Latest Papers in Condensed Matter Physics

Mesoscale And Nanoscale Physics

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Homogenous alloys on ZnO substrates: A new approach for high performance thermoelectric materials (1905.03769v1)

Yining Feng, Evan Witkoske, Bahadir Kucukgok, Yee Rui Koh, Ali Shakouri, Ian T. Ferguson, Mark Lundstrom, Na Lu

2019-05-09

High performance thermoelectric materials for wide-range temperature applications still remains a challenge. In this study, we have produced high-quality homogeneous on ZnO substrates, with no phase separation at high Indium content, using metal organic chemical vapor deposition for thermoelectric applications. A record high room temperature figure of merit zT is obtained of 0.86, which is five times larger than that of SiGe, the current state of the art high temperature thermoelectric material. These materials are shown to have a nearly perfect doping concentration to maximize zT regardless of the scattering mechanism. This almost one order of magnitude increase in zT is due to large electrical conductivities from oxygen co-doping as well as low thermal conductivities from alloy scattering. The maximum power factor reached was at 300K for alloys at a carrier concentration . This work indicates that alloys have great potential for thermoelectric applications especially at a high temperature range.

Discrete nonlinear domains for polariton fluids in a flat band (1905.03759v1)

V. Goblot, B. Rauer, F. Vicentini, A. Le Boité, E. Galopin, A. Lemaître, L. Le Gratiet, A. Harouri, I. Sagnes, S. Ravets, C. Ciuti, A. Amo, J. Bloch

2019-05-09

Phase frustration in periodic lattices is responsible for the formation of dispersionless flat bands. The absence of any kinetic energy scale makes flat band physics critically sensitive to perturbations and interactions. We report here on the experimental investigation of the nonlinear dynamics of cavity polaritons in the gapped flat band of a one-dimensional Lieb lattice. We observe the formation of gap solitons with quantized size and very abrupt edges, signature of the frozen propagation of switching fronts. This type of gap solitons belongs to the class of truncated Bloch waves, and had only been observed in closed systems up to now. Here the driven-dissipative character of the system gives rise to a complex multistability of the nonlinear domains generated in the flat band. These results open up interesting perspective regarding more complex 2D lattices and the generation of correlated photon phases.

The Hierarchy of Excitation Lifetimes in Two-Dimensional Fermi Gases (1905.03751v1)

Patrick J Ledwith, Haoyu Guo, Leonid Levitov

2019-05-09

Momentum-conserving quasiparticle collisions in two-dimensional Fermi gases give rise to a large family of exceptionally long-lived excitation modes. The lifetimes of these modes exceed by a factor the conventional Landau Fermi-liquid lifetimes . The long-lived modes have a distinct angular structure, taking the form of and with odd values for a circular Fermi surface, with relaxation rate dependence on of the form , valid at not-too-large . In contrast, the even- harmonics feature conventional lifetimes with a weak dependence. The long-time dynamics, governed by the long-lived modes, takes the form of angular (super)diffusion over the Fermi surface. Altogether, this leads to unusual long-time memory effects, defining an intriguing transport regime that lies between the conventional ballistic and hydrodynamic regimes.

Dynamical singularities of Floquet higher-order topological insulators (1905.03727v1)

Haiping Hu, Biao Huang, Erhai Zhao, W. Vincent Liu

2019-05-09

We propose a versatile framework to dynamically generate Floquet higher-order topological insulators by multi-step driving of topologically trivial Hamiltonians. Two analytically solvable examples are used to illustrate this procedure to yield Floquet quadrupole and octupole insulators with zero- and/or -corner modes protected by mirror symmetries. We introduce dynamical topological invariants from the full unitary return map and show its phase bands contain Weyl singularities whose topological charges form dynamical multipole moments in the Brillouin zone. Combining them with the topological index of Floquet Hamiltonian gives a pair of invariant and which fully characterize the higher-order topology and predict the appearance of zero- and -corner modes. Our work establishes a systematic route to construct and characterize Floquet higher-order topological phases.

Synthetic spin-orbit coupling and topological polaritons in Janeys-Cummings lattices (1801.08426v4)

Feng-Lei Gu, Jia Liu, Feng Mei, Suotang Jia, Dan-Wei Zhang, Zheng-Yuan Xue

2018-01-25

The interaction between a photon and a qubit in the Janeys-Cummings (JC) model generates a kind of quasiparticle called polariton. While they are widely used in quantum optics, difficulties in engineering controllable coupling of them severely limit their applications to simulate spinful quantum systems. Here we show that, in the superconducting quantum circuit context, polariton states in the single-excitation manifold of a JC lattice can be used to simulate a spin-1/2 system, based on which tunable synthetic spin-orbit coupling and novel topological polaritons can be generated and explored. The lattice is formed by a sequence of coupled transmission line resonators, each of which is connected to a transmon qubit. Synthetic spin-orbit coupling and effective Zeeman field of the polariton can both be tuned by modulating the coupling strength between neighbouring resonators, allowing for the realization of a large variety of polaritonic topological semimetal bands. Methods for detecting the polaritonic topological edge states and topological invariants are also proposed. Therefore, our work suggests that the JC lattice is a versatile platform for exploring spinful topological states of matter, which may inspire developments of topologically protected quantum optical and information processing devices.

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