Anisotropic Pauli spin blockade in hole quantum dots

Abstract

We present measurements on gate-defined double quantum dots in Ge-Si core-shell nanowires, which we tune to a regime with visible shell filling in both dots. We observe a Pauli spin blockade and can assign the measured leakage current at low magnetic fields to spin-flip cotunneling, for which we measure a strong anisotropy related to an anisotropic g factor. At higher magnetic fields we see signatures for leakage current caused by spin-orbit coupling between (1,1)-singlet and (2,0)-triplet states. Taking into account these anisotropic spin-flip mechanisms, we can choose the magnetic field direction with the longest spin lifetime for improved spin-orbit qubits.

Hyperfine and Spin-Orbit Coupling Effects on Decay of Spin-Valley States in a Carbon Nanotube

“…Related anisotropic Pauli blockade was previously seen in nanotubes in Ref. [3], in nanowires consisting of InAs [26], InSb [29], and SiGe [27], and in planar silicon devices [28]. This work is the first to measure and explain the distinctive triple peak in leakage current (Fig.…”

Spin blockade in hole quantum dots: Tuning exchange electrically and probing Zeeman interactions

“…The period of the anisotropic leakage is critically dependent on the relative magnitude of Zeeman interaction terms linear and cubic in the magnetic field. The current and singlet-triplet exchange splitting can be effectively adjusted by an appropriate choice of field direction, providing a simple control variable for quantum information processing and a way of tailoring magnetic interactions in hole spin qubits.Spin-based quantum information processing platforms relying on hole quantum dots (QDs) have recently attracted considerable attention [1][2][3][4][5][6][7][8][9][10][11], since they permit long spin coherence and electrically driven spin resonance thanks to the strong hole spinorbit (SO) interaction [12][13][14][15][16][17][18][19][20]. Owing to their effective spin J = 3 2 , spin dynamics in hole systems often exhibits physics not found in electron systems [21][22][23][24][25][26].…”

“…Probing the strengths of SO coupling and hole-hole interactions is thus highly relevant for quantum computing. Pauli spin blockade [31,32], the blocking of charge transport through QDs due to the Pauli exclusion principle, may be employed to perform this task in InSb, Si, Ge-Si core-shell wires, and GaAs [7,8,11,33].Pauli spin blockade (PSB) is lifted by spin-flip processes most commonly originating in the SO or hyperfine interactions. Electron PSBs at low magnetic fields are primarily lifted by the hyperfine coupling to the nuclei [34][35][36], unless the singlet-triplet splitting is large due to a sizable interdot tunnel coupling [37][38][39].…”

“…For hole QDs, in contrast, the strong SO interaction is expected to be the dominant blockade lifting mechanism [7,8,11,33] even at low magnetic fields, particularly due to the suppression of hole contact hyperfine interaction. Spin-flip cotunneling processes may also give rise to a leakage current [11].Here we investigate PSB in a gate-defined hole double QD in an in-plane magnetic field. We derive an effective SO tunneling Hamiltonian between (1, 1) and (0, 2), with (N L , N R ) charge state on the left and right dot.…”

“…The other contribution to the leakage I (albeit implicitly) is introduced by Γ 11 . We have considered Γ 11 on the order of MHz, making the calculated I on the order of pA [11,33].The anisotropic I(θ) can be manipulated by varying θ and employed in probing the power of B in the Zeeman interaction via the signal period. Because ∆ ± may be determined from the singlet-triplet anticrossing (along with t 0 extracted from the anticrossing at ǫ = 0), the strength |E Z | can be extracted via I(B).…”