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【摘要】

When a strong electric field is applied to an insulator, electrons can tunnel through the band gap, causing electrical breakdown. In the simplest model, the transition probability of electrons follows the Landau–Zener formula, determined by the band dispersions and the field strength. Recent studies have shown a correction to this formula due to the geometric nature of the Bloch wavefunction, shift vector, which consists of the Berry connections of adjacent bands and causes nonreciprocal responses in time-reversal symmetric systems.
In the seminar, I will discuss how spin degrees of freedom affect tunneling in insulators and propose a mechanism for generating spin-polarized current due to this geometric correction. This mechanism is significant in PT-symmetric insulators, where bands are doubly degenerate with opposite spins and no spin current typically appears. However, a strong electric field can induce an AC spin current in such a system with a finite shift vector. I will present a minimal model of a PT-symmetric insulator with a zigzag chain structure to show the essential role of the shift vector in spin-dependent tunneling.