Electronic phase transitions and space charge doping in 2D materials

Abhay Shukla

Institut de Minéralogie, de Physique des Matériaux et de CosmoschimieCNRS UMR 7590, Université Pierre et Marie Curie, Paris 6

2D materials yesterday

• Carriers confined to the vicinity of junctions

• Variation of carrier concentration.

•• Well-defined interface.

2D materials yesterday• A lot of rich physics but not much material

variety

• Not 2D in the strict sense

• Complications for making materials, devices.

Oxide interfaces

Novoselov et al. PNAS 2005

2D materials today

JOHAN BISCARAS, ANDREA PARADISI,ZHESHENG CHEN, EDOARDO STERPETTI

2D materials in my group

2D Materials

Two dimensional (2D) materials: insulators, semiconductors, semi-metals, metals…

Graphene MoS2InSe Heterostructure

Transition metal dichalcogenides

(TMDC)

Semi-metal

III-VI semiconductor

s

Stacking different 2D materials

Good photo-electric conversionGood transport property Good photo-detector+ =

O2-Na+

Na2O =>2Na+ + O2-

Anodic Bondingfor making 2D materials

2D Materials: Fabrication

Shukla, Kumar, Mazher, Balan, Solid State Commun, 149 , 718, 2009 Gacem, Boukhicha, Chen, Shukla, Nanotechnology 23, 50579, 2012

MoS2 NbSe2

CuGeO3GaS

GaSe

Bi2Sr2CaCu2Ox

3L

1L

1L

1L 2L 3L

2L

1L

1L1L

1L

1L1L

2L

2D Materials: Fabrication

Insulator Metal transition:Change carrier density

• Pressure• Chemical doping• Electrostatic doping

2D Materials: Electrostatic dopingor

Band gaps, metals and insulators

Ahn, Triscone, Mannhart,Reviews of Modern Physics (2006)

Induced charge ~ VGεr/d

Doping

VG

d

Doping

Electrostatic doping techniques

SiO2 (300nm) on Si. Maximum doping : 1012 cm-2

Al2O3, HfO2, etc.Maximum doping : 1013 cm-2 for HfO2.

Liquid electrolyteMaximum doping > 1014 cm-2.

Space Charge doping: Graphene

• Commercial CVD graphene• borosilicate or soda-lime glass

Reversible, Ambipolar

Paradisi, Biscaras and Shukla, Applied Physics Letters, 107, 143103 (2015)

Graphene as a transparent conducting electrode

Raman mapping of peak intensity ratio

MoS2 : Electronic phase transitions at the flick of a switch

Doping

Insulator to Metal

Metal to Incomplete Superconductor

Confirm Superconductivity

Superconductivity in few layer MoS2

Biscaras, Chen, Paradisi and Shukla, Nature Communications6:8826 doi: 10.1038/ncomms9826 (2015)

Taniguchi groupIwasa group

Ye et al. Science (2012)Taniguchi et al. APL (2011)

Perspectives

• Other materials

• Other phase transitions: charge density wave, topological …

• Other interactions: correlations, magnetism

• Applications

Acknowledgements

funding• ANR SUPERTRAMP• LABEX MATISSE

facilities• INSP electromagnet• ENS Ulm Clean room