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Tuning the structure in the atomic scale enables manipulation of the quantum state in a molecular based system. Here, Hiraokaet al. tune the Kondo coupling between molecular spins and the Au electrode by controlling the position of Fe²⁺ions in the molecular cage with a tip.

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.

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.

The mechanism underlying screening of a Kondo lattice of magnetic moments by conduction electrons is an important unsolved problem. Figgins et al. use STM techniques to assemble nanoscale Kondo droplets that extrapolate between a single moment and the Kondo lattice, providing a platform for further study.

Understanding the structure of the Kondo cloud formed by conduction electrons screening the impurity spin is a long-standing problem in many-body physics. Shim et al. propose the spatial and energy structure of the multichannel Kondo cloud, by studying quantum entanglement between the impurity and the channels.

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.

The competition between Kondo correlations and magnetic ordering in heavy fermion materials leads to emergent physics that is not fully understood. Seiro et al. show inter-site Kondo correlations only dominate over local ones at temperatures well below the single-ion Kondo temperature but this is a prerequisite for quantum critical behavior.

The existence of the Kondo cloud is revealed by the spatially resolved characterization of the oscillations of the Kondo temperature in a Fabry–Pérot interferometer and its extent is shown to be several micrometres.

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.

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.

In metals, electronic scattering from defects by the two-channel Kondo effect is expected to cause deviation from standard low temperature behaviour, however this effect has not been unambiguously shown. Here, the authors present evidence consistent with all transport signatures of the effect in ferromagnetic L1₀-MnAl films.

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.

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.

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.

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 Kondo insulator samarium hexaboride exhibits low-temperature transport anomalies, which might be due to topological surface states. Here Jiang et al.perform angle-resolved photoemission and its circular dichroism measurements, which suggest that the anomalies might be of topological origin.

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.

This study reports on the simultaneous emergence of the impurity Kondo effect and incommensurate magnetic ordering in the layered material AgCrSe₂ these usually mutually exclusive phenomena complement each other. The ability to enable Kondo effect in association with the antiferromagnetic order, provides a novel route to tune the competition between magnetic correlations and Kondo screening.

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.

Sensitive measurements of fluctuations in the current through carbon-nanotube-based quantum dots provide insight into the many-body physics of such systems.

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.

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

The interaction of two magnetic moments on a metallic surface is usually understood as a competition between an indirect surface-mediated exchange interaction and the Kondo effect. Now, a different mechanism, involving chemical interactions driving a quantum phase transition, is reported.

The interaction of localized and conduction electrons in some heavy fermion materials is believed to give rise to a Kondo insulating state. Kushwaha et al. present evidence that Ce3Bi4Pd3 is a Kondo insulator with a gap small enough to be driven into a Fermi liquid phase with accessible magnetic fields.

Although evidence indicates that defects induce magnetism in graphite, it’s unclear whether this extends to graphene. An observation of the gate-tunable Kondo effect in ion-beam-damaged graphene suggests it does.

This study of magic-angle twisted trilayer graphene moiré superconductors using scanning tunnelling microscopy and spectroscopy identifies two energy gaps that develop from many-body resonance in this highly tunable class of materials.

A route connecting density functional theory and the numerical renormalization group method represents the first approach to studying atomic contacts—including magnetic elements—at an atomic level. When applied to the case of a nickel impurity in a gold nanowire, the strategy provides a clear connection between the geometry and the transport properties.

Using terahertz pulses, the quasiparticle dynamics of the heavy-fermion compound CeCu_6−xAu are investigated in the vicinity of its quantum critical point.

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.

Unconventional superconductivity is usually associated with a layered system. But how thin can a layered superconductor be and continue to be superconducting? Painstakingly grown superlattices of the heavy-fermion superconductor CeCoIn₅ suggest it could be as thin as a single layer.

Transitions between stable quantum phases of matter typically involve going through an unstable quantum critical point, the unique properties of which have become a focus of research in the past decade or so. Extensive bulk measurements on the nickel oxypnictide system CeNiAsO uncover heavy-fermion behaviour, suggesting the family of oxipnictides may be ideal materials for examining quantum criticality more broadly.

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.

High-energy-resolution spectroscopic measurements performed on the Kondo insulator SmB₆ reveal the presence of correlation-driven heavy surface states—the heavy Dirac fermions—and shed light on the search for the correlated topological materials.

The experimental realisation of a Kondo lattice and the interplay with Mott–Hubbard charge localisation is one of the many challenges in condensed matter physics. The authors deposit f-elements onto a metallic substrate to elucidate the conditions required to obtain a Kondo lattice on a superlattice and investigate the interplay with the Mott physics.

Zero-temperature quantum phase transitions and their associated quantum critical points are believed to underpin the exotic finite-temperature behaviours of many strongly correlated electronic systems, but identifying the microscopic origins of these transitions can be challenging and controversial; Iftikhar et al. (see also the related paper by Keller et al.) show how such behaviours can be engineered into nanoelectronic quantum dots, which permit both precise experimental control of the quantum critical behaviour and its exact theoretical characterization.

This work aims at clarifying the puzzling magnetism of several U intermetallics, in particular the pressure-induced magnetism of UTe₂. By an ab initio treatment of electronic correlations, the authors show that a momentum dependent f-d hybridization is responsible for the magnetic moments arising from the van Hove singularity of renormalized f electrons.

The Yu-Shiba-Rusinov state, arising from exchange coupling between a magnetic impurity and a superconductor, undergoes a quantum phase transition at a critical coupling. In a scanning tunnelling microscopy experiment, Karan et al. reveal distinct tunnelling spectra on each side of the transition in a magnetic field, which allows them to distinguish the free spin regime from the screened spin regime.