arXiv subjects

Yunlei Sun

Publications and source records attributed to Yunlei Sun.

7 recordsLinked to original sources

arXiv2026

Interface Engineered Moir\'e Graphene Superlattices: Breaking the Auger Carrier Multiplication Limit for Infrared Single-Photon Detection

Hot electrons undergo Auger scattering during their relaxation process has a multiplication effect,which can generate more electrons above the Fermi level, thus improving the efficiency of photoelectric signal conversion.However,the photo-current gain brought by the Auger carrier multiplication is generally limited with a value less than 5,due to the rapid recombination of photo-generated charge-carriers and the inherently low light absorption of two-dimensional materials.Herein,by twisting graphene to an interlayer angle of 10 o ,we report a layer-dependent electronic correlations leading to an efficient carrier multiplication gain of 10 3 .This is primarily offered by the additional localized density-of-states at interface of the bi-layer 10 o ,moire graphene,and the enhanced interlayer coupling of electron waves in a five-layer moire graphene superlattice structure.Therefore,we can harvest the hot electrons during their energy relaxation through a thermalized optical phonon bottleneck effect.It is this effect that promotes the accumulated hot electrons to achieve a maximum Auger scattering rate ~ 10 10 *ps -1 *cm -2 .Furthermore,the ballistic transport of these hot electrons and Schottky barrier from a 90 nm thick silicon-on-insulator (SOI) silicon effectively block the thermal noise,thus leading to a highly sensitive near-infrared detection characteristic.At a low incident light power of ~ 10 -13 W/cm 2 ,the resulting signal-to-noise ratio is more than 100 dB.The strengthened electromagnetic interaction from highly thermalized optical phonon in stacked moire graphene is utilized in this work.The hot electron multiplication suggests the applicability of Van der Waals moire superlattice architecture for harvesting charge carriers,thus paving the pathway to design infrared single-photon avalanche detectors.

physics.app-ph↗

arXiv2017

Absence of magnetism in the superconductor Ba2Ti2Fe2As4O: Insights from inelastic neutron scattering measurements and ab initio calculations of phonon spectra

Ba2Ti2Fe2As4O is a self-doped superconductor exhibiting a Tc ~ 21.5 K and containing, distinctively with respect to other Fe-based superconductors, not only [Fe2As2] layers but also conducting [Ti2O] sheets. This compound exhibits a transition at T* ~ 125 K which has tentatively been assigned in the literature to a possible density-wave order. However, the nature of this density wave (whether it is a charge- or spin-induced) is still under debate. Magnetism in Ba2Ti2Fe2As4O has never been experimentally confirmed, which raises the question whether this superconductor might be non-magnetic or exhibiting a very weak magnetism. Here, we report evidence from inelastic neutron scattering (INS) measurements and ab initio calculations of phonon spectra pointing towards absence of magnetism in Ba2Ti2Fe2As4O. The INS measurements did not reveal any noticeable change of the phonon spectra across Tc, neither could magnetic effects be observed within the accessible (Q, E) space, setting Ba2Ti2Fe2As4O as an unconventional superconductor. The effect of magnetism on describing phonon spectra was further investigated by performing ab initio calculations. In this context, non-magnetic calculations reproduced well the measured phonon spectra. Therefore, our results indicate a non-magnetic and unconventional character of the superconductor Ba2Ti2Fe2As4O.

cond-mat.mtrl-sci↗

arXiv2014

Correlation-induced self-doping in intercalated iron-pnictide superconductor Ba2Ti2Fe2As4O

The electronic structure of the intercalated iron-based superconductor Ba2Ti2Fe2As4O (Tc - 21.5 K) has been investigated by using angle-resolved photoemission spectroscopy and combined local density approximation and dynamical mean field theory calculations. The electronic states near the Fermi level are dominated by both the Fe 3d and Ti 3d orbitals, indicating that the spacing layers separating different FeAs layers are also metallic. By counting the enclosed volumes of the Fermi surface sheets, we observe a large self-doping effect, i.e. 0.25 electrons per unit cell are transferred from the FeAs layer to the Ti2As2O layer, leaving the FeAs layer in a hole-doped state. This exotic behavior is successfully reproduced by our dynamical mean field calculations, in which the self-doping effect is attributed to the electronic correlations in the Fe 3d shell. Our work provides an alternative route of effective doping without element substitution for iron-based superconductors.

cond-mat.supr-con↗

arXiv2013

Sr and Mn co-doped LaCuSO: A wide band gap oxide diluted magnetic semiconductor with TC around 200K

Here we report the synthesis of a bulk oxide diluted magnetic semiconductor (DMS) system La1-xSrxCu0.925Mn0.075SO (x=0, 0.025, 0.05, 0.075, and 0.1). As a wide band gap p-type oxide semiconductor, LaCuSO satisfies all the conditions forecasted theoretically to be a room temperature DMS. The Curie temperature (TC) is around 200K as x>0.05, which is among the highest TC record of known bulk DMS materials up to now. The system provides a rare example of oxide DMS system with p-type conduction, which is important for formation of high temperature spintronic devices.

cond-mat.mtrl-sci↗

arXiv2013

(La1-xBax)(Zn1-xMnx)AsO: A Two Dimensional "1111" Diluted Magnetic Semiconductor in Bulk Form

We report the synthesis and characterization of a bulk diluted magnetic semiconductor (La1-xBax)(Zn1-xMnx)AsO (0 <= x <= 0.2) with a layered crystal structure identical to that of the "1111" FeAs superconductors. No ferromagnetic order occurs for (Zn,Mn) substitution in the parent compound LaZnAsO without charge doping. Together with carrier doping via (La,Ba) sub- stitution, a small amount of Mn substituting for Zn results in ferromagnetic order with TC up to ~40 K, although the system remains semiconducting. Muon spin relaxation measurements confirm the development of ferromagnetic order in the entire volume, with the relationship between the internal field and TC consistent with the trend found in (Ga,Mn)As, the "111" Li(Zn,Mn)As, and the "122" (Ba,K)(Zn,Mn)2As2 systems.

cond-mat.str-el↗

arXiv2011

Insulator-to-metal transition and large thermoelectric effect in La$_{1-x}$Sr$_{x}$MnAsO

We report the Sr substitution effect in an antiferromagnetic insulator LaMnAsO. The Sr doping limit is $x\sim$ 0.10 under the synthesis conditions, as revealed by x-ray diffractions indicate. Upon Sr doping, the room-temperature resistivity drops by five orders of magnitude down to $\sim$0.01 $Ω\cdot$cm, and the temperature dependence of resistivity shows essentially metallic behavior for $x\geq$0.08. Hall and Seebeck measurements confirm consistently that the insulator-to-metal transition is due to hole doping. Strikingly, the room-temperature Seebeck coefficient for the metallic samples is as high as $\sim240 μ$V/K, making the system as a possible candidate for thermoelectric applications.

cond-mat.str-el↗

arXiv2010

Self doping effect and successive magnetic transitions in superconducting Sr$_2$VFeAsO$_3$

We have studied a quinary Fe-based superconductor Sr$_2$VFeAsO$_3$ by the measurements of x-ray diffraction, x-ray absorption, Mössbauer spectrum, resistivity, magnetization and specific heat. This apparently undoped oxyarsenide is shown to be self doped via electron transfer from the V$^{3+}$ ions. We observed successive magnetic transitions within the VO$_2$ layers: an antiferromagnetic transition at 150 K followed by a weak ferromagnetic transition at 55 K. The spin orderings within the VO$_2$ planes are discussed based on mixed valence of V$^{3+}$ and V$^{4+}$.

cond-mat.supr-con↗