Andreev reflection in a Y-shaped graphene-superconductor device

Abstract

Using the non-equilibrium Green function method, we study the Andreev reflection in a Y-shaped graphene-superconductor device by tight-binding model. Considering both the zigzag and armchair terminals, we confirm that the zigzag terminals are the better choice for detecting the Andreev reflection without no external field. Due to scattering from the boundaries of the finite-size centre region, the difference between Andreev retroreflection and specular reflection is hard to be distinguished. Although adjusting the size of the device makes the difference visible, to distinguish them quantitatively is still impossible through the transport conductance. The problem is circumvented when applying a perpendicular magnetic field on the centre region, which makes the incident electrons and the reflected holes propagate along the edge or the interface. In this case, the retroreflected and specular reflected holes from the different bands have opposite effective masses, therefore the moving direction of one is opposite to the other. Which external terminal the reflected holes flow into depends entirely on the kind of the Andreev reflection. Therefore, the specular Andreev reflection can be clearly distinguished from the retroreflected one in the presence of strong magnetic field, even for the device with finite size.

Topological classification of defects in non-Hermitian systems

“…It has been unveiled that non-Hermitian systems exhibit many different properties from the Hermitian systems, e.g., biorthonormal eigenvectors 56 , the existence of exception points [65][66][67][68] , unusual bulk-edge correspondence [53][54][55][56] and emergence of non-Hermitian skin effect in non-reciprocal systems 55,56,[69][70][71][72][73] . Effects of non-Hermiticity on defect states are also studied for some specific non-Hermitian topological models [74][75][76][77] . Except the fundamental inter-est of understanding these differences, novel topological properties of non-Hermitian systems may bring potential application in topological lasers and high-sensitive sensors.…”

Topological charge pumping by a sliding moiré pattern

“…The electron pumping experiments have been performed in various semiconductor-based nanoscale devices [2][3][4]. More recently, the topological charge pump was realized in ultracold atoms in optical superlattices [5][6][7], and it was also extensively studied in theory [8][9][10][11][12][13][14][15].…”

Anomalous features of non-Hermitian topological states

“…Fortunately, some recent attempts pave the way for constructing it [7,8]. Non-Hermitian topological edge states were initially found in simple models such as complex extensions of the Su-Schrieffer-Heeger (SSH) model [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] and Kitaev model [29][30][31][32][33]. Then more complex models has been introduced and studied in the literature .…”