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

Maxwell Drimmer, Sjoerd Telkamp, Felix L Fischer et al.

The performance of superconducting microwave circuits is strongly influenced by the material properties of the superconducting film and substrate. While progress has been made in understanding the importance of surface preparation and the effect of surface oxides, the complex effect of superconductor film structure on microwave losses is not yet fully understood. In this study, we investigate the microwave properties of niobium resonators with different crystalline properties and related surface topographies. We analyze a series of magnetron sputtered films in which the Nb crystal orientation and surface topography are changed by varying the substrate temperatures between room temperature and 975 K. The lowest-loss resonators that we measure have quality factors of over 10 ^6 at single-photon powers, among the best ever recorded using the Nb on sapphire platform. We observe the highest quality factors in films grown at an intermediate temperature regime of the growth series (550 K) where the films display both preferential ordering of the crystal domains and low surface roughness. Furthermore, we analyze the temperature-dependent behavior of our resonators to learn about how the quasiparticle density in the Nb film is affected by the niobium crystal structure and the presence of grain boundaries. Our results stress the connection between the crystal structure of superconducting films and the loss mechanisms suffered by the resonators and indicate that even a moderate change in temperature during thin film deposition can significantly affect the resulting quality factors.

Kota Katsumi, Yann Gallais, Ryo Shimano

Abstract Nonlinear light-matter interaction at low energy, particularly in the terahertz (THz) frequency range, hosts unique phenomena distinct from the optical excitation with photon energy of a few eV. In cuprate superconductors Bi2Sr2CaCu2O8+x , the THz nonlinear response is identified via the optical reflectivity change and interpreted as the amplitude mode of the superconducting condensate, namely the Higgs mode [K. Katsumi et al., Phys. Rev. Lett. 120, 117001 (2018)]. However, the origin of the THz nonlinearity has been questioned because the pair-breaking process, identified in Raman spectroscopy, can also contribute to it. Here, we reexamined the THz-driven nonequilibrium dynamics in cuprates Bi2Sr2CaCu2O8+x by comparing it with the Raman susceptibility. In the optical reflectivity change, we found an oscillatory behavior following the squared THz waveform (THz Kerr signal), as well as the relaxation of the quasiparticle excitation. Careful insight into the data revealed that the oscillatory and decaying contributions exhibit different doping dependence. Remarkably, the doping and temperature evolutions of the THz Kerr signal are distinct from those of the Raman susceptibility, which is described by the pair-breaking due to diamagnetic light–matter interaction. These results indicate the importance of the paramagnetic light–matter coupling in the THz Kerr signal in the cuprate superconductors, likely arising from the Higgs mode.

Chuanqi Zheng, Xiaoxue Liu

Abstract Moiré superlattices have emerged as an excellent platform for investigating a plethora of exotic quantum states in condensed matter physics. Recent advancements have unveiled abundant discoveries in two-dimensional moiré superlattices. In this paper, we will present a review of the recent progresses in superconductivity and topological physics within graphene and transition metal dichalcogenides-based moiré superlattices. Additionally, we outline future potential challenges and desirable efforts for discovering, understanding, and controlling these novel states in two-dimensional moiré superlattices.

Zhenfeng Ouyang, Miao Gao, Zhong-Yi Lu

Abstract An experimental study found superconductivity in bilayer phase of La3Ni2O7, with the highest superconducting transition temperature (T c ) ∼ 80 K under pressure. Recently, some reports claimed that there exists a competitive monolayer-trilayer structural phase in La3Ni2O7 compounds. We perform the first-principles calculations and find that bilayer phase of La3Ni2O7 is energetically favorable under pressure. Although extensive studies have been done to investigate the electronic correlation and potential superconducting pairing mechanism in bilayer phase of La3Ni2O7, the phonon properties and electron-phonon coupling (EPC) in the high-pressure I4/mmm phase of La3Ni2O7 are not reported. Using the density functional theory (DFT) combined with Wannier interpolation technique, we study the phonon properties and EPC in bilayer phase of La3Ni2O7 under 29.5 GPa. Our findings reveal that EPC is insufficient to explain the observed superconducting T c ∼ 80 K. And the calculated Fermi surface nesting may explain the experimentally observed charge density wave (CDW) transition in bilayer phase of La3Ni2O7. Our calculations substantiate that bilayer phase of La3Ni2O7 is an unconventional superconductor.

Hui-Ke Jin, Wilhelm Kadow, Michael Knap et al.

Abstract We study the effect of hole doping on the Kitaev spin liquid (KSL) and find that for ferromagnetic (FM) Kitaev exchange K the system is very susceptible to the formation of a FM spin polarization. Through density matrix renormalization group simulations on finite systems, we uncover that the introduction of a single hole, corresponding to ≈1% hole doping for the system size we consider, with a hopping strength of just t ~ 0.28K is enough to disrupt fractionalization and polarize the spins in the [001] direction due to an order-by-disorder mechanism. Taking into account a material relevant FM anisotropic exchange Γ drives the polarization towards the [111] direction via a transition into a topological FM state with chiral magnon excitations. We develop a parton mean-field theory incorporating fermionic holons and bosonic magnons, which accounts for the doping induced FM phases and topological magnon excitations. We discuss experimental implications for Kitaev candidate materials.

Lior Shani, Pim Lueb, Gavin Menning et al.

Quantum devices based on InSb nanowires (NWs) are a prime candidate system for realizing and exploring topologically-protected quantum states and for electrically-controlled spin-based qubits. The influence of disorder on achieving reliable quantum transport regimes has been studied theoretically, highlighting the importance of optimizing both growth and nanofabrication. In this work, we consider both aspects. We developed InSb NW with thin diameters, as well as a novel gating approach, involving few-layer graphene and atomic layer deposition-grown AlO _x . Low-temperature electronic transport measurements of these devices reveal conductance plateaus and Fabry–Pérot interference, evidencing phase-coherent transport in the regime of few quantum modes. The approaches developed in this work could help mitigate the role of material and fabrication-induced disorder in semiconductor-based quantum devices.

Yanyan Zhao, Jijun Zhao, Yu Guo et al.

Abstract In chiral materials, spins and chirality are coupled via spin-orbit interaction, provoking a fast-growing field of chiral spintronics. Compared with the widely explored chiral molecules, exploration of chirality-dependent spin effects in crystals and supramolecules remain limited. Here we assemble chiral superatomic crystals MXTe4 (M = transition metal; X = Ga or Ge) using telluride tetrahedra clusters as building blocks. Distinct from atomic crystals, these assembled monolayers have tunable symmetries and electronic characteristics by tilting the tetrahedral units through the variation of inter-cluster interaction. Dresselhaus-type spin textures and anisotropic spin Hall effect with inversed sign of spin current under opposite geometrical handedness are demonstrated in these chiral monolayers by symmetry analysis and verified by ab initio calculations. These results provide an innovative paradigm for assembling superatomic crystals with designated symmetry and hierarchical structures to access the chirality-driven quantum effects.

Hui Zhou, Hang Liu, Hongyan Ji et al.

Abstract The lattice geometry induced second-order topological corner states in breathing Kagome lattice have attracted enormous research interests, while the realistic breathing Kagome materials identified as second-order topological insulators are still lacking. Here, we report by first-principles calculations the second-order topological states emerging in two-dimensional d-orbital breathing Kagome crystals, i.e., monolayer niobium/tantalum chalcogenide halides M3QX7 (M = Nb, Ta; Q = S, Se, Te; X = Cl, Br, I). We find that the orbital degree of freedom of d orbitals can give rise to multiple sets of corner states. Combining fraction corner anomaly, orbital components and real space distribution of the corner states, we can also identify the topology of these corner states. Our work not only extends the lattice geometry induced second-order topological states to realistic materials, but also builds a clear and complete picture on their multiple sets of second-order topological states.

Hidefumi Takahashi, Tomohiro Sasaki, Akitoshi Nakano et al.

Abstract Given the rarity of metallic systems that exhibit ferroelectric-like transitions, it is apparently challenging to find a system that simultaneously possesses superconductivity and ferroelectric-like structural instability. Here, we report the observation of superconductivity at 2.4 K in a layered semimetal SrAuBi characterized by strong spin–orbit coupling (SOC) and ferroelectric-like lattice distortion. Single crystals of SrAuBi have been successfully synthesized and found to show a polar-nonpolar structure transition at 214 K, which is associated with the buckling of Au-Bi honeycomb lattice. On the basis of the band calculations considering SOC, we found significant Rashba-type spin splitting and symmetry-protected multiple Dirac points near the Fermi level. We believe that this discovery opens up new possibilities of pursuing exotic superconducting states associated with the semimetallic band structure without space inversion symmetry and the topological surface state with the strong SOC.

Peng Li, Tongrui Li, Sen Liao et al.

Abstract Using angle resolved photoemission spectroscopy measurements and first principle calculations, we report that the possible unconventional 2q antiferromagnetic (AFM) order in NdSb can induce unusual modulation on its electronic structure. The obvious extra bands observed in the AFM phase of NdSb are well reproduced by theoretical calculations, in which the Fermi-arc-like structures and sharp extra bands are originated from the in-gap surface states. However, they are demonstrated to be topological trivial. By tuning the chemical potential, the AFM phase of NdSb would go through a topological phase transition, realizing a magnetic topological insulator phase. Hence, our study sheds new light on the rare earth monopnictides for searching unusual AFM structure and the potential of intrinsic magnetic topological materials.

Stuart Harwood, Claudio Gambella, Dimitar Trenev et al.

The determination of vehicle routes fulfilling connectivity, time, and operational constraints is a well-studied combinatorial optimization problem. The NP-hard complexity of vehicle routing problems has fostered the adoption of tailored exact approaches, matheuristics, and metaheuristics on classical computing devices. The ongoing evolution of quantum computing hardware and the recent advances of quantum algorithms (i.e., VQE, QAOA, and ADMM) for mathematical programming make decision-making for routing problems an avenue of research worthwhile to be explored on quantum devices. In this article, we propose several mathematical formulations for inventory routing cast as vehicle routing with time windows and comment on their strengths and weaknesses. The optimization models are compared from a quantum computing perspective, specifically with metrics to evaluate the difficulty in solving the underlying quadratic unconstrained binary optimization problems. Finally, the solutions obtained on simulated quantum devices demonstrate the relative benefits of different algorithms and their robustness when put into practice.

R. M. Vernydub, O. I. Kyrylenko, O. V. Konoreva et al.

The features of the current-voltage characteristics of LEDs obtained on the basis of GaP-GaAsP solid solutions are considered. The results of studies of the effect of electron irradiation (E = 2 MeV, F = 3 · 1014 ÷ 2.6 · 1016 cm-2) on the main electrophysical parameters of GaAs1-xPx diodes (x = 0.85 – yellow, x = 0.45 – orange) are given. The increase of differential resistance, the series resistance of the base, and barrier potential are revealed. The processes of recovery of the investigated quantities during isochronous annealing are analyzed, the mechanisms of degradation-recovery phenomena are discussed.

Junseong Song, Byung Cheol Park, Kyung Ik Sim et al.

Abstract Topological Dirac semimetals have emerged as a platform to engineer Berry curvature with time-reversal symmetry breaking, which allows to access diverse quantum states in a single material system. It is of interest to realize such diversity in Dirac semimetals that provides insight on correlation between Berry curvature and quantum transport phenomena. Here, we report the transition between anomalous Hall and chiral fermion states in three-dimensional topological Dirac semimetal KZnBi, which is demonstrated by tuning the direction and flux of Berry curvature. Angle-dependent magneto-transport measurements show that both anomalous Hall resistance and positive magnetoresistance are maximized at 0° between net Berry curvature and rotational axis. We find that the unexpected crossover of anomalous Hall resistance and negative magnetoresistance suddenly occurs when the angle reaches to ~70°, indicating that Berry curvature strongly correlates with quantum transports of Dirac and chiral fermions. It would be interesting to tune Berry curvature within other quantum phases such as topological superconductivity.

Rui Zhou, Daniel D. Scherer, Hadrien Mayaffre et al.

Abstract FeSe is arguably the simplest, yet the most enigmatic, iron-based superconductor. Its nematic but non-magnetic ground state is unprecedented in this class of materials and stands out as a current puzzle. Here, our nuclear magnetic resonance measurements in the nematic state of mechanically detwinned FeSe reveal that both the Knight-shift and the spin–lattice relaxation rate 1/T 1 possess an in-plane anisotropy opposite to that of the iron pnictides LaFeAsO and BaFe2As2. Using a microscopic electron model that includes spin–orbit coupling, our calculations show that an opposite quasiparticle weight ratio between the d x z and d y z orbitals leads to an opposite anisotropy of the orbital magnetic susceptibility, which explains our Knight-shift results. We attribute this property to a different nature of nematic order in the two compounds, predominantly bond type in FeSe and onsite ferro-orbital in pnictides. The T 1 anisotropy is found to be inconsistent with existing neutron scattering data in FeSe, showing that the spin fluctuation spectrum reveals surprises at low energy, possibly from fluctuations that do not break C 4 symmetry. Therefore, our results reveal that important information is hidden in these anisotropies and they place stringent constraints on the low-energy spin correlations as well as on the nature of nematicity in FeSe.

Yuansu Luo, Konrad Samwer

Johannes Roth

V. A. Babenko, V. N. Pavlovych

Main characteristic properties of ignition and development of self-sustaining nuclear chain reaction (SCR) in the fuel-containing masses (FCM) of the object “Ukryttya”, and also the main properties of SCR for a number of its typical essentially possible modes were studied. System of differential equations for the main physical quantities describing FCM was formulated. Numerical analysis and calculations according to this system show that the main possible modes of SCR are exponential growth of the neutron flux, mode of the solitary neutron flux burst of differing strength, and also mode of the neutron flux oscillations. Mode of the flux oscillations is of great interest and exhibits various properties. According to calculations, the neutron flux burst of extremely high strength appears to be possible under some likely and reasonable physical conditions in presence of the sufficient accumulation of fissile materials. But the most realistic and close to the experiment mode of SCR appears to be the mode of slow growth of the neutron flux progressively, as the system is flooded by water, and further subsequent transition into the mode of the neutron flux oscillations in the neighbourhood of the critical state.

O. A. Ponkratenko, A. A. Rudchik, A. T. Rudchik et al.

Detailed study of the behavior of experimental differential cross sections for the 16О + 12С-, 12С + 12С-elastic scatte¬ring in the energy range from 1 to 200 MeV/nucleon have been carried out. It is found that differential cross sections in the range of transfer momentum from 0 to 3-4 fm-1 shows the diffraction character for scattering in the overall energy range. The behavior features of the allocations of the first eight diffraction maxima and minima as well values of cross-sections in the maxima at the change of the interaction energy have been analyzed. It has been received energy-dependent optical potentials of the interaction for examines systems at the full range of energies. The obtained potentials describe the available experimental data satisfactorily and reproduce typical features of diffractive scattering cross sections.

T. Kojo