arXiv subjects

Chengyu Yan

Publications and source records attributed to Chengyu Yan.

At least 19 recordsLinked to original sources

arXiv2026

Electrically tunable circular photocurrent via local-field induced symmetry breaking at a metal-MoTe2 interface

Transition metal dichalcogenides (TMDCs) constitute a promising platform for symmetry-engineered responses to circularly polarized light. The high crystal symmetry of centrosymmetric 2H-phase TMDCs inherently forbids the circular photogalvanic effect, thereby necessitating external stimuli such as electric fields or strain to lower the symmetry for its activation. While Schottky junctions provide a ubiquitous built-in field for potentially inducing circular photocurrents, the mechanism for the generation and control of circular photocurrents in TMDCs is not understood. In this study, we fabricated a localized gold-MoTe2 heterostructure and demonstrate a pronounced circular photocurrent at the interface under normal incidence. The photocurrent is attributed to circular photogalvanic effect governed by the strength and direction of the built-in electric field, enabling continuous modulation via an external bias. First-principles calculations show that the gold interface induces a spin splitting in the valence bands of MoTe2, establishing a valley-dependent spin ordering. The observed circular photocurrent from multilayer 2H-MoTe2 under normal incidence indicates the breaking of C3 rotational symmetry by the local in-plane field. These results establish an effective strategy for developing voltage-tunable circularly polarized photodetectors and valleytronic devices.

cond-mat.mtrl-sci↗

arXiv2025

A Symmetric Superconducting Dome Hosts Non-Fermi Liquid Behavior at Optimal Doping in MoS2

The similarities between the phase diagrams of ionic liquid-gated transition metal dichalcogenides (TMDCs) and high-temperature superconductors have garnered considerable interest due to the presence of a superconducting dome with a non-monotonic dependence of the superconducting order parameter as a function of charge carrier density. However, the lack of a complete superconducting dome and insights into the normal state in ionic liquid-gated TMDCs prevents a detailed mapping between the two systems. In this work, we obtain a symmetric superconducting dome that extends from deep underdoped regime all the way to deep overdoped regime in ionic liquid gated MoS2 with a refined gating protocol. We demonstrate that the dome is anticorrelated with the evolution of non-Fermi liquid behavior in the normal states. The scattering rate in the non-Fermi liquid regime can reach Planckian limit. The results may shed light on the emergence of superconductivity in TMDCs.

cond-mat.supr-con↗

arXiv2025

Dual-mode superconducting diode effect enabled by in-plane and out-of-plane magnetic field

The discovery of the superconducting diode effect (SDE) has been cherished as a milestone in developing superconducting electronics. Tremendous efforts are being dedicated to realizing SDE in a wide variety of material platforms. Despite the diversity in the hosting materials and device designs, SDE is usually operated in a single mode which is enabled by either out-of-plane or in-plane magnetic field/magnetization. In this work, we report the realization of a dual-mode SDE in 2H-$\mathrm{NbS_2}$/2H-$\mathrm{NbSe_2}$ heterostructures where both the out-of-plane magnetic field $B_{\perp}$ and in-plane magnetic field $B_{||}$ can independently generate and manipulate SDE. The two modes share similar diode efficiency but differ in two aspects: 1. $B_{\perp}$-induced SDE is activated by a field on the order of 1 mT while $B_{||}$-induced SDE requires a field on the order of 100 mT; 2. $\eta$ of $B_{\perp}$-induced SDE exhibits a square-root like temperature dependence while $\eta$ of $B_{||}$-induced SDE takes a more linear-like one. We demonstrate that the dual-mode SDE is most likely a result of mirror symmetry breaking along multiple orientations. Thanks to the two orders difference in the operational field for the two modes, we propose a dual-functionality device scheme to showcase the potential of the dual-mode SDE in realizing advanced superconducting architecture, where fast polarity-switching functionality is implemented with $B_{\perp}$-induced SDE and high-fidelity functionality is enabled with $B_{\perp}$-induced SDE.

cond-mat.supr-con↗

arXiv2025

Evolution of quantum criticality in underdoped cuprates

Quantum criticality, with both static and dynamic information of the system intrinsically encoded in characteristic length scales, serves as one of the most sensitive and universal probes to monitor quantum phase transition. Qualitatively different quantum criticality behaviours have been widely observed even in the same condensed matter system. The discrepancy is attributed to sample specificity but has not been systemically addressed. Here we report a single-parameter driven three-stage evolution of quantum criticality unveiled in superconductor-insulator transition in underdoped Bi2Sr2CaCu2O8+{\delta} flakes. The evolution starts with a single quantum critical point emerging at the boundary between the superconducting and antiferromagnetic phases, then evolving into anomalous quantum Griffiths singularity at the medium doping levels and eventually being replaced by quantum Griffiths singularity in the deep superconducting regime. A puddle model that incorporates the developments of antiferromagnetic correlation can capture the evolution. The results offer a new aspect to examine previous seemingly sample-specific quantum critical behavior and lay the foundation for further exploring complex quantum criticality in strongly correlated systems; meanwhile they shed light on the detailed interaction between superconductivity and antiferromagnetism in cuprates.

cond-mat.supr-con↗

arXiv2025

Enhanced Backgate Tunability on Interfacial Carrier Concentration in Ionic Liquid-Gated MoS2 Devices

The periodic spatial modulation potential arising from the zig-zag distribution of ions at large gate voltage in an ionic liquid gated device may enable functionalities in a similar way as nanopatterning and moir\'e engineering. However, the inherent coupling between periodic modulation potential and carrier concentration in ionic liquid devices has hindered further exploration. Here, we demonstrate the feasibility of decoupling manipulation on periodic modulation potential and carrier density in an ionic liquid device by using a conventional backgate. The backgate is found to have a tunability on carrier concentration comparable to that of ionic gating, especially at large ionic liquid gate voltage, by activating the bulk channels mediated back tunneling between the trapped bands and interfacial channel.

cond-mat.mes-hall↗

arXiv2024

Orbital Fulde-Ferrell-Larkin-Ovchinnikov state in 2H-NbS2 flakes

Symmetry breaking in a layered superconductor with Ising spin-orbit coupling has offered an opportunity to realize unconventional superconductivity. To be more specific, orbital Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, exhibiting layer-dependent finite-momentum pairing, may emerge in transition metal dichalcogenides materials (TMDC) in the presence of an in-plane magnetic field. Orbital FFLO state can be more robust against the magnetic field than the conventional superconducting state with zero-momentum pairing. This feature renders its potential in field-resilient superconducting functionality. Although, orbital FFLO state has been reported in NbSe2 and MoS2, it is not yet clear if orbital FFLO state can be extended to other TMDC superconductor. Here, we report the observation of orbital FFLO state in 2H-NbS2 flakes and its dependence on the thickness of flake. We conclude that the relatively weak interlayer coupling is instrumental in stabilizing orbital FFLO state at higher temperature with respect to the critical temperature and lower magnetic field with respect to paramagnetic limit in NbS2 in comparison to its NbSe2 counterpart.

cond-mat.supr-con↗

arXiv2024

Circular Photocurrents in Centrosymmetric Semiconductors with Hidden Spin Polarization

Centrosymmetric materials with site inversion asymmetries possess hidden spin polarization, which remains challenging to be converted into spin currents because the global inversion symmetry is still conserved. This study demonstrates the spin-polarized DC circular photocurrents (CPC) in centrosymmetric transition metal dichalcogenides (TMDCs) at normal incidence without applying electric bias. The global inversion symmetry is broken by using a spatially-varying circularly polarized light beam, which could generate spin gradient owing to the hidden spin polarization. The dependences of the CPC on electrode configuration, illumination position, and beam spot size indicate an emergence of circulating electric current under spatially inhomogeneous light, which is associated with the deflection of spin-polarized current through the inverse spin Hall effect (ISHE). The CPC is subsequently utilized to probe the spin polarization and ISHE under different excitation wavelengths and temperatures. The results of this study demonstrate the feasibility of using centrosymmetric materials with hidden spin polarization and non-vanishing Berry curvature for spintronic device applications.

cond-mat.mtrl-sci↗

arXiv2023

Exploring the interfacial coupling between graphene and the antiferromagnetic insulator MnPSe$_3$

Interfacial coupling between graphene and other 2D materials can give rise to intriguing physical phenomena. In particular, several theoretical studies predict that the interplay between graphene and an antiferromagnetic insulator could lead to the emergence of quantum anomalous Hall phases. However, such phases have not been observed experimentally yet, and further experimental studies are needed to reveal the interaction between graphene and antiferromagnetic insulators. Here, we report the study in heterostructures composed of graphene and the antiferromagnetic insulator MnPSe$_3$. It is found that the MnPSe$_3$ has little impact on the quantum Hall phases apart from doping graphene via interfacial charge transfer. However, the magnetic order can contribute indirectly via process like Kondo effect, as evidenced by the observed minimum in the temperature-resistance curve between 20-40 K, far below the N\'eel temperature (70 K).

cond-mat.mtrl-sci↗

arXiv2022

Vortex-driven periodic and aperiodic magnetoresistance oscillations in cuprates

The study of the interaction between superconductivity and charge ordering is helpful to resolve the pairing mechanism in high-temperature superconductors. Recently, several resistance oscillations studies trigger the speculation that a long-range charge ordering, with an enormous mesh size of several tens of nanometer, can possibly emerge in underdoped high Tc superconductor. However, spectroscopy studies have not traced this kind of long-range charge ordering. Here, we clarify the disagreement between the transport and spectroscopy studies on the mysterious long-range charge ordering by investigating the magneto-oscillations in underdoped Bi2Sr2CaCu2O8+{\delta} flakes. Inspired by the observation that the oscillations evolve from a periodic to an aperiodic one with decreasing doping level, we conclude that the magneto-oscillations can be generated by the interaction between vortices and superconducting loops that enclose randomly distributed underdoped puddles while an assumption of long-range charge ordering is not necessary.

cond-mat.supr-con↗

arXiv2022

Josephson Effect in NbS$_{2}$ van der Waals Junctions

Van der Waals (vdW) Josephson junctions can possibly accelerate the development of advanced superconducting device that utilizes the unique properties of two-dimensional (2D) transition metal dichalcogenide (TMD) superconductors such as spin-orbit coupling, spin-valley locking. Here, we fabricate vertically stacked NbS$_{2}$/NbS$_{2}$ Josephson junctions using a modified all-dry transfer technique and characterize the device performance via systematic low-temperature transport measurements. The experimental results show that the superconducting transition temperature of the NbS$_{2}$/NbS$_{2}$ Josephson junction is 5.84 K, and the critical current density reaches 3975 A/cm$^{2}$ at 2K. Moreover, we extract a superconducting energy gap $\Delta=0.58$ meV, which is considerably smaller than that expected from the single band s-wave Bardeen-Cooper-Schrieffer (BCS) model ($\Delta=0.89$ meV).

cond-mat.supr-con↗

arXiv2021

A low-noise on-chip coherent microwave source

The scaleup of quantum computers operating in the microwave domain requires advanced control electronics, and the use of integrated components that operate at the temperature of the quantum devices is potentially beneficial. However, such an approach requires ultra-low power dissipation and high signal quality in order to ensure quantum-coherent operations. Here, we report an on-chip device that is based on a Josephson junction coupled to a spiral resonator and is capable of coherent continuous-wave microwave emission. We show that characteristics of the device accurately follow a theory based on a perturbative treatment of the capacitively shunted Josephson junction as a gain element. The infidelity of typical quantum gate operations due to the phase noise of this cryogenic 25-pW microwave source is less than 0.1% up to 10-ms evolution times, which is below the infidelity caused by dephasing in state-of-the-art superconducting qubits. Together with future cryogenic amplitude and phase modulation techniques, our approach may lead to scalable cryogenic control systems for quantum processors.

quant-ph↗

arXiv2020

Broadband Tunable Phase Shifter For Microwaves

We implement a broadly tunable phase shifter for microwaves based on superconducting quantum interference devices (SQUIDs) and study it both experimentally and theoretically. At different frequencies, a unit transmission coefficient, $|S_{21}|=1$, can be theoretically achieved along a curve where the phase shift is controllable by magnetic flux. The fabricated device consists of three equidistant SQUIDs interrupting a transmission line. We model each SQUID embedded at different positions along the transmission line with two parameters, capacitance and inductance, the values of which we extract from the experiments. In our experiments, the tunability of the phase shift varies from from $0.07\times\pi$ to $0.14\times\pi$ radians along the full-transmission curve with the input frequency ranging from 6.00 to 6.28~GHz. The reported measurements are in good agreement with simulations, which is promising for future design work of phase shifters for different applications.

physics.app-ph↗

arXiv2020

Demonstration of electron focusing using electronic lenses in low-dimensional system

We report an all-electric integrable electron focusing lens in n-type GaAs. It is shown that a pronounced focusing peak takes place when the focal point aligns with an on-chip detector. The intensity and full width half maximum (FWHM) of the focusing peak are associated with the collimation of injected electrons. To demonstrate the reported focusing lens can be a useful tool, we investigate characteristic of an asymmetrically gate biased quantum point contact with the assistance of focusing lens. A correlation between the occurrence of conductance anomaly in low conductance regime and increase in FWHM of focusing peak is observed. The correlation is likely due to the electron-electron interaction. The reported electron focusing lens is essential for a more advanced electron optics device.

cond-mat.mes-hall↗

arXiv2019

Thermoelectric property of a one dimensional channel in the presence of a transverse magnetic field

We studied the thermal conduction through a quantum point contact (QPC), defined in GaAs-AlGaAs heterostructure, in the presence of a transverse magnetic field. A shift in the position of thermo-voltage peak is observed with increasing field. The position of the thermo-voltage peak follows the Cutler-Mott relation in the small field regime (B < 0.5 T); it starts diverging from the Cutler-Mott relation in the moderate field regime, where a cubic magnetic field term dominates over the trivial quadratic term; eventually the shift saturates in the large field regime (B > 3.0 T). Our results suggest that additional calibration is necessary when using QPC as thermometry, especially when the transverse magnetic field is applied.

cond-mat.mes-hall↗

arXiv2018

Magnetoresistance in an electronic cavity coupled to one-dimensional systems

In this work, we performed magnetoresistance measurement in a hybrid system consisting of an arc-shaped quantum point contact (QPC) and a flat, rectangular QPC, both of which together form an electronic cavity between them. The results highlight a transition between collimation-induced resistance dip to a magnetoresistance peak as the strength of coupling between the QPC and the electronic cavity was increased. The initial results show the promise of hybrid quantum system for future quantum technologies.

cond-mat.mes-hall↗

arXiv2018

Incipient singlet-triplet states in a hybrid mesoscopic system

In the present work we provide an easily accessible way to achieve the singlet-triplet Kondo effect in a hybrid system consisting of a quantum point contact (QPC) coupled to an electronic cavity. We show that by activating the coupling between the QPC and cavity, a zero-bias anomaly occurs in a low conductance regime, a coexistence of zero-bias and finite-bias anomaly (FBA) in a medium conductance regime, and a FBA-only anomaly in a high conductance regime. The latter two observations are due to the singlet-triplet Kondo effect.

cond-mat.mes-hall↗

arXiv2018

Coherent Spin Amplification Using a Beam Splitter

We report spin amplification using a capacitive beam splitter in n-type GaAs where the spin polarization is monitored via transverse electron focusing measurement. It is shown that partially spin-polarized current injected by the emitter can be precisely controlled and the spin polarization associated with it can be amplified by the beam splitter, such that a considerably high spin polarization of around 50% can be obtained. Additionally, the spin remains coherent as shown by the observation of quantum interference. Our results illustrate that spin polarization amplification can be achieved in materials without strong spin-orbit interaction.

cond-mat.mes-hall↗

arXiv2017

Temperature Dependence of Spin-Split Peaks in Transverse Electron Focusing

We present experimental results of transverse electron-focusing measurements performed using n-type GaAs. In the presence of a small transverse magnetic field (B), electrons are focused from the injector to detector leading to focusing peaks periodic in B. We show that the odd-focusing peaks exhibit a split, where each sub-peak represents a population of a particular spin branch emanating from the injector. The temperature dependence reveals that the peak splitting is well defined at low temperature whereas it smears out at high temperature indicating the exchange-driven spin polarisation in the injector is dominant at low temperatures.

cond-mat.mes-hall↗