Nonanalytic behavior of the Casimir force across a Lifshitz transition in a spin-orbit-coupled material

Allocca, Andrew A.; Wilson, Justin H.; Galitski, Victor

doi:10.1103/physrevb.90.075420

Cited by 3 publications

(3 citation statements)

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“…2. It is worth mentioning that fluctuation-induced effects in equilibrium have been studied extensively in the presence of topological materials [33][34][35][36][37][38][39]. In particular, it is found that the force between two TI slabs is proportional to α 2 .…”

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confidence: 99%

Fluctuation-Induced Torque on a Topological Insulator out of Thermal Equilibrium

Maghrebi

Gorshkov

2019

Phys. Rev. Lett.

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Topological insulators with the time reversal symmetry broken exhibit strong magnetoelectric and magneto-optic effects. While these effects are well-understood in or near equilibrium, nonequilibrium physics is richer yet less explored. We consider a topological insulator thin film, weakly coupled to a ferromagnet, out of thermal equilibrium with a cold environment (quantum electrodynamics vacuum). We show that the heat flow to the environment is strongly circularly polarized, thus carrying away angular momentum and exerting a purely fluctuation-driven torque on the topological insulator film. Utilizing the Keldysh framework, we investigate the universal nonequilibrium response of the TI to the temperature difference with the environment. Finally, we argue that experimental observation of this effect is within reach. arXiv:1811.06080v1 [cond-mat.mes-hall]

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confidence: 99%

Fluctuation-Induced Torque on a Topological Insulator out of Thermal Equilibrium

Maghrebi

Gorshkov

2019

Phys. Rev. Lett.

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“…Any tip–sample force that can be modulated can drive the HM technique. Recent experiments show that it is possible to use the sideband technique, from which HM is generalized, with magnetic and photoinduced forces as well as the electrostatic force. ,, Moreover, it is expected that other forces present at the nanoscale can be controlled as well, such as van der Waals/Casimir forces, , which may be useful for detecting impurities in metals . The total tip–sample force can even be modulated by changing the tip–sample separation.…”

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confidence: 99%

Multiscale Functional Imaging of Interfaces through Atomic Force Microscopy Using Harmonic Mixing

Garrett

Leite

Munday

2018

ACS Appl. Mater. Interfaces

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The spatial resolution of atomic force microscopy (AFM) needed to resolve material interfaces is limited by the tip-sample separation ( d) dependence of the force used to record an image. Here, we present a new multiscale functional imaging technique that allows for in situ tunable spatial resolution, which can be applied to a wide range of inhomogeneous materials, devices, and interfaces. Our approach uses a multifrequency method to generate a signal whose d-dependence is controlled by mixing harmonics of the cantilever's oscillation with a modulated force. The spatial resolution of the resulting image is determined by the signal's d-dependence. Our measurements using harmonic mixing (HM) show that we can change the d-dependence of a force signal to improve spatial resolution by up to a factor of two compared to conventional methods. We demonstrate the technique with both Kelvin probe force microscopy (KPFM) and bimodal AFM to show its generality. Bimodal AFM with harmonic mixing actuation separates conservative from dissipative forces and is used to identify the regions of adhesive residue on exfoliated graphene. Our electrostatic measurements with open-loop KPFM demonstrate that multiple force modulations may be applied at once. Further, this method can be applied to any tip-sample force that can be modulated, for example, electrostatic, magnetic, and photoinduced forces, showing its universality. Because HM enables in situ switching between high sensitivity and high spatial resolution with any periodic driving force, we foresee this technique as a critical advancement for multiscale functional imaging.

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“…can lead to interesting transitions [18]), and a Hall effect that is too strong can suppress Kerr rotation and hence lead to attraction. The latter case is an interesting phenomenon where "more" of a repulsive material can lead to attraction.…”

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Repulsive Casimir force between Weyl semimetals

2015

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Weyl semimetals are a class of topological materials that exhibit a bulk Hall effect due to timereversal symmetry breaking. We show that for the idealized semi-infinite case, the Casimir force between two identical Weyl semimetals is repulsive at short range and attractive at long range. Considering plates of finite thickness, we can reduce the size of the long-range attraction even making it repulsive for all distances when thin enough. In the thin-film limit, we study the appearance of an attractive Casimir force at shorter distances due to the longitudinal conductivity. Magnetic field, thickness, and chemical potential provide tunable nobs for this effect, controlling the Casimir force: whether it is attractive or repulsive, the magnitude of the effect, and the positions and existence of a trap and antitrap. In 1948, Casimir [1] showed that quantum fluctuations in the electromagnetic field cause a force between two perfectly conducting, electrically neutral objects. This has since been extended to other materials [2,3]. Throughout this time, Casimir repulsion between two materials in vacuum has been a long sought after phenomenon [4,5]. There are principally four categories in which repulsion can be achieved: (i) modifying the dielectric of the intervening medium [4,6,7], (ii) pairing a dielectric object and a permeable object [5] (such as with metamaterials [8]), (iii) using different geometries [9][10][11], and (iv) breaking time-reversal symmetry [12,13]. In this paper, we are concerned with Casimir repulsion in identical time-reversal broken systems. Specifically, we will study how Weyl semimetals with time-reversal symmetry breaking can exhibit Casimir repulsion. The key ingredient to Casimir repulsion in this paper is the existence of a nonzero bulk Hall conductance σ xy = 0, σ xy = −σ yx [14].It is a general theorem that mirror symmetric objects without time-reversal symmetry breaking can only attract one another with the Casimir effect [15]. This is understood with the Lifshitz formula [2] where if we have two materials characterized by the two reflection matrices R 1 and R 2 and separated by a distance a in a parallel plate geometry, we havewhere the trace is a matrix trace and q z = √ ω 2 + k 2 . This integral generally yields an attractive force; however, if we break time reversal symmetry, obtaining antisymmetric off-diagonal terms in the reflection matrix R xy = −R yx there is the possibility of Casimir repulsion [16]. One candidate is a two-dimensional Hall material [12], and similarly, another is a topological insulator where the surface states have been gapped by a magnetic field [13,17]. A Hall conductance does not guarantee repulsion; longitudinal conductance can overwhelm any repulsion from the Hall effect (although the magnetic field FIG. 1. The setup we will consider here is two Weyl semimetals separated by a distance a in vacuum and with distance between Weyl cones 2b in k space (split in the z direction).can lead to interesting transitions [18]), and a Hall effect that is too strong c...

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Nonanalytic behavior of the Casimir force across a Lifshitz transition in a spin-orbit-coupled material

Cited by 3 publications

References 55 publications

Fluctuation-Induced Torque on a Topological Insulator out of Thermal Equilibrium

Fluctuation-Induced Torque on a Topological Insulator out of Thermal Equilibrium

Multiscale Functional Imaging of Interfaces through Atomic Force Microscopy Using Harmonic Mixing

Repulsive Casimir force between Weyl semimetals

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