Lifeboat Foundation

Experiments reveal the factors that determine the friction between the single-atom-thick layers in van der Waals materials, which may have uses in lubrication technology.

Van der Waals (vdW) materials consist of stacked, single-atom-thick layers, and these layers can experience very low friction as they slide over one another, a property that might be exploited for lubrication. A research team has now distinguished several contributions to this low friction and has shown that effects at the edges of the sliding regions dominate [1]. Some of their experiments involved sliding a several-layer-thick flake across a surface made of a similar material containing a crack, which allowed the team to systematically control the edge length. The findings could guide efforts to engineer controllable frictional forces into such materials in micromechanical devices.

The very low friction, called superlubricity, exhibited by vdW materials has been previously shown to depend on the relative orientations of the layers. If one layer is rotated by some angle, called the twist angle, with respect to the layer below, the two layers form a “superlattice” in which the two atomic lattices fall periodically in and out of registry, like a pair of overlaid combs with slightly different spacings. This arrangement is called a Moiré pattern, and the repeating elements, or unit cells, of the superlattice are called Moiré tiles. Superlubricity arises because, in general, the contributions to the frictional force from the atoms within one Moiré tile cancel each other out: Some exert a push, while others exert a pull.

A Bose-Einstein condensate of cold atoms occupying a periodic lattice can flow like a superfluid. But if the atoms’ mutual repulsion is strengthened and the lattice potential deepened, the atoms can become immobilized in a state known as a Mott insulator. Now Hepeng Yao of the University of Geneva and his collaborators have examined the Mott transition of cold atoms trapped in a lattice that is quasiperiodic rather than periodic [1]. Given that quasiperiodicity and other kinds of disorder tend to trap particles, the researchers were surprised to discover that their quasiperiodic lattice sustained the superfluid state rather than weakening it.

Yao and his collaborators trapped potassium-39 atoms in a one-dimensional optical lattice formed by the standing waves of two lasers. If the ratio of the lasers’ wavelengths was a rational number, the lattice was periodic. Otherwise, the lattice was quasiperiodic. By adjusting various experimental parameters, they could control the depth of the confining potentials, the strength of the interatomic repulsion, and whether the lattice sites were fully occupied. To determine whether a given set of parameters yielded a static, insulating state or a mobile, superfluid one, they turned off the trap and observed how the atoms flew apart.

The team found that the Mott transitions for the periodic and quasiperiodic lattices were both characterized by a critical value of the interparticle repulsion, but the critical value in the quasiperiodic case was higher. Quantum Monte Carlo simulations pointed to the reason. The commensurability between the lattice period and the particle number is a key factor in pinning particles in a Mott insulator. However, the quasiperiodic lattice blurs this commensurate period, thereby destabilizing the Mott phase to the profit of the superfluid one.

Antiferromagnets are materials in which the magnetic moments of neighboring atoms are aligned in an alternating pattern, resulting in no net macroscopic magnetism. These materials have interesting properties that could be favorable for the development of spintronic and electronic devices.

After an unexpected measurement by the Collider Detector at Fermilab (CDF) experiment in 2022, physicists on the Compact Muon Solenoid experiment (CMS) at the Large Hadron Collider (LHC) announced today a new mass measurement of the W boson, one of nature’s force-carrying particles.

Researchers from the School of Physics & Astronomy have been involved in an important new measurement of the top quark made using data provided by the Large Hadron Collider (LHC).

One of the most surprising predictions of physics is entanglement, a phenomenon where objects can be some distance apart but still linked together. The best-known examples of entanglement involve tiny chunks of light (photons), and low energies.

Particles of light can spend “negative time” passing through a cloud of extremely cold atoms – without breaking the laws of physics.

By Karmela Padavic-Callaghan

In the ever-evolving landscape of scientific discovery, certain paradigms periodically challenge the established norms, compelling us to reconsider the boundaries of what we deem as ‘science.’ One such paradigm is the intersection of quantum physics and metaphysical science. Despite skepticism, there is a growing body of evidence suggesting that these two fields are not only compatible but also complementary. This blog delves into how quantum physics supports metaphysical science and argues for its integration into mainstream scientific discourse, underpinned by historical precedents.

“The day science begins to study non-physical phenomena; it will make more progress in one decade than in all the previous centuries of its existence.” — Nikola Tesla

Quantum physics, the study of particles at the smallest scales of energy levels, has fundamentally altered our understanding of reality. The principles of quantum mechanics, such as superposition, entanglement, and wave-particle duality, have revealed a universe far more intricate and interconnected than classical physics ever suggested. These concepts resonate profoundly with metaphysical science, which explores the nature of reality, consciousness, and existence beyond the physical.

Results could aid understanding of how black holes produce vast intergalactic jets. Scientists have observed new details of how plasma interacts with magnetic fields, potentially providing insight into the formation of enormous plasma jets that stretch between the stars.

Whether between galaxies or within doughnut-shaped fusion devices known as tokamaks, the electrically charged fourth state of matter known as plasma regularly encounters powerful magnetic fields, changing shape and sloshing in space. Now, a new measurement technique using protons, subatomic particles that form the nuclei of atoms, has captured details of this sloshing for the first time, potentially providing insight into the formation of enormous plasma jets that stretch between the stars.

Scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) created detailed pictures of a magnetic field bending outward because of the pressure created by expanding plasma. As the plasma pushed on the magnetic field, bubbling and frothing known as magneto-Rayleigh Taylor instabilities arose at the boundaries, creating structures resembling columns and mushrooms.