High Transverse Field Research Articles

Statistical aspects of a quantum Hopfield model

In this paper, we study the eigenstate properties of a quantum Hopfield model by the exact diagonalization method. The local permutational symmetry in this model organizes the spins into clusters, which can each be considered a large quantum spin interacting with others. It is shown that such a quantum Hopfield model, even though without dissipation, is interesting in its own right as an example of quantum frustrated magnetism and quantum spin glass. It exhibits three distinct phases: a low-energy spin-glass phase at a low transverse field, a thermal paramagnetic phase at a high transverse field, and a nonthermal high-energy paramagnetic phase. The dynamics of the revival probability starting from a memory pattern in such a closed quantum many-body model has also been studied.

Role of quantum fluctuation ininducing ergodicity inthe spin glass phase and its effect inquantum annealing.

We review the numerical studies on the critical behaviour of the quantum Sherrington-Kirkpatrick (SK) spin glass model, which indicate that aquantum critical behaviour is observed up to a low but non-zero value of temperature. We revisit the numerical investigations on the spin glass order parameter distributions, which identify a low temperature along with high transverse field spin glass phase where the order parameter distribution becomes a delta function in the thermodynamic limit indicating the restoration of replica symmetry and ergodic nature of the system. In the remaining spin glass phase associated with high temperature and low transverse field, the observed distribution is broad akin to the Parisi order parameter distribution. This essentially indicates the non-ergodic behaviour of the system. We further discuss the annealing dynamics studies on the quantum SK model. Such investigations reveal the system size independence of annealing time when the annealing paths go through the ergodic spin glass region. Interestingly, when such dynamics are performed in the non-ergodic spin glass phase the annealing time becomes an increasing function of the system size. Spin autocorrelation shows faster relaxation in the ergodic spin glass region compared with that found in the non-ergodic spin glass region. This article is part of the theme issue 'Quantum annealing and computation: challenges and perspectives'.

Cable Design and Development for the High-Temperature Superconductor Cable Test Facility Magnet

A large bore “High-Temperature Superconductor Cable Test Facility Magnet” for testing advanced cables and inserts in high transverse field is in its design phase. This magnet will be the core component of a facility for developing conductors and accelerator magnets operating above 15 T, an enabling technology for next-generation fusion devices using magnetic confinement of plasma and for future energy frontier colliders. The procurement of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn conductor, fabrication of cables, winding of coils, and assembly of the dipole magnet will be done at Lawrence Berkeley National Laboratory (LBNL) and the test pit and cryostat will be constructed at Fermi National Accelerator Laboratory. This article will present the conductor element of the LBNL project, specifically cable design parameters (based on the Bruker OST RRP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\bigcirc \!\!\!\! {\hbox{R}}}$</tex-math></inline-formula> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconducting wire) and the development phase cable fabrication experience. Challenges of the cable fabrication will be discussed. The wire and cable planned for this magnet are similar to those under study for the Future Circular Collider and other large facility magnets. The successful fabrication of the development cable has positive implications for these other projects.

Magnetic and Mechanical Analysis of a Large Aperture 15 T Cable Test Facility Dipole Magnet

The US Department of Energy (DOE) Office of Science (SC), is funding a large bore “Cable Test Facility Magnet” for testing advanced cables and inserts in high transverse field. This is a joint effort between the Office of High Energy Physics (HEP) and the Office of Fusion Energy Sciences (FES). The background field magnet for this facility is being developed at Lawrence Berkeley National Laboratory (LBNL) while the cryostat and test facility will be located and operated by Fermi National Accelerator Laboratory (FNAL). The Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3 </sub> Sn dipole magnet, which will provide the transverse background field, is designed to generate a field of 15 T in a 100 × 150 mm bore at 1.9 K. The conceptual design of a block-type dipole with flared ends and a structure based on key-and-bladder technology will be introduced. The results of the magnetic and mechanical analysis will be presented.

Glide symmetry breaking and Ising criticality in the quasi-1D magnet CoNb2O6

We construct a microscopic spin-exchange Hamiltonian for the quasi-one-dimensional (1D) Ising magnet [Formula: see text] that captures detailed and hitherto-unexplained aspects of its dynamic spin structure factor. We perform a symmetry analysis that recalls that an individual Ising chain in this material is buckled, with two sites in each unit cell related by a glide symmetry. Combining this with numerical simulations benchmarked against neutron scattering experiments, we argue that the single-chain Hamiltonian contains a staggered spin-exchange term. We further argue that the transverse-field-tuned quantum critical point in [Formula: see text] corresponds to breaking this glide symmetry, rather than an on-site Ising symmetry as previously believed. This gives a unified microscopic explanation of the dispersion of confined states in the ordered phase and quasiparticle breakdown in the polarized phase at high transverse field.

Investigation of air-assisted sprays submitted to high frequency transverse acoustic fields: Droplet clustering

An experimental investigation of the effects of a high amplitude transverse acoustic field on coaxial jets is presented in this paper. Water and air are used as working fluids at ambient pressure. The coaxial injectors are placed on the top of a semi-open resonant cavity where the acoustic pressure fluctuations of the standing wave can reach a maximum peak-to-peak amplitude of 12 kPa at the forcing frequency of 1 kHz. Several test conditions are considered in order to quantify the influence of injection conditions, acoustic field amplitude, and injector position with respect to the standing wave acoustic field. A high speed back-light visualization technique is used to characterize the jet response. Image processing is used to obtain valuable information about the jet behavior. It is shown that the acoustic field drastically affects the atomization process for all atomization regimes. The position of the injector in the acoustic field determines the jet response, and a droplet-clustering phenomenon is highlighted in multi-point injection conditions and quantified by determining discrete droplet location distributions. A theoretical model based on nonlinear acoustics related to the spatial distribution of the radiation pressure exerted on an object explains the behavior observed.

Barkhausen noise in the random field Ising magnetNd2Fe14B

With sintered needles aligned and a magnetic field applied transverse to its easy axis, the rare-earth ferromagnet Nd_2Fe_(14)B becomes a room-temperature realization of the random field Ising model. The transverse field tunes the pinning potential of the magnetic domains in a continuous fashion. We study the magnetic domain reversal and avalanche dynamics between liquid helium and room temperatures at a series of transverse fields using a Barkhausen noise technique. The avalanche size and energy distributions follow power-law behavior with a cutoff dependent on the pinning strength dialed in by the transverse field, consistent with theoretical predictions for Barkhausen avalanches in disordered materials. A scaling analysis reveals two regimes of behavior: one at low temperature and high transverse field, where the dynamics are governed by the randomness, and the second at high temperature and low transverse field, where thermal fluctuations dominate the dynamics.

The effect of the demagnetizing field in cylindrical samples in high transverse field μ+SR experiments

We investigate the spatial variation of the demagnetizing field for uniformly magnetized, cylindrical samples using a recently developed Fourier space approach. We show that the demagnetizing response of the sample leads to a position dependence of the magnetic field, which varies most strongly near the radial boundary of the cylinder. Furthermore, we demonstrate that the demagnetizing field leads to a subsequent broadening of the field distribution, as experienced by the muons implanted in the sample, with a characteristic shape including a low field tail and a sharp high-field cutoff. We present a detailed study of this field broadening as a function of the aspect ratio of the cylinder and find that it is significant and largest for aspect ratios typical for cylindrical samples grown in mirror furnaces. We identify two strategies to minimize this broadening: adding a degrader so that muons implant closer to the surface of the sample and using a circular mask to stop muons from implanting near the radial edge. This could help identify whether an experimentally observed broadening is caused by the demagnetization response or the intrinsic properties of the sample.

High-field study of muonium states in HfO2 and ZrO2

We present high-transverse field measurements, as a function of temperature, in monoclinic ZrO2 and HfO2. In monoclinic zirconia and hafnia, a diamagnetic component had been previously reported in low-transverse-fields, but a significant fraction of the total muon polarization was missing in these experiments. We now characterize this missing fraction using the high-field capabilities at TRIUMF: a high relaxation component (above 100 μs−1 in monoclinic ZrO2, about 10 μs−1 in HfO2) is observed, which we relate to the formation of compact muonium in these materials. A model for the formation of muonium in these materials is presented.

Quasiparticle breakdown in the quasi-one-dimensional Ising ferromagnetCoNb2O6

We present experimental and theoretical evidence that an interesting quantum many-body effect -- quasi-particle breakdown -- occurs in the quasi-one-dimensional spin-1/2 Ising-like ferromagnet CoNb$_2$O$_6$ in its paramagnetic phase at high transverse field as a result of explicit breaking of spin inversion symmetry. We propose a quantum spin Hamiltonian capturing the essential one-dimensional physics of CoNb$_2$O$_6$ and determine the exchange parameters of this model by fitting the calculated single particle dispersion to the one observed experimentally in applied transverse magnetic fields. We present high-resolution inelastic neutron scattering measurements of the single particle dispersion which observe "anomalous broadening" effects over a narrow energy range at intermediate energies. We propose that this effect originates from the decay of the one particle mode into two-particle states. This decay arises from (i) a finite overlap between the one-particle dispersion and the two-particle continuum in a narrow energy-momentum range and (ii) a small misalignment of the applied field away from the direction perpendicular to the Ising axis in the experiments, which allows for non-zero matrix elements for decay by breaking the $\mathbb{Z}_2$ spin inversion symmetry of the Hamiltonian.

Simulation of DC Characteristics of Nano-Scale Hydrogen-Terminated Diamond MISFETs

ABSTRACTAn improved 2D device model is generated to simulate the DC properties of hydrogen- terminated diamond MISFETs by taking into account the effect of electric field on hole mobility. At high lateral field, the mobility degrades due to velocity saturation and at high transverse field, the mobility decreases because of strong surface phonon scattering. As either field increases to a certain level (∼ 1MV/cm), the mobility becomes independent of doping concentration and the maximum transverse field appears at the boundary between surface acceptor region and bulk. The threshold voltage is found to be a strong function of gate length and can change from negative to positive, which will change the operation mode of the device. In addition, the simulation also shows that the transconductance reaches a maximum value at 80nm gate length but decreases after further shrinkage, which might be also related to the velocity saturation effect induced by large lateral field.

Quantum deflagration and supersonic fronts of tunneling in molecular magnets

The theory of magnetic deflagration taking into account dipolar-controlled spin tunneling has been applied to the realistic model of molecular magnet Mn${}_{12}$Ac. At small transverse field, the front speed $v$ has tunneling maxima on the bias field ${B}_{z}$, reflecting those of the molecular spin's relaxation rate calculated from the density-matrix equation. At high transverse field, spin tunneling directly out of the metastable ground state leads to front speeds that can exceed the speed of sound. Both for the weak and strong transverse fields, the spatial profile of the deflagration front near tunneling resonances shows a front of tunneling that triggers a burning front behind it.

μ+ diffusion in cubic f-electron compounds observed by high transverse field μ+ SR

Positive muon (μ+) diffusion was observed in cubic f-electron compounds PrPb3 and SmAg2In by means of the μ+ spin rotation (μ+SR) method in high transverse field applied along the [001] direction. The applied field splits one crystallographic site into two magnetically inequivalent sites. The μ+ diffusion between these magnetically different sites drastically influences the μ+SR frequencies, so that two lines are gradually merged into one line at increasing temperature due to the motional narrowing effect. The μ+ hopping rate Ω derived from the μ+SR line shape follows the Arrhenius law, namely, Ω = Ω0 exp(−U/kBT) in both cases. The preexponential factor Ω0 suggests that the dominant mechanism of μ+ diffusion is classical over-the-barrier hopping in PrPb3 for 140<T<200 K and phonon-assisted quantum tunneling in SmAg2In for 40<T<70 K.

High transverse field with -RF pulse spin control technique

Abstract We report on the time-differential μ SR measurement at 200 MHz (under a transverse field of 1.475 T) using a pulsed muon beam at KEK ( δ ≃ 50 ns ). The initial muon spin direction is flipped by 90 ∘ using a radio-frequency (RF) pulse immediately after muon implantation, which allows observation of μ SR time spectra without limitation of beam pulse width δ . A prospect for the routine use of this π / 2 -RF pulse technique at the J-PARC MUSE is discussed.

Anomalous normal-state magnetism coupled to superconductivity in and

Abstract High transverse-field (TF) μ SR measurements on hole-doped cuprates showing a spatially inhomogeneous response to magnetic field far above the bulk superconducting transition temperature ( T c ) are discussed. Particular attention is paid to the intermediate hole-doping regime, where an inhomogeneous magnetic response has recently been observed in the normal state of YBa 2 Cu 3 O y (YBCO) and La 2 - x Sr x CuO 4 (LSCO) that tracks the hole-doping dependences of both T c and the density of the superconducting carriers n s below T c .

Magnetic domain wall propagation in nanowires under transverse magnetic fields

We have investigated the propagation of transverse domain walls in magnetic nanowires under axial and transverse magnetic fields using three-dimensional micromagnetic modeling. Transverse magnetic fields change the domain wall width and, below the Walker field, either increase or decrease the domain wall velocity depending when the field and wall magnetization are parallel or antiparallel, respectively. Furthermore, differences in the Walker field also appear for opposite transverse fields, and a surprising result is that under relatively high axial and transverse fields, Walker breakdown can be completely suppressed and the domain wall velocity returns to several hundreds of ms−1.

Instabilities of a tangential discontinuity

A critical analysis of Landau and Lifshitz’s data concerning the instability of a tangential discontinuity in a compressible liquid is given. The simplest case when the liquid flow velocity alone experiences a discontinuity is considered. The influence of a high transverse gravitational field on the stability of a tangential discontinuity is investigated.

Direct Detection of Nonlinear Ferromagnetic Resonance in Thin Films by the Magneto-Optical Kerr Effect

The longitudinal magneto-optical Kerr effect is used to obtain a calibrated measure of the dynamic magnetization response over the ferromagnetic resonance (FMR) profile for in-plane magnetized Permalloy films excited with high power in-plane transverse microwave fields at 1.25 to 3.75 GHz and in-plane precession angles up to about 20 degrees. The data provide a profound demonstration of the Suhl threshold effect for parametric spin wave generation for angles above about 14 degrees, the magnetization precession lock-up just above threshold, and the complicated response over the full FMR profile at very high powers.

Electron Mobility in Silicon Nanowires

The low-field electron mobility in rectangular silicon nanowire (SiNW) transistors was computed using a self-consistent Poisson-Schr\"{o}dinger-Monte Carlo solver. The behavior of the phonon-limited and surface-roughness-limited components of the mobility was investigated by decreasing the wire width from 30 nm to 8 nm, the width range capturing a crossover between two-dimensional (2D) and one-dimensional (1D) electron transport. The phonon-limited mobility, which characterizes transport at low and moderate transverse fields, is found to decrease with decreasing wire width due to an increase in the electron-phonon wavefunction overlap. In contrast, the mobility at very high transverse fields, which is limited by surface roughness scattering, increases with decreasing wire width due to volume inversion. The importance of acoustic phonon confinement is also discussed briefly.

Electron Transport in Si Nanowires

We investigate electron transport in silicon nanowires taking into account acoustic, non-polar optical phonons and surface/interface roughness scattering. We find that at very high transverse fields the reduced density of final states to which the carriers can scatter into gives rise to a reduced influence of interface-roughness scattering, which is promising result from a fabrication point of view.