Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A62: Undisguised View of the Mott TransitionInvited
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Sponsoring Units: DCMP Chair: Martin Dressel, University of Stuttgart Room: BCEC 258C |
Monday, March 4, 2019 8:00AM - 8:36AM |
A62.00001: Inequivalence of the zero-momentum Limits of Transverse and Longitudinal Dielectric Response in the Cuprates Invited Speaker: Chandan Setty In this talk, I will address the question of the mismatch between the zero momentum limits of the transverse (optical conductivity) and longitudinal (momentum resolved EELS) dielectric functions observed in the cuprates. This question translates to whether or not the order in which the longitudinal and transverse momentum transfers are taken to zero commute. While the two limits commute for both isotropic and anisotropic Drude metals, I will argue that a scaleless vertex interaction is sufficient to achieve non-commutativity of the two limits even for a system that is inherently isotropic. |
Monday, March 4, 2019 8:36AM - 9:12AM |
A62.00002: Quasi-Continuous Mott Transition from a Spin Liquid to a Fermi Liquid at Low Temperatures Invited Speaker: Tetsuya Furukawa For a long time, the Mott transition has been believed to be the first-order transition with a clear discontinuity at low temperatures, as shown by various experiments and the celebrated dynamical mean-field theory. Recent theoretical works, however, suggest that the transition can be continuous if the Mott insulator carries a spin liquid with a spinon Fermi surface[1,2]. Indeed, recent several experimental studies have suggested the existence of such spin liquids[3]; an organic triangular-lattice system κ-(ET)2Cu2(CN)3 is one of the spin-liquid candidates with a spinon Fermi surface. In the present study, we demonstrate the case of a quasi-continuous Mott transition from a Fermi liquid to a spin liquid in κ-(ET)2Cu2(CN)3[4]. We performed electric transport experiments under fine pressure tuning and found that as the Mott transition is approached, the Fermi-liquid coherence temperature continuously falls to the scale of kelvins, with a divergent quasi-particle decay rate on the metal side, and the charge gap gradually closes on the insulator side. A Clausius-Clapeyron analysis of the pressure-temperature phase diagram provides thermodynamic evidence for the extremely weak first-order nature of the Mott transition. These findings provide additional support for the existence of a spinon Fermi surface, which becomes an electron Fermi surface when charges are delocalized. |
Monday, March 4, 2019 9:12AM - 9:48AM |
A62.00003: Coherent Spin Excitations and Correlated Fermi Liquid in Genuine Mott Systems Invited Speaker: Andrej Pustogow Recent success in determining the electronic correlation strength in Mott insulators by means of optical spectroscopy [1] enables a quantitative comparison among (i) different materials and (ii) between experiment and theory. We identify frustrated molecular conductors as ideal realizations of the single-band Hubbard model in contrast to transition-metal oxides with a more complicated band structure, such as the charge-transfer insulator Herbertsmithite [2]. This finally allows us to selectively probe specific regions in the unified phase diagram and unveil exotic phenomena in absence of magnetic order [1,3]. Deep in the insulating state of a quantum spin liquid, coherent spin excitations show up in the optical conductivity when the charge degrees of freedom are sufficiently suppressed within the Mott gap [3,4]. Turning to the correlated metallic state, we can unambiguously identify the spectral features of coherent and bad-metallic transport. We observe a pronounced quadratic temperature and frequency dependence of the scattering rate in the Fermi-liquid state. All data collapse on a generalized energy scale in excellent agreement with the theoretical framework of Landau and Gurzhi from the 1950's. We monitor the effective mass enhancement as correlations increase and infer that the Fermi liquid retains its intrinsic properties towards the Mott transition. |
Monday, March 4, 2019 9:48AM - 10:24AM |
A62.00004: A unified perspective on cuprates and layered organic superconductors Invited Speaker: Andre-Marie Tremblay Layered organic superconductors of the BEDT family are model systems for understanding the interplay of the Mott transition with magnetic order and frustration, ingredients that are essential to understand superconductivity also in cuprate high-temperature superconductors. Cellular Dyanmical Mean-Field Theory yields a unified theoretical perspective on the corresponding phase diagrams containing superconducting, antiferromagnetic and spin-liquid phases. In particular, the superconducting dome is tied to the Mott transition and its continuation as a transition (Sordi transition) separating pseudogap phase from correlated metal in doped BEDT compounds, as in the cuprates. Contrary to heavy fermions, the maximum of the dome is not attached to an antiferromagnetic quantum critical point. The experimental superfluid stiffness shows highly non-BCS behavior that can also be explained. A few experimental predictions follow. In particular, destroying superconductivity with a magnetic field in the doped compounds should reveal the normal state transition between pseudogap and correlated metal. |
Monday, March 4, 2019 10:24AM - 11:00AM |
A62.00005: Electron-Hole Doping Asymmetry of Superconductivity in a Strain-Tuned Organic Mott Transistor Invited Speaker: Yoshitaka Kawasugi Yoshitaka Kawasugi : The electron correlation in solids, or the Mott physics, offers intriguing phenomena in materials such as unconventional superconductivity. The key parameters for controlling the Mott physics are the electronic band filling and bandwidth. However, the simultaneous control of these parameters has been lacking so far, leaving a comprehensive phase diagram of correlated materials inaccessible. By combining electrostatic doping and bending-strain techniques, we are able to control the band filling and bandwidth of an organic Mott insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl in a single sample. As a result, doping-asymmetric ambipolar superconductivity has been observed in the proximity of the Mott transition. |
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