Search

Galactic dark matter may consist of axionlike particles (ALPs) that can be described as an "ultralight bosonic field" oscillating at the ALP Compton frequency. The ALP field can be searched for using nuclear magnetic resonance (NMR), where resonant precession of spins of a polarized sample can be sensitively detected. The ALP mass to which the experiment is sensitive is scanned by sweeping the bias magnetic field. The scanning either results in detection of ALP dark matter or rules out ALP dark matter with sufficiently strong couplings to nuclear spins over the range of ALP masses corresponding to the covered span of Larmor frequencies. In this work, scanning strategies are analyzed with the goal of optimizing the parameter‐space coverage via a proper choice of experimental parameters (e.g., the effective transverse relaxation time). [ABSTRACT FROM AUTHOR]

Shortcuts to adiabaticity (STA) are broadly accepted as a powerful control technique intended to accelerate quantum adiabatic processes, therefore, avoiding the undesired actions of decoherence, noise and particle losses. Here, a general state-independent scheme to speed up a quantum evolution is proposed, which can work as a STA whenever the reference process is adiabatic. The method consists in adding and auxiliary Hamiltonian to a reference one, as in the case of the well-known counterdiabatic driving protocol, however, without requiring knowledge about the eigenvalues and eigenstates of the latter. We use the important scenarios of the parametric oscillator and the spin 1/2 in a magnetic field to illustrate our findings. [ABSTRACT FROM AUTHOR]

It was predicted that the spin precession frequency of a stationary gyroscope shows various anomalies in the strong gravity regime if its orbit shrinks, and eventually, its precession frequency becomes arbitrarily high very close to the horizon of a rotating black hole. Considering the gravity waves of a flowing fluid with a vortex in a shallow basin, which acts as a rotating analogue black hole, one can observe the predicted strong gravity effect on the spin precession in the laboratory. Attaching a thread with the buoyant particles and anchoring it to the bottom of the fluid container with a short-length miniature chain, one can construct a simple local test gyroscope to measure the spin precession frequency in the vicinity of the gravity wave analogue black hole. The thread acts as the axis of the gyroscope. By regulating the orbital frequency of the test gyroscope, one can also measure the strong gravity Lense–Thirring effect and geodetic/de-Sitter effect with this experimental set-up as the special cases. For example, to measure the Lense–Thirring effect, the length of the miniature chain can be set to zero, so that the gyroscope becomes static. One can also measure the geodetic precession with this system by orbiting the test gyroscope in the so-called Keplerian frequency around the non-rotating analogue black hole that can be constructed by making the rotation of the fluid/vortex negligible compared to its radial velocity. [ABSTRACT FROM AUTHOR]

In this paper, we study the effects of the external magnetic field on the Lense–Thirring (LT) precession of a test gyroscope attached to an observer in magnetized black hole spacetime. For this, we consider a Kerr–Newman black hole embedded in the external magnetic field. The LT precession of a test gyroscope diverges near the ergosurface and remains finite everywhere outside the ergosurface. It is seen that by increasing the external magnetic field, the LT precession frequency in the region of large r decreases as B increases, while the precession frequency in the region of small r increases as B increases, whereas it increases with increasing the charge of the black hole. The LT precession of a test gyroscope attached to observers moving along the directions close to the polar axis is greater than that of the observer moving in the equatorial plane. [ABSTRACT FROM AUTHOR]

Magnetic fluids based on single-domain magnetic spinel ferrite nanoparticles dispersed in various liquid media are of particular practical and scientific interest. This paper presents a muon spectroscopy study of a ferrofluid based on magnetic nanoparticles of CoFe2O4 molecules dispersed in water (H2O) with a nanoparticle concentration of 3%. In this study, it was determined that the structure and magnitude of the magnetization of a ferrofluid depend on the viscosity of the liquid itself. It was shown that, at room temperature (290 K) and under an external magnetic field of 527 G, the observed additional magnetization was ~20 G. In a small fraction of the sample under study (~20%), negative magnetization (diamagnetism) was observed. At low temperatures (~30 K), the sample acted as a paramagnet in a magnetic field. For the first time, the magnetic field inside and in the immediate vicinity of a CoFe2O4 nanoparticle has been measured experimentally using the μSR method: the value was 1.96 ± 0.44 kG; thus, direct measurement of the magnetization of a nanoscale object was performed. [ABSTRACT FROM AUTHOR]

It was predicted that the spin precession frequency of a stationary gyroscope shows various anomalies in the strong gravity regime if its orbit shrinks, and eventually, its precession frequency becomes arbitrarily high very close to the horizon of a rotating black hole. Considering the gravity waves of a flowing fluid with a vortex in a shallow basin, which acts as a rotating analogue black hole, one can observe the predicted strong gravity effect on the spin precession in the laboratory. Attaching a thread with the buoyant particles and anchoring it to the bottom of the fluid container with a short-length miniature chain, one can construct a simple local test gyroscope to measure the spin precession frequency in the vicinity of the gravity wave analogue black hole. The thread acts as the axis of the gyroscope. By regulating the orbital frequency of the test gyroscope, one can also measure the strong gravity Lense–Thirring effect and geodetic/de-Sitter effect with this experimental set-up as the special cases. For example, to measure the Lense–Thirring effect, the length of the miniature chain can be set to zero, so that the gyroscope becomes static. One can also measure the geodetic precession with this system by orbiting the test gyroscope in the so-called Keplerian frequency around the non-rotating analogue black hole that can be constructed by making the rotation of the fluid/vortex negligible compared to its radial velocity.

Electronic spin precession and filtering are measured in the molecular field of magnetic thin films. Lab‐on‐chip experiments allow injection of electrons with energies between 0.8 and 1.1 eV, an energy range not yet explored in spin precession experiments. While filtering angles agree with previous reported values measured at much higher electron energies, spin precession angles of 2.5° in CoFe and 0.7° in Co per nanometer film thickness could be measured which are 30 times smaller than those previously measured at 7 eV. On the basis of ab initio calculations, the results are explained and it is shown that the band structure and layer roughness are playing a key role at low energy. [ABSTRACT FROM AUTHOR]

In this paper, we develop circuit models for spintronic devices that are under the application of electric and magnetic fields. Starting from time-dependent drift-diffusion equations in nonmagnets and ferromagnets, we spatially and temporally discretize the resulting current-voltage relations using linear multistep methods, which yield equivalent circuit models characterized by finite-difference versions of the so-called 4 × 4 conductance matrices. By using a time-dependent formulation, introducing a new model for ferromagnets, and including ubiquitous effects such as spin dissipation, spin precession, as well as thermal noise, our model serves as a framework to unify and expand the existing models in the literature. To demonstrate our model's utility in applications, we performed simulations on several spintronic devices and validated the results against simulated and measured data. We also discuss extensions to the model and general directions for the future research.

Magnetic fluids based on single-domain magnetic spinel ferrite nanoparticles dispersed in various liquid media are of particular practical and scientific interest. This paper presents a muon spectroscopy study of a ferrofluid based on magnetic nanoparticles of CoFe2O4 molecules dispersed in water (H2O) with a nanoparticle concentration of 3%. In this study, it was determined that the structure and magnitude of the magnetization of a ferrofluid depend on the viscosity of the liquid itself. It was shown that, at room temperature (290 K) and under an external magnetic field of 527 G, the observed additional magnetization was ~20 G. In a small fraction of the sample under study (~20%), negative magnetization (diamagnetism) was observed. At low temperatures (~30 K), the sample acted as a paramagnet in a magnetic field. For the first time, the magnetic field inside and in the immediate vicinity of a CoFe2O4 nanoparticle has been measured experimentally using the μSR method: the value was 1.96 ± 0.44 kG; thus, direct measurement of the magnetization of a nanoscale object was performed.

• Dynamical evolution of spin is exactly solved in linear response to an applied electric field. • The transient behavior and asymptotic solution of spin dynamics in 2D spin-orbit coupled systems is obtained. • The connection between the asymptotic solution and stationary state of the system is exhibited. • The resulting dissipative effect for spin dynamics agrees with the prediction of Kubo formula. We investigate the spin dynamics in the two-dimensional spin-orbit coupled system subject to an in-plane (x - y plane) constant electric field, which is assumed to be turned on at the moment t = 0. The equation of spin precession in linear response to the switch-on of the electric field is derived in terms of Heisenberg's equation by the perturbation method up to the first order of the electric field. The dissipative effect, which is responsible for bringing the dynamical response to an asymptotic result, is phenomenologically implemented à la the Landau-Lifshitz-Gilbert equation by introducing damping terms upon the equation of spin dynamics. Mediated by the dissipative effect, the resulting spin dynamics asymptotes to a stationary state, where the spin and the momentum-dependent effective magnetic field are aligned again and have nonzero components in the out-of-plane (z) direction. In the linear response regime, the asymptotic response obtained by the dynamical treatment is in full agreement with the stationary response as calculated in the Kubo formula, which is a time-independent approach treating the applied electric field as completely time-independent. Our method provides a new perspective on the connection between the dynamical and stationary responses. [ABSTRACT FROM AUTHOR]

Abstract By using the one-dimensional tight-binding model, we theoretically investigate the effect of magnetic field on the collision of the oppositely charged polarons with their spin antiparallel in cis -polyacetylene. We adopt the non-adiabatic approach to simulate the dynamical evolution of polaron spin. Under the effect of electric field with a moderate strength, the polarons initially localized at the chain-end of polyacetylene move towards each other. During the collision process, an obvious spin precession is obtained, and the precession period is found to be inversely proportional to the strength of magnetic field. While after including electron-electron interaction in form of Hubbard model, the period is no longer constant. With the decrease of distance between the oppositely charged polarons, the precession of their spin slows down. We also find that there is a critical value of electron-electron interaction strength, over which the spin precession of polaron disappears. In addition, we demonstrate that under the effect of magnetic field, the polarons could recombine or pass through each other to form the singlet exciton, rather than be dissociated after collision between them with the strong electron-electron interaction, and then the electroluminescence efficiency of organic optoelectronic devices is improved. Graphical abstract Image 1 Highlights • We simulate collision process of oppositely charged polarons in conjugated polymer. • By introducing magnetic field in form of Zeeman effect, we observe spin precession. • The precession period is inversely proportional to the strength of magnetic field. • Electron-electron interaction restrains spin precession when polarons come close. • At strong electron-electron interaction, magnetic field promotes exciton formation. [ABSTRACT FROM AUTHOR]

We investigate the spin-Hall conductivity (SHC) in the two-dimensional spin–orbit coupled systems by taking spin precession into account. The influence of spin precession on the spin-Hall current in the presence of disorder is investigated. Perturbation method leads to the result that the spin dynamics is composed of Larmor (periodic) and non-Larmor (non-periodic) precession. The non-Larmor component of spin is found to be the same result obtained from the Kubo formula in the short time limit. The Larmor component of spin, i.e., spin precession in the unperturbed system, was neglected in the previous studies, but it plays an important role in the linear response theory. The Larmor precession of spin should be zero after time average over several complete periods because there is no specific orientation perpendicular to the plane. By using the requirement of vanishing time-averaged Larmor precession of spin, we calculate the time-averaged non-Larmor SHC for k -cubic Rashba system by using the conventional definition of the spin current. Our result is 2.1( q /8 π ) which is very close to the experimental value 2.2( q /8 π ) by Wunderlich et al [2005 Phys. Rev. Lett. 94 , 047204], where − q is the electric charge.

We describe quantum limits to field sensing that relate noise, geometry and measurement duration to fundamental constants, with no reference to particle number. We cast the Tesche and Clarke (TC) bound on dc-SQUID sensitivity as such a limit, and find analogous limits for volumetric spin-precession magnetometers. We describe how randomly-arrayed spins, coupled to an external magnetic field of interest and to each other by the magnetic dipole–dipole interaction, execute a spin dynamics that depolarizes the spin ensemble even in the absence of coupling to an external reservoir. We show the resulting spin dynamics are scale invariant, with a depolarization rate proportional to spin number density and thus a number-independent quantum limit on the energy resolution per bandwidth E _R . Numerically, we find E _R ⩾ αℏ , α ∼ 1, in agreement with the TC limit, for paradigmatic spin-based measurements of static and oscillating magnetic fields.

Ultracold neutrons (UCN) have very low kinetic energies 0-300 neV, thereby can be stored in specific material or magnetic confinements for many hundreds of seconds. This makes them a very useful tool in probing fundamental symmetries of nature (for instance charge-parity violation by neutron electric dipole moment experiments) and contributing important parameters for the Big Bang nucleosynthesis (neutron lifetime measurements). Improved precision experiments are in construction at new and planned UCN sources around the world. MC simulations play an important role in the optimization of such systems with a large number of parameters, but also in the estimation of systematic effects, in benchmarking of analysis codes, or as part of the analysis. The MCUCN code written at PSI has been extensively used for the optimization of the UCN source optics and in the optimization and analysis of (test) experiments within the nEDM project based at PSI. In this paper we present the main features of MCUCN and interesting benchmark and application examples. [ABSTRACT FROM AUTHOR]