Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R44: Quantum Criticality |
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Sponsoring Units: DCMP Chair: Shizeng Lin, Los Alamos National Laboratory Room: LACC 504 |
Thursday, March 8, 2018 8:00AM - 8:12AM |
R44.00001: Charge density waves and quantum criticality in high-Tc cuprates revealed by high-magnetic fields Mun Chan, Arkady Shekhter, Ross McDonald, Jonathan Betts, Eric Bauer, Neil Harrison The small reconstructed Fermi surface revealed by high-magnetic field quantum oscillation measurements in bilayer YBa2Cu3O6+x opened a path towards identifying broken symmetry states in underdoped cuprate supercoductors. Recent quantum oscillation measurements on the structurally simpler HgBa2CuO4+d indicate that the Fermi surface comprises only a single quasi-two dimensional pocket. These results suggests Fermi-surface reconstruction attributable to the charge-density-wave observed with other spectroscopic methods. However, the relationship of this charge-density-wave to high-temperature superconductivity and quantum criticality remains a pressing open question. We will present new insights into the low temperature electronic structure of the cuprates probed with electrical transport in magnetic fields up to 90 tesla. |
Thursday, March 8, 2018 8:12AM - 8:24AM |
R44.00002: Analysis of diverging effective mass near quantum critical point of x=0.3 in BaFe2(As1-xPx)2 Hyun-Tak Kim The quantum critical point (QCP) is the metal-insulator (or superconductor)-transition point at T=0 K and has been observed in many superconducting materials. To reveal the identity of the QCP is most important for clarifying the superconductor mechanism in compound superconductors. A particular phenomenon is a diverging effective mass (DEM) near the QCP. For BaFe2(As1-xPx)2, the effective mass of quasiparticle in metal diverges near the QCP of x=0.3 and the inverse effective mass is linearly proportional to carrier density [1]. This was observed by measurements of heat capacity [1], penetration depth [2], the dHvA effect [1], and superconducting critical field [3]. Here, we demonstrate the linear behavior in inverse effective mass and reveal that the QCP has the maximum carrier density, through a fitting of the DEM near x=0.3 using m*/m=1/(1-ρ4) and ρ=(0.29/x) in the extended Brinkman-Rice picture [4]. the DEM's physical meaning indicates that the extent of a non-metallic phase increases with increasing x from the QCP. [1] PRL 110, 257002 (2013), [2] Science 336 (2012) 1154, [3] arXiv:1705.00695v1, [4] arXiv:1710.07754. |
Thursday, March 8, 2018 8:24AM - 8:36AM |
R44.00003: Strongly-coupled quantum critical point in the all-in-all-out antiferromagnet Cd2Os2O7 Yishu Wang, Thomas Rosenbaum, Alex Palmer, Yang Ren, Jong Woo Kim, David Mandrus, Yejun Feng We employed resonant X-ray magnetic diffraction to directly probe the evolution with pressure of all-in-all-out (AIAO) antiferromagnetic order in the cubic pyrochlore Cd2Os2O7. The AIAO order is suppressed through a continuous quantum phase transition with neither an abrupt change in the electronic configuration nor a discontinuity in the lattice constant at a critical pressure, Pc=36.5GPa. Concomitant with the recovery of time-reversal symmetry in the magnetically disordered state, the crystal lattice experiences a spontaneous inversion symmetry breaking with the symmetry group continuously changing from Fd-3m to F-43m. An insulator-metal transition appears to accompany the magnetic and structural transitions. As spin fluctuations, lattice breathing modes, and quasiparticle excitations interact in the quantum critical region, we argue that they present the necessary components for strongly-coupled quantum criticality in this three-dimensional magnet. |
Thursday, March 8, 2018 8:36AM - 8:48AM |
R44.00004: Interplay between superconductivity and charge order near an antiferromagnetic quantum critical point: insights from Quantum Monte Carlo study Xiaoyu Wang, Yuxuan Wang, Yoni Schattner, Erez Berg, Rafael Fernandes In hole-doped cuprates, besides antiferromagnetism (AFM), charge order (CO) is also observed near the superconducting (SC) dome. Under certain approximations, the spin-fermion model, in which electrons interact by exchanging AFM fluctuations, was shown to have an emergent low-energy symmetry that makes CO and SC degenerate near an AFM quantum critical point. However, the robustness of this symmetry and the CO wave-vector remains widely debated. Here, we perform sign-problem-free Quantum Monte Carlo simulations of the spin-fermion model to address these issues. We find that, when particle-hole symmetry is present, AFM fluctuations equally promote d-wave SC and d-wave CO with a diagonal wave-vector. However, small deviations from particle-hole symmetry completely lift this degeneracy, resulting in a strong suppression of CO. Inside the AFM state, the CO wave-vector shifts from diagonal to axial, presumably due to the gapping of the antinodal region of the Fermi surface. Our work shows that while SC is universally promoted near an AFM quantum critical point, CO requires additional fine-tuning of the low-energy electronic dispersion. |
Thursday, March 8, 2018 8:48AM - 9:00AM |
R44.00005: Quantum critical behavior of a three-dimensional superfluid-Mott glass transition Jack Crewse, Thomas Vojta, Cameron Lerch
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Thursday, March 8, 2018 9:00AM - 9:12AM |
R44.00006: Gradient terms in quantum-critical theories of itinerant fermions Dmitrii Maslov, Prachi Sharma, Dmitrii Torbunov, Andrey Chubukov We investigate the origin and renormalization of the gradient (Q2) term in the propagator of soft bosonic fluctuations in theories of itinerant fermions near a quantum critical point (QCP) of the nematic type. In principle, the gradient term come from the two distinct energy scales. The first one is the high-energy (HE) scale, ranging from the upper cutoff of the effective low-energy theory and to the bandwidth. The second, low-energy (LE), scale is of the order vFQ. We calculated the HE contribution to the Q2 term for the model of a Fermi gas with Coulomb interaction and for the Hubbard model and found that the HE contribution is of the same order but numerically much smaller than the LE one. The numerical smallness is especially pronounced in 2D. We argue that if the LE part of the gradient term is the dominant one, its renormalized value has to be calculated self consistently, which may give rise to a novel quantum-critical behavior. Following up on these results, we discuss two possible ways of formulating the theory of a nematic QCP. |
Thursday, March 8, 2018 9:12AM - 9:24AM |
R44.00007: Itinerant quantum critical point with frustration and non-Fermi-liquid ZiHong Liu, Xiao Yan Xu, Yang Qi, Kai Sun, ZiYang Meng Employing the self-learning quantum Monte Carlo algorithm, we investigate the frustrated transverse-field triangle-lattice Ising model coupled to a Fermi surface. Without fermions, the spin degrees of freedom undergoes a second-order quantum phase transition between paramagnetic and clock-ordered phases. This quantum critical point (QCP) has an emergent U(1) symmetry and thus belongs to the 2+1D XY universality class. In the presence of fermions, spin fluctuations introduce effective interactions among fermions and distort the bare Fermi surface towards an interacting one with hot spots and fermi pockets. Near the QCP, non-Fermi-liquid behavior are observed at the hot spots, and the QCP is rendered into a different universality with Hertz-Millis type exponents. The detailed properties of this QCP and possibly related experimental systems are also discussed. |
Thursday, March 8, 2018 9:24AM - 9:36AM |
R44.00008: Deconfined quantum critical point in fermionic systems Zixiang Li, Hong Yao We consider a microscopic interacting model of spin-1/2 fermions on the honeycomb lattice [1] and study its quantum phase diagram by sign-problem-free Quantum Monte Carlo simulations. Our large-scale simulations show that there is a quantum phase transition between the Neel state and Kekule valence-bond-solid (VBS) phase. Remarkably, we find convincing evidences that this quantum phase transition is continuous, featuring a deconfined quantum critical point (DQCP) that is beyond the conventional Landau-Ginzburg-Wilson (LGW) paradigm [2]. We further compare this DQCP in fermionic systems with the bosonic DQCP in quantum spin models. Our study could pave a new avenue to understand exotic quantum phase transition beyond the conventional LGW paradigm. |
Thursday, March 8, 2018 9:36AM - 9:48AM |
R44.00009: Quantum Annealed Criticality Premala Chandra, Piers Coleman, Mucio Continentino, Gilbert Lonzarich Experimentally there exist several materials with classical first-order transitions that display quantum criticality, and here we provide a theoretical basis for this observed behavior. At a first-order transition the quartic mode-mode coupling of the effective action becomes negative. A common mechanism for this phenomenon, studied by Larkin and Pikin, involves the coupling of the critical energy density to the lattice; the singular nature of the specific heat drives the bulk modulus negative leading to a first-order transition. Here we generalize the Larkin-Pikin criterion in terms of response functions. Furthermore we show that if the T=0 quantum system lies above its upper critical dimension, the line of first-order transitions ends in a quantum critical point (continuous quantum phase transition). We discuss specific measurements to probe this behavior and also extensions to metallic systems. |
Thursday, March 8, 2018 9:48AM - 10:00AM |
R44.00010: Zero-field splitting of the Kondo resonance and quantum criticality in triple quantum dots. Arturo Wong, Francisco Mireles Magnetic fields are known to be detrimental to the Kondo effect. In quantum dots (QDs), this is signaled by the splitting of the Kondo resonance (KR). However, zero-field splitting of the KR is predicted to occur in T-shaped QDs, where the hanging dot is within the Kondo regime and the second dot behaves as a resonant noninteracting level [1]. In this work we use the numerical renormalization group method to study a triple QD system in which two effective noninteracting dots are connected in parallel to metallic leads, as well to a third interacting dot. In absence of external fields, the fine tuning of the noninteracting levels causes a splitting of the KR, in such a way that the spectral function of the interacting dot vanishes at the Fermi level, without undermining the Kondo correlations. In addition, the system can be tuned to a pseudogap regime, which presents a competition between the Fano-Kondo effect and a quantum phase transition of the Kosterlitz-Thouless type. Signatures of these behaviors can be experimentally studied through conductance measurements [2]. |
Thursday, March 8, 2018 10:00AM - 10:12AM |
R44.00011: Deconfined quantum criticality of easy-plane J-Q model Nusen Ma, Anders Sandvik, Cenke Xu, Yizhuang You, ZiYang Meng Motivated by the recently confirmed duality relation between bosonic topological phase transition and deconfined quantum critical (DQC) point [1], we perform systematic numerical investigations of the critical properties of the easy-plane JQ model, in which the DQC point is realized. By means of stochastic series expansion quantum Monte Carlos simulation and finite-size analysis, we investigate the quantum phase transition between the antiferromagnetic XY phase and the valence-bond solid phase at varies values of the uniaxial anisotropy. In the easy-plane limit the transition is found to be first order, but for a range of weaker anisotropies the transition is continuous and governed by the DQC point with emergent SO(4) symmetry. We demonstrate this using scaling analysis for several quantities. |
Thursday, March 8, 2018 10:12AM - 10:24AM |
R44.00012: Gross-Neveu-Yukawa models at four loops and quantum critical behavior of Dirac systems Michael Scherer, Nikolai Zerf, Luminita Mihaila, Peter Marquard, Igor Herbut, Bernhard Ihrig Dirac and Weyl fermions appear as quasi-particle excitations in many different condensed-matter systems. They display various quantum transitions which represent unconventional universality classes related to the variants of the Gross-Neveu model. In my talk, I present a study of the bosonized version of the standard Gross-Neveu models -- the Gross-Neveu-Yukawa theories -- at four-loop order, and compute critical exponents in 4−epsilon dimensions for general number of fermion flavors. Our results fully encompass the previously known two-loop calculations, and agree with the known four-loop results in the purely bosonic limit of the theory. We also find the exponents to satisfy the emergent super-scaling relations in the limit of a single-component fermion, order by order up to four loops. Finally, we apply the computed series for the exponents and their Pade approximants to several phase transitions of current interest: metal-insulator transitions of spin-1/2 and spinless fermions on the honeycomb lattice, emergent supersymmetric surface field theory in topological phases, as well as the disorder-induced quantum transition in Weyl semimetals. Comparison with the results of other analytical and numerical methods is discussed. |
Thursday, March 8, 2018 10:24AM - 10:36AM |
R44.00013: Quantum Critical Point of Hubbard Model in Finite Dimensions Samuel Kellar The Hubbard model, at various dimensions, shows to have signs of a quantum critical point. By using Dynamical Mean Field Theory signals of a quantum critical point, for the Hubbard model in infinite dimensions, can be seen through ω/t scaling of the local spin susceptibility. In finite dimensions, Dynamical Cluster Approximation gives insight into the Hubbard model. The quasiparticle weight of the 2D Hubbard model shows evidence of a quantum critical point. As doping increases, the quasiparticle weight exhibits the change from non-Fermi liquid, to marginal Fermi liquid, and eventually to Fermi liquid. The existence of a singular density of state of the 2D model may facilitate an anti-ferromagnetic fluctuations and the formation of a pseudogap. As the 3D density of states does not contain a Van Hove singularity, it is an interesting model for the study of quantum criticality. We investigate the relationship of the quantum critical point in 3D and its similarities to points in other dimensions. |
Thursday, March 8, 2018 10:36AM - 10:48AM |
R44.00014: Deconfined Quantum Critical Point on the Triangular Lattice Chao-Ming Jian, Alex Thomson, Alexander Rasmussen, Zhen Bi, Cenke Xu We first propose a topological term that captures the "intertwinement" between the standard antiferromagnetic order (or the so-called 120 degree state) and the valence solid bond (VBS) order for spin-1/2 systems on a triangular lattice. Then using a controlled renormalization group calculation, we demonstrate that there exists an unfine-tuned direct continuous deconfined quantum critical point (dQCP) between the two ordered phases mentioned above. This dQCP is described by the Nf=4 quantum electrodynamics (QED) with an emergent PSU(4)=SU(4)/Z4 symmetry only at the critical point. The topological term aforementioned is also naturally derived from the Nf=4 QED. We also point out that physics around this dQCP is analogous to the boundary of a 3d bosonic symmetry protected topological state with on-site symmetries only. |
Thursday, March 8, 2018 10:48AM - 11:00AM |
R44.00015: Two-dimensional conductors with interactions and disorder from particle-vortex duality Hart Goldman, Michael Mulligan, Srinivas Raghu, Gonzalo Torroba, Max Zimet We study Dirac fermions in two spatial dimensions (2D) coupled to strongly fluctuating U(1) gauge fields in the presence of quenched disorder. Such systems are dual to theories of free Dirac fermions, which are vortices of the original theory. In analogy to superconductivity, when these fermionic vortices localize, the original system becomes a perfect conductor, and when the vortices possess a finite conductivity, the original fermions do as well. We provide several realizations of this principle and thereby introduce new examples of strongly interacting 2D metals that evade Anderson localization. |
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