All-electrical generation and control of odd-frequencys-wave Cooper pairs in double quantum dots

Abstract

We propose an all-electrical experimental setup to detect and manipulate the amplitude of oddfrequency pairing in a double quantum dot. Odd-frequency pair amplitude is induced from the breakdown of orbital symmetry when Cooper pairs are injected in the double dot with electrons in different dots. When the dot levels are aligned with the Fermi energy, i.e., on resonance, nonlocal Andreev processes are directly connected to the presence of odd-frequency pairing. Therefore, their amplitude can be manipulated by tuning the level positions. Detection of nonlocal Andreev processes by conductance measurements contributes a direct proof of the existence of odd-frequency pair amplitude and is available using current experimental techniques. Introduction.-The symmetry analysis of Cooper pairs is a key element in the study of superconductivity. For example, Cooper pairs at conventional BCS superconductors form a spin-singlet even-parity state, where the electrons have opposite spins and are coupled in momentum space by the isotropic s-wave channel. A current trend in the study of superconductivity is to engineer unconventional superconductors by breaking down symmetries of a BCS superconductor. Consequently, a new type of pairing emerges which is odd in frequency, i.e., odd under an exchange of the time coordinates [1][2][3][4]. Plenty of theoretical studies suggest ubiquitous presence of odd-frequency superconductivity at inhomogeneous superconducting systems [5][6][7][8][9][10][11][12][13][14][15]. Unfortunately, experimental evidence for odd-frequency pair amplitude is very limited. Odd-frequency spin-triplet swave superconductivity can explain the long-range proximity effect [16,17], the intrinsic paramagnetic Meissner effect [18][19][20][21], and the subgap structure [22] observed in ferromagnet-superconductor hybrids. However, oddfrequency pairs are mixed with conventional ones and their amplitude is not tunable but accidentally determined by the configuration of magnetic moments realized at the junction. To unambiguously establish the presence of odd-frequency pairing, new proposals that filter oddfrequency pairs and allow to control their amplitude are required.

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