCID: PMC11157647 DOI: 10.1021/acs.nanolett.4c01277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2024] [Revised: 05/17/2024] [Accepted: 05/21/2024] [Indexed: 05/29/2024]
Abstract
Photovoltaic efficiency in solar cells is hindered by many unwanted effects. Radiative channels (emission of photons) sometimes mediated by nonradiative ones (emission of phonons) are principally responsible for the decrease in exciton population before charge separation can take place. One such mechanism is electron-hole recombination at surfaces or defects where the in-gap edge states serve as the nonradiative channels. In topological insulators (TIs), which are rarely explored from an optoelectronics standpoint, we show that their characteristic surface states constitute a nonradiative decay channel that can be exploited to generate a protected photovoltaic current. Focusing on two-dimensional TIs, and specifically for illustration purposes on a Bi(111) monolayer, we obtain the transition rates from the bulk excitons to the edge states. By breaking the appropriate symmetries of the system, one can induce an edge charge accumulation and edge currents under illumination, demonstrating the potential of TI nanoribbons for photovoltaics.
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Affiliation(s)
- Alejandro José Uría-Álvarez
- Departamento de Física de la
Materia Condensada, Condensed Matter Physics Center (IFIMAC), and
Instituto Nicolás Cabrera (INC), Universidad Autónoma de Madrid, Cantoblanco 28049, Madrid, Spain
| | - Juan José Palacios
- Departamento de Física de la
Materia Condensada, Condensed Matter Physics Center (IFIMAC), and
Instituto Nicolás Cabrera (INC), Universidad Autónoma de Madrid, Cantoblanco 28049, Madrid, Spain
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2
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Li J, Wang L, Wang Y, Tao Z, Zhong W, Su Z, Xue S, Miao G, Wang W, Peng H, Guo J, Zhu X. Observation of the nonanalytic behavior of optical phonons in monolayer hexagonal boron nitride. Nat Commun 2024; 15:1938. [PMID: 38431679 PMCID: PMC10908826 DOI: 10.1038/s41467-024-46229-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Accepted: 02/20/2024] [Indexed: 03/05/2024] Open
Abstract
Phonon splitting of the longitudinal and transverse optical modes (LO-TO splitting), a ubiquitous phenomenon in three-dimensional polar materials, will break down in two-dimensional (2D) polar systems. Theoretical predictions propose that the LO phonon in 2D polar monolayers becomes degenerate with the TO phonon, displaying a distinctive "V-shaped" nonanalytic behavior near the center of the Brillouin zone. However, the full experimental verification of these nonanalytic behaviors has been lacking. Here, using monolayer hexagonal boron nitride (h-BN) as a prototypical example, we report the comprehensive and direct experimental verification of the nonanalytic behavior of LO phonons by inelastic electron scattering spectroscopy. Interestingly, the slope of the LO phonon in our measurements is lower than the theoretically predicted value for a freestanding monolayer due to the screening of the Cu foil substrate. This enables the phonon polaritons in monolayer h-BN/Cu foil to exhibit ultra-slow group velocity (~5 × 10-6 c, c is the speed of light) and ultra-high confinement (~ 4000 times smaller wavelength than that of light). These exotic behaviors of the optical phonons in h-BN presents promising prospects for future optoelectronic applications.
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Affiliation(s)
- Jiade Li
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100049, Beijing, China
| | - Li Wang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Yani Wang
- Center for Nanochemistry, Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, 100871, Beijing, China
- Beijing Graphene Institute (BGI), 100095, Beijing, China
| | - Zhiyu Tao
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100049, Beijing, China
| | - Weiliang Zhong
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100049, Beijing, China
| | - Zhibin Su
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100049, Beijing, China
| | - Siwei Xue
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Guangyao Miao
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Weihua Wang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Hailin Peng
- Center for Nanochemistry, Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, 100871, Beijing, China
- Beijing Graphene Institute (BGI), 100095, Beijing, China
| | - Jiandong Guo
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China.
- School of Physical Sciences, University of Chinese Academy of Sciences, 100049, Beijing, China.
| | - Xuetao Zhu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China.
- School of Physical Sciences, University of Chinese Academy of Sciences, 100049, Beijing, China.
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Talukdar D, Bora SS, Ahmed GA. Electronic, optical, and adsorption properties of Li-doped hexagonal boron nitride: a GW approach. Phys Chem Chem Phys 2024; 26:4021-4028. [PMID: 38224145 DOI: 10.1039/d3cp04710e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2024]
Abstract
This study employs quasiparticle-corrected DFT calculations to explore the electronic, optical, and surface adsorption properties of Li-doped hexagonal boron nitride (h-BNLi) monolayers. The results reveal that Li doping introduces two defect states into the wide band gap of the monolayer, reducing the band gap from 5.73 eV to 3.72 eV at the K-Γ point of the Brillouin zone. Using the GW approach to incorporate quasiparticle energies demonstrates a distinct advantage over conventional DFT, leading to qualitative shifts in band alignment across the Brillouin zone. Additionally, we identify intragap transitions driven by these defect states, resulting in a significant red shift in the optical gap, decreasing it from 5.73 eV to 1.61 eV in the doped monolayer. Moreover, Li doping enhances the detection of carbon-based gas molecules, raising the surface adsorption energy by -0.42 eV and -0.45 eV compared to the pristine monolayer. These findings hold substantial promise for the application of h-BNLi in electronic, optoelectronic, optical, and sensing devices, effectively subjugating the challenge posed by its wide band gap.
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Affiliation(s)
- Dhanjit Talukdar
- Optoelectronics and Photonics Laboratory, Department of Physics, Tezpur University, Napaam 784028, Assam, India.
| | - Shilpi Stuti Bora
- Optoelectronics and Photonics Laboratory, Department of Physics, Tezpur University, Napaam 784028, Assam, India.
| | - Gazi A Ahmed
- Optoelectronics and Photonics Laboratory, Department of Physics, Tezpur University, Napaam 784028, Assam, India.
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Adhikary S, Dutta S. Circular dichroism in two-dimensional BC 6N and B 3C 2N 3in absence of intervalley excitonic coupling. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 36:125304. [PMID: 38064753 DOI: 10.1088/1361-648x/ad13d7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Accepted: 12/08/2023] [Indexed: 12/19/2023]
Abstract
Two-dimensional (2D) noncentrosymmetric systems offer potential opportunities for exploiting the valley degrees of freedom for advanced information processing, owing to non-zero Berry curvature. However, such valley polarization in 2D materials is crucially governed by the intervalley excitonic scattering in momentum space due to reduced electronic degrees of freedom and consequent enhanced electronic correlation. Here, we study the valley excitonic properties of two 2D noncentrosymmetric complementary structures, namely, BC6N and B3C2N3using first principles-based GW calculations combined with the Bethe-Salpeter equation, that brings the many-body interactions among the quasiparticles. Thek-resolved oscillator strength of their first bright exciton indicates their ability to exhibit valley polarization under the irradiation of circularly polarized light of different chiralities. Both the systems show significant singlet excitonic binding energies of 0.74 eV and 1.31 eV, respectively. Higher stability of dark triplet excitons as compared to the singlet one can lead to higher quantum efficiency in both the systems. The combination of large excitonic binding energies and the valley polarization ability with minimal intervalley scattering make them promising candidates for applications in advanced optical devices and information storage technologies.
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Affiliation(s)
- Souren Adhikary
- Department of Physics, Indian Institute of Science Education and Research (IISER) Tirupati, Tirupati 517507, Andhra Pradesh, India
| | - Sudipta Dutta
- Department of Physics, Indian Institute of Science Education and Research (IISER) Tirupati, Tirupati 517507, Andhra Pradesh, India
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Hu C, Naik MH, Chan YH, Louie SG. Excitonic Interactions and Mechanism for Ultrafast Interlayer Photoexcited Response in van der Waals Heterostructures. PHYSICAL REVIEW LETTERS 2023; 131:236904. [PMID: 38134768 DOI: 10.1103/physrevlett.131.236904] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Accepted: 11/09/2023] [Indexed: 12/24/2023]
Abstract
Optical dynamics in van der Waals heterobilayers is of fundamental scientific and practical interest. Based on a time-dependent adiabatic GW approach, we discover a new many-electron (excitonic) channel for converting photoexcited intralayer to interlayer excitations and the associated ultrafast optical responses in heterobilayers, which is conceptually different from the conventional single-particle picture. We find strong electron-hole interactions drive the dynamics and enhance the pump-probe optical responses by an order of magnitude with a rise time of ∼300 fs in MoSe_{2}/WSe_{2} heterobilayers, in agreement with experiment.
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Affiliation(s)
- Chen Hu
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Mit H Naik
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Yang-Hao Chan
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Institute of Atomic and Molecular Sciences, Academia Sinica, and Physics Division, National Center for Theoretical Sciences, Taipei, 10617, Taiwan
| | - Steven G Louie
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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Hou B, Wang D, Barker BA, Qiu DY. Exchange-Driven Intermixing of Bulk and Topological Surface States by Chiral Excitons in Bi_{2}Se_{3}. PHYSICAL REVIEW LETTERS 2023; 130:216402. [PMID: 37295093 DOI: 10.1103/physrevlett.130.216402] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Revised: 02/17/2023] [Accepted: 05/01/2023] [Indexed: 06/12/2023]
Abstract
Topological surface states (TSS) in the prototypical topological insulator (TI) Bi_{2}Se_{3} are frequently characterized using optical probes, but electron-hole interactions and their effect on surface localization and optical response of the TSS remain unexplored. Here, we use ab initio calculations to understand excitonic effects in the bulk and surface of Bi_{2}Se_{3}. We identify multiple series of chiral excitons that exhibit both bulk and TSS character, due to exchange-driven mixing. Our results address fundamental questions about the degree to which electron-hole interactions can relax the topological protection of surface states and dipole selection rules for circularly polarized light in TIs by elucidating the complex intermixture of bulk and surface states excited in optical measurements and their coupling to light.
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Affiliation(s)
- Bowen Hou
- Department of Mechanical Engineering and Material Sciences, Yale University, New Haven, Connecticut 06511, USA
| | - Dan Wang
- Department of Mechanical Engineering and Material Sciences, Yale University, New Haven, Connecticut 06511, USA
| | - Bradford A Barker
- Department of Physics, University of California, Merced, California 95343, USA
| | - Diana Y Qiu
- Department of Mechanical Engineering and Material Sciences, Yale University, New Haven, Connecticut 06511, USA
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