2fa Physical Key
Berk Boyraz
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Cavity confinement of quantum materials can induce a strong coupling between the electronic system and the quantum electromagnetic field, potentially leading to novel quantum phenomena of light and matter. The authors study here how the ultrastrong light-matter coupling can affect the Kondo effect. Nonperturbative analyses show that the ultrastrong coupling can enhance the Kondo temperature and give rise to several notable phenomena, including universal scalings of the cavity-modified Kondo effect, the photon occupation number, and the entanglement entropy between the cavity and electrons.
Spatial current patterns observed on the macroscale encode information about carrier dynamics on the microscale. In particular, vortices, manifested through currents flowing against externally applied electric fields, attract interest as a telltale signature of electron hydrodynamics. Previous studies have often regarded vorticity as a distinct feature of the hydrodynamic phase. Here, the authors explore the conditions under which vortex patterns can arise in electron systems, finding that the requirements for vortices prove to be considerably less stringent than previous work have suggested.
The authors study here the ultrafast dynamics of photoexcited carriers in the Weyl semiconductor Te in the vicinity of Weyl nodes using mid-infrared transient reflection spectroscopy. The relaxation process in a 20-nm Te flake is found to be 10 times faster than a 100-nm flake due to surface defect assisted recombination. The reflection modulation depth of the 20-nm sample is up to 60%, promising great potential for fast optical switch and optical modulator applications in the mid-infrared region.
This study is an experimental observation and characterization of the long-anticipated topological phase transition between different types of nodal electronic spectra in pyrochlore iridates. A unique combination of theory and measurements reveal that an incoherent part of the Raman scattering spectrum can unambiguously distinguish between Weyl and quadratic band-touching quasiparticles in correlated topological materials, while extracting Fermi energy relative to the node, Coulomb interaction effects and the amount of disorder. The results provide a critical verification of some prominent expectations that have been driving the research on pyrochlore iridates in recent years.
In a quantum many-body system, any two contiguous subsystems are typically either weakly entangled, or this entanglement decays with their separation. Could one observe strong long-range entanglement in a natural setup? Through exact calculations, the authors show here that such a remarkable behavior emerges in a simple 1D wire containing free fermions with a single scatterer, subject to temperature or voltage bias. The phenomenon arises from the coherent nature of the scattering, and may bear implications to more complex nonequilibrium systems.
Defining topological invariants in systems with dense energy spectrum is inherently challenging due to the absence of gaps. Here, the authors define a topological invariant for time quasiperiodically driven superconducting systems using spectral localizers, a recently developed tool for probing real-space topology. The invariant is shown to identify the number and quasienergy of quasiperiodic Majorana modes hosted by the system. Drawing insights from non-Hermitian physics, the authors also establish a criterion and provide a physical interpretation for spectral localizers, thereby widening their applicability.
OLED-based displays are now ubiquitous, and yet the very way positive and negative charges interact with each other to generate excitons and the overall fate of these species in the process of light emission still holds several mysteries. By investigating the operation of OLEDs containing protonated or deuterated organic semiconductors at low temperatures and moderate magnetic fields, the authors reveal here a nonmonotonic dependence of OLED light intensity on magnetic field, which is magnetoelectroluminescence. This enables distinction of interactions between carriers and molecular excitations.
The quantum geometric tensor (QGT) encodes information of the local geometry and topology of quantum states. While the QGT of pure quantum states is well known, its generalization to mixed quantum states requires a full characterization of the underlying geometric structure. Here, the authors derive the gauge-invariant QGT of mixed states based on the mathematically rigorous Uhlmann fiber bundle and highlight the similarities and differences of the local geometries of pure and mixed states.
The authors develop here an analytical theory to describe the interaction between moir electrons and K-phonons, which is responsible for the replica flat bands of twisted bilayer graphene observed in experiments. They perform an exhaustive numerical, analytical, and symmetry-based description of phonon-mediated attractive interaction and superconducting pairing channels from the K-phonon, and find the competing singlet gapped inter-Chern-band channel and nematic gapless intra-Chern-band channel. The latter shows a gapless spectrum with nodes, a feature observed in recent experiments.
The authors explore here the many-body localization (MBL) transition through a novel approach based on an analogy with directed polymers in random media. This study reveals how rare long-range resonances, typically absent in small samples, destabilize the MBL phase in the thermodynamic limit in a broad region of the phase diagram, and shift the transition to much higher disorder levels, offering new insights into quantum avalanches and anomalous transport and relaxation near the transition.
The authors theoretically study here laser-induced magnetization dynamics in van der Waals antiferromagnetic CrSBr films by analyzing the spatiotemporal evolution of the magnetization from thermal and nonthermal mechanisms. For the thermal mechanism, the presence and the symmetry of spatial patterns strongly rely on the nonuniformity of shear stress and the strength of the magnetic field. For the nonthermal one, an isotropic spin-wave propagation appears at zero field and becomes anisotropic at finite magnetic field.
Physical Review B is proud to announce the creation of an Early Career Researcher Advisory Board (ECAB). The 18 inaugural members are listed on the PRB Editorial Team page. We thank them for agreeing to serve. They will act as a focus group and provide advice from their perspective on how PRB can best serve the needs of early career researchers and maintain its important role in condensed matter and materials physics going into the future. The new board members are based in 10 different countries. Stephen Nagler, PRB Lead Editor, will chair the board.
APS has selected 156 Outstanding Referees for 2024 who have demonstrated exceptional work in the assessment of manuscripts published in the Physical Review journals. A full list of the Outstanding Referees is available online.
Physical activity is beneficial to health and well-being and conversely, physical inactivity increases risk for noncommunicable diseases (NCDs) and other poor health outcomes. Together, physical inactivity and sedentary behaviours are contributing to the rise in NCDs and placing a burden on healthcare systems.
Improving levels of physical activity will benefit health and well-being and contribute to attainment of global NCD targets and a number of the Sustainable Development Goals. However, this will require increased commitments and investments by Member States; innovation and contributions from non-state actors; cross sector coordination and collaboration; and ongoing guidance and monitoring from WHO.
Physical inactivity is one of the leading risk factors for noncommunicable diseases mortality. People who are insufficiently active have a 20% to 30% increased risk of death compared to people who are sufficiently active. Regular physical activity is associated with:
Sedentary behaviour is any period of low-energy expenditure while awake such as sitting, reclining or lying. Lives are becoming increasingly sedentary through the use of motorized transport and the increased use of screens for work, education and recreation. Evidence shows higher amounts of sedentary behaviour are associated with the following poor health outcomes:
The WHO Global guidelines on physical activity and sedentary behaviour provide recommendations for children (age 5 and up), adolescents, adults, older adults, pregnant and post-partum women, and people living with chronic conditions and disabilities. The recommendations detail the amount of physical activity (frequency, intensity and duration) required to offer significant health benefits and to reduce health risks. The guidelines highlight that any amount of physical activity is better than none; all physical activity counts; all age groups should limit the amount of time being sedentary; and muscle strengthening benefits everyone.
The WHO Guidelines on physical activity, sedentary behaviour and sleep for children under 5 years of age provide recommendations on the amount of time in a 24-hour day that young children, under 5 years of age, should spend being physically active or sleeping for their health and well-being, and the maximum recommended time these children should spend on screen-based sedentary activities or time restrained.
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