Isothermal current-driven insulator-to-metal transition in VO2_\text{2} through strong correlation effect

Electric current has been experimentally demonstrated to be able to drive the insulator-to-metal transition (IMT) in VO$_2$. The main mechanisms involved are believed to be the Joule heating effect and the strong electron-correlation effect. These effects are often entangled with each other in experiments, which complicates the understanding of the essential nature of the observations. We formulate a phase-field model to investigate theoretically in mesoscale the pure correlation effect brought by the current on the IMT in VO$_2$, i.e., the isothermal process under the current. We find that a current with a large density ($\sim 10^1$ nA/nm$^2$) induces a few-nanosecond ultrafast switch in VO$_2$, in agreement with the experiment. The temperature-current phase diagram is further calculated, which reveals that the current may induce the M2 phase at low temperatures. The current is also shown capable of driving domain walls to move. Our work may assist related experiments and provide guidance to the engineering of VO$_2$-based electric switching devices.Comment: 7 pages, 4 figures, 1 tabl

Blowing Polar Skyrmion Bubbles in Oxide Superlattices

Particle-like topological structures such as skyrmions and vortices have garnered ever-increasing interests due to the rich physical insights and potential broad applications. Here we discover the reversible switching between polar skyrmion bubbles and ordered vortex arrays in ferroelectric superlattices under an electric field, reminiscent of the Plateau-Raleigh instability in fluid mechanics. Electric field phase diagram is constructed, showing wide stability window for the observed polar skyrmions. This study is a demonstration for the computational design of ferroelectric topological structures and field-induced topological phase transitions.Comment: 16 Pages 4 figure

End-to-end driving simulation via angle branched network

Imitation learning for end-to-end autonomous driving has drawn attention from academic communities. Current methods either only use images as the input which is ambiguous when a car approaches an intersection, or use additional command information to navigate the vehicle but not automated enough. Focusing on making the vehicle drive along the given path, we propose a new navigation command that does not require human's participation and a novel model architecture called angle branched network. Both the new navigation command and the angle branched network are easy to understand and effective. Besides, we find that not only segmentation information but also depth information can boost the performance of the driving model. We conduct experiments in a 3D urban simulator and both qualitative and quantitative evaluation results show the effectiveness of our model.Comment: 10 pages,6 figure

Probing Higgs Width and Top Quark Yukawa Coupling from ttˉHt\bar{t}H and ttˉttˉt\bar{t}t\bar{t} Productions

We demonstrate that four top-quark production is a powerful tool to constrain the top Yukawa coupling. The constraint is robust in the sense that it does not rely on the Higgs boson decay. Taking into account the projection of the $t\bar{t}H$ production by the ATLAS collaobration, we obtain a bound on Higgs boson width, $\Gamma_H\leq 3.1~\Gamma_H^{\rm SM}$, at the 14 TeV LHC with an integrated luminosity of $300~{\rm fb}^{-1}$. Increasing the luminosity to $500~{\rm fb}^{-1}$ yields $\Gamma_H\leq 2.1~\Gamma_H^{\rm SM}$

A Thermal Harmonic Field Description of Phase Transition: The Alternative Approach to the Landau Theory

The study of critical phenomena and phase transitions is an important part of modern condensed matter physics. In this regard, the phenomenological Landau theory has been extraordinarily useful. Hereby we present an alternative theoretical description to the Landau theory for a system under phase transition, based on a priori assumption that the macroscopic system is made of the thermal mixing among multi harmonics each of them can be distinguished by crystal orientation, polar direction, magnetic direction, or even momentum etc. Our theory naturally gives rise to a long range field and is able to account for both the type of lattice and the spatial dimensionality, in addition to that the excess free energy is referenced to the low temperature structure together with the positive excess entropy. The improvements over the Landau theory are demonstrated using ferroelectric-paraelectric system of PbTiO3 on its phase transition and associated thermodynamic behaviors.Comment: 18 pages including 3 figure

Conclusive quantum-state transfer with a single randomly coupled spin chain

We studied the quantum state transfer in randomly coupled spin chains. By using local memories storing the information and dividing the task into transfer portion and decoding portion, conclusive transfer was ingeniously achieved with just one single spin chain. In our scheme, the probability of successful transfer can be made arbitrary close to unity. Especially, our scheme is a good protocol to decode information from memories without adding another spin chain. Compared with Time-reversed protocol, the average decoding time is much less in our scheme.Comment: 13 pages, 3 figure

Strong CP Problem, Neutrino Masses and the 750 GeV Diphoton Resonance

We present an $SU(3)^{}_{c}\times SU(2)^{}_{L}\times SU(2)^{}_{R}\times U(1)_{L}^{}\times U(1)_{R}^{}\rightarrow SU(3)^{}_{c}\times SU(2)^{}_{L}\times SU(2)^{}_{R}\times U(1)^{}_{B-L}$ left-right symmetric model with a discrete parity symmetry to realize a universal seesaw scenario. The model can simultaneously solve the strong CP problem without resorting to the unobserved axion and explain the 750 GeV diphoton resonance reported recently by the ATLAS and CMS collaborations at the LHC. Owing to large suppressions in the two-loop induced Dirac mass terms, the Majorana mass matrices of left- and right-handed neutrinos naturally share the same structure. That allows us to quantitatively study the neutrinoless double beta decay induced by the right-handed currents

Phase-field modeling of non-isothermal grain coalescence in the unconventional sintering techniques

A thermodynamically consistent phase-field model is developed to study the non-isothermal grain coalescence during the sintering process, with a potential application to the simulation in unconventional sintering techniques, e.g. spark plasma sintering, field-assisted sintering, and selective laser sintering, where non-equilibrium and high temperature gradient exist. In the model, order parameters are adopted to represent the bulk and atmosphere/pore region, as well as the crystallographic orientations. Based on the entropy analysis, the temperature-dependent free energy density is developed, which includes contributions from the internal energy (induced by the change of temperature and order parameters) and the order parameter related configurational entropy. The temperature-dependent model parameters are determined by using the experimental data of surface and grain boundary energies and interface width. From laws of thermodynamics, the kinetics for the order parameters and the order-parameter-coupled heat transfer are derived. The model is numerically implemented by the finite element method. Grain coalescence from two identical particles shows that non-isothermal condition leads to the unsymmetric morphology and curved grain boundary due to the gradients of on-site surface and grain-boundary energies induced by the local temperature inhomogeneity. More simulations on the non-isothermal grain coalescence from two non-identical and multiple particles present the temporal evolution of grain shrinkage/growth, neck growth, and porosity, demonstrating the capability and versatility of the model. It is anticipated that the work could provide a contribution to the research community of unconventional sintering techniques that can be used to model the non-isothermal related microstructural features

Strain induced incommensurate phases in hexagonal manganites

An incommensurate phase refers to a solid state in which the period of a superstructure is incommensurable with the primitive unit cell. Recently the incommensurate phase is induced by applying an in-plane strain to hexagonal manganites, which demonstrates single chiral modulation of six domain variants. Here we employ Landau theory in combination with the phase-field method to investigate the incommensurate phase in hexagonal manganites. It is shown that the equilibrium wave length of the incommensurate phase is determined by temperature and the magnitude of the applied strain, and a temperature-strain phase diagram is constructed for the stability of the incommensurate phase. Temporal evolution of domain structures reveals that the applied strain not only produces the force pulling the vortices and anti-vortices in opposite directions, but also results in the creation and annihilation of vortex-antivortex pairs.Comment: 23 pages, 7 figure

Transient Electronic Phase Separation During Metal-Insulator Transitions

From thermodynamic analysis we demonstrate that during metal-insulator transitions in pure matters, a nonequilibrium homogeneous state may be unstable against charge density modulations with certain wavelengths, and thus evolves to the equilibrium phase through transient electronic phase separation. This phase instability occurs as two inequalities between the first and the second derivatives of the free energy with respect to the order parameter are fulfilled. The dominant wavelength of the modulated phase is also derived. The computer simulation further confirms the theoretical derivation. Employing the pre-established phase-field model of VO$_2$, we show that this transient electronic phase separation may take place in VO$_2$ upon photoexcitation.Comment: 5 pages, 3 figure