Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R20: Exotic Condensates and Helium |
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Sponsoring Units: DCMP Chair: James A. Sauls, northwestern University Room: 280 |
Thursday, March 16, 2017 8:00AM - 8:12AM |
R20.00001: Unearthing the hidden link between composite fermions and the exciton condensate in quantum Hall bilayers Inti Sodemann, Itamar Kimchi, Chong Wang, T. Senthil Particle-vortex dualities have been a powerful conceptual device to understand fractionalized phases of matter over the years. Very recently, a remarkable incarnation of particle-vortex duality has been applied to the compressible state observed in half-filled Landau levels. The basic idea is that the celebrated composite fermion is a vortex-like object with Dirac nature. Superconductors of these composite fermion vortices are found to correspond to insulators of physical electrons. We have constructed an extension of these ideas to quantum Hall bilayers. We will demonstrate that the experimentally realized exciton condensate at filling factor 1/2+1/2 in Gallium Arsenide bilayers has an equivalent dual description as a superconductor of composite fermions paired in a specific particle-hole invariant interlayer channel. We will discuss how various characteristic phenomena of the exciton condensate, such as its superfluidity for layer charge imbalance and its fractionally charged vortices, find a natural dual description in the composite fermion perspective. [Preview Abstract] |
Thursday, March 16, 2017 8:12AM - 8:24AM |
R20.00002: Particle-hole symmetry and a bosonic duality for quantum Hall bilayers and half-filled multicomponent Landau levels Itamar Kimchi, Inti Sodemann, Chong Wang, T. Senthil Duality mappings let theorists study a given system through two distinct and complementary descriptions. We will discuss the roles played by a particular particle-hole CT symmetry in a quantum Hall bilayer corresponding to two half-filled Landau levels. We discuss Cooper pairing instabilities of composite fermions in the double-expansion renormalization group approach for the composite non-Fermi-liquid. Using a bosonic duality to describe the exciton condensate in the composite-fermion-superconductor regime offers a simple explanation for a surprising CT Kramer's doublet nature of double vortices, and suggests their unusual role near the finite temperature Kosterlitz-Thouless transition. Finally, we describe a related Z2 gauge theory with spin-half visons for idealized fully-symmetric graphene, and argue for symmetry-enforced gaplessness under full SU(4) flavor symmetry. [Preview Abstract] |
Thursday, March 16, 2017 8:24AM - 8:36AM |
R20.00003: Disorder-induced Revival of the Bose-Einstein Condensation at High Magnetic Fields in Ni(Cl$_{1-x}$Br$_x$)$_2$-4SC(NH$_2$)$_2$ Nicolas Laflorencie, Maxime Dupont, Sylvain Capponi Building on recent NMR experiments [arXiv:1607.02360], we theoretically investigate the high magnetic field regime of the disordered quasi-one-dimensional $S=1$ antiferromagnetic material Ni(Cl$_{1-x}$Br$_x$)$_2$-4SC(NH$_2$)$_2$. The interplay between disorder, chemically controlled by Br-doping, interactions, and the external magnetic field, leads to a very rich phase diagram. Beyond the well-known antiferromagnetically ordered regime, analog of a Bose condensate of magnons, which disappears when $H\ge 12.3$ T, we unveil a resurgence of phase coherence at higher field $H\sim 13.6$ T, induced by the doping. Interchain couplings stabilize finite temperature long-range order whose extension in the field -- temperature space is governed by the concentration of impurities $x$. Such a ``mini-condensation'' contrasts with previously reported Bose-glass physics in the same regime by Yu {\it{et al.}} [Nature 489, 379 (2012)], and should be accessible to future experiments. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R20.00004: Ising lattice gauge theory at finite fermion density: Symmetry breaking, confinement, and emergent Dirac excitation Snir Gazit, Mohit Randeria, Ashvin Vishwanath Ising gauge theories represent the simplest form of topological order and have been invoked to describe spin liquids and correlated electronic systems. Due to the sign problem, gauge theories are notoriously hard to analyze in the presence of a finite density of fermions. Here we study the phase diagram of the Ising gauge theory in 2+1 dimensions in the presence of a conserved charge, which we show is free of the sign problem at arbitrary fermion density, with an even number of fermion flavors. At generic filling, we find that gauge fluctuations mediate pairing leading to a transition between a deconfined BCS state to a confined BEC. At half-filling, a $\pi$-flux phase is generated spontaneously with emergent Dirac fermions. The deconfined Dirac phase, with a vanishing Fermi surface volume is a non-trivial example of violation of Luttinger's theorem due to fractionalization. At strong coupling, we find a single continuous transition between the deconfined Dirac phase and the confined BEC, in contrast to the expected split transition. [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R20.00005: Comparison of strong-coupling free-energy functionals for superfluid $^{3}{\rm He}$ Benjamin Stein-Lubrano, Joseph Serene Strong-coupling corrections to weak-coupling BCS theory have long been known to determine the equilibrium phase diagram of bulk superfluid $^{3}{\rm He}$. Recently Wiman and Sauls demonstrated the importance of strong-coupling corrections for phase diagrams of superfluid $^{3}{\rm He}$ in confined geometries, and introduced a computationally tractable extension of the strong-coupling Ginzburg-Landau free-energy as an alternative to the exact (through order $(T_c/T_F)^3)$ strong-coupling free-energy functional.\footnote{J.J. Wiman and J.A. Sauls, Phys. Rev. B {\bf 92}, 144515 (2015)} We will discuss the accuracy and range of applicability of the Wiman-Sauls functional using comparisons to calculations with the full strong-coupling theory.\footnote{J.W. Serene and D. Rainer, Phys. Rep. {\bf 101}, 221 (1983)} [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:12AM |
R20.00006: Superfluid phases for a model of 3He confined in nematic aerogels Joshua Wiman, J A Sauls Recently, superfluid $^3$He has been observed in disordered ``nematic aerogel'' (N-aerogel) materials.\footnote{V. V. Dmitriev, A. A. Senin, A. A. Soldatov, and A. N. Yudin, Phys. Rev. Lett. 115, 165304 (2015).} N-aerogels consist of $9$ nm diameter strands that are predominantly oriented along one axis, producing far more anisotropy in confinement than was possible with previous experiments using anisotropic silica aerogels. In one class of N-aerogels, Dmitriev et al. have reported the first observation of the superfluid Polar phase, a phase which is stabilized by uniaxial anisotropy and not present in pure bulk $^3$He. The strong nematic order and small radius of the strands suggest that they may be modeled as arrays of parallel line impurities. We show that the experimentally determined phase diagram, including Polar, polar-distorted A, and B phases, for this class of N-aerogels is well accounted for by strong-coupling Ginzburg-Landau theory with a regular array of such line impurities. We also determine the locations of these phase transitions to be insensitive to positional disorder of the impurities. [Preview Abstract] |
Thursday, March 16, 2017 9:12AM - 9:24AM |
R20.00007: Vacuum Polarization Corrections to the Bosonic Mass Spectrum of Superfluid $^3$He-B James Sauls, Takeshi Mizushima $^3$He is a $S=1$, $L=1$ BCS condensate with total spin $J=0$. In addition to broken $U(1)$ symmetry, spin and orbital rotation symmetries are broken to $SO(3)_{J}$. Fermions acquire a mass, $m_{F}\equiv\Delta$, given by the BCS gap $\Delta$, and there are 18 Bosonic excitations - 4 Nambu-Goldstone (NG) and 14 Higgs modes - labeled by $J\in\{0,1,2\}$, and charge conjugation parity, $C=\pm 1$. For each $J,J_z$, there are two Bosonic partners with $C=\pm 1$. Based this Nambu proposed a sum rule relating the Fermion and Boson masses for BCS type theories: $M_{J^+}^2 + M_{J^-}^2 = 4m_{F}^2$, for each family labelled by $J$, where $M_{J^C}$ is the mass of the Bosonic excitation labelled by $(J,C)$. Nambu's sum rule (NSR) has recently been discussed in the context of the standard model to speculate on possible partners to the recently discovered Higgs Boson. We point out that Nambu's Fermion-Boson mass relations are not exact. Corrections to the masses of the Higgs modes arising from polarization of the parent Fermionic vacuum lead to substantial violations of Nambu's sum rule. Vacuum polarization corrections to the $J=2^{\pm}$ masses, as well as the NSR, are presented. A comparison between theory and experiment for the masses of the $J=2^{\pm}$ modes of $^3$He-B is presented. [Preview Abstract] |
Thursday, March 16, 2017 9:24AM - 9:36AM |
R20.00008: The stripe phase as a dynamical instability of the $J=2^{+}$, $m_J=0$ Higgs field in confined superfluid $^3$He Takeshi Mizushima, J. A. Sauls Superfluid $^3$He exhibits a variety of topological and broken symmetry phases. In a thin film, a ``stripe'' phase that spontaneously breaks translational symmetry has been predicted on the basis of weak-coupling quasiclassical theory,\footnote{A.B. Vorontsov and J.A. Sauls, PRL {\bf 98}, 045301 (2007).} and within strong-coupling Ginzburg-Landau (GL) theory.\footnote{J.J. Wiman and J.A. Sauls, JLTP {\bf 184}, 1054 (2016).} Starting from a Lagrangian formulation for the dynamics of the order parameter for $^3$He, we show that a superfluid film with translational symmetry is dynamically unstable for a range of film thicknesses of order several coherence lengths. The time-dependent GL Lagrangian describes the space-time Bosonic fluctuations around a stationary state of the GL functional. For a translationally invariant B-phase film the amplitude of the Bosonic mode dispersing from the $J=2^{+},m_J=0$ Higgs mode softens at a finite wavevector, $Q\simeq 0.3/\xi_0$, then develops a pole in the upper half of the complex frequency plane signalling a dynamical instability with exponential growth towards a new ground state with spontaneously broken translation symmetry. We discuss the dynamical instability and its relation to the predicted stripe phase of thin films of superfluid $^3$He. [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R20.00009: Anomalous Hall Effect for Electrons in $^3$He-A -- A Sensitive Probe of the Quasiparticle-Ion T-matrix Oleksii Shevtsov, J A Sauls An anomalous Hall effect for electron transport in superfluid $^3$He-A, reported by the RIKEN group, provided the first direct experimental signature of broken mirror and time-reversal symmetries in this topological superfluid. We developed a theory of the anomalous Hall effect of negative ions in $^3$He-A, which is in quantitative agreement with the RIKEN measurements. The main ingredient to the theory is the effective quasiparticle-ion (QP-ion) interaction potential, which uniquely determines the sub-gap excitation spectrum and transport properties of the ion. Here we present our analysis of the ion mobility as a spectroscopy of the QP-ion effective interaction. We report results for a set of potentials that determine the QP-ion t-matrix, including the hard-sphere potential, constrained random-phase-shifts, and interactions with short-range repulsion and intermediate range attraction. Our analysis shows that the transverse force on the moving ion, responsible for the anomalous Hall effect, is particularly sensitive to the structure of the QP-ion potential, and that strong short-range repulsion, captured by the hard-sphere potential, provides an accurate model for computing the forces acting on the moving electron bubble in superfluid $^3$He-A. [Preview Abstract] |
Thursday, March 16, 2017 9:48AM - 10:00AM |
R20.00010: Slip motion of a dimple lattice associated with Wigner solid on liquid He K. Kono, D. G. Rees, B.-C. Lee, S.-S. Yeh, N. R. Beysengulov, D. A. Tayurskii, J.-J. Lin, F. I. B. Williams 2D electrons on a surface of liquid helium undergo a phase transition to the Wigner solid (WS). When the WS forms, an electron starts to localize at each lattice site. The force exerted by electrons to the surface becomes inhomogeneous, and resulting in a dimple lattice commensurate with a WS lattice. A sliding phenomenon of the Wigner solid was discovered, which was ascribed to a decoupling of the WS from the dimple lattice [1]. The sliding threshold was interpreted by escape of the WS from a tilted washboard potential. Later, however, the Bragg-Cherenkov mechanism was proposed, which causes an infinite growth of the dimple lattice when the WS speed approaches the phase velocity of a surface capillary wave [2]. Since then, the determination mechanism of sliding threshold has been a long standing mystery. The recent observation of stick-slip motion of the WS gives an insight for this problem. [1] K. Shirahama and K. Kono, Phys. Rev. Lett \textbf{74}, 5 (1995). [2] M. I. Dykman and Yuri G. Rubo, Phys. Rev. Lett \textbf{75}, 25 (1997). [3] D. G. Rees, N. R. Beysengulov, J.-J. Lin and K. Kono, Phys. Rev. Lett. \textbf{116}, 206801 (2016). [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R20.00011: Pressure Dependence of the Phase Diagram of Superfluid $^3$He in Negatively Strained Aerogel A. M. Zimmerman, M. D. Nguyen, W. P. Halperin Many recent experimental and theoretical studies of the unconventional superfluid phases of $^3$He have shown that the introduction of confinement and impurity scattering on the scale of the superfluid coherence length can be used to engineer the superfluid phase diagram, altering the relative phase stability and nucleating entirely new phases not present in bulk superfluid $^3$He. One such system which has been proven to be particularly interesting is $\approx 98 \% $ porosity silica aerogel. In previous experiments, it was shown that the isotropic superfluid B-phase was stabilized by scattering from isotropic aerogel, while introducing anisotropic scattering by positively straining the aerogel strongly favored the anisotropic A-phase.$^{1,2}$ Interestingly, anisotropy induced by applying negative strain to the aerogel stabilizes the isotropic B-phase, requiring a magnetic field greater than a critical value to produce the A-phase. Here we report the results of recent investigations of the pressure dependence of of the phase diagram in these negatively strained silica aerogels.Research was supported by the NSF DMR-1103625. \\ \\ 1. J. Pollanen {\it et al}, Nat.Phys., {\bf 8}, 317–320 (2012). \\ 2. J. Pollanen {\it et al}, Phys. Rev. Lett., {\bf 107}, 195301, (2011). \\ [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R20.00012: The A-B transition of superfluid $^{\mathrm{3}}$He under confinement Jeevak Parpia, Nikolay Zhelev, T.S. Abhilash, Eric Smith, Robert Bennett, Lev Levitin, Xavier Rojas, John Saunders The influence of confinement on the phase diagram of superfluid $^{\mathrm{3}}$He is studied using the torsional pendulum method. We focus on the phase transition between the chiral A-phase and the time-reversal-invariant B-phase, motivated by the prediction of a spatially-modulated (stripe) phase at the A-B phase boundary. We confine superfluid $^{\mathrm{3}}$He to a single 1.08 $\mu $m thick nanofluidic cavity incorporated into a high-precision torsion pendulum, and map the phase diagram between 0.1 and 5.6 bar, the region of interest for the existence of the stripe phase. We observe only small supercooling of the A-phase, in comparison to bulk or when confined in aerogel. This has a non-monotonic pressure dependence, suggesting that a new intrinsic B-phase nucleation mechanism operates under confinement, mediated by the putative stripe phase. Both the phase diagram and the relative superfluid fraction of the A and B phases, show that strong coupling is present at all pressures, with implications for the stability of the stripe phase. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R20.00013: Texture Transition in the Superfluid B-phase of $^3$He in Anisotropic Silica Aerogel Man Nguyen, Andrew Zimmerman, William Halperin Superfluid $^3$He in the presence of silica aerogel is a model system to reveal the effects of disorder in condensed matter systems. Our NMR spectroscopy uncovered strikingly different phase diagrams between isotropically and anisotropically distributed impurities, indicating that the precise nature of impurities plays a strong role in the relative stability of phases.$^{1,2}$ Anisotropy, introduced through either negative or positive strain on the aerogel, acts as another experimental control parameter. Here we report observations of a strain-driven, textual transition of the order parameter in the B-like superfluid phase of $^3$He in negatively strained aerogel. The interplay between strain and other control parameters such as pressure and magnetic field is also discussed. Results suggest multiple lengths-scales introduced by the anisotropic aerogel are important in stabilizing phases and textures. This work was supported by the National Science Foundation, DMR-1103625. \newline 1. J. I. A. Li {\it et al.}, Phys. Rev. Lett. \textbf{112}, 115303 (2014) \newline 2. J. I. A. Li {\it et al.}, Phys. Rev. Lett. \textbf{114}, 105302 (2015) [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R20.00014: Pulsed NMR experiment on $^{\mathrm{3}}$He adsorbed on MCM-41 Chao Huan, Naoto Masuhara, Neil Sullivan The properties of the one-dimensional states have been an intriguing topic for the condensed matter physics community with growing interest in quantum systems in the last few years. In previous research, a metaporous material of MCM-41 has been used to study the crossover from 2D motion to 1D motion of adsorbed 3He atoms due to the uniqueness of the pore shape of MCM-41. In this experimental study, we applied pulsed NMR techniques to measure the nuclear susceptibility, the spin-lattice relaxation times (T1) and spin-spin relaxation times (T2) in the temperature region of 0.08-1.0 Kelvin. Preliminary measurements on an adsorbed 3He sample of multiple layers on MCM-41 show that the nuclear susceptibility deviates from the prediction of the Fermi liquid theory and both T1 and T2 decrease with temperature down to 80 mK. [Preview Abstract] |
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