Letters in 2020

The strange metal phase in unconventional superconductors is probed by Hall measurements. This reveals that quantum criticality drives the Hall effect, which also correlates with the superconductivity. This indicates that all three may be linked.

Magnons are collective excitations that dictate many of a magnet’s low-temperature properties. By means of Raman scattering, the magnon spectra of CrI₃ are measured in the monolayer limit.

A protocol for the reliable, efficient and precise characterization of quantum noise is reported and implemented in an architecture consisting of 14 superconducting qubits. Correlated noise within arbitrary sets of qubits can be easily detected.

Using doped BaFe₂As₂, the authors test whether nematicity is linked to superconductivity in the iron pnictides by applying the conjugate field to nematicity—a specific form of strain—and observe that the critical temperature decreases.

The flat electronic bands that are associated with ordered phases in twisted bilayer graphene at a magic twist angle have been imaged using angle-resolved photoemission spectroscopy.

The Mott insulator ground state is a crucial feature of high-temperature superconductors such as the cuprates. Here, the authors find an exactly solvable model that contains both superconductivity and Mottness.

Thermal transport measurements show that there is a thermal Hall effect in the out-of-plane direction in two cuprates in the pseudogap regime. This indicates that phonons are carrying the heat and that they have a handedness of unknown origin.

By sliding one layer with respect to the other in a van der Waals heterostructure, Edelberg et al. create a honeycomb network of solitons. Vertices of the network trap electrons, allowing strain-tunable control of confined states.

Using scanning tunnelling spectroscopy, the flat bands in twisted bilayer WSe₂ are shown near both 0° and 60° twist angles.

When a quantum system couples with its surroundings, macroscopic irreversibility emerges even though the microscopic Hamiltonian is itself time-reversal symmetric, causing the phenomena associated with certain symmetry-protected topological phases to be unstable.

A quasiparticle in Andreev levels was coupled to a superconducting microwave resonator and its spin was monitored in real time. This has potential applications in the readout of superconducting spin qubits and measurements of Majorana fermions.

Strong-field-induced nonlinearities from the injection of electrons into the conduction band contribute to harmonic generation in amorphous quartz. Close to the damage threshold, they dominate over intraband and interband contributions.

A memory device is proposed that uses a dynamical modification of the stacking order of few-layer WTe₂ to encode information. The change in stacking modifies both the Berry curvature and the Hall transport, allowing two states to be distinguished.

Transport and optical conductivity measurements reveal the non-Fermi liquid behaviour in correlated semimetal Nd₂Ir₂O₇. The result implies the emergent collective charge transport in this compound, not reconcilable with conventional band theory.

The spin polarization of a quantum Hall system is determined by a spin-resolved tunnelling method. This technique shows a substantial regime where the weakly interacting composite fermion picture is not valid.

The quantum Hall effect is realized in a two-dimensional quantum gas system consisting of one spatial dimension and one synthetic dimension encoded in the atomic spin. Measurements show distinct bulk properties rooted in the topological structure.

The quantum effective action describing non-equilibrium dynamics of a many-body system can be inferred from experiment using analogue quantum simulators. Here is an example of how it works for a quasi-one-dimensional spinor Bose gas out of equilibrium.

Error-corrected quantum gates that can tolerate dominant errors during the execution of quantum operations have been demonstrated. Substantial improvement of the gate fidelity sheds light on fault-tolerant universal quantum computation.

In laser–plasma experiments complemented by simulations, electron acceleration is observed in turbulent collisionless shocks. This work clarifies the pre-acceleration to relativistic energies required for the onset of diffusive shock acceleration.

Here, it is shown that superconductivity can exist without correlated insulating states in twisted bilayer graphene devices a little away from the magic angle. This indicates the two phases compete with each other, in contrast to previous claims.