Hailong Fu

Quantum Griffiths singularity of superconductor-metal transition in Ga thin films

Cooling to see the effects of disorder In sufficiently strong external magnetic fields, thin superconducting films typically become insulating. The presence of disorder can affect this phase transition. Theorists have proposed that disorder can cause the so-called Griffiths singularity, where the behavior of the system is determined by a small number of superconducting islands that form above the critical magnetic field. Xing et al. observed a signature of such a singularity in thin films of gallium by analyzing transport data taken at very low temperatures (see the Perspective by Markovic). In this regime, thermal fluctuations were not strong enough to homogenize the system, which allowed the rare islands to form. Science, this issue p. 542; see also p. 509 Systematic transport measurements at low temperatures and in magnetic fields indicate the divergence of the dynamical critical exponent. [Also see Perspective by Markovic] The Griffiths singularity in a phase transition, caused by disorder effects, was predicted more than 40 years ago. Its signature, the divergence of the dynamical critical exponent, is challenging to observe experimentally. We report the experimental observation of the quantum Griffiths singularity in a two-dimensional superconducting system. We measured the transport properties of atomically thin gallium films and found that the films undergo superconductor-metal transitions with increasing magnetic field. Approaching the zero-temperature quantum critical point, we observed divergence of the dynamical critical exponent, which is consistent with the Griffiths singularity behavior. We interpret the observed superconductor-metal quantum phase transition as the infinite-randomness critical point, where the properties of the system are controlled by rare large superconducting regions.

Observation of a Helical Luttinger-Liquid in InAs/GaSb Quantum Spin Hall Edges

We report on the observation of a helical Luttinger liquid in the edge of an InAs/GaSb quantum spin Hall insulator, which shows characteristic suppression of conductance at low temperature and low bias voltage. Moreover, the conductance shows power-law behavior as a function of temperature and bias voltage. The results underscore the strong electron-electron interaction effect in transport of InAs/GaSb edge states. Because of the fact that the Fermi velocity of the edge modes is controlled by gates, the Luttinger parameter can be fine tuned. Realization of a tunable Luttinger liquid offers a one-dimensional model system for future studies of predicted correlation effects.

Ising Superconductivity and Quantum Phase Transition in Macro-Size Monolayer NbSe2

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have a range of unique physics properties and could be used in the development of electronics, photonics, spintronics, and quantum computing devices. The mechanical exfoliation technique of microsize TMD flakes has attracted particular interest due to its simplicity and cost effectiveness. However, for most applications, large-area and high-quality films are preferred. Furthermore, when the thickness of crystalline films is down to the 2D limit (monolayer), exotic properties can be expected due to the quantum confinement and symmetry breaking. In this paper, we have successfully prepared macro-size atomically flat monolayer NbSe2 films on bilayer graphene terminated surface of 6H-SiC(0001) substrates by a molecular beam epitaxy (MBE) method. The films exhibit an onset superconducting critical transition temperature (Tconset) above 6 K and the zero resistance superconducting critical transition temperature (Tczero) up to 2.40 K. Simultaneously, the transport measurements at high magnetic fields and low temperatures reveal that the parallel characteristic field Bc//(T = 0) is above 5 times of the paramagnetic limiting field, consistent with Zeeman-protected Ising superconductivity mechanism. Besides, by ultralow temperature electrical transport measurements, the monolayer NbSe2 film shows the signature of quantum Griffiths singularity (QGS) when approaching the zero-temperature quantum critical point.

Observation of quantum Griffiths singularity and ferromagnetism at the superconducting LaAl O 3 / SrTi O 3 ( 110 ) interface

Diverse phenomena emerge at the interface between band insulators

Depinning transition of bubble phases in a high Landau level

\mathrm{LaAl}{\mathrm{O}}_{3}

Stability of the 5/2 fractional quantum Hall state in a Corbino disc sample with in-plane electric fields

and

Growth and Electronic Transport Property of Layered BiOCl Microplates

\mathrm{SrTi}{\mathrm{O}}_{3}

Scaling properties of the plateau transitions in the two-dimensional hole gas system

, such as superconductivity and ferromagnetism, showing an opportunity for potential applications as well as contributing to fundamental research interests. Here, we report the superconductor-metal transition driven by a perpendicular magnetic field in superconducting two-dimensional electron gas formed at the

Coherence length saturation at the low temperature limit in two-dimensional hole gas

\mathrm{LaAl}{\mathrm{O}}_{3}/\mathrm{SrTi}{\mathrm{O}}_{3}(110)

3/2 fractional quantum Hall plateau in a single layer two-dimensional electron gas

interface, which offers an appealing platform for quantum phase transition from a superconductor to a weakly localized metal. Interestingly, when approaching the quantum critical point, the dynamic critical exponent is not a constant but a diverging value, which is direct evidence of a quantum Griffiths singularity arising from quenched disorder at ultralow temperatures. Furthermore, the hysteretic property of magnetoresistance is observed at the