| The discovery of cuprate oxide superconductors is one of the most significant scientific phenomena in the condensed matter physics in the 20 th century. In the cuprates, superconductivity usually occurs in certain doping level, accompanied with the competition of spin- or charge-strip phases, pseudo-gap, spin-glass state, charge order, antiferromagnetism, and charge density wave. Searching for a universal theory to describe the relationship between superconductivity and these competitive phases is one of the hottest topics in the condensed matter physics. The experimental exploration of this relationship would offer an opportunity for searching new superconductors.The disorder induced by cation substitution has greatly affected superconductivity. However, it usually induces the chemical inhomogeneous, phase separation. These ingredients prevent us from distinguishing the relationship between disorder and superconductivity. Thus, how the disorder affects the physical properties of cuprate oxide superconductors and its relationship with superconductivity are still mysterious. In this way, it is significant to find certain clean variation to modulate and control superconductivity at a fixed doping level.Pressure could tune the crystal parameters of sample without introducing other impurities that would change its electronic structure to affect its physical properties. Therefore, it is considered as a clean and independent physical parameter, and becomes an effective way to study the properties of cuprate cuprate oxide superconductors. The current studies reveal that the disorder, phase transition, and phase separation induced by pressure would greatly affect superconductivity. However, there studies are not systematic, and couldn’t clearly resolve their relationship. Therefore, the corresponding systematic study on such relationship would benefit us in exploring the superconducting mechanism.In Tl- and Bi- cuprate oxide superconductors, there exists disorder at room temperature under ambient pressure. However, it is still unclear whether disorder would be induced by high pressure and the effect of disorder and pressure on superconductivity in Tl- and Bicuprate oxide superconductors. In this paper, by combining high-pressure synchrotron radiation X-ray diffraction and Raman spectroscopy, we have studied the structural properties and vibrational modes of underdoped double-layered Bi- cuprate oxide superconductors and nearly optimal-doped double- and triple-layered Tl- cuprate oxide superconductors under high pressure. Meanwhile, we have studied the evolution of their superconducting transition temperatures with pressure. The main results are concluded as below:(1)For the nearly optimal-doped Tl2Ba2CaCu2O8+?, the synchrotron radiation X-ray diffraction and Raman data taken under high pressure indicate the occurrence of disorder induced by pressure over 9 GPa. AC susceptibility measurements under pressure reveal that superconducting transition temperature rises with enhanced pressure at first, then reaches maximum around 7 GPa, and is suppressed with more pressure. This parabolic-like Tc-P behavior is determined by the pressure and its induced disorder.(2)For the nearly optimal-doped Tl2Ba2Ca2Cu3O10+?, AC susceptibility measurements indicate that superconducting transition temperature rises with enhanced pressure at first, and then reaches maximum around 8 GPa. However, superconducting transition temperature is not monotonically suppressed with more pressure. Instead, it rises again around 15 GPa. Above that, superconducting transition temperature is monotonically suppressed. This unique behavior could be induced by the cooperation of the outer Cu-O layer and the activation of inner Cu-O layer under the pressure ranged from 8 to 15 GPa. In similar pressure range, the Raman spectra also reveal the occurrence of vibrational modes in the wavelength of 400-500 and 200-250cm-1, which could be attributed to the activation of inner Cu-O layer. Both Raman spectral and synchrotron radiation X-ray diffraction data show the occurrence of disorder induced by pressure over 17 GPa. In conclusion, we believe the unique behavior of superconducting transition temperature under the pressure ranged from 8 to 15 GPa is due to the cooperation of the outer Cu-O layer and the activation of inner Cu-O layer, and the monotonic decrease of superconducting transition temperature is due to the disorder induced by pressure.(3)For the underdoped Bi2Sr2CaCu2O8+?, AC susceptibility measurements under pressure indicate superconducting transition temperature reaches maximal value of 73 K around 17.5 GPa and monotonically decreases with enhanced pressure. Its structure begins to collapse around 17.3 GPa, and completed around 23 GPa. The anomaly behavior of the micro-stress and 2c/(a+b) above 20 GPa combined with the sudden broaden of half-width of Raman vibrational modes indicate the occurrence of disorder induced by pressure. In conclusion, the parabolic-like Tc-P behavior is decided by both pressure and its induced disorder.(4)For the the nearly optimal-doped Bi2Sr2CaCu2O8+?, AC susceptibility measurements under pressure indicate superconducting transition temperature reaches maximal value of 102 K around 10 GPa and monotonically decreases with enhanced pressure. The synchrotron radiation X-ray diffraction taken under high pressure indicate the occurrence of disorder induced by pressure over 10 GPa. In conclusion, the parabolic-like Tc-P behavior is decided by both pressure and its induced disorder. |
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