The Comparative Study of the Temperature Distribution of Fiber Laser with Different Pump Schemes

Based on the structure of the long fiber laser (YDCFLs) with different pump schemes using high pump power, the nonlinear coupled and heat dissipation equations are solved numerically. Using the finite-difference method, we have determined the temperature distribution along the radial and axial directions of the fiber laser (YDCFLs) for the forward pump schemes of 200 W with reflection Rp2, backward pump schemes of 200 W with reflection Rp1 and for bidirectional pump scheme of 100 W each side. The results are: the temperature distribution for bidirectional pump mode is more even than that for forward pump with reflection Rp2 and than that for backward pump with reflection Rp1. The results show that the maximum temperature difference between different schemes is 57.51°C, and when the air-clad width decreases, the temperature in the core regions also decreases and does not affect to the cladding radius regions. We summarize that the temperature in the core and in cladding radius regions decreases when the outer radius cladding increases.

Observation of a Ubiquitous(π,π)-Type Nematic Superconducting Order in the Whole Superconducting Dome of Ultra-Thin BaFe_(2-x)Ni_(x)As_(2) Single Crystals

In iron-based superconductors,the(0,π) or(π,0) nematicity,which describes an electronic anisotropy with a fourfold symmetry breaking,is well established and believed to be important for understanding the superconducting mechanism.However,how exactly such a nematic order observed in the normal state can be related to the superconducting pairing is still elusive.Here,by performing angular-dependent in-plane magnetoresistivity using ultra-thin flakes in the steep superconducting transition region,we unveil a nematic superconducting order along the(π,π) direction in electron-doped BaFe_(2-x)Ni_(x)As_(2) from under-doped to heavily overdoped regimes with x=0.065- 0.18.It shows superconducting gap maxima along the(π,π) direction rotated by 45° from the nematicity along(0, π) or(π,0) direction observed in the normal state.A similar(π,π)-type nematicity is also observed in the under-doped and optimally doped hole-type Ba1-yKyFe2 As_(2),with y=0.2-0.5.These results suggest that the(π,π) nematic superconducting order is a universal feature that needs to be taken into account in the superconducting pairing mechanism in iron-based superconductors.

Superconductor-Metal Quantum Transition at the EuO/KTaO3 Interface

We report the experimental investigation of the superconductor-metal quantum phase transition of the Eu O/KTa O3 interface.Around the transition,a divergence of the dynamical critical exponent is observed,which supports the quantum Griffiths singularity in the Eu O/KTa O3 interface.The quantum Griffiths singularity could be attributed to large rare superconducting regions and quenched disorders at the interface.Our results could pave the way for studying the exotic superconducting properties at the Eu O/KTa O3 interface.

The CP^1 nonlinear sigma model with ChernSimons term in the Faddeev-Jachiw quantization formalism

Using the Faddeev-Jackiw （FJ） quantization method, this paper treats the CP^1nonlinear sigma model with ChernSimons term. The generalized FJ brackets are obtained in the framework of this quantization method, which agree with the results obtained by using the Dirac＇s method.

Tuning magnetic anisotropy by interfacial engineering in La2/3Sr1/3Co1-xMnxO2.5+δ/La2/3Sr1/3MnO3/La2/3Sr1/3Co1-xMnxO2.5+δ trilayers

Grouping different oxide materials with coupled charge, spin, and orbital degrees of freedom together to form heterostructures provides a rich playground to explore the emergent interfacial phenomena. The perovskite/brownmillerite heterostructure is particularly interesting since symmetry mismatch may produce considerable interface reconstruction and unexpected physical effects. Here, we systemically study the magnetic anisotropy of tensely strained La2/3Sr1/3Co1-xMnxO2.5+δ/La2/3Sr1/3MnO3/La2/3Sr1/3Co1-xMnxO2.5+δ trilayers with interface structures changing from perovskite/brownmillerite type to perovskite/perovskite type. Without Mn doping, the initial La2/3Sr1/3CoO2.5+δ/La2/3Sr1/3MnO3/La2/3Sr1/3CoO2.5+δ trilayer with perovskite/brownmillerite interface type exhibits perpendicular magnetic anisotropy and the maximal anisotropy constant is 3.385×106 erg/cm3, which is more than one orders of magnitude larger than that of same strained LSMO film. By increasing the Mn doping concentration, the anisotropy constant displays monotonic reduction and even changes from perpendicular magnetic anisotropy to in-plane magnetic anisotropy, which is possible because of the reduced CoO4 tetrahedra concentration in the La2/3Sr1/3Co1-xMnxO2.5+δ layers near the interface. Based on the analysis of the x-ray linear dichroism, the orbital reconstruction of Mn ions occurs at the interface of the trilayers and thus results in the controllable magnetic anisotropy.

Bethe ansatz solutions of the 1D extended Hubbard-model

We construct an integrable 1D extended Hubbard model within the framework of the quantum inverse scattering method.With the help of the nested algebraic Bethe ansatz method,the eigenvalue Hamiltonian problem is solved by a set of Bethe ansatz equations,whose solutions are supposed to give the correct energy spectrum.

Evidence for nematic superconductivity of topological surface states in PbTaSe2

Spontaneous symmetry breaking has been a paradigm to describe the phase transitions in condensed matter physics.In addition to the continuous electromagnetic gauge symmetry,an unconventional superconductor can break discrete symmetries simultaneously,such as time reversal and lattice rotational symmetry.In this work we report a characteristic in-plane 2-fold behaviour of the resistive upper critical field and point-contact spectra on the superconducting semimetal PbTaSe2 with topological nodal-rings,despite its hexagonal lattice symmetry(or D3 h in bulk while C3 v on surface,to be precise).The 2-fold behaviour persists up to its surface upper critical field Hc2R even though bulk superconductivity has been suppressed at its bulk upper critical field Hc2HC<<Hc2R,signaling its probable surface-only electronic nematicity.In addition,we do not observe any lattice rotational symmetry breaking signal from field-angle-dependent specific heat within the resolution.It is worth noting that such surface-only electronic nematicity is in sharp contrast to the observation in the topological superconductor candidate,CuxBi2Se3,where the nematicity occurs in various bulk measurements.In combination with theory,superconducting nematicity is likely to emerge from the topological surface states of PbTaSe2,rather than the proximity effect.The issue of time reversal symmetry breaking is also addressed.Thus,our results on PbTaSe2 shed new light on possible routes to realize nematic superconductivity with nontrivial topology.

Polymorph Structures,Rich Physical Properties and Potential Applications of Two-Dimensional MoTe_(2),WTe_(2) and Their Alloys

2D MoTe_(2),WTe_(2) and their alloys have received intensive research interest because of their unique properties arising from the polymorph structures,chiral anomaly,strong spin-orbit coupling,and so on.In this review,we have summarized recent advances of 2D MoTe_(2),WTe_(2) and their alloys from the materials perspective with special focus on the synthesis,electrical and magnetic properties.The polymorph structures of MoTe_(2),WTe_(2) and their alloys are presented first and then the preparation methods have been discussed,including mechanical exfoliation,metal-organic chemical vapor deposition(MOCVD),molecular beam epitaxy(MBE),chemical vapor deposition(CVD)and solution-phase method.After that,fascinating physical properties arising from the large spin-orbit coupling and non-trivial band structures have been summarized,including phase transition,optoelectri-cal properties,Weyl semimetal state,superconducting and ferromagnetism.At last,potential device applications of MoTe_(2),WTe_(2) and their alloys are reviewed,including field-effect transistors(FETs),memory devices,spin-to-charge conversion,solar cells,and so on.

Exact solution to a class of generalized Kitaev spin-1/2 models in arbitrary dimensions

We construct a class of exactly solvable generalized Kitaev spin-1/2 models in arbitrary dimensions, which is beyond the category of quantum compass models. The Jordan-Wigner transformation is employed to prove the exact solvability. An exactly solvable quantum spin-1/2 model can be mapped to a gas of free Majorana fermions coupled to static Z2 gauge fields. We classify these exactly solvable models according to their parent models. Any model belonging to this class can be generated by one of the parent models. For illustration, a two dimensional(2D) tetragon-octagon model and a three dimensional(3D) xy bond model are studied.

Ultra-flexible all-in-one anti-freeze photothermally enhanced supercapacitors

Wearable electronics powered by flexible energy storage devices have captured global attention.Under low-temperature conditions,unfortunately,solidification of flexible hydrogel electrolyte and decreased pseudo-capacity of these devices largely hamper their practical use.In this study,photothermally-active Prussian blue(PB)was introduced onto poly(3,4-ethylenedioxythiophene)/polyacrylamide(PEDOT/PAM)networks to address the challenges of electrolyte solidification and degraded pseudo-capacitance for flexible all-in-one device at low temperatures.The as-constructed PB/PEDOT/PAM hydrogel device delivers stable electrochemical performance and remarkable mechanical property with 1652%elongation.Importantly,this hydrogel device well retains its flexibility in cold environment with a freezing point below−30℃.The incorporation of PB extends the voltage range to 1.5 V as a single device,thus significantly enhancing the electrochemical performance as an all-inone integrated device.Benefitting from the outstanding photo-to-thermal conversion ability of embedded PB nanocubes,the temperature of the assembled all-in-one PB/PEDOT/PAM device increased from^(−2)0 to 17.7℃ after solar-light irradiation for only 5 min.Moreover,the degraded pseudo-capacitance was subsequently boosted to 287.1%of its original capacitance at−20℃.This study establishes a connection between flexible all-solid-state hydrogel devices and photothermally enhanced pseudocapacitors in freezing environments,thereby expanding the potential applications of multi-functional pseudo-capacitors.

High-temperature interface superconductivity in bilayer copper oxide films by pulsed laser deposition

In a seminal work, Gozar et al. reported on the high-temperature interface superconductivity in bilayers of insulating La2Cu O4 and metallic La2-xSrxCuO4(x=0.45). An interesting question to address is how general and robust this interface superconductivity is. In the past, the cuprate bilayers were grown in a unique atomic-layer molecular beam epitaxy system, with a Sr doping range of x≤0.47, and the atomically flat interface was thought to be indispensable. Here, we have fabricated bilayers of La2CuO4 and La2-xSrxCuO4 by pulsed laser deposition. We have tried to extend the nominal doping range of Sr from the previous maximum of 0.47 to the present1.70(the nominal Sr content in the targets). X-ray diffraction result indicates that our La2-xSrxCuO4 films with x≤0.60 have very high crystalline quality;but the film crystalline structure degrades gradually with further increasing x, and finally the structure is fully lost when x reaches 1.40 and higher. Although the film quality scatters dramatically, our experiments show that there exists superconductivity for bilayers in nearly the entire over-doped Sr range, except for a non-superconducting region at x^0.80. These observations demonstrate that the interface superconductivity in copper oxides is very general and robust.