About

Kemp W. Plumb is an Associate Professor of Physics at Brown University, having joined the department in 2017. He earned his Ph.D. from the University of Toronto in 2014, following a Master’s degree from McGill University in 2009 and a Bachelor’s degree from Queen's University in 2007. His research focuses on neutron scattering, quantum materials, and x-ray scattering, with a particular interest in the study of magnetic excitations, quantum spin liquids, and strongly correlated electron systems. His work involves investigating the fundamental properties of complex materials, contributing to the understanding of quantum magnetism and related phenomena. Professor Plumb has contributed to numerous significant publications in the field, exploring topics such as quantum fluctuations in Heisenberg magnets, magnetic order in honeycomb-lattice quantum magnets, and the behavior of spin-orbit Mott insulators. His research employs advanced scattering techniques to probe the microscopic properties of materials, advancing knowledge in condensed matter physics and quantum materials. He is actively involved in teaching courses related to physics fundamentals, quantum mechanics, thermodynamics, statistical mechanics, and computational physics at Brown University.

Research topics

• Physics
• Materials science
• Chemistry
• Condensed matter physics
• Quantum mechanics
• Atomic physics
• Crystallography
• Nuclear magnetic resonance

Selected publications

• Evolution of electronic and magnetic properties in Mn- and Co-alloyed ferromagnetic kagome metal Fe3Sn2

  APL Materials · 2026-01-01

  articleOpen access

  Kagome metals are an intriguing class of quantum materials as the presence of both flat bands and Dirac points provides access to functional properties present in strongly correlated and topological materials. To fully harness these electronic features, the ability to tune the Fermi level relative to the band positions is needed. Here, we explore the structural, electronic, and magnetic impacts of substitutional alloying within ferromagnetic kagome metal Fe3Sn2 in thin films grown by molecular beam epitaxy. Transition metals, Mn and Co, are chosen as substitutes for Fe to reduce or increase the d-band electron count, thereby moving the Fermi level accordingly. We find that Co is not incorporated into the Fe3Sn2 structure but instead results in a two-phase Fe–Co and (Fe,Co)Sn composite. In contrast, Fe3−xMnxSn2 films are realized with x of up to 1.0, retaining crystalline quality comparable with the parent phase. The incorporation of Mn repositions the flat bands relative to the Fermi level in a manner consistent with hole-doping, as revealed by hard x-ray photoemission and density functional theory. The Fe3−xMnxSn2 films retain room temperature ferromagnetism, with x-ray magnetic circular dichroism measurements confirming that the Fe and Mn moments are ferromagnetically aligned. The ability to hole-dope this magnetic kagome metal provides a platform for tuning properties, such as anomalous Hall and Nernst responses.

  PublisherDOI

• Non-Fermi liquid quasiparticles in strain-tuned Sr2RuO4

  ArXiv.org · 2025-03-14

  preprintOpen access

  Interacting electrons can form metallic states beyond the Fermi liquid paradigm, a conceptual frontier of many-body physics mainly explored via bulk thermodynamics and transport. In contrast, the microscopics of anomalous single-particle excitations underlying non-Fermi liquid properties have largely remained in the dark. Here we spectroscopically map such quantum-critical excitations in Sr$_2$RuO$_4$ under uniaxial pressure, an experimental challenge overcome by technical advances combining focused ion beam micro-milling with laser angle resolved photoemission. We show that quasiparticle excitations acquire a non-Fermi liquid scattering rate near the critical point but remain remarkably robust throughout the transition. These experiments serve as a benchmark for the theory of anomalous metals and settle the long-standing question if quantum-critical systems host quasiparticle excitations.

  PublisherOA PDFDOI

• Continuum of magnetic excitations in the Kitaev honeycomb iridate D3LiIr2O6

  npj Quantum Materials · 2025-03-29 · 3 citations

  articleOpen access

  Abstract Inelastic neutron scattering (INS) measurements of powder D 3 ( 7 Li)( 193 Ir) 2 O 6 reveal low energy magnetic excitations with a scattering cross-section that is broad in ∣ Q ∣ and energy transfer. The magnetic nature of the excitation spectrum is demonstrated by longitudinally polarized neutron scattering. The total magnetic moment of 1.8(4) μ B /Ir inferred from the observed magnetic scattering cross-section is consistent with the effective moment inferred from magnetic susceptibility data and expectations for the J eff = 1/2 single ion state. The rise in the dynamic correlation function $${\mathcal{S}}(Q,\omega )$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>S</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mrow> <mml:mi>Q</mml:mi> <mml:mo>,</mml:mo> <mml:mi>ω</mml:mi> </mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> for ℏ ω &lt; 5 meV can be described by a simple model assuming nearest-neighbor anisotropic spin exchange, such as that found in the Kitaev model. Exchange disorder associated with the D site likely plays an important role in stabilizing the low T quantum fluctuating state 1,2 .

  PublisherOA PDFDOI

• Pressure tuning of competing interactions on a honeycomb lattice

  Nature Communications · 2025-05-21 · 3 citations

  articleOpen access

  Exchange interactions are mediated via orbital overlaps across chemical bonds. Thus, modifying the bond angles by physical pressure or strain can tune the relative strength of competing interactions. Here we present a remarkable case of such tuning between the Heisenberg (J) and Kitaev (K) exchange, which respectively establish magnetically ordered and spin liquid phases on a honeycomb lattice. We observe a rapid suppression of the Néel temperature (TN) with pressure in Ag3LiRh2O6, a spin-1/2 honeycomb lattice with both J and K couplings. Using a combined analysis of x-ray data and first-principles calculations, we find that pressure modifies the bond angles in a way that increases the ∣K/J∣ ratio and thereby suppresses TN. Consistent with this picture, we observe a spontaneous onset of muon spin relaxation (μSR) oscillations below TN at low pressure, whereas in the high pressure phase, oscillations appear only when T < TN/2. Unlike other candidate Kitaev materials, Ag3LiRh2O6is tuned toward a quantum critical point by pressure while avoiding a structural dimerization in the relevant pressure range. Kitaev interactions on a honeycomb lattice can potentially lead to a quantum spin liquid state. Unfortunately, materials hosting Kitaev interactions also host Heisenberg interactions favouring long range order. Here, Sakrikar, Shen, Poldi and coauthors find that the relative strength of the Heisenberg and Kitaev interactions can be tuned by pressure in Ag3LiRh2O6.

  PublisherOA PDFDOI

• Characterizing sample degradation from synchrotron based X-ray measurements of ultra-thin exfoliated flakes

  Frontiers in Electronic Materials · 2025-06-25

  articleOpen accessSenior authorCorresponding

  It is undeniable that novel 2D devices and heterostructures will have a lasting impact on the advancement of future technologies. However, the inherent instability of many exfoliated van der Waals (vdW) materials is a well-known hurdle yet to be overcome. Thus, the sustained interest in exfoliated vdW materials underscores the importance of understanding the mechanisms of sample degradation to establish proactive protective measures. Here, the impact of prolonged synchrotron-based X-ray beam exposure on exfoliated flakes of two contemporary vdW materials, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m1"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:mi mathvariant="normal">P</mml:mi><mml:mi mathvariant="normal">S</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m2"><mml:mrow><mml:mi>α</mml:mi></mml:mrow></mml:math> - <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m3"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">R</mml:mi><mml:mi mathvariant="normal">u</mml:mi><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">l</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> , is explored using resonant inelastic X-ray scattering (RIXS) and total fluorescence yield X-ray absorption spectroscopy (XAS). In <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m4"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:mi mathvariant="normal">P</mml:mi><mml:mi mathvariant="normal">S</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> , the resulting RIXS and XAS spectra show a suppression, then vanishing, of NiS 6 multiplet excitations coupled with an upward shift of the peak energy of the XAS as a function of X-ray dose. In <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m5"><mml:mrow><mml:mi>α</mml:mi></mml:mrow></mml:math> - <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m6"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">R</mml:mi><mml:mi mathvariant="normal">u</mml:mi><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">l</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> , the signs of beam damage from the RIXS spectra are less evident. However, the post-experiment characterization of both materials using Raman spectroscopy exhibits signals of an amorphous and disordered system compared to pristine flakes; in addition, energy-dispersive X-ray spectroscopy of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m7"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:mi mathvariant="normal">P</mml:mi><mml:mi mathvariant="normal">S</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> shows evidence of ligand vacancies. As synchrotron radiation is fast becoming a required probe to study 2D vdW materials, these findings lay the groundwork for the development of future protective measures for synchrotron-based prolonged X-ray beam exposure, as well as for X-ray free electron laser.

  PublisherOA PDFDOI

• Dynamic phase transition in 1T-TaS2 via a thermal quench

  Nature Physics · 2025-06-27 · 4 citations

  articleSenior author
  PublisherDOI

• Elucidating the Role of Dimensionality on the Electronic Structure of the Van der Waals Antiferromagnet NiPS₃

  Advanced Physics Research · 2024 · 15 citations

  Senior authorCorresponding
  • Condensed matter physics
  • Chemistry
  • Materials science

  Abstract The sustained interest in investigating magnetism in the 2D limit of insulating antiferromagnets is driven by the possibilities of discovering, or engineering, novel magnetic phases through layer stacking. However, due to the difficulty of directly measuring magnetic interactions in 2D antiferromagnets, it is not yet understood how intra layer magnetic interactions in insulating , strongly correlated, materials can be modified through layer proximity. Herein, the impact of reduced dimensionality in the model van der Waals antiferromagnet NiPS 3 is explored by measuring electronic excitations in exfoliated samples using Resonant Inelastic X‐ray Scattering (RIXS). The resulting spectra shows systematic broadening of NiS 6 multiplet excitations with decreasing layer count from bulk down to three atomic layers (3L). It is shown that these trends originate from a decrease in transition metal‐ligand and ligand–ligand hopping integrals, and by charge‐transfer energy evolving from Δ = 0.83 eV in the bulk to 0.37 eV in 3L NiPS 3 . Relevant intralayer magnetic exchange integrals computed from the electronic parameters exhibit a decrease in the average interaction strength with thickness. This study underscores the influence of inter layer electronic interactions on intra layer ones in insulating magnets, indicating that magnetic Hamiltonians in few‐layer insulating magnets can greatly deviate from their bulk counterparts.

  PublisherOA PDFDOI

• Pseudosymmetry in Tetragonal Perovskite SrIrO$_3$ Synthesized under High Pressure

  arXiv (Cornell University) · 2024-07-10

  preprintOpen access

  In this study, we report a tetragonal perovskite structure of SrIrO$_3$ (P4/mmm, a = 3.9362(9) Å, c = 7.880(3) Å) synthesized at 6 GPa and 1400 $°$C, employing the ambient pressure monoclinic SrIrO$_3$ with distorted 6H structure as a precursor. The crystal structure of tetragonal SrIrO3 was evaluated on the basis of single crystal and powder X-ray diffraction. A cubic indexing was observed attributed to overlooked superlattice reflections. Weak fractional peaks in the H and K dimensions suggest possible structure modulation by oxygen defects. Magnetization study reveals weak paramagnetic behavior down to 2 K, indicative of the interplay between spin-orbit coupling, electron correlations, and crystal electric field. Additionally, measurements of electrical resistivity display metallic behavior with an upturn at about 54 K, ascribed to weak electron localization and possible structural defects.

  PublisherOA PDFDOI

• Jahn-Teller driven quadrupolar ordering and spin-orbital dimer formation in GaNb$_{4}$Se$_{8}$

  arXiv (Cornell University) · 2024-01-09

  preprintOpen accessSenior author

  The lacunar spinel GaNb$_4$Se$_8$ is a tetrahedral cluster Mott insulator where spin-orbit coupling on molecular orbitals and Jahn-Teller energy scales are competitive. GaNb$_4$Se$_8$ undergoes a structural and anti-polar ordering transition at T$_Q$ = 50 K that corresponds to a quadrupolar ordering of molecular orbitals on Nb$_4$ clusters. A second transition occurs at T$_M$ = 29 K, where local distortions on the Nb$_4$ clusters rearrange. We present a single crystal x-ray diffraction investigation these phase transitions and solve the crystal structure in the intermediate T$_M$ &lt; T &lt; T$_Q$ and low T &lt; T$_M$ temperature phases. The intermediate phase is a primitive cubic P2$_1$3 structure with a staggered arrangement of Nb4 cluster distortions. A symmetry mode analysis reveals that the transition at TQ is continuous and described by a single Jahn-Teller active amplitude mode. In the low temperature phase, the symmetry of Nb$_4$ clusters is further reduced and the unit cell doubles into an orthorhombic P2$_1$2$_1$2$_1$ space group. Nb$_4$ clusters rearrange through this transition to form a staggered arrangement of intercluster dimers, suggesting a valence bond solid magnetic state.

  PublisherOA PDFDOI

• Nanoscale electronic inhomogeneities in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>1</mml:mn><mml:mi>T</mml:mi><mml:msub><mml:mtext>-TaS</mml:mtext><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

  Physical Review Materials · 2024-03-06 · 5 citations

  articleOpen access

  In 1T-TaS2, native defects create electronic inhomogeneities spanning 5-10 nanometers that coexist with a well-formed commensurate charge density wave with a 1.3 nm period. Over these inhomogeneities, the band center shifts by up to 60meV and the gap varies by more than 100 meV. Surprisingly, the charge density wave order is unperturbed. These results reopen questions of how disorder affects charge density wave phases in correlated systems and emphasize the importance of real-space measurements in resolving the structural and electronic properties of quantum materials.

  PublisherOA PDFDOI

Frequent coauthors

• A. de la Torre

  38 shared

• C. Broholm

  Johns Hopkins University

  29 shared

• Tyrel M. McQueen

  21 shared

• B. Zager

  Brown University

  20 shared

• Young‐June Kim

  17 shared

• J. A. Rodriguez‐Rivera

  13 shared

• G. Fabbris

  11 shared

• Hitesh J. Changlani

  Florida State University

  10 shared

Labs

• Kemp Plumb's LabPI

  N/A

Education

• Ph.D.

  University of Toronto

• Other

  Johns Hopkins University