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Giant anisotropy of spin relaxation and spin-valley mixing in a silicon quantum dot
Physical Review Letters ( IF 9.227 ) Pub Date : 
Xin Zhang; Rui-Zi Hu; Hai-Ou Li; Fang-Ming Jing; Yuan Zhou; Rong-Long Ma; Ming Ni; Gang Luo; Gang Cao; Gui-Lei Wang; Xuedong Hu; Hong-Wen Jiang; Guang-Can Guo; Guo-Ping Guo

In silicon quantum dots (QDs), at a certain magnetic field commonly referred to as the “hot spot’‘, the electron spin relaxation rate (T1−1) can be drastically enhanced due to strong spin-valley mixing. Here, we experimentally find that with a valley splitting of $78.2\pm 1.6\thinspace \mu eV$, this “hot spot’’ in spin relaxation can be suppressed by more than 2 orders of magnitude when the in-plane magnetic field is oriented at an optimal angle, about 9from the [100] sample plane. This directional anisotropy exhibits a sinusoidal modulation with a 180periodicity. We explain the magnitude and phase of this modulation using a model that accounts for both spin-valley mixing and intravalley spin-orbit mixing. The generality of this phenomenon is also confirmed by tuning the electric field and the valley splitting up to 268.5±0.7μeV. Main text Single-spin qubits in Si quantum dots (QDs) are considered one of the most promising contenders for large scale quantum computation …[1-3]. In silicon, the relatively weak spin-orbit interaction (SOI) and the existence of an abundant spin-zero isotope allow the electron spin to preserve its quantum state for exceptionally long times, leading to a spin relaxation time (T1) over hundreds of milliseconds …[4-6] and a spin coherence time (T2) over tens of microseconds …[7,8]. However, adverse effects from an imperfect substrate may weaken some of these advantages [2]. In silicon QDs, the energy gap between the lowest two valley-orbit states, which are obtained by breaking six-fold degeneracy of the conduction band minima (valley), is sensitive to the interface disorder …[9-12]. For spin relaxation, this energy gap, also called valley splitting, introduces a spin relaxation”hot spot’’ when its magnitude $E_{VS}$ matches the Zeeman energy EZ [13]. As a result, spin relaxation rate can be enhanced to 103 to 10$^{6\thinspace }$s−1 …[6,14-16] depending on the environment. To mitigate such effects, it is crucial to better understand and control the interactions between the spin and valley degrees of freedom in silicon. Over the past decade, spin relaxation in Si QDs has been investigated both experimentally …[4-6,14-17] and theoretically …[13,18,19]. It was found that electrical noise via SOI plays an important role in determining spin relaxation in silicon. For magnetic fields near the spin relaxation”hot spot’‘, the relaxation process is dominated by the SOI with valley states (spin-valley mixing), while for magnetic fields away from the "hot spot’’, especially higher fields, T1 is dominated by the intravalley SOI with higher orbital states (intravalley spin-orbit mixing). The effect of SOI on spin relaxation can be viewed as a result of an effective spin-orbit magnetic field 𝐁𝐒𝐎. A finite angle between 𝐁𝐒𝐎 and the external magnetic field 𝐁𝐞𝐱𝐭 leads to mixing of spin eigenstates …[20,21], allowing electrical noises to induce spin transitions between the excited and ground states. Within this physical picture, spin mixing would vary as the angle between 𝐁𝐒𝐎 and …
更新日期:2020-05-28

 

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