Electron – holeinstabilities in TiSe2

Gaël MonneyUniversity of Fribourg, Switzerland

Our group & collaborators

Electron spectroscopy group in Fribourg• Clément Didiot, Zuzana Vydrova,

Nicolas Mariotti (Gunnar Garnier, Eike Schwier)

• Philipp Aebi Collaborations• Hans Beck, Univ. of Neuchâtel• Claude Monney, PSI, Switzerland• H. Berger, EPFL

1

Part 1 :

The context

Charge density waves (CDW) Peierls transitions (electron signature)

2

Charge density waves (CDW) Kohn anomaly (phonon signature)

3

CDW : driving forces Fermi Surface Nesting

Jahn-Teller effect

Excitons

4

TiSe2 properties

Reciprocal space

Real space

TiSe

Di S

alvo

et a

l., P

RB,

1976

5

Part 2 :

Experiments

Electronic signatures (by ARPES)

6

Other measurements 7

Part 3 :

The models

Exciton BCS model ( )

Hamiltonian

Green’s functions

Anomalous Green’s functions

Order parameter

8

Exciton BCS model ( )

9

Previous model : Hervé Cercellier et al., PRL, 2007

Electron – hole fluctuations ( ) The model

Definitions

Electron-hole susceptibility

Bethe-Salpeter equation

10

Electron – hole fluctuations The physics

11

Part 4 :

The results

Crossings vs. nesting 12

Electron renormalization Comparison

13

Phonon renormalization 14

Part 5 :

Outlook

Chirality 15

Thanks

Part I : CDWs

Part 2 : Experiments

Part 3 : Models

Part 4 : Results