Sadhukhan Krishanu, Politano Antonio, Agarwal Amit
Department of Physics, Indian Institute of Technology, Kanpur 208016, India.
Dipartimento di Scienze Fisiche e Chimiche (DSFC), Università dell'Aquila, Via Vetoio 10, I-67100 L'Aquila, Italy.
Phys Rev Lett. 2020 Jan 31;124(4):046803. doi: 10.1103/PhysRevLett.124.046803.
We predict the existence of a novel long-lived gapless plasmon mode in a type-II Dirac semimetal (DSM). This gapless mode arises from the out-of-phase oscillations of the density fluctuations in the electron and the hole pockets of a type-II DSM. It originates beyond a critical wave vector along the direction of the tilt axis, owing to the momentum separation of the electron and hole pockets. A similar out-of-phase plasmon mode arises in other multicomponent charged fluids as well, but generally, it is Landau damped and lies within the particle-hole continuum. In the case of a type-II DSM, the open Fermi surface prohibits low-energy finite momentum single-particle excitations, creating a "gap" in the particle-hole continuum. The gapless plasmon mode lies within this particle-hole continuum gap and, thus, it is protected from Landau damping.
我们预测在II型狄拉克半金属（DSM）中存在一种新型的长寿命无隙等离激元模式。这种无隙模式源于II型DSM的电子和空穴口袋中密度涨落的异相振荡。由于电子和空穴口袋的动量分离，它在沿倾斜轴方向超过临界波矢时出现。类似的异相等离激元模式也出现在其他多组分带电流体中，但通常它会受到朗道阻尼并位于粒子-空穴连续区之内。在II型DSM的情况下，开放的费米面禁止低能有限动量单粒子激发，在粒子-空穴连续区中产生一个“间隙”。无隙等离激元模式位于这个粒子-空穴连续区间隙内，因此它受到保护而不会受到朗道阻尼。
