Interfacial Magnetoelectric Coupling in Tri-component Superlattices

Using first-principles density functional theory, we investigate the interfacial magnetoelectric coupling in a tri-component superlattice composed of a ferromagnetic metal (FM), ferroelectric (FE), and normal metal (NM). Using Fe/FE/Pt as a model system, we show that a net and cumulative interfacial magnetization is induced in the FM metal near the FM/FE interface. A carefully analysis of the magnetic moments in Fe reveals that the interfacial magnetization is a consequence of a complex interplay of interfacial charge transfer, chemical bonding, and spin dependent electrostatic screening. The last effect is linear in the FE polarization, is switchable upon its reversal, and yields a substantial interfacial magnetoelectric coupling.Comment: 5 pages, 6 figure

Magnetic control of the valley degree of freedom of massive Dirac fermions with application to transition metal dichalcogenides

We study the valley-dependent magnetic and transport properties of massive Dirac fermions in multivalley systems such as the transition metal dichalcogenides. The asymmetry of the zeroth Landau level between valleys and the enhanced magnetic susceptibility can be attributed to the different orbital magnetic moment tied with each valley. This allows the valley polarization to be controlled by tuning the external magnetic field and the doping level. As a result of this magnetic field induced valley polarization, there exists an extra contribution to the ordinary Hall effect. All these effects can be captured by a low energy effective theory with a valley-orbit coupling term.Comment: 9 pages, 6 figure

Magnetoelectric Coupling and Electric Control of Magnetization in Ferromagnet-Ferroelectric-Metal Superlattices

Ferromagnet-ferroelectric-metal superlattices are proposed to realize the large room-temperature magnetoelectric effect. Spin dependent electron screening is the fundamental mechanism at the microscopic level. We also predict an electric control of magnetization in this structure. The naturally broken inversion symmetry in our tri-component structure introduces a magnetoelectric coupling energy of $P M^2$. Such a magnetoelectric coupling effect is general in ferromagnet-ferroelectric heterostructures, independent of particular chemical or physical bonding, and will play an important role in the field of multiferroics.Comment: 5 pages including 3 figures and 1 tabl

Muon Beam for Neutrino CP Violation: connecting energy and neutrino frontiers

We propose here a proposal to connect neutrino and energy frontiers, by exploiting collimated muon beams for neutrino oscillations, which generate symmetric neutrino and antineutrino sources: $\mu^+\rightarrow e^+\,\bar{\nu}_{\mu}\, \nu_{e}$ and $\mu^-\rightarrow e^-\, \nu_{\mu} \,\bar{\nu}_{e}$. Interfacing with long baseline neutrino detectors such as DUNE and T2K, this experiment can be applicable to measure tau neutrino properties, and also to probe neutrino CP phase, by measuring muon electron (anti-)neutrino mixing or tau (anti-)neutrino appearance, and differences between neutrino and antineutrino rates. There are several significant benefits leading to large neutrino flux and high sensitivity on CP phase, including 1) collimated and manipulable muon beams, which lead to a larger acceptance of neutrino sources in the far detector side; 2) symmetric $\mu^+$ and $\mu^-$ beams, and thus symmetric neutrino and antineutrino sources, which make this proposal ideally useful for measuring neutrino CP violation. More importantly, $\bar{\nu}_{e,\mu}\rightarrow\bar{\nu}_\tau$ and $\nu_{e,\mu}\rightarrow \nu_\tau$, and, $\bar{\nu}_{e}\rightarrow\bar{\nu}_\mu$ and $\nu_{e}\rightarrow \nu_\mu$ oscillation signals can be collected simultaneously, with no needs for separate specific runs for neutrinos or antineutrinos. Based on a simulation of neutrino oscillation experiment, we estimate $10^4$ tau (anti-) neutrinos can be collected within 5 years which makes this proposal suitable for a brighter tau neutrino factory. Moreover, more than 7 standard deviations of sensitivity can be reached for \dcp = |\pi/2|, within only five ears of data taking, by combining tau and muon (anti-) neutrino appearances. With the development of a more intensive muon beam targeting future muon collider, the neutrino potential of the current proposal will surely be further improved.Comment: Additional fixes included. In this new version, we have now strengthened our results by carrying out a solid physics simulation with the help of GLoBES, a sophisticated software package for the simulation of long baseline neutrino oscillation experiments. The results are compared with previous qualitative estimations, and are found to be in reasonable agreemen

Searching for Majorana Neutrinos at a Same-Sign Muon Collider

Majorana properties of neutrinos have long been a focus in the pursuit of possible new physics beyond the standard model, which has motivated lots of dedicated theoretical and experimental studies. A future same-sign muon collider is an ideal platform to search for Majorana neutrinos through the Lepton Number Violation process. Specifically, this t-channel kind of process is less kinematically suppressed and has a good advantage in probing Majorana neutrinos at high mass regions up to 10 TeV. In this paper, we perform a detailed fast Monte Carlo simulation study through examining three different final states: 1) pure-leptonic state with electrons or muons, 2) semi-leptonic state, and 3) pure-hadronic state in the resolved or merged categories. Furthermore, we perform a full simulation study on the pure-leptonic final state to validate our fast simulation results.Comment: 15 pages, 8 figure

Crystallization-Driven Self-Assembly of Coil-Comb-Shaped Polypeptoid Block Copolymers: Solution Morphology and Self-Assembly Pathways

Copyright © 2019 American Chemical Society. Crystallization-driven self-assembly (CDSA) of amphiphilic polymers into well-defined nanoscopic structures with different morphologies and functionalities has attracted increasing attention. Here, we investigate the CDSA of coil-comb-shaped diblock copolypeptoids, namely, poly(N-methyl glycine)-b-poly(N-decyl glycine) (PNMG-b-PNDG), in dilute methanol solution using X-ray/neutron solution scattering in conjunction with cryogenic transmission electron microscopy techniques. A series of PNMG-b-PNDGs were synthesized by sequential benzyl amine-initiated ring-opening polymerizations of the corresponding N-substituted N-carboxyanhydrides, in which the degree of polymerization and the length of the blocks were varied. The PNMG-b-PNDG polymers with a lower volume fraction of the crystalline PNDG blocks (fPNDG = 0.44) were found to slowly self-assemble into one-dimensional long wormlike nanofibrils in methanol. The nanofibrils bear an anisotropic crystalline core where the comb-shaped PNDG blocks were stacked in a face-to-face fashion along the long axis of the nanofibrils. Upon increasing fPNDG to 0.61 and 0.68, the final morphology of PNMG-b-PNDG micelles changed from wormlike nanofibrils to rigid short nanorods and then two-dimensional nanosheets. The nanofibrils were formed by a self-seeding growth pathway that involves the initial formation of a few seeded crystals followed by the addition of soluble unimers to the preferred crystal facets resulting in the gradual elongation of the micelles. By contrast, the nanorods were formed by a two-stage process involving the formation of spherical micelles with an amorphous core in the first stage and rapid confined crystallization of the micellar core and their fusion into rodlike nanostructures at the second stage. Understanding the relationship between chemical composition, micellar morphology, and CDSA pathway of coil-comb-shaped diblock copolypeptoids is an important step toward the rational design of anisotropic polymeric nanostructures with tailorable morphology