AG Held

  

  

  

  

Anna Galler

Dr. Patrik ThunströmCiro Taranto

Thomas Schäfer Elias Assmann Dr. Jan Tomczak

&

Dr. Marco Battiato

Liang Si

Dr. Georg Rohringer

Markus Wallerberger

Patrik Gunacker

Dr. Zhicheng Zhong

Recent/Current PAs Monika Stipsitz, Patrik Gunacker,  Rainer Bachleitner, Tin Ribic, Stefan Donsa, Lukas Semmelrock, Georg Harrer, Lorenz Auzinger 

Dr. Angelo  Valli

AG Toschi

Theory @ IFP

AG Held: Research topics

 computational materials science: LDA+DMFT           

 quantum field theory: DA            

 physics of strongly correlated electron systems:       thermoelectrics, kinks, QCP, heterostructures...           

 physics of nanoscopic systems:       NanoDMFT,   decoherence, Kondo, RMT qdots...             

       

Computational Materials ScienceLDA bandstructure theory many body theory

+ • material specific • many electron physics− • effective one-particle approach • model Hamiltonian

Computational Materials ScienceLDA bandstructure theory many body theory

+ • material specific • many electron physics− • effective one-particle approach • model Hamiltonian

: Coulomb WW

⇒ correlations

←lattice potenti-

al

Computational Materials ScienceLDA bandstructure theory many body theory

+ • material specific • many electron physics− • effective one-particle approach • model Hamiltonian

: Coulomb WW

⇒ correlations

←lattice pot.

Computational Materials ScienceLDA bandstructure theory many body theory

+ • material specific • many electron physics− • effective one-particle approach • model Hamiltonian

: Coulomb WW

⇒ correlations

←lattice pot.

time averaged

electron density

−→

Computational Materials ScienceLDA bandstructure theory many body theory

+ • material specific • many electron physics− • effective one-particle approach • model Hamiltonian

time averaged

electron density

−→

Computational Materials ScienceLDA bandstructure theory many body theory

+ • material specific • many electron physics− • effective one-particle approach • model Hamiltonian

time averaged

electron density

−→

Local density approximation (LDA) + dynamical mean field theory (DMFT):realistic calculation of strongly correlated materials

Quantum Field Theory for Solids

Development of new methods

e.g. dynamical vertex approximation (DΓA), 1PI functional

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j

G

=

j

i i

i

k

j j+ ...

Γ

ΓΓ

Γ

Γ

i j

i

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Γred

=Σ

• Magnons

• Quantum criticality

• High temperature superconductivity

ERC grant AbinitioDΓA

Physics of correlated electron systems

Kinks

0

0.01

0.02

0.03

0.04

0.05

0 0.02 0.04 0.06 0.08

χ s-1

(Q,ω

=0

)

T/D

TNTN

DΓA

DMFTTN

DMFT

DΓA 2d U=D

Fit: a e-2 b/T

DΓA 3d, U=1.25 D

Fit: c (T-TN)2ν

Criticality Hubbard model

0 200 400 600 800 1000 12000

50

100

150

200

250

xNa = 0.7,sing. cryst., exp.xNa = 0.7,sing. cryst.,exp.xNa = 0.76,sing. cryst.,exp.xNa ∼ 0.6,poly cryst.,exp.xNa = 0.6,DMFTxNa = 0.7,DMFTxNa = 0.8,DMFT

T [K]

S[µ

V/K

]

Thermoelectrics (here NaxCoO2)

Physics of nanoscopic systems

decoherence, Kondo effect,random matrix theory in qdots

NanoDMFT for coupled quantum dots,macromolecules, clusters on surfaces ...

Topic 1 (PA): Thermoelectricity – Boltzmann equationFestkorpertheorie

Puzzling large thermopower in FeSb2

Modelling thermopower by semiconducting gap plus in-gap statesinclude finite bandwidth in Boltzmann equation

Prerequisite: good theory skills, C, FORTRAN or mathematica

Supervisor: Battiato, Tomczak

Topic 2 (PA): Ferromagentism in (110) heterostructuresFestkorpertheorie

0.40.20.0-0.2-0.4

kM (Å-1

)

0.1

00

.05

0.0

0

EB (

eV

)

(e

V)

j

[110]

t2

t1

t2

t1

×[001]

[110]

x

×

y

z

e SrTiO3(110) subbands

3.0

2.0

1.0

En

erg

y (e

V)

ГZ M(0,0,/a) (/2a,/2a,0)(0,0,0)

kZ

kM

dyz

, dzx

dxy

Analysis of tight binding model (from LDA) correlations by Hartree-FockPrerequisite: good theory skillsSupervisor: Zhong, Held

Topic 3 (PA): Spin-orbit couplingFestkorpertheorie

0.40.20.0-0.2-0.4

kM (Å-1

)

0.1

00

.05

0.0

0

EB (

eV

)

(e

V)

j

Analysis of tight binding model (from LDA)

modelling correlation effects by Hartree-Fock

H = Htightbinding + ζLS +∑

iασ,α′σ′

Uniασ〈niα′σ′〉 (1)

Prerequisite: good theory skills

Supervisor: Zhong, Held

Topic 4 (PA): Magnetism in graphene nanoflakesComputational Materials Science

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Dynamical mean field theory

Tight binding model correlations by Hartree-Fock

Prerequisite: good theory skills, FORTRAN, C or python

Supervisor: Valli, Held