Wenshuai Gao

Wavy cleavage fracture of bulk metallic glass

Dynamic instability is one of the typical cleavage fracture features in brittle materials. The authors find that dynamic instability of metallic glass starts to occur in the mirror region on the fracture surface through a wavy cracking propagation with the formation of periodic nanoscale steps. This kind of dynamic instability is associated with the early crack curving due to the intrinsic isotropic structure of metallic glass. Furthermore, they classify dynamic instabilities of cleavage fracture as crack curving at low velocity and crack branching at high velocity, corresponding to the mirror and hackle regions of metallic glass, respectively.

Interfacial barrier in manganite junctions with different crystallographic orientations

We performed a comprehensive study on the La1−xCaxMnO3/SrTiO3:Nb junctions with different hole content and film thickness. It is found that the interfacial barrier, which determines the physical properties of the junctions, shows a strong dependence on crystallographic orientation, and it is substantially higher for the (110) than for the (100)-orientated junctions. The difference in barrier height is further found to exhibit a systematic variation with Ca content and film thickness (t). It reduces from ∼0.09 to 0.02 eV for a x increase from 0.1 to 1 with a fixed t=200 nm, and experiences a growth by ∼0.06 eV corresponding to the variation in t from 10 to 160 nm for a constant x=0.33. Similar phenomena have been observed in the La0.67Ba0.33MnO3/SrTiO3:Nb junctions. In the scenario of different polarity mismatches at the (100) and (110) interfaces in the two series of junctions, these results can be qualitatively understood.

Field-induced topological phase transition from a three-dimensional Weyl semimetal to a two-dimensional massive Dirac metal in ZrTe5

Symmetry protected Dirac semimetals can be transformed into Weyl semimetals by breaking the protecting symmetry, leading to many exotic quantum phenomena such as chiral anomaly and anomalous Hall effect. Here we show that, due to the large Zeeman g factor and small band width along b-axis in Dirac semimetal ZrTe5, a magnetic field of about 8 T along b-axis direction may annihilate the Weyl points and open up a two-dimensional (2D) Dirac mass gap, when the Zeeman splitting exceeds the band width along b-axis. This is manifested by a sharp drop of magnetoresistance (MR) above 8 T, which is probably due to additional carriers induced by the orbital splitting of the zeroth Landau level associated with the 2D Dirac point, which is descendant of the original Weyl points. Further evidence of the additional carriers is provided by the Hall effect and different anisotropic magnetoresistance (AMR) in low and high field regions. Our experiment reveals a probable topological quantum phase transition of field induced Weyl points annihilation in Dirac semimetal ZrTe5 and gives an alternative explanation for the drop of MR at high field.

Effect of temperature on the La1-xCaxMnO3/SrTiO3:Nb (x=0-0.75) heterojunctions

Influence of temperature on the La1-xCaxMnO3/SrTiO3:Nb heterojunctions with the Ca content ranging from 0 to 0.75 has been experimentally studied. Obvious temperature effect occurs in the junction with a Ca content of 0.1. As experimentally shown, the interfacial barrier is insensitive to temperature below 340 K, and experiences a decrease from ∼1.24 to 0.85 eV as temperature grows from 340 to 375 K. However, the temperature effect in other junctions is weak, and the energy barrier change is typically ∼0.03–0.08 eV. In the scenario of temperature-driven orbital order-disorder transition in the La0.9Ca0.1MnO3 film, the temperature effect can be qualitatively understood.

Recognition of Fermi-arc states through the magnetoresistance quantum oscillations in Dirac semimetal Cd3As2 nanoplates

Disjointed Fermi arcs in Weyl semimetals can intertwine with chiral bulk modes and participate in unusual closed magnetic orbits in the presence of a vertical magnetic field. Here, we carry out a quantum oscillation study of such unusual Weyl magnetic orbits in the Dirac semimetal

Buffer-layer-enhanced magnetic field effect in La0.5Ca0.5MnO3/LaMnO3/SrTiO3:Nb heterojunctions

\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}

A possible candidate for triply degenerate point fermions in trigonal layered PtBi 2

, a close cousin of Weyl semimetals. We find that extra two-dimensional (2D) quantum oscillations emerge at high fields, which superimpose on a three-dimensional bulk background and can be attributed to the Weyl magnetic orbits, when the thickness of the nanoplates is smaller than the mean free path of the electrons. Further evidence of 2D quantum oscillations from the Weyl magnetic orbits is provided by nonlocal detection, which demonstrates an alternative way to study the quantum transport properties of Fermi arcs under magnetic fields.

Electrical and anisotropic magnetic properties in layered Mn1/3TaS2 crystals

The transport behaviors of La0.5Ca0.5MnO3/LaMnO3/SrTiO3:Nb heterojunctions with a LaMnO3 layer thickness of between 0 and 12 nm have been systematically studied. The effect of the magnetic field on the junction without the buffer layer is weak. The influence of the magnetic field on the junction is maximized when the layer thickness is ∼3 nm, demonstrated by a significant field-induced increase in current when the bias voltage is fixed. The corresponding magnetoresistance of the junction is negative, and its maximal value is ∼−32% for a field change of 5 T at 80 K. Based on a quantitative analysis of the current-voltage characteristics, the interfacial barrier can be derived, and it shows a complex variation with an increase in layer thickness, first decreasing and then increasing. This is the apparent reason for the change in buffer-layer-enhanced negative magnetoresistance of the junctions for different layer thicknesses.

Extremely Large Magnetoresistance in a Topological Semimetal Candidate Pyrite PtBi2

Triply degenerate point (TP) fermions in tungsten–carbide-type materials (e.g., MoP), which represent new topological states of quantum matter, have generated immense interest recently. However, the TPs in these materials are found to be far below the Fermi level, leading to the TP fermions having less contribution to low-energy quasiparticle excitations. Here, we theoretically predict the existence of TP fermions with TP points close to the Fermi level in trigonal layered PtBi2 by ab initio calculations, and experimentally verify the predicted band topology by magnetotransport measurements under high magnetic fields up to 40 T. Analyses of both the pronounced Shubnikov–de Haas and de Haas–van Alphen oscillations reveal the existence of six principal Fermi pockets. Our experimental results, together with those from ab initio calculations, reveal the interplay between transport behaviors and unique electronic structures, and support the existence of TP fermions in trigonal layered PtBi2.Triply degenerate point (TP) fermions have been reported in MoP but the TPs are far below the Fermi level. Here, Guo et al. predict and verify the possible existence of TP fermions in trigonal layered PtBi2, where the TP points are close to the Fermi level.

Probing the Chiral Anomaly by Planar Hall Effect in Three-dimensional Dirac Semimetal Cd3As2 Nanoplates

We report electrical transport and anisotropic magnetic properties of Mn-intercalated 2H-TaS2, a layered transition-metal dichalcogenide with a hexagonal structure. The single crystal MnxTaS2 with x = 1/3 exhibits a transition from paramagnetism to ferromagnetism near 70 K, below which both the magnetoresistance and magnetization properties present strong anisotropic behavior. Its anisotropic magnetoresistance effect and in-plane soft ferromagnetic property suggests that this layered material would be a good candidate for exploring the physics of two-dimensional ferromagnetism.We report electrical transport and anisotropic magnetic properties of Mn-intercalated 2H-TaS2, a layered transition-metal dichalcogenide with a hexagonal structure. The single crystal MnxTaS2 with x = 1/3 exhibits a transition from paramagnetism to ferromagnetism near 70 K, below which both the magnetoresistance and magnetization properties present strong anisotropic behavior. Its anisotropic magnetoresistance effect and in-plane soft ferromagnetic property suggests that this layered material would be a good candidate for exploring the physics of two-dimensional ferromagnetism.