Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P37b: Quantum Critical Point and non-Fermi-Liquid |
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Sponsoring Units: DCMP GMAG Chair: Sheng Ran, University of California, San Diego Room: 384 |
Wednesday, March 15, 2017 2:30PM - 2:42PM |
P37b.00001: Non-Fermi liquid transport phenomena in SrIrO3 thin films: Role of disorder in a nematic phase Kyoung-Min Kim, Ki-Seok Kim Recently, non-Fermi liquid transport phenomena have been found in SrIrO3 thin films on various substrates: Increasing the lattice mismatch between SrIrO3 thin films and substrates, the exponent $\alpha $ of electrical resistivity $\Delta \rho \sim $T$^{\mathrm{\alpha }}$ shows the variation from$_{\mathrm{\thinspace }}\alpha =$4/5, $\alpha =$1, to $\alpha =$3/2. Such experiments confirmed that these thin films lie away from a magnetic quantum critical point. On the other hand, we suggest that the presence of strong spin orbit coupling may give rise to an electron nematic phase. As a result of combined effects between quantum criticality of electron nematicity and nonmagnetic quenched disorders, we suspect that the continuous evolution of the power-law exponent may be involved with quantum Griffiths effects. Performing the renormalization group analysis, we discuss a possible origin of this non-Fermi liquid physics. [Preview Abstract] |
Wednesday, March 15, 2017 2:42PM - 2:54PM |
P37b.00002: Quantum Criticality and 2-D dissipative quantum XY ferromagnetism in single crystalline YFe2Al10 from MuSR investivations Kevin Huang, Cheng Tan, Jian Zhang, Zhaofeng Ding, Douglas MacLaughlin, Oscar Bernal, Pei-Chun Ho, L. Wu, Meigan Aronson, Lei Shu We have performed Muon spin relaxation ($\mu$SR) measurements on single crystalline YFe$_2$Al$_{10}$ down to 19 mK and in magnetic fields up to $\sim$100 Oe with fields applied along the b-axis and c-axis. Zero-field-$\mu$SR measurements showed no evidence of magnetic order down to 19 mK, consistent with previous measurements. Interestingly we also find that the depolarization rate $\Lambda$ is temperature independent above 1 K but displays a strong diverging temperature dependence for $T <$ 1 K, different than what was observed for polycrystals of YFe$_2$Al$_{10}$. Longitudinal-field $\mu$SR measurements also reveals a time-field scaling for multiple temperatures in fields up to 200 Oe. From this work we find that single crystalline YFe$_2$Al$_{10}$ is in close proximity to a ferromagnetic quantum critical point and find evidence that it is the first experimental realization of a 2-D dissipative XY-model ferromagnet. [Preview Abstract] |
Wednesday, March 15, 2017 2:54PM - 3:06PM |
P37b.00003: Scaling behavior near the itinerant ferromagnetic quantum critical point (FQCP) of NiCoCr$_{\mathrm{x}}$ for 0.8 \textless x \textless 0.95 Brian Sales, Ke Jin, Hongbin Bei, John Nichols, Matthew Chisholm, Andrew May, Michael McGuire Low temperature magnetization, resistivity and heat capacity data are reported for the concentrated solid solution NiCoCr$_{\mathrm{x}}$ as a function of temperature and magnetic field. In the quantum critical region the low field (0.001-0.01 T) magnetic susceptibility, Chi, diverges as $\approx $ T$^{\mathrm{-1/2}}$ and the magnetization data exhibits T/B scaling from 0.001 \textless B \textless 2 Tesla for T \textless 30 K. At the lowest temperatures the ratio of Chi/C$_{\mathrm{p}}$ diverges consistent with the expectations of a FQCP. At higher magnetic fields, B \textgreater 2 Tesla, the crossover temperature from the QC to Fermi liquid regime is no longer linear in B, and is better described by B$^{\mathrm{0.75}}$. This scaling behavior is particularly accurate in describing the normalized magnetoresistance data [Rho(B,T)-Rho(0,T)]/T, which is equivalent to the ratio of relaxation rates associated with magnetic field and temperature $\approx $ Tau$_{\mathrm{T}}$/Tau$_{\mathrm{B}}$. The location of the QCP is sensitive to the composition x and the strain generated during synthesis. These medium-entropy alloys are interesting model systems to explore the role of chemical disorder at FQCP. Research supported by the DOE Office of Science, Materials Science and Engineering Division, and the Energy Dissipation to Defect Evolution EFRC. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:18PM |
P37b.00004: Comparison of RG and Eliashberg analyses of fermion pairing with competing attractive and repulsive critical bosonic fluctuations. Luis Mendoza, N.E. Bonesteel |
Wednesday, March 15, 2017 3:18PM - 3:30PM |
P37b.00005: Abstract Withdrawn We study the spectral properties of a Hubbard ladder with anti-ferromagnetic long range order by introducing a staggered Heisenberg interaction that decays algebraically. Unlike an alternating field or the $t-J_z$ model, our problem preserves both $SU(2)$ and translational invariance. We solve the problem with the time-dependent density matrix renormalization group and analyze the binding between holons and spinons and the structure of the elementary excitations. We discuss the implications in the context of the 2D Hubbard model at, and away from half-filling by using cluster perturbation theory (CPT). |
Wednesday, March 15, 2017 3:30PM - 3:42PM |
P37b.00006: Radiation from a strongly correlated one-dimensional electron liquids Wade DeGottardi, Suraj Hegde, Michael Gullans, Smitha Vishveshwara, Mohammad Hafezi We present the properties of radiation from a strongly correlated one-dimensional electron liquid. Because of the large mismatch between the speed of light and the Fermi velocity, radiation serves as a direct test of spectral weight of the system which is far `off-shell'. In the Luttinger liquid model, excitations of the electron liquid are described by non-interacting bosons and this spectral weight vanishes. Thus, radiation offers a direct test of behavior which is beyond the Luttinger liquid paradigm. We present several examples of systems for which such radiation can be observed. [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 3:54PM |
P37b.00007: 2D non-Fermi liquids from coupled Leech wires Eugeniu Plamadeala, Dominic Else, Michael Mulligan, Chetan Nayak We present a completely stable gapless quantum critical point of interacting electrons in two dimensions. It is obtained by coupling an infinite parallel array of quantum wires, each described by a CFT associated with Leech lattice. The low energy theory decomposes into two sectors: a chiral Fermi liquid with an open Fermi surface, and a chiral Luttinger liquid on each wire, with no inter-wire hopping. The stability of the fixed point to all perturbations is due to special (but not fine-tuned) large values of the interactions between the channels, as well as kinematic suppression of potentially relevant perturbations. The QCP describes a hyperconductor, and is immune to disorder-induced localization along the wires. [Preview Abstract] |
Wednesday, March 15, 2017 3:54PM - 4:06PM |
P37b.00008: Exact critical exponents for the antiferromagnetic quantum critical metal near three dimensions Peter Lunts, Andres Schlief, Sung-Sik Lee We study the low energy field theory that describes the antiferromagnetic quantum critical metal. Earlier works have approached this problem by extending the spatial dimension from $d = 2$ to $d = 3 - \epsilon$ to gain perturbative control. We extend this work and find that the low energy theory can be studied in a controlled way even when $\epsilon$ is not small due to an emergent control parameter. This allows us to find exact values for the critical exponents of the theory. We describe the limitation of the $\epsilon$ expansion and the strategy of the non-perturbative framework that eventually lead to the solution in $d=2$. \newline S. Sur, S.-S. Lee, \textit{Phys. Rev. B} \textbf{91}, 125136 (2015). \newline P. Lunts, A. Schlief, and S.-S. Lee, arXiv:1701.08218 \newline A. Schlief, P. Lunts, and S.-S. Lee, arXiv:1608.06927 \newline A. Schlief, P. Lunts, and S.-S. Lee, \textit{in preparation} [Preview Abstract] |
Wednesday, March 15, 2017 4:06PM - 4:18PM |
P37b.00009: Exact Critical Exponents for the Antiferromagnetic Quantum Critical Metal Supporting a One-Dimensional Fermi Surface in General Space Dimension Andres Schlief, Peter Lunts, Sung-Sik Lee Antiferromagnetic quantum phase transitions play an important role in strongly correlated systems like electron-doped cuprates , iron pnictides and heavy fermion compounds. In this talk, we will present recent theoretical progress in understanding the scaling properties of the strange metal that arises at the antiferromagnetic quantum critical point. Using a non-perturbative field theoretic renormalization group analysis we extract the \textit{exact} critical exponents characterizing the quantum critical metal that supports a one-dimensional Fermi surface in $d$-spatial dimensions. In particular, for $d=2$ we predict the scaling form of the fermion spectral function and the spin susceptibility at low temperatures, which are testable through angle resolved photo-emission spectroscopy (ARPES) and neutron scattering experiments, respectively. \begin{enumerate} \item P. Lunts, A. Schlief, S. Sur and S.-S Lee. To appear. \item A. Schlief, P. Lunts and S.-S. Lee. To appear. \item A. Schlief, P. Lunts and S.-S. Lee. arXiv:1608.06927. \end{enumerate} [Preview Abstract] |
Wednesday, March 15, 2017 4:18PM - 4:30PM |
P37b.00010: Stability of two dimensional disordered metals Pallab Goswami, Hart Goldman, Srinivas Raghu Metallic phases have been observed in several disordered two dimensional systems, including thin films near a superconductor-insulator transition, and quantum Hall systems near plateau transitions. If metallic ground states do exist in such systems, they can only do so due to electron-electron interactions. Motivated by these phenomena, we consider general circumstances under which two dimensional electron systems in the presence of both interactions and disorder may exhibit metallic ground states. We formulate a general stability criterion for a large class of non-Fermi liquid ground states against disorder. As an explicit example, we consider (2+1)-dimensional quantum electrodynamics with a large even number of fermion flavors in the presence of disorder. We show the existence of a stable metallic or non-Fermi liquid phase and its quantum phase transition to a disorder dominated phase. [Preview Abstract] |
Wednesday, March 15, 2017 4:30PM - 4:42PM |
P37b.00011: Non-Fermi glasses: fractionalizing electrons at finite energy density Siddharth Parameswaran, Sarang Gopalakrishnan Non-Fermi liquids are metals that cannot be adiabatically deformed into free fermion states. We argue for the existence of ``non-Fermi glasses,'' which are phases of interacting disordered fermions that are fully many-body localized, yet cannot be deformed into an Anderson insulator without an eigenstate phase transition. We explore the properties of such non-Fermi glasses, focusing on a specific solvable example. At high temperature, non-Fermi glasses have qualitatively similar spectral features to Anderson insulators. We identify a diagnostic, based on ratios of correlation functions, that sharply distinguishes between the two phases even at infinite temperature. We argue that our results and diagnostic should generically apply to the high-temperature behavior of the many-body localized descendants of fractionalized phases. [Preview Abstract] |
Wednesday, March 15, 2017 4:42PM - 4:54PM |
P37b.00012: Non-Equilibrium Crossover near a Non-Fermi-Liquid Quantum Critical Point: Conductance of a Dissipative Quantum Dot Gu Zhang, E. Novais, Harold Baranger We study the non-equilibrium conductance of a dissipative system as it crosses over from a non-Fermi liquid (NFL) critical point to the Fermi liquid (FL) ground state. The system consists of a spin-polarized quantum dot connected to two dissipative leads whose resistance is $R$. The NFL critical point of this system is similar to that of the two-channel Kondo model; it is unstable under hybridization asymmetry or detuning of the level in the dot, both of which cause flow to a FL ground state. For a particular value of the resistance, $R=R_Q$, using results from Sela and Affleck [PRB 2009] and the Keldysh formalism, we calculate analytically the non-equilibrium conductance in the crossover regime. From this result, one can make a conjecture for the general case, $R \neq R_Q$. Comparison to existing experiments [Mebrahtu, et al. Nat.Phys. 2013] shows good agreement. [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:06PM |
P37b.00013: Non-existence of the Luttinger-Ward functional and misleading convergence of skeleton diagrammatic series for Hubbard-like models Evgeny Kozik, Michel Ferrero, Antoine Georges The Luttinger-Ward functional $\Phi[\mathbf{G}]$, which expresses the thermodynamic grand potential in terms of the interacting single-particle Green's function $\mathbf{G}$, is found to be ill-defined for fermionic models with the Hubbard on-site interaction. In particular, we show that the self-energy $\mathbf{\Sigma}[\mathbf{G}] \propto\delta\Phi[\mathbf{G}]/\delta \mathbf{G}$ is not a single-valued functional of $\mathbf{G}$: in addition to the physical solution for $\mathbf{\Sigma}[\mathbf{G}]$, there exists at least one qualitatively distinct unphysical branch. This result is demonstrated for several models with the Hubbard interaction: the Hubbard atom, the Anderson impurity model, and the full two-dimensional Hubbard model. Despite this pathology, the skeleton Feynman diagrammatic series for $\mathbf{\Sigma}$ in terms of $\mathbf{G}$ is found to converge at least for moderately low temperatures. However, at strong interactions, its convergence is to the unphysical branch. This reveals a new scenario of breaking down of diagrammatic expansions. In contrast, the bare series in terms of the non-interacting Green's function $\mathbf{G}_0$ converges to the correct physical branch of $\mathbf{\Sigma}$ in all cases currently accessible by diagrammatic Monte Carlo. [Preview Abstract] |
Wednesday, March 15, 2017 5:06PM - 5:18PM |
P37b.00014: Observation of replica dispersions in interacting 1D wires Christopher Ford, Yiqing Jin, Maria Moreno, Wooi Liat Tan, Ankita Anirban, Jon Griffiths, Ian Farrer, David Ritchie, Anne Anthore, Oleksandr Tsyplyatyev, Andrew Schofield At low excitation energies, a system of interacting one-dimensional (1D) electrons can be described theoretically as a Tomonaga-Luttinger liquid. However, it is only in the last few years that theoreticians have developed models of the behaviour at energies comparable to the Fermi energy, predicting `replicas' of the dispersion relation offset by multiples of the Fermi wave-vector. We measure momentum-resolved tunnelling of electrons between 1D wires formed within a GaAs heterostructure and a 2D electron gas used as a spectrometer and have previously found well-resolved spin-charge separation at low energy with appreciable interaction strength. Now we have detected structure resembling a replica, which dies away quite rapidly at high momentum, in line with the most recent theory. We have fabricated arrays of wires with lengths between 1 and 20$\mu$m, after developing a reliable technique to make thousands of `air-bridges' on each device. The replica seems strongest in the short wires, again as predicted by the theory. [Moreno \textit{et al., Nat. Commun.} {\bf 7}, 12784 (2016); Tsyplyatyev \textit{et al., Phys. Rev. Lett.} {\bf 114}, 19640 (2015); Tsyplyatyev \textit{et al., Phys. Rev. B}, {\bf 93}, 075147 (2016).] [Preview Abstract] |
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