At the beginning of 2021, eight Physical Review journals began publishing Letters which are intended for the accelerated publication of important new results targeted to the specific readership of each journal.

The quasi-two-dimensional kagome superconductors $A$V${}_3$Sb${}_5$ ($A$ $=$ K, Rb, and Cs) have attracted great interest due to various exotic quantum phenomena, such as topological charge density waves and the giant anomalous Hall effect. Here, the authors find two-dome unconventional superconductivity in CsV${}_3$Sb${}_5$ under high pressure. They also confirm the absence of a structural phase transition up to 43.1 GPa through high-pressure synchrotron x-ray diffraction measurements, suggesting that the novel reemergent superconductivity dome can be attributed to the Fermi surface reconstruction caused by the Lifshitz transition.

Conclusively identifying Majorana modes in nanowires is an long-standing experimental challenge. Within the field, consensus is emerging that achieving this goal will require measurements on three-terminal devices. Here, the authors report some of the first results on such devices using nonlocal conductance. They find that zero-bias peaks are preceded by the closure of the bulk gap, which indicates that in these devices zero-bias peaks are associated with bulk properties of the nanowire. However, the behavior of the device after gap closure suggests that disorder remains an important limitation.

Stacks of nanostructured 2D materials can display properties distinct from those of the parent materials. In heterostructures of transition metal dichalcogenides, the authors find here that dissimilar chalcogen species induce a spontaneous compression of the van der Waals gap. This compression is a result of the induced charge displacement within and between the layers, which modifies the out-of-plane polarizability, and can stabilize charge density waves or induce ferroelectricity. The authors hope to stimulate experimental investigation of tunability in mixed chalcogen systems.

Ruthenium is a unique metal that can admit valence states from $-2$ to $+8$. In particular, Ru${}^{3+}$ is one of the best known Kitaev magnets, Ru${}^{4+}$ dimerizes forming a covalent-bond fluid, while Ru${}^{5+}$ in SrRu${}_2$O${}_6$ is argued to feature unusual quasimolecular orbitals (QMO), combining strong electronic localization on the QMO level with full intra-QMO delocalization. Here, the authors study, using a battery of experimental and theoretical methods, another putative QMO compound – AgRuO${}_3$ – and find a rich spectrum of interesting phenomena.

Nondecaying dc currents in systems showing ballistic transport are characterized by a constant, known as the Drude weight. Here, the authors obtain analytical results for the spin Drude weight in the interacting anisotropic Heisenberg spin-$\frac{1}{2}$ chain at low temperatures. The obtained analytical formula reveals that the Drude weight for any finite temperature exhibits a nowhere-continuous dependence on the spin anisotropy of the model.

This study demonstrates that, contrary to earlier claims in the field involving analyses of a so-called “zero Hall plateau”, it is more intricate than expected to unambiguously reveal the existence of an axion insulator. In particular, the authors find from their scaling analysis of transport experiments on V-doped (Bi,Sb)${}_2$Te${}_3$ films of varying thickness that the truly three-dimensional bulk character is a necessary condition for axion insulators, a condition that is likely not satisfied for the materials exhibiting a zero Hall plateau.

The pairing mechanism in twisted bilayer graphene (TBG) remains a central question, which is often contrasted with pairing in other strong-coupled superconductors. However, TBG is unique in many ways. Its phonon dispersion contains many minioptical bands with frequencies exceeding the electronic bandwidth. Here, the authors develop a theory of electronic pairing resulting from this complex phonon structure and find that it mediates stronger interaction, compared to a purely electronic plasmonic mechanism. They also predict experimental signatures of both phonon umklapp and plasmon pairing mechanisms.

Using infrared spectroscopy, the authors study here how the low-energy charge carrier dynamics and band structure of the candidate axion topological insulator EuIn${}_2$As${}_2$ are affected by its antiferromagnetic transition at $T_{\text{N}}$ =18 K. The free carriers are shown to have a plasma frequency of about 2000 cm${}^{-1}$, and a scattering rate with a cusplike maximum at $T_{\text{N}}$ that signifies their strong interaction with the fluctuating Eu spins. The authors also observe large band splittings and a phonon anomaly below $T_{\text{N}}$, which indicate that the charge, spin, and lattice excitations are strongly coupled.

MnBi${}_2$Te${}_4$ and MnSb${}_2$Te${}_4$ are the first examples of antiferromagnetic topological insulators. However, the presence of magnetic defects in the form of antisite mixing between Mn and Bi or Sb introduces defect-driven ferrimagnetism. The application of a large magnetic field of ~50 Tesla aligns the magnetic defects with the main Mn layer, allowing for estimates of the defect concentration and the strength of the antiferromagnetic coupling ($J^{\prime }$) between Mn defects and the main layer, which is by far the largest magnetic coupling in the system.

While the linear Drude weight in quantum many-body systems has been studied extensively, its nonlinear counterparts – called nonlinear Drude weights (NLDWs) – remain largely unexplored. Here, the authors present the first exact results for the NLDWs of the spin-$\frac{1}{2}$ XXZ chain, a paradigmatic quantum many-body system. Their exact results based on the Bethe ansatz reveal that the NLDWs diverge with the system size in certain parameter regions. Also, the analytical expressions for the NLDWs are obtained when they converge.

Several methods to polarize nuclear spins nearby nitrogen-vacancy centers rely on electron spin polarization and therefore on the intersystem crossing rates. Here, the authors consider the effect of these rates on nuclear polarization methods based on the level anticrossing, and precession of the nuclear population while the electronic spin is on the ground state for different nuclear spins. These results are relevant for validating the models for intersystem crossing rates and achieving a higher nuclear polarization.

APS Editor in Chief, Michael Thoennessen, discusses a new opportunity for communicating authors to include their pronouns together with their contact email in order to promote a more respectful, inclusive, and equitable environment.