Quantum Fluctuations & Vortex Dynamics in Cuprate Superconductor

1. (H  c) Vortex Liquid Hc2(T) H HM(T) Vortex Glass HG(T) Bragg Glass Hc1(T) 0 Tc T Habc2(0) Habc2(T) Habirr(T) Tc Quantum Fluctuations & Vortex Dynamics in Cuprate Superconductor Nai-Chang Yeh,California Institute of Technology, DMR 0405088 • Intellectual Merit: It is well established that high-temperature superconducting cuprates are extreme type-II superconductors that exhibit strong fluctuation effects in their vortex state. However, little has been considered for the microscopic origin that leads to these macroscopic phenomena. We have recently established the connection between the strong fluctuation effects in the vortex state and the proximity of the cuprates to a quantum criticality that separates a pure superconducting (SC) state from a coexisting state of SC and competing orders (CO). By applying magnetic fields parallel to the CuO2 plane and studying its vortex dynamics at the lowest temperature (T ~ 0) to minimize the disorder and thermal fluctuations, we still find strong suppression of the magnetically irreversible vortex state, implying large quantum fluctuations. The degree of quantum fluctuations of the cuprates, as manifested by the macroscopic magnetic properties and vortex phase diagrams (Fig.1), is correlated with the its microscopic proximity to the quantum criticality and the quasiparticle spectra. • Publications emanated from this support in FY2005: • V. S. Zapf et al, Phys. Rev. B 71, 134526 (2005). • N.-C. Yeh et al, Int. J. Mod. Phys. B 19, 285 (2005). • N.-C. Yeh et al, Chinese J. Phys. 43, 505 Suppl. 2 (2005). • N.-C. Yeh et al, Proceedings of SPIE 5932 (2005), invited paper, • accepted for publication. • N.-C. Yeh et al, Physica C 408-410, 792 (2004). Fig.1: Effects of quantum, thermal and disorder fluctuations on vortex phase diagrams of cuprates (Dominant thermal & disorder fluctuations) (Dominant thermal & disorder fluctuations, weak quantum fluc.) (Strong quantum fluctuations at T  0 due to competing orders) Experimental: Theoretical: Hirr(T): irreversible field Hc2(T): upper critical field Hc20 = Hc2(T=0) S(X): vortex smectic (crystal) IS(IX): incommensurate S(X) VL: vortex liquid Representative experimental results from Hg-1234 (HgBa2Ca3Cu4Ox) and La-112 (Sr0.9La0.1CuO2) for H || ab, consistent with strong quantum fluctuations at T  0.

2. Mean-field Mean-field theory not applicable;  stronger quantum fluctuations. Mean-field theory applicable  weaker fluctuations. Quantum Fluctuations & Vortex Dynamics in Cuprate Superconductors Nai-Chang Yeh,California Institute of Technology, DMR 0405088 • Broader Impact: Better understanding of the vortex dynamics in superconductors is crucial for a wide range of applications. In general, strong fluctuations in the vortex state are not desirable because they lead to dissipation at a finite time scale. With the establishment of the microscopic origin for strong fluctuations in the vortex state of cuprate superconductors, we can better decide on which cuprates to use in device applications. Specifically, our studies suggest that it is advisable to choose cuprates farther away from the “quantum criticality” that separates a pure SC phase from a coexisting SC and CO phase in zero magnetic field (H) so as to minimize fluctuation effects. In Fig. 3 we compile a list of cuprates that have been studied by us to reveal their different proximity to the quantum criticality at ac(a: a material parameter, closer to ac corresponds to stronger quantum fluctuations),and we recommend that cuprates such as YBa2Cu3O7-x are better candidates for device applications. • Education: • Trainees involved in this research • Graduate students: Ching-Tzu Chen, Andrew D. Beyer, • Cameron R. Hughes, Marcus Teague • Postdoctoral scholar: Slobodan Mitrovic • Undergraduate student: Victor Alvarez • Honor received by the PI • Elected Fellow, American Physical Society (2004). Fig.3: Determining the proximity of different cuprates to the quantum criticality (at a = ac) from experiments h*(a): A characteristic field obtained from the vortex-state magnetic measurements, normalized to the upper critical field Hc2 || CuO2 planes Hg-1245: HgBa2Ca4Cu5Ox Hg-1234: HgBa2Ca3Cu4Ox La-112: Sr0.9La0.1CuO2 Y-123: YBa2Cu3O7-x SC: superconductivity CO: competing order N: normal state (See publications listed in the previous slide for details) Fig.4: Microscopic verification of quantum fluctuations using scanning tunneling spectroscopy