Compile |Feng Weiwei
nature, 15 feb 2024, volume 626 issue 7999
Nature, February 15, 2024, Vol. 626, No. 7999
Physics
rapid spin changes around a magnetar fast radio burst
Fast radio bursts that rotate rapidly around magnetars
Authors: Chin-Ping Hu, Takuto Narita, Teruaki Enoto, George Younes, Zorawar Wadiasingh, Matthew G baring, wynn c. g. ho, sebastien guillot, paul s. ray, tolga güver, kaustubh rajwade, z**en arzoumanian, chryssa kouveliotou, alice k. harding & keith c. gendreau
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Summary:
Magnetars are neutron stars with extremely high magnetic fields (about 1014 gauss) that exhibit a wide variety of X-ray phenomena such as sporadic subsecond bursts, long-lasting flux enhancements, and variable rotational period derivatives. In 2020, scientists detected fast radio bursts (FRBs), similar to cosmological millisecond-duration radio bursts, from the galactic magnetar SGR 1935+2154, confirming the long-standing association between some fast radio bursts and magnetars.
However, the mechanism by which fast radio bursts are generated in magnetars remains unclear. The researchers reported X-ray observations of two glitches of SGR 1935+2154 at an interval of approximately 9 hours, including a fast radio burst that occurred on October 14, 2022.
Each glitch involves a significant increase in the spin frequency of magnetars, one of the largest mutations in the rotation of neutron stars observed to date. In between these glitches, magnetars exhibit a rapid spin descent phase, accompanied by a sustained increase in X-ray emission and burst rate and subsequent decline. The researchers hypothesize that strong and short-lived magnetospheric winds provide the torque that rapidly slows the rotation of the star.
The trigger of the first glitch binds the star's crust to its magnetosphere, enhances various X-ray signals, and creates winds that alter magnetosphere conditions, which can produce fast radio bursts.
▲ abstract：
magnetars are neutron stars with extremely high magnetic fields (
1014gauss) that exhibit various x-ray phenomena such as sporadic subsecond bursts, long-term persistent flux enhancements and variable rotation-period derivative. in 2020, a fast radio burst (frb), akin to cosmological millisecond-duration radio bursts, was detected from the galactic magnetar sgr 1935+2154, confirming the long-suspected association between some frbs and magnetars. however, the mechanism for frb generation in magnetars remains unclear. here we report the x-ray observation of two glitches in sgr 1935+2154 within a time interval of approximately nine hours, bracketing an frb that occurred on 14 october 2022. each glitch involved a significant increase in the magnetar’s spin frequency, being among the largest abrupt changes in neutron-star rotation observed so far. between the glitches, the magnetar exhibited a rapid spin-down phase, accompanied by an increase and subsequent decline in its persistent x-ray emission and burst rate. we postulate that a strong, ephemeral, magnetospheric wind provides the torque that rapidly slows the star’s rotation. the trigger for the first glitch couples the star’s crust to its magnetosphere, enhances the various x-ray signals and spawns the wind that alters magnetospheric conditions that might produce the frb.
room-temperature quantum optomechanics using an ultralow noise c**ity
Room-temperature quantum photomechanics using an ultra-low noise cavity
Authors: Guanhao Huang, Alberto Beccari, Nils J engelsen & tobias j. kippenberg
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Summary:
At room temperature, mechanical motion, driven by the quantum inverse of light, was previously only observed in seminal experiments in which optical restoring forces controlled the stiffness of oscillators. For the solid-state mechanical resonator with rigid material control oscillation, the observation of resonator oscillation is affected by factors such as low mechanical mass factor, frequency fluctuation of optical cavity, thermal intermodulation noise and photothermal instability. Researchers overcame these challenges with phonon-engineered membranes for intermediate systems.
By using a phononic crystal pattern endoscope, they reduced the cavity frequency noise by more than 700 times. In this ultra-low noise cavity, a membrane resonator with high thermal conductivity was inserted with a mass factor (q) of 1800 million, designed with recently developed soft clamp technology.
These advances have enabled the system to operate at the Heisenberg displacement sensing limit of 2Within 5 times, the compression of the probe laser is 1 percent lower than the vacuum fluctuation09(1)db。This study extends the quantum control of solid-state macroscopic oscillators to room temperature.
▲ abstract：
at room temperature, mechanical motion driven by the quantum backaction of light has been observed only in pioneering experiments in which an optical restoring force controls the oscillator stiffness. for solid-state mechanical resonators in which oscillations are controlled by the material rigidity, the observation of these effects has been hindered by low mechanical quality factors, optical c**ity frequency fluctuations, thermal intermodulation noise and photothermal instabilities. here we overcome these challenges with a phononic-engineered membrane-in-the-middle system. by using phononic-crystal-patterned c**ity mirrors, we reduce the c**ity frequency noise by more than 700-fold. in this ultralow noise c**ity, we insert a membrane resonator with high thermal conductance and a quality factor (q) of 180 million, engineered using recently developed soft-clamping techniques. these advances enable the operation of the system within a factor of 2.5 of the heisenberg limit for displacement sensing8, leading to the squeezing of the probe laser by 1.09(1)db below the vacuum fluctuations. moreover, the long thermal decoherence time of the membrane oscillator (30 vibrational periods) enables us to prepare conditional displaced thermal states of motion with an occupation of 0.97(2) phonons using a multimode kalman filter. our work extends the quantum control of solid-state macroscopic oscillators to room temperature.
observation of plaid-like spin splitting in a noncoplanar antiferromagnet
Observation of lattice spin** in non-coplanar antiferromagnets
Author:Yu-Peng Zhu, Xiaobing Chen, Xiang-Rui Liu, Yuntian Liu, Pengfei Liu, Heming Zhana, Gexing Qu, Caiyun Hong, Jiayu Li, Zhicheng Jiang, Xiao-Ming Ma, Yu-Jie Hao, Ming-Yuan Zhu, Wenjing Liu, meng zeng, sreehari jayaram, malik lenger, jianyang ding, shu mo, kiyohisa tanaka, masashi arita, zhengtai liu, mao ye, dawei shen, ...chang liu
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Summary:
The separation of space, momentum, and energy of electron spins in condensed matter systems has guided the development of new devices for generating and manipulating spin polarization currents. Recent attention to a previously neglected set of symmetrical operations in magnetic materials has led to the emergence of a new type of spin** that enables the energy bands on selected antiferromagnets to have large and momentum-dependent spin polarization. Despite a growing body of theories, direct spectral evidence for this spin is still lacking.
The new study provides solid spectral and computational evidence for the existence of this material. In non-coplanar antiferromagnetic manganese telluride (MNTE2), the in-plane component of the spin is antisymmetric on the high symmetry plane in the Brivan zone, and a lattice-like spin texture is formed in the antiferromagnetic (AFM) ground state. This unconventional spin mode, further found to be reduced in the high-temperature paramagnetic state, stems from the inherent AFM order rather than spin-orbit coupling (SoC).
This discovery demonstrates a novel quadratic spin texture induced by time-reversal fracture, laying a solid foundation for AFM spintronics and paving the way for the study of exotic quantum phenomena in related materials.
▲ abstract：
spatial, momentum and energy separation of electronic spins in condensed-matter systems guides the development of new devices in which spin-polarized current is generated and manipulated. recent attention on a set of previously overlooked symmetry operations in magnetic materials leads to the emergence of a new type of spin splitting, enabling giant and momentum-dependent spin polarization of energy bands on selected antiferromagnets. despite the ever-growing theoretical predictions, the direct spectroscopic proof of such spin splitting is still lacking. here we provide solid spectroscopic and computational evidence for the existence of such materials. in the noncoplanar antiferromagnet manganese ditelluride (mnte2), the in-plane components of spin are found to be antisymmetric about the high-symmetry planes of the brillouin zone, comprising a plaid-like spin texture in the antiferromagnetic (afm) ground state. such an unconventional spin pattern, further found to diminish at the high-temperature paramagnetic state, originates from the intrinsic afm order instead of spin–orbit coupling (soc). our finding demonstrates a new type of quadratic spin texture induced by time-reversal breaking, placing afm spintronics on a firm basis and p**ing the way for studying exotic quantum phenomena in related materials.
Two-dimensional ferroelectric vortex diagram in a distorted batio3 independent layer
Author: G sánchez-santolino, v. rouco, s. puebla, h. aramberri, v. zamora, m. cabero, f. a. cuellar, c. munuera, f. mompean, m. garcia-hernandez, a. castellanos-gomez, j. íiguez, c. leon & j. santamaria
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Summary:
The abundance of complex polar topologies recently discovered in nanoscale ferroelectrics stems from the delicate balance between the inherent tendency of materials to develop uniform polarization and the electrical and mechanical boundary conditions imposed on them. The ferroelectric interface is a model system in which the polarization curl originates from the open-circuit sample electrical boundary condition to avoid the accumulation of polarization charges, which evolves into a vortex structure at the nanoscale level by forming a flux closed domain.
Although ferroelectricity is known to be strongly coupled to strain (homogeneous and heterogeneous), mechanical constraints have relatively little effect on the nanoscale ferroelectricity of thin films due to the relative lack of strain modes that can be achieved experimentally.
The researchers demonstrated that the stacking of independent ferroelectric perovskite layers with controlled torsion angles provides an opportunity to tailor these topological nanostructures in a way determined by the lateral strain modulation associated with torsion. In addition, they found that the flexible electrical coupling of polarization with strain gradient produces a special polarization vortex and anti-vortex pattern.
This discovery provides an opportunity to create two-dimensional high-density vortex crystals, enabling the exploration of previously unknown physical effects and functions.
▲ abstract：
the wealth of complex polar topologies recently found in nanoscale ferroelectrics results from a delicate balance between the intrinsic tendency of the materials to develop a homogeneous polarization and the electric and mechanical boundary conditions imposed on them. ferroelectric–dielectric interfaces are model systems in which polarization curling originates from open circuit-like electric boundary conditions, to **oid the build-up of polarization charges through the formation of flux-closure domains that evolve into vortex-like structures at the nanoscale level. although ferroelectricity is known to couple strongly with strain (both homogeneous18 and inhomogeneous), the effect of mechanical constraints on thin-film nanoscale ferroelectrics has been comparatively less explored because of the relative paucity of strain patterns that can be implemented experimentally. here we show that the stacking of freestanding ferroelectric perovskite layers with controlled twist angles provides an opportunity to tailor these topological nanostructures in a way determined by the lateral strain modulation associated with the twisting. furthermore, we find that a peculiar pattern of polarization vortices and antivortices emerges from the flexoelectric coupling of polarization to strain gradients. this finding provides opportunities to create two-dimensional high-density vortex crystals that would enable us to explore previously unknown physical effects and functionalities.
Chemistry
designer phospholipid capping ligands for soft metal halide nanocrystals
Design of soft metal halide nanocrystalline phospholipid capping ligands
Authors: Viktoriia Morad, Andrey Stelmakh, Maria Svyrydenko, Leon G feld, simon c. boehme, marcel aebli, joel affolter, christoph j. kaul, nadine j. schrenker, sara bals, yesim sahin, dmitry n. dirin, ihor cherniukh, gabriele raino, andrij baumketner & maksym v. kovalenko
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Summary:
The success of colloidal semiconductor nanocrystals (NCS) in the fields of science and optoelectronics is inseparable from their surface properties. The functionalization of lead halide perovskite NCS poses a significant challenge because of their structurally unstable capping, unlike the covalent ligand cap of traditional semiconductor NCS.
The researchers hypothesize that the vast and simple molecular engineering of phospholipids as zwitterionic surfactants could provide highly customized surface chemistry for metal halide NCS. Molecular dynamics simulations show that the surface affinity of ligand-NC is mainly determined by the structure of the zwitterionic head group, especially the geometric fit of the anion and cation moieties to the surface lattice position, which is confirmed by NMR and FTIR spectroscopy data.
Lattice-matched primary ammonium phospholipids enhance the structural and colloidal integrity of organic-inorganic lead halide perovskites (FapBBR3 and MAPBBR3) and lead-free metal halide NCS. The molecular structure of the tail of the organic ligand determines long-term colloidal stability and compatibility with a wide range of polar solvents, from hydrocarbons to acetone and alcohols.
These nanomaterials have more than 96% photoluminescence quantum yields in solution and solids, minimal photoluminescence intermittency at the single-particle level, an average ON fraction of up to 94%, and bright and high-purity (about 95%) single-photon emission.
▲ abstract：
the success of colloidal semiconductor nanocrystals (ncs) in science and optoelectronics is inextricable from their surfaces. the functionalization of lead halide perovskite ncs poses a formidable challenge because of their structural lability, unlike the well-established covalent ligand capping of conventional semiconductor ncs. we posited that the vast and facile molecular engineering of phospholipids as zwitterionic surfactants can deliver highly customized surface chemistries for metal halide ncs. molecular dynamics simulations implied that ligand–nc surface affinity is primarily governed by the structure of the zwitterionic head group, particularly by the geometric fitness of the anionic and cationic moieties into the surface lattice sites, as corroborated by the nuclear magnetic resonance and fourier-transform infrared spectroscopy data. lattice-matched primary-ammonium phospholipids enhance the structural and colloidal integrity of hybrid organic–inorganic lead halide perovskites (fapbbr3 and mapbbr3 (fa, formamidinium; ma, methylammonium)) and lead-free metal halide ncs. the molecular structure of the organic ligand tail governs the long-term colloidal stability and compatibility with solvents of diverse polarity, from hydrocarbons to acetone and alcohols. these ncs exhibit photoluminescence quantum yield of more than 96% in solution and solids and minimal photoluminescence intermittency at the single particle level with an **erage on fraction as high as 94%, as well as bright and high-purity (about 95%) single-photon emission.
climate
global population profile of tropical cyclone exposure from 2002 to 2019
Global demographic profile of tropical cyclone exposures from 2002 to 2019
Authors: Renzhi Jing, Sam Heft-Neal, Daniel R ch**as, max griswold, zetianyu wang, aaron clark-ginsberg, debarati guha-sapir, eran bend**id & zachary wagner
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Summary:
Tropical cyclones can have far-reaching impacts on livelihoods and population health, often lasting years after an event. Characterizing the demographic and socio-economic status and vulnerability characteristics of affected populations is essential for assessing the health and other risks associated with future tropical cyclone events.
Estimates of the extent of tropical cyclone impacts tend to be regional rather than global and do not take into account population vulnerability. The researchers combined spatially resolved annual demographic estimates with tropical cyclone field estimates to construct a global profile of the population affected by tropical cyclones from 2002 to 2019.
They found that about 5600 million people were affected, and the number of people affected increased across all hurricane intensities during the study period. Compared to the beginning of the century, the age distribution of those exposed has shifted in recent years from children (under 5 years old) to older people (over 60 years old).
Within the same country, people affected by tropical cyclones are more socioeconomically poor than those who are not, and this relationship is more pronounced among those affected by more intense storms. By describing the patterns and vulnerabilities of affected populations, the results of the study can help identify mitigation strategies and assess the global burden and future risks of tropical cyclones.
▲ abstract：
tropical cyclones h**e far-reaching impacts on livelihoods and population health that often persist years after the event. characterizing the demographic and socioeconomic profile and the vulnerabilities of exposed populations is essential to assess health and other risks associated with future tropical cyclone events. estimates of exposure to tropical cyclones are often regional rather than global and do not consider population vulnerabilities. here we combine spatially resolved annual demographic estimates with tropical cyclone wind fields estimates to construct a global profile of the populations exposed to tropical cyclones between 2002 and 2019. we find that approximately 560 million people are exposed yearly and that the number of people exposed has increased across all cyclone intensities over the study period. the age distribution of those exposed has shifted away from children (less than 5 years old) and towards older people (more than 60 years old) in recent years compared with the early 2000s. populations exposed to tropical cyclones are more socioeconomically deprived than those unexposed within the same country, and this relationship is more pronounced for people exposed to higher-intensity storms. by characterizing the patterns and vulnerabilities of exposed populations, our results can help identify mitigation strategies and assess the global burden and future risks of tropical cyclones.