arXiv subjects

Lei Pan

Publications and source records attributed to Lei Pan.

96 records · Page 6Linked to original sources

arXiv2015

Strongly interacting one-dimensional quantum gas mixtures with weak p-wave interactions

We study one-dimensional strongly interacting quantum gas mixtures, including both the Bose-Fermi and spin-1/2 Fermi-Fermi mixtures, with weak p-wave interactions between intra-component fermions, and demonstrate that the weak p-wave interaction can not be omitted in the strongly interacting regime where the strength of p-wave interactions is comparable with the inverse of the strength of strongly repulsive s-wave interactions. While the total density distribution is not sensitive to the weak p-wave interaction, we find that the p-wave interaction plays an important role in determining the species-dependent (or spin-dependent) density distributions and produces significant physical effects on the low-energy spin dynamics. We also derive effective spin-exchange models for strongly interacting quantum gas mixtures with weak p-wave interactions, which indicate that a quantum phase transition from anti-ferromagnetic state to ferromagnetic state can be induced by tuning the relative strengths of intra-component and inter-component interactions.

cond-mat.quant-gas↗

arXiv2015

Resonant magneto-optic Kerr effect in the magnetic topological insulator Cr:(Sb$_x$,Bi$_{1-x}$)$_2$Te$_3$

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 $(\text{Cr}_{0.12}\text{Bi}_{0.26}\text{Sb}_{0.62})_2\text{Te}_3$. Measurements of the complex Kerr angle, $Θ_K$, were performed as a function of photon energy in the range $0.8\text{ eV}<\hbarω<3.0\text{ eV}$. We observed a peak in the real part of $Θ_K(ω)$ and zero crossing in the imaginary part that we attribute to resonant interaction with a spin-orbit avoided crossing located $\approx$ 1.6 eV above the Fermi energy. The resonant enhancement allows measurement of the temperature and magnetic field dependence of $Θ_K$ in the ultrathin film limit, $d\geq2$ quintuple layers. 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.

cond-mat.mes-hall↗

arXiv2015

Electric-field control of spin-orbit torque in a magnetically doped topological insulator

Electric-field manipulation of magnetic order has proved of both fundamental and technological importance in spintronic devices. So far, electric-field control of ferromagnetism, magnetization and magnetic anisotropy has been explored in various magnetic materials, but the efficient electric-field control of spin-orbit torque (SOT) still remains elusive. Here, we report the effective electric-field control of a giant SOT in a Cr-doped topological insulator (TI) thin film using a top-gate FET structure. The SOT strength can be modulated by a factor of 4 within the accessible gate voltage range, and it shows strong correlation with the spin-polarized surface current in the film. Furthermore, we demonstrate the magnetization switching by scanning gate voltage with constant current and in-plane magnetic field applied in the film. The effective electric-field control of SOT and the giant spin-torque efficiency in Cr-doped TI may lead to the development of energy-efficient gate-controlled spin-torque devices compatible with modern field-effect semiconductor technologies.

cond-mat.str-el↗

arXiv2015

Metal-to-Insulator Switching in Quantum Anomalous Hall States

After decades of searching for the dissipationless transport in the absence of any external magnetic field, quantum anomalous Hall effect (QAHE) was recently achieved in magnetic topological insulator (TI) films. However, the universal phase diagram of QAHE and its relation with quantum Hall effect (QHE) remain to be investigated. Here, we report the experimental observation of the giant longitudinal resistance peak and zero Hall conductance plateau at the coercive field in the 6 quintuple-layer (Cr0.12Bi0.26Sb0.62)2Te3 film, and demonstrate the metal-to-insulator switching between two opposite QAHE plateau states up to 0.3 K. Moreover, the universal QAHE phase diagram is realized through the angle-dependent measurements. Our results address that the quantum phase transitions in both QAHE and QHE regimes are in the same universality class, yet the microscopic details are different. In addition, the realization of the QAHE insulating state unveils new ways to explore quantum phase-related physics and applications.

cond-mat.mes-hall↗

arXiv2015

Precise quantization of anomalous Hall effect near zero magnetic field

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 Hall resistance to within a part per 10,000 and longitudinal resistivity under 1 ohm per square, with chiral edge transport explicitly confirmed by non-local measurements. Deviations from this behavior are found to be caused by thermally-activated carriers, which can be eliminated by taking advantage of an unexpected magnetocaloric effect.

cond-mat.mes-hall↗

arXiv2014

Scale-Invariant Dissipationless Chiral Transport in Magnetic Topological Insulators beyond the Two-Dimensional Limit

We investigate the quantum anomalous Hall Effect (QAHE) and related chiral transport in the millimeter-size (Cr0.12Bi0.26Sb0.62)2Te3 films. With high sample quality and robust magnetism at low temperatures, the quantized Hall conductance of e2/h is found to persist even when the film thickness is beyond the two-dimensional (2D) hybridization limit. Meanwhile, the Chern insulator-featured chiral edge conduction is manifested by the non-local transport measurements. In contrast to the 2D hybridized thin film, an additional weakly field-dependent longitudinal resistance is observed in the 10 quintuple-layer film, suggesting the influence of the film thickness on the dissipative edge channel in the QAHE regime. The extension of QAHE into the three-dimensional thickness region addresses the universality of this quantum transport phenomenon and motivates the exploration of new QAHE phases with tunable Chern numbers. In addition, the observation of the scale-invariant dissipationless chiral propagation on a macroscopic scale makes a major stride towards ideal low-power interconnect applications.

cond-mat.mes-hall↗