| In recent years, people have found a class of special metals known as Weyl semimetals whose low-energy excitations could be described by a two-component Dirac equation, i.e., the Weyl equation in particle physics. With the time-reversal symmetry or the inversion symmetry broken, the massless three-dimensional Dirac semimetal turns into Weyl semimetal (WSM), thus a Dirac point is split into two Weyl points with a linear dispersion relation. The bulk energy band is gapless but still has topological non-trivial behaviors, such as, the Topological protection of Weyl points with opposite chirality appearing in pairs, the discontinuous Fermi Arcs on the surface,and negative magnetoresistance effect. However, the study of superconducting Weyl semimetals and the detection of their superconducting states lack enough, an effective way to detect them is by Andreev reflection spectrum. Although there have been some studies on superconducting Weyl semimetal heterojunction, they were only limited to the Andreev reflection of single junction and did not deal with more abundant scattering processes of double junctions especially the nonlocal Andreev reflection,conductance and noise spectrum.Applying the theoretical method based on an extended Bogoliubiv-de Gennes(BdG) equation, we study the electronic transport properties in a WSM/superconducting WSM/WSM topological semimetal junction, specifically, the features of four scattering processes including the normal reflection, the transmission,the local and nonlocal Andreev reflections (ARs), together with the conductance and the noise power. Particularly, we investigate the influences caused by the angle a between the line connecting a pair of Weyl points and the normal of the junction under the BCS and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing states and then the difference between the two pairing states.The results show that under the same pairing state, the four scattering processes,the spectrum of the conductance and noise are great different, stemming from the opposite chirality of the pairing Weyl points and the spin binding on momentum. For the BCS pairing state, the pairing electrons come from the two paring Weyl nodes with opposite chirality, which leads to an effective superconducting energy gap induced by ?, as a result, the probabilities of scattering processes of the two Weyl nodes, conductance and the noise display anisotropic properties. However, the pairing electrons come from the same paring Weyl node for the FFLO pairing state, so that display isotropic properties.Moreover, the experimentally measured conductance and noise power include the contributions coming from the two pairing Weyl nodes. For the BCS pairing state,the total conductance first decreases then increases and decreases lastly with eV,accompanied by a valley and a peak, and a has a significant influence on the valley and peak's position and value. However, for FFLO pairing state, the total conductance firstly increases slowly and then decreases quickly with eV, which has nothing to do with a. For noise power, with the increase of eV, the total noise power for BCS pairing state, first decrease quickly from positive to a negative value, and then quickly increase to the positive, accompanied by a valley. With increasing a, the valley shifts along the direction of enhancing eV. However, the total noise for the FFLO pairing state is always negative, and first slowly increase, then rapidly decrease with the increase of eV, which has nothing to do with a. Therefore, the results can be experimentally used to distinguish between the BCS and the FFLO pairing states from two aspects. One is to observe the characteristics of the conductance or noise with varying eV. The other is that one can change a by tuning the doping concentration in the WSM to observe the properties of the conductance peak or the noise valley. The above-mentioned device can be realized with current technology, which has practical significance in topological superconducting semimetal electronics. |
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