论文标题
通过定期驱动的电势通过正常金属区域连接的两个超导体泵送的非绝热电荷泵送
Nonadiabatic charge pumping across two superconductors connected through a normal metal region by periodically driven potentials
论文作者
论文摘要
当激发态能量与基态能量之间的差异是$ \ hbar $乘以驾驶频率的整数倍数时，定期驱动的系统会表现出共鸣。另一方面，当两个超导体之间保持超导相位差时，将出现带有约瑟夫森电流的子段状态。因此，驱动的约瑟夫森交界处开辟了一个有趣的途径，在这种途径中，由于施加驾驶引起的激发会影响从一个超导体流向另一个超导体的电流。在此激励的情况下，我们研究了在超导体非正式金属螺旋体（SNS）连接中的电荷转运，在该连接器中，将振荡电势应用于正常金属区域。我们发现，对于振荡电势的较小幅度，当一个站点驱动会逆转超导相位差异的电流方向，而当未经自我的汉密尔顿的子仪特征因之间的差异是$ \ hbar $ $ \ hbar $的整数倍数。对于更大的振荡潜力振幅，在一个站点上驾驶具有更丰富的特征。我们表明，即使将两个超导体保持在同一超导阶段时，也可以通过将振荡电势施加到正常金属中的两个位点，从而驱动电流。我们发现，当未发出的系统中有非零的约瑟夫森电流时，该系统的局部峰和山谷以小于超导间隙的振幅振幅驱动的振动势驱动的系统中，表示系统中的急剧激发。在绝热限制中，我们发现当约瑟夫森电流流动在非晶体系统中时，一个时间段转移的电荷是带泵送频率的电动爪。我们的计算是精确的，可以应用于有限系统。我们讨论了可以测试预测的可能的实验设置。
Periodically driven systems exhibit resonance when the difference between an excited state energy and the ground state energy is an integer multiple of $\hbar$ times the driving frequency. On the other hand, when a superconducting phase difference is maintained between two superconductors, subgap states appear which carry a Josephson current. A driven Josephson junction therefore opens up an interesting avenue where the excitations due to applied driving affect the current flowing from one superconductor to the other. Motivated by this, we study charge transport in a superconductor-normal metal-superconductor (SNS) junction where oscillating potentials are applied to the normal metal region. We find that for small amplitudes of the oscillating potential, driving at one site reverses the direction of current at the superconducting phase differences when difference between the subgap eigenenergies of the undriven Hamiltonian is integer multiple of $\hbar$ times the driving frequency. For larger amplitudes of oscillating potential, driving at one site exhibits richer features. We show that even when the two superconductors are maintained at same superconducting phase, a current can be driven by applying oscillating potentials to two sites in the normal metal differing by a phase. We find that when there is a nonzero Josephson current in the undriven system, the local peaks and valleys in current of the system driven with an amplitude of oscillating potential smaller than the superconducting gap indicates sharp excitations in the system. In the adiabatic limit, we find that charge transferred in one time period diverges as a powerlaw with pumping frequency when a Josephson current flows in the undriven system. Our calculations are exact and can be applied to finite systems. We discuss possible experimental setups where our predictions can be tested.
