Eli Fox
Stanford University
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Featured researches published by Eli Fox.
Physical Review Letters | 2015
Andrew Bestwick; Eli Fox; Xufeng Kou; Lei Pan; Kang L. Wang; David Goldhaber-Gordon
We report a nearly ideal quantum anomalous Hall effect in a three-dimensional topological insulator thin film with ferromagnetic doping. Near zero applied magnetic field we measure exact quantization in the Hall resistance to within a part per 10 000 and a longitudinal resistivity under 1 Ω per square, with chiral edge transport explicitly confirmed by nonlocal measurements. Deviations from this behavior are found to be caused by thermally activated carriers, as indicated by an Arrhenius law temperature dependence. Using the deviations as a thermometer, we demonstrate an unexpected magnetocaloric effect and use it to reach near-perfect quantization by cooling the sample below the dilution refrigerator base temperature in a process approximating adiabatic demagnetization refrigeration.
Physical Review B | 2015
Shreyas Patankar; J. P. Hinton; Joel Griesmar; J. Orenstein; J. S. Dodge; Xufeng Kou; Lei Pan; Kang L. Wang; Andrew Bestwick; Eli Fox; David Goldhaber-Gordon; Jing Wang; Shou-Cheng Zhang
Here, we report measurements of the polar Kerr effect, proportional to the out-of-plane component of the magnetization, in thin films of the magnetically doped topological insulator (Cr0.12Bi0.26Sb0.62)2Te3. Measurements of the complex Kerr angle ΘK were performed as a function of photon energy in the range 0.8eV < ℏω < 3.0eV. We observed a peak in the real part of ΘK(ω) and zero crossing in the imaginary part that we attribute to a resonant interaction with a spin-orbit avoided crossing located ≈ 1.6 eV above the Fermi energy. The resonant enhancement allows measurement of the temperature and magnetic field dependence of ΘK in the ultrathin film limit, d ≥ 2 quintuple layers (QL). We find a sharp transition to zero remanent magnetization at 6 K for d < 8 QL, consistent with theories of the dependence of impurity spin interactions on film thickness and their location relative to topological insulator surfaces.
Nature Communications | 2017
Alice Mahoney; James Colless; Lucas Peeters; S. J. Pauka; Eli Fox; Xufeng Kou; Lei Pan; Kang L. Wang; David Goldhaber-Gordon; D. J. Reilly
Incorporating ferromagnetic dopants into three-dimensional topological insulator thin films has recently led to the realisation of the quantum anomalous Hall effect. These materials are of great interest since they may support electrical currents that flow without resistance, even at zero magnetic field. To date, the quantum anomalous Hall effect has been investigated using low-frequency transport measurements. However, transport results can be difficult to interpret due to the presence of parallel conductive paths, or because additional non-chiral edge channels may exist. Here we move beyond transport measurements by probing the microwave response of a magnetised disk of Cr-(Bi,Sb)2Te3. We identify features associated with chiral edge plasmons, a signature that robust edge channels are intrinsic to this material system. Our results provide a measure of the velocity of edge excitations without contacting the sample, and pave the way for an on-chip circuit element of practical importance: the zero-field microwave circulator.Direct measurement of edge transport in the quantum anomalous Hall effect can be made difficult due to the presence of parallel conductive paths. Here, Mahoney et al. report features associated with chiral edge plasmons, a signature of robust edge states, by probing the zero-field microwave response of a magnetised disk of Cr-(Bi,Sb)2Te3.
Physical Review Letters | 2017
Maria R. Calvo; F. de Juan; Roni Ilan; Eli Fox; Andrew Bestwick; Mathias Mühlbauer; Jun Wang; C. Ames; Philipp Leubner; Christoph Brune; Sipei Zhang; H. Buhmann; L. W. Molenkamp; David Goldhaber-Gordon
We study the electronic transport across an electrostatically gated lateral junction in a HgTe quantum well, a canonical 2D topological insulator, with and without an applied magnetic field. We control the carrier density inside and outside a junction region independently and hence tune the number and nature of 1D edge modes propagating in each of those regions. Outside the bulk gap, the magnetic field drives the system to the quantum Hall regime, and chiral states propagate at the edge. In this regime, we observe fractional plateaus that reflect the equilibration between 1D chiral modes across the junction. As the carrier density approaches zero in the central region and at moderate fields, we observe oscillations in the resistance that we attribute to Fabry-Perot interference in the helical states, enabled by the broken time reversal symmetry. At higher fields, those oscillations disappear, in agreement with the expected absence of helical states when band inversion is lifted.
arXiv: Mesoscale and Nanoscale Physics | 2017
Ilan Rosen; Eli Fox; Xufeng Kou; Lei Pan; Kang L. Wang; David Goldhaber-Gordon
Physical Review B | 2018
Eli Fox; Ilan Rosen; Yanfei Yang; George R. Jones; Randolph E. Elmquist; Xufeng Kou; Lei Pan; Kang L. Wang; David Goldhaber-Gordon
Bulletin of the American Physical Society | 2018
Ilan Rosen; Eli Fox; Lei Pan; Xufeng Kou; Kang L. Wang; David Goldhaber-Gordon
Bulletin of the American Physical Society | 2018
Eli Fox; Ilan Rosen; David Goldhaber-Gordon; Lei Pan; Xufeng Kou; Kang L. Wang
Bulletin of the American Physical Society | 2018
David Goldhaber-Gordon; Eli Fox; Ilan Rosen; Yanfei Yang; George R. Jones; Randolf Elmquist; Xufeng Kou; Lei Pan; Kang L. Wang
Bulletin of the American Physical Society | 2017
Eli Fox; Ilan Rosen; David Goldhaber-Gordon; Yanfei Yang; George R. Jones; Randolph E. Elmquist; Xufeng Kou; Lei Pan; Kang L. Wang