鐵酸鉍鐵電極性疇壁對釔鋇銅氧超導表現的影響

Abstract

自高溫超導體釔鋇銅氧(YBa2Cu3O7-δ,YBCO)被發現以來，調控其超導特性的相關研究逐漸受人注目。已有相關研究發現不同極性方向的鐵電性材料鐵酸鉍(BiFeO3, BFO)與釔鋇銅氧接合，會量測到不一樣的超導臨界溫度Tc，證實鐵電極性與超導的交互作用會造成對釔鋇銅氧超導特性的抑制或助長。為了觀察釔鋇銅氧在鄰近鐵酸鉍的疇域(Domains, DMs)與疇壁(Domain Walls, DWs)的超導行為，本研究工作在鐵酸鉍之上成長釔鋇銅氧，並藉由剖面式掃描穿隧顯微鏡(Cross-sectional Scanning Tunneling Microscope, XSTM)從剖面處直接量測樣品釔鋇銅氧/鐵酸鉍(其中鐵酸鉍分別有109°和71°疇壁兩種結構)的介面處之電子結構。研究結果可獲知在介面處釔鋇銅氧的超導態如何受鐵酸鉍不同極性方向所影響，實驗結果顯示鐵酸鉍極性方向指向釔鋇銅氧比極性方向指離釔鋇銅氧的超導能隙2Δ值小，鐵酸鉍疇域的極性方向可調控釔鋇銅氧超導能隙。

Since the high-temperature superconductor YBa2Cu3O7-δ(YBCO) was found, the modulation of its superconductivity became a popular topic among the field of materials science. Recent researches have revealed that different direction of the ferroelectric polarization in the multiferroics BiFeO3 (BFO) grown upon the superconductor YBCO leads to the variant critical temperature Tc of YBCO, and deducedthat interaction between ferroelectricity and superconductivity has abilities to suppress or raise superconducting properties of YBCO. To observe the superconducting states of YBCO near the domains (DMs) and the domain walls (DWs) of BFO, YBCO was grown on BFO. The electronic structures of the specimens YBa2Cu3O7-δ/ BiFeO3 (109°DWs) and YBa2Cu3O7-δ/ BiFeO3 (71°DWs) at the interface were measured by cross-sectional scanning tunneling microscopy (XSTM) directly in this study. Through the experimental result, how the superconducting state ofYBCO at the interface is influenced by the direction of ferroelectric polarization in BFO is revealed. The value of the superconducting energy gap 2Δis smaller when the direction of polarization points to YBCO than pointing away YBCO. In summary, the superconducting energy band gap of YBCO can be changed by the direction of ferroelectric polarization in BFO.