Anomalous magnon Nernst effect of topological magnonic materials

The magnon transport driven by thermal gradient in a perpendicularly magnetized honeycomb lattice is studied. The system with the nearest-neighbor pseudodipolar interaction and the next-nearest-neighbor Dzyaloshinskii-Moriya interaction (DMI) has various topologically nontrivial phases. When an in-plane thermal gradient is applied, a transverse in-plane magnon current is generated. This phenomenon is termed as the anomalous magnon Nernst effect that closely resembles the anomalous Nernst effect for an electronic system. The anomalous magnon Nernst coefficient and its sign are determined by the magnon Berry curvatures distribution in the momentum space and magnon populations in the magnon bands. We predict a temperature-induced sign reversal in anomalous magnon Nernst effect under certain conditions

A thermodynamic theory for thermal-gradient-driven domain wall motion

Spin waves (or magnons) interact with magnetic domain walls (DWs) in a complicated way that a DW can propagate either along or against magnon flow. However, thermally activated magnons always drive a DW to the hotter region of a nanowire of magnetic insulators under a temperature gradient. We theoretically illustrate why it is surely so by showing that DW entropy is always larger than that of a domain as long as material parameters do not depend on spin textures. Equivalently, the total free energy of the wire can be lowered when the DW moves to the hotter region. The larger DW entropy is related to the increase of magnon density of states at low energy originated from the gapless magnon bound states

Gauge field in ultra-cold bipartite atoms

The effects of entanglement and spin-spin collision on the gauge field in ultracold atoms are presented in this paper. Two gauge fields are calculated and discussed. One of the fields comes from space dependent spin-spin collisions in ultra-cold atoms, while another results from the usual Born-Oppenheimer method, which separates the center-of-mass motion from the relative motion in the two-body problem. Adiabatic conditions that lead to the key results of this paper are also presented and discussed. Entanglement shared between the two atoms is shown to affect the atomic motion. In the presence of entanglement, the additional scalar potential disappears, this is different from the case of atoms in separable states.Comment: 4 pages, 1 figur

Thermal spin current and spin accumulation at ferromagnetic insulator/nonmagnetic metal interface

Spin current injection and spin accumulation near a ferromagnetic insulator (FI)/nonmagnetic metal (NM) bilayer film under a thermal gradient is investigated theoretically. Using the Fermi golden rule and the Boltzmann equations, we find that FI and NM can exchange spins via interfacial electron-magnon scattering because of the imbalance between magnon emission and absorption caused by either non-equilibrium distribution of magnons or non-equilibrium between magnons and electrons. A temperature gradient in FI and/or a temperature difference across the FI/NM interface generates a spin current which carries angular momenta parallel to the magnetization of FI from the hotter side to the colder one. Interestingly, the spin current induced by a temperature gradient in NM is negligibly small due to the nonmagnetic nature of the non-equilibrium electron distributions. The results agree well with all existing experiments.Comment: 8 pages, 2 figure

Synchronous phase clustering in a network of neurons with spatially decaying excitatory coupling

Synchronization is studied in a spatially-distributed network of weekly-coupled, excitatory neurons of Hodgkin-Huxley type. All neurons are coupled to each other synaptically with a fixed time delay and a coupling strength inversely proportional to the distance between two neurons. We found that a robust, noise-resistant phase clustering state occurred regardless of the initial phase distribution. This has not been shown in previous studies where similar clustering states were found only when the coupling was inhibitory. The spatial distribution of neurons in each synchronous cluster is determined by the spatial distribution of the coupling strength. Phase-interaction properties of the model neurons in the network are used to explain why can such a clustering state be robust

Spectral Efficiency of the Cellular Two-Way Relaying with Large Antenna Arrays

This paper considers a multiuser cellular two-way relay network (cTWRN) where multiple users exchange information with a base station (BS) via a relay station (RS). Each user is equipped with a single antenna, while both the BS and the RS are equipped with a very large antenna array. We investigate the performance of the cTWRN with amplify-and-forward (AF) based physical-layer network coding, and derive closed-form expression for the asymptotic spectral efficiency when both the number of antennas at the BS and the RS grow large. It is shown that the noise propagation of the non-regenerative relaying protocol can be greatly suppressed, and the AF relaying scheme can approach the cut-set bound under certain conditions. We also investigate the performance of the AF relaying scheme under two power-scaling cases, and show that the transmit power of the BS and each user can be made inversely proportional to the number of relay antennas while maintaining a given quality-of-service. Numerical results are presented to verify the analytical results.Comment: submitted to ICC 201

Power Minimization in Multi-pair Two-Way Relaying

This doc provides some proofs in our submitted journal paper.Comment: This paper has been withdrawn by the authors as this article provides some proofs for the results in the paper arXiv:1307.005

On the anisotropic hyperdissipative Navier-Stokes equations

We consider the global Cauchy problem for the generalized incompressible Navier- Stokes system in 3D whole space $$u_t+u\cdot\nabla u+\nabla p=\mathcal{A}_h u,$$ \begin{equation}\label{main0} \nabla\cdot u=0, \end{equation} $$u(x,0)=u_0(x),$$ where $u=(u_1, u_2, u_3)\in\mathbf{R}^3$ and $p$ are the fluid velocity field and pressure. The initial data $u_0(x)$ is assumed to be smooth, rapidly decreasing and divergence free. Here $\mathcal{A}_h$ is the anisotropic hyperdissipative operator. When $\mathcal{A}_hu=-(-\Delta)^{5/4}$, it is called the critical case and the global smooth solution exists. We consider the anisotropic operator with $\mathcal{A}_hu= \left(\begin{array}{c} \partial_{x_1x_1} u_1+\partial_{x_2x_2} u_1- M_3^{2\alpha} u_1 \\partial_{x_1x_1} u_2+\partial_{x_2x_2} u_2-M_3^{2\alpha} u_2 \ - M_1^{2\gamma} u_3-M_2^{2\gamma} u_3-M_3^{2\alpha} u_3 \end{array} \right).$ and establish global regularity

Quantum key distribution with asymmetric channel noise

We show that one may take advantages in both robusty and key rate of asymmetric channel noise.Comment: 2 figure

A protocol for secure and deterministic quantum key expansion

In all existing protocols of private communication with encryption and decryption, the pre-shared key can be used for only one time. We give a deterministic quantum key expansion protocol where the pre-shared key can be recycled. Our protocol is exponentially secure. Our protocol costs less qubits and almost zero classical communications with authentication steps being included. Since our protocol can distribute the deterministic bits, it can also be used for direct communication.Comment: 5 page