Speaker: Prof. Paritosh Karnatak, Research Scientist at Basel.

Title: "Scanning SQUID on Lever  Probing Magnetism and Topology"
Date: Friday, November 14, 2025 - Time: 11:30 AM
Hi-Tea & Coffee: 11 AM

Venue: CeNSE Seminar Hall 

Abstract:
A topological superconductor is a highly sought-after phase of matter that, if realised, 
could enable topological quantum computation. I will present our attempts at engineering topological 
superconductivity in van der Waals materials [1–3] and discuss the challenges involved. In this 
context, I will present scanning microscopy based on a superconducting quantum interference 
device (SQUID), which we implemented on commercial silicon cantilevers [4]. Such local 
probes offer a powerful approach to investigate novel condensed matter phases and are 
complementary to quantum transport, which only accesses average quantities. Our scanning 
SQUID microscope (SSM) offers multimode imaging (topography, magne tometry, and thermometry), 
and is operable until ∼ 1 T. Moreover, with reliable sample-to-tip distance feedback (∼ 1 µm) it is robust 
under typical scanning conditions, making it a versatile probe for novel phenomena in topological materials,
 magnetic systems, and superconductors at the local scale (down to tens of nanometers) [5, 6]. Using SSM, we 
investigate the magnetic behavior of CrPS4, a weakly anisotropic vdW in terlayer antiferromagnet. We find that 
at the monolayer limit CrPS4 shows no remanence and a zero coercive field, unlike thicker odd layers that 
exhibit ∼ 50 mT coercivity and nearly 100% remanence. Layer-dependent studies reveal that interlayer coupling 
and dimensionality gov ern magnetic responses. These findings provide insight into mechanisms driving long-range 
magnetic order in two-dimensions. Finally, I will discuss our measurements in a magnetic topological insulator 
and outline plans for the future development of these probes. 

References 1D. I. Indolese, P. Karnatak, A. Kononov, R. Delagrange, R. Haller, L. Wang, P. Makk, K. Watanabe, 
T. Taniguchi, and C. Schönenberger, “Compact SQUID realized in a double-layer graphene heterostructure”, 
Nano letters 20, 7129–7135 (2020). 2P. Karnatak, Z. Mingazheva, K. Watanabe, T. Taniguchi, H. Berger, L. Forro, 
and C. Scho nenberger, “Origin of Subgap States in Normal-Insulator-Superconductor van der Waals Het erostructures”, 
Nano Lett 23, 2454–2459 (2023). 1 3L. Veyrat, C. Déprez, A. Coissard, X. Li, F. Gay, K. Watanabe, T. Taniguchi, 
Z. Han, B. A. Piot, H. Sellier, et al., “Helical quantum hall phase in graphene on SrTiO3”, Science 367, 781 786 
(2020). 4M. Wyss, K. Bagani, D. Jetter, E. Marchiori, A. Vervelaki, B. Gross, J. Ridderbos, S. Gliga, C. Schönenberger, 
and M.Poggio,“Magnetic, thermal, and topographic imaging with ananometer scale SQUID-On-Lever scanning probe”, 
Phys. Rev. Appl. 17, 034002 (2022). 5K. Bagani, A. Vervelaki, D. Jetter, A. Devarakonda, M. A. Tschudin, et al., 
“Imaging strain controlled magnetic reversal in thin CrSBr”, Nano Letters 24, 13068–13074 (2024). 6E. Marchiori, 
L. Ceccarelli, N. Rossi, G. Romagnoli, J. Herrmann, J.-C. Besse, S. Krinner, A. Wallraff, and M. Poggio, 
“Magnetic imaging of superconducting qubit devices with scanning SQUID-on-tip”, Applied Physics Letters 121 (2022).

Biography:

Paritosh earned a Bachelor’s and a Master’s degree in Physics at Indian Institute of Technology Kanpur. 
He later obtained his Ph.D. in Physics from Indian Institute of Science Bangalore, 
working with Prof. Arindam Ghosh, studying a wide range of phenomena in high mobility graphene devices.

After completing his Ph.D., he pursued postdoctoral research at the University of Basel, Switzerland 
working on superconducting van der Waals materials. Currently, Paritosh is a Research Scientist at 
Basel and employs scanning SQUID microscopy to study magnetic and topological materials.


Host Faculty:  Prof. Chandan Kumar