High-T _c Cooper-pair injection in a semiconductor–superconductor structure

Abstract

We observe Andreev reflection in a YBCO-GaN junction through differential conductance spectroscopy. A strong characteristic zero-bias peak was observed and persisted up to the critical temperature of the superconductor with a smaller superconducting order parameter Δ ∼ 1 meV. The presence of Andreev reflection with the small Δ in comparison to its value for high-T c superconductors forms an important milestone toward demonstration of superconducting proximity in high-T c /semiconductor junctions. Experimental results were then compared to the theoretical model with good agreement. Efficient injection of Cooper pairs into direct bandgap semiconducting structures, together with high transition temperature of YBCO, can pave the way to novel optoelectronics and quantum optical studies of high-T c materials.

Generation of odd-frequency surface superconductivity with spontaneous spin current due to the zero-energy Andreev bound state

“…)]/2 also approaches to zero near the magnetic criticality [30], the edge s odd wave gap will not affect the LDOS at zero-energy. This result is consistent with the ubiquitous presence of zerobias conductance peak in the tunneling spectroscopy of cuprates [10,11,65,66] Here, we elucidate the emergence of nontrivial edge supercurrent in the d + s odd wave state. In the present cluster model with the d + s odd wave gap, the charge current along the x-axis from layer y (Fig.…”

The Positive Temperature Coefficient of Resistivity in BiFeO3 Films

“…This was illustrated when a cooper-pair was injected into the BFO films. The phenomenon of a superconducting cooper-pair entering a superconductor-semiconductor structure has been reported previously [ 34 , 35 ]. However, more studies are required to understand the relation between the PTCR and the superconductivity of YBCO.…”

Tunnelling conductance of $d+ip$-wave superconductor

“…The conductance spectra of cuprate superconductors observed in experiments so far are peak-structure at the zero energy 8,9,[11][12][13][14][15] even though several experiments reported the splitting of the ZBCP 10,37,38 . Our theoretical study, where the p-wave surface attractive interaction is phenomenologically taken into account, demonstrated that the p-wave subdominant pair potential does not split the zero-bias peak.…”

“…Theoretically, the subdominant s-wave component splits the zero-energy peak in the local density of states (LDOS) [33][34][35] and gives rise to a spontaneous surface current with breaking the time reversal symmetry (TRS) 36 . In experiments, however, such peak splitting nor TRS breaking has not been observed 8,9,[11][12][13][14][15][16] except for several cases 10,37,38 . More seriously, the induced s-wave pair potential requires an on-site attractive interaction in contradiction to the strong repulsive interaction in the cuprate.…”

“…Unconventional superconductor (SC) can host surface bound states, the Andreev bound states (ABSs), forming the zero-energy flat band 1-6 . The zero-energy ABSs can be observed as the zero-bias conductance peak (ZBCP) in the quasiparticle tunneling spectra of the junctions of a normal metal and a high-T c cuprate (i.e., a spin-singlet dwave SC) [7][8][9][10][11][12][13][14][15][16] . In addition, the ABSs induce the Josephson current with a low-temperature anomaly [17][18][19] and the paramagnetic Meissner current [20][21][22][23][24][25][26][27][28][29] .…”