Casimir and electrostatic forces from Bi2Se3 thin films of varying thickness

Abstract

We explore here the decisive role of film thickness on Casimir and electrostatic forces from topological insulating Bi 2 Se 3 films. The forces were measured for the Au-Bi 2 Se 3 system under ambient conditions to simulate realistic applications. It is shown that the electrostatic forces associated with a nonzero contact potential of V o ∼ 200 mV played a dominant role, and could not be compensated for thinner films ( 20 nm thick). However, for thicker films the measured force, after voltage compensation, started to approach the genuine Casimir force in very good agreement with Lifshitz theory. Our results point out that any gradual deviation from theory for thinner films underlies the presence of strong electrostatic effects.

The Casimir Effect in Topological Matter

“…To discover the Casimir repulsion in a putative experiment, one would need to account for such electrostatic contributions. Recently, there was indeed an experiment performed on a topological insulator thin film system (Bi 2 Se 3 ) that takes electrostatic contributions into account [135]; however, the adopted topological insulator is time reversal-symmetric, which excludes the possibility of Casimir repulsion. For a putative experiment to detect Casimir repulsion between Chern insulators, one would also need to account for the effect of the dielectric substrate, as Chern insulators are typically grown by molecular beam epitaxy on such substrates [80,99].…”

Nonlinear Actuation of Casimir Oscillators toward Chaos: Comparison of Topological Insulators and Metals

“…For this purpose, the imaginary part of the frequency-dependent dielectric function ε(ω) is an essential input. Therefore, the optical properties of all samples, including Au, Bi 2 Se 3 , and Al 2 O 3 , were characterized with ellipsometry using the VUV-VASE (0.5-9.34 eV) and IR-VASE (0.03-0.5 eV) ellipsometers [17,26,27]. Bi 2 Se 3 is a well-known 3D Topological insulator [26], and Au is used in devices due to its high conductivity ( ω p 2 / ω τ Au 1600 eV) [17,27].…”

“…Therefore, the optical properties of all samples, including Au, Bi 2 Se 3 , and Al 2 O 3 , were characterized with ellipsometry using the VUV-VASE (0.5-9.34 eV) and IR-VASE (0.03-0.5 eV) ellipsometers [17,26,27]. Bi 2 Se 3 is a well-known 3D Topological insulator [26], and Au is used in devices due to its high conductivity ( ω p 2 / ω τ Au 1600 eV) [17,27]. The imaginary part ε"(ω) of frequency-dependent dielectric response function ε(ω) of Bi 2 Se 3 and Al 2 O 3 and the corresponding functions at imaginary frequencies ε(iξ) are shown in Figure 1a,b.…”

“…The elastic restoring force F res = −K(d − z) of the spring with stiffness K counterbalanced the attractive Casimir force. It was assumed that both plates were coated with an optically bulk Au film (thickness:~100 nm) or a 100 nm layer of Bi 2 Se 3 deposited on a bulk sapphire (Al 2 O 3 ) as described by the authors of [26]. For our calculation, we considered initial separations d between the actuating plates in the range 250 nm to 1 µm, and any thermal effects were not taken into account (assuming, basically, a temperature of 0 K).…”

“…Hence, any conditions for the occurrence of a repulsive force are of paramount importance for stable motion. In addition, the attractive Casimir forces from TIs can be sufficiently weak to allow the stable operation of actuating devices with suitable compensation of contact potentials due to their conductive surface states [26], while stable operation cannot be achieved using good conductive materials, for example, Au, due to significantly stronger Casimir forces [6,7].…”