Latest Papers in Condensed Matter Physics

Mesoscale And Nanoscale Physics

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Gate tunable quantum Hall effects in defect-suppressed Bi2Se3 films (1903.10945v2)

N. Koirala, M. Salehi, J. Moon, S. Oh

2019-03-26

Despite many years of efforts, attempts to reach the quantum regime of topological surface states (TSS) on an electrically tunable topological insulator (TI) platform have so far failed on binary TI compounds such as Bi2Se3 due to high density of interfacial defects. Here, utilizing an optimal buffer layer on a gatable substrate, we demonstrate the first electrically tunable quantum Hall effects (QHE) on TSS of Bi2Se3. On the n-side, well-defined QHE shows up, but it diminishes near the charge neutrality point (CNP) and completely disappears on the p-side. Furthermore, around the CNP the system transitions from a metallic to a highly resistive state as the magnetic field is increased, whose temperature dependence indicates presence of an insulating ground state at high magnetic fields.

Nanoscale ultrasensing using a nonbonding plasmon resonance (1907.08174v1)

Jer-Shing Huang, Gary Razinskas, Philipp Grimm, Bert Hecht

2019-07-18

Placing a plasmonic nanorod near the termination of a plasmonic nanowire dramatically changes the reflection of the wire's guided mode. By carefully choosing the length of the nanorod, the reflectivity at the wire termination nearly vanishes due to destructive interference between the directly reflected wire mode and the infinite sum of the partial transmissions back into the wire of the reflected modes inside the nanorod. We show that this near-zero reflection condition corresponds to the so far overlooked nonbonding resonance which corresponds to a minimal coupling condition with extreme sensitivity to any changes in the nanorod's local environment. We explicitly quantify the sensitivity of the nonbonding condition towards small local and global perturbations of the refractive index and outline a method to exploit the nonbonding condition for near-field ultrasensing.

Understanding the Linewidth of the ESR Spectrum Detected by a Single NV Center in Diamond (1907.08156v1)

Benjamin Fortman, Susumu Takahashi

2019-07-18

Spectral analysis of electron spin resonance (ESR) is a powerful technique for various investigations including characterization of spin systems, measurements of spin concentration, and probing spin dynamics. The nitrogen-vacancy (NV) center in diamond is a promising magnetic sensor enabling improvement of ESR sensitivity to the level of a single spin. Therefore, understanding the nature of NV-detected ESR (NV-ESR) spectrum is critical for applications to nanoscale ESR. Within this work we investigate the linewidth of NV-ESR from single substitutional nitrogen centers (called P1 centers). NV-ESR is detected by a double electron-electron resonance (DEER) technique. By studying the dependence of the DEER excitation bandwidth on NV-ESR linewidth, we find that the spectral resolution is improved significantly and eventually limited by inhomogeneous broadening of the detected P1 ESR. Moreover, we show that the NV-ESR linewidth can be as narrow as 0.3 MHz.

Stacking order-dependent sign-change of microwave phase due to eddy currents in nanometer-scale NiFe/Cu heterostructures (1902.06501v3)

O. Gladii, R. L. Seeger, L. Frangou, G. Forestier, U. Ebels, S. Auffret, V. Baltz

2019-02-18

In the field of spintronics, ferromagnetic/non-magnetic metallic multilayers are core building blocks for emerging technologies. Resonance experiments using stripline transducers are commonly used to characterize and engineer these stacks for applications. Up to now in these experiments, the influence of eddy currents on the excitation of the dynamics of ferromagnetic magnetization below the skin-depth limit was most often neglected. Here, using a coplanar stripline transducer, we experimentally investigated the broadband ferromagnetic resonance response of NiFe/Cu bilayers a few nanometers thick in the sub-skin-depth regime. Asymmetry in the absorption spectrum gradually built up as the excitation frequency and Cu-layer thickness increased. Most significantly, the sign of the asymmetry depended on the stacking order. Experimental data were consistent with a quantitative analysis considering eddy currents generated in the Cu layers and the subsequent phaseshift of the feedback magnetic field generated by the eddy currents. These results extend our understanding of the impact of eddy currents below the microwave magnetic skin-depth and explain the lineshape asymmetry and phase lags reported in stripline experiments.

Efficient computation of demagnetising fields for magnetic multilayers using multilayered convolution (1906.00813v2)

Serban Lepadatu

2019-06-03

As research into magnetic thin films and spintronics devices is moving from single to multiple magnetic layers, there is a need for micromagnetics modelling tools specifically designed to efficiently handle magnetic multilayers. Here we show an exact method of computing demagnetising fields in magnetic multilayers, which is able to handle layers with arbitrary spacing, arbitrary thicknesses, and arbitrary relative positioning between them without impacting on the computational performance, or sacrificing numerical accuracy. The multilayered convolution method is a generalisation of the well-known convolution method used to compute demagnetising fields in a single magnetic body. In typical use cases, such as multilayered stacks used to study skyrmions, we show the multilayered convolution method can be up to 8 times faster, implemented both for central processors and graphics processors, compared to the simple convolution method.

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