arXiv subjects

Tapas Senapati

Publications and source records attributed to Tapas Senapati.

4 recordsLinked to original sources

arXiv2026

Observation of Time-Domain Braiding of Non-Abelian Anyons at $\nu = 5/2$ State

Unlike elementary particles, which obey either bosonic or fermionic exchange statistics, certain quasiparticles, known as anyons, are predicted to exhibit Abelian or non-Abelian braiding statistics. While braiding Abelian anyons modifies the wavefunction by a 'statistical phase', braiding non-Abelian anyons implements a unitary transformation of the state within a degenerate subspace of states. Experimental evidence of non-Abelian braiding has thus far remained elusive. Here, we report a 'time-domain braiding' signature of non-Abelian anyons in the $\nu = 5/2$ fractional quantum Hall state, by extending our previously demonstrated approach with Abelian anyons at $\nu = 1/3$. Our approach is based on measurements of the current fluctuations arising from weak partitioning of a highly dilute one-dimensional edge mode. We independently probe the partition noise of the downstream charged mode and also that of the upstream neutral mode. These independent measurements agree with our theoretical predictions for 'time-domain braiding' of the downstream Abelian and the upstream non-Abelian anyons, respectively, in the 'particle-hole Pfaffian' topological order. Together, these results provide evidence for the presence of non-Abelian anyons.

cond-mat.mes-hall↗

arXiv2026

Observation of e/4 charge at $\nu=1/2$ in GaAs

Even-denominator fractional quantum Hall states (FQHSs) fall outside the standard Laughlin's and Jain's odd-denominator hierarchy. In this work, we study the FQHS $\nu=1/2$ in the lowest Landau level. The state is confined within a 70 nm-wide GaAs quantum well, where the electrons exhibit a bilayer-like charge distribution. Inter-layer interactions stabilize the $\nu=1/2$ FQHS, which is predicted to host quasiparticles with charge e/4 - with either Abelian or non-Abelian topological order. Here, we report on shot-noise measurements of partitioned quasiparticles at $\nu=1/2$, where charge partitioning is generated by a unique etch-defined quantum point contact. Our measurements were performed on two nominally identical devices, at two independent experimental setups. Analysis of shot noise in the weak-backscattering regime in each device reveals quasiparticles with charge e/4. These observations provide a clear benchmark for future studies aimed at probing the topological order of the $\nu=1/2$ FQHS and its quasiparticles' exchange statistics.

cond-mat.mes-hall↗

arXiv2024

Sensing magnetic flux of Langmuir-Blodgett films of a molecular magnetic system using superconducting films and nano-SQUID devices

We report a study on the response of superconducitng micro-tracks and quantum interference devices (SQUIDs) to a proximal SMM film. As a test case, Langmuir-Blodgett $Mn_{12}$-ac SMM films have been grown on 2 $\mu$m wide Nb tracks and Nb nano-SQUIDs to observe the proximity effect of magnetic moment and magnetization tunneling, respectively. The superconducting critical temperature of thin Nb tracks (thinner than the coherence length of Nb) were found to decrease by the magnetic moment of $Mn_{12}$-ac SMM. Following the thermally activated flux flow (TAFF) model, we found an increase in the vortex unbinding energy of the SMM coated Nb tracks, near critical temperature. More importantly, the random alignment of moments of the $Mn_{12}$-ac molecules at low fields seemed to have the enhancing effect on vortex unbinding energy rather than the saturated state of $Mn_{12}$-ac molecules at high fields. In the fully superconducting state, on the other hand, the vortex pinning effects were found to be more effective in the saturated state of the $Mn_{12}$-ac molecules, as seen from magnetoresistance and field dependent critical current measurements. In a separate experiment, a Langmuir-Blodgett film of SMM was grown on a nano-SQUID to look for local changes in magnetization arising from magnetizatin tunnelling phenomenon in SMMs. Upon magnetizing the SMM (deposited on SQUIDs) at 2 K along the plane of the film and allowing it to relax, we found occasional jumps in the underlying SQUID voltage, unlike bare nano-SQUIDs, which did not show any such jumps over several hours. Therefore, we believe that the jumps in the SQUID voltage are the signatures of random tunneling of magnetization in the SMM layer.

cond-mat.supr-con↗

arXiv2023

Phase biasing of a Josephson junction using Rashba-Edelstein effect

Manifestation of orbital coupling of spin degree of freedom in condensed matter systems has opened up a new dimension for the field of spintronics. The most appealing aspect of the spin-orbit coupling is the apparent Magnus force sensed by a spin system which locks the Fermi momentum with electron spin in a fascinating manner. In the current carrying state, the resulting macroscopic spin polarization becomes directly accessible in the form of spin current or spin density. At a Rashba interface, for example, a charge current shifts the spin-locked Fermi surface, leading to a non-equilibrium spin density at the interface, commonly known as the Rashba-Edelstein effect. Since the Rashba-Edelstein effect is an intrinsically interface property, direct detection of the spin moment is harder to set-up. Here we demonstrate that a simple planar Josephson Junction geometry, realized by placing two closely spaced superconducting electrodes on such a Rashba interface, allows a direct estimation of strength of the non-equilibrium spin moment. Measurements of Fraunhofer patterns of Nb-(Pt/Cu)-Nb planar Josephson junctions in a perpendicular magnetic field showed a shift of the center of the Fraunhofer pattern to a non-zero field value. By performing extensive control measurements, we argue that the screening currents in the junction effectively lock the external field with the spin moment of the Rashba-Edelstein effect induced spin-density, leading to the observed shift in the Fraunhofer patterns. This simple experiment offers a fresh perspective on direct detection of spin polarization induced by various spin-orbit effects. Very interestingly, this device platform also offers the possibility of retaining a controllable phase at zero field in the junction without using any magnetic material, and thereby useful as phase batteries for superconducting quantum circuits.

cond-mat.mes-hall↗