Neutrino spin oscillations in gravitational fields

We study neutrino spin oscillations in gravitational fields. The quasi-classical approach is used to describe the neutrino spin evolution. First we examine the case of a weak gravitational field. We obtain the effective Hamiltonian for the description of neutrino spin oscillations. We also receive the neutrino transition probability when a particle propagates in the gravitational field of a rotating massive object. Then we apply the general technique to the description of neutrino spin oscillations in the Schwarzschild metric. The neutrino spin evolution equation for the case of the neutrino motion in the vicinity of a black hole is obtained. The effective Hamiltonian and the transition probability are also derived. We examine the neutrino oscillations process on different circular orbits and analyze the frequencies of spin transitions. The validity of the quasi-classical approach is also considered.Comment: RevTeX4, 9 pages, 1 esp figure; article was revised, some misprints were corrected, 6 references added; accepted for publication in Int.J.Mod.Phys.

Neutrino Physics with Dark Matter Experiments and the Signature of New Baryonic Neutral Currents

New neutrino states \nu_b, sterile under the Standard Model interactions, can be coupled to baryons via the isoscalar vector currents that are much stronger than the Standard Model weak interactions. If some fraction of solar neutrinos oscillate into \nu_b on their way to Earth, the coherently enhanced elastic \nu_b-nucleus scattering can generate a strong signal in the dark matter detectors. For the interaction strength a few hundred times stronger than the weak force, the elastic \nu_b-nucleus scattering via new baryonic currents may account for the existing anomalies in the direct detection dark matter experiments at low recoil. We point out that for solar neutrino energies the baryon-current-induced inelastic scattering is suppressed, so that the possible enhancement of new force is not in conflict with signals at dedicated neutrino detectors. We check this explicitly by calculating the \nu_b-induced deuteron breakup, and the excitation of 4.4 MeV \gamma-line in ^{12}C. Stronger-than-weak force coupled to baryonic current implies the existence of new abelian gauge group U(1)_B with a relatively light gauge boson.Comment: 20 pages, 5 figures. References added, inconsistent treatment of neutrino oscillations corrected, conclusions unchange

Muon Flux Limits for Majorana Dark Matter Particles

We analyze the effects of capture of dark matter (DM) particles, with successive annihilations, predicted in the minimal walking technicolor model (MWT) by the Sun and the Earth. We show that the Super-Kamiokande (SK) upper limit on excessive muon flux disfavors the mass interval between 100-200 GeV for MWT DM with a suppressed Standard Model interaction (due to a mixing angle), and the mass interval between 0-1500 GeV for MWT DM without such suppression, upon making the standard assumption about the value of the local DM distribution. In the first case, the exclusion interval is found to be very sensitive to the DM distribution parameters and can vanish at the extreme of the acceptable values.Comment: 20 pages, 12 figures. The revised version has minor addition (without change of the result) as the following: 1) Comparison of our estimations with analogous previous ones is included in the Figure 7; a paragraph regarding it was added in Discussion. 2) The Introduction, Acknowledgements and References have been a little extende

Nanoscale Doping and Its Impact on the Ferroelectric and Piezoelectric Properties of Hf0.5_{0.5}Zr0.5_{0.5}O2_2

Ferroelectric hafnium oxide thin films—the most promising materials in microelectronics’ non-volatile memory—exhibit both unconventional ferroelectricity and unconventional piezoelectricity. Their exact origin remains controversial, and the relationship between ferroelectric and piezoelectric properties remains unclear. We introduce a new method to investigate this issue, which consists in a local controlled modification of the ferroelectric and piezoelectric properties within a single Hf$_{0.5}$Zr$_{0.5}$O$_2$ capacitor device through local doping and a further comparative nanoscopic analysis of the modified regions. By comparing the ferroelectric properties of Ga-doped Hf$_{0.5}$Zr$_{0.5}$O$_2$ thin films with the results of piezoresponse force microscopy and their simulation, as well as with the results of in situ synchrotron X-ray microdiffractometry, we demonstrate that, depending on the doping concentration, ferroelectric Hf$_{0.5}$Zr$_{0.5}$O$_2$ has either a negative or a positive longitudinal piezoelectric coefficient, and its maximal value is −0.3 pm/V. This is several hundreds or thousands of times less than those of classical ferroelectrics. These changes in piezoelectric properties are accompanied by either improved or decreased remnant polarization, as well as partial or complete domain switching. We conclude that various ferroelectric and piezoelectric properties, and the relationships between them, can be designed for Hf$_{0.5}$Zr$_{0.5}$O$_2$ via oxygen vacancies and mechanical-strain engineering, e.g., by doping ferroelectric films

Origin of the retention loss in ferroelectric Hf0.5Zr0.5O2Hf_{0.5}Zr_{0.5}O_{2}-based memory devices

For the decade, ferroelectric hafnium oxide films are attracting the interest as a promising functional material for nonvolatile ferroelectric random access memory due to full scalability and complementary metal-oxide-semiconductor integratability. Despite the significant progress in key performance parameters, particularly, the readout charge and voltage as well as the endurance, the developed devices can only be implemented by the electronics industry if they exhibit a standard retention time of 10 years. Material engineering modifies not only target ferroelectric properties, but also the retention time. To understand how to maintain the sufficient retention, the physical mechanism behind it should be clarified. For this purpose, we have fabricated the capacitor memory cell with a high rate of retention loss. Comparing the device performance with the results of capacitance transient spectroscopy, operando hard X-ray photoelectron spectroscopy and in situ piezoresponse force microscopy, we have concluded that the retention loss is caused by the accumulation of the positively charged oxygen vacancies at the interfaces with capacitor electrodes. The redistribution of charges during long-term storage of information is fully defined by the domain structure in memory cell

Ferroelectric Second-Order Memristor

While the conductance of a first-order memristor is defined entirely by the external stimuli, in the second-order memristor it is governed by the both the external stimuli and its instant internal state. As a result, the dynamics of such devices allows to naturally emulate the temporal behavior of biological synapses, which encodes the spike timing information in synaptic weights. Here, we demonstrate a new type of second-order memristor functionality in the ferroelectric HfO2-based tunnel junction on silicon. The continuous change of conductance in the p+-Si/Hf0.5Zr0.5O2/TiN tunnel junction is achieved via the gradual switching of polarization in ferroelectric domains of polycrystalline Hf0.5Zr0.5O2 layer, whereas the combined dynamics of the built-in electric field and charge trapping/detrapping at the defect states at the bottom Si interface defines the temporal behavior of the memristor device, similar to synapses in biological systems. The implemented ferroelectric second-order memristor exhibits various synaptic functionalities, such as paired-pulse potentiation/depression and spike-rate-dependent plasticity, and can serve as a building block for the development of neuromorphic computing architectures