Planckian DissipationEdit
Planckian Dissipation is the name given to a family of observations in condensed matter physics where the inelastic scattering rate of electrons appears to be set by temperature in a way that ties directly to fundamental constants. The quintessential statement is that the scattering time τ scales like τ ~ ħ/(k_B T), a relation sometimes described in terms of a Planckian time τ_P = ħ/(k_B T). This phenomenology shows up most clearly in metals that defy simple quasiparticle descriptions, including so‑called strange metals and several high-temperature superconductors in their normal state. The idea is not that every material behaves identically, but that a surprisingly wide class of strongly interacting electron systems seems to organize its dissipation around a time scale set by temperature and a few universal constants.
The notion has become a focal point for discussions about how far we can push a universal schematic of dissipation in quantum many‑body systems. While the basic pattern—linear-in-T resistivity and related spectroscopic signatures—has been repeatedly observed, the claim that a single, material‑independent bound governs all inelastic scattering is debated. Critics emphasize that the precise coefficient in front of T can vary with material, measurement method, and the way one separates different scattering channels (for example, phonons vs. electronic interactions). Proponents argue that the observed tangle of data across cuprates, certain heavy‑fermion compounds, graphene and related materials, and holographic models points to a common, underlying dynamical principle. In practice, Planckian dissipation is a powerful organizing idea, but not an airtight universal law.
This article surveys the physics, the empirical signatures, the main theoretical interpretations, and the debates that surround Planckian dissipation, with attention to how different communities describe the phenomenon and what is gained by treating it as a guiding principle rather than a rigid axiom.
Physical foundations
The central empirical claim is that, in many strongly interacting metals, the rate at which electrons lose momentum and energy to the rest of the system—i.e., the inelastic scattering rate—is proportional to temperature with a coefficient that involves fundamental constants. A common way to express this is through a characteristic time τ_P defined by τ_P ≈ ħ/(k_B T). In transport measurements this often manifests as a resistivity that grows linearly with temperature over a broad range, rather than following a conventional Fermi‑liquid dependence. The idea ties together the notion of quantum coherence, temperature as a driver of fluctuations, and the idea that in a strongly interacting medium there is a natural time scale set by the same constants that define quantum mechanics and statistical mechanics.
The mathematical underpinning is not a formal theorem, but a heuristic that emerges when one estimates a scattering time from, for example, a Drude‑like interpretation of conductivity, spectral widths inferred from Angle-resolved photoemission spectroscopy or Optical conductivity, and the widths of features in spectroscopic data. The result is a timescale that is short in a precise sense for many materials at a given temperature, suggesting that the system dissipates energy and momentum rapidly as T rises. Core references often connect these ideas to the Planck constant Planck constant and the Boltzmann constant Boltzmann constant, highlighting how quantum and thermal scales intertwine in strongly correlated matter.
From a broader theoretical vantage, Planckian dissipation sits at the intersection of quantum criticality, unconventional transport, and strong coupling dynamics. It resonates with ideas from Quantum criticality and Strange metal behavior, and it has found a natural playground in holographic models based on the AdS/CFT correspondence that are used to study strongly coupled quantum systems. It also interfaces with more traditional frameworks such as Fermi liquid theory and its breakdowns, and with alternative descriptions like Marginal Fermi liquid theory that were proposed to account for anomalous spectroscopic lineshapes and transport.
Experimental signatures
Linear-in-T resistivity: In many materials exhibiting Planckian dissipation, the normal-state resistivity rises approximately linearly with temperature over a broad interval, implying a scattering rate that tracks T. This is a hallmark often discussed alongside other transport probes such as the Hall effect and magnetoresistance.
Spectroscopic widths: Techniques like Angle-resolved photoemission spectroscopy (ARPES) and optical probes can reveal linewidths or scattering rates that scale with temperature in a way consistent with a Planckian time. When interpreted carefully, these widths suggest a relaxation process that is not easily separated into conventional, weakly interacting quasiparticle processes.
Universality questions across materials: Similar signatures are reported in a variety of systems, including some Cuprate superconductors in the normal state and certain heavy‑fermion compounds, though the degree of universality and the precise numerical coefficients are still subjects of discussion.
Deviations and boundaries: There are materials and regimes where the simple τ ~ ħ/(k_B T) picture breaks down—for example, at very low temperatures, in systems with strong disorder, or where multiple scattering channels with distinct energy scales compete. These deviations are as informative as the clean cases, narrowing the domain where a simple Planckian description applies.
Strange metal behavior, a term used to describe metals that do not conform to the standard Fermi‑liquid paradigm, is closely associated with Planckian dissipation in the literature. The relevant physics often involves a competition between quantum critical fluctuations and lattice or impurity effects, and it is common to discuss Planckian ideas alongside Quantum criticality and Mott–Ioffe–Regel limit considerations.
Theoretical frameworks
Quantum criticality: Near a quantum critical point, fluctuations persist down to low energies and temperatures, producing scattering rates that scale with temperature in a way that can resemble a Planckian form. This viewpoint treats Planckian dissipation as a manifestation of critical dynamics, rather than a separate, universal law. See Quantum criticality and Strange metal.
Marginal Fermi liquid and related phenomenology: Early proposals suggested that deviations from conventional Fermi liquid behavior could explain linear‑in‑T scattering without invoking a strict universal bound. Marginal Fermi liquid theory remains a reference point for interpreting spectroscopic lineshapes and transport.
Electron–phonon and other conventional channels: At higher temperatures, phonons contribute to scattering in ways that can mimic or mask Planckian scaling. Distinguishing purely electronic Planckian dissipation from phonon‑driven processes requires careful analysis of multiple experiments, including Electron–phonon interaction models and temperature regimes where phonons dominate.
Holographic and strong‑coupling approaches: The AdS/CFT framework has produced toy models that naturally yield linear‑in‑T resistivity and fast relaxation dynamics reminiscent of Planckian dissipation. These models are not exact descriptions of real materials, but they provide a structural language for understanding how strong coupling might enforce rapid dissipation in a way that is not captured by weakly interacting theories. See AdS/CFT correspondence.
Universality vs. material specificity: A central tension in the literature is whether the Planckian pattern is a universal principle applicable to all strongly interacting metals or a widely observed motif that can still depend on the microscopic details of a given material. This debate shapes how researchers connect transport measurements, spectroscopy, and microscopic models.
Controversies and debates
Universality vs. variability: Proponents argue that a striking array of materials show a scattering rate on the order of k_B T/ħ, suggesting a common dynamical constraint in strongly interacting electron systems. Critics caution that coefficients vary, coexistence with other scattering mechanisms is common, and care is needed in separating electronic versus lattice contributions. In particular, some materials adhere to the Planckian scaling only over a limited temperature window or under specific sample conditions.
Fundamental status: Is Planckian dissipation a deep, fundamental bound or a practical organizing principle? The consensus leans toward the latter: it is a powerful heuristic that helps unify disparate observations, but it is not a formal theorem of quantum many‑body physics. The distinction matters for how aggressively one generalizes the idea to new systems or uses it to infer microscopic mechanisms.
Interpretive diversity: The same data can be framed in multiple ways. Some researchers emphasize quantum critical fluctuations and strong coupling as the heart of the matter, while others highlight electron–phonon interactions, disorder, or multiband effects as essential to understanding specific materials. This plurality of interpretations is typical in a field where experiment, spectroscopy, and theory intersect under complex conditions.
Political and cultural framing in science discourse: In any field with high visibility, broader cultural trends can influence discussions about priority, funding, or the direction of research. A pragmatic stance is to evaluate Planckian dissipation on the basis of predictive power and empirical support, rather than on broader ideological narratives. Scientific progress, in this view, comes from testable hypotheses, transparency about uncertainties, and careful cross‑checking across independent experiments and methods. Critics of overextended claims argue that focusing on universal narratives can overshadow material‑specific physics and empirical falsifiability, while proponents contend that such narratives help synthesize a large and varied data set into a coherent picture.
Why arguments framed as daily political critiques are not productive to the physics: Planckian dissipation is a technical concept about how electrons lose energy in solids. While philosophers of science and political commentators may discuss the social context of science, the core progress comes from measurements, models, and falsifiable predictions. The most robust position in the physics community is to advance clear, testable statements about when and where Planckian behavior holds, and to be explicit about exceptions and uncertainties.