The Nano-twinning Induced Metal-insulator Transition of Ultra-thin La_0.7Sr_0.3MnO₃ on SrTiO₃（001）

【作者】 殷立峰； 沈健；

【机构】 复旦大学物理系；

【摘要】 We utilize real space imaging to uncover a unique strain relaxation mechanism of La0.7Sr0.3MnO3/SrTiO3(001)thin films.During cooling farom the growth temperature,one-dimensional pseudo-periodic nano-twinning waves are formed spontaneously due to the shear strain between the rhombohedral La0.7Sr0.3MnO3 film and the cubic perovskite SrTiO3 substrate.The average wavelength of nano-twinning patterns a observed to decrease with deceasing thickness,while shrinks quickly between 14 unit cell and 7 unit cell.At the critical thickness of 7 unit cell,the film is atomically flat without any trace of nano-twinning waves and free of dislocations.Remarkably,scanning tunneling spectroscopy shows that the fully strained 7 unit cell film is insulator with a gap of 0.25V.The film recovers the metallic state immediately when the nano-twinnging waves are formed at 9 unit cell.The strongly correlated critical thickness of the metal-insulator transition and the nano-twinning formation indicates the recovery of double exchange in ultrathin La0.7Sr0.3MnO3 is associated with the relaxation of elastic shear energy.更多还原

【Abstract】 We utilize real space imaging to uncover a unique strain relaxation mechanism of La0.7Sr0.3MnO3/SrTiO3(001)thin films.During cooling farom the growth temperature,one-dimensional pseudo-periodic nano-twinning waves are formed spontaneously due to the shear strain between the rhombohedral La0.7Sr0.3MnO3 film and the cubic perovskite SrTiO3 substrate.The average wavelength of nano-twinning patterns a observed to decrease with deceasing thickness,while shrinks quickly between 14 unit cell and 7 unit cell.At the critical thickness of 7 unit cell,the film is atomically flat without any trace of nano-twinning waves and free of dislocations.Remarkably,scanning tunneling spectroscopy shows that the fully strained 7 unit cell film is insulator with a gap of 0.25V.The film recovers the metallic state immediately when the nano-twinnging waves are formed at 9 unit cell.The strongly correlated critical thickness of the metal-insulator transition and the nano-twinning formation indicates the recovery of double exchange in ultrathin La0.7Sr0.3MnO3 is associated with the relaxation of elastic shear energy.更多还原