Charge density waves arise when electrons in a crystal spontaneously organize into a standing wave of charge, dragging the atomic lattice along with them into a periodic distortion. In 1T-TaS2, a layered transition metal dichalcogenide, this wave evolves through a sequence of phases as temperature falls: an incommensurate wave that barely notices the underlying lattice, a nearly commensurate intermediate, and finally the fully commensurate state, in which the wave period locks into an exact rational relationship with the atomic lattice. That last phase is the crown jewel of the material. It hosts a Mott insulating state, supports unusual spin behavior that has been linked to quantum spin liquid physics, and can be driven into superconductivity or hidden metastable states by pressure, doping, or ultrafast light pulses. Every one of those phenomena, however, has historically demanded a cold sample.

The intrinsic temperature limit has frustrated researchers for decades. The commensurate phase in pristine 1T-TaS2 gives way to the nearly commensurate state well below room temperature, meaning that experiments on its most exotic correlated behavior require liquid nitrogen cooling or worse. Various strategies have been tried to stabilize the phase at higher temperatures, including epitaxial growth on carefully matched substrates, endotaxial structuring, electrostatic gating, and chemical intercalation with metal atoms. Each approach has produced partial successes, but none has offered a simple, general, and chemically tunable route to a room-temperature commensurate charge density wave in bulk hybrid crystals. The new work argues that the missing ingredient was not more aggressive perturbation but gentler, more precisely tuned molecular interactions.

The UCLA-led team, working with collaborators at the University of Southern California, the University of California Irvine, Tamkang University in Taiwan, and the University of Chemistry and Technology Prague, built on their earlier development of molecular intercalation superlattices, in which organic molecules are inserted between the van der Waals layers of a layered crystal to create artificial hybrid solids. In the new study they intercalated arginine, an amino acid with a strongly basic guanidinium group and multiple hydrogen-bonding sites, into 1T-TaS2. Structural characterization, including X-ray diffraction and high-resolution electron microscopy, confirmed that the molecules form ordered galleries between the tantalum sulfide layers, producing a genuine hybrid superlattice rather than a random, disordered mixture.

The critical discovery was that arginine does not merely sit inertly between the layers. The molecules engage in strong non-covalent interactions with the 1T-TaS2 sheets, and those interactions feed directly into the electronic structure of the crystal. Raman spectroscopy, electrical transport measurements, and differential scanning calorimetry all tracked the charge density wave phase transitions in the hybrid crystals, and the results were striking: the commensurate phase, which in pristine material vanishes far below room temperature, persisted up to 330 kelvin in the arginine intercalated superlattices. The team also observed ferro-rotational order among the commensurate charge density wave domains, a chiral degree of freedom in which domains of the wave adopt different rotational orientations, adding another controllable order parameter to the hybrid material.

Not every amino acid worked. The researchers tested other, weakly interacting amino acids and found that they produced only modest shifts in the charge density wave phase transitions. That contrast is scientifically important because it isolates the mechanism. The stabilization is not simply a generic consequence of spacing the layers apart or diluting the electronic system; it depends on the specific strength and geometry of the chemical interaction between the guest molecule and the host lattice. Arginine, with its charged guanidinium head group and flexible backbone, appears uniquely suited among the molecules tested to couple to the tantalum sulfide layers strongly enough to reshape the electronic energy landscape.

Computational modelling by the team’s theory collaborators clarified what that reshaping means energetically. Density functional theory calculations showed that the arginine molecules modify the energy landscape of the charge density wave phases in two complementary ways. Thermodynamically, the commensurate state becomes more stable relative to competing phases, lowering the free energy cost of maintaining the locked-in wave. Kinetically, the energy barriers separating the phases increase, making the commensurate state more robust against thermal fluctuations that would otherwise nudge the crystal back toward the nearly commensurate configuration. Both effects together explain why the phase survives at temperatures where it would normally surrender, and they suggest a design principle: choose molecules whose interaction strength with the host can be tuned to engineer the relative energies of correlated phases.

The implications reach well beyond one material. 1T-TaS2 sits at the center of a dense web of emergent quantum phenomena, including Mott physics, superconductivity under pressure or doping, ultrafast switching into hidden states, memristive behavior exploited in neuromorphic device concepts, and candidate quantum spin liquid behavior. Making the commensurate charge density wave stable at room temperature means that all of these phenomena become accessible under ordinary laboratory conditions, without cryogenic infrastructure. It also means that devices built on phase switching, such as memory elements or optical detectors that exploit the dramatic resistance changes between charge density wave phases, could operate at ambient temperature rather than requiring cooling. The team’s broader program of hybrid superlattices, which has already yielded chiral molecular intercalation systems and unconventional superconductivity in molecule-TaS2 hybrids, now gains a new handle: molecular identity as a dial for correlated phase stability.

There is also a conceptual shift embedded in the result. Correlated electron states are usually treated as delicate collective phenomena that materials scientists try to protect from perturbation, since disorder and impurities typically destroy them. Here, the opposite logic prevails: a deliberately introduced molecular perturbation, applied in an ordered and periodic fashion, strengthens the collective state rather than degrading it. The ordered molecular layers act as a coherent boundary condition on the electronic system, in effect programming the lattice from the outside in. That reframing, from contamination to design element, is likely to influence how researchers approach other van der Waals materials with fragile electronic orders, from charge density wave systems like VSe2 and CuTe to Mott and magnetic layered compounds.

Challenges remain before the strategy matures into technology. The intercalation chemistry must be controlled with precision to maintain long-range ordering of the molecules, and the long-term stability of the hybrid crystals under repeated thermal cycling and device operation will need to be established. Still, the demonstration that a single amino acid can raise the operating temperature of a prototypical quantum phase by a decisive margin marks a milestone in molecular engineering of correlated matter. If the principle generalizes, the quantum materials of the future may be assembled less like semiconductors and more like chemistry sets, with molecules chosen as deliberately as atoms to dictate which electronic orders survive and which yield.

Subject of Research: Molecular intercalation engineering of charge density wave stability in 1T-TaS2 hybrid superlattices

Article Title: Molecular engineering stabilizes the commensurate charge density wave state in 1T-TaS2/arginine hybrid superlattices

Article References: Zhou, J., Zhou, B., Hsu, C.-E., Pettersen, K., Zhou, J., Wan, Z., Yan, X., Ren, H., Qian, Q., Zhang, A., Peng, B., Tang, R., Pan, X., Sofer, Z., Hsueh, H.-C., Li, Z., Huang, Y., & Duan, X. (2026). Molecular engineering stabilizes the commensurate charge density wave state in 1T-TaS2/arginine hybrid superlattices. Nature Chemistry. https://doi.org/10.1038/s41557-026-02241-3

Image Credits: AI Generated

DOI: 10.1038/s41557-026-02241-3

Keywords: charge density wave, 1T-TaS2, arginine, hybrid superlattices, molecular intercalation, correlated electrons, quantum materials, van der Waals materials, Mott insulator, Nature Chemistry, room temperature stability, amino acids

A new numerical study published in Nature Physics by Simone Fratini, Ivan Duchemin, Arnaud Ralko and Sergio Ciuchi now offers a strikingly simple answer. Working within the two-dimensional t–J model, the canonical minimal model of doped Mott insulators used to describe cuprate superconductors, the team shows that strange metallicity is not an exotic phase requiring special ingredients. Instead, it emerges pervasively across the temperature-doping phase diagram whenever antiferromagnetic order is suppressed. The strange metal, in their results, is the natural descendant of the bad metal that underlies it, and its hallmark properties follow from the quantum statistics of the charge carriers rather than from any special temperature dependence of the processes that scatter them.

The bad metal concept, introduced in the early 2000s, describes a regime in which the electrical resistivity exceeds the Mott–Ioffe–Regel limit, the value at which an electron’s mean free path becomes comparable to its own wavelength. In such a regime, the very notion of a well-defined quasiparticle travelling between collisions breaks down, and transport must be understood through more general principles of quantum diffusion. Bad metallicity had been observed in numerical studies of doped Mott insulators for years, but its relationship to the strange metal phenomenology of the cuprates, with its linear resistivity and Planckian dissipation, remained ambiguous. The new work argues that the two are, in a precise sense, the same phenomenon viewed at different levels of description.

The technical achievement that makes this conclusion possible lies in recent improvements to the finite-temperature Lanczos method, a numerically exact technique for computing the thermodynamic properties of strongly correlated lattice models at finite temperature. The Lanczos approach works by iteratively building a small set of basis vectors that span the low-energy part of the Hilbert space, allowing accurate evaluation of correlation functions without ever handling the exponentially large full space. Recent methodological advances, building on decades of development since the original finite-temperature Lanczos work of the 1990s, now enable exact calculations at low temperatures and with high spectral resolution, precisely the regime where strange metal behaviour lives and where earlier approximations faltered.

Using this machinery, the researchers computed both the direct-current and the frequency-dependent conductivity of the two-dimensional t–J model across a broad range of temperatures and dopings. The t–J model describes holes moving through an antiferromagnetic background of spin-one-half particles, with a superexchange coupling J between neighbouring spins and a hopping amplitude t that is strongly constrained by the no-double-occupancy condition. This constraint, a remnant of the large on-site repulsion of the underlying Hubbard model, is what makes the model so difficult and so rich. It is also, according to the new results, what makes it strange: the interplay of quantum statistics and the constrained motion of carriers produces transport that looks Planckian without requiring any exotic scattering mechanism.

A central question in the strange metal literature concerns the origin of Planckian relaxation, the observation that the scattering time in these materials is of order ħ divided by the Boltzmann constant times temperature, the fastest timescale that quantum mechanics permits for a thermal system. Some theorists have proposed that Planckian behaviour signals proximity to a quantum critical point, where fluctuations occur at all scales and times. Others have pointed to spatially random interactions, to spin fluctuations, or to specific scattering channels as the culprit. The new study addresses this question directly by extending the analysis into the frequency and time domains, where the dynamics of the charge response can be watched as it unfolds rather than merely inferred from the final resistivity.

What emerges from this time-resolved picture is that Planckian behaviour is rooted in the quantum statistical nature of the charge response itself. The carriers in the doped antiferromagnet are incoherent from the outset, and their transport is governed by the statistical mechanics of a dense quantum fluid rather than by the collision history of individual particles. The temperature dependence of the scattering processes, which in conventional thinking would determine the resistivity, turns out to play a secondary role. In effect, the strange metal does not become strange because something unusual starts scattering its electrons at high temperatures; it is strange because the carriers were never the well-behaved quasiparticles of Fermi liquid theory in the first place.

This reframing has significant implications for how physicists interpret experiments on the cuprates and related materials. The linear-in-temperature resistivity observed over wide doping ranges in compounds such as La2−xSrxCuO4 and Bi-based cuprates has often been treated as a fingerprint of a specific mechanism, to be isolated and identified. If the new numerical results are a faithful guide, the linear resistivity instead reflects a generic property of doped Mott insulators once long-range magnetic order gives way to a quantum paramagnet. The experimental phase diagrams of the cuprates, in which the strange metal region tracks the suppression of antiferromagnetism and the pseudogap boundary, are consistent with this picture, and recent measurements of spin-charge correlations at the onset of the pseudogap add further context for testing it.

The study also connects to a broader theoretical programme aimed at understanding transport in systems where quasiparticles fail. Previous work on the Hubbard model, on extremely correlated Fermi liquid theory, and on random-interaction models of strange metals has each highlighted different aspects of non-quasiparticle transport. By demonstrating that a single, well-defined minimal model reproduces the full phenomenology, from bad metallicity at high temperatures to Planckian strange metal behaviour at lower temperatures, the new results provide a unifying numerical benchmark against which analytical theories can be tested. The authors have made both their data and their code publicly available on GitHub, lowering the barrier for other groups to verify and extend the calculations.

For the field of quantum materials, the message is both humbling and clarifying. The strange metal, the state that parents high-temperature superconductivity and has resisted explanation since the discovery of the cuprates in 1986, may not require new particles, hidden criticality, or exotic interactions. It may simply be what a strongly correlated quantum fluid looks like when the usual quasiparticle picture is abandoned and the quantum statistics of the carriers are taken seriously. If further work confirms that the t–J model captures the essential physics, the path toward a complete theory of the cuprates becomes clearer: understand the constrained quantum statistics of doped antiferromagnets, and the strange metal, along with perhaps the superconductivity that emerges from it, will follow. The puzzle is far from solved, but the new results suggest that the answer may have been hiding in one of the oldest and simplest models in the theorist’s toolkit.

Subject of Research: The microscopic origin of strange metal behaviour and Planckian transport in doped Mott insulators

Article Title: Strange metal behaviour from underlying bad metallicity

Article References: Fratini, S., Duchemin, I., Ralko, A., & Ciuchi, S. (2026). Strange metal behaviour from underlying bad metallicity. Nature Physics. https://doi.org/10.1038/s41567-026-03441-x

Image Credits: AI Generated

DOI: 10.1038/s41567-026-03441-x

Keywords: strange metal, bad metal, Planckian dissipation, t–J model, cuprates, high-temperature superconductivity, Mott insulator, finite-temperature Lanczos method, quantum statistics, antiferromagnetism, electrical resistivity, strongly correlated electrons