Letters in 2014

A quantum spin liquid is a spin state with no magnetic order even at the lowest temperatures. To explain neutron scattering data on a ‘kagome lattice’ antiferromagnet, visons (elementary excitations of vortices) must be included, in addition to the usual fractionalized spinons.

Bacteria often reside in fluids. Now, it is shown that hydrodynamic shear, which creates forces and torques on bacterial suspensions, stimulates the attachment of bacteria to surfaces and seriously hinders chemotaxis.

Quantum measurements affect the state of the system, so they can be used both as probe and control knob. This idea is demonstrated in an experiment with nuclear spin qubits in diamond that are manipulated by measurements alone.

Oxygen-mediated superexchange (or Dzyaloshinskii–Moriya) interactions result in weak ferromagnetism in oxides. A method based on the interference of synchrotron X-ray radiation is now shown to enable the determination of the sign of the Dzyaloshinskii–Moriya interaction in the prototypical weak ferromagnet iron borate.

The physics of one-dimensional many-body systems is rich but still insufficiently understood. An ultracold atom experiment investigates the behaviour of one-dimensional strongly correlated fermions with a tunable number of spin components.

To better understand the mechanisms of double ionization following the absorption of one photon, a combination of experimental techniques has been developed to probe the electron emission times in xenon on the attosecond timescale.

Magnetic monopoles can exist in frustrated magnetic systems known as spin ices. The study of these exotic objects is challenging, but a technique that uses the quench parameters to control the number of monopoles could help.

Quantum critical behaviour has been observed in many metallic systems that do not behave conventionally as Fermi liquids. High-magnetic-field experiments now reveal clear evidence for quantum criticality in an iron-based high-temperature superconductor.

Ensembles of micrometre-sized water droplets in a laminar oil flow are ideal systems for studying non-equilibrium dynamics. In the case of two-dimensional confinement, the interactions between the droplets’ flow-induced dipole moments lead to long-range velocity correlations and four-fold angular symmetry—behaviour that can be understood from first-principle hydrodynamics calculations.

Ultracold atoms could help in understanding the physics of strongly interacting many-body systems, but the creation of degenerate Bose gases at unitarity has been hampered by the losses. An experiment overcomes these problems and investigates the time evolution of a unitary Bose gas.

Monolayer and few-layer materials present interesting spin and pseudospin states. A study of the coupling between spin, valley and layer degrees of freedom in bilayer WSe₂ reveals coherent superpositions of distinct valley configurations and suggests the possibility of electrical control of the spin states.