Download presentation

Presentation is loading. Please wait.

Published byPatricia Rose Modified about 1 year ago

1
Vortex Glass, Dislocation Glass, Stripe Glass: Long Range Interactions at Work 1. Vortex Glass: Long vs. Short Range Interactions 2. Dislocation Structures in 2D Vortex Matter 3. Stripe Glasses in Magnetic Films & 2DEG M. Chandran, C. Pike, R. Scalettar M. Winklhofer & G.T. Zimanyi U.C. Davis B. Bako, G. Gyorgyi & I. Groma Budapest

2
Long Range Interactions Form Slow Structures in Cuprates Competing Energies: Kinetic energy Short range magnetic Long range Coulomb - Phase separation (Emery, Kivelson) - Stripe formation (Littlewood, Zaanen Emery, Kivelson, …) Experiment (Davis, Yazdani, …) J.C. Davis, Physics Today, September 2004

3
1. Vortex Glass: The Original Proposition

4
Vortex Glass with Long Range Interactions: the Gauge Glass No Screening: Glass Transition (Young 91)

5
Expt.: No Extended Defects - No Vortex Glass Yeh (1997) Lopez, Kwok (1997) Lobb (2001) Foglietti, Koch (1989)

6
Screening: Short Range Interactions: No Gauge Glass Young (95)

7
Vortex Glass Transition Arrested by Screening: Vortex Molasses Jc does not vanish as a power law: levels off around Langevin dynamics for vortices: 1. Interacting elastic lines 2. In random potential 3. Overdamped dynamics

8
Resistivity in Vortex Molasses Resistivity finite below “J sc ”: Vortex Molasses Resistivity can be fitted by a - power law; or the - Vogel-Fulcher law

9
Finite Size Scaling Long Range Interaction Short Range Interaction

10
log (T-T G ) Vortex Glass Vortex Molasses Interaction Crossover from Long Range to Short Range Causes Criticality Crossover from Scaling to Structural Glasses Vortex Molasses short range interactions long range interactions

11
2. Dislocation Glass In 2D Disordered Vortex Matter dislocations were supposed to: Distributed homogeneously Characterized by single length scale D Giamarchi-Le Doussal ’00 Inspired by KT-Halperin- Nelson-Young theory of 2D melting

12
Magnetic Field Sweep B/B c2 = 0.1 (a) 0.4 (b) 0.5 (c) 0.6 (d) 0.8 (e) 0.9 (f) v Blue & Red dots: 5 & 7 coordinated vortices: disclinations Come in pairs: dislocations Dislocations form domain walls at intermediate fields

13
What is the physics? Dislocations are dipoles of disclinations, with anisotropic logarithmic interaction. Theory averages anisotropy and applies pair unbinding picture ~ KTHNY melting. However: - The dipole-dipole interaction is strongly anisotropic: - parallel dipoles attract when aligned; - energy is minimized by wall formation; - energetics different from KTHNY. Dislocation structures formed by anisotropic interactions

14
“Absence of Amorphous Vortex Matter” Fasano, Menghini, de La Cruz, Paltiel, Myasoedov, Zeldov, Higgins, Bhattacharya, PRB, 66, 020512 (2002) NbSe 2 T= 3-7K H= 36-72 Oe Simulations NbSe 2

15
Low Disorder Medium Disorder NbSe 2 Simulation Domain Configurations We accessed lowest dislocation densities

16
Dislocation Domain Structures in Crystals Pattern formation is typical Rudolph (2005)

17
Dislocation Simulations 1. Overdamped dynamics 2. is the glide/climb component of the stress-related Peach-Kohler force 3. Dislocation interaction is in-plane dipole-dipole type 4. No disorder Novelty: 1. Dislocations move in 2D: B g - glide mobility, B c - climb mobility; 2. Dislocations rotate: through antisymmetric part of the displacement tensor 3. Advanced acceleration technique Glide Climb

18
Computational Details Kleinert formalism 1. Separate elastic and inelastic displacement 2. Isolate the antisymmetric component of displacement tensor 3. Rotate Burgers vector

19
Observation I: Separation of Time Scales Fast fluctuations: from near dislocations Slow fluctuations: large scale dynamics from far dislocations

20
Observation II: Stress Distribution Modeling

21
Stochastic Coarse Graining 1. Divide simulation space into boxes 2. Calculate mean (coarse grained) dislocation density for each box 3. Slow interactions (AX): Approximate stress from box A in box X by using coarse grained density. 4. Fast interactions (BX): Generate random stress t from distribution P(t) with average stress t ave. 5. Move dislocations by eq. of motion. 6. Repeat from 2. 1-10 million dislocations simulated in 128x128 boxes X A B

22
Stochastic Coarse Graining: No Climb, No Rotation, Shearing Full simulations: -1 million dislocations -(~20 million vortices) -Profound structure formation -Sensitive to boundary, history -Work/current hardening

23
Stochastic Coarse Graining: No Climb, No Rotation, Shearing Box counting: - Domains have fractal dimension -D=1.86 - No single characteristic length scale Number of domains N(L) of size L with no dislocations

24
Stochastic Coarse Graining: Climb, No Rotation, No Shearing Climb promotes structure formation, even without shearing

25
Stochastic Coarse Graining: Climb, Rotation, No Shearing log(time) B c /B g =1.0 B c /B g =0.1 1. Domain structure formation without shear 2. Climb makes domain structures possible 3. Domain distribution: not fractal 4. Effective diffusion const goes to zero: Domain structure freezes: Dislocation Glass

26
Andrei group PRL 81, 2354 (1998) Expt.: Shearing Increases Ic

27
Rudolph et al Expt.: GaAs: Increasing Climb Induces Domain Structure Formation Climb

28
3. Stripe Glass Co/Pt magnetic easy axis: out of plane Potential perpendicular recording media [Co(4Å)/Pt(7Å)] N : Hellwig, Denbeaux, Kortright, Fullerton, Physica B 336, 136 (2003). Co Pt H app N=50

29
Transmission X-ray Microscopy 3m3m Stage 1: Sudden propagation of reversal domains. Stage 2:Expansion/contraction of domains, domain topology preserved. Stage 3:Annihilation of reversal domains.

30
Modeling Magnetic Films Classical spins, pointing out of the plane Spins correspond to total spin of individual domains: spin length is continuous variable Competing interactions: –Exchange interaction: nearest neighbor ferromagnetic –Dipolar interaction: long range antiferromagnetic (perpendicular media) Finite temperature Metropolis algorithm (length updated) Spivak-Kivelson: Hamiltonian same as 2DEG & Coulomb systems Tom Rosenbaum: Glassy phases in dipolar LiHoYF

31
T C(T) Equilibrium Phases

32
Expt.: Two Phases Observed in FeSiBCuNb Films Henninger

33
Non-equilibrium Anneal: Supercooled Stripe Liquid Stripe Glass Protocol: 1.Cool at a finite rate to T 2.Study relaxation at T Typically configuration is far from equilibrium: Supercooled Stripe Liquid Stripe Glass ~ Schmalian-Wolynes

34
T 1/T ~ Fragile Glass ~ Strong Glass Relaxation of Persistence

35
Aging P(t, t w ) t w =10 4 t w =10 5 t w =10 6 t w =10 7 Good fit: P(t, t w ) = P[(t-tw)/tw] t Blue regions: frozen

36
Summary 1. Vortex Glass: - Crossover of range of interaction from long to short changes Glass transition from Scaling to Molasses transition 2. Dislocation Glass: - In 2D in-plane dipoles form frozen domain structures: Dislocations, Vortex matter - Climb, rotation, shearing, disorder - Stochastic Coarse Gaining, ~ 10 million vortices 3. Stripe Glass: - In 2D out-of plane dipoles form Stripe Glass: Magnetic films, 2DEG, Coulomb systems - Persistence, aging - Strong and Fragile Glass aspects observed How to see your glass? Low frequency spectrum of noise is large (Popovic), slow dynamics, imaging

Similar presentations

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google