About

Hongfei Lin is the Arthur W. Zafiropoulo Professor of Chemical Engineering at Northeastern University, joining the institution in July 2025. His professional career is dedicated to advancing sustainable energy systems, with a focus on developing AI-driven catalysis for sustainable manufacturing, critical materials recovery, and clean energy. His current research activities are centered on coupling chemical processes with novel material systems to produce renewable energy and clean fuels. Specifically, he designs multifunctional heterogeneous catalysts at a molecular level to develop highly efficient and cost-effective processes for converting solid biomass into liquid transportation fuels or renewable chemicals. Additionally, Dr. Lin conducts fundamental studies of advanced materials using modern characterization techniques to better control catalytic processes and maximize overall efficiency. He leads the IMPACT Laboratory at the Egan Research Center, which focuses on projects such as carbon capture, waste plastic recycling, chemical hydrogen storage, biofuels, and machine-learning guided high throughput catalytic platforms, all aimed at establishing a sustainable low-carbon economy.

Research topics

• Physics
• Condensed matter physics
• Quantum mechanics
• Materials science
• Computer Science
• Mathematics
• Algorithm
• Optoelectronics
• Chemistry
• Statistics
• Stereochemistry
• Nanotechnology
• Optics
• Combinatorics
• Geometry

Selected publications

• Quantum metric non-linear Hall effect in an antiferromagnetic topological insulator thin-film EuSn<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si140.svg" display="inline" id="d1e761"><mml:msub><mml:mrow/><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>As<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si140.svg" display="inline" id="d1e769"><mml:msub><mml:mrow/><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>

  Materials Today Quantum · 2025-02-17 · 1 citations

  articleOpen access

  The quantum geometric structure of electrons introduces fundamental insights into understanding quantum effects in materials. One notable manifestation is the non-linear Hall effect (NLHE), which has drawn considerable interest for its potential to overcome the intrinsic limitations of semiconductor diodes at low input power and high frequency. In this study, we investigate NLHE stemming from the real part of the quantum geometric tensor, specifically the quantum metric, in an antiferromagnetic topological material, EuSn 2 As 2 , using density functional theory. Our calculations predict a remarkable NLHE arising from a symmetry-protected, single Type-II surface Dirac cone in the even-numbered-layer two-dimensional slab thin-film, yielding a non-linear Hall conductivity exceeding 20 mA/V 2 —an order of magnitude larger than previously reported. This single Dirac band dispersion represents the simplest model for generating NLHE, positioning the EuSn 2 As 2 thin-film as a “hydrogen atom” for NLHE systems. Additionally, we observe NLHE from band-edge states near the Fermi level. Our findings also reveal that 30% phosphorus (P) doping can double the non-linear Hall conductivity. With its substantial and tunable NLHE, EuSn 2 As 2 thin-films present promising applications in antiferromagnetic spintronics and rectification devices.

  PublisherDOI

• Emergent spin Hall quantization and high-order van Hove singularities in square-octagonal MA$_2$Z$_4$

  ArXiv.org · 2025-10-14

  preprintOpen access

  Quantum spin Hall (QSH) insulators are versatile platforms for exploring exotic quantum phases, especially when combined with high-order van Hove singularities (VHSs) that enhance electron correlations. However, perfect spin Hall quantization is often hindered by spin mixing from strong spin-orbit coupling, and the emergence of such VHSs is highly sensitive to material-specific electronic structures. Here, we predict a class of seven-layered square-octagonal MA$_2$Z$_4$ (M = Mo/W, A = Si/Ge, Z = Pnictogen) isomers that host a robust, large-gap QSH phase with nearly quantized spin Hall conductivity and intrinsic high-order VHSs. Topological and symmetry analyses reveal that compounds with Z = P, As, and Sb are $\mathbb{Z}_2$ nontrivial with spin Chern number $C_s = 1$ and support $S_z$-polarized edge states, while those with Z = N are trivial insulators. The QSH phase features an $S_z$-conserving spin Hamiltonian consistent with an emergent spin $\mathrm{U}(1)$ quasi-symmetry, yielding spin Hall conductivity $\sim 2e^2/h$. Notably, MA$_2$(As, Sb)$_4$ compounds exhibit quasi-flat bands near the Fermi level in the inverted regime, with WSi$_2$Sb$_4$ additionally hosting four high-order VHSs at generic momentum points. These results position square-octagonal MA$_2$Z$_4$ materials as robust QSH insulators for realizing quantized spin Hall conductivity and correlated topological phases, including fractionalized states and possibly non-Abelian anyons.

  PublisherOA PDFDOI

• Strain-Induced Charge Density Waves with Emergent Topological States in Monolayer NbSe₂

  ACS Nano · 2025-05-06 · 6 citations

  articleOpen access

  Emergence of topological states in strongly correlated systems, particularly two-dimensional (2D) transition-metal dichalcogenides, offers a platform for manipulating electronic properties in quantum materials. However, a comprehensive understanding of the intricate interplay between correlations and topology remains elusive. Here we employ first-principles modeling to reveal two distinct 2 × 2 charge density wave (CDW) phases in monolayer 1H-NbSe2, which become energetically favorable over the conventional 3 × 3 CDWs under modest biaxial tensile strain of about 1%. These strain-induced CDW phases coexist with numerous topological states characterized by Z2 topology, high mirror Chern numbers, topological nodal lines, and higher-order topological states, which we have verified rigorously by computing the topological indices and the presence of robust edge states and localized corner states. Remarkably, these topological properties emerge because of the CDW rather than a pre-existing topology in the pristine phase. These results elucidate the interplay between correlations, topology, and geometry in 2D materials and indicate that strain-induced correlation effects can be used to engineer topological states in materials with initially trivial topology. Our findings may be applied in electronics, spintronics, and other advanced quantum devices that require robust and tunable topological states.

  PublisherDOI

• Topological Nature of Orbital Chern Insulators

  ArXiv.org · 2025-03-11

  preprintOpen access

  Ground state topologies in quantum materials have unveiled many unique topological phases with novel Hall responses. Recently, the orbital Hall effect in insulators has suggested the existence of orbital Chern insulators (OCIs) in which the orbital angular momentum drives the Hall response. Studies on OCIs, however, have so far been restricted to valley-locked or spinful systems, but candidate materials for systematic studies of OCIs are lacking. Here we discuss a framework for investigating OCIs using the feature-spectrum topology approach. To characterize the ground-state topology in the orbital degree of freedom, we introduce the orbital Chern number and orbital-feature Berry curvature and demonstrate the bulk-boundary correspondence and orbital Hall response. We also uncover a parameter-driven topological phase transition, which would offer tunability of the OCIs. In this way, we identify monolayer blue-phosphorene (traditionally considered topologically trivial) as the primal 'hydrogen atom' of OCIs as a spinless, valley-free OCI material. Our study gives insight into the nature of orbital-driven topological phases and reveals a new facet of blue-phosphorene, and provides a new pathway for advancements in orbitronics and the discovery of novel topological materials.

  PublisherOA PDFDOI

• Orthorhombic TaAs: A New Topological Phase of the Archetypical Weyl Semimetal

  ACS Applied Materials & Interfaces · 2025-08-25 · 2 citations

  articleCorresponding

  We report on a new, topologically nontrivial phase of TaAs identified in thin TaAs layers grown by molecular beam epitaxy. Structural investigations clearly show a new atom arrangement, confirmed by the presence of 104 reflections in the X-ray diffraction pattern, forbidden for the well-known tetragonal phase. Density functional theory confirms the presence of a new orthorhombic phase and reveals that its formation energy is slightly higher (by ∼0.6 meV per atom) than for the tetragonal phase. The orthorhombic TaAs is a topological Weyl semimetal with 20 Weyl nodes. Weak antilocalization of a topological origin is observed at low temperatures. With the Fermi energy relatively deep in the valence band, no other signatures of the chiral properties are resolved. The demonstration of the new phase, combined with the molecular beam epitaxy capabilities of doping and strain adjustment, opens a new way toward the fine-tuning of Weyl semimetal layers and heterostructures.

  PublisherDOI

• Observation of charge density wave excitonic order parameter in topological insulator monolayer WTe2

  ArXiv.org · 2025-05-27

  preprintOpen access

  Strong electron-hole interactions in a semimetal or narrow-gap semiconductor may drive a ground state of condensed excitons. Monolayer WTe2 has been proposed as a host material for such an exciton condensate, but the order parameter - the key signature of a macroscopic quantum-coherent condensate - has not been observed. Here we use Fourier-transform scanning tunnelling spectroscopy (FT-STS) to study quasi-particle interference (QPI) and periodic modulations of the local density of states (LDOS) in monolayer WTe2. In WTe2 on graphene, in which the carrier density can be varied via back-gating, FT-STS shows QPI features in the 2D bulk bands, confirming the interacting nature of the bandgap in neutral WTe2 and the semi-metallic nature of highly n- and p-doped WTe2. We observe additional non-dispersive spatial modulations in the LDOS imprinted on the topological edge mode of neutral WTe2 on metallic substrates (graphene and graphite), which we interpret as the interaction of the topological edge mode with the expected charge density wave order parameter of the excitonic condensate in WTe2 at low interaction strength due to screening by the metallic substrates.

  PublisherOA PDFDOI

• Observation of the axion quasiparticle in 2D MnBi2Te4

  Nature · 2025-04-16 · 30 citations

  articleOpen access
  PublisherOA PDFDOI

• Spatially Tunable Interfacial Ferroelectricity in Low-Symmetric WTe ₂

  Nano Letters · 2025-12-17 · 1 citations

  articleOpen access

  Interfacial ferroelectricity, recently discovered in van der Waals (vdW) materials, exhibits switchable dipoles at the interface. Most experiments are realized by stacking high-symmetry two-dimensional (2D) lattices in specific stacking configurations. A prototype based on a synthetic and low-symmetry 2D lattice is robust for switchable dipoles with broken symmetry at the interface. Here, we show that interfacial ferroelectricity can be spatially tunable by controlling the odd–even layer number in the synthetic low-symmetry lattice of 1T′-WTe2. A high ferroelectric transition temperature (TC) of >550 K is confirmed. The density functional theory (DFT) calculations indicate that interlayer sliding along the b-axis enables polarization switching of the interfacial dipoles. This study moves a significant step toward spatially tunable interfacial ferroelectricity.

  PublisherDOI

• Topological characteristics and bulk-boundary correspondence in the orbital Hall effect

  Physical review. B./Physical review. B · 2025-05-01 · 3 citations

  article

  The orbital Hall effect (OHE) is attracting interest due to its fundamental science implications and potential applications in orbitronics and spintronics. Unlike the spin Hall effect, the connection between the OHE and band topology is not well understood. Here we present an approach for understanding the OHE based on analyzing the projected orbital angular momentum (POAM) spectrum. By considering monolayers of group IV elements, we demonstrate that the Wannier charge centers of the POAM spectrum display topologically nontrivial windings. The orbital Hall conductivity is found to form a plateau within the band gap as a direct consequence of the Chern number carried by the POAM spectrum. Importantly, we show that the topological orbital Hall phase yields a new form of bulk-boundary correspondence, which features gapless states in the POAM spectrum and induces nonzero orbital textures at the boundaries that would be amenable to experimental verification through circular dichroism in angle-resolved photoemission spectroscopy (CD-ARPES) experiments. Our study presents a systematic method for investigating the topological OHE and provides a pathway for its broader exploration in two-dimensional materials.

  PublisherDOI

• Phase-sensitive Surface Second-harmonic Generation of Topological Dirac Semimetal

  2025-01-01

  article

  We report anomalously strong, surface-specific, purely out-of-plane optical nonlinearity in PdTe 2 Dirac semimetal through polarization-dependent heterodyne-interferometric rotational-anisotropic second-harmonic generation. This strong nonlinearity is correlated to the topological surface states via surface and orbital-projected band calculations.

  PublisherDOI

Frequent coauthors

• Arun Bansil

  Northeastern University

  352 shared

• Tay‐Rong Chang

  National Center for Theoretical Sciences, Physics Division

  204 shared

• M. Zahid Hasan

  169 shared

• Horng‐Tay Jeng

  National Center for Theoretical Sciences

  132 shared

• Ilya Belopolski

  127 shared

• Guoqing Chang

  Nanyang Technological University

  120 shared

• Feng‐Chuan Chuang

  114 shared

• Su‐Yang Xu

  Harvard University

  107 shared

Labs

• IMPACT LaboratoryPI

Awards & honors

• Arthur W. Zafiropoulo Professor of Chemical Engineering