Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session A22: Nano-scale Perspectives on Phase Transitions in Correlated OxidesInvited
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Sponsoring Units: DCMP Chair: Dmitri Basov, Columbia University Room: New Orleans Theater A |
Monday, March 13, 2017 8:00AM - 8:36AM |
A22.00001: Electronic structure and electronic order in lightly doped cuprates studied by STM Invited Speaker: Yayu Wang Although the mechanism of superconductivity in the cuprates remains elusive, it is generally agreed that at the heart of the problem is the physics of doped Mott insulators. A crucial step for solving the high temperature superconductivity puzzle is to elucidate the electronic structure of the parent compound and the behaviour of doped charge carriers. In this talk we report recent scanning tunnelling microscopy studies of the atomic-scale electronic structure and electronic order in the parent and lightly doped cuprates in the antiferromagnetic insulating regime. In the parent compound, the full electronic spectrum across the Mott--Hubbard gap, or more precisely the charge transfer gap, is uncovered by scanning tunnelling spectroscopy. The size of the charge transfer gap shows strong variations for different cuprate families, and may have important implications to the maximum transition temperature that can be achieved at optimal doping. Defect-induced charge carriers are found to create broad in-gap electronic states that are strongly localized in space. In lightly doped insulating Bi-2201 compound, we find that the main effect of charge doping is to induce a spectral weight transfer from the high energy Hubbard band to the low energy in-gap states. At sufficiently high doping, a sharp energy gap reminiscent of the pseudogap starts to form near the Fermi level, and is accompanied by the emergence of a checkerboard-like charge order. Our results demonstrate that the first ordered phase in the doped Mott insulator is a charge ordered insulator, which will gradually evolve into the superconducting state upon further doping. [Preview Abstract] |
Monday, March 13, 2017 8:36AM - 9:12AM |
A22.00002: Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning. Invited Speaker: Yasutomo Uemura RENiO$_{\mathrm{3}}$ (RE $=$ rare-earth element) and V$_{\mathrm{2}}$O$_{\mathrm{3}}$ are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO$_{\mathrm{3}})$ or hydrostatic pressure (V$_{\mathrm{2}}$O$_{\mathrm{3}})$, they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. We demonstrate through muon spin relaxation/rotation ($\mu $SR) experiments that the QPT in RENiO$_{\mathrm{3}}$ and V$_{\mathrm{2}}$O$_{\mathrm{3}}$ is ?rst order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. [1] These two cases correspond to the band-width tuning of Mott transitions, and also associated with structural phase transitions, Volume evolutions of antiferromagnetic transition from $\mu $SR will be compared to those of structure by x-ray and metallicity by nano optics, in first-order thermal Mott transition in a V$_{\mathrm{2}}$O$_{\mathrm{3}}$ film at ambient pressure. These results will be compared to the process of destruction of magnetic order in another Mott transition system Ba(Co,Ni)S$_{\mathrm{2}}$ in ``filling control'' without structural transition, and in parent compounds of high-Tc cuprates and Fe-based superconductors. We will also discuss roles of first-order quantum transition in generating soft modes relevant to magnetic resonance mode in unconventional superconductors [2]. Work performed in collaboration with the groups of: J.A. Alonso (Madrid), H. Kageyama (Kyoto). E. Morenzoni (PSI), G.M. Luke (McMaster), C.Q. Jin (IOP Beijing), F.L. Ning (Zhejian), S.J.L. Billinge (Columbia), S. Shamoto, W. Higemoto (JAEA), A. Fujimori (Tokyo), A. Gauzzi (Paris), R. de Renzi (Parma), G. Kotliar (Rutgers), M. Imada (Tokyo), D. Basov (UCSD), I, Schuller (UCSD). [1] B.A. Frandsen et al., Nature Communications 7 (2016) 12519. [2] Y.J. Uemura, Nature Materials 8 (2009) 253-255. [Preview Abstract] |
Monday, March 13, 2017 9:12AM - 9:48AM |
A22.00003: Nanotextured phase coexistence in the correlated insulator V$_{\mathrm{2}}$O$_{\mathrm{3}}$ Invited Speaker: Alexander McLeod The Mott insulator--metal transition remains among the most studied phenomena in correlated electron physics. However, the formation of spontaneous spatial patterns amidst coexisting insulating and metallic phases remains poorly explored on the meso- and nanoscales. Here we present real-space evolution of the insulator--metal transition in a thin film of V$_{\mathrm{2}}$O$_{\mathrm{3}}$, the ``canonical'' Mott insulator, imaged at high spatial resolution by cryogenic near-field infrared microscopy. We resolve spontaneously nanotextured coexistence of metal and correlated Mott insulator phases near the insulator--metal transition ($T \quad =$ 160--180 K) associated with percolation and an underlying structural phase transition. Augmented with macroscopic temperature-resolved X-ray diffraction measurements of the same film, a quantitative analysis of nano-infrared images acquired across the transition suggests decoupling of electronic and structural transformations. Persistent low-temperature metallicity is accompanied by unconventional dimensional scaling among metallic ``puddles,'' implicating relevance of a long-range Coulombic interaction through the film's first-order insulator--metal transition. [Preview Abstract] |
Monday, March 13, 2017 9:48AM - 10:24AM |
A22.00004: New Insight into the Metal-to-Insulator Transition in Vanadium Dioxide. Invited Speaker: Kevin E. Smith The metal-insulator transition (MIT) in VO$_{2}$ is of both fundamental and technical interest, the former due to important questions about its origins, and the latter due to possible applications in electronic devices such as ultrafast optical switches and field effect transistors. In bulk VO$_{2}$, a large structural distortion accompanies the conductivity transition from the metallic (rutile) to the insulating (monoclinic) phase, which is known to impose a significant bottleneck on the timescale of the transition. Recently, the ability to control the transition temperature of the MIT in VO$_{2}$ through chemical doping and/or nanoscale engineering has heralded renewed interest in VO$_{2}$ as a novel functional material. I will present the results of synchrotron radiation-excited photoemission, x-ray emission, and x-ray absorption spectroscopy studies of the MIT in strained VO$_{2}$ thin films. Our results reveal that the MIT may be driven towards a purely electronic transition, (i.e. one without a crystal symmetry transition), by the application of mechanical strain. Comparison with a moderately strained system, which does involve the lattice, demonstrates a crossover from Peierls-like to Mott-like transitions. We furthermore have observed striped phases through the transition, and these reveal new information on the nature of the MIT. [Preview Abstract] |
Monday, March 13, 2017 10:24AM - 11:00AM |
A22.00005: Spatial complexity in correlated electronic systems Invited Speaker: Erica Carlson There is growing experimental evidence that many strongly correlated electronic systems such as vanadium oxides, cuprates, and nickelates (among others) exhibit nano- and meso-scale variations in the local electronic properties. The interplay of many degrees of freedom and strong correlations can lead to competing electronic phases. In the environment of a host crystal, disorder can act as nucleation points for these competing states, leading to spatial complexity and multiscale pattern formation.[1] Rapidly expanding experimental capabilities have led to a growing wealth of data on multiple length scales, revealing rich electronic textures at the nanoscale and mesoscale in many correlated oxides. We have developed a new conceptual framework for interpreting the wealth of spatial information contained in the geometric properties of these textures.[2,3] By importing geometric cluster analysis techniques from disordered statistical mechanics, we identify universal scaling properties of the spatial complexity in strongly correlated materials. Because of the long equilibration times associated with these patterns, we expect glassiness and hysteresis effects to be prominent in strongly correlated systems with competing phases.[4] [1] E. Dagotto, Science 309, 257 (2005). [2] B. Phillabaum et al., Nature Commun. 3, 915 (2012). [3] S. Liu et al., Phys. Rev. Lett. 116, 036401 (2016). [4] E. W. Carlson and K. A. Dahmen, Nature Commun., 2, 379 (2011). [Preview Abstract] |
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