We propose a new electrical breakdown mechanism for exciton insulators in the BCS limit, which differs fundamentally from the Zener breakdown mechanism observed in traditional band insulators. Our new mechanism results from the instability of the many-body ground state for exciton condensation, caused by the strong competition between the polarization and condensation energies in the presence of an electric field. We refer to this mechanism as “many-body breakdown.” To investigate this new mechanism, we propose a BCS-type trial wave function under finite electric fields and use it to study the many-body breakdown numerically. Our results reveal two different types of electric breakdown behavior. If the system size is larger than a critical value, the Zener tunneling process is first turned on when an electrical field is applied, but the excitonic gap remains until the field strength reaches the critical value of the many-body breakdown, after which the excitonic gap disappears and the system becomes a highly conductive metallic state. However, if the system size is much smaller than the critical value, the intermediate tunneling phase disappears since the many-body breakdown happens before the onset of Zener tunneling. The sudden disappearance of the local gap leads to an “off-on” feature in the current-voltage ($I\text{−}V$) curve, providing a straightforward way to distinguish excitonic insulators from normal insulators.

中文翻译：

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激子绝缘体的电击穿


我们提出了一种新的BCS极限内激子绝缘体的电击穿机制，该机制与传统带状绝缘体中观察到的齐纳击穿机制有根本的不同。我们的新机制源于激子凝聚的多体基态的不稳定性，这是由于电场存在下极化能和凝聚能之间的强烈竞争造成的。我们将这种机制称为“多体崩溃”。为了研究这种新机制，我们提出了有限电场下的 BCS 型试验波函数，并用它来数值研究多体击穿。我们的结果揭示了两种不同类型的电击穿行为。如果系统尺寸大于临界值，则在施加电场时齐纳隧道过程首先开启，但激子间隙仍然存在，直到场强达到多体击穿的临界值，之后激子间隙消失，系统变成高导电金属态。然而，如果系统尺寸远小于临界值，中间隧道阶段就会消失，因为多体击穿发生在齐纳隧道开始之前。局部间隙的突然消失导致电流-电压 ( $I\text{−}V$ ) 曲线出现“关-开”特征，从而提供了一种区分激子绝缘体与普通绝缘体的直接方法。