Enhanced ferromagnetism and conductivity of ultrathin freestanding La_(0.7)Sr_(0.3)MnO_(3)membranes

We report a universal method to transfer freestanding La_(0.7)Sr_(0.3)MnO_(3)membranes to target substrates.The 4-unit-cell-thick freestanding La_(0.7)Sr_(0.3)MnO_(3)membrane exhibits the enhanced ferromagnetism,conductivity and out-of-plane magnetic anisotropy,which otherwise shows nonmagnetic/antiferromagnetic and insulating behavior due to the intrinsic epitaxial strain.This work facilitates the promising applications of ultrathin freestanding correlated oxide membranes in electronics and spintronics.

Large-Area Freestanding Weyl Semimetal WTe_(2) Membranes

We report a universal transfer methodology for producing artificial heterostructures of large-area freestanding single-crystalline WTe_(2) membranes on diverse target substrates.The transferred WTe_(2) membranes exhibit a nondestructive structure with a carrier mobility comparable to that of as-grown films(∼179–1055 cm^(2)·V^(−1)·s^(−1)).Furthermore,the transferred membranes show distinct Shubnikov–de Haas quantum oscillations as well as weak localization/weak anti-localization.These results provide a new approach to the development of atom manufacturing and devices based on atomic-level,large-area topological quantum films.

Observation of Shubnikov-de Haas Oscillations in Large-Scale Weyl Semimetai WTe2 Films

Topological Weyl semimetal WTe2 with large-scale Him form has a promising prospect for new-generation spintronic devices.However,it remains a hard task to suppress the defect states in large-scale WTe2 films due to the chemical nature.Here we significantly improve the crystalline quality and remove the Te vacancies in WTe2 films by post annealing.We observe the distinct Shubnikov-de Haas quantum oscillations in WTe2 films.The nontrivial Berry phase can be revealed by Landau fan diagram analysis.The Hall mobility of WTe2 films can reach 1245cm^2V^-1s^-1 and 1423cm^2V^-1s^-1 for holes and electrons with the carrier density of 5× 10^19 cm^-3 and 2 × 10^19 cm^-3,respectively.Our work provides a feasible route to obtain high-quality Weyl semimetal films for the future topological quantum device applications.

Anisotropic phonon dynamics in Dirac semimetal PtTe2 thin films enabled by helicity-dependent ultrafast light excitation

Coherent phonons have aroused considerable attention in condensed matter physics owing to their extraordinary capacity of reflecting and controlling the physical properties of matter.However,the investigation on the interaction between coherent phonons and other microscopic particles on the ultrafast timescale within topological systems continues to be an active and unresolved area.Here,we show the energy transfer of coherent optical phonons(COP)in Dirac semimetal PtTe2 thin films using ultrafast optical pump-probe spectroscopy.Specifically,the helicitydependent light-driven anisotropic COP signals disclose their direct connection with the light-excited anisotropic spinpolarized electrons via an angular momentum transfer.Furthermore,we observe the notable decreases in the COP oscillation frequency and the decay rate with increasing temperatures due to the anharmonic phonon-phonon scattering and electron-phonon scattering in the COP dissipation process,respectively.Our work paves the way for uncovering the coherent phonons in Dirac semimetals for the potential applications in optoelectronics and optospintronics.

Third-order nonlinear optical properties of WTe2 films synthesized by pulsed laser deposition

The prominent third-order nonlinear optical properties of WTe2 films are studied through the Z-scan technique using a femtosecond pulsed laser at 1030 nm.Open-aperture(OA)and closed-aperture(CA)Z-scan measurements are performed at different intensities to investigate the nonlinear absorption and refraction properties of WTe2 films.OA Z-scan results show that WTe2 films always hold a saturable absorption characteristic without transition to reverse saturable absorption.Further,a large nonlinear absorption coefficientβis determined to be-3.37×10^3 cm∕GW by fitting the OA Z-scan curve at the peak intensity of 15.603 GW∕cm^2.In addition,through the slow saturation absorption model,the ground state absorption cross section,excited state absorption cross section,and absorber's density were found to be 1.4938×10^-16 cm^2,1.2536×10^-16 cm^2,and 6.2396×10^20 cm^-3,respectively.CA Z-scan results exhibit a classic peak–valley shape of the CA Z-scan signal,which reveals a self-defocusing optical effect of WTe2 films under the measured environment.Furthermore,a considerable nonlinear refractive index value n2 can be obtained at-1.629×10^-2 cm^2∕GW.Ultimately,the values of the real and imaginary parts of the third-order nonlinear susceptibility of WTe2 are roughly estimated to be-5.93×10^-9 and-1.01×10^-8 esu with the help of first-principles calculations.WTe2 possesses sizeable thirdorder nonlinear coefficients compared with other materials,which suggests that it has great potential to improve performance in nonlinear optical devices.