arXiv subjects

Sachiraj Mishra

Publications and source records attributed to Sachiraj Mishra.

11 recordsLinked to original sources

arXiv2026

Effect of electron-hole asymmetry on $Δ_T$ noise in metal/quantum point contact/metal and metal/quantum point contact/superconductor junctions

This work examines charge $Δ_T$ noise in two-terminal hybrid nanostructures featuring a quantum point contact (QPC), realized either between two normal metallic leads (NQN) or between a normal metal and a superconducting lead (NQS). The energy-dependent transmission of a QPC breaks electron-hole (e-h) symmetry, leading to a finite thermovoltage under an applied temperature and voltage bias. In contrast, in earlier studies on hybrid junctions incorporating insulating barriers, as electron-hole symmetry is preserved, have vanishing thermovoltage, and consequently, charge $Δ_T$ noise is calculated at zero thermovoltage. In our setup, the broken e-h symmetry allows for a finite thermovoltage, at which we compute the corresponding charge $Δ_T$ noise. Unlike earlier studies restricted by electron-hole symmetry and vanishing thermovoltage, our work establishes a self-consistent thermoelectric noise framework in mesoscopic hybrid junctions, revealing how Andreev reflection fundamentally reshapes charge $Δ_T$ noise once electron-hole symmetry is broken. This broad access to charge fluctuation signatures provides a more comprehensive understanding of non-equilibrium transport in linear response. To the best of our knowledge, this is the first work that systematically explores the interplay between Andreev reflection and electron-hole symmetry breaking in the context of quantum noise and $Δ_T$ noise in mesoscopic hybrid structures.

cond-mat.mes-hall↗

arXiv2026

Colored $Δ_T$ noise probes the topological character of edge modes

We investigate colored $Δ_T$ noise, i.e., finite-frequency $Δ_T$ noise, as a probe of edge-mode (EM) transport in quantum Hall and quantum spin Hall systems. Colored $Δ_T$ noise probes finite-frequency nonequilibrium current fluctuations and dynamical transport properties that are often obscured in DC measurements of conductance and noise. Since $Δ_T$ noise is driven solely by a temperature and voltage bias under zero average charge current conditions, it eliminates current-induced Joule heating and directly probes intrinsic thermal fluctuations. We show that chiral, spin-conserving helical, and spin-flip helical (trivial) EMs exhibit distinct colored $Δ_T$-noise signatures under appropriate bias protocols. Incorporating energy-dependent scattering through a quantum point contact, we demonstrate that electron-hole asymmetry significantly modifies the finite-frequency spectrum while preserving these distinguishing features. Notably, colored $Δ_T$ noise exhibits a frequency-dependent sign reversal absent in the corresponding white ($ω=0$) $Δ_T$ noise. We further investigate zero-temperature colored quantum shot noise and find that it vanishes identically for chiral EMs, whereas the spin-conserving helical response changes sign with frequency. By contrast, spin-flip helical (trivial) EMs exhibit a positive colored shot-noise spectrum. However, the corresponding colored $Δ_T$ noise retains its characteristic sign reversal, providing a robust distinction between spin-conserving helical and spin-flip helical (trivial) EM transport. These results establish colored $Δ_T$ noise as a robust, experimentally accessible, complementary probe for identifying chiral, spin-conserving helical, and spin-flip helical (trivial) EM transport in mesoscopic topological systems.

cond-mat.mes-hall↗

arXiv2026

Temperature-Bias Noise and Quantum Shot Noise as Probes of Pairing Symmetry in Iron Pnictides

Quantum noise has long served as a powerful probe of quantum transport in mesoscopic junctions. Recently, temperature-driven noise, or $Δ_T$ noise, has attracted growing interest due to its presence even in the absence of average charge current. In this work, we investigate a normal metal-insulator-iron-pnictide junction and demonstrate how zero temperature quantum shot noise, finite temperature quantum noise and $Δ_T$ noise can discriminate between $S_{++}$ and $S_{+-}$ pairing symmetries, which are relevant to iron-based superconductors. We introduce $Δ_T$ noise as a novel probe for distinguishing between the two pairing symmetries. In contrast to conductance, which exhibits a single peak for both $S_{++}$ and $S_{+-}$ states with only a difference in magnitude, the $Δ_T$ noise reveals qualitatively distinct features: a twin-peak structure for the $S_{++}$ pairing symmetry and a single-peak profile for the $S_{+-}$ state. A similar symmetry-dependent contrast is observed in both zero temperature quantum shot noise and finite temperature quantum noise, where the $S_{++}$ state consistently exhibits a twin-peak structure, while the $S_{+-}$ state shows a single-peak response. Our results demonstrate that noise-based measurements form a mutually reinforcing set of probes that enables reliable identification of superconducting gap symmetry in Iron Pnictide superconductors.

cond-mat.supr-con↗

arXiv2026

$Δ_T$ Noise as a Robust Diagnostic for Chiral, Helical and Trivial Edge Modes

In this article, we demonstrate that $Δ_T$ noise provides a sensitive, practical probe for distinguishing chiral edge modes from topological helical and trivial (non-topological) helical edge transport. Measured under zero-current conditions, $Δ_T$ noise reveals contrasts that conventional conductance measurements typically miss. Crucially, $Δ_T$ noise requires no external energy input in the form of an applied voltage bias, yet encodes the same intrinsic information that shot noise yields in the zero-temperature, finite-bias limit, without the distorting effects of Joule heating. This absence of bias-induced heating makes $Δ_T$ noise both more precise and more reliable than conventional shot-noise approaches.

cond-mat.mes-hall↗

arXiv2026

Negative Spin $Δ_T$ noise Induced by Spin-Flip Scattering and Andreev Reflection

We study charge $Δ_T$ noise, followed by an examination of spin $Δ_T$ noise, in the normal metal-spin flipper-normal metal-insulator-superconductor (N-sf-N-I-S) junction. Our analysis reveals a key contrast: while charge $Δ_T$ noise remains strictly positive, spin $Δ_T$ noise undergoes a sign reversal from positive to negative, driven by the interplay between spin-flip scattering as well as Andreev reflection. In contrast, charge quantum shot noise remains positive and sign-definite, which is also valid for spin quantum shot noise. The emergence of negative spin $Δ_T$ noise has two major implications. First, it establishes a clear distinction between spin-resolved $Δ_T$ noise and quantum shot noise: the former is dominated by opposite-spin correlations, whereas the latter is led by same-spin correlations. Second, it provides access to scattering mechanisms that are not captured by quantum shot noise alone. Thus, negative spin $Δ_T$ noise serves as a unique probe of the cooperative effects of Andreev reflection and spin flipping. We further place our results in context by comparing them with earlier reports of negative $Δ_T$ noise in strongly correlated systems, such as fractional quantum Hall states, and in multiterminal hybrid superconducting junctions. Overall, this work offers new insights into the mechanisms governing sign reversals in $Δ_T$ noise and highlights their role as distinctive fingerprints of spin-dependent scattering in superconducting hybrid devices.

cond-mat.mes-hall↗

arXiv2025

$Δ_T$ Noise in Mesoscopic Hybrid Junctions: Influence of Barrier Strength and Thermal Bias

Quantum noise is a fundamental probe of quantum transport phenomena, offering insights into current correlations and wave-particle duality. A particularly intriguing form of such noise, $Δ_T$ noise, emerges under a finite temperature difference in the absence of charge current at zero voltage bias. In this work, we investigate $Δ_T$ noise in mesoscopic hybrid junctions incorporating insulating barriers, where the average charge current remains zero at zero bias. Using quantum shot noise measurements, we demonstrate that $Δ_T$ noise in metal-insulator-superconductor (NIS) junctions is approximately $16$ times greater than in metal-insulator-metal (NIN) counterparts. Our analysis further reveals that $Δ_T$ noise exhibits a non-monotonic dependence on barrier strength, rising to a peak before declining, while increasing monotonically with the applied temperature bias. These findings underscore the rich interplay between thermal gradients and barrier properties in determining quantum noise characteristics in hybrid mesoscopic systems.

cond-mat.mes-hall↗

arXiv2025

Probing the dichotomy between Yu-Shiba-Rusinov and Majorana bound states via conductance, quantum noise and $Δ_T$ noise

We investigate charge and spin conductance, charge and spin quantum noise, along with charge and spin $Δ_T$ noise, as diagnostic tools to distinguish Yu-Shiba-Rusinov (YSR) states from Majorana-bound states (MBS) in a one-dimensional metal/spin-flipper/metal/insulator/superconductor junction. YSR states arise from magnetic impurities acting as spin-flippers within a trivial s-wave superconducting gap, while MBS emerge in topological superconductors, often leading to ambiguity in experiments where magnetic impurities mimic zero-energy MBS signatures. By replacing the trivial superconductor with a topological one exhibiting triplet pairing (e.g., chiral p or spinless p-wave nanowires), we identify robust and distinguishing features of YSR and MBS states. Our analysis demonstrates that combined measurements of both charge and spin conductance, charge and spin quantum noise, and their $Δ_T$ noise counterparts offer unique and reliable signatures to differentiate YSR states from genuine MBS, thereby reducing false-positive interpretations in topological superconductivity experiments.

cond-mat.mes-hall↗

arXiv2024

Reaching Van den Broeck limit in linear response and Whitney limit in nonlinear response in edge mode quantum thermoelectrics and refrigeration

Quantum heat engines and quantum refrigerators are proposed in three-terminal quantum Hall (QH) and quantum spin Hall (QSH) setups with a voltage-temperature probe in both the linear and nonlinear transport regimes. In the linear response regime, we find that efficiency at maximum power approaches the Van den Broeck limit in both QH and QSH setups. Similarly, in nonlinear response, we find that efficiency at maximum power reaches the Whitney bounds. This is for the first time, we see that in the same setup and using quantum point contacts, the thermoelectric efficiency limits in linear and nonlinear response being achieved.

cond-mat.mes-hall↗

arXiv2024

Majorana Thermoelectrics and Refrigeration

A two-terminal quantum spin-Hall heat engine and refrigerator with embedded Majorana bound states (MBS) is analyzed for optimality in thermoelectric performance using the Landaeur-Buttiker approach. This investigation can be an effective tool to detect MBS. Furthermore, the occurrence of MBS can enhance the performance to rival, as well as outperform, some modern nanoscale quantum heat engines and quantum refrigerators. The optimal performance of this MBS quantum heat engine and quantum refrigerator can be further enhanced by an Aharonov-Bohm flux.

cond-mat.mes-hall↗

arXiv2024

Majorana fermion induced power-law scaling in the violations of the Wiedemann-Franz law

Violation of the Wiedemann-Franz law in a 2D topological insulator due to Majorana bound states is studied via the Lorenz ratio in the single-particle picture. We study the scaling of the Lorenz ratio in the presence and absence of Majorana bound states with inelastic scattering modeled using a Buttiker voltage-temperature probe. We compare our results with that seen in a quantum dot junction in the Luttinger liquid picture operating in the topological Kondo regime. We explore the scaling of the Lorentz ratio in our setup when either phase and momentum relaxation or phase relaxation is present. This scaling differs from that predicted by the Luttinger liquid picture for both uncoupled and coupled Majorana cases.

cond-mat.mes-hall↗

arXiv2023

Finite temperature quantum noise correlations as a probe for topological helical edge modes

The distinction between chiral, trivial helical, and topological helical edge modes can be effectively made using quantum noise measurements at finite temperatures. Quantum noise measurements consist of mainly two components. The first is thermal noise, whose provenance is thermal fluctuations, and the second is shot noise, whose origin is the quantum nature of charge particles. Studying these edge modes at finite temperatures is important as it more accurately reflects the conditions in real-world experiments. Additionally, we have verified that our results for finite temperature quantum noise correlations are valid at finite frequencies too.

cond-mat.mes-hall↗