Latest Papers in Condensed Matter Physics

Mesoscale And Nanoscale Physics

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Quantized Photocurrents in the Chiral Multifold Fermion System RhSi (1902.03230v1)

Dylan Rees, Kaustuv Manna, Baozhu Lu, Takahiro Morimoto, Horst Borrmann, Claudia Felser, J. E. Moore, Darius H. Torchinsky, J. Orenstein

2019-02-08

The rapid pace of discovery of new classes of Weyl semimetals is driving a search for properties that derive from their unique bandstructure topology. One of the most striking of the predicted properties is the quantized circular photogalvanic effect (QCPGE), whereby excitation of Weyl fermions by helical photons generates a current that is quantized in units of material-independent fundamental constants over a range of photon energies. Although this remarkable result was initially derived for the simplest case of a two-band crossing, it was later shown to apply to more complex multifold fermion band crossings, where the photocurrent is actually enhanced by larger topological charges. Real materials that exhibit this property are difficult to find in practice as the QCPGE requires that Weyl nodes with opposite topological charge, and hence oppositely directed photocurrent, lie at different energies. This condition in turn dictates that the host crystal must break all mirror symmetries and therefore be chiral. Here we report measurements of photocurrent in the multifold chiral semimetal RhSi that confirm the unique aspects of the predicted multifold fermion response. Specifically, the photocurrent spectrum displays a prominent, mesa-like structure, in which a frequency-independent plateau at low photon energy abruptly falls-off above 0.66 eV, precisely the energy at which the bandstructure indicates the onset of cancelling photocurrent from Weyl nodes of opposite topological charge. The magnitude of photocurrent on this mesa is consistent, within errors arising from indirect estimation of the current relaxation time, with the value expected from quantization, suggesting that RhSi is the first material to support a quantized injection photocurrent of topological origin.

Quantitative analysis of the interaction between a dc SQUID and an integrated micromechanical doubly clamped cantilever (1902.03199v1)

Majdi Salman, Georgina M Klemencic, Soumen Mandal, Scott Manifold, Luqman Mustafa, Oliver A Williams, Sean R Giblin

2019-02-08

Based on the superconducting quantum interference device (SQUID) equations described by the resistively- and capacitively-shunted junction model coupled to the equation of motion of a damped harmonic oscillator, we provide simulations to quantitatively describe the interaction between a dc SQUID and an integrated doubly clamped cantilever. We have chosen to investigate an existing experimental configuration and have explored the motion of the cantilever and the reaction of the SQUID as a function of the voltage-flux characteristics. We clearly observe the Lorentz force back-action interaction and demonstrate how a sharp transition state drives the system into a nonlinear-like regime, and modulates the cantilever displacement amplitude, simply by tuning the SQUID parameters.

Submillimeter - sized proximity effect in graphite and bismuth (1902.03181v1)

Bruno Cury Camargo, Piotr Gierlowski, Ramon Ferreira de Jesus, Paulo Purreur, Yakov Kopelevich

2019-02-08

In this work, we probe the electrical properties of macroscopic graphite and bismuth in which the electrical current is injected via superconducting electrodes, few millimeters apart from each other. Results reveal the induction of a partial superconducting-like transition in these semimetals, at ranges much above those expected for the conventional superconducting proximity effect. We characterize the phenomenon and compare our observations to measurements of antimony single crystals, which did not present such behavior.

Non-linear Hall effect in three-dimensional Weyl and Dirac semimetals (1902.02699v2)

O. O. Shvetsov, V. D. Esin, A. V. Timonina, N. N. Kolesnikov, E. V. Deviatov

2019-02-07

We experimentally investigate a non-linear Hall effect for three-dimensional WTe and CdAs single crystals, representing Weyl and Dirac semimetals, respectively. We observe finite second-harmonic Hall voltage, which depends quadratically on the longitudinal current in zero magnetic field. Despite this observation well corresponds to the theoretical predictions, only magnetic field dependence allows to distinguish the non-linear Hall effect from a thermoelectric response. We demonstrate that second-harmonic Hall voltage shows odd-type dependence on the direction of the magnetic field, which is a strong argument in favor of current-magnetization effects. In contrast, one order of magnitude higher thermopower signal is independent of the magnetic field direction.

Electron-phonon cooling power in Anderson insulators (1809.09888v2)

Mikhail V. Feigel'man, Vladimir E. Kravtsov

2018-09-26

First microscopic theory for electron-phonon energy exchange in Anderson insulators is developed. The major contribution to the cooling power as a function of electron temperature is shown to be directly related to the correlation function of the local density of electron states at small energy difference argument. In Anderson insulators not far from localization transition, this correlation function is strongly enhanced by wave-function's multi-fractality and, additionally, by the presence of Mott's resonant pairs of localized states. The theory we develop explains huge enhancement of the cooling power observed in insulating Indium Oxide films as compared to predictions of the theory previously developed for disordered metals. Our results open the way to predict the conditions appropriate for the observation of Many Body Localization transition those presence in electronic insulators was advocated in the seminal paper by Basko, Aleiner and Altshuler (2006) but have not been convincingly demonstrated yet.

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