Intrinsic Breaking Research Articles

Ferromagnetism and valley polarization in Janus single-layer VSCl

Two-dimensional ferromagnetic semiconductors have received extensive attention due to their promising application for valleytronics along with the opportunity to realize spontaneous valley polarization. Herein, by means of the first-principles calculations, we design a two-dimensional ferromagnetic semiconductor single-layer VSCl with the direct band gap is 0.88 eV, and magnetic moment is 2 μB per unit. The Curie temperature of single-layer VSCl is estimated to be 125 K based on the mean field approximation. In addition, the ferromagnetism can be further improved by adopting moderate tensile strain. Importantly, the intrinsic breaking of time and spatial inversion symmetry leads to the spontaneous valley polarization in single-layer VSCl. The corresponding valley polarization energy is about 57.8 meV, which is sizeable enough for practical operations. Our findings provide a candidate material for realizing the potential application of two-dimensional valleytronic devices.

Orbital-enhanced warping effect in px,py-derived Rashba spin splitting of monatomic bismuth surface alloy

Spin-split Rashba bands have been exploited to efficiently control the spin degree of freedom of moving electrons, which possesses a great potential in frontier applications of designing spintronic devices and processing spin-based information. Given an intrinsic breaking of inversion symmetry and sizeable spin–orbit interaction, two-dimensional (2D) surface alloys formed by heavy metal elements exhibit a pronounced Rashba-type spin splitting of the surface states. Here, we have revealed the essential role of atomic orbital symmetry in the hexagonally warped Rashba spin-split surface state of the sqrt 3 times sqrt 3 R30^0 BiCu2 monatomic alloy by scanning tunneling spectroscopy (STS) and density functional theory (DFT). From dI/dU spectra and calculated band structures, three hole-like Rashba-split bands hybridized from distinct orbital symmetries have been identified in the unoccupied energy region. Because of the hexagonally deformed Fermi surface, quasi-particle interference (QPI) mappings have resolved scattering channels opened from interband transitions of px,py (mj = 1/2) band. In contrast to the s,pz-derived band, the hexagonal warping is predominately accompanied by substantial out-of-plane spin polarization Sz up to 24% in the dispersion of px,py (mj = 1/2) band with an in-plane orbital symmetry.

Breaking the Vainshtein screening in clusters of galaxies

In this work we will test an alternative model of gravity belonging to the large family of galileon models. It is characterized by an intrinsic breaking of the Vainshtein mechanism inside large astrophysical objects, thus having possibly detectable observational signatures. We will compare theoretical predictions from this model with the observed total mass profile for a sample of clusters of galaxies. The profiles are derived using two complementary tools: X-ray hot intra-cluster gas dynamics, and strong and weak gravitational lensing. We find that a dependence with the dynamical internal status of each cluster is possible; for those clusters which are very close to be relaxed, and thus less perturbed by possible astrophysical local processes, the galileon model gives a quite good fit to both X-ray and lensing observations. Both masses and concentrations for the dark matter halos are consistent with earlier results found in numerical simulations and in the literature, and no compelling statistical evidence for a deviation from general relativity is detectable from the present observational state. Actually, the characteristic galileon parameter $\Upsilon$ is always consistent with zero, and only an upper limit ($\lesssim0.086$ at $1\sigma$, $\lesssim0.16$ at $2\sigma$, and $\lesssim0.23$ at $3\sigma$) can be established. Some interesting distinctive deviations might be operative, but the statistical validity of the results is far from strong, and better data would be needed in order to either confirm or reject a potential tension with general relativity.

The Nonlinear Elasticity of Hexagonal Ti2C Monolayer from First-Principles Calculations

In this work, the nonlinear elasticity of hexagonal Ti2C monolayer is studied by first-principles calculations. The second-and third-order elastic constants were calculated using nonlinear elasticity theory. The nonlinear stress-strain relationship depending on higher order elastic constants was also revealed. The intrinsic breaking strength and corresponding breaking strain were deduced as 11.9 N/m at the maximum strain 16.6% for Ti2C monolayer.

Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene

We measured the elastic properties and intrinsic breaking strength of free-standing monolayer graphene membranes by nanoindentation in an atomic force microscope. The force-displacement behavior is interpreted within a framework of nonlinear elastic stress-strain response, and yields second- and third-order elastic stiffnesses of 340 newtons per meter (N m(-1)) and -690 Nm(-1), respectively. The breaking strength is 42 N m(-1) and represents the intrinsic strength of a defect-free sheet. These quantities correspond to a Young's modulus of E = 1.0 terapascals, third-order elastic stiffness of D = -2.0 terapascals, and intrinsic strength of sigma(int) = 130 gigapascals for bulk graphite. These experiments establish graphene as the strongest material ever measured, and show that atomically perfect nanoscale materials can be mechanically tested to deformations well beyond the linear regime.

Direct comparison between experiments and computations at the atomic length scale: a case study of graphene

This paper discusses a set of recent experimental results in which the mechanical properties of monolayer graphene molecules were determined. The results included the second-order elastic modulus which determines the linear elastic behavior and an estimate of the third-order elastic modulus which determines the non-linear elastic behavior. In addition, the distribution of the breaking force strongly suggested the graphene to be free of defects, so the measured breaking strength of the films represented the intrinsic breaking strength of the underlying carbon covalent bonds. The results of recent simulation efforts to predict the mechanical properties of graphene are discussed in light of the experiments. Finally, this paper contains a discussion of some of the extra challenges associated with experimental validation of multi-scale models.

The nonlinear surface impedance of YBa2Cu3O7−δ thin films in zero and large applied fields

We present coplanar resonator measurements of the nonlinear microwave surface impedance of laser ablated and electron-beam coevaporated YBa2Cu3O7−δ thin films at 8 GHz in zero and applied magnetic fields, including the effects of irradiation with heavy ions. Correlations between the changes in surface resistance and reactance as a function of microwave current suggest that there are different contributions to the nonlinear behavior at low and high microwave currents in both zero and applied fields. In zero field, we suggest that microwave-induced flux lines are responsible for the observed nonlinear behavior, resulting in thermal runaway at large, sample dependent, microwave currents. The observed nonlinearity completely masks any possible contribution from the intrinsic pair breaking expected for a d-wave superconductor. In a magnetic field at relatively low currents, the nonlinearity can be described by the nonlinear dynamics of flux lines pinned by defects with a continuous range of pinning strengths. At higher currents, microwave field nucleation of flux lines is again considered important. On irradiation with 3.6 MeV/nucleon Xe-129 ions, the microwave losses and nonlinearity are significantly decreased in both zero and applied fields, which could have important implications for microwave device applications.

Numerical Investigation of Intrinsic Mechanical Properties of Carbon Fibers

This paper evaluates a loop bending test that can measure the intrinsic strength and breaking strain of carbon fibers. The discussion extends from the applicability of a closed-form solution for prismatic bar flexure, subjected to large deformations, to an interpretation of the test results. The assumptions embedded in the closed-form solution are verified by finite element computer simulations of the loop test.

Evaluation of the intrinsic mechanical properties of carbon fibres

The bending method, which provides a measurement of intrinsic strenght and failure strain of carbon fibres, is evaluated. This method, applied to linear elastic material, is based on a mathematical framework resulting from flexure theory. The results obtained demonstrate that for the carbon fibres studied those with the lowest value of stress concentration factor are characterised by an intrinsic breaking strain, ε f, of 3·25% and an intrinsic tensile strength, σ f , of 7·33 GPa.

Hybrid symmetry breaking and additional Z boson coupled to baryon and lepton currents

We demonstrate that renormalizability and hybrid symmetry breaking could be compatible. This result is applied to generalize the electroweak theory to include an intrinsic breaking of theU(1) symmetry of baryon and lepton numbers. There is an additional Z boson, called «chino», which couples to conserved lepton and baryon currents. The chino mass is 246 GeV, based on dimensional argument.

CP violation in particle physics and cosmology: Is there any connection?

We discuss, in the framework of unified gauge theories, the possible connection between the CP-violating phase(s) ( δ B) responsible for matter-antimatter asymmetry and those phase(s) ( δ K responsible for low-energy CP-violating observables, like ϵ and ϵ′ in the kaon system and the electric dipole moment of the neutron. We conclude, from the study of a variety of models with either intrinsic or spontaneous breaking of CP symmetry, that due to the existence of the SU(2) L × U(1) phase transition in general δ B and δ K bear no relation to each other, although they are both expressible in terms of the parameters characterizing the effective lagrangian of the theory.

Breaking of Line Reverse Relation and Exotics

Under a hypothesis that the meson-baryon reaction amplitude corresponds to the urbaryon rearrangement diagram (URD), the X type (t-u dual) URD is related to the H type (s-t dual) one in the forward region by reversing the urbaryon line. It has been taken that the X type amplitude has the magnitude equal to the H type one and is real, and that the Z .type (s-u dual) amplitude is negligible; line reverse relation (LRR). There are, however, indications that the LRR is more or less broken. Two simple models resulting in the LR breaking under the URD hypothesis are investigated. (1) Zrr model. One· of the three Z type URD's, which is named Zrr, has a remarkable peculiarity that its t-channel quantum numbers are non-exotic irrespective of the exoticfour­ urbaryon configuration. If the Zrr amplitude survives up to high energies from this peculiarity, an apparent LR breaking results in KN-'nrY vs. rrN~KY processes. (2) Im X model. The imaginary part of the X amplitude, which may be compatible with the possible KN s-channel exotics such as Zo (P112) and Z 1 (P,;,), gives rise to an intrinsic LR breaking. A comparison between the two models and their consequences are examined. LR breakings in decuplet baryon production and of baryon exchange are also discussed.

Phenomenological use of the Callan-Symanzik equation

We find that the Callan-Symanzik equation with the intrinsic breaking term omitted suggests ansatz for the differential cross section in the high energy wide angle limit. The agreement with experimental data for the reactions ep → ep, π −p → π −p, pp → pp is very satisfactory.

Dynamical rearrangement of approximate symmetries

An example of a combination of spontaneous and intrinsic breakdown of symmetry is studied. When the effect of spontaneous breakdown is much stronger than that of intrinsic breakdown, the original symmetry is replaced by a new symmetry and the symmetry transformation is mainly taken care of by the transformation of spinless boson. When the intrinsic breaking term becomes stronger, the symmetry transformation comes closer to its original form, while the spinless boson remains. The divergence of helicity current written in terms of physical field is obtained in the form effectively similar to PCAC. A possible application to the spurion theory of the weak phenomena is suggested.