arXiv subjects

D. Fang

Publications and source records attributed to D. Fang.

11 recordsLinked to original sources

arXiv2024

Ab initio study of Z(N) = 6 magicity

The existence of magic numbers of protons and neutrons in nuclei is essential for understanding nuclear structure and fundamental nuclear forces. Over decades, researchers have conducted theoretical and experimental studies on the new magic number Z(N) = 6, focusing on observables such as radii, binding energy, electromagnetic transition, and nucleon separation energies. We perform the ab initio no-core shell model calculations for the occupation numbers of the lowest single particle states in the ground states of Z(N) = 6 and Z(N) = 8 isotopes (isotones). Our calculations do not support Z(N) = 6 as a magic number over a span of atomic numbers. However, 14C and 14O exhibit the characteristics of double-magic nuclei.

nucl-th↗

arXiv2024

Quadrupole dynamics of carbon isotopes and 10Be

Electric quadrupole (E2) moments and transitions provide measures of nuclear deformation and related collective structure. However, matrix elements of the E2 operator are sensitive to the nuclear wave function at large distances and are poorly convergent within the ab initio no-core shell model approach. We demonstrate for the first time that the ratio of neutron to proton quadrupole transition matrix elements, Mn/Mp, is well-converged in the ab initio no-core shell model and provides a new and robust tool for comparing with experimental results. We find that our parameter-free results for Mn/Mp for the carbon isotopes and 10Be compare well with experiment, where available, and offer new insight into the quadrupole dynamics of nuclear response.

nucl-th↗

arXiv2023

NvDEx-100 Conceptual Design Report

Observing nuclear neutrinoless double beta (0vbb) decay would be a revolutionary result in particle physics. Observing such a decay would prove that the neutrinos are their own antiparticles, help to study the absolute mass of neutrinos, explore the origin of their mass, and may explain the matter-antimatter asymmetry in our universe by lepton number violation. We propose developing a time projection chamber (TPC) using high-pressure 82SeF6 gas and top-metal silicon sensors for read-out in the China Jinping Underground Laboratory (CJPL) to search for neutrinoless double beta decay of 82Se, called the NvDEx experiment. Besides being located at CJPL with the world's thickest rock shielding, NvDEx combines the advantages of the high Qbb (2.996 MeV) of 82Se and the TPC's ability to distinguish signal and background events using their different topological characteristics. This makes NvDEx unique, with great potential for low-background and high-sensitivity 0vbb searches. NvDEx-100, a NvDEx experiment phase with 100 kg of SeF6 gas, is being built, with plans to complete installation at CJPL by 2025. This report introduces 0vbb physics, the NvDEx concept and its advantages, and the schematic design of NvDEx-100, its subsystems, and background and sensitivity estimation.

physics.ins-det↗

arXiv2022

Status and initial physics performance studies of the MPD experiment at NICA

The Nuclotron-base Ion Collider fAcility (NICA) is under construction at the Joint Institute for Nuclear Research (JINR), with commissioning of the facility expected in late 2022. The Multi-Purpose Detector (MPD) has been designed to operate at NICA and its components are currently in production. The detector is expected to be ready for data taking with the first beams from NICA. This document provides an overview of the landscape of the investigation of the QCD phase diagram in the region of maximum baryonic density, where NICA and MPD will be able to provide significant and unique input. It also provides a detailed description of the MPD set-up, including its various subsystems as well as its support and computing infrastructures. Selected performance studies for particular physics measurements at MPD are presented and discussed in the context of existing data and theoretical expectations.

physics.ins-det↗

arXiv2018

Searching for states analogous to the 12C Hoyle state in heavier nuclei using the thick target inverse kinematics technique

Identification of alpha cluster states analogous to the 12C Hoyle state in heavier alpha- conjugate nuclei can provide tests of the existence of alpha condensates in nuclei. Such states are predicted for 16O, 20Ne, 24Mg, 28Si etc. at excitation energies slightly above the multi-alpha particle decay threshold, but have not yet been experimentally identified. The Thick Target Inverse Kinematics (TTIK) technique can be used to study the breakup of excited self-conjugate nuclei into many alpha particles. The reaction 20Ne+{\alpha} was studied using a 20Ne beam at 12 MeV/nucleon from the K150 cyclotron at Texas A&M University. The TTIK method was used to study both single {\alpha}-particle emission and multiple {\alpha}-particle decays. Events with alpha multiplicity up to four were analyzed. The analysis of the three {\alpha} - particle emission data allowed the identification of the Hoyle state and other 12C excited states decaying into three alpha particles. The results are shown and compared with other data available in the literature. Although the statistics for events with alpha multiplicity four is low, the data show a structure at about 15.2 MeV that could indicate the existence in 16O of a state analogous to the 12C Hoyle state. This structure is confirmed by the re-analysis of alpha multiplicity four events from a previous experiment performed at 9.7 MeV/nucleon with a similar setup but lower granularity. Moreover, the reconstructed excitation energy of 24Mg for these events peaks at around 34 MeV, very close to the predicted excitation energy for an excited state analogous to the 12C Hoyle state in 24Mg.

nucl-ex↗

arXiv2013

Observation of a Berry phase anti-damping spin-orbit torque

Recent observations of current-induced magnetization switching at ferromagnet/normal-conductor interfaces have important consequences for future magnetic memory technology. In one interpretation, the switching originates from carriers with spin-dependent scattering giving rise to a relativistic anti-damping spin-orbit torque (SOT) in structures with broken space-inversion symmetry. The alternative interpretation combines the relativistic spin Hall effect (SHE), making the normal-conductor an injector of a spin-current, with the non-relativistic spin-transfer torque (STT) in the ferromagnet. Remarkably, the SHE in these experiments originates from the Berry phase effect in the band structure of a clean crystal and the anti-damping STT is also based on a disorder-independent transfer of spin from carriers to magnetization. Here we report the observation of an anti-damping SOT stemming from an analogous Berry phase effect to the SHE. The SOT alone can therefore induce magnetization dynamics based on a scattering-independent principle. The ferromagnetic semiconductor (Ga,Mn)As we use has a broken space-inversion symmetry in the crystal. This allows us to consider a bare ferromagnetic element which eliminates by design any SHE related contribution to the spin torque. We provide an intuitive picture of the Berry phase origin of the anti-damping SOT and a microscopic modeling of measured data.

cond-mat.mes-hall↗

arXiv2012

Electrical excitation and detection of magnetic dynamics with impedance matching

Motivated by the prospects of increased measurement bandwidth, improved signal to noise ratio and access to the full complex magnetic susceptibility we develop a technique to extract microwave voltages from our high resistance (10 kΩ) (Ga,Mn)As microbars. We drive magnetization precession with microwave frequency current, using a mechanism that relies on the spin orbit interaction. A capacitively coupled lambda/2 microstrip resonator is employed as an impedance matching network, enabling us to measure the microwave voltage generated during magnetisation precession.

cond-mat.mes-hall↗

arXiv2012

Enhanced Inverse Spin-Hall Effect in Ultrathin Ferromagnetic/Normal Metal Bilayers

We measure electrically detected ferromagnetic resonance in microdevices patterned from ultra-thin Co/Pt bilayers. Spin pumping and rectification voltages are observed and distinguished via their angular dependence. The spin-pumping voltage shows an unexpected increase as the cobalt thickness is reduced below 2 nm. This enhancement allows more efficient conversion of spin to charge current and motivates a theory modelling the dependence of impurity scattering on surface roughness.

cond-mat.mes-hall↗

arXiv2012

Hindered proton collectivity in 28S: Possible magic number at Z=16

The reduced transition probability B(E2;0 ->2+) for 28S was obtained experimentally using Coulomb excitation at 53 MeV/nucleon. The resultant B(E2) value 181(31) e2fm4 is smaller than the expectation based on empirical B(E2) systematics. The double ratio |M_n/M_p|/(N/Z) of the 0+ ->2+ transition in 28S was determined to be 1.9(2) by evaluating the M_n value from the known B(E2) value of the mirror nucleus 28Mg, showing the hindrance of proton collectivity relative to that of neutrons. These results indicate the emergence of the magic number Z=16 in the |T_z|=2 nucleus 28S.

nucl-ex↗

arXiv2011

The $^{150}$Nd($^3$He,$t$) and $^{150}$Sm($t$,$^3$He) reactions with applications to $ββ$ decay of $^{150}$Nd

The $^{150}$Nd($^3$He,$t$) reaction at 140 MeV/u and $^{150}$Sm($t$,$^3$He) reaction at 115 MeV/u were measured, populating excited states in $^{150}$Pm. The transitions studied populate intermediate states of importance for the (neutrinoless) $ββ$ decay of $^{150}$Nd to $^{150}$Sm. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of Quasiparticle Random-Phase Approximation (QRPA), which is one of the main methods employed for estimating the half-life of the neutrinoless $ββ$ decay ($0νββ$) of $^{150}$Nd. The present results thus provide useful information on the neutrino responses for evaluating the $0νββ$ and $2νββ$ matrix elements. The $2νββ$ matrix element calculated from the Gamow-Teller transitions through the lowest $1^{+}$ state in the intermediate nucleus is maximally about half of that deduced from the half-life measured in $2νββ$ direct counting experiments and at least several transitions through $1^{+}$ intermediate states in $^{150}$Pm are required to explain the $2νββ$ half-life. Because Gamow-Teller transitions in the $^{150}$Sm($t$,$^3$He) experiment are strongly Pauli-blocked, the extraction of Gamow-Teller strengths was complicated by the excitation of the $2\hbarω$, $ΔL=0$, $ΔS=1$ isovector spin-flip giant monopole resonance (IVSGMR). However, the near absence of Gamow-Teller transition strength made it possible to cleanly identify this resonance, and the strength observed is consistent with the full exhaustion of the non-energy-weighted sum rule for the IVSGMR.

nucl-ex↗

arXiv2010

Spin-orbit driven ferromagnetic resonance: A nanoscale magnetic characterisation technique

We demonstrate a scalable new ferromagnetic resonance (FMR) technique based on the spin-orbit interaction. An alternating current drives FMR in uniform ferromagnetic structures patterned from the dilute magnetic semiconductors (Ga,Mn)As and (Ga,Mn)(As,P). This allows the direct measurement of magnetic anisotropy coefficients and damping parameters for individual nano-bars. By analysing the ferromagnetic resonance lineshape, we perform vector magnetometry on the current-induced driving field, observing contributions with symmetries of both the Dresselhaus and Rashba spin-orbit interactions.

cond-mat.mes-hall↗