Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K37b: Metal Insulator Phase Transitions II: Experiment |
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Sponsoring Units: DCMP Chair: Tiglet Besara, National High Magnetic Field Laboratory: Florida State University Room: 384 |
Wednesday, March 15, 2017 8:00AM - 8:12AM |
K37b.00001: Complex magnetic fluctuations and their consequences in bilayer ruthenate Ca$_3$Ru$_2$O$_7$ probed by “$k$-dependent” magneto thermoelectric measurements Hui Xing, Libin Wen, Jiaming He, Shun Wang, Chenyi Shen, Jin Peng, Jian-jian Ge, Minglian Tian, Zhuan Xu, Zhiqiang Mao, Wei Ku, Ying Liu The bilayer ruthenate Ca$_3$Ru$_2$O$_7$ is among the most interesting 4d and 5d transition metal oxides, featuring a complex structure-property relation as well as correlated effects, especially those originating from magnetic fluctuations. The underlying electronic states and the transport mechanism, especially that below the metal-nonmetal transition, highlighted by the emergence of a coherent state at low temperature, remains to be understood. Here we provide evidence from our magneto transport and thermoelectric transport measurements that two Fermi pockets with opposite carriers dominate the transport property at low temperatures, with the electron pocket prevailing due to the increased electron mean free path. We find a strong energy dependence of the conductance on at least the dominating Fermi surfaces, pointing to a significant carrier scattering due to magnetic fluctuation in this system. This mechanism is further corroborated by the anisotropic magnetoresistance in the AFM-b magnetic phase, where the application of an external magnetic field will enhance or depress the magnetic fluctuations depending on the magnetic field orientation. [Preview Abstract] |
Wednesday, March 15, 2017 8:12AM - 8:24AM |
K37b.00002: Spin easy axis switching from the out-of-plane to in-plane direction driven by 2{\%} Fe doping in Sr$_{\mathrm{\mathbf{4}}}${Ru}$_{\mathrm{\mathbf{3}}}${O}$_{\mathrm{\mathbf{10}}}$ Peigang Li, Yanglin Zhu, Jinyu Liu, Yu Wang, Zhiqiang Mao Sr$_{\mathrm{4}}$Ru$_{\mathrm{3}}$O$_{\mathrm{10}}$, a layered strongly correlated system, has been known as an itinerant ferromagnet with T$_{\mathrm{C\thinspace }}$\textasciitilde 105 K $^{\mathrm{[1]}}$; its spin easy axis lies along the c-direction. A puzzling phenomenon of its FM state is that a metamagnetic transition can be induced by in-plane field $^{\mathrm{[1,\thinspace 2]}}$. In this presentation, we will report that 2{\%} Fe-doping in this material results in drastic changes in its FM properties: its spin easy axis switches from the out-of-plane to in-plane direction, whereas the metamagnetic transition takes place for the field aligned along the out-of-plane direction. These surprising phenomena could be attributed to strong lattice-orbital coupling. The possible scenario is that Fe acts as a strong scattering center, thus resulting in global structure distortion, which in turn leads to the change of the Ru 4$d_{xy}$ and $d_{xz/yzz}$ orbital states. [1] G. Cao, L. Balicas, W. H. Song, \textit{et al.} \textit{Phys. Rev. B} \textbf{68}, 174409(2003) [2] Z. Q. Mao, M. Zhou, J. Hooper, \textit{et al. }Phys. Rev. Lett. \textbf{96, }077205 (2006) [Preview Abstract] |
Wednesday, March 15, 2017 8:24AM - 8:36AM |
K37b.00003: Enhanced thermopower and ferromagnetic fluctuations in Sc-substituted CaRuO$_{3}$: An experimental study of the Kelvin formula Takafumi D. Yamamoto, Ryo Yatagai, Kenji Tanabe, Ryuji Okazaki, Hiroki Taniguchi, Yukio Yasui, Satoshi Iguchi, Takahiko Sasaki, Ichiro Terasaki We report both thermoelectric and thermodynamic properties of a non-uniform magnetic system CaRu$_{0.8}$Sc$_{0.2}$O$_3$, in which a ferromagnetic component induced by Sc$^{3+}$ is embedded in a paramagnetic component of CaRuO$_3$ [T. D. Yamamoto \textit{et al}., J. Phys. Soc. Jpn. \textbf{84}, 014708 (2015); \textbf{85}, 034711 (2016)]. Our thermoelectric measurement shows that the thermopower is significantly suppressed by a magnetic field at around a quasi-ferromagnetic transition temperature of 30 K, below which ferromagnetic clusters start to be formed. Furthermore, negative magnetic entropy change takes a maximum in the same temperature range, indicating the suppression of ferromagnetic fluctuations. We discuss the relationship of the thermopower to the spin entropy in this material based on the Kelvin formula, which has been used as a good approximate expression for strongly correlated materials. [Preview Abstract] |
Wednesday, March 15, 2017 8:36AM - 8:48AM |
K37b.00004: Local orbital fluctuations and $t2g$ degeneracy lifting in the metallic regime of CuIr$_{2}$S$_{4}$ Emil S. Bozin, Milinda Abeykoon, Alexandros Lappas, Yew San Hor, John F. Mitchell, Simon J.L. Billinge High temperature metallic regime of CuIr$_{2}$S$_{4}$ possessing Fd$\overline 3$m cubic average structure is found to exhibit local structural distortions of the pyrochlore Ir sublattice compatible with tetragonal I4$_{1}$/amd structure. X-ray total scattering based atomic pair distribution function approach further shows that the distortions are stabilized by Cr-doping induced strain fields, but remain poorly spatially correlated. Presence of such local spatially (and presumably temporally) fluctuating tetragonal distortions suggests that the $t2g$ orbital degeneracy is already lifted locally deep in the metallic regime (such a state persists up to at least 780 K), as a precursor to the metal-insulator transition (MIT) which is observed at low temperature (230 K). Underlying short range orbital ordering is limited to the nearest neighbor Ir-sites only, resembling orbital liquid-like state. This observation provides a rationale for reportedly poor and unusual metallicity at high temperature, and further suggests that the MIT can be seen, at least in part, as crystallization into a long-range orbitally ordered lattice. Notably, Ir-dimer order seen in the insulating phase melts across the MIT on all length-scales, and no dimers survive in the metallic state, as reported earlier. [Preview Abstract] |
Wednesday, March 15, 2017 8:48AM - 9:00AM |
K37b.00005: Magnetotransport properties of BaMn$_2$Pn$_2$ compounds Khuong K. Huynh, Keita Kitahara, Takuma Ogasawara, Satoshi Heguri, Yoichi Tanabe, Katsumi Tanigaki We report interesting magnetotransport properties observed in BaMn$_2$Pn$_2$ (BMPn, with Pn = As, Sb, Bi) systems. BMPn materials have the same layered crystal structure with that of BaFe$_2$As$_2$, one of the parent compounds for iron-based superconductors. The large Hund's coupling in the half-filled $3d^5$ orbitals promotes a localized high spin state of Mn$^{2+}$ ions and results in a G-type antiferromagnetic insulator with a fairly high $T_{\mathrm{N}}$ [1, 2]. Our experiments show that the resistivities in all BMPn's have complex dependencies on both temperature and magnetic field. Measurements of resistivity under magnetic fields indicate sizable and anisotropic magnetoresistance that vary strongly with temperature. On the other hand, a detailed analysis of the temperature dependencies of the resistivity indicates a transition-like feature at which the behaviors of magnetoresistance and Hall effect completely change. Interestingly, by changing the pnictide site in BMPn from As to Bi, the features of the magnetotransport properties are systematically varied.\\ 1. Singh \emph{et al}, PRB 79, 2, (2009).\\ 2. McNally \emph{et al}, PRB 92, 115142 (2015). [Preview Abstract] |
Wednesday, March 15, 2017 9:00AM - 9:12AM |
K37b.00006: High field fermiology of the metallized Mott insulator NiS$_2$ Jordan Baglo, Hui Chang, Konstantin Semeniuk, Xiaoye Chen, Pascal Reiss, Hong En Tan, Patricia Alireza, Alix McCollam, Inge Leermakers, Sven Friedemann, Monika Gamza, Audrey Grockowiak, William Coniglio, Stanley Tozer, F. Malte Grosche Long a prominent theme in the physics of strongly correlated electron systems, the Mott metal-to-insulator transition continues to be an active topic of investigation; various mechanisms have been proposed for the formation of the Mott insulating state, but its precise nature remains an open question. In many such systems under study, filling (via chemical doping) is used as a tuning parameter, but the resultant disorder hinders the use of sensitive quantum oscillation techniques to study Fermi surface properties. In the prototypical Mott insulator NiS$_2$, one can instead use pressure to cleanly tune the ratio $U/t$ of onsite Coulomb repulsion to kinetic energy across the phase diagram. We will present our recent quantum oscillation measurements of NiS$_2$ under hydrostatic pressures from near the Mott transition up to 55 kbar, comparing the evolution of the Fermi surface and effective masses upon approaching the Mott transition to expectations from DFT calculations. We observe a large Fermi surface persisting to the transition along with a divergent effective mass, consistent with a Brinkman-Rice picture. [Preview Abstract] |
Wednesday, March 15, 2017 9:12AM - 9:24AM |
K37b.00007: Doping dependent correlation effects in (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$ Gregory Affeldt, Tom Hogan, Jonathan Denlinger, Stephen Wilson, Alessandra Lanzara The layered perovskite iridate Sr$_3$Ir$_2$O$_7$ exhibits a spin-orbit Mott insulating state due to both strong spin-orbit coupling and electron-electron correlations, which gives way to a metallic state upon carrier doping. We will show ARPES results illustrating the changing signatures of electronic correlations with doping in (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$, and discuss connections to other doped Mott insulators. [Preview Abstract] |
Wednesday, March 15, 2017 9:24AM - 9:36AM |
K37b.00008: Visualizing spatial electronic reorganization across the Mott insulating transition in Mn-doped Sr$_{3}$Ru$_{2}$O$_{7}$ Justin Leshen, Mariam Kavai, Ioannis Giannakis, Shantanu Mukherjee, Yoshio Kaneko, Yoshi Tokura, Wei-Cheng Lee, Pegor Aynajian Doped Mott insulators are susceptible to intertwined electronic ordering. A fascinating pseudogap state with a universal charge ordering intertwined with superconductivity has been the hallmark of high temperature superconducting cuprates. Here we investigate the doping induced quantum phase transition from a metallic to an AFM Mott insulating state in Sr$_{3}$(Ru$_{1-x}$Mn$_{x})_{2}$O$_{7}$ - the 4d counterpart of the 3d cuprates - using spectroscopic imaging with the scanning tunneling microscope. We visualize the evolution of the electronic states and their spatial reorganization as the system is driven through the Mott insulating state by dilute Mn doping. Our experiments reveal a complex interplay between charge spin and orbital degrees of freedom and draws similarities to cuprates and Fe pnictides. [Preview Abstract] |
Wednesday, March 15, 2017 9:36AM - 9:48AM |
K37b.00009: Thickness dependent metal-insulator transition of a correlated oxide heterostructure integrated directly on Si Kamyar Ahmadi Majlan, Tongjie Chen, Ricky Hensley, Patrick Conlin, Zheng Hui Lim, Reza Moghadam, Dong Su, Divine P. Kumah, Joseph H. Ngai Strongly correlated oxides that exhibit metal-insulator transitions have tremendous potential for use in a variety of applications, ranging from microelectronics to sensing. Integration of such correlated oxides on a technological platform such as Si is thus important. Here we show a thickness dependent metal-insulator transition in epitaxial LaTiO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$ heterostructures, that have been integrated directly on Si (100) by oxide molecular beam epitaxy. Fermi-liquid behavior and enhanced electron-electron scattering is observed in the transport characteristics as the transition to the insulating state is approached. The transition occurs well below the Mott limit and the insulating state is characterized by Arrhenius or activated-type transport. We will discuss structural changes that arise as the thickness of the LaTiO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$ heterostructures is varied, in particular the potential role that strain gradients play in driving the metal-insulator-transition. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K37b.00010: Spin-orbit coupling in strongly correlated two-dimensional systems undergoing MIT Jian Huang, Loren Pfeiffer, Ken West Experimental studies of the spin-orbit coupling (SOC) often utilize systems that lack inversion symmetries, i.e. 2D hole systems in p-GaAs heterostructures, where SOC is known to drive both classical and quantum effects. They are usually perturbations in weakly interacting systems. However, in a strongly correlated system, the effects due to the SOC-interaction interplay are more profound in relation to the exchange interaction, i.e. it leads to diverging density of states in the limit of low carrier densities. Adopting ultraclean 2D holes in undoped GaAs/AlGaAs field-effect-transistors, we have measured the magnetoresistance (MR) for a large r$_{\mathrm{s}}$ range of 20-60 (or carrier densities from 2x10$^{\mathrm{10\thinspace }}$down to 2x10$^{\mathrm{9}}$cm$^{\mathrm{-2}})$. Two unique behaviors directly linked to SOC are reported. First, in correspondence to the zero-field MIT, the sign of the MR switches, from being positive in the metallic regime to being negative in the insulating regime, when the density is lowered across the critical density of MIT (at r$_{\mathrm{s}}$\textasciitilde 39). Second, in the close vicinity of the critical density, a nonmonotonic density-dependence due to SOC results in a substantial correction to the MR beyond perturbation. This peculiar behavior echoes with a trend of delocalization long suspected for the SOC-interaction interplay. [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K37b.00011: Unique metal to insulator transition in a rare earth nickelate observed using near field microscopy Kirk Post, A.S. McLeod, M. Hepting, M. Bluschke, Yifan Wang, G. Cristiani, G. Logvenov, E. Benckiser, E.W. Carlson, B. Keimer, D.N. Basov Using scanning near-field optical microscopy (SNOM), in conjunction with resonant x-ray scattering, and far-field ellipsometry, we have uncovered unique optical behavior through the insulator-to-metal transition of the rare earth nickelate, NdNiO$_3$. Our experiments indicate that NdNiO$_3$ transitions directly between the high temperature metallic and low temperature insulating end phases, without any obvious intermediary phase in the SNOM images. Our nano-optical images also resolve the emergence of distinct real-space textures through the transition, including metallic percolation, a long-range ‘stripe’ in addition to persistent nano-scale metallic puddles, with transition temperatures in the latter two structures, suppressed relative to the overall sample. Furthermore, SNOM images show nuanced differences between warming and cooling branches of the transition, suggestive of distinct physics underlying the transition in these two regimes. [Preview Abstract] |
Wednesday, March 15, 2017 10:12AM - 10:24AM |
K37b.00012: Infrared Nano-imaging and nano-spectroscopy of phase transition in Ca$_{\mathrm{2}}$RuO$_{\mathrm{4}}$ Jiawei Zhang, Hans Bechtel, Thomas Ciavatti, Xinzhong Chen, Stephanie Corder, Ziheng Yao, Meigan Aronson, Michael Martin, Chanchal Sow, Fumihiko Nakamura, Yoshiteru Maeno, Mengkun Liu We investigated the electric-field-induced insulator-to-metal transition (IMT) in bulk single crystal Ca$_{\mathrm{2}}$RuO$_{\mathrm{4}}$. Ca$_{\mathrm{2}}$RuO$_{\mathrm{4}}$ is a 4$d$ electron transition metal oxide which has an IMT above 358 K. By applying a DC voltage above the threshold of 40 V/cm, a discontinuous conductivity jump can be readily observed with a dramatic change of electron and phonon signatures at the infrared frequency range. With infrared nano-imaging and nano-spectroscopy enabled by the scattering-type scanning near-field microscope (s-SNOM) techniques, this phase transition and the propagation of insulator-metal phase boundary are revealed with 10 nm resolution. We will discuss different stages of the phase transition and the nano-textures observed during the experiment. [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K37b.00013: Nature of the metal-insulator transition in transition-metal dichalchogenides Joseph Prestigiacomo, Anindya Nath, Thomas Sutto, Michael Osofsky It is well known that disorder and electron-electron interactions can dominate the transport properties of materials near the metal-insulator transition (MIT). However, it remains unclear what role these effects play in the emergence of other properties that often appear at the MIT, such as superconductivity in the transition-metal dichalcogenides MoS2 and WS2. We will attempt to clarify this role by examining the normal-state magnetotransport properties of such materials as they are tuned through the MIT by ionic liquid gating, a method that can drastically vary the carrier concentration to levels usually accessible only by doping while allowing the disorder to remain constant as well. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K37b.00014: Melting of the Mott state in electron-doped iridates Koen M Bastiaans, Irene Battisti, Vitaly Fedoseev, Alberto de la Torre, Nikos Iliopoulos, Anna Tamai, Emily C Hunter, Robin S Perry, Jan Zaanen, Felix Baumberger, Milan P Allan High temperature superconductivity as it manifests in the cuprates was for long time suspected to be strongly related to the copper oxide layers, and therefore specific to only this family of materials. Here, we investigate the iridate (Sr$_{1-x}$La$_x$)$_2$IrO$_4$, belonging to a new class of quasi-2D effective Mott insulators [1], which we have shown to exhibit phenomena strikingly similar to the cuprates [2-4]. We focus here on the very low doping region of the phase diagram (x$<$4\%) and use spectroscopic-imaging scanning tunneling microscopy to visualize the electronic structure at different doping concentrations. We measure fully gapped spectra even at the precise location of dopant atoms that are visible in the topograph. This is evidence for an impurity band Mott transition of the extra carriers, and that they are more deeply trapped than in the cuprates. Only at a certain doping threshold, the gap collapses revealing complex charge arrangements. [1] Kim, B. J., et al. PRL 101.7(2008):076402. [2] Kim, Y. K., et al. Nature Physics 12.1(2016):37-41. [3] De La Torre, A., et al. PRL 115.17(2015):176402. [4] Battisti, I., Bastiaans,K.M., et al. Nature Physics AOP [Preview Abstract] |
Wednesday, March 15, 2017 10:48AM - 11:00AM |
K37b.00015: Universality of pseudogap and emergent order in lightly doped Mott insulators Irene Battisti, Koen M. Bastiaans, Vitaly Fedoseev, Alberto de la Torre, Nikos Iliopoulos, Anna Tamai, Emily C. Hunter, Robin S. Perry, Jan Zaanen, Felix Baumberger, Milan P. Allan It is often assumed that high-T$_c$ superconductivity in the cuprates emerges from doped Mott insulators. When doping these materials, the electrons become mobile but still feel the strong correlations from the Mott state, leading to electronic order, a pseudogap phase and superconductivity. How the insertion of dopant atoms drives this evolution is not known, nor whether these phenomena belong only to hole-doped cuprates. Using spectroscopic-imaging scanning tunneling microscopy, we visualize the electronic states of the iridate (Sr$_{1-x}$La$_x$)$_2$IrO$_4$, which is chemically radically different from the cuprates but also an effective Mott insulator [1]. We find that above a certain doping threshold a phase separated state emerges, with the nucleation of pseudogap puddles around clusters of dopant atoms. Within these puddles, we observe the same iconic electronic order that is seen in underdoped cuprates. Our results clarify the melting of the Mott state, and establish phase separation and electronic order as generic features of doped Mott insulators [2]. [1] B.J. Kim et al., PRL 101, 076402 (2008) [2] I. Battisti et al., Nat. Phys. AOP, DOI:10.1038/nphys3894 (2016) [Preview Abstract] |
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