arXiv subjects

P. Xiong

Publications and source records attributed to P. Xiong.

10 recordsLinked to original sources

arXiv2022

Quantum interference in asymmetric superconducting nanowire loops

Macroscopic phase coherence in superconductors enables quantum interference and phase manipulation at realistic device length scales. Numerous superconducting electronic devices are based on the modulation of the supercurrent in superconducting loops. While the overall behavior of symmetric superconducting loops have been studied, the effects of asymmetries in such devices remain under-explored and poorly understood. Here we report on an experimental and theoretical study of the flux modulation of the persistent current in a doubly-connected asymmetric aluminum nanowire loop. A model considering the length and electronic cross-section asymmetries in the loop provides a quantitative account of the observations. Comparison with experiments give essential parameters such as persistent and critical currents as well as the amount of asymmetry which can provide feedback into the design of superconducting quantum devices.

cond-mat.supr-con↗

arXiv2021

Hourly Warning for Strong Earthquakes

A promising perspective is presented that humans can provide hourly warning for strong land earthquakes (EQs, Ms6). Two important atmospheric electrostatic signal features are described. A table that lists 9 strong land EQs with shock time, epicenter, magnitude, weather in the region near the epicenter, precursor beginning time, and precursor duration demonstrates that at approximately several hours to one day before a strong land EQ, the weather conditions are fair near the epicenter, and an abnormal negative atmospheric electrostatic signal is very obvious. Moreover, the mechanism is explained. A method by which someone could determine the epicenter and the magnitude of a forthcoming strong EQ is suggested. Finally, the possibility of realizing hourly warning for strong land EQs in the near future is pointed out.

physics.geo-ph↗

arXiv2015

Orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films

We report the first experimental realization of orbital two-channel Kondo (2CK) effect from two-level systems (TLSs) in epitaxial L10-MnAl films with giant perpendicular magnetic anisotropy. The resistivity exhibits a low-temperature (T) upturn with a clear transition from a lnT-dependence to T1/2-dependence and deviation from it in three distinct T regimes, which are independent of applied magnetic fields. The magnitudes of Kondo temperature and energy splitting of the TLSs are greatly enhanced in comparison to those in other systems exhibiting orbital 2CK, suggesting strong coupling between the tunneling centers with conduction electrons via resonant scattering. These results point to a considerable robustness of the orbital 2CK effect even in the presence of ferromagnetic ordering and significant spin polarization of the conduction electrons.

cond-mat.str-el↗

arXiv2013

Signatures of electronic phase separation in the Hall effect of anisotropically strained La0.67Ca0.33MnO3 films

Systematic transport measurements have been performed on a series of La0.67Ca0.33MnO3 (LCMO) thin films with varying degrees of anisotropic strain. The strain is induced via epitaxial growth on NdGaO3(001) substrates and varied by controlling the thermal annealing time. An antiferromagnetic insulating (AFI) state, possibly associated with charge ordering, emerges upon thermal annealing. The Hall effect in these materials exhibits features that are indicative of a percolative phase transition and correlate closely with the emergence of the AFI state. In the paramagnetic phase, the Hall resistivity takes on two slopes in all samples: a decreasing negative slope with increasing temperature at low fields, which is attributed to the carrier hopping motion, and an almost temperature independent positive slope at high fields due to diffusive transport of holes. Significantly, the crossover fields of the Hall resistivity slope at different temperatures correspond to the same magnetization, which is interpreted as the critical point of a magnetic field-driven percolative phase transition. At lower temperatures near the zero-field metal-insulator transition, pronounced enhancement of the Hall coefficient with the development of the AFI state is observed. The enhancement peaks near the magnetic field-driven percolation; its magnitude correlates with the strength of the AFI state and is suppressed with the melting of the AFI state by an in-plane magnetic field. The observations resemble many features of the enhancement of the Hall coefficient in granular metal films near the composition-driven percolation.

cond-mat.str-el↗

arXiv2012

Magnetically-driven electronic phase separation in the semimetallic ferromagnet EuB$_6$

From measurements of fluctuation spectroscopy and weak nonlinear transport on the semimetallic ferromagnet EuB$_6$ we find direct evidence for magnetically-driven electronic phase separation consistent with the picture of percolation of magnetic polarons (MP), which form highly conducting magnetically-ordered clusters in a paramagnetic and 'poorly conducting' background. These different parts of the conducting network are probed separately by the noise spectroscopy/nonlinear transport and the conventional linear resistivity. We suggest a comprehensive and 'universal' scenario for the MP percolation, which occurs at a critical magnetization either induced by ferromagnetic order at zero field or externally applied magnetic fields in the paramagentic region.

cond-mat.str-el↗

arXiv2011

Andreev nanoprobe of half-metallic CrO$_{2}$ films using superconducting cuprate tips

Superconducting tips of YBa$_{2} $Cu$_{3}$O$_{7-x}$ were used to perform point-contact Andreev reflection spectroscopy on half-metallic CrO$_{2}$ thin films. At 4.2K, strong suppression of the d-wave Andreev reflection characteristics was observed, consistent with the high spin polarization of CrO$_{2}$. Our technique was validated by comparison with data taken on non-magnetic Au films, and with data taken by superconducting Pb tips. The point contacts were estimated to be $\lesssim$ 10nm in size, attesting to their ballistic and microscopic nature. Our results demonstrate the feasibility of using superconducting cuprate tips as spin-sensitive nanoprobes of ferromagnets.

cond-mat.supr-con↗

arXiv2007

Measurement of the spin polarization of the magnetic semiconductor EuS with zero-field and Zeeman-split Andreev reflection spectroscopy

We report measurements of the spin polarization (\textbf{\textit{P}}) of the concentrated magnetic semiconductor EuS using both zero-field and Zeeman-split Andreev reflection spectroscopy (ARS) with EuS/Al planar junctions. The zero-field ARS spectra are well described by the modified (spin-polarized) BTK model with expected superconducting energy gap and actual measurement temperature (no additional spectral broadening). The fittings consistently yield \textbf{\textit{P}} close to 80% regardless of the barrier strength. Moreover, we performed ARS in the presence of a Zeeman-splitting of the quasiparticle density of states in Al. To describe the Zeeman-split ARS spectra, we develop a theoretical model which incorporates the solution to the Maki-Fulde equations into the modified BTK analysis. The method enables the determination of the magnitude as well as the sign of \textbf{\textit{P}} with ARS, and the results are consistent with those from the zero-field ARS. The experiments extend the utility of field-split superconducting spectroscopy from tunnel junctions to Andreev junctions of arbitrary barrier strengths.

cond-mat.mtrl-sci↗

arXiv2006

Superconducting quantum phase transitions tuned by magnetic impurity and magnetic field in ultrathin a-Pb films

Superconducting quantum phase transitions tuned by disorder (d), paramagnetic impurity (MI) and perpendicular magnetic field (B) have been studied in homogeneously disordered ultrathin a-Pb films. The MI-tuned transition is characterized by progressive suppression of the critical temperature to zero and a continuous transition to a weakly insulating normal state with increasing MI density. In all important aspects, the d-tuned transition closely resembles the MI-tuned transition and both appear to be fermionic in nature. The B-tuned transition is qualitatively different and probably bosonic. In the critical region it exhibits transport behavior that suggests a B-induced mesoscale phase separation and presence of Cooper pairing in the insulating state.

cond-mat.supr-con↗

arXiv2006

High-Performance, Hysteresis-Free Carbon Nanotube FETs via Directed Assembly

High-performance single-wall carbon nanotube field-effect transistors (SWNT-FETs) are fabricated using directed assembly and mass-produced carbon nanotubes (CNTs). These FETs exhibit operating characteristics comparable to state-of-the-art devices, and the process provides a route to large-scale functional CNT circuit assembly that circumvents problems inherent in processes relying on chemical vapor deposition (CVD). Furthermore, the integration of hydrophobic self-assembled monolayers (SAMs) in the device structure eliminates the primary source of gating hysteresis in SWNT-FETs, which leads to hysteresis-free FET operation while exposing unmodified nanotube surfaces to ambient air.

cond-mat.mes-hall↗

arXiv2000

Noise Probe of the Dynamic Phase Separation in La2/3Ca1/3MnO3

Giant Random Telegraph Noise (RTN) in the resistance fluctuation of a macroscopic film of perovskite-type manganese oxide La2/3Ca1/3MnO3 has been observed at various temperatures ranging from 4K to 170K, well below the Curie temperature (TC = 210K). The amplitudes of the two-level-fluctuations (TLF) vary from 0.01% to 0.2%. We use a statistical analysis of the life-times of the TLF to gain insight into the microscopic electronic and magnetic state of this manganite. At low temperature (below 30K) The TLF is well described by a thermally activated two-level model. An estimate of the energy difference between the two states is inferred. At higher temperature (between 60K and 170K) we observed critical effects of the temperature on the life-times of the TLF. We discuss this peculiar temperature dependence in terms of a sharp change in the free energy functional of the fluctuators. We attribute the origin of the RTN to be a dynamic mixed-phase percolative conduction process, where manganese clusters switch back and forth between two phases that differ in their conductivity and magnetization.

cond-mat.str-el↗