arXiv subjects

Aabir Mukhopadhyay

Publications and source records attributed to Aabir Mukhopadhyay.

6 recordsLinked to original sources

arXiv2026

Synthetic Flat Bands, Hierarchical Topology, and Phase-Fluctuation-Insensitive Quantized Transconductance in Josephson Junctions

We uncover hierarchy of topological phases within the synthetic Brillouin zone of a three-terminal Josephson junction's (3-TJJ's) Bogoliubov-de Gennes spectrum. We demonstrate that the above-gap continuum realizes a Chern insulator phase with quantized monopole charges (\pm 1), while the subgap Andreev bound states (ABS) are characterized by a quantized dipolar invariant. By breaking time-reversal symmetry at the junction, we induce synthetic flat bands that suppress DC Josephson currents across the entire phase-bias space. Furthermore, under voltage bias, the junction exhibits a robust quantization of the time-averaged transconductance that is reminiscent of a quantized Hall conductance plateau owing to the flat band limit and its dipole phase. As a byproduct, the flat band produces a global "sweet plateau" of phase insensitivity, surpassing localized sweet spots of conventional superconducting qubits and enabling a robust architecture for symmetry-protected Andreev qubits.

cond-mat.mes-hall↗

arXiv2024

Identification of odd-frequency superconducting pairing in Josephson junctions

Optimal choice of spin polarization enables electron injection into the helical edge state at a precise position, despite the uncertainty principle, permitting access to specific nonlocal Green's functions. We show, within 1D effective description, that this fact facilitates a direct identification of odd-frequency pairing through parity measurement (under frequency reversal) of the nonlocal differential conductance in a setup comprising the Josephson junction on the helical edge state of a 2D topological insulator with two spin-polarized probes tunnel-coupled to the junction region. A 2D numerical simulation has also been conducted to confirm theoretical predictions as well as to demonstrate the experimental feasibility of the proposal.

cond-mat.mes-hall↗

arXiv2023

Anomalous topology and synthetic flat band in multi-terminal Josephson Junctions

Andreev bound states trapped in a multi-terminal Josephson junction (JJ) can be assigned a synthetic band topology owing to their periodic dependence on the Josephson phase bias. We demonstrate that the BdG symmetry adds a twist to this topological character, i.e., gap closing points may or \textit{may not} correspond to change of Chern number, hence extending the standard paradigm for topological bands. We further show that the topology of Andreev bands depends only on the scattering matrix of the junction and is independent of the topological nature of superconductors forming the JJ hence indicating a universal behaviour of multi-terminal JJ. We also show that the chiral junction, supported by quantum Hall state at the junction region, leads to flat Andreev bands (implying absence of DC Josephson effects) that are devoid of Berry curvature ( implying absence of AC Josephson effects). Such electrically inert JJ may be useful for storage of quantum information in future quantum devices.

cond-mat.mes-hall↗

arXiv2022

Chiral detection of Majorana bound states at the edge of a quantum spin Hall insulator

A hybrid setup consisting of a superconductivity-proximitized quantum spin Hall (QSH) insulator and a quantum anomalous Hall (QAH) insulator is proposed for chiral injection of electrons into the Majorana bound state (MBS). An unexplored region of the phase space involving the exchange field induced boost of the helical edge state is then proposed for the detection of the MBS. 2-D transport simulations of our proposed setup is compared with the corresponding setup in the absence of the QAH region, when moderate disorder and a small but finite bulk out-of-plane magnetic field and a Rashba field are included. The remarkable contrast between the two results demonstrates the possibility for an unprecedented immunity from disorder-induced masking of the MBS detection in our proposed setup.

cond-mat.mes-hall↗

arXiv2021

Thermoelectric response of Josephson junction: from ballistic to disordered

It is known that Josephson junction (JJ) hosting scattering centers with energy-dependent scattering amplitudes which breaks the $ω\rightarrow-ω$ symmetry (where $ω$ is the excitation energy of electron about the Fermi level) exhibits finite thermoelectric response. In contrast, here we show that even in a ballistic JJ this symmetry is broken and it leads to a non-zero thermoelectric response when the junction length is of the order of coherence length of the superconductor and the corresponding thermoelectric coefficient confirms to the universal sinusoidal dependence on $ϕ_{12}$, where $ϕ_{12}$ is the superconducting phase bias. In presence of multiple scatterers in the junction region, we have numerically shown that the sign of the even-in-$ϕ_{12}$ part of the thermoelectric coefficient fluctuates violently from one disorder configuration to another hence averaging to vanishingly small values while the odd part tends towards the universal sinusoidal dependence on $ϕ_{12}$ as we approach the large disorder limit under disorder averaging.

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arXiv2019

Thermal signature of Majorana fermions in Josephson junction

Existence of distinctive correlation between the thermal conductance and the Josephson current across a 1-D topological Josephson junction (T-JJ) is established and an expression connecting the two is derived in the short junction limit. It is shown that the three terminal T-JJ provides us with an ideal set-up for exploiting the distinctive correlations which aid in identifying hallmarks of Majorana bound state localized at the junction. Our approach combines information form sub-gap Cooper pair transport and transport of above-gap thermally excited quasiparticle which is complementary to the existing studies.

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