Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session W40: Invited Session: Electronic Correlations in Unconventional Superconductors |
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Sponsoring Units: DCMP Chair: Dung-Hai Lee, University of California, Berkeley Room: Mile High Ballroom 2B-3B |
Thursday, March 6, 2014 2:30PM - 3:06PM |
W40.00001: Angular fluctuations of a multi-component order describe the pseudogap regime of the cuprate superconductors Invited Speaker: Subir Sachdev The hole-doped cuprate high temperature superconductors enter the pseudogap regime as their superconducting critical temperature, $T_c$, falls with decreasing hole density. Experiments have probed this regime for over two decades, but we argue that decisive new information has emerged from recent X-ray scattering experiments. The experiments observe incommensurate charge density wave fluctuations whose strength rises gradually over a wide temperature range above $T_c$, but then decreases as the temperature is lowered below $T_c$. We propose a theory in which the superconducting and charge-density wave orders exhibit angular fluctuations in a 6-dimensional space. The theory provides a natural quantitative fit to the X-ray data, and is consistent with other observed characteristics of the pseudogap. Results will also be presented on the microscopic origins of these order parameters. [Preview Abstract] |
Thursday, March 6, 2014 3:06PM - 3:42PM |
W40.00002: Quantum critical point underlying the pseudogap state in underdoped cuprate superconductors Invited Speaker: Catherine Pepin Cuprate superconductors rank among the most complex materials that are known in the universe. Faced with this complexity, scientists have adopted two types of approaches. In a bottom up approach, one considers that strong correlations occur at a high energy scale of roughly 1 eV upon very strong Coulomb interactions. In the top down approach one considers that one universal singularity at very low temperatures is responsible for complexity of the phase diagram. In this talk we will argue that the strong quantum fluctuations experienced at the proximity to a anti-ferromagnetic Quantum Critical Point (QCP) is responsible for a cascade of phase transitions in the charge and superconducting channels. We will discuss in this context the emergence of the pseudo-gap and charge order modulations. Symmetries and relations to experimental observations will be addressed. [Preview Abstract] |
Thursday, March 6, 2014 3:42PM - 4:18PM |
W40.00003: A universal order underlying the pseudogap regime of the underdoped high $T_{\rm c}$ cuprates Invited Speaker: Neil Harrison A major achievement in condensed matter physics in the last quarter century has been a step towards the understanding of the unconventional d-wave superconducting state in the copper-oxide materials. Surprisingly, the normal state out of which the superconducting state emerges remains a mystery at low charge carrier densities, i.e., in the underdoped regime. This regime is of particular interest because it is characterised by an unusual momentum dependent energy pseudogap in the excitation spectrum that has defied explanation and is key to a full understanding of the unconventional d-wave superconducting state. I will present new quantum oscillation experimental results within the pseudogap regime of the high $T_{\rm c}$ superconductors YBa$_2$Cu$_3$O$_{6+x}$ and YBa$_2$Cu$_4$O$_8$ which now extend up to the optimally-doped regime. These data reveal the evolution of the Fermi surface approaching the putative quantum critical point under the superconducting dome. A comprehensive angle-resolved study of the Fermi surface enables us to unambiguously identify a specific form of order that accounts for the observed quantum oscillations as well as other spectroscopic, transport and thermodynamic probes within the pseudogap regime. The author would like to thank B. Ramshaw, S. Sebastian, F. Balakirev, C. Mielke, M. Altarawneh, P. Goddard, S. Sabok, B. Babrowski, D. Bonn, W. Hardy, R. Liang and G. Lonzarich. [Preview Abstract] |
Thursday, March 6, 2014 4:18PM - 4:54PM |
W40.00004: Electron Correlations and Superconductivity in Iron Pnictides and Chalcogenides Invited Speaker: Qimiao Si In the iron pnictides, the bad metal behaviour in the normal state suggests the importance of electron correlations, which is further underscored by the existence of a Mott insulator state in the overall phase diagram of the iron chalcogenides. This has motivated a strong-coupling approach based on a proximity to the Mott transition. In this talk, I will briefly summarize earlier theoretical studies within this approach, which led to the proposal for a quantum critical point in the isoelectronically tuned iron pnictides [1]; this has since been verified in the P-doped iron arsenides. I will in addition show how the approach provides a natural understanding of a major issue in the field, namely the superconducting $T_c$ of the iron chalcogenides is comparably high as in the iron pnictides in spite of their qualitatively distinct Fermi surfaces [2]. I will also consider the multi-orbital aspects of the electron correlations more generally, including a proposed orbital-selective Mott phase [3] in the normal state and implications for gap anisotropy and spin resonances [4] in the superconducting state. Finally, I will discuss how these results expand on the notion [5] that the iron-based superconductivity primarily originates from strong electron correlations, as well as some implications for the general phenomenon of unconventional superconductivity at the border of magnetism. \\[4pt] [1] J. Dai, Q. Si, J.-X. Zhu, \& E. Abrahams, PNAS {\bf 106}, 4118 (2009). \\[0pt] [2] R. Yu, P. Goswami, Q. Si, P. Nikolic, \& J.-X. Zhu, Nat. Commun. {\bf 4}, 2783 (2013). \\[0pt] [3] R. Yu and Q. Si, Phys. Rev. Lett. {\bf 110}, 146402 (2013); M. Yi et al., Phys. Rev. Lett. {\bf 110}, 067003 (2013). \\[0pt] [4] R. Yu, J.-X. Zhu, \& Q. Si, arxiv:1306.4184; C. Zhang et al., Phys. Rev. Lett. {\bf 111}, 207002 (2013). \\[0pt] [5] Q. Si and E. Abrahams, Phys. Rev. Lett. {\bf 101}, 076401 (2008). [Preview Abstract] |
Thursday, March 6, 2014 4:54PM - 5:30PM |
W40.00005: Emergence of superconductivity, valence bond order and Mott insulators in Pd[(dmit)2] based organic salts Invited Speaker: Hae-Young Kee The EtMe$_3$P and EtMe$_3$Sb nearly triangular organic salts are distinguished from most other Pd[(dmit)$_2$] based salts, as they display valence bond and no long range order, respectively. Under pressure, a superconducting phase is revealed in EtMe$_3$P near the boundary of valence bond order. We use slave-rotor theory with an enlarged unit cell to study competition between uniform and broken translational symmetry states, offering a theoretical framework capturing the superconducting, valence bond order, spin liquid, and metallic phases on an isotropic triangular lattice. Our finite temperature phase diagram manifests a remarkable resemblance to the phase diagram of the EtMe$_3$P salt, where the re-entrant transitions of the type insulator-metal-insulator can be explained by an entropy difference between metal and the U(1) spin liquid. We find that the superconducting pairing symmetry is $d \pm i d$, and predict different temperature dependences of the specific heat between the spin liquid and metal. [Preview Abstract] |
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