arXiv subjects

Daniel Gresta

Publications and source records attributed to Daniel Gresta.

6 recordsLinked to original sources

arXiv2026

Limits of Thermal Conductance Quantization in Chiral Topological Josephson Junctions

We investigate thermal and non-local electrical transport in four-terminal Josephson junctions formed by a normal region coupled to two transverse chiral superconducting leads, supporting phases characterized by Chern numbers ${\cal C}=0,\,1$\,and\,2. We identify the conditions under which a single chiral Majorana mode (${\cal C}=1$) produces a robust half-quantized thermal conductance, while non-local electrical conductance remains strongly suppressed by particle-hole symmetry. Thermal conductance quantization occurs near a superconducting phase difference $\pi$, but only in the low-doping regime of the central region and in the intermediate- to long-junction limits. At finite Zeeman fields, the thermal response broadly follows the topology of the isolated superconducting leads for the $C=1$ phase while, in the ${\cal C}=2$ phase, the thermal conductance generally deviates from quantization, depending on the momentum-space location of the Majorana modes. Our results establish clear criteria for probing chiral Majorana modes in Josephson junctions and highlight the essential role of momentum-space structure, finite-size geometry, and sample parameters in thermal transport.

cond-mat.supr-con↗

arXiv2025

Transport signatures of inverted Andreev bands in topological Josephson junctions

We study the thermoelectrical transport transverse to conventional and topological Josephson junctions with a central quantum dot (QD). For that purpose, we derive an effective resonant tunneling model where the QD is renormalized with an induced superconducting gap. By applying the Keldysh Green's function technique, we compute the local density of states as well as the transmission functions. In the latter case, we observe that the Andreev bound states forming on the QD are inverted if the junction has $p$-wave symmetry, meaning that electron and hole orbitals switch roles. We calculate the thermoelectric transport coefficients both analytically and numerically and show how the induced gaps and the band inversion are reflected in the electrical and heat conductance as well as the Seebeck coefficient, the latter experiencing a sign change in the topological case.

cond-mat.mes-hall↗

arXiv2023

Majorana-mediated thermoelectric transport in multiterminal junctions

The unambiguous identification of Majorana zero modes (MZMs) is one of the most outstanding problems of condensed matter physics. Thermal transport provides a detection tool that is sensitive to these chargeless quasiparticles. We study thermoelectric transport between metallic leads transverse to a Josephson junction. The central double quantum dot hosts conventional or topological Andreev states that depend on the phase difference $\phi$. We show that the presence of MZMs can be identified by a significant amplification of both the electrical and thermal conductance at $\phi \approx \pi$ as well as the Seebeck coefficient at $\phi \approx 0$. In addition, we show that the Wiedemann-Franz law is strongly violated in the presence of MZMs around $\phi \approx \pi$ when compared to the conventional case. We further investigate the robustness of our results against Cooper pair splitting processes.

cond-mat.mes-hall↗

arXiv2020

Signatures of Jackiw-Rebbi resonance in the thermal conductance of topological Josephson junctions with magnetic islands

Josephson junctions in two-dimensional topological insulators with embedded magnetic domains can host a number of topological phases, in particular, Jackiw-Rebbi solitons and Majorana zero modes. These different non-trivial phases appear in such junctions for multiple-domain magnetic islands, showing a rich multi-gap structure. Features related to the interplay between superconductivity and magnetism in these systems cannot be easily discerned looking at behavior of the Andreev spectrum and the concomitant dc Josephson effect. Instead, the thermal conductance is very sensitive to the nature of the junction and the domain structure of the magnetic island. We present a detailed analysis of these properties in the case of a topological Josephson junction with a single and two-domain magnetic island. Configurations hosting soliton magnetic modes lead to a peculiar behavior of the thermal conductance relative to the thermal quantum, characterized by a negative slope as a function of the temperature, just above the superconducting critical temperature. At low temperatures, these junctions also show characteristic coherence patters in the behavior of the thermal conductance as function of the Josephson phase bias and the angle between the magnetizations of the domains.

cond-mat.mes-hall↗

arXiv2020

Thermoelectricity in Quantum-Hall Corbino Structures

We measure the thermoelectric response of Corbino structures in the quantum Hall effect regime and compare it with a theoretical analysis. The measured thermoelectric voltages are qualitatively and quantitatively simulated based upon the independent measurement of the conductivity indicating that they originate predominantly from the electron diffusion. Electron-phonon interaction does not lead to a phonon-drag contribution in contrast to earlier Hall-bar experiments. This implies a description of the Onsager coefficients on the basis of a single transmission function, from which both thermovoltage and conductivity can be predicted with a single fitting parameter. It furthermore let us predict a figure of merit for the efficiency of thermoelectric cooling which becomes very large for partially filled Landau levels (LL) and high magnetic fieldse of merit can be estimated which becomes very large for partially filled Landau levels and high magnetic fields.

cond-mat.mes-hall↗

arXiv2019

Optimal thermoelectricity with quantum spin-Hall edge states

We study the thermoelectric properties of a Kramers pair of helical edge states of the quantum spin Hall effect coupled to a nanomagnet with a component of the magnetization perpendicular to the direction of the spin-orbit interaction of the host. We show that the transmission function of this structure has the desired qualities for optimal thermoelectric performance in the quantum coherent regime. For a single magnetic domain there is a power generation close to the optimal bound. In a configuration with two magnetic domains with different orientations, pronounced peaks in the transmission functions and resonances lead to a high figure of merit. We provide estimates for the fabrication of this device with HgTe quantum-well topological insulators.

cond-mat.mes-hall↗