About

Professor Piers Coleman is a faculty member in the Department of Physics and Astronomy at Rutgers University, where he is part of the Materials Theory Group. His research focuses on condensed matter physics, particularly in the areas of quantum materials, heavy fermion physics, and many-body physics. He has delivered numerous talks on topics such as order fractionalization, strange metal behavior, and the rise of topology in heavy fermions, reflecting his engagement with frontier science in emergent materials. Professor Coleman's work is supported by the Department of Energy and the National Science Foundation, and he is actively involved in the Rutgers Center for Materials Theory and related seminars and journal clubs. His academic contributions include teaching advanced courses in condensed matter physics, statistical mechanics, and quantum mechanics, as well as participating in international workshops and conferences on complex adaptive matter and correlated materials.

Research topics

• Physics
• Condensed matter physics
• Quantum mechanics
• Materials science
• Computer Science
• Statistical physics

Selected publications

• Topological Mixed Valence Model for Twisted Bilayer Graphene

  Physical Review X · 2025-04-24 · 11 citations

  articleOpen accessSenior author

  Song and Bernevig (SB) have recently proposed a topological heavy-fermion description of the physics of magic angle twisted bilayer graphene (MATBG), involving the hybridization of flat-band electrons with a relativistic conduction sea. Here, we explore the consequences of this model, seeking a synthesis of understanding drawn from heavy-fermion physics and MATBG experiments. Our work identifies a key discrepancy between measured and calculated on-site Coulomb interactions, implicating renormalization effects that are not contained in the current model. With these considerations in mind, we consider a SB model with a single, renormalized on-site interaction between the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>f</a:mi></a:math> electrons, containing a phenomenological heavy-fermion binding potential on the moiré <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>A</c:mi><c:mi>A</c:mi></c:math> sites. This feature allows the simplified model to capture the periodic reset of the chemical potential with filling and the observed stability of local moment behavior. We argue that a two-stage Kondo effect will develop in MATBG as a consequence of the relativistic conduction band: Kondo I occurs at high temperatures, establishing a coherent hybridization at the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi mathvariant="normal">Γ</e:mi></e:math> points and a non-Fermi liquid of incoherent fermions at the moiré <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mi>K</h:mi></h:math> points; at much lower temperatures, Kondo II leads to a Fermi liquid in the flat band. Utilizing an auxiliary-rotor approach, we formulate a mean-field treatment of MATBG that captures this physics, describing the evolution of the normal state across a full range of filling factors. By contrasting the relative timescales of phonons and valence fluctuations in bulk heavy-fermion materials with that of MATBG, we are led to propose a valley-polaron origin to the Coulomb renormalization and the heavy-fermion binding potential identified from experiment. We also discuss the possibility that the two-fluid, non-Fermi liquid physics of the relativistic Kondo lattice is responsible for the strange-metal physics observed in MATBG.

  PublisherOA PDFDOI

• A microscopic model of fractionalized Fermi liquid

  arXiv (Cornell University) · 2025-11-02

  preprintOpen access1st authorCorresponding

  In this short letter we identify a relationship between the Kondo lattice model formulated in Coleman {\it et.al}, Phys. Rev. Lett. {\bf 129}, 177601 (2022) and Ancilla Layer formulation of the Hubbard model recently proposed by Zhang and Sachdev.

  PublisherOA PDFDOI

• Triplet pairing, orbital selectivity, and correlations in iron-based superconductors

  Physical review. B./Physical review. B · 2025-09-10

  articleSenior author

  We use a slave-boson approach to study the band renormalization and pair susceptibility in the normal state of iron-based superconductors in presence of strong Coulomb repulsion and Hund's interaction. Our results show orbital selectivity toward localization of $xy$ orbitals and its interplay with superconductivity. We also compare the recently proposed triplet resonating valence bond (tRVB) theory of superconductivity in iron-based superconductors with the more conventional ${s}_{\ifmmode\pm\else\textpm\fi{}}$ pairing. We show that both favor a superconductivity when the $xy$ orbital is delocalized, but the tRVB superconductivity supports a second weaker dome when $xy$ orbital is localized.

  PublisherDOI

• Critical fluctuations and conserved dynamics in a strange ferromagnetic metal

  arXiv (Cornell University) · 2025-10-23

  preprintOpen access

  The origin of the strange metallic behavior observed in a wide range of quantum materials is an open challenge to condensed matter physics. Historically, strange metals were uniquely associated with antiferromagnetic quantum critical points (QCPs), but a new generation of materials reveals their association with uniform order parameters, such as ferromagnetism, valley or nematic order, suggesting a deeper common denominator. At a QCP, order parameter fluctuations are characterized by the dynamical critical exponent $z$, which quantifies the space-time scaling asymmetry. Here, we report the observation of a divergence in the Grüneisen ratio at the QCP of the strange-metal ferromagnet CeRh$_6$Ge$_4$ with a dynamical critical exponent $z=3$, signaling that the underlying quantum singularity involves a conserved degree of freedom. Yet the magnetization of this easy-plane ferromagnet is not conserved. We argue that the $z=3$ strange criticality requires a description beyond the Landau paradigm, proposing a link with the gauge modes of the small-to-large Fermi surface transition and the associated gauge charge of the delocalizing heavy electrons.

  PublisherOA PDFDOI

• Microscopic Theory of Pair Density Waves in Spin-Orbit Coupled Kondo Lattice

  Physical Review Letters · 2025-06-26 · 1 citations

  articleOpen accessSenior author

  We demonstrate that the discommensuration between the Fermi surfaces of a conduction sea and an underlying spin liquid provides a natural mechanism for the spontaneous formation of pair density waves. Using a recent formulation of the Kondo lattice model that incorporates a Yao Lee spin liquid proposed by the authors, we demonstrate that doping away from half filling induces finite-momentum electron-Majorana pair condensation, resulting in amplitude-modulated pair density waves (PDWs). Our approach provides a precise, analytically tractable pathway for understanding the spontaneous formation of PDWs in higher dimensions and offers a natural mechanism for PDW formation in the absence of Zeeman splitting.

  PublisherDOI

• Dual View of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Z</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>-Gauged XY Model in 3D

  Physical Review Letters · 2025-05-12

  article1st authorCorresponding

  The Z_{2}-gauged XY model is of long-standing interest both in the context of nematic order, and the study of fractionalization and superconductivity. This Letter presents heuristic arguments that no deconfinement of the XY field occurs in this model and presents results of a large-scale Monte Carlo simulations on a cubic lattice that are consistent with this conclusion. The correlation radius determining the confinement is found to be growing rapidly as a function of the parameters in the phase featuring the nematic order. Thus, mesoscopic properties of the system can mimic deconfinement with high accuracy in some part of the phase diagram.

  PublisherDOI

• Oscillate and renormalize: Fast phonons reshape the Kondo effect in flat-band systems

  Physical review. B./Physical review. B · 2025-06-03 · 2 citations

  articleOpen accessSenior author

  We examine the interplay between electron correlations and phonons in an Anderson-Holstein impurity model with an Einstein phonon. When the phonons are slow compared to charge fluctuations (frequency $ω_0 \ll U/2$, the onsite Coulomb scale $U/2$), we demonstrate analytically that the expected phonon-mediated reduction of interactions is completely suppressed, even in the strong coupling regime. This suppression arises from the oscillator's inability to respond to rapid charge fluctuations, manifested as a compensation effect between the polaronic cloud and the excited-state phonons associated with valence fluctuations. We identify a novel frozen mixed valence phase, above a threshold dimensionless electron-phonon coupling $α^*$ when the phonons are slow, where the static phonon cloud locks the impurity into specific valence configurations, potentially explaining the puzzling coexistence of mixed valence behavior and insulating properties in materials like rust. Conversely, when the phonon is fast ($ω_0 \gtrsim U/2$), the system exhibits conventional polaronic behavior with renormalized onsite interactions effectively $U_{\text{eff}}$ due to phonon mediated attraction, with additional satellite features in the local spectral function due to phonon excitations. Using numerical renormalization group (NRG) calculations, a fully dynamic renormalization technique, we confirm these behaviors in both regimes. These findings have important implications for strongly correlated systems where phonon energy scales may be comparable to the Coulomb scale, such as in twisted bilayer graphene, necessitating careful consideration of interaction renormalizations in theoretical models.

  PublisherOA PDFDOI

• Thermal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>R</mml:mi> <mml:mi>C</mml:mi> </mml:mrow> </mml:math> circuit model for resolving the thermal paradox

  Physical review. B./Physical review. B · 2025-10-09

  preprintOpen accessSenior author

  Thermal measurements of heat capacity and thermal conductivity in a wide range of insulators and superconductors exhibit a ``thermal paradox'': a large linear specific heat reminiscent of neutral Fermi surfaces (associated with fractionalized quasiparticles) in nonmetallic samples that exhibit no corresponding linear temperature coefficient to the thermal conductivity. At first sight, these observations appear to support the formation of a continuum of thermally localized many-body excitations, a form of many-body localization that would be fascinating in its own right. Here, by mapping thermal conductivity measurements onto thermal $RC$ circuits, we argue that the development of extremely long thermal relaxation times, a ``thermal bottleneck,'' is likely in systems with either many-body localization or neutral Fermi surfaces due to the large ratio between the electron and phonon specific heat capacities. We present a reevaluation of thermal conductivity measurements in materials exhibiting a thermal paradox that can be used in future experiments to deliberate between these two exciting alternatives.

  PublisherOA PDFDOI

• Axionic tunneling from a topological Kondo insulator

  ArXiv.org · 2025-12-04

  preprintOpen accessSenior author

  Discoveries over the past two decades have revealed the remarkable ability of quantum materials to emulate relativistic properties of the vacuum, from Dirac cones in graphene to the Weyl surface states of topological insulators. Yet the most elusive consequence of topology in quantum matter is the axionic $E\cdot B$ term in the electromagnetic response. Here we report a direct signature of axionic physics obtained through scanning tunneling microscopy (STM). Although recent STM experiments using SmB$_6$ nanowires have been interpreted as evidence for spin-polarized currents arising from topological surface states, we show that the observed spin polarization instead originates from axionic electrodynamics. Our analysis reveals a striking voltage-induced magnetization: extremely small voltages ($\sim$ 30 meV) generate tip moments of order 0.1 $μ_B$ that reverse sign with the applied bias. The magnitude, tunability, and reversibility of this signal are consistent with an axionic $E \cdot B$ coupling, and fully account for the magnetic component of the tip density of states, ruling out static magnetism. Millivolt-scale control of spin polarization in a tunnel junction provides a new route for probing axionic electrodynamics and opens avenues for future STM and spintronics applications.

  PublisherOA PDFDOI

• Odd-parity superconductivity underpinned by antiferromagnetism in heavy fermion metal YbRh$_2$Si$_2$

  ArXiv.org · 2025-02-10

  preprintOpen access

  Topological superconductors are essential elements of the periodic table of topological quantum matter. However, the relevant odd-parity spin-triplet superconductors are rare. We report high-resolution measurements of the complex electrical impedance of YbRh$_2$Si$_2$ down to 0.4 mK, that reveal the presence of several superconducting states, suppressed differently by magnetic field, both Pauli-limited and beyond the Pauli limit. Superconductivity is abruptly switched off at the critical field of the primary antiferromagnetic order. The onset of electro-nuclear spin density wave order enhances the superconductivity, which we account for by the simultaneous formation of a spin-triplet pair density wave. Together these observations provide compelling evidence for odd-parity superconductivity, and its underpinning by antiferromagnetism, and allow us to identify the topological helical state.

  PublisherOA PDFDOI

Recent grants

• Local Moment and Heavy Fermion Physics

  NSF · $330k · 2009–2014

• Local Moment and Heavy Fermion Physics

  NSF · $366k · 2006–2010

• Entanglement Physics of Quantum f-electron Materials

  NSF · $540k · 2019–2024

• Local Moment and Heavy Fermion Physics

  NSF · $270k · 2013–2016

• Local Moment and Heavy Fermion Physics

  NSF · $366k · 2003–2007

Frequent coauthors

• Premala Chandra

  Rutgers, The State University of New Jersey

  108 shared

• Marianna Maltseva

  58 shared

• Yashar Komijani

  56 shared

• Ikuya Yamada

  Metropolitan University

  49 shared

• Masahiro Ono

  49 shared

• T. Hanaguri

  RIKEN Center for Emergent Matter Science

  49 shared

• H. Takagi

  49 shared

• M. Takano

  Eisai (Japan)

  49 shared

Awards & honors

• 2025 APS Outstanding Referee