arXiv subjects

Piers Coleman

Publications and source records attributed to Piers Coleman.

At least 19 recordsLinked to original sources

arXiv2026

Bose metal near pair-density-wave order in a spin-orbit-coupled Kondo lattice

We show that a three-dimensional superconductor with a non-Abelian SU(2) order parameter can support an extended resistive regime a Bose metal, in which transport is carried by bosonic electron-Majorana bound states - separating a uniform superconductor from a pair-density-wave (PDW) phase. The setting is a solvable Kondo lattice model introduced previously by the present authors, in which Kondo screening of a Yao-Lee $\mathbb{Z}_2$ spin liquid generates an order parameter with SU(2), rather than conventional U(1), symmetry, containing both superconducting and spin-density-wave components. Two effects cooperate to make fluctuations anomalously strong in three dimensions: the vanishing of the quadratic superconducting stiffness near the Lifshitz point where the optimal pairing momentum shifts from zero to finite $Q$, and the enlarged SU(2) order-parameter manifold. Building on our prior result that doping away from half-filling drives amplitude-modulated PDW order via finite-momentum electron-Majorana condensation, we analyze the fluctuation-dominated regime above that phase using a nonlinear sigma model. We find that the order-parameter propagator develops a ring of soft modes throughout the disordered phase, and that the resulting resistivity scales approximately as $R \sim T^3$ in three dimensions.

cond-mat.str-el↗

arXiv2026

Tractable model for a fractionalized Fermi liquid (FL$^*$) on a square lattice

Motivated by the continued interest in Fermi-surface reconstruction without symmetry breaking, we present an analytically tractable microscopic model of a fractionalized Fermi liquid (FL$^*$) on a square lattice and discuss its potential relevance to the cuprates. As in ancilla-qubit constructions, the model is related to Kondo lattice systems, but in this case, the conduction electrons interact with a $\mathbb{Z}_2$ spin liquid of the Yao--Lee type, with a Majorana Fermi surface. The associated $\mathbb Z_2$ gauge theory is static so that the model can be analytically solved to leading-logarithic accuracy. There are two phases: one in which the fractionalized fermions of the spin liquid hybridize with conduction electrons to form a common Fermi surface violating the naive Luttinger count, and one in which they remain decoupled. We discuss the salient features of the small Fermi-surface phase, including analytically derived momentum dependent coherence factors responsible for the appearance of Fermi arcs \`{a} la Yang-Rice-Zhang. We further discuss the impact of quantum and thermal fluctuations, including a strong diamagnetic response and a logarithmically divergent Sommerfeld coefficient at the onset of the pseudogap.

cond-mat.str-el↗

arXiv2025

A Landau Theory for Pair Density Modulation in Fe(Te,Se) flakes

Motivated by recent scanning tunneling microscopy (STM) experiments reporting a pair-density modulation (PDM) in flakes of FeTe${_{0.55}}$Se${_{0.45}}$, we develop a Landau theory to elucidate its physical origin. We analyze the PDM in terms of screw and glide symmetries, interpreting it as a hybridized state of two order parameters with opposite glide and screw parity. To explain the absence of PDM in the bulk, we argue that the breaking of glide symmetry at the surface allows nematic order to selectively stabilize the PDM in thin flakes. From these symmetry constraints, we show that the opposing glide and screw parities of the condensate favor a site-based, rather than bond-based, pairing mechanism. Thus the discovery of PDM in superconducting flakes suggests that the pairing in iron-based superconductors is local to the iron atoms, possibly driven by Hunds coupling. We argue that the mismatch in Knight shift between the even and odd parity order parameters will lead to a magnetic-field enhancement of the PDM at low fields, and a reentrant triplet phase at high fields that can be tested in STM experiments.

cond-mat.supr-con↗

arXiv2025

Axionic tunneling from a topological Kondo insulator

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 $\mu_B$ 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.

cond-mat.mes-hall↗

arXiv2025

Philip Warren Anderson

Philip Warren Anderson was a pioneering theoretical physicist whose work fundamentally shaped our understanding of complex systems. Anderson received the Nobel Prize in Physics in 1977 for his groundbreaking research on localization and magnetism, yet he did so much more. His work on magnetism included antiferromagnetism, superexchange, the Kondo problem and local magnetic moments in metals. Anderson pointed out the importance of disorder through his work on localization, non-crystalline solids and spin glasses. In superconductivity, he is known for the dirty superconductor theorem, showing the gauge-invariance of the BCS theory, his study of flux creep, and for his collaboration with experimentalists to realize the Josephson effect. Anderson's resonating valence bond theory may yet play an important role in high temperature superconductivity. Anderson was also fascinated by broken symmetry, and he laid the theoretical groundwork for what is now known as the Anderson-Higgs mechanism, showing how gauge bosons can acquire mass - an insight that played a foundational role in the Standard Model of particle physics. In his seminal "More is Different" paper, Anderson argued that the collective emergent phenomena that arise in complex interacting systems cannot be deduced from their fundamental parts. Anderson's legacy endures not only through the lasting impact of his scientific work but also through his influence on generations of physicists who continue to explore the rich landscape of collective behavior in nature.

physics.hist-ph↗

arXiv2025

Critical fluctuations and conserved dynamics in a strange ferromagnetic metal

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 Gr\"uneisen 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.

cond-mat.str-el↗

arXiv2025

Breakdown of Stoner Ferromagnetism by Intrinsic Altermagnetism

The Stoner criterion for ferromagnetism arises from interaction-driven asymmetric filling of spin bands, requiring that the spin susceptibility: (i) peaks dominantly at $\mathbf{Q}=\bm{0}$; and (ii) diverges at a critical interaction strength. Here, we demonstrate that this Stoner mechanism breaks down due to competition with altermagnetic orders, even when both conditions are met. Altermagnetism in solids is characterized by collinear antiparallel spin alignment that preserves translational symmetry, and inherently fulfills these requirements. As a proof of concept, we study a two-orbital Hubbard model with electron filling near Van Hove singularities at high-symmetry momenta. Our results reveal that orbital-resolved spin fluctuations, amplified by strong inter-orbital hopping, stabilize intrinsic altermagnetic order. A quantum phase transition from altermagnetism to ferromagnetism occurs at critical Hund's coupling $J_H$. We further propose directional spin conductivity anisotropy as a detectable signature of this transition via non-local spin transport. This work establishes the pivotal role of altermagnetism in correlated systems.

cond-mat.str-el↗

arXiv2025

Particle-hole Symmetric Slave Boson Method for the Mixed Valence Problem

We introduce an analytic slave boson method for treating the finite $U$ Anderson impurity model. Our approach introduces two bosons to track both $Q\rightleftharpoons Q\pm1$ valence fluctuations and reduces to a single symmetric $s$-boson in the effective action, encoding all the high energy atomic physics information in the boson's kinematics, while the low energy part of the action remains unchanged across finite $U$, infinite $U$, and Kondo limits. We recover the infinite $U$ and Kondo limit actions from our approach and show that the Kondo resonance already develops in the normal state when the slave boson has yet to condense. We show that the slave rotor and $s$-boson have the same algebraic structure, and we establish a unified functional integral framework connecting the $s$-boson and slave rotor representations for the single impurity Anderson model.

cond-mat.str-el↗

arXiv2025

A higher dimensional generalization of the Kitaev spin liquid

We construct an exactly solvable model of a four-dimensional Kitaev spin liquid. The lattice structure is orthorhombic and each unit-cell contains six sublattice degrees of freedom. We demonstrate that the Fermi surface of the model is made up of two-dimensional surfaces. Additionally, we evaluate the energy cost of creating visons using scattering theory. The positive bond-flip energy suggests that the system's ground state is flux-free, similar to the two-dimensional Kitaev honeycomb model. Our model sheds light on the realization of higher-dimensional fractionalization.

cond-mat.str-el↗

arXiv2025

Oscillate and Renormalize: Fast Phonons Reshape the Kondo Effect in Flat Band Systems

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 $\omega_0 \ll U/2$, 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 $\alpha^*$ 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 ($\omega_0 \gtrsim U/2$), 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.

cond-mat.str-el↗

arXiv2025

Resolving the Thermal Paradox: Many-body localization or fractionalization?

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 in 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 re-evaluation of thermal conductivity measurements in materials exhibiting a thermal paradox that can be used in future experiments to deliberate between these two exciting alternatives.

cond-mat.str-el↗

arXiv2025

Dual view of the Z$_2$-Gauged XY Model in 3D

The $Z_2$ gauged neutral XY model is of long-standing interest both in the context of nematic order, and the study of fractionalization and superconductivity. This paper 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 which 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.

cond-mat.supr-con↗

arXiv2025

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

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.

cond-mat.supr-con↗

arXiv2024

Microscopic theory of pair density waves in spin-orbit coupled Kondo lattice

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 which 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 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 a Zeeman field.

cond-mat.str-el↗

arXiv2024

Topological superconductivity in a spin-orbit coupled Kondo lattice

We consider the effect of spin-orbit coupling on a two-dimensional Kondo Lattice model, in which conduction electrons are antiferromagnetically coupled to a Yao-Lee spin liquid. When a Rashba spin-orbit interaction and a nearest-neighbor Kondo interaction is introduced, the low-energy Majorana bands become gapped and develop Chern numbers, protecting unidirectionally propagating Majorana edge modes. Our model describes a chiral topological superconductor with fractionalized charge-$e$ order parameter and spontaneously broken time-reversal symmetry, which may be of interest for certain heavy fermion superconductors, such as UTe$_2$.

cond-mat.str-el↗

arXiv2024

Quantum order by disorder in Frustrated Spin Nanotubes

We investigate quantum order by disorder in a frustrated spin nanotube formed by wrapping a $J_1$-$J_2$ Heisenberg model at 45$^\circ$ around a cylinder. Using Schwinger boson theory and Density Matrix Renormalization Group (DMRG), we have computed the ground-state phase diagram to reveal a $\mathbb{Z}_2$ phase in which collinear spin stripes form a right or left handed helix around the nanotube. We have derived an analytic estimate for the critical $η_c=J_1/2J_2$ of the $\mathbb{Z}_2$ helical phase transition, which is in agreement with the DMRG results. By evaluating the entanglement spectrum and nonlocal string order parameters we discuss the topology of the $\mathbb{Z}_2$-helical phase.

cond-mat.str-el↗

arXiv2024

Analytic calculation of the vison gap in the Kitaev spin liquid

Although the ground-state energy of the Kitaev spin liquid can be calculated exactly, the associated vison gap energy has to date only been calculated numerically from finite size diagonalization. Here we show that the phase shift for scattering Majorana fermions off a single bond-flip can be calculated analytically, leading to a closed-form expression for the vison gap energy $Δ= 0.2633J$. Generalizations of our approach can be applied to Kitaev spin liquids on more complex lattices such as the three dimensional hyper-octagonal lattice.

cond-mat.str-el↗

arXiv2024

Breakdown of order-fractionalization in the CPT model

We present an analysis of the half-filled CPT model, an analytically tractable Kondo lattice model with Yao-Lee spin-spin interactions on a 3D hyperoctagon lattice, proposed by Coleman, Panigrahi, and Tsvelik. Previous studies have established that the CPT model exhibits odd-frequency triplet superconductivity and order fractionalization. Through asymptotic analyses in the small $J$ and large $J$ Kondo coupling limits, we identify a quantum critical point at $J_c$, marking a transition from a superconductor to a Kondo insulator. By estimating the vison gap energy to account for thermal gauge fluctuations, we determine the energy scales governing the thermal breakdown of order fractionalization. Moreover, at large $J$ the Kondo insulator undergoes orbital decoupling, leading to the formation of a decoupled Kitaev orbital liquid. These findings and analogies with the $\mathbb{Z}_2$-gauged $XY$ model lead us to propose a tentative phase diagram for the CPT model at half-filling.

cond-mat.str-el↗