About

Alfred Zong is an Assistant Professor of Physics and Applied Physics at Stanford University. His research group focuses on the study of light-induced non-equilibrium phenomena in quantum materials, exploring the intersection between condensed matter physics and ultrafast science. To investigate the ultrafast dynamics on the nanoscale, his team develops techniques such as ultrafast electron diffraction and microscopy, attosecond transient absorption spectroscopy, and coherent diffraction imaging. These time-resolved probes are integrated with complex sample environments, including in-situ strain and electrostatic gating, to design, discover, and understand non-equilibrium phases of quantum materials. Zong holds a B.S. in Physics and an M.S. in Computer Science from Stanford University, obtained in 2015, and a Ph.D. in Physics from the Massachusetts Institute of Technology, completed in 2020. He was a Miller Fellow at the University of California, Berkeley, in 2023.

Research topics

• Physics
• Quantum mechanics
• Geometry
• Nanotechnology
• Statistical physics
• Mathematics
• Chemical physics
• Materials science
• Stereochemistry
• Chemistry
• Economics
• Condensed matter physics
• Acoustics

Selected publications

• Room-temperature multistage metastability in a moiré superstructure

  ArXiv.org · 2026-04-21

  articleOpen access

  Metastability is fundamental not only to phase ordering and transitions, but also to a broad range of modern technologies, from memory devices to metallic glasses. In condensed-matter physics, charge density waves (CDWs) offer versatile platforms for accessing metastable states due to their sensitivity to external stimuli. However, most metastable CDW states are stabilized only at low temperatures, limiting their practical utility. In this study, we report the observation of electrically driven, room-temperature, nonvolatile metastable states in the bulk form of EuTe$_4$, a recently discovered compound that hosts an innate moiré superlattice characterized by the stacking of incommensurate monolayer and bilayer CDWs. Systematic transport measurements reveal discrete resistivity plateaus and strong electric-field sensitivity, with a large number of metastable states readily induced across a wide temperature window within a giant hysteresis loop, making them well-suited for high-temperature, multi-bit memory applications. By integrating photoemission spectroscopy, diffraction, and in-situ transport measurements, we uncover that these metastable states do not stem from conventional mechanisms such as the emergence of new ordered phases or changes in incommensurate periodicity. Instead, they are characterized by a suppression of the original CDW amplitude and a reduction in correlation length, pointing to a unique electric-field-induced switching of out-of-plane CDW phases in the moiré superstructure. Our findings not only provide critical insights into metastable phenomena in moiré systems with stacked electronic orders but also establish EuTe$_4$ as a promising platform for developing room-temperature, multi-bit memory devices.

  PublisherOA PDF

• Atomically Resolved Acoustic Dynamics Coupled with Magnetic Order in a van der Waals Antiferromagnet

  arXiv (Cornell University) · 2026-01-23

  articleOpen access

  Magnetoelastic coupling in van der Waals (vdW) magnetic materials enables a unique interplay between the spin and lattice degrees of freedom. Characterizing the elastic responses with atomic and femtosecond resolution across the magnetic transition is essential for guiding the design of magnetically tunable actuators and strain-mediated spintronic devices. Here, ultrafast x-ray diffraction employed at a free-electron laser reveals that the atomic displacements, wave vectors, and dispersion relations of acoustic phonon modes in a vdW antiferromagnet FePS$_3$ are coupled with the magnetic order, by tracking both in-plane and out-of-plane Bragg peaks upon optical excitation across the Néel temperature (T$_N$). One transverse mode shows that a quasi-out-of-plane atomic displacement undergoes a significant directional change across T$_N$. Its quasi-in-plane wave vector is derived by the comparison between the measured sound velocity and the first-principles calculations. The other transverse mode is an interlayer shear acoustic mode whose amplitude is strongly enhanced in the antiferromagnetic phase, exhibiting eight times stronger amplitude than the longitudinal acoustic mode below T$_N$. The atomically resolved characterization of acoustic phonon dynamics that couple with magnetic ordering opens opportunities for harnessing unique magnetoelastic coupling in vdW magnets on ultrafast timescales.

  PublisherOA PDF

• Atomically Resolved Acoustic Dynamics Coupled with Magnetic Order in a van der Waals Antiferromagnet

  Open MIND · 2026-01-23

  preprint

  Magnetoelastic coupling in van der Waals (vdW) magnetic materials enables a unique interplay between the spin and lattice degrees of freedom. Characterizing the elastic responses with atomic and femtosecond resolution across the magnetic transition is essential for guiding the design of magnetically tunable actuators and strain-mediated spintronic devices. Here, ultrafast x-ray diffraction employed at a free-electron laser reveals that the atomic displacements, wave vectors, and dispersion relations of acoustic phonon modes in a vdW antiferromagnet FePS$_3$ are coupled with the magnetic order, by tracking both in-plane and out-of-plane Bragg peaks upon optical excitation across the Néel temperature (T$_N$). One transverse mode shows that a quasi-out-of-plane atomic displacement undergoes a significant directional change across T$_N$. Its quasi-in-plane wave vector is derived by the comparison between the measured sound velocity and the first-principles calculations. The other transverse mode is an interlayer shear acoustic mode whose amplitude is strongly enhanced in the antiferromagnetic phase, exhibiting eight times stronger amplitude than the longitudinal acoustic mode below T$_N$. The atomically resolved characterization of acoustic phonon dynamics that couple with magnetic ordering opens opportunities for harnessing unique magnetoelastic coupling in vdW magnets on ultrafast timescales.

  DOI

• Atomically Resolved Acoustic Dynamics Coupled with Magnetic Order in a Van der Waals Antiferromagnet

  Advanced Materials · 2026-02-01

  articleOpen access

  ABSTRACT Magnetoelastic coupling in van der Waals (vdW) magnetic materials enables a unique interplay between the spin and lattice degrees of freedom. Characterizing the elastic responses with atomic and femtosecond resolution across the magnetic transition is essential for guiding the design of magnetically tunable actuators and strain‐mediated spintronic devices. Here, ultrafast X‐ray diffraction employed at a free‐electron laser reveals that the atomic displacements, wave vectors, and dispersion relations of acoustic phonon modes in a vdW antiferromagnet FePS 3 are coupled with the magnetic order, by tracking both in‐plane and out‐of‐plane Bragg peaks upon optical excitation across the Néel temperature ( T N ). One transverse mode shows that a quasi‐out‐of‐plane atomic displacement undergoes a significant directional change across T N . Its quasi‐in‐plane wave vector is derived by comparing the measured sound velocity and the first‐principles calculations. The other transverse mode is an interlayer shear acoustic mode whose amplitude is strongly enhanced in the antiferromagnetic phase, exhibiting eight times stronger amplitude than the longitudinal acoustic mode below T N . The atomically resolved characterization of acoustic phonon dynamics that couple with magnetic ordering opens opportunities for harnessing unique magnetoelastic coupling in vdW magnets on ultrafast timescales.

  PublisherOA PDFDOI

• Room-temperature multistage metastability in a moiré superstructure

  arXiv (Cornell University) · 2026-04-21

  preprintOpen access

  Metastability is fundamental not only to phase ordering and transitions, but also to a broad range of modern technologies, from memory devices to metallic glasses. In condensed-matter physics, charge density waves (CDWs) offer versatile platforms for accessing metastable states due to their sensitivity to external stimuli. However, most metastable CDW states are stabilized only at low temperatures, limiting their practical utility. In this study, we report the observation of electrically driven, room-temperature, nonvolatile metastable states in the bulk form of EuTe$_4$, a recently discovered compound that hosts an innate moiré superlattice characterized by the stacking of incommensurate monolayer and bilayer CDWs. Systematic transport measurements reveal discrete resistivity plateaus and strong electric-field sensitivity, with a large number of metastable states readily induced across a wide temperature window within a giant hysteresis loop, making them well-suited for high-temperature, multi-bit memory applications. By integrating photoemission spectroscopy, diffraction, and in-situ transport measurements, we uncover that these metastable states do not stem from conventional mechanisms such as the emergence of new ordered phases or changes in incommensurate periodicity. Instead, they are characterized by a suppression of the original CDW amplitude and a reduction in correlation length, pointing to a unique electric-field-induced switching of out-of-plane CDW phases in the moiré superstructure. Our findings not only provide critical insights into metastable phenomena in moiré systems with stacked electronic orders but also establish EuTe$_4$ as a promising platform for developing room-temperature, multi-bit memory devices.

  PublisherDOI

• Photoinduced correlations in stochastic dynamics of a solid-state ionic conductor

  Nature Communications · 2026-05-15

  articleOpen accessCorresponding

  Photoexcitation by ultrashort laser pulses plays a crucial role in controlling reaction pathways, creating nonequilibrium material properties, and probing complex molecular dynamics. The photoresponse following a laser pulse is generally nonidentical between exposures due to spatiotemporal fluctuations or the stochastic nature of dynamical pathways. However, most ultrafast pump-probe experiments struggle to distinguish intrinsic sample fluctuations from extrinsic apparatus noise, often missing deviations from the averaged response. Leveraging the stability and high photon flux of time-resolved X-ray micro-diffraction at a synchrotron, we characterized stochastic photoinduced dynamics in a solid-state ionic conductor. By analyzing temporal evolutions of the lattice parameter of a single grain, we found that shot-to-shot fluctuations are not independent. Instead, correlations exist between nonequilibrium lattice trajectories following adjacent shots, with a characteristic correlation length of approximately 1500 shots, corresponding to an energy barrier of 0.4 ± 0.1 eV, close to the activation energy of lithium-ion diffusion.

  PublisherOA PDFDOI

• Correlated spin-wave generation and domain-wall oscillation in a topologically textured magnetic film

  Nature Materials · 2025-01-27 · 20 citations

  articleOpen access
  PublisherOA PDFDOI

• Joint commensuration in moiré charge-order superlattices drives shear topological defects

  ArXiv.org · 2025-09-20

  preprintOpen access

  The advent of two-dimensional moiré systems has revolutionized the exploration of phenomena arising from strong correlations and nontrivial band topology. Recently, a moiré superstructure formed by two coexisting charge density wave (CDW) orders with slightly mismatched wavevectors has been realized. These incommensurate CDWs can collectively exhibit commensurability, resulting in the jointly commensurate CDW (JC-CDW). This JC-CDW hosts phenomena including electronic anisotropy and phase-modulated hysteresis, and holds promise for non-volatile optoelectronic memory devices. Realizing such functionality requires understanding how the spatial periodicity, coherence, and amplitude of this order evolve under perturbations. Here, we address these questions using time- and momentum-resolved techniques to probe light-induced dynamics in EuTe$_4$. Our time-resolved diffraction results show that under intense photoexcitation, the JC-CDW wavevector and coherence length remain locked along the CDW direction, indicating preserved moiré periodicity while the moiré potential depth is suppressed. This robustness governs the configuration of the photoexcited JC-CDW and leads to the formation of previously underexplored shear-type topological defects. Furthermore, we developed an approach to simultaneously track the temporal evolution of the amplitude and phase of a CDW by following two diffraction peaks corresponding to one order, with findings verified by time-resolved photoemission and electron diffraction. This methodology enables reconstruction of the momentum- and time-resolved evolution of the JC-CDW and direct visualization of shear-type topological defect formation. These findings not only highlight the unique robustness of JC-CDWs out of equilibrium, but also establish a platform for optical moiré engineering and manipulation of quantum materials through topological defect control.

  PublisherOA PDFDOI

• Structural Contribution to Light-Induced Gap Suppression in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Ta</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>NiSe</mml:mi></mml:mrow><mml:mrow><mml:mn>5</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:mrow></mml:math>

  Physical Review Letters · 2025-08-26 · 3 citations

  article

  An excitonic insulator is a material that hosts an exotic ground state, where an energy gap opens due to spontaneous condensation of bound electron-hole pairs. Ta_{2}NiSe_{5} is a promising candidate for this type of material, but the coexistence of a structural phase transition with the gap opening has led to a long-standing debate regarding the origin of the insulating gap. Here we employ MeV ultrafast electron diffraction to obtain quantitative insights into the atomic displacements in Ta_{2}NiSe_{5} following photoexcitation, which has been overlooked in previous time-resolved spectroscopy studies. In conjunction with first-principles calculations using the measured atomic displacements, we find that the structural change can largely account for the photoinduced reduction in the energy gap without considering excitonic effects. Our Letter illustrates the importance of a quantitative reconstruction of individual atomic pathways during nonequilibrium phase transitions, paving the way for a mechanistic understanding of a diverse array of phase transitions in correlated materials where lattice dynamics can play a pivotal role.

  PublisherDOI

• Observation of Orbital-Selective Dual Modulations in an Anisotropic Antiferromagnetic Kagome Metal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>TbTi</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Bi</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

  Physical Review X · 2025-06-10 · 2 citations

  articleOpen access

  Orbital selectivity is pivotal in dictating the phase diagrams of multiorbital systems, with prominent examples including the orbital-selective Mott phase and superconductivity. The intercalation of anisotropic layers represents an effective method for enhancing orbital selectivity and thereby shaping the low-energy physics of multiorbital systems. Despite its potential, related experimental studies, especially those elucidating the correlation between orbital selectivity and magnetism, remain limited. In this work, we systematically examine the interplay between orbital selectivity and magnetism in the newly discovered anisotropic kagome <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msub><a:mi>TbTi</a:mi><a:mn>3</a:mn></a:msub><a:msub><a:mi>Bi</a:mi><a:mn>4</a:mn></a:msub></a:mrow></a:math> single crystal, and report the coexistence of orbital-selective dual-band modulations (<c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:msub><c:mrow><c:mi>q</c:mi></c:mrow><c:mrow><c:mn>1</c:mn></c:mrow></c:msub><c:mo>∼</c:mo><c:mn>1</c:mn><c:mo>/</c:mo><c:mn>3</c:mn><c:msup><c:mrow><c:mi>a</c:mi></c:mrow><c:mrow><c:mo>*</c:mo></c:mrow></c:msup></c:mrow></c:math>, <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:msub><e:mrow><e:mi>q</e:mi></e:mrow><e:mrow><e:mn>2</e:mn></e:mrow></e:msub><e:mo>∼</e:mo><e:mn>0.28</e:mn><e:msup><e:mrow><e:mi>b</e:mi></e:mrow><e:mrow><e:mo>*</e:mo></e:mrow></e:msup></e:mrow></e:math>) within the antiferromagnetic (AFM) state. By combining soft x-ray and vacuum ultraviolet angle-resolved photoemission spectroscopy measurements, neutron powder diffraction, scanning tunneling microscopy, and density-functional-theory calculations, we identify these dual-band reconstructions as manifestations of the AFM order driven by a (approximately <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:mn>1</g:mn><g:mo>/</g:mo><g:mn>3</g:mn></g:mrow></g:math>, 0.28, 0) nesting instability of the intercalated Tb <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mrow><i:mn>5</i:mn><i:msub><i:mi>d</i:mi><i:mrow><i:mi>x</i:mi><i:mi>z</i:mi></i:mrow></i:msub></i:mrow></i:math> orbitals. These orbital-selective modulations induce unusual momentum-dependent band folding and lead to the emergence of Dirac cones only at the <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mrow><k:msub><k:mover accent="true"><k:mi>M</k:mi><k:mo stretchy="false">¯</k:mo></k:mover><k:mn>1</k:mn></k:msub></k:mrow></k:math> point, signaling a topological phase transition in the AFM state. Importantly, the discovery of orbital-selective (approximately <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mrow><o:mn>1</o:mn><o:mo>/</o:mo><o:mn>3</o:mn></o:mrow></o:math>, 0.28, 0) AFM order offers crucial insights into the mechanism underlying the fractional magnetization plateau in this kagome AFM metal. Our findings not only underscore the essential role of both conducting and localized electrons in determining the magnetic orders of <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:mrow><q:mi>Ln</q:mi><q:msub><q:mrow><q:mi>Ti</q:mi></q:mrow><q:mrow><q:mn>3</q:mn></q:mrow></q:msub><q:msub><q:mrow><q:mi>Bi</q:mi></q:mrow><q:mrow><q:mn>4</q:mn></q:mrow></q:msub></q:mrow></q:math> (<s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"><s:mrow><s:mi>Ln</s:mi><s:mo>=</s:mo><s:mi>lanthanide</s:mi></s:mrow></s:math>) kagome metals but also offer a pathway for manipulating magnetism through selective control of anisotropic electronic structures.

  PublisherDOI

Frequent coauthors

• Nuh Gedik

  Massachusetts Institute of Technology

  56 shared

• Anshul Kogar

  University of California, Los Angeles

  52 shared

• Michael Zuerch

  Lawrence Berkeley National Laboratory

  32 shared

• Timm Rohwer

  Center for Free-Electron Laser Science

  24 shared

• Joshua Straquadine

  Stanford University

  24 shared

• I. R. Fisher

  22 shared

• Pablo Jarillo‐Herrero

  21 shared

• Edoardo Baldini

  21 shared

Education

• Ph.D., Applied Physics

  Stanford University

  2005

• M.S., Applied Physics

  Stanford University

  2002

• B.S., Physics

  University of California, Berkeley

  1999

Awards & honors

• Miller Fellow, University of California, Berkeley, 2023