Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session R66: Exploring the Relation Between Electron Nematicity and Superconductivity in Strongly Correlated Electronic SystemsInvited
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Sponsoring Units: DCMP Chair: Daniel Arovas, University of California, San Diego Room: Four Seasons 1 |
Thursday, March 5, 2020 8:00AM - 8:36AM |
R66.00001: Strain sensitivity and other experimental consequences of nematic-mediated superconductivity Invited Speaker: Samuel Lederer In many unconventional superconductors, nematic quantum fluctuations are strongest where the critical temperature is highest, inviting the conjecture that nematicity plays an important role in the pairing mechanism. Recently, strontium-doped barium nickel oxide has been identified as a tunable nematic system that provides an ideal testing ground for this proposition. We therefore propose several sharp empirical tests, supported by quantitative calculations in a simple model of this material. The most stringent predictions concern experiments under uniaxial strain, which has recently emerged as a powerful tuning parameter in the study of correlated materials. Since uniaxial strain so precisely targets nematic fluctuations, such experiments may provide compelling evidence for nematic-mediated pairing in this and other materials, analogous to the isotope effect in conventional superconductors. |
Thursday, March 5, 2020 8:36AM - 9:12AM |
R66.00002: Sixfold enhancement of superconductivity in a tunable electronic nematic system Invited Speaker: Johnpierre Paglione The electronic nematic phase - in which electronic degrees of freedom lower the crystal rotational symmetry - is commonly observed in high-temperature superconductors. However, understanding the role of nematicity and nematic fluctuations in Cooper pairing is often made more complicated by the coexistence of other orders, particularly long-range magnetic order. Here we report the enhancement of superconductivity in a model electronic nematic system that is not magnetic, and show that the enhancement is directly born out of strong nematic fluctuations associated with a quantum phase transition. We present measurements of the resistance as a function of strain in Ba$_{1-x}$Sr$_{x}$Ni$_2$As$_2$ to show that strontium substitution promotes an electronically-driven nematic order in this system. In addition, the complete suppression of that order to absolute zero temperature leads to an enhancement of the pairing strength, as evidenced by a sixfold increase in the superconducting transition temperature. The direct relation between enhanced pairing and nematic fluctuations in this model system, as well as the interplay with a unidirectional charge density wave order comparable to that found in the cuprates, offers a means to investigate the role of nematicity in boosting superconductivity. |
Thursday, March 5, 2020 9:12AM - 9:48AM |
R66.00003: Atomic-scale Interplay of the Charge Density Wave, Pair Density Wave and Nematic States of Cuprates. Invited Speaker: J.C. Seamus Davis The antiferromagnetic insulator state of CuO2 is transformed by hole-doping onto the oxygen sites, into an exotic quantum fluid that is usually referred to as the pseudogap (PG) phase. Its defining characteristic is a strong suppression of the electronic density-of-states for energies E<D, where D is the pseudogap energy scale. Within the pseudogap phase, complex broken-symmetry phases have been detected by a very wide variety of techniques. First, there is the finite-Q charge-density-wave (CDW) state that is locally commensurate and unidirectional, with 4a0 periodicity and a d-symmetry form factor. Second, is the finite-Q pair-density-wave (PDW) state which is detected with superconducting-tip STM as having a 4a0 periodicity in the magnitude of Josephson currents and an 8a0 periodicity in its energy-gap modulations. Third, there is the nematic (NE) state which breaks rotational symmetry at Q=0. |
Thursday, March 5, 2020 9:48AM - 10:24AM |
R66.00004: Strain-tuning nematic order and signatures of nematic quantum criticality Invited Speaker: Ian Fisher Quantum criticality associated with electronic nematic order has been suggested as a possible avenue for a range of exotic electronic effects, from non-Fermi liquid behavior to superconductivity. In order to study the behavior of metals proximate to such a quantum critical point, it is useful to establish effective tuning parameters that can drive the critical temperature of an electronic nematic phase to zero. I will describe how both symmetric and orthogonal antisymmetric strains can play this role, and demonstrate these effects in an archetypal Fe-based superconductor. For compositions progressively closer to the putative nematic quantum critical point, these tuning parameters become increasingly more effective, the precise variation of which provides evidence for a wide range of composition and temperature over which quantum critical fluctuations play a key role in shaping the properties of this family of materials. Additional evidence can be found in the temperature and doping dependence of the nematic suceptibility, which, by applying large magnetic fields, can be measured in the absence of superconductivity down to low temperatures. Further insights can be obtained by consideration of other model material systems, in particular materials that undergo ferroquadrupolar order of local 4f atomic orbitals. |
Thursday, March 5, 2020 10:24AM - 11:00AM |
R66.00005: Divergent nematic susceptibility near the pseudogap critical point in Bi-cuprate superconductors Invited Speaker: Takasada Shibauchi In strongly correlated materials, superconductivity is often found near a magnetic quantum critical point (QCP) where a magnetic phase vanishes in the zero-temperature limit. Moreover, the maximum of superconducting transition temperature Tc frequently locates near the magnetic QCP, suggesting that the proliferation of critical spin fluctuations emanating from the QCP plays an important role in Cooper pairing. In cuprate superconductors, however, the superconducting dome is usually separated from the antiferromagnetic phase and Tc attains its maximum value near the verge of enigmatic pseudogap state that appears below doping-dependent temperature T*. Thus a clue to the pairing mechanism resides in the pseudogap and associated anomalous transport properties. Recent experiments suggested a phase transition at T* but the key question is what kind of fluctuations are associated with the pseudogap. Here we report elastoresistance measurements of nematic susceptibility in (Bi,Pb)2Sr2CaCu2O8+δ, which is sensitive to an electronic order with twofold in-plane anisotropy. The nematic susceptibility shows an anomaly at T* evidencing a phase transition with broken rotational symmetry. Near the pseudogap end point, nematic susceptibility becomes singular and divergent. This signifies the presence of a nematic QCP, which has emerging links to the high-Tc superconductivity and strange metallic behaviours in cuprates. |
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