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Although quantum phase transitions are attracting increasing attention as the conceptual link between conventional and exotic states of quantum matter—having been implicated, for example, in the properties of high-temperature superconductors—there are few model systems in which they can be studied and understood. Now it is revealed that placing simple elemental chromium under pressure suppresses its normal magnetic state and gives direct experimental access to the underlying quantum phase transition responsible for these changes.

Transition of superfluid to insulator is observed in the layer-imbalanced regime of bilayer magnetoexcitons.

Owing to electron localization, two-dimensional materials are not expected to be metallic at low temperatures, but a field-induced quantum metal phase emerges in NbSe₂, whose behaviour is consistent with the Bose-metal model.

The authors study epitaxial thin films of the pyrochlore-sublattice compound LiTi2O4 by RIXS and ARPES. They observe cooperation between strong electron correlations and strong electron-phonon coupling, giving rise to a mobile polaronic ground state in which charge motion and lattice distortions are coupled.

The authors report superconducting topological surface states (TSS) on MBE-grown Fe(Te,Se) films by high-resolution laser-ARPES. Near the FeTe limit, the surface state disappears due to an electron-correlation-driven topological transition associated with decoherence of the d_xy-orbital-derived bands.

The authors study microstructured UTe₂ by high-field transport, focusing on the field-reinforced superconducting phase. They reveal a highly-directional vortex pinning force typical of quasi-2D superconductors, indicating a vortex lock-in state and consistent with a change of order parameter from the low-field superconducting phase.

In the charge-density-wave Weyl semimetal (TaSe₄)₂I, an axion is observed and identified as a sliding mode in the charge-density-wave phase characterized by anomalous magnetoelectric transport effects.

Vortex dynamics and mutual friction in quantum fluids are intimately connected to the fundamental properties of superfluids. Here, the authors reveal previously unexplored mechanisms underlying the mutual friction coefficients in ultracold Fermi superfluids in the unitary limit, suggesting bound quasiparticles within the vortex core play a significant role.

Finite momentum superconducting pairing refers to a class of unconventional superconducting states where Cooper pairs acquire a non-zero momentum. Here the authors report a new superconducting state in bulk 4Hb-TaS₂, where magnetic fields induce finite momentum pairing via magnetoelectric coupling.

Thin FeSe film on SrTiO₃ substrate becomes a superconductor with a transition temperature over 100 K, yet the origin remains controversial. Here, Seo et al. show superconductivity below 20 K on the electron-doped surface of an FeSe crystal, suggesting a decisive role of interfacial effects in the enhancement of superconductivity.

The epitaxial growth of hyperdoped Ga:Ge films and trilayer heterostructures by molecular-beam epitaxy yield superconductivity with a critical temperature of 3.5 K and may enable quantum functionalities in this material system, which is accessible with well-established semiconductor technologies.

Pairing interaction appears at room temperature in traditional superconductors with a Cooper instability in the Fermi sea. Here, Maier et al.report that in the pseudogap phase of cuprate, where this instability is absent, superconductivity arises from an increase in the strength of the spin fluctuation pairing interaction as the temperature decreases.

A proposed theoretical explanation for the electronic behaviour of moiré graphene is the coexistence of light and heavy electrons. Now local thermoelectric measurements hint that this model could be accurate.

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.

The authors present scanning tunnelling spectroscopy data that show that the mechanism of superconductivity in overdoped cuprate superconductors is qualitatively different from conventional mean-field theory.

A moiré quasicrystal constructed by twisting three layers of graphene with two different twist angles shows high tunability between a periodic-like regime at low energies and a strongly quasiperiodic regime at higher energies alongside strong interactions and superconductivity.

Realizing topological superconductivity is essential for applicable fault-tolerant quantum computation. Here, Trang et al. report migration of Dirac-cone from TlBiSe₂ substrate to top surface of superconducting Pb film due to topological proximity effect, suggesting realization of topological superconductivity.

Iron-based superconductors could be useful in the development of superconducting magnets and related applications. Fang et al. show that a low density of columnar defects in SmFeAsO_0.8F_0.15can increase its critical current to record-high values and reduce its superconducting anisotropy.

Low-temperature scanning tunnelling microscopy imaging combined with a comprehensive quantum treatment of a silicon–dopant system forms a metrology technique that can pinpoint dopant locations in silicon with exact lattice site precision.

A superconducting field-effect transistor was demonstrated with a structure made of different Bardeen–Cooper–Schrieffer superconductors.

Spin-charge interactions are at the core of electronic correlation phenomena in Mott insulators. Here, the authors observe a positive anomalous magnetoresistance in a SrIrO₃/SrTiO₃ superlattice, indicative of strong spin-charge fluctuations in this pseudospin-half square-lattice Mott insulator.

Superconductivity in doped SrTiO₃ near to a ferroelectric quantum critical point emerges due to a strong interaction driving the formation of Cooper pairs, the nature of which has remained elusive for several decades.  Here, the authors reveal that pairing is due to the exchange of longitudinal hybrid polar modes rather than transverse critical modes.

Electrostatic doping drives a transition from single condensate to two condensate superconductivity at the (110)-oriented LaAlO₃/SrTiO₃ interface.

Detecting Majorana quasi-particles requires unambiguous and experimentally accessible fingerprints. Here, the authors demonstrate the existence of a 8π-periodic fractional Josephson effect in a Kitaev wire as a signature for Majorana quasi-particles, and propose a cold atom experiment for its detection.

The relationship between electronic ordering and superconductivity, crucial to understand high-T_c superconductors, remains elusive. Here, Sun et al. report the pressure-induced dome shape of a magnetic phase superceding the nematic order in FeSe, suggesting competing nature between magnetism and superconductivity.

Although heavy fermion and cuprate superconductors are both unconventional superconductors, their composition and structure differ markedly. Yet, microwave spectra collected by Truncik et al. reveal a similarity in the charge dynamics of the heavy fermion superconductor CeCoIn5 and the cuprates.

Disorder leads to localization of electrons at low temperatures, changing metals to insulators. In a superconductor the electrons are paired up, and scanning tunnelling microscopy shows that the pairs localize together rather than breaking up and forming localized single electrons in the insulating state.

The microscopic pairing mechanism in high-temperature superconductors remains debated. Here, the authors offer a new perspective on this problem by proposing that the strong pairing in Fermi-Hubbard type models relevant to cuprates is driven by a Feshbach resonance, which enhances interactions between doped holes.

The layered iron pnictide superconductors are known for their unconventional electronic properties and high critical temperatures. Now, SmFeAs(O,F) is shown to undergo a transition from pinned Abrikosov-like to mobile Josephson-like vortices as the system is cooled below its critical temperature.

Electron doping is a powerful way to induce quantum phase transitions in materials and explore exotic states of matter. Here, Wen et al. present carefully-controlled potassium dosing in FeSe films and FeSe_0.93S_0.07bulk, which enhances superconductivity and induces other anomalous phases, revealing a complex phase diagram.

Ginzburg–Landau theory provides a powerful framework for describing the behaviour of conventional superconductors without detailed microscopic information about them. Bao et al.construct a similar framework for describing spin superconductivity, a recently proposed analogue of conventional superconductivity.

Individual layers of FeSe grown on SrTiO3 superconduct at far higher temperatures than in bulk, but the effect of the film-substrate interface is poorly understood. Peng et al. find that modifying this interface has a significant non-trivial effect on the superconducting characteristics of FeSe films.

A problem in the treatment of 1D quantum magnetic systems is the shortage of theoretical models applicable for general confinement. Here, Volosniev et al.introduce an energy-functional technique to solve 1D fermionic and bosonic systems with strong short-range interaction in arbitrary geometry.

Unconventional superconductivity may be triggered when graphene is deposited on a high temperature superconductor. Here, Di Bernardoet al. observe spectroscopic evidence for p-wave superconductivity in single layer graphene on an electron-doped cuprate superconductor.

Interface transparency between 2D semiconductors and superconductors is a longstanding problem, seriously hindering potential applications. Here, using a new hybrid system, Kjaergaard et al. report quantized conductance doubling and a hard superconducting gap measured via a quantum point contact, indicating a near pristine interface.

The authors present a material-specific ab initio understanding of doped cuprates. Their method correctly captures two known experimental trends: the pressure effect, where the pairing order and gap increase with intra-layer pressure, and the layer effect, where the pairing order and gap vary with the number of copper-oxygen layers.