Physics

Researchers at Northeastern have discovered a new quantum phenomenon in a specific class of materials, called antiferromagnetic insulators, that could yield new ways of powering "spintronic" and other technological devices of the future. The discovery illuminates "how heat flows in a magnetic insulator, [and] how [researchers] can detect that heat...

As physicists delve deeper into the quantum realm, they are discovering an infinitesimally small world composed of a strange and surprising array of links, knots and winding. Some quantum materials exhibit magnetic whirls called skyrmions—unique configurations described as "subatomic hurricanes." Others host a form of superconductivity that twists into vortices.

High temperature superconductivity is something of a holy grail for researchers studying quantum materials. Superconductors, which conduct electricity without dissipating energy, promise to revolutionize our energy and telecommunication power systems. However, superconductors typically work at extremely low temperatures, requiring elaborate freezers or expensive coolants. For this reason, scientist have been relentlessly working on understanding the fundamental mechanisms at the base of high-temperature superconductivity with the ultimate goal to design and engineer new quantum materials superconducting close to room temperature.

Researchers from PSI's Spectroscopy of Quantum Materials group together with scientists from Beijing Normal University have solved a puzzle at the forefront of research into iron-based superconductors: the origin of FeSe's electronic nematicity. Using Resonant inelastic X-ray scattering (RIXS) at the Swiss Light Source (SLS), they discovered that, surprisingly, this electronic phenomenon is primarily spin driven. Electronic nematicity is believed to be an important ingredient in high-temperature superconductivity, but whether it helps or hinders it is still unknown. Their findings are published in Nature Physics.

Bose-Einstein condensates (BECs), created in ultracold bosonic atoms and degenerate quantum gases, are a macroscopic quantum phenomenon and are considered as a single particle in mean-filed theory. By preparing the BECs or ultracold atomic gases onto optical lattices, the existence of nonlinear matter-wave solitons and their dynamics and simulation in condensed-matter physics can be investigated.

The systems of active Brownian grains can be considered as open systems, in which there is an exchange of energy and matter with the environment. The collective phenomena of active Brownian grains can demonstrate analogies with ordinary phase transitions. We study the active Brownian motion of light-absorbing and strongly interacting grains far from equilibrium suspended in gas discharge under laser irradiation when the nature and intensity of the active motion depend on the effect of radiation. Active Brownian motion is caused by photophoresis, i.e., absorption of laser radiation at the metal-coated surface of the grain creates radiometric force, which in turn drives the grains. We experimentally observed the active Brownian motion of charged grains in the transition of the grain monolayer from the solid to liquid state. An analysis of the character of motion, including the mean-square and linear displacement and persistence length at various values of the randomization (coupling parameter) of the grain structure, was presented.

Metamaterials—artificial media with tailored subwavelength structures—have now encompassed a broad range of novel properties that are unavailable in nature. This field of research has stretched across different wave platforms, leading to the discovery and demonstration of a wealth of exotic wave phenomena. Most recently, metamaterial concepts have been extended to the temporal domain, paving the way to completely new concepts for wave control, such as nonreciprocal propagation, time-reversal, new forms of optical gain and drag.

Ever since the discovery of the quantum Hall effect (Nobel Prize 1985), symmetry has been the guiding principle in the search for topological materials. Now an international team of researchers from Germany, Switzerland, and the U.S. has introduced an alternative guiding principle, "quasi-symmetry," which leads to the discovery of a new type of topological material with great potential for applications in spintronics and quantum technologies. This work has been published in Nature Physics.

Obtaining structurally uniform nanocarbons in order to properly relate structure and function, ideally as single molecules, is a great challenge in the field of nanocarbon science. Thus, the construction of structurally uniform nanocarbons is crucial for the development of functional materials in nanotechnology, electronics, optics, and biomedical applications. An important tool for achieving this goal is molecular nanocarbon science, which is a bottom-up approach toward creating nanocarbons using synthetic organic chemistry. However, the molecular nanocarbons synthesized so far have simple structures, such as that of a ring, bowl, or belt. In order to realize unexplored and theoretically predicted nanocarbons, it is necessary to develop new methodologies for synthesizing molecular nanocarbons with more complex structures.

When atoms interact with each other, they behave as a whole rather than individual entities. That can give rise to synchronized responses to inputs, a phenomenon that, if properly understood and controlled, may prove useful for developing light sources, building sensors that can take ultraprecise measurements, and understanding dissipation in quantum computers.

Understanding the ultrashort time scale structural dynamics of the FeRh metamagnetic phase transition is a key element in developing a complete explanation of the mechanism driving the evolution from an antiferromagnetic to ferromagnetic state. Using an X-ray free electron laser we determine, with sub-ps time resolution, the time evolution of the ("“101) lattice diffraction peak following excitation using a 35Â fs laser pulse. The dynamics at higher laser fluence indicates the existence of a transient lattice state distinct from the high temperature ferromagnetic phase. By extracting the lattice temperature and comparing it with values obtained in a quasi-static diffraction measurement, we estimate the electron"“phonon coupling in FeRh thin films as a function of laser excitation fluence. A model is presented which demonstrates that the transient state is paramagnetic and can be reached by a subset of the phonon bands. A complete description of the FeRh structural dynamics requires consideration of coupling strength variation across the phonon frequencies.

Recently, spin-bearing molecules have been experimentally demonstrated to have great potential as building blocks for quantum information processing due to their substantial advantages including tunability, portability, and scalability. Here, we propose a theoretical model based on the theory of open quantum systems for spin dynamics in a molecule containing one radical, which can interact with the triplet state arising from another part of the molecule owing to optical excitation and intersystem crossing. With the initial state being a classical mixture of a radical \(\frac{1}{2}\)-spin, the exchange interaction between the radical and the triplet produces a spin coherent state, which could potentially be used for a qubit-qutrit quantum entangling gate. Our calculations for the time-resolved electron paramagnetic resonance spectra showed good qualitative agreement with the related experimental results for radical-bearing molecules at high temperature (~77"‰K, the boiling point of liquid nitrogen). This work therefore lays a solid theoretical cornerstone for optically driven quantum gate operations in radical-bearing molecular materials, aiming toward high-temperature quantum information processing.

Russian scientists have developed a unique material based on halide perovskites for use in high-speed and highly sensitive ionizing radiation detectors. The study has been published in the Journal of Materials Chemistry C. Halide perovskites are a new class of semiconductor materials with a unique combination of optical and electronic...

Over the past few years, many physicists and material scientists have been investigating superconductivity, the complete disappearance of electrical resistance observed in some solid materials. Superconductivity has so far been primarily observed in materials that are cooled to very low temperatures, typically below 20 K. Some materials, however, exhibit superconductivity...

Diamond and graphite are two naturally occurring carbon allotropes that we have known about for thousands of years. They are elemental carbons that are arranged in a manner so that they consist of sp3 and sp2 hybridized carbon atoms, respectively. More recently, the discovery of various other carbon allotrope materials, such as graphene, fullerene, carbon nanotube, graphyne, and graphdiyne, has been revolutionizing modern nanomaterials science. In particular, graphene research has made significant advances in modern chemistry and physics because of its fascinating properties.

For the past half century or so, a theory known by the understated name of the Standard Model has dominated the field of particle physics. This theory provides us with a detailed description of the 17 known fundamental particles, telling us how they should each behave and interact. Since its...

Kagome lattice composed of transition-metal ions provides a great opportunity to explore the intertwining between geometry, electronic orders and band topology. The discovery of multiple competing orders that connect intimately with the underlying topological band structure in nonmagnetic kagome metals AV3Sb5 (A"‰="‰K, Rb, Cs) further pushes this topic to the quantum frontier. Here we report a new class of vanadium-based compounds with kagome bilayers, namely AV6Sb6 (A"‰="‰K, Rb, Cs) and V6Sb4, which, together with AV3Sb5, compose a series of kagome compounds with a generic chemical formula (Am-1Sb2m)(V3Sb)n (m"‰="‰1, 2; n"‰="‰1, 2). Theoretical calculations combined with angle-resolved photoemission measurements reveal that these compounds feature Dirac nodal lines in close vicinity to the Fermi level. Pressure-induced superconductivity in AV6Sb6 further suggests promising emergent phenomena in these materials. The establishment of a new family of layered kagome materials paves the way for designer of fascinating kagome systems with diverse topological nontrivialities and collective ground states.

The origin of the electronic nematicity in FeSe is one of the most important unresolved puzzles in the study of iron-based superconductors. In both spin- and orbital-nematic models, the intrinsic magnetic excitations at Q1"‰="‰(1, 0) and Q2"‰="‰(0, 1) of twin-free FeSe are expected to provide decisive criteria for clarifying this issue. Although a spin-fluctuation anisotropy below 10"‰meV between Q1 and Q2 has been observed by inelastic neutron scattering at low temperature, it remains unclear whether such an anisotropy also persists at higher energies and associates with the nematic transition Ts. Here we use resonant inelastic X-ray scattering to probe the high-energy magnetic excitations of detwinned FeSe. A prominent anisotropy between the magnetic excitations along the H and K directions is found to persist to E"‰â‰ˆ"‰200"‰meV, which decreases gradually with increasing temperature and finally vanishes at a temperature around Ts. The measured high-energy spin excitations are dispersive and underdamped, which can be understood from a local-moment perspective.Taking together the large energy scale far beyond the dxz/dyz orbital splitting, we suggest that the nematicity in FeSe is probably spin-driven.