| 1. |
- Aydin, Alhun, et al.
(författare)
-
Thermodefect voltage in graphene nanoribbon junctions
- 2022
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 34:19
-
Tidskriftsartikel (refereegranskat)abstract
- Thermoelectric junctions are often made of components of different materials characterized by distinct transport properties. Single material junctions, with the same type of charge carriers, have also been considered to investigate various classical and quantum effects on the thermoelectric properties of nanostructured materials. We here introduce the concept of defect-induced thermoelectric voltage, namely, thermodefect voltage, in graphene nanoribbon (GNR) junctions under a temperature gradient. Our thermodefect junction is formed by two GNRs with identical properties except the existence of defects in one of the nanoribbons. At room temperature the thermodefect voltage is highly sensitive to the types of defects, their locations, as well as the width and edge configurations of the GNRs. We computationally demonstrate that the thermodefect voltage can be as high as 1.7 mV K-1 for 555-777 defects in semiconducting armchair GNRs. We further investigate the Seebeck coefficient, electrical conductance, and electronic thermal conductance, and also the power factor of the individual junction components to explain the thermodefect effect. Taken together, our study presents a new pathway to enhance the thermoelectric properties of nanomaterials.
|
|
| 2. |
- Cayao, Jorge, et al.
(författare)
-
Phase-tunable electron transport assisted by odd-frequency Cooper pairs in topological Josephson junctions
- 2022
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:10
-
Tidskriftsartikel (refereegranskat)abstract
- We consider a finite-size topological Josephson junction formed at the edge of a two-dimensional topological insulator in proximity to conventional superconductors and study the impact of Cooper pair symmetries on the electron transport. We find that, due to the finite junction size, electron transport is highly tunable by the superconducting phase difference Phi across the junction. At zero frequency and Phi = pi, the setup exhibits vanishing local Andreev reflection and perfect normal transmission due to the interplay of finite junction size and formation of topological Andreev bound states in the middle of the junction. We reveal that this striking behavior enables odd-frequency Cooper pairs to become the only type of pairing inside the topological junction that contribute to transport. Our paper thus offers a highly tunable detection scheme for odd-frequency Cooper pairs.
|
|
| 3. |
- Dutta, Paramita, et al.
(författare)
-
Finite bulk Josephson currents and chirality blockade removal from interorbital pairing in magnetic Weyl semimetals
- 2020
-
Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 101:6
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic Weyl semimetals (WSMs) have been presumed to be immune to proximity-induced spin-singlet superconducting pairing due to a chirality blockade of the regular Andreev reflection. In this work, we study all possible superconducting pairing induced in a WSM sandwiched between two conventional superconductors in a Josephson junction setup. We confirm that, while conventional intraorbital s-wave pairing is present on the surface of the WSM, it cannot propagate into the bulk due to the chirality blockade. However, interorbital s-wave pairing, with both even-frequency spin-singlet and odd-frequency mixed-spin-triplet symmetry, propagates into the bulk of the WSM, as do several p-wave symmetries. To demonstrate the importance of these finite interorbital and p-wave pair amplitudes in an experimental setup, we calculate the Josephson current and find a finite and even increasing current when the chirality blockade effect for the conventional intraorbital pairing is enhanced.
|
|
| 4. |
- Dutta, Paramita, et al.
(författare)
-
Nonlocality of Majorana bound states revealed by electron waiting times in a topological Andreev interferometer
- 2024
-
Ingår i: Physical Review Research. - : American Physical Society. - 2643-1564. ; 6:1
-
Tidskriftsartikel (refereegranskat)abstract
- The analysis of waiting times of electron transfers has recently become experimentally accessible owing to advances in noninvasive probes working in the short-time regime. We study electron waiting times in a topological Andreev interferometer: a superconducting loop with controllable phase difference connected to a quantum spin Hall edge, where the edge state helicity enables the transfer of electrons and holes into separate leads, with transmission controlled by the loop's phase difference ϕ. This setup features gapless Majorana bound states at ϕ=π. The waiting times for electron transfers across the junction are sensitive to the presence of the gapless states, but are uncorrelated for all ϕ. By contrast, at ϕ=π the waiting times of Andreev-scattered holes show a strong correlation and the crossed (hole-electron) distributions feature a unique behavior. Both effects exclusively result from the nonlocal properties of Majorana bound states. Consequently, electron waiting times and their correlations could circumvent some of the challenges for detecting topological superconductivity and Majorana states beyond conductance signatures.
|
|
| 5. |
- Dutta, Paramita, et al.
(författare)
-
Signature of odd-frequency equal-spin triplet pairing in the Josephson current on the surface of Weyl nodal loop semimetals
- 2019
-
Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 100:10
-
Tidskriftsartikel (refereegranskat)abstract
- We theoretically predict proximity-induced odd-frequency (odd-omega) pairing on the surface of a Weyl nodal loop semimetal, characterized by a nodal loop Fermi surface and drumheadlike surface states (DSSs), attached to conventional spin-singlet s-wave superconducting leads. Due to the complete spin polarization of the DSS, only odd-omega equal-spin triplet pairing is present, and we show that it gives rise to a finite Josephson current. Placing an additional ferromagnet in the junction can also generate odd-omega) mixed-spin triplet pairing, but the pairing and current are not affected if the magnetization is orthogonal to the DSS spin polarization, which further confirms the equal-spin structure of the pairing.
|
|
| 6. |
- Dutta, Paramita, et al.
(författare)
-
Superconductivity in spin-3/2 systems : Symmetry classification, odd-frequency pairs, and Bogoliubov Fermi surfaces
- 2021
-
Ingår i: Physical Review Research. - : American Physical Society. - 2643-1564. ; 3:3
-
Tidskriftsartikel (refereegranskat)abstract
- The possible symmetries of the superconducting pair amplitude is a consequence of the fermionic nature of the Cooper pairs. For spin-1/2 systems this leads to the SPOT = -1 classification of superconductivity, where S, P, O, and T refer to the exchange operators for spin, parity, orbital, and time between the paired electrons. However, this classification no longer holds for higher spin fermions, where each electron also possesses a finite orbital angular momentum strongly coupled with the spin degree of freedom, giving instead a conserved total angular moment. For such systems, we here instead introduce the JPT = -1 classification, where J is the exchange operator for the z component of the total angular momentum quantum numbers. We then specifically focus on spin-3/2 fermion systems and several superconducting cubic half-Heusler compounds that have recently been proposed to be spin-3/2 superconductors. By using a generic Hamiltonian suitable for these compounds we calculate the superconducting pair amplitudes and find finite pair amplitudes for all possible symmetries obeying the JPT = -1 classification, including all possible odd-frequency (odd-omega)) combinations. Moreover, one of the very interesting properties of spin-3/2 superconductors is the possibility of them hosting a Bogoliubov Fermi surface (BFS), where the superconducting energy gap is closed across a finite area. We show that a spin3/2 superconductor with a pair potential satisfying an odd-gap time-reversal product and being noncommuting with the normal-state Hamiltonian hosts both a BFS and has finite odd-omega) pair amplitudes. We then reduce the full spin-3/2 Hamiltonian to an effective two-band model and show that odd-omega) pairing is inevitably present in superconductors with a BFS and vice versa.
|
|
| 7. |
- Dutta, Paramita, et al.
(författare)
-
Thermoelectricity carried by proximity-induced odd-frequency pairing in ferromagnet/superconductor junctions
- 2020
-
Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 102:9
-
Tidskriftsartikel (refereegranskat)abstract
- We explore the role of proximity-induced odd-frequency pairing in the thermoelectricity of a ferromagnet when coupled to a conventional s-wave spin-singlet superconductor through a spin-active interface. By varying both the polarization and its direction in the ferromagnet and the interfacial spin-orbit interaction strength, we analyze the behavior of all proximity-induced pair amplitudes in the ferromagnet and their contributions to the thermoelectric coefficients. Based on our results for the Seebeck coefficient, we predict that odd-frequency spin-triplet Cooper pairs are much more efficient than the conventional spin-singlet even-frequency pairs in enhancing thermoelectricity of the junction, and especially mixed-spin triplet pairing is favorable. Our results on the thermoelectric figure of merit show that ferromagnet/superconductor junctions are very good thermoelectric systems when superconductivity is dominated by odd-frequency pairing.
|
|
| 8. |
- Jakobsen, Martin F., et al.
(författare)
-
Electrical and thermal transport in antiferromagnet-superconductor junctions
- 2020
-
Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 102:14
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that antiferromagnet-superconductor (AF-S) junctions show qualitatively different transport properties than normal metal-superconductor (N-S) and ferromagnet-superconductor (F-S) junctions. We attribute these transport features to the presence of two different scattering processes in AF-S junctions, i.e., specular reflection of holes and retroreflection of electrons. Using the Blonder-Tinkham-Klapwijk formalism, we find that the electrical and thermal conductances depend nontrivially on antiferromagnetic exchange strength, voltage, and temperature bias. Furthermore, we show that the interplay between the Neel vector direction and the interfacial Rashba spin-orbit coupling leads to a large anisotropic magnetoresistance. The unusual transport properties make AF-S interfaces unique among the traditional condensed-matter-system-based superconducting junctions.
|
|
| 9. |
- Paul, Ganesh C., et al.
(författare)
-
Signatures of interfacial topological chiral modes via RKKY exchange interaction in Dirac and Weyl systems
- 2021
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:11
-
Tidskriftsartikel (refereegranskat)abstract
- We theoretically investigate the features of Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction between two magnetic impurities, mediated by the interfacial bound states inside a domain wall (DW). The latter separates the two regions with oppositely signed inversion symmetry broken terms in graphene and Weyl semimetal. The DW is modeled by a smooth quantum well which hosts a number of discrete bound states including a pair of gapless, metallic modes with opposite chiralities. We find clear signatures of these interfacial chiral bound states in spin response (RKKY exchange interaction) which is robust to the deformation of the quantum well.
|
|
