arXiv subjects

Qianghua Wang

Publications and source records attributed to Qianghua Wang.

8 recordsLinked to original sources

arXiv2026

2.4 GHz Flip-flop Device within Nonequilibrium Superconducting Diode

Superconducting diode effect exhibits asymmetric critical supercurrent and has profound implications for condensed matter physics. The technical appeals of such superconducting diodes are their ultrahigh on-off ratio and diode efficiency for superconducting electronics owing to the dissipationless supercurrent therein. However, realizing superconducting diode operation at high working frequency, which is a key requirement for practical applications, remains elusive and challenging. Here, we demonstrate a polarity-controllable superconducting diode with non-equilibrium Josephson junction and its edge-triggered flip-flop operation at a high frequency up to 2.4 GHz, within a van der Waals superconductor 2M-WS$_2$. By simply tuning the thickness of superconducting 2M-WS$_2$ nanoflakes to engineer inversion asymmetry in the junction, we achieve a high diode efficiency of 67% and an on-off ratio exceeding 10$^5$. Importantly, the pulse width and duty cycle of output pulse signals in such superconducting diode flip-flop devices can be controlled in a broadband frequency range crossing 12 orders of magnitude. Theoretical analysis reveals that the non-equilibrium dynamic nature of supercurrent in these Josephson junctions enables such a high diode operating frequency and the polarity control of supercurrent. The 2.4 GHz non-equilibrium Josephson diode developed here provides a promising platform for advanced superconducting logic circuits and broadband telecommunication applications.

cond-mat.supr-con↗

arXiv2025

Chemical vapor deposition growth of continuous monolayer antiferromagnetic CrOCl films

The discovery of two-dimensional magnetic materials has provided an ideal platform for exploring physical phenomena in the two-dimensional limit. However, intrinsic two-dimensional antiferromagnetic materials have been rarely reported, limiting systematic studies of their electronic properties. The discovery of novel intrinsic two-dimensional antiferromagnets and the development of robust synthesis strategies, therefore, remain significant challenges. Here, we report the chemical vapor deposition synthesis of CrOCl monolayer films and nanosheets that exhibit excellent air stability. The CrOCl morphology is tunable, ranging from two-dimensional nanosheets to three-dimensional flower-like structures, with lateral sizes ranging from several microns to continuous monolayer films. Structural characterization confirms the materials composition and high crystalline quality. Furthermore, magnetic measurements, supported by theoretical calculations, reveal a Néel temperature for CrOCl of ~14 K. This work provides a reliable route for preparing two-dimensional antiferromagnetic materials.

cond-mat.mes-hall↗

arXiv2024

Chiral kagome superconductivity modulations with residual Fermi arcs in KV3Sb5 and CsV3Sb5

Superconductivity involving finite momentum pairing can lead to spatial gap and pair density modulations, as well as Bogoliubov Fermi states within the superconducting gap. However, the experimental realization of their intertwined relations has been challenging. Here, we detect chiral kagome superconductivity modulations with residual Fermi arcs in KV3Sb5 and CsV3Sb5 by normal and Josephson scanning tunneling microscopy down to 30mK with resolved electronic energy difference at microelectronvolt level. We observe a U-shaped superconducting gap with flat residual in-gap states. This gap exhibits chiral 2 by 2 spatial modulations with magnetic field tunable chirality, which align with the chiral 2 by 2 pair density modulations observed through Josephson tunneling. These findings demonstrate a chiral pair density wave (PDW) that breaks time-reversal symmetry. Quasiparticle interference imaging of the in-gap zero-energy states reveals segmented arcs, with high-temperature data linking them to parts of the reconstructed V d-orbital states within the charge order. The detected residual Fermi arcs can be explained by the partial suppression of these d-orbital states through an interorbital 2 by 2 PDW and thus serve as candidate Bogoliubov Fermi states. Additionally, we differentiate the observed PDW order from impurity-induced gap modulations. Our observations not only uncover a chiral PDW order with orbital-selectivity, but also illuminate the fundamental space-momentum correspondence inherent in finite momentum paired superconductivity.

cond-mat.supr-con↗

arXiv2024

Superconducting gap modulations: are they from pair density waves or pair-breaking scattering?

In his seminal work published in Acta Physica Sinica in 1965, Yu Lu pointed out that the superconducting gap exhibits weak modulations near the pair-breaking magnetic impurity in a superconductor. In the past ten years, a series of high-resolution scanning tunneling microscopy works reported weak superconducting gap modulations in certain superconductors and explained these phenomena as pair density waves. In line with Yu's discovery, Lee DH et al. pointed out that in many cases, the interference effect of pair-breaking scattering can also lead to superconducting gap modulations in space. We will discuss the distinction and unification of these two kinds of mechanisms, as well as their relevance to recent experimental observations.

cond-mat.supr-con↗

arXiv2019

Quasiparticle interference and charge order in a heavily overdoped non-superconducting cuprate

One of the key issues in unraveling the mystery of high Tc superconductivity in the cuprates is to understand the normal state outside the superconducting dome. Here we perform scanning tunneling microscopy and spectroscopy measurements on a heavily overdoped, non-superconducting (Bi,Pb)2Sr2CuO6+x cuprate. Spectroscopic imaging reveals dispersive quasiparticle interferences and the Fourier transforms uncover the evolution of momentum space topology. More interestingly, we observe nanoscale patches of static charge order with sqrt(2)*sqrt(2) periodicity. Both the dispersive quasiparticle interference and static charge order can be qualitatively explained by theoretical calculations, which reveal the unique electronic structure of strongly overdoped cuprate.

cond-mat.supr-con↗

arXiv2018

Response and phase transition of a Kitaev spin liquid in a local magnetic field

We study the response of the Kitaev spin liquid (KSL) to a local magnetic field perpendicular to the Kitaev honeycomb lattice. The local magnetic field induces a dynamical excitation of a flux pair in the spin liquid and the system can be described by a generally particle-hole asymmetric interacting resonant level model. The dynamical excitation of the flux pair closes the flux gap in the spectrum of the spin correlation function locally for the gapless KSL even from the perturbative response to a weak magnetic field. Beyond the perturbative regime, the p-h asymmetry competes with the magnetic field and results in a rich phase diagram. Moreover, the magnetic field breaks the gauge equivalence of the ferromagnetic and anti-ferromagnetic Kitaev couplings of the ground state and leads to very different behaviors for the two cases. The anti-ferromagnetic case experiences a first order phase transition to the polarized state during magnetization whereas the ferromagnetic case does not. This study can be generalized to the Kitaev model in a uniform magnetic field and may help understand issues in recent experiments on KSL candidates.

cond-mat.str-el↗

arXiv2018

Intermediate gapless phase and topological phase transition of Kitaev model in a uniform magnetic field

We study the Kitaev spin liquid (KSL) in a [001] magnetic field employing the mean field theory (MFT/MF) in the Majorana fermion representation. The MF Hamiltonian of the system has the Bogoliubov de-Gennes (BdG) form of a 2D Weyl superconductor. We discover a robust gapless regime in intermediate magnetic field for both gapless and gapped AFM KSL with Jx = Jy before the system is polarized in high magnetic field. A topological phase transition (PT) connecting two gapless phases with nodal lines takes place at a critical magnetic field hc1 in this regime. While the nodal lines at hc1 is protected by the mirror symmetry with Jx = Jy and disappear at Jx 6= Jy with a gap opening near the critical field, the nodal points at E = 0 can exist at intermediate fields even without mirror symmetry. We reveal that the phase evolution of the KSL in the magnetic field is driven by the competition between the magnetic field and the particle-hole (p-h) asymmetry of the normal state of the BdG Hamiltonian, which results in the robust intermediate gapless phase for AFM KSL. For FM KSL, there is no intermediate PT before polarization. The above phase diagrams are confirmed by dynamical MFT (DMFT) results.

cond-mat.str-el↗

arXiv2012

Experimental evidence on the Altshuler-Aronov-Spivak interference of the topological surface states in the exfoliated Bi2Te3 nanoflakes

Here we demonstrate the Altshuler-Aronov-Spivak (AAS) interference of the topological surface states on the exfoliated Bi2Te3 microflakes by a flux period of h/2e in their magnetoresistance oscillations and its weak field character. Both the osillations with the period of h/e and h/2e are observed. The h/2e-period AAS oscillation gradually dominates with increasing the sample widths and the temperatures. This reveals the transition of the Dirac Fermions' transport to the diffusive regime.

cond-mat.mes-hall↗