| 1. |
- Aad, G, et al.
(author)
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- 2015
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swepub:Mat__t
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| 2. |
- Principi, Alessandro, et al.
(author)
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Pseudo-Euler equations from nonlinear optics : Plasmon-assisted photodetection beyond hydrodynamics
- 2019
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In: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 99:7
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Journal article (peer-reviewed)abstract
- A great deal of theoretical and experimental efforts have been devoted in the last decades to the study of long-wavelength photodetection mechanisms in field-effect transistors hosting two-dimensional (2D) electron systems. A particularly interesting subclass of these mechanisms is intrinsic and based on the conversion of the incoming electromagnetic radiation into plasmons, which resonantly enhance the photoresponse, and subsequent rectification via hydrodynamic nonlinearities. In this paper, we show that such a conversion and subsequent rectification occur well beyond the frequency regime in which hydrodynamic theory applies. We consider the nonlinear optical response of generic 2D electron systems and derive pseudo-Euler equations of motion for suitable collective variables. These are solved in one- and two-dimensional geometries for the case of graphene and the results are compared with those of hydrodynamic theory. Significant qualitative differences are found, which are amenable to experimental studies. Our theory expands the knowledge of the fundamental physics behind long-wavelength photodetection.
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| 3. |
- Rostami, Habib, et al.
(author)
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Gauge invariance and Ward identities in nonlinear response theory
- 2021
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In: Annals of Physics. - : Elsevier BV. - 0003-4916 .- 1096-035X. ; 431
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Journal article (peer-reviewed)abstract
- We present a formal analysis of nonlinear response functions in terms of correlation functions in real-and imaginary-time domains. In particular, we show that causal nonlinear response functions, expressed in terms of nested commutators in real time, can be obtained from the analytic continuation of time ordered response functions, which are more easily amenable to diagrammatic calculation. This generalizes the well-known result of linear response theory. We then use gauge invariance arguments to derive exact relations between second-order response functions in density and current channels. These identities, which are non-perturbative in the strength of inter-particle interactions, allow us to establish exact connections between nonlinear optics calculations done in different electromagnetic gauges.
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| 4. |
- Rostami, Habib, et al.
(author)
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Piezoelectricity and valley chern number in inhomogeneous hexagonal 2D crystals
- 2018
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In: npj 2D Materials and Applications. - : Nature Publishing Group. - 2397-7132. ; 2, s. 1-6
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Journal article (peer-reviewed)abstract
- Conversion of mechanical forces to electric signal is possible in non-centrosymmetric materials due to linear piezoelectricity. The extraordinary mechanical properties of two-dimensional materials and their high crystallinity make them exceptional platforms to study and exploit the piezoelectric effect. Here, the piezoelectric response of non-centrosymmetric hexagonal two-dimensional crystals is studied using the modern theory of polarization and k-p model Hamiltonians. An analytical expression for the piezoelectric constant is obtained in terms of topological quantities, such as the valley Chern number. The theory is applied to semiconducting transition metal dichalcogenides and hexagonal Boron Nitride. We find good agreement with available experimental measurements for MoS2. We further generalize the theory to study the polarization of samples subjected to inhomogeneous strain (e.g., nanobubbles). We obtain a simple expression in terms of the strain tensor, and show that charge densities greater than or similar to 10(11)cm(-2) can be induced by realistic inhomogeneous strains, epsilon approximate to 0.01-0.03.
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| 5. |
- Aad, G., et al.
(author)
-
- 2015
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Journal article (peer-reviewed)
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