सीएसआईआर-राष्ट्रीय भौतिक प्रयोगशाला

CSIR-National Physical Laboratory

Quantum Resistance Metrology and 2D Physics

The group focuses on the growth, synthesis and characterization of quantum materials. These include two-dimensional (2D) systems such as vander Waal’s materials and heterostructures, topological insulators and strongly correlated oxide materials. The primary goal of the group is to develop an indigenous technology towards the realization of quantum resistance metrology by exploiting the integer quantum Hall effect (IQHE) for which the current focus is on epitaxial graphene, oxide heterostructures and topological insulator.  Experiments are corroborated using the first principles of density functional theory-based electronic structure calculations.

The group also carries out high precision QHE measurements with accuracy of 20 ppb or better. A 1 kOhm standard is directly measured against the GaAs/AlGaAs QHE and subsequently resistances in the range 1 Ohm to 1 MOhm are measured with very high accuracy. The CMC of the group for 1 kOhm measurement against QHE (Uc (k=2) = 80ppb) has been peer reviewed twice and it is at the BIPM website.

The group has 06 Scientists and 15 Ph.D students working on the various aspects of quantum materials, which includes (i) growth and synthesis using PLD, sputtering, etc  (ii) Materials characterization of structure, electronic, magnetic, optical and transport properties, and (iii) Theoretical and computational studies.

  • Growth and optimization of epitaxial graphene for indigenous development of graphene-based Quantum Hall Resistance Standard
  • Realization of quasi-2DEG in oxide heterostructures with focus on enhancing the carrier mobility at the hetero-interface.
  • Growth and characterization of topological insulator (TI) thin films, laser MBE epitaxial III-nitrides and two-dimensional (2D) materials
  • Band gap engineering in Two-dimensional materials and their interfaces through band-width  and band-filling control
  • Electronic structure study of surfaces and interfaces using photoemission spectroscopy
  • Defect engineering and metal-insulator transition in oxide surfaces and interfaces
  • Multi-scale materials modeling using ab-initio electronic structure calculations
  • Pulsed Laser Deposition (PLD) system with RHEED for the growth of all oxide 2DEG heterointerfaces
    pulsed_laser_deposition_system_with_RHEED_for_the_growth_of_all_oxide_2DEG heterointerfaces
  • Three source UHV-magnetron sputtering systems for the growth of intermetallic thin film superlattices/heterostructures (like TIs) for QAHE and SHE

  • Two HV-magnetron sputtering systems for the growth of all oxide FM/AFM, Superconductor/FM heterostructures, and topological insulator thin films/ heterostructures
  • Growth system for Graphene Epitaxy (GrapE): An indigenously developed system for growth of epitaxial graphene on SiC

  • High precision magnetotransport measurement and resistance ratio measurement system used in quantum resistance (QHR) metrology
    Typical specifications of the GaAs/AlGaAs based QHE devices used at NPL Device: GaAs-AlxGa1-xAs (x=0.3), GaAs (1.5eV) is lightly p-doped, AlGaAs (2.2eV) is n-doped, ~ 10-20 T-1, n ~ 3-6 x 1015 m-2, B (i=2)~ 7-9 T.
    contact_schematic_(right)_and_actual_device_on_To8_ holder_with_contacts

    Contact schematic (right) and actual device on To8 holder with contacts

    Longitudinal and transverse (Hall) resistance of a GaAs-AlxGa1-xAs (x=0.3) device measured at 1.3 K

  • Temperature dependent photoconductivity measurement
  • 3 Zone tube furnace for 2D materials growth
  • Thermal evaporation
  • Wire bonder