Hasil untuk "Atomic physics. Constitution and properties of matter"

Linda Ye, Jorge I. Facio, Madhav Prasad Ghimire et al.

Abstract We report a study of Shubnikov–de Haas oscillations in high-quality single crystals of ferromagnetic Weyl semimetal Co3Sn2S2. The Fermi surfaces resolved in our experiments are three-dimensional and reflect an underlying trigonal crystallographic symmetry. Combined with density functional calculations, we identify that multiple Fermi surfaces in the system—of both electron and hole nature—arise from the energy dispersion of the (spin-orbit gapped) mirror-protected nodal rings. We observe an evolution of the Fermi surfaces with in-plane magnetic fields, in contrast to field perpendicular to the kagome lattice planes, which has little effect. Viewed alongside the easy-axis anisotropy of the system, our observation reveals an evolution of the electronic structure of Co3Sn2S2—including the Weyl points—with the ferromagnetic moment orientation. Through the case study of Co3Sn2S2, our results provide concrete experimental evidence of an anisotropic interplay via spin-orbit coupling between the magnetic degrees of freedom and electronic band singularities, which has long been expected in semimetallic and metallic magnetic systems.

F. Schilberth, M. Kondákor, D. Ukolov et al.

Abstract Lattice vibrations are highly sensitive to crystal symmetries and their changes across phase transitions. The latter can modify irreducible (co)representations and corresponding infrared and Raman selection rules of phonons. This concept is established for relativistic magnetic point groups, simultaneously transforming spatial and spin coordinates. However, in altermagnets described by non-relativistic spin groups with disjunct symmetry operations for both vector spaces, the phonon selection rules have remained unexplored. Here, we present a detailed study of the infrared- and Raman-active modes in the collinear antiferromagnet and altermagnet candidate Co2Mo3O8. Comparing to ab initio calculations accurately capturing the eigenfrequencies, we identify all expected phonon modes at room temperature and deduce their selection rules using both symmetry approaches. Importantly, we observe the change of selection rules upon antiferromagnetic ordering, agreeing with the relativistic symmetry approach, while the spin group formalism predicts no changes. Therefore, optical phonons sensing the symmetry of the magnetic order can reveal if relevant magnon-phonon coupling is compatible with the spin-group approach or not.

Minseong Kwon, Mingi Kim, Yoonji Gong et al.

Superconductors exhibit dissipationless supercurrents even under finite bias and magnetic field conditions, provided these remain below the critical values. However, type-II superconductors in the flux flow regime display Ohmic dissipation arising from vortex dynamics under finite magnetic fields. The interplay between supercurrent and Ohmic dissipation in a type-II superconductor is dictated by vortex motion and the robustness of vortex pinning forces. In this study, we present an experimental investigation of the superconducting phase transitions and vortex dynamics in the atomically thin type-II superconductor 2H-NbSe _2 . We fabricated a high-quality multilayer 2H-NbSe _2 with a step junction, demonstrating supercurrent in clean limit below a critical temperature of 6.6 K and a high residual resistance ratio of 17. The upper critical field was estimated to be 4.5 T and the Ginzburg–Landau coherence length 8.6 nm. Additionally, we observed phase transitions induced by vortex viscous dynamics in the 2H-NbSe _2 step junction. Analysis of the pinning force density using the Dew-Hughes model indicates that the pinning force in the 2H-NbSe _2 device can be attributed to step junction, related to the surface-Δ κ type of pinning centers. Our findings pave the way for engineering pinning forces by introducing artificial pinning centers through partial atomic thickness variation in layered 2D superconductors while minimizing unwanted quality degradation in the system.

V. O. Zheltonozhsky, A. M. Savrasov, P. S. Derechkey et al.

For the first time, the flux-weighted average yields were measured of the 130Ba(γ, n)129Ba, 132Ba(γ, n)131Bam+g, 136Ba(γ, n)135Bam, 142Nd(γ, n)141Ndm, 142Nd(γ, n)141Ndm+g and 150Nd(γ, n)149Nd at Ebr = 19 MeV, the values of which were: 114(+7.4)(10), 113(8), 17.0(12), 9.5(7), 104.5(80) and 83(8) mb, respectively. The measured flux-weighted average yields of most reactions are in satisfactory agreement with the results, obtained from the works of other authors and with the results of simulations within the TALYS-1.96 code. The statistical mechanism of all the above-mentioned reactions is established.

D. Richardson, J. Dee, B. N. Kayim et al.

Rydberg atom receivers have the potential to supplement or replace traditional sensing technologies due to the theoretically high sensitivity, electrically small packaging, and unconventional field detection mechanisms they can provide. Given the importance of angle of arrival (AoA) estimation for geolocation and the potential impact of these technologies, more work is needed to understand the Rydberg sensor’s impact on AoA estimation. While there have been many experimental and theoretical efforts to improve the sensitivity and bandwidth of these quantum sensors, few papers have explored the impact these technologies will have on AoA estimation. This paper presents a numerical study of AoA estimation using a simulated linear array of Rydberg atom receivers consisting of vapor cells with laser-defined sense volumes. By utilizing atomic physics and electromagnetics simulations, it is shown that uncompensated atomic transient effects and RF geometric interactions in glass vapor cell arrays can substantially degrade AoA estimation when compared with a traditional dipole array.

Siyu Cheng, Zheng Ren, Hong Li et al.

Abstract Charge density waves (CDWs) in kagome metals have been tied to many exotic phenomena. Here, using spectroscopic-imaging scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we study the charge order in kagome metal ScV6Sn6. The similarity of electronic band structures of ScV6Sn6 and TbV6Sn6 (where charge ordering is absent) suggests that charge ordering in ScV6Sn6 is unlikely to be primarily driven by Fermi surface nesting of the Van Hove singularities. In contrast to the CDW state of cousin kagome metals, we find no evidence supporting rotation symmetry breaking. Differential conductance dI/dV spectra show a partial gap Δ 1 CO ≈ 20 meV at the Fermi level. Interestingly, dI/dV maps reveal that charge modulations exhibit an abrupt phase shift as a function of energy at energy much higher than Δ 1 CO, which we attribute to another spectral gap. Our experiments reveal a distinctive nature of the charge order in ScV6Sn6 with fundamental differences compared to other kagome metals.

V. P. Krasnov, O. V. Zhukovskyi, S. V. Sukhovetska et al.

Research on the modern distribution of 137Cs in soils of different forest site types in black alder (Alnus glutinosa (L.) Gaerth.) stands was conducted. In forest litter, there is not a high percentage of its total activity in soil: in moist fairly fertile site type (C3) – 13.4 %, damp fairly fertile site type (C4) – 16.3 %, and wet fairly fertile site type (C5) – 3.8 %. The mineral part of the soil in moist and damp fairly fertile site type is characterized by decreased density of radioactive contamination of soil layers with depth. In wet fairly fertile site type, this indicator increases to a depth of 6 - 8 cm and decreases with further deepening. A 10-cm layer of moist fairly fertile site type (C3) contains 61.8 % of the total radionuclide activity in soil, damp fairly fertile site type (C4) – 68.1%, and wet fairly fertile site type (C5) – 70.1 %, correspondingly; a 20-cm layer has 75.4, 78.3, 91.9 % and a 30-cm layer – 80.9, 82.2, 96.0 % of the total radionuclide activity.

Huazhou Li, Han Li, Zhaohui Wang et al.

Abstract The pairing mechanism of high-temperature superconductivity in cuprates is regarded as one of the most challenging issues in condensed matter physics. The core issue concerns how the Cooper pairs are formed. Here we report spin-resolved tunneling measurements on extremely underdoped Bi2Sr2−x La x CuO6+δ. Our data reveal that, when holes are doped into the system, the antiferromagnetic order is destroyed, while at the same time an increasing density of states (DOS) peaked at around 200 meV appears within the charge transfer gap. Meanwhile, an electronic structure with 4a 0 × 4a 0 basic plaquettes emerges inhomogeneously, with an area fraction that grows with hole doping. In each plaquette, there are some unidirectional bars (along the Cu-O bond) which are most pronounced at energies near peaks in the DOS around at 25 meV, with an intensity that is especially pronounced at oxygen sites. We argue that the atomically resolved low-energy DOS and related gap are closely associated with some kinds of density waves, possibly reflecting modulations of the electron density, or a pair-density wave, i.e. a modulation of the local pairing. Our work sheds new light on the doping induced electronic evolution from the “parent” insulator of the cuprate superconductors.

Wei Xiong, Peng Gao, Zhan-Ying Yang et al.

Abstract We present a possible way to control matter-wave solitons, which is through the collision between solitons and an accelerating atomic mirror. The acceleration of the mirror has a nontrivial effect on the dynamical characters of the reflected solitons. In the one-dimensional Bose–Einstein condensates, when the acceleration of the mirror has the identical direction with the initial soliton’s velocity, the soliton will diffuse after collision; in the contrasting case, the soliton will shrink and then diffuse. We quantitatively explain the above dynamical phenomena by analyzing the atoms’ movement in the soliton, and demonstrate that the method can generate a similar effect to the phase imprinting technology. Moreover, considering the dipolar effect between atoms, this approach can be used for the generation and control of breathing solitons.

Han Wu, Alannah M. Hallas, Xiaochan Cai et al.

Abstract Topological semimetals with symmetry-protected band crossings have emerged as a rich landscape to explore intriguing electronic phenomena. Nonsymmorphic symmetries in particular have been shown to play an important role in protecting the crossings along a line (rather than a point) in momentum space. Here we report experimental and theoretical evidence for Dirac nodal line crossings along the Brillouin zone boundaries in PtPb4, arising from the nonsymmorphic symmetry of its crystal structure. Interestingly, while the nodal lines would remain gapless in the absence of spin–orbit coupling (SOC), the SOC, in this case, plays a detrimental role to topology by lifting the band degeneracy everywhere except at a set of isolated points. Nevertheless, the nodal line is observed to have a bandwidth much smaller than that found in density functional theory (DFT). Our findings reveal PtPb4 to be a material system with narrow crossings approximately protected by nonsymmorphic crystalline symmetries.

Jun-Qing Cheng, Jun Li, Zijian Xiong et al.

Abstract Using quantum Monte Carlo, exact diagonalization, and perturbation theory, we study the spectrum of the S = 1/2 antiferromagnetic Heisenberg trimer chain by varying the ratio g = J 2/J 1 of the intertrimer and intratrimer coupling strengths. The doublet ground states of trimers form effective interacting S = 1/2 degrees of freedom described by a Heisenberg chain. Therefore, the conventional two-spinon continuum of width ∝ J 1 when g = 1 evolves into to a similar continuum of width ∝ J 2 when g → 0. The intermediate-energy and high-energy modes are termed doublons and quartons which fractionalize with increasing g to form the conventional spinon continuum. In particular, at g ≈ 0.716, the gap between the low-energy spinon branch and the high-energy band with mixed doublons, quartons, and spinons closes. These features should be observable in inelastic neutron scattering experiments if a quasi-one-dimensional quantum magnet with the linear trimer structure and J 2 < J 1 can be identified. Our results may open a window for exploring the high-energy fractional excitations.

Takahiko Satoh, Shun Oomura, Michihiko Sugawara et al.

In this article, we demonstrate that, by employing the OpenPulse design kit for IBM superconducting quantum devices, the controlled-V gate (<sc>cv</sc> gate) can be implemented in about half the gate time to the controlled-X gate (<sc>cx</sc> or <sc>cnot</sc> gate) and consequently 65.5&#x0025; reduced gate time compared to the <sc>cx</sc>-based implementation of <sc>cv</sc>. Then, based on the theory of Cartan decomposition, we characterize the set of all two-qubit gates implemented with only two or three <sc>cv</sc> gates; using pulse-engineered <sc>cv</sc> gates, enables us to implement these gates with shorter gate time and possibly better gate fidelity than the <sc>cx</sc>-based one, as actually demonstrated in two examples. Moreover, we showcase the improvement of linearly coupled three-qubit Toffoli gate by implementing it with the pulse-engineered <sc>cv</sc> gate, both in gate time and the averaged output-state fidelity. These results imply the importance of our <sc>cv</sc> gate implementation technique, which, as an additional option for the basis gate set design, may shorten the overall computation time and consequently improve the precision of several quantum algorithms executed on a real device.

Yueshen Wu, Qi Wang, Xiang Zhou et al.

Abstract Nonreciprocal charge transport phenomena are widely studied in two-dimensional superconductors, which demonstrate unidirectional-anisotropy magnetoresistances as a result of symmetry breaking. Here, we report a strong nonreciprocal transport phenomenon in superconducting CsV3Sb5 thin flakes. The second harmonic voltages, mainly originating from the rectification effect of vortex motion, are unambiguously developed with in-plane and out-of-plane magnetic fields, and their magnitudes are comparable to those in noncentrosymmetric superconductors. The second harmonic magnetoresistances split into several peaks and some of them reverse their signs by ramping the magnetic field or the current within the superconducting transition. The nonreciprocity suggests a strong asymmetry in CsV3Sb5. The centrosymmetric structure and symmetric electronic phases in CsV3Sb5 can hardly induce the distinct nonreciprocal transport phenomenon, which could be correlated to a symmetry breaking from an unconventional superconducting order parameter symmetry.

Makoto Masuko, Minoru Kawamura, Ryutaro Yoshimi et al.

Abstract In a hybrid system of topological insulator (TI)/superconductor (SC), the proximity-induced topological superconductivity is expected to appear at the interface. Here we propose and demonstrate that a TI/SC hybrid Bi2Te3/PdTe2 heterostructure serves as a platform for exploring topological superconductivity with various features: all made of tellurium compounds, epitaxial growth, and a small charge transfer interface. In the Bi2Te3/PdTe2 heterostructure films, we observe large nonreciprocal charge transport near the superconducting transition temperature under a transverse in-plane magnetic field. The observation indicates the interplay between the topological surface state and superconductivity, suggesting that the Bi2Te3/PdTe2 heterostructure is a candidate for a topological superconductor. Also observed is an unexpected sign reversal of the nonreciprocal coefficient when the in-plane magnetic field is slightly tilted toward the out-of-plane direction. The analysis reveals that the sign reversal occurs with the change of dominant vortex type, that is, the change from spontaneous vortices to external-field induced ones.

Luca Salasnich

R Besson, L Thuinet, M-A Louchez

Abstract We performed atomic-scale ab initio calculations to investigate the stacking fault (SF) properties of the metastable ζ -Zr 2 H zirconium hydride. The effect of H near the SF was found to entail the existence of negative SF energies, showing that the ζ compound is probably unstable with respect to shearing in the basal plane. The effect of temperature on SFs was investigated by means of free energy calculations in the quasiharmonic approximation. This evidenced unexpectedly large temperature effects, confirming the main conclusions drawn at 0 K, in particular the ζ mechanical instability. The complex behaviour of H atoms during the shear process suggested ζ -hcp  →  Zr 2 H -fcc as a plausible shear path leading to an fcc compound with same composition as ζ . Finally, as shown by an analysis based on microelasticity, this Zr 2 H -fcc intermediate compound may be relevant for better interpreting the currently intricate issue of hydride habit planes in zirconium.

Pau Amaro-Seoane

Abstract It is now well-established that a dark, compact object, very likely a massive black hole (MBH) of around four million solar masses is lurking at the centre of the Milky Way. While a consensus is emerging about the origin and growth of supermassive black holes (with masses larger than a billion solar masses), MBHs with smaller masses, such as the one in our galactic centre, remain understudied and enigmatic. The key to understanding these holes—how some of them grow by orders of magnitude in mass—lies in understanding the dynamics of the stars in the galactic neighbourhood. Stars interact with the central MBH primarily through their gradual inspiral due to the emission of gravitational radiation. Also stars produce gases which will subsequently be accreted by the MBH through collisions and disruptions brought about by the strong central tidal field. Such processes can contribute significantly to the mass of the MBH and progress in understanding them requires theoretical work in preparation for future gravitational radiation millihertz missions and X-ray observatories. In particular, a unique probe of these regions is the gravitational radiation that is emitted by some compact stars very close to the black holes and which could be surveyed by a millihertz gravitational-wave interferometer scrutinizing the range of masses fundamental to understanding the origin and growth of supermassive black holes. By extracting the information carried by the gravitational radiation, we can determine the mass and spin of the central MBH with unprecedented precision and we can determine how the holes “eat” stars that happen to be near them.

Yu. V. Bondar, S. V. Kuzenko, V. M. Slyvinsky et al.

New composite adsorbent based on modified polyacrylonitrile fibers is synthesized by in situ deposition of potassium-nickel ferrocyanide layer on the fibers’ surface. It is shown that the ferrocyanide phase forms a compact homogeneous layer on the fibers’ surface consisted of rounded nanoaggregates (∼ 40 - 50 nm). Composite fibers are chemically stable in both acidic and alkaline solutions. Sorption experiments have demonstrated that synthesized fibers are high-selective adsorbents and can be used for the purification of natural waters and high-salt solutions from cesium radionuclides.

Y. Toyozawa, S. Elsheikhi

Jeff Colvin, Jon Larsen

Most matter in the Universe, from the deep interior of planets to the core of stars, is at high temperature or high pressure compared to the matter of our ordinary experience. This book offers a comprehensive introduction to the basic physical theory on matter at such extreme conditions and the mathematical modeling techniques involved in numerical simulations of its properties and behavior. Focusing on computational modeling, the book discusses topics such as the basic properties of dense plasmas; ionization physics; the physical mechanisms by which laser light is absorbed in matter; radiation transport in matter; the basics of hydrodynamics and shock-wave formation and propagation; and numerical simulation of radiation-hydrodynamics phenomenology. End-of-chapter exercises allow the reader to test their understanding of the material and introduce additional physics, making this an invaluable resource for researchers and graduate students in this broad and interdisciplinary area of physics.