Application of the edge of chaos in combinatorial optimization

Many problems in science,engineering and real life are related to the combinatorial optimization.However,many combinatorial optimization problems belong to a class of the NP-hard problems,and their globally optimal solutions are usually difficult to solve.Therefore,great attention has been attracted to the algorithms of searching the globally optimal solution or near-optimal solution for the combinatorial optimization problems.As a typical combinatorial optimization problem,the traveling salesman problem(TSP)often serves as a touchstone for novel approaches.It has been found that natural systems,particularly brain nervous systems,work at the critical region between order and disorder,namely,on the edge of chaos.In this work,an algorithm for the combinatorial optimization problems is proposed based on the neural networks on the edge of chaos(ECNN).The algorithm is then applied to TSPs of 10 cities,21 cities,48 cities and 70 cities.The results show that ECNN algorithm has strong ability to drive the networks away from local minimums.Compared with the transiently chaotic neural network(TCNN),the stochastic chaotic neural network(SCNN)algorithms and other optimization algorithms,much higher rates of globally optimal solutions and near-optimal solutions are obtained with ECNN algorithm.To conclude,our algorithm provides an effective way for solving the combinatorial optimization problems.

Large unsaturated positive and negative magnetoresistance in Weyl semimetal TaP

After successfully growing single-crystal Ta P, we measured its longitudinal resistivity(ρxx) and Hall resistivity(ρyx) at magnetic fields up to 9 T in the temperature range of 2-300 K. At 8 T, the magnetoresistance(MR) reached 3.28 × 105% at 2 K, 176%at 300 K. Neither value appeared saturated. We confirmed that Ta P is a hole-electron compensated semimetal with a low carrier concentration and high hole mobility of μh=3.71 × 10~5cm^2/V s, and found that a magnetic-field-induced metal-insulator transition occurs at room temperature. Remarkably, because a magnetic field(H) was applied in parallel to the electric field(E), a negative MR due to a chiral anomaly was observed and reached-3000% at 9 T without any sign of saturation, either, which is in contrast to other Weyl semimetals(WSMs). The analysis of the Shubnikov-de Haas(Sd H) oscillations superimposed on the MR revealed that a nontrivial Berry's phase with a strong offset of 0.3958, which is the characteristic feature of charge carriers enclosing a Weyl node. These results indicate that Ta P is a promising candidate not only for revealing fundamental physics of the WSM state but also for some novel applications.

Bulk superconductivity in the Dirac semimetal TlSb

A feasible strategy for realizing the Majorana fermions is searching for a simple compound with both bulk superconductivity and Dirac surface states.In this paper,we perform calculations of electronic band structure,the Fermi surface,and the surface states,and measure the resistivity,magnetization,and specific heat of a TlSb compound with a CsCl-type structure.The band structure calculations show that TlSb is a Dirac semimetal when spin-orbit coupling is considered.TlSb is first determined to be a type-Ⅱsuperconductor with T_(c)=4.38 K,Hc1(0)=148 Oe,H_(c2)(0)=1.12 T,andκ_(GL)=10.6.We also confirm that TlSb is a moderately coupled s-wave superconductor.Although we cannot determine the band near the Fermi level EF that is responsible for superconductivity,its coexistence with topological surface states implies that the TlSb compound may be a simple material platform to realize the fault-tolerant quantum computations.

Metamagnetic transitions and anomalous magnetoresistance in EuAg4As2 crystals

In this work,we systematically studied the magnetic and transport properties of EuAg4As2 single crystals.It was found that the two antiferromagnetic transitions(TN1=10 K and TN2=15 K)were driven to lower temperatures by an applied magnetic field.Below TN1,two successive metamagnetic transitions were observed when a magnetic field was applied in the ab plane(H//abplane).For both H//ab and H//c,EuAg4As2 showed a positive,unexpectedly large magnetoresistance(up to 202%)in lower magnetic fields below TN1,and a large negative magnetoresistance(up to-78%)at high fields/intermediate temperatures,thus presenting potential applications in magnetic sensors.Finally,the magnetic phase diagrams of EuAg4As2 were constructed for both H//ab and H//c using the resistivity and magnetisation data.