Letters in 2021

When interactions between electrons in a material are strong, they can start to behave hydrodynamically. Spatially resolved imaging of current flow in a three-dimensional material suggests that electron–electron interactions are mediated by phonons.

Schrödinger cat states are observed in intense laser–atom interactions. These are a superposition of the initial state of the laser and the coherent state that results from the interaction between the light and atoms.

A levitated nanosphere that is strongly coupled to an optical cavity mode forms an optomechanical system with three degrees of freedom, which supports hybrid light–mechanical states of a vectorial nature.

The Hubbard model describes many fascinating phenomena, but relating it to complicated quantum materials is difficult. Now, atomic-resolution measurements can estimate the interaction parameters that appear in the model for real materials.

It has been difficult to establish which ground state forms in kagome lattice antiferromagnets. Nuclear resonance measurements have overcome the issue of disorder to observe spin singlets consistent with a proposed quantum spin liquid phase.

Ultrashort light pulses generate nanometre-scale wavepackets of magnons that propagate coherently and at high speed in an antiferromagnet. This pushes antiferromagnetic magnonics forward as a future platform for information processing.

In vitro experiments and theory reveal that a protein associated with DNA transcription mediates condensation of a protein–DNA phase via a first-order transition. The forces uncovered in the study may contribute to chromatin remodelling in the cell.

Antiferromagnetic systems are a source of several interesting many-body phases. Now a Heisenberg antiferromagnet has been made from ultracold bosons, providing a highly tunable starting point for experimental investigations that simulate such models.

The nonlinear properties of photonic topological insulators remain largely unexplored, as band topology is linked to linear systems. But nonlinear topological corner states and solitons can form in a second-order topological insulator, as shown by experiments.

In general, it isn’t known when a quantum computer will have an advantage over a classical device. Now it’s proven that computers with limited working memory are more powerful if they are quantum.

Ultrafast optical excitation of a charge density wave leads to the formation of a metastable gapped state that synchronizes with the underlying correlated phase.

The interplay of superconductivity and nematicity of electrons remains unclear in a wide range of materials. Now, more evidence emerges that nematic fluctuations can be pinned into a static phase by disorder, which hinders the superconductivity.

Measurements of observables sensitive to the neutron’s spin precession are extended to a regime that probes distances of the size of the nucleon. They are found to disagree with predictions from chiral effective field theory.

Microswimmers tend to accumulate in regions where their speed is significantly reduced, but experimental and numerical evidence now points towards a viscophobic turning mechanism that biases certain microalgae away from high-viscosity areas.

During the early development of an organism, some cells are fated to grow while other seemingly healthy cells die. Experiments and theory now reveal that a hydraulic instability is the key to this decision.

Transport measurements on the Kitaev quantum spin liquid candidate α-RuCl3 subjected to a magnetic field reveal oscillating behaviour in its thermal conductivity, reminiscent of Shubnikov de Haas oscillations in metals.

Many applications of quantum systems require them to be joined by strong, controllable interactions. Exploiting the physics of quantum squeezing can amplify the strength of boson-mediated interactions, yielding higher performance.

Isotope ratio measurements are complicated by the instabilities of composition in reference samples. Now a calibration-free method relying on infrared spectroscopy provides measurements that are traceable to International System of Units standards.

The two-dimensional electron gas at an oxide interface is patterned to form a channel with a periodic potential imposed on top. This replicates the textbook Kronig–Penney model and leads to fractionalization of electron bands in the channel.

Transport and thermodynamic measurements on strongly correlated Kondo metal YbB₁₂ reveal the coexistence of charged and charge-neutral fermions in the material and the crucial role played by the latter in the quantum oscillations of resistivity.