Mesoscale And Nanoscale Physics
Quantum transport through a coupled non-linear exciton-phonon system (1902.05060v1)
Sima Pouyandeh, Hadi Zahir Olyaei
2019-02-13
Wavepacket transport across a nonlinear region is studied numerically at zero and finite temperatures. In contrary to the zero temperature case which demonstrates ballistic transport, finite temperature lattice vibrations suppresses the transport drastically. The interface between the linear and the nonlinear chain plays the role of a high barrier at finite temperature when anharmonicity factor is small compared to the typical inverse cubic interatomic distance. Inverse participation ratio of the central region shows that for small anharmonicity and finite temperatures lattice vibrations give rise to self-trapping in the nonlinear chain which lasts for considerable times with a subdiffusive leakage of the wavepacket, almost equally, to both leads. The scenario changes when the anharmonicity becomes comparable with average inverse cubic interatomic distances as the lattice dynamics gives a profound boost to the transmission and starts to be almost transparent for the incoming pulse.
Machine learning topological phases in real space (1901.01963v2)
N. L. Holanda, M. A. R. Griffith
2019-01-07
We develop a supervised machine learning algorithm that is able to learn topological phases for finite systems in real space. The algorithm employs diagonalization in real space together with any supervised learning algorithm to learn topological phases through an eigenvector-ensembling procedure. We employ our algorithm to successfully recover topological phase diagrams of Su-Schrieffer-Heeger models from data in real space using decision trees and show how entropy-based criteria can be used to retrieve a topological signal detailing how topological information is distributed along the lattice. Our results demonstrate that learning topological phases in real space may be a viable alternative to wavevector space computations, especially in cases when computing topological invariants in wavevector space is impossible or infeasible (e.g. in disordered systems).
Higher Order Topological Phases: A General Principle of Construction (1808.08965v2)
Dumitru Calugaru, Vladimir Juricic, Bitan Roy
2018-08-27
We propose a general principle for constructing higher-order topological (HOT) phases. We argue that if a
-dimensional first-order or regular topological phase involves
Hermitian matrices that anti-commute with additional
mutually anti-commuting matrices, it is conceivable to realize an
th-order HOT phase, where
, with appropriate combinations of discrete symmetry-breaking Wilsonian masses. An
or 1 representations. The former system permits an unprecedented realization of a fourth-order phase, without any surface zero modes. Our construction can be generalized to HOT insulators and superconductors in any dimension and symmetry class.
Temperature dependence of side-jump spin Hall conductivity (1811.03229v2)
Cong Xiao, Yi Liu, Zhe Yuan, Shengyuan A. Yang, Qian Niu
2018-11-08
In the conventional paradigm of the spin Hall effect, the side-jump contribution to the spin Hall conductivity is independent of the density of disorder, thus remains unchanged in clean samples when the phonon density varies with temperature. To the contrary, in this work we reveal that the side-jump contribution due to electron-phonon scattering is temperature-dependent when the temperature drops below the classical regime of equipartition law. The reason for this temperature-dependence differs from that of the phonon-limited longitudinal resistivity. We demonstrate this phenomenon in an analytic model, supplemented by a first-principles calculation for pure Pt. Experimentally accessible high-purity Pt is proposed to be suitable for observing the predicted prominent variation of the spin Hall conductivity below 80 K.
Full Electrostatic Control of Nanomechanical Buckling (1902.05037v1)
Selcuk Oguz Erbil, Utku Hatipoglu, Cenk Yanik, Mahyar Ghavami, Atakan B. Ari, Mert Yuksel, M. Selim Hanay
2019-02-13
Buckling at the micro and nanoscale generates distant bistable states which can be beneficial for sensing, shape-reconfiguration and mechanical computation applications. Although different approaches have been developed to access buckling at small scales, such as the use heating or pre-stressing beams, very little attention has been paid so far to dynamically and precisely control all the critical bifurcation parameters, the compressive stress and the lateral force on the beam. Precise and on-demand generation of compressive stress on individually addressable microstructures is especially critical for morphologically reconfigurable devices. Here, we develop an all-electrostatic architecture to control the compressive force, as well as the direction and amount of buckling, without significant heat generation on micro/nano structures. With this architecture, we demonstrated fundamental aspects of device function and dynamics. By applying voltages at any of the digital electronics standards, we have controlled the direction of buckling. Lateral deflections as large as 12% of the beam length were achieved. By modulating the compressive stress and lateral electrostatic force acting on the beam, we tuned the potential energy barrier between the post-bifurcation stable states and characterized snap-through transitions between these states. The proposed architecture opens avenues for further studies that can enable efficient actuators and multiplexed shape-shifting devices.
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