Identifying the graphene d-wave superconducting symmetry by an anomalous splitting zero-bias conductance peak

Abstract

Not until recently, was a gate-tunable, high-temperature superconducting proximity effect in graphene demonstrated experimentally. And usually in d-wave superconductor (SC) hybrid structure, ferromagnetism and spin-triplet states could result in a splitting zero-bias conductance peak (ZBCP). Herein, we theoretically present an anomalous splitting ZBCP in a graphene-based ferromagnet/ Rashba spin-orbit coupling (RSOC)/insulator/d-wave SC hybrid structure. With increasing the exchange field from h/E F =0, the ZBCP starts to turn into a splitting one with a zero-bias conductance dip (ZBCD) sandwiched in between two subpeaks, while from h/E F =1, the two subpeaks and ZBCD begin to gradually shrink till the ZBCP reappears. The anomalous splitting ZBCP can be modulated by the RSOC strength, magnitude of Fermi wave vector mismatch as well as insulator barrier strength. These peculiar features are ascribed to the novel spin-triplet Andreev reflection in the context of the RSOC, characteristic by the anisotropic d-wave pair symmetry combined with the relativistic nodal fermions, which in turn can be experimentally used to directly identify not only the proximity-induced ferromagnetism and RSOC but d-wave pair symmetry in graphene. These results pave the way to a new class of tunable, high-temperature superconducting spintronic devices based on large-scale graphene.

Photoinduced spin-polarized transport and controllable valley-triplet pairing states in a silicene-superconductor junction

“…The above discussions are restricted to the case of lE z = 0, where the silicene band structure is valley degenerate. In this case, the valley-triplet pairing states are absent resembling the spin-triplet case [3]. We now proceed to discuss the generation of exclusive valley-triplet paring process in the coexistence of electric field and light field.…”

“…That is, generally, an electron incoming from the NM side with energy below the superconducting energy gap ∆ 0 (ε < ∆ 0 ) can not enter the superconductor, but it is reflected as a hole backwards at the interface with a Cooper pair being transferred into in the SC lead. Experimentally, AR can be characterized based on the finite subgap conductance of the NM-SC interface and the subgap conductance spectrum may offer an opportunity to test the physical properties of superconductivity in materials by scanning tunneling microscopy [2][3][4]. In addition, it can be also used to measure the spin and valley polarizations of a material by a superconducting contact [5,6].…”

Andreev reflection in graphene nanoribbons induced by d-wave superconductors

“…It is pointed out that the conductance of the lattice-mismatched system corresponds to the tunneling conductance even for t GS = t, as for the red curves, due to the scattering at the GS interface. The tunneling conductance has been shown to exhibit the zero-bias peak when the d-wave superconductor is attached to a sheet of graphene [20][21][22][23][24]. The peak is hence expected to be recovered when a large number of propagating modes are occupied in the GNR to resemble a two-dimensional system [19].…”

“…The quantization of the wavevector imposed by the transverse confinement is responsible for the suppression. The transport properties in the junctions of graphene and a d-wave superconductor have been investigated not only theoretically [20][21][22][23][24] but also experimentally [25,26]. Here, the electronic states in the theoretical models were described using plane waves, i.e.…”

Anomalous thermal phenomena in a temperature biased graphene-based N/I/p-wave SC junction

“…2) Due to the peculiar electronic structure, a variety of unusual electronic transport properties in the graphene-based hybrid structures composed of SCs are revealed. [3][4][5][6][7][8] For example, the anomalous charge conductance and shot noise spectra are exhibited in a graphene-based normal segment (N)/insulator (I)/p-wave SC junction, 6,8) which is ascribed to the low-energy relativistic nature of fermions in graphene. Here, the I region refers to a normal segment of graphene on which an external gate voltage is applied.…”