Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E43: Quantum Criticality and Phase TransitionsLive
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Sponsoring Units: DCMP Chair: Sachith Dissanayake, Duke University |
Tuesday, March 16, 2021 8:00AM - 8:12AM Live |
E43.00001: NMR Investigation of Ferroquadrupolar Order in TmVO4 Igor Vinograd, Zhipan Wang, Kent R Shirer, Andrew Mackenzie, Daphne Garcia, Mladen Horvatić, Pierre Massat, Ian R Fisher TmVO4 undergoes a tetragonal to orthorhombic structural phase transition below 2.2K due to a cooperative Jahn-Teller distortion. The Tm ions experience a crystal-field effect with a non-Kramer’s ground state doublet, and undergo ferroquadrupolar order that breaks the C4 symmetry of the lattice. This material is therefore a model system to investigate Ising nematic ordering without competing phases. While previous 51V NMR has been hampered by significant line broadening due to demagnetization fields at low temperature, here we present improved results where we are able to separate magnetic and quadrupolar relaxation channels in a single crystal of ellipsoidal shape for which this broadening is absent. These are the first NMR measurements in which an ellipsoidal sample is used that has been carefully cut by a focused ion beam (FIB). |
Tuesday, March 16, 2021 8:12AM - 8:24AM Live |
E43.00002: Direct determination of Ti-3d1 orbital state in YTiO3 using synchrotron X-ray diffraction Shunsuke Kitou, Taishun Manjo, Naoyuki Katayama, Tatsuya Shishidou, Taka-hisa Arima, Yasujiro Taguchi, Yoshinori Tokura, Toshikazu Nakamura, Toshihiko Yokoyama, Kunihisa Sugimoto, Hiroshi Sawa The orbital degree of freedom of electrons greatly influences the physical properties of materials such as magnetism and unconventional superconductivity. An orbital is a minimal unit of “shape”, and the orbital state can be unraveled by observing the spatial anisotropic distribution of electrons. However, it is difficult to experimentally extract the orbital information in a crystal because of various technical problems. In this study, the Ti-3d orbital state in a perovskite-type oxide YTiO3 is directly determined by a core differential Fourier synthesis (CDFS) method using synchrotron X-ray diffraction [1]. The valence electron density distribution, including information on the anisotropy and the hybridization between atomic orbitals, can be extracted from the CDFS analysis. Our study provides a non-trivial picture of the orbital state reconstructed by the orbital hybridization. |
Tuesday, March 16, 2021 8:24AM - 8:36AM Live |
E43.00003: Reinvestigation of the homogeneous spin model in YbMgGaO4 Shaozhi Li Recently, an inelastic neutron scattering experiment on YbMgGaO4 reported that the magnetic field can induce a phase transition between the stripe state and the AFM state. However, all existed theoretical models cannot describe this phase transition. In this talk, I will present the phase diagram of the spin model relevant to YbMgGaO4. I find that the magnetic field can induce phase transitions between the spin liquid or stripe states and the AFM state. These phase transitions are suppressed by the next-nearest neighbor exchange interaction J2/J1 and vanishes as J2/J1>0.11. I analyze a parameter space at J2/J1=0.1, in which a phase transition from the spin liquid state to the AFM state can be achieved and the deviation of theoretical spin excitation energies from experimental data is only about 5.4%. My results imply that an effective homogeneous spin model still works in YbMgGaO4. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E43.00004: Theory of charge loop current in quasi-one-dimensional systems based on functional renormalization group study Rina Tazai, Youichi Yamakawa, Hiroshi Kondani Various symmetry-breaking phenomena are the central issues in strongly correlated metals. For instance, violations of C_{4} rotational symmetry in tetragonal systems, so called the quantum liquid phase, has been intensively studied on Fe-, Cu-based and heavy fermion superconductors. One of the origin of the symmetry breaking is spontaneous current phase due to odd-parity loop current (LC) ordering. Until now, various types of LC orders, like the ferro-LC order along Cu-O and O-O bonds and the antiferro-LC order along Cu-Cu bonds have been discussed. Here, we study spin-fluctuation-driven LC order mechanism based on the functional renormalization group (fRG) theory. Our proposed mechanism leads to the ferro LC order in a quasi-one-dimensional systems, which accompanies the magnetic field that is measurable experimentally. |
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E43.00005: Dual Orbital Degeneracy Lifting in a Strongly Correlated Electron System Robert Koch, Ryan P Sinclair, Marshall McDonnell, Runze Yu, Milinda Abeykoon, Matt Tucker, Alexei Tsvelik, Simon L Billinge, Haidong Zhou, Weiguo Yin, Emil Bozin The local structure of NaTiSi2O6 is examined across its Ti-dimerization orbital-assisted Peierls transition at 210 K. An atomic pair distribution function approach evidences local symmetry breaking preexisting far above the transition. The analysis unravels that on warming the dimers evolve into a short range orbital degeneracy lifted (ODL) state of dual orbital character, persisting up to at least 490 K. The ODL state is correlated over the length scale spanning ~6 sites of the Ti zigzag chains. Results imply that the ODL phenomenology extends to strongly correlated electron systems. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E43.00006: Two species Wigner lattice state of unconfined electron-positron plasma and application to the theory of ball lighting Daniel Miller Thunderstorms generates strong flows of 512 keV gamma-rays, indicating that substantial amount of positrons participate in this process. This takes people to an idea that ball lighting is the vortex of electron-positron plasma. The stability of the plasma can be achieved by balancing the attractive Coulomb forces between electron and positron by the kinetic energy and the temperature. The concept of the first order phase transition leading to formation of electron–hole drops in semiconductors is known since 70ies. However, the electron–hole liquid drop has short life time and cannot describe relatively long lived ball lighting. Here I report two–species Wigner crystal solution to the equation of state, which is only possible when positive and negative charges have exactly same mass. The model is valid for all observed ball lighting temperatures; the density of electron–positron pairs in the crystal n ∼ (0.65T/e2)3, ranges from 1.7×1015cm−3 at the room temperature, to 1.7×1020cm−3 at 14000C. The annihilation of electron–positron pairs and evaporation of electrons and positrons from the crystal surface set the ball lighting life time. For the above temperature range the estimated life time for typical ball lighting is between few hundreds seconds and few seconds. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E43.00007: Transitions between symmetry-protected topological phases from pivoting Nathanan Tantivasadakarn, Ryan Thorngren, Ruben Verresen, Ashvin Vishwanath We introduce a novel mechanism, ‘pivoting’, which aids in the construction of Hamiltonians realizing symmetry-protected topological (SPT) phases in general dimensions. Moreover, this approach elucidates discrete and continuous duality symmetries that can emerge at SPT transitions. We support our findings with numerical investigations. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E43.00008: Normal state properties of quantum-critical metals at finite temperatures Avraham Klein, Yoni Schattner, Erez Berg, Andrey Chubukov Recent years have seen an intense effort to study models of fermionic quantum criticality and superconductivity via sign-problem-free quantum Monte Carlo. These studies found a number of puzzling features, which are in qualitative disagreement with quantum-critical-scaling theories and, in particular, cast doubt on the validity of Eliashberg-type approaches to quantum criticality. I will discuss how thermal fluctuations destroy the nice scaling properties of quantum-critical systems and show that after generalizing Eliashberg theory to account for thermal fluctuations many of the disagreements vanish. This work provides concrete guidelines for analyzing ongoing numerical work. |
Tuesday, March 16, 2021 9:36AM - 9:48AM Live |
E43.00009: Infinite critical boson non-Fermi liquid Xiao-Tian Zhang, Gang Chen We study a novel type of non-Fermi liquid where there exist an infinite number of critical boson modes instead of discrete and finite bosonic modes for the conventional ones. We consider itinerant magnets with both conduction electrons and fluctuating magnetic moments in three dimensions. With the Dzyaloshinskii-Moriya interaction, the moments fluctuate near a boson surface in the reciprocal space at low energies when the system approaches an ordering transition. The infinite number of critical modes on the boson surface strongly scatter the conduction electrons on the Fermi surface and convert the metallic sector into a non-Fermi liquid. We explain the thermodynamic, spectroscopic, transport properties of this novel non-Fermi liquid metal. On the ordered side, a conventional non-Fermi liquid emerges due to the scattering by the gapless Goldstone mode that arises from the spontaneous breaking of the global rotational symmetry. We discuss the general structure of the phase diagram in the vicinity of the quantum phase transition and clarify various crossover behaviors. |
Tuesday, March 16, 2021 9:48AM - 10:00AM Live |
E43.00010: Observation of non-Fermi liquid physics in a quantum critical metal via quantum loop topography George Driskell, Samuel Lederer, Carsten Bauer, Simon Trebst, Eun-Ah Kim Non-Fermi liquid physics is a ubiquitous feature in strongly correlated metals, manifesting itself in anomalous transport properties, such as a T-linear resistivity in experiments. However, its theoretical understanding in terms of microscopic models is lacking despite decades of conceptual work and numerical simulations. Here we demonstrate that a combination of sign problem-free quantum Monte Carlo sampling and quantum loop topography, a physics-inspired machine learning approach, can map out the emergence of non-Fermi liquid physics in the vicinity of a quantum critical point with little prior knowledge. Using only three parameter points for training the underlying neural network, we are able to reproducibly identify a stable non-Fermi liquid regime tracing the fans of metallic quantum critical points at the onset of both spin-density wave and nematic order. Our study thereby provides an important proof-of-principle example that new physics can be detected via unbiased machine-learning approaches. |
Tuesday, March 16, 2021 10:00AM - 10:12AM Live |
E43.00011: Emergence of non-Landau quasiparticle at geometric quantum criticality Hao Song, Catherine Kallin, Sung-Sik Lee Metals can undergo geometric quantum phase transitions that do not involve change in symmetry or topology. Around geometric quantum critical points, there exist inflection points at which the curvature of Fermi surface vanishes, and quasiparticles exhibit an anomalous decay rate. In this paper, we study a geometric quantum phase transition that divides a globally convex Fermi surface from a Fermi surface with locally concave sections in two dimensions. It is shown that non-Landau quasiparticles with a decay rate that goes as Eα with 1<α<2 as a function of quasiparticle energy E emerge in the presence of short-range interactions. |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E43.00012: Pulse echo study of the field-tuned nematic quantum phase transition in TmVO4 Patrick Hollister, Pierre Massat, Ian R Fisher, Brad Ramshaw Nematicity appears in a diverse array of strongly correlated systems – from high Tc to the fractional quantum Hall effect. In such materials, nematicity appears in conjunction with superconductivity, magnetism, and inevitably, disorder. The presence of metallic charge carriers makes understanding the impact of nematicity a non-trivial task, inspiring the search for a model system where nematicity occurs without conduction electrons. Ferroquadrupolar order of local moments provides one such realization. Here we explore a model system, TmVO4, which undergoes a nematic ferroquadrupolar transition driven by the cooperative Jahn-Teller effect. Using pulse echo ultrasound, we measure the elastic constants as a function of temperature and applied magnetic field to determine the behavior of the quadrupole strain susceptibility (i.e. the nematic susceptibility) proximate to the field-tuned quantum phase transition. The softening of the c66 elastic constant yields the strength of the short and long range quadrupolar interactions, while the ultrasonic attenuation characterizes the dynamics of the phase transition. Measurements on the doped system (Tm1-xYx)VO4 for x= .05, x=.1, reveal the interplay between nematicity and disorder in the vicinity of the quantum critical point. |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E43.00013: Field-induced phase transitions of symmetry protected topological states in integer spin chains Shi Feng, Gonzalo Alvarez, Nandini Trivedi We investigate spin chains with bilinear-biquadratic spin interactions in the gapped symmetry protected topological (SPT) state and at the critical Uimin-Lai-Sutherland (ULS) point as a function of an applied magnetic field. From calculations of the dynamical structure factor S(q,ω) using time-dependent density matrix renormalization group (DMRG), we observe a phase transition from the gapped to a gapless phase driven by a field in the Haldane phase. In the ULS critical phase, we see a phase transition at hc1 from a gapless phase with two degenerate soft modes at 2π/3 and 4π/3 to another gapless phase with a soft mode at π. From S(q,ω) we observe the fractionalization of modes below hc1 and their recombining to form new modes above hc1. We show that some aspects of the dispersion of these modes can be qualitatively understood within a single-mode approximation. |
Tuesday, March 16, 2021 10:36AM - 10:48AM Live |
E43.00014: Self-tuned criticality and non-Fermi liquid pairing in a Yukawa-SYK model Yuxuan Wang We present a Sachdev-Ye-Kitaev-like model describing random Yukawa interactions between localized fermions and dynamical bosons in quantum dots. We show that by varying the fermion density the system undergoes a transition between a gapped insulating phase and a quantum-critical non-Fermi liquid phase. The non-Fermi liquid phase displays exotic pairing behavior — depending on parameters, the system either develops superconductivity or persists as a non-Fermi liquid down to zero temperature, despite the strong attractive interaction mediated by the critical boson. We supplement our analytical large-$N$ results with quantum Monte Carlo simulations, showing excellent agreement. |
Tuesday, March 16, 2021 10:48AM - 11:00AM Live |
E43.00015: Surface Critical Exponents of the 3D Clean Ising Model and 3D Random Field Ising Model Forrest Simmons, Erica W Carlson, Karin Andrea Dahmen At continuous phase transitions, power law behavior can give rise to intricate pattern formation reminiscent of the complex patterns that form at the surface of many strongly correlated quantum materials. Such patterns in quantum materials have been shown to exhibit fractal behavior and have scaling laws that are characterized by critical exponents.[1-3] Here, we use simulations to calculate the critical exponents at a free surface of the 3-dimensional Clean Ising Model and of the 3-dimensional Random Field Ising Model. We discuss the difference between the surface patterns and those arising in the bulk. The critical exponents extracted from surface probe data in experimental systems can be compared against these theoretical results, in order to determine whether patterns observed on the surface of a material are confined to that surface or penetrate into the bulk of the material. |
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