Latest Papers in Condensed Matter Physics

Mesoscale And Nanoscale Physics

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Versatile Hall magnetometer with variable sensitivity assembly for characterization of the magnetic properties of nanoparticles (1905.05741v2)

Jefferson F. D. F. Araujo, Daniel R. P. Vieira, Fredy Osorio, Walmir E. Pöttker, Felipe A. La Porta, Patricia de la Presa, Geronimo Perez, Antonio C. Bruno

2019-05-14

A Hall magnetometer with variable sensitivity is constructed to measure the magnetic properties of magnetic nanoparticles manufactured by different methods. This novel magnetometer can also be used to measure bulk materials and samples in liquids. The magnetometer is constructed with two commercial Hall-effect sensors in an acrylic structure, which serves as the support for a micrometer and the circuit board with the sensors. For operation, the magnetometer it acquires a complete magnetization curve in a few minutes. If has a magnetic moment sensitivity of 1.3*10-9 Am2 to sensitivity of 493 mV/mT, the sensitivity can be adjustable in the range of 10 to 493 mV/mT. Its performance is tested with magnetic nanoparticles. As an application example, we estimate the mean diameter of the nanoparticles using the magnetic curves. The results are compared with those obtained by other techniques, such as transmission electron microscopy (TEM), X-ray diffraction (XRD) and dynamic light scattering (DLS). The magnetization results are also compared with those obtained by independent commercial magnetometers, which reveals errors of approximately 0.31 Am2/kg (i.e., 0.6%) in the saturation region.

Evidence of orbit-selective electronic kagome lattice with planar flat-band in correlated paramagnetic YCr6Ge6 (1906.07140v1)

T. Y. Yang, Q. Wan, Y. H. Wang, M. Song, J. Tang, Z. W. Wang, H. Z. Lv, N. C. Plumb, M. Radovic, G. W. Wang, G. Y. Wang, Z. Sun, R. Yu, M. Shi, Y. M. Xiong, N. Xu

2019-06-17

Electronic properties of kagome lattice have drawn great attention recently. In associate with flat-band induced by destructive interference and Dirac cone-type dispersion, abundant exotic phenomena have been theoretically discussed. The material realization of electronic kagome lattice is a crucial step towards comprehending kagome physics and achieving novel quantum phases. Here, combining angle-resolved photoemission spectroscopy, transport measurements and first-principle calculations, we expose a planar flat-band in paramagnetic YCr6Ge6 as a typical signature of electronic kagome lattice. We unearth that the planar flat-band arises from the dz2 electrons with intra-kagome-plane hopping forbidden by destructive interference. On the other hand, the destructive interference and flatness of the dx2-y2 and dxy bands are decomposed possibly due to additional in-plane hopping terms, but the Dirac cone-type dispersion is reserved near chemical potential. We explicitly unveil that orbital character plays an essential role to realize electronic kagome lattice in bulk materials with transition metal kagome layers. Paramagnetic YCr6Ge6 provides an opportunity to comprehend intrinsic properties of electronic kagome lattice as well as its interplays with spin orbit coupling and electronic correlation of Cr-3d electrons, and be free from complications induced by strong local moment of ions in kagome planes.

Superfluid weight and Berezinskii-Kosterlitz-Thouless transition temperature of twisted bilayer graphene (1906.06313v2)

Aleksi Julku, Teemu J. Peltonen, Long Liang, Tero T. Heikkilä, Päivi Törmä

2019-06-14

We study superconductivity of twisted bilayer graphene with local and non-local attractive interactions. We obtain the superfluid weight and Berezinskii-Kosterlitz-Thouless (BKT) transition temperature for microscopic tight-binding and low-energy continuum models. We predict qualitative differences between local and non-local interaction schemes which could be distinguished experimentally. In the flat band limit where the pair potential exceeds the band width we show that the superfluid weight and BKT temperature are determined by multiband processes and quantum geometry of the band.

Magnetically Activated Rotational Vacuum Friction (1706.02924v3)

Deng Pan, Hongxing Xu, F. Javier García de Abajo

2017-06-09

We predict the existence of a torque acting on an isotropic neutral nanosphere activated by a static magnetic field when the particle temperature differs from the surrounding vacuum. This phenomenon originates in time-reversal symmetry breaking of the particle interaction with the vacuum electromagnetic field. We present a rigorous quantum treatment of photons and particle excitations that leads to a nonzero torque even in a motionless particle. We also find that the dynamical evolution of the particle temperature and rotation frequency follow an exotic dynamics, including spontaneous changes in the rotation direction. Magnetically activated thermal vacuum torques open a unique avenue for the investigation of the effect of time-reversal symmetry-breaking in thermal and Casimir physics.

Topological spin excitations in Harper-Heisenberg spin chains (1906.07090v1)

J. L. Lado, Oded Zilberberg

2019-06-17

Many-body spin systems represent a paradigmatic platform for the realization of emergent states of matter in a strongly interacting regime. Spin models are commonly studied in one-dimensional periodic chains with a lattice constant on the order of the spin-spin distance. However, in cold atomic setups or functionalized twisted van der Waals heterostructures, long-range modulations of the spin physics can be engineered. Here we show that such superlattice modulations in a many-body spin Hamiltonian can give rise to observable topological boundary modes in the excitation spectrum of the spin chain. In the case of an XY spin- chain, these boundary modes stem from a mathematical correspondence with the chiral edge modes of a two-dimensional quantum Hall state. Our results show that the addition of many-body interactions does not close some of the topological gaps in the excitation spectrum, and the topological boundary modes visibly persist in the isotropic Heisenberg limit. These observations persist when the spin moment is increased and a large-spin limit of the phenomenon is established. Our results show that such spin superlattices provide a promising route to observe many-body topological boundary effects in cold atomic setups and functionalized twisted van der Waals materials.

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