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<p>The linear photogalvanic effect (LPGE) in monolayer Td-WTe<sub>2</sub> is systematically investigated under two complementary strain-engineering strategies—lateral strain gradients and single-end bending—using a combined nonequilibrium Green’s function and density functional theory approach. Unlike uniform tensile or compressive strains, which induce only limited and narrowly tunable responses, both gradient and bending strains significantly reshape the electronic structure near the Fermi level, introducing flat bands and high-density states that generate internal electric fields and promote carrier separation. For lateral strain gradients, progressively smoother profiles lead to stronger band distortion, enhanced density of states, and redshifted, amplified LPGE response. The maximum photoresponse <i>R</i><sub>max</sub> rises from 12.5 <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\text{a}}_{0}^{2}\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mtext>a</mtext> <mrow> <mn>0</mn> </mrow> <mn>2</mn> </msubsup> </math></EquationSource> </InlineEquation>/photon at 3.5&#xa0;eV (steep) to 283.4 <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({\text{a}}_{0}^{2}\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mtext>a</mtext> <mrow> <mn>0</mn> </mrow> <mn>2</mn> </msubsup> </math></EquationSource> </InlineEquation>/photon at 2.2&#xa0;eV (gradual), a 22.7-fold increase (where a<sub>0</sub> is the Bohr radius, <InlineEquation ID="IEq200"> <EquationSource Format="TEX">\({\text{a}}_{0}^{2}\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mtext>a</mtext> <mrow> <mn>0</mn> </mrow> <mn>2</mn> </msubsup> </math></EquationSource> </InlineEquation> is the unit of area associated with photons). Polarization selectivity also improves, with the extinction ratio (ER) reaching up to 173.7. Under bending strain, a similar modulation mechanism emerges: increasing curvature flattens bands and redistributes states near the Fermi level. At a 30° bending angle, <i>R</i><sub>max</sub> reaches 26.63 <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\({\text{a}}_{0}^{2}\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mtext>a</mtext> <mrow> <mn>0</mn> </mrow> <mn>2</mn> </msubsup> </math></EquationSource> </InlineEquation>/photon at 2.7&#xa0;eV—an enhancement of 166.4 times over the unstrained case—with strong polarization anisotropy (ER = 172.9 at 2.6&#xa0;eV). These results establish a unified strain-engineering framework wherein both lateral gradients and bending curvature serve as effective and tunable means to amplify LPGE magnitude, shift spectral response, and enhance polarization sensitivity. The study offers valuable theoretical guidance for designing next-generation broadband, polarization-sensitive, and flexible optoelectronic devices based on two-dimensional semimetals.</p> Graphical abstract <p></p>

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In-plane and out-of-plane strain gradient modulation of the linear photogalvanic effect in monolayer Td-WTe2

  • 期刊论文

  • 发表日期：

    2025年12月24日

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  • Jia Liu,
  • Pei-Xu Cao,
  • Jin-Xiao Bao,
  • Guo-Qing Liu,
  • Luo-Meng Chao,
  • Leong Chuan Kwek

摘要

The linear photogalvanic effect (LPGE) in monolayer Td-WTe2 is systematically investigated under two complementary strain-engineering strategies—lateral strain gradients and single-end bending—using a combined nonequilibrium Green’s function and density functional theory approach. Unlike uniform tensile or compressive strains, which induce only limited and narrowly tunable responses, both gradient and bending strains significantly reshape the electronic structure near the Fermi level, introducing flat bands and high-density states that generate internal electric fields and promote carrier separation. For lateral strain gradients, progressively smoother profiles lead to stronger band distortion, enhanced density of states, and redshifted, amplified LPGE response. The maximum photoresponse Rmax rises from 12.5 \({\text{a}}_{0}^{2}\) a 0 2 /photon at 3.5 eV (steep) to 283.4  \({\text{a}}_{0}^{2}\) a 0 2 /photon at 2.2 eV (gradual), a 22.7-fold increase (where a0 is the Bohr radius, \({\text{a}}_{0}^{2}\) a 0 2 is the unit of area associated with photons). Polarization selectivity also improves, with the extinction ratio (ER) reaching up to 173.7. Under bending strain, a similar modulation mechanism emerges: increasing curvature flattens bands and redistributes states near the Fermi level. At a 30° bending angle, Rmax reaches 26.63  \({\text{a}}_{0}^{2}\) a 0 2 /photon at 2.7 eV—an enhancement of 166.4 times over the unstrained case—with strong polarization anisotropy (ER = 172.9 at 2.6 eV). These results establish a unified strain-engineering framework wherein both lateral gradients and bending curvature serve as effective and tunable means to amplify LPGE magnitude, shift spectral response, and enhance polarization sensitivity. The study offers valuable theoretical guidance for designing next-generation broadband, polarization-sensitive, and flexible optoelectronic devices based on two-dimensional semimetals.

Graphical abstract