quantum phase transitions in anisotropic dipolar magnets l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Quantum phase transitions in anisotropic dipolar magnets PowerPoint Presentation
Download Presentation
Quantum phase transitions in anisotropic dipolar magnets

Loading in 2 Seconds...

play fullscreen
1 / 33

Quantum phase transitions in anisotropic dipolar magnets - PowerPoint PPT Presentation


  • 131 Views
  • Uploaded on

Quantum phase transitions in anisotropic dipolar magnets. Moshe Schechter. University of British Columbia. In collaboration with: Philip Stamp, Nicolas laflorencie. LiHoY F. x. 1-x. 4. 1. Transverse field Ising model:. LiHoY F. x. 1-x. 4. 1. Transverse field Ising model:.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Quantum phase transitions in anisotropic dipolar magnets' - nevaeh


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
quantum phase transitions in anisotropic dipolar magnets
Quantum phase transitions in anisotropic dipolar magnets

Moshe Schechter

University of British Columbia

In collaboration with: Philip Stamp, Nicolas laflorencie

lihoy f
LiHoY F

x

1-x

4

1. Transverse field Ising model:

lihoy f3
LiHoY F

x

1-x

4

1. Transverse field Ising model:

2. Dilution!

Reich et al, PRB 42, 4631 (1990)

qpt in dipolar magnets
QPT in dipolar magnets

Thermal and quantum transitions

MF of TFIM

MF with hyperfine

Bitko, Rosenbaum, Aeppli PRL 77, 940 (1996)

various dilutions
Various dilutions

Ghosh, Parthasarathy, Rosenbaum, Aeppli Science 296, 2195 (2002)

Brooke, Bitko, Rosenbaum, Aeppli Science 284, 779 (1999)

Ronnow et. Al. Science 308, 389 (2005)

Giraud et. Al. PRL 87, 057203 (2001)

lihof a model quantum magnet
LiHoF - a model quantum magnet

4

S. Sachdev, Physics World 12, 33 (1999)

dilution quantum spin glass
Dilution: quantum spin-glass

-Thermal vs. Quantum disorder

-Cusp diminishes as T lowered

Wu, Bitko, Rosenbaum, Aeppli, PRL 71, 1919 (1993)

fall and rise of qpt in dilute dipolar magnets
Fall and rise of QPT in dilute dipolar magnets
  • Hyperfine interactions and off-diagonal dipolar terms
  • No QPT in spin-glass regime
  • In FM regime can study classical and quantum phase transitions with controlled disorder and with coupling to spin bath
anisotropic dipolar magnets

S

-S

Anisotropic dipolar magnets

Large spin, strong lattice anisotropy

anisotropic dipolar magnets10

S

-S

Anisotropic dipolar magnets

Large spin, strong lattice anisotropy

Single molecular magnets

Magnetic insulators

anisotropic dipolar magnets tfim

S

-S

Anisotropic dipolar magnets - TFIM

Large spin, strong lattice anisotropy

hyperfine interaction electro nuclear ising states13
Hyperfine interaction: electro-nuclear Ising states

Hyperfine spacing: 200 mK

- M.S. and P. Stamp, PRL 95, 267208 (2005)

phase diagram transverse hyperfine and dipolar interactions
Phase diagram – transverse hyperfine and dipolar interactions

Splitting

PM

SG

Experiment

No off. dip.

With off. dip.

- M.S. and P. Stamp, PRL 95, 267208 (2005)

anisotropic dipolar systems offdiagonal terms16

S

-S

Anisotropic dipolar systems – offdiagonal terms

symmetry

symmetry

M. S. and N. Laflorencie, PRL 97, 137204 (2006)

imry ma argument
Imry-Ma argument

Ground state:

(all spins up)

Domain:

(spins down)

Energy cost

Energy gain

Spontaneous formation of domains

Critical dimension: 2 (for Heisenberg interaction: 4)

Y. Imry and S. K. Ma, PRL 35, 1399 (1975)

spin glass correlation length
Spin glass – correlation length

Energy gain:

Y. Imry and S. K. Ma, PRL 35, 1399 (1975)

M.S. and N. Laflorencie, PRL 97, 137204 (2006)

spin glass correlation length19
Spin glass – correlation length

Energy gain:

Energy cost:

Y. Imry and S. K. Ma, PRL 35, 1399 (1975)

M.S. and N. Laflorencie, PRL 97, 137204 (2006)

spin glass correlation length20
Spin glass – correlation length

Energy gain:

Energy cost:

Only extra sqrt of surface bonds are

satisfied, can optimize boundary.

Fisher, Huse PRL 56, 1601 (86); PRB 38, 386 (88)

M.S. and N. Laflorencie, PRL 97, 137204 (2006)

spin glass correlation length21
Spin glass – correlation length

Energy gain:

Energy cost:

Only extra sqrt of surface bonds are

satisfied, can optimize boundary.

Flip a droplet – gain vs. cost:

Fisher, Huse PRL 56, 1601 (86); PRB 38, 386 (88)

M.S. and N. Laflorencie, PRL 97, 137204 (2006)

spin glass correlation length22
Spin glass – correlation length

Energy gain:

Energy cost:

Only extra sqrt of surface bonds are

satisfied, can optimize boundary.

Flip a droplet – gain vs. cost:

Droplet size –

Correlation length

Fisher, Huse PRL 56, 1601 (86); PRB 38, 386 (88)

M.S. and N. Laflorencie, PRL 97, 137204 (2006)

sg unstable to transverse field

quasi

SG

SG unstable to transverse field!

Finite, transverse field dependent correlation length

M. S. and N. Laflorencie, PRL 97, 137204 (2006)

enhanced transverse field phase diagram

PM

SG

Experiment

No off. dip.

With off. dip.

Enhanced transverse field – phase diagram

Quantum disordering harder

than thermal disordering

Main reason – hyperfine interactions

Off-diagonal dipolar terms in

transverse field – also enhanced

effective transverse field

M.S. and P. Stamp, PRL 95, 267208 (2005)

random fields not particular to sg
Random fields not particular to SG!

Reich et al, PRB 42, 4631 (1990)

interest in fm rfim
Interest in FM RFIM

Diluted anti-ferromagnets:

- Equivalence only near transition

- No constant field in the staggered magnetization

- Not FM - applications

interest in fm rfim27
Interest in FM RFIM
  • Verifying interesting results on DAFM
  • Experimental techniques
  • Novel fundamental research (away from transition, conjugate field, quantum term)
  • Applications in ferromagnets, e.g. domain wall dynamics in random fields
are the fields random
Are the fields random?

Square of energy

gain vs. N,

different dilutions

Inset: Slope as

Function of dilution

M. S., cond-mat/0611063

random field and quantum term are independently tunable

S

-S

Random field and quantum term are independently tunable!

M. S., cond-mat/0611063

M. S. and P. Stamp, PRL 95, 267208 (2005)

ferromagnetic rfim

S

-S

Ferromagnetic RFIM

M. S., cond-mat/0611063

M. S. and P. Stamp, PRL 95, 267208 (2005)

ferromagnetic rfim31

S

-S

Ferromagnetic RFIM

- Independently tunable

random and transverse fields!

M. S., cond-mat/0611063

- Classical RFIM despite

applied transverse field

M. S. and P. Stamp, PRL 95, 267208 (2005)

realization of fm rfim
Realization of FM RFIM

Sharp transition at high T,

Rounding at low T

(high transverse fields)

Silevitch et al., Nature 448, 567 (2007)

conclusions
Conclusions
  • Strong hyperfine interactions in LiHo result in electro-nuclear Ising states. Dictates quantum dynamics and phase diagram in various dilutions
  • Ising model with tunable quantum and random effective fields can be realized in anisotropic dipolar systems
  • SG unstable to transverse field, no SG-PM QPT
  • First FM RFIM – implications to fundamental research and applications