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Heavily doping silicon with phosphorus produces a dense population of metallic conduction electrons and localized magnetic moments. Low-temperature measurements show evidence of strongly correlated state.

Magnetic atoms on a surface possess diverse correlated phases under an applied magnetic field due to a balance of exchange interaction and carrier-mediated coupling. Here, the authors use scanning tunnel microscopy to explore the phase diagram of coupled Co atom pairs on the surface of Cu₂N/Cu(100).

Double quantum dots are proving themselves to be an excellent test bed for many-body physics. These artificial atoms now demonstrate a phenomenon in which the capacitive coupling between them causes the spin and charge degrees of freedom of the electrons in the system to become entangled—the so-called SU(4) Kondo effect.

In the Kondo effect, a bath of conduction electrons screens a localized magnetic moment. Here, the authors demonstrate Kondo screening of a normally isolated 4f-like moment in a magnetic molecule on a Cu(001) surface that is modulated by strong ligand-mediated coupling.

The study and application of the conductive surface states of topological insulators are often restricted by the presence of bulk conduction states. Here, Xu et al. present evidence for such topological surface states with true bulk insulation in the strongly correlated Kondo insulator SmB₆.

A family of topologically protected Kondo insulators, termed Möbius Kondo insulators, is predicted. A re-analysis of archival resistivity measurements of Ce₃Bi₄Pt₃ and CeNiSn suggests they may be good candidate members of this class.

The competition between interactions promoting magnetic order and those suppressing magnetism causes unusual electronic behaviour in Kondo lattice materials. Here, the authors show the energy scale for valence fluctuations is not controlled by the Kondo scale, contrary to expectations from single-site models.

Previous work on charge Kondo circuits, in which a spin is formed by two degenerate charge states of a metallic island, has been limited to transport measurements of multi-channel Kondo problems. Piquard et al. use thermodynamic measurements via a charge sensor to study the evolution of a single Kondo impurity.

Examples of materials with non-trivial band topology in the presence of strong electron correlations are rare. Now it is shown that quantum fluctuations near a quantum phase transition can promote topological phases in a heavy-fermion compound.

Reports of quantum oscillations in the absence of an electronic Fermi surface in Kondo insulator candidates such as SmB₆ and YbB₁₂ have been under intense study. Here the authors report the thermodynamic properties of YbB₁₂ in a magnetic field pointing to the presence of in-gap fermionic excitations.

The Kondo effect usually refers to increased electrical resistance in metals due to spin-spin interactions between localized magnetic impurities and conduction electrons. Here the authors report a Kondo-like coupling between a light-induced exciton and localized impurity spins in Nd-doped hybrid perovskite.

Unconventional properties in heavy fermion compounds are thought to arise from competing interactions between conduction electrons and localized magnetic moments. Here, the authors build one-dimensional lattices of cobalt atoms on a metallic surface and observe the onset of heavy fermion behaviour.

Flat electronic bands can give rise to correlation-driven phases but for this, they need to be tuned to the Fermi level. Here the authors predict flat bands pinned at the Fermi level due to orbital-selective interactions and discuss implications for the design of topological Kondo semimetal in d-electron systems.

Semiconducting graphene nanoribbon provides a platform for band-gap engineering desired for electronic and optoelectronic applications. Here, Li et al. show that graphene nanoribbon can effectively mediate the interaction of molecular magnetic moment and electronic spin in underlying metallic substrates.

The Kondo effect from magnetic impurities has been proposed as a probe of fractionalized excitations in a topological quantum spin liquid. Lee et al. experimentally demonstrate the Kondo effect in a Kitaev candidate material α-RuCl3 with dilute Cr impurities.

Recently the Kondo effect has been observed in transition metal dichalcogenide heterobilayers, but the evidence for low-temperature coherent state has been missing. Wan et al. observe signatures of such state in the form of a split Kondo peak with a characteristic magnetic-field dependence by STM at 340 mK.

Kondo materials exhibit extremely rich physics, from unconventional superconductivity to topological phases. Unfortunately, for a real material, direct solution of the Kondo lattice is practically impossible. Here, Simeth et al. present a tractable approach to this problem, showing how a multi-orbital periodic Anderson model can be reduced to a Kondo lattice model, and be applied to relevant materials and quantitatively validated with neutron spectroscopy.

Exploring the interplay of quantum effects enriches the scientific and technological understanding in nanoscale devices. The authors find that two apparently different quantum effects, quantum interference and the Kondo effect, can be unified to describe electron transport in single-molecule junctions.

Interactions between a localized magnetic moment and electrons in a metal can produce an emergent resonance that affects the metal’s properties. A realization of this Kondo effect in MoS₂ provides an opportunity to study it in microscopic detail.

Long-range magnetic order hardly ever emerges in a two-dimensional system due to the competition of fundamental magnetic interactions. Here, Girovskyet al. directly observe a long-range ferrimagnetic order emerging in a two-dimensional supramolecular Kondo lattice.

Understanding the physics of transition metal oxides that move beyond the commonly studied 3d orbital state is important for future studies. Taking the (CaCu₃)B₄O₁₂ family as an example, Meyers et al.examine the electronic and magnetic structure as the B-site changes from Co to Rh and Ir.

The quantum critical behaviour of a two-impurity Kondo model variant is observed in a system of hybrid-semiconductor islands that could provide a scalable platform for solid-state quantum simulation

Unconventional quasiparticles carrying spin but not electric charge emerge in quantum spin liquid phases. The Kondo interaction of these spinon quasiparticles with magnetic impurities may now have been observed.

The Kondo hybridization typically occurs in heavy-fermion systems containing f electrons, although recently it has been reported in d-electron systems. Kim et al. report spectroscopic evidence of the Kondo hybridization in FeTe and discuss it role in the mechanism of the magnetic order.

The electrical conductance across quantum point contacts shows quantum steps that are well understood except for some anomalies. Here, the authors are able to explain their origin in terms of spontaneously localized electron states by tuning the potential landscape of the contact with a scanning gate microscope.

In rare-earth intermetallics, interaction between localized 4f electrons and itinerant electrons can result in exotic states of matter. Here, the authors use photoemission spectroscopy to reveal and study this interaction in the bulk and at the surface of the Kondo lattice antiferromagnet CeRh₂Si₂.

Non-local spin valves that inject spin currents into non-magnetic metals hold great promise for spintronics, but a decrease in spin signal on cooling has perplexed researchers. O’Brien et al. now show this results from local magnetic moments forming in the nominally non-magnetic metals.

The many-body Kondo effect manifests in low-temperature Coulomb blockaded quantum dots as a zero-bias conductance peak, which arises due to charge-fluctuation-driven transport. Here, the authors demonstrate a counterintuitive Kondo effect in which these conduction channels are blocked.

Samarium hexaboride, a well-known Kondo insulator, shows transport anomalies at low temperatures, which recently have been proposed to be of topological origin. Using laser- and synchrotron-based photoemission techniques, Neupane et al. find evidence for a topological Fermi surface.

The fate of high-energy degrees of freedom, such as spin-orbit interactions, in the coherent state of Kondo lattice materials remains unclear. Here, the authors use resonant inelastic x-ray scattering in CePd₃ to show how Kondo-quasiparticle excitations are renormalized and develop a pronounced momentum dependence, while maintaining a largely unchanged spin-orbit gap.

The ferromagnet CeRh₆Ge₄ is found to exhibit strange-metal behaviour at a quantum critical point, suggesting that changes in the pattern of quantum entanglement, not antiferromagnetism, underlie the development of strange metals.

Experimental study of the Kondo insulator SmB₆ provides an alternative route to realize a Fermi surface in the absence of a conventional Fermi liquid.

Thermoelectric clathrates host guest atoms that can rattle inside their surrounding cages, yielding unusual phononic properties. Ikeda et al. show that ab initio calculations fail to account for thermodynamic and thermal transport data and propose a Kondo-like mechanism to explain the discrepancy.

Electronic correlation, geometric frustration, and topology are known to individually drive intriguing properties in materials. Here, the authors explore these interactions in the quasi-kagome Kondo Weyl semimetal Ce₃TiSb₅, revealing unconventional Hall effects that underscore the complex interplay of these factors, with implications for understanding topological and magnetic phenomena

A quantum critical point occurs when different stable phases of matter are in equilibrium at absolute zero temperature. Describing quantum criticality with a theoretical framework that unifies different types of transitions is highly desirable to understand how phenomena such as superconductivity and magnetism interact in correlated electron systems. A study now provides an indication of an underlying universality of quantum criticality, and highlights the role of dimensionality in such a unified theory.

Surface-dominated conduction is found to dominate up to 240 K in the strongly correlated mixed-valence Kondo insulator SmB₆ under the application of large strain.

The Kondo effect—the screening of a magnetic impurity’s local moment by the electron Fermi sea in a metal—has been observed in a charge-insulating quantum spin liquid material, where the spinon excitations take the role of electrons.

In a quantum dot in the Kondo regime, electrical charges are effectively frozen, but the quantum dot remains electrically conducting owing to strong electron–electron correlations.